Introduction The rapid development and practical deployment of hyperspectral detection technology render conventional camouflage materials increasingly inadequate for covert protection in complex forest environments,primarily due to their insufficient spectral matching and limited functionality.A critical challenge in forest camouflage lies in the accurate replication of four characteristic spectral signatures of natural vegetation,i.e.,the green peak,the red edge,the near-infrared plateau,and the near-infrared water absorption peak.These features form the unique spectral"fingerprint"of vegetation,which serves as a fundamental basis for evading multi-band,high-precision detection.Among them,the green peak governs a visual concealment within the visible region,while the near-infrared water absorption peak acts as a decisive marker for distinguishing vegetation from artificial materials,which are essential for effective camouflage.However,the existing forest camouflage paints and simulation materials are constrained by inadequate structural design and limited functional integration.Most commercially available products can only partially mimic certain spectral traits of vegetation and commonly exhibit deficiencies in core performance.Note that it remains particularly difficult to simultaneously and accurately match both the green peak of healthy foliage and the near-infrared water absorption peak.This shortfall makes such materials susceptible to rapid identification under hyperspectral imaging,thereby severely limiting the practical effectiveness of the existing forest camouflage technologies.Consequently,there is an urgent need for the research and development of novel camouflage materials capable of comprehensive spectral simulation. Methods Six types of sulfate intercalated Mg/Cr layered double hydroxides(LDHs)were synthesized by a coprecipitation method.The crystalline structure of the as-prepared materials was examined by X-ray diffraction(XRD).The molecular structures and characteristic absorption features were determined by Fourier-transform infrared spectroscopy(FT-IR).The thermal decomposition behavior and mass loss profiles were analyzed by thermogravimetry-differential thermal analysis(TG-DTA).The surface morphology and particle size distribution were characterized by scanning electron microscopy(SEM).These characterization techniques provided a comprehensive structural and physicochemical profile of the synthesized LDHs.Subsequently,to meet the requirement of reproducing the green spectral peak in jungle camouflage,a functional camouflage coating was fabricated via blending the optimized LDHs material with chromium-based green pigment.This formulation enhanced the green-peak characteristics in the visible region and preserved the pronounced water-absorption peak in the near-infrared range.The spectral performance of the coating was evaluated by visible-near-infrared spectroscopy(Vis-NIR),and its thermal camouflage capability was assessed by infrared thermographic imaging. Results and discussion The results systematically indicate that a series of chromium-containing hydrotalcite materials,prepared by a controlled synthesis process,exhibit typical crystalline structural characteristics of layered double hydroxides(LDHs).The XRD patterns reveal sharp and symmetric diffraction peaks,with the characteristic peaks corresponding to the layered structure displaying a high intensity and a regular shape,indicating a good crystallinity and a well-ordered interlayer arrangement.Among the series of chromium-containing hydrotalcites,sulfate-intercalated magnesium chromium hydrotalcite(MgCr-SO42--LDHs)demonstrates unique structural advantages,i.e.,its interlayer spacing is significantly larger than that of other intercalated types of magnesium chromium hydrotalcites.Simultaneously,The TG-DTA thermal analysis indicates that this material exhibits the maximum mass loss of 26.38%at 25-400℃.This is directly related to the content of water molecules stored within the interlayers.The spatial configuration and charge distribution characteristics of the sulfate intercalation ions provide a sufficient space for the stable adsorption and storage of water molecules.As a result,MgCr-SO42--LDHs possesses the most abundant interlayer water content among the prepared samples.This rich interlayer water constitutes the core structural basis for simulating the near-infrared water absorption peak of vegetation.The visible to near-infrared spectra(400-2500 nm)further reveal the optical properties of the Mg/Cr hydrotalcite.In the visible region,the material shows a distinct characteristic absorption peak at 490 nm(blue region),attributed to its intrinsic electronic transition behavior.In the near-infrared region,intense and sharp water absorption peaks clearly occur at approximately 1400 nm and 1900 nm,showing a high similarity to the near-infrared water absorption features of natural vegetation leaves.Sulfate-intercalated magnesium chromium hydrotalcite(MgCr-SO42--LDHs)is modified with chromium(III)oxide(Cr₂O₃)by an in-situ coating process via leveraging these characteristics.The near-infrared water absorption properties imparted by the abundant interlayer water in MgCr-SO42--LDHs were combined with the green optical characteristics of Cr2O3.This complementary interaction successfully offset the influence of the intrinsic blue absorption peak at 490 nm from the magnesium chromium hydrotalcite.Ultimately,a jungle camouflage coating simulation material is prepared,having both green visual characteristics and distinct near-infrared water absorption peaks.This provides a key material foundation for subsequent high-similarity spectral matching with natural vegetation. Conclusions The camouflage coating fabricated with an optimal MgCr-SO42--LDHs@Cr2O3:MgCr-SO42--LDHs ratio of 3:7 could enable a precise spectral matching with natural vegetation leaves.It accurately replicated both the green peak and the near-infrared water absorption peak,achieving a spectral similarity of up to 95.80%.Furthermore,the results of thermal imaging tests revealed no significant difference between the coating and natural vegetation.This study on dual-functional materials that simulated color and the near-infrared water absorption peak could thus offer a promising direction for the development of advanced vegetation camouflage technologies.
Introduction The sulfate source in calcium sulfoaluminate(CSA)cement is an important factor that determines its hydration characteristics,and the properties of CSA cement can be controlled via adjusting the molar ratio of calcium sulfate to ye'elimite(generally referred to as the"M-value").Sulphosilicate cement is a novel cementitious material developed via incorporating ternesite(C5S2$)and free-calcium sulfate(f-C$)into the mineral composition of CSA cement.The calculation of the M-value must comprehensively account for their contents in the clinker due to the presence of SO3 in C5S2$ and f-C$.This study optimized the conventional calculation formula for the M-value and systematically investigated its influence on the compressive strength and expansion behavior of sulphosilicate cement.In addition,the mechanism underlying the effect of anhydrite dosage on cement hydration was also elucidated through the evolution of hydration products. Methods In this experiment,sulphosilicate clinker was synthesized with limestone,fly ash,phosphogypsum,and bauxite as raw materials.The raw materials were calcined at 1250℃for 1 h,followed by rapid air quenching to obtain the clinker.Five groups of sulphosilicate cement with M-values of 0,0.9,1.8,2.7,and 3.6 were designed.Mortar specimens were prepared to evaluate compressive strength and expansion rate,while paste specimens were prepared for analyzing hydration product characteristics at specific ages.The hydration heat release was measured by an isothermal calorimeter.The phase compositions and microstructure of the hydration products were analyzed by X-ray diffractometer,thermal behavior analyzer and field-emission environmental scanning electron microscope.The pore structure was performed by a mercury intrusion porosimeter. Results and discussion Among the various sulphoaluminate cement groups,the M1.8 specimen demonstrates the maximum compressive strength of 43.9 MPa after 3-d hydration.As hydration progresses,the compressive strength of the M2.7 and M3.6 groups shows a significant growth,with the M3.6 group reaching 56.7 MPa at 14 d.However,the M3.6 specimen exhibits a notable strength retrogression,which,is decreased by 4.3 MPa,after 28-d hydration.In contrast,the compressive strength of the M0.9 group increases markedly from 14 d to 28 d,with an improvement of 12.3 MPa. For specimens with the M-value below 1,the early hydration products at 3 d are dominated by AFm phases with insufficient AFt content,resulting in an initial shrinkage.As hydration progresses,the dissolution of SO3 from anhydrite and C5S2$ promotes AFt formation,leading to a measurable expansion after 7 d.At low M-values,AFt contributes to pore refinement,while the reaction of C5S2$ and C2S in later stages generates C-(A)-S-H gel and stratlingite(C2ASH8),refining the microstructure of hydration products and enhancing long-term strength.In contrast,specimens with higher M-values(i.e.,1.8,2.7,and 3.6)exhibit expansion as early as 3 d.Increased anhydrite content and prolonged hydration amplify the crystallographic stress exerted by AFt crystals on the surrounding matrix,causing coarsening of pores,and elevated total porosity,and resulting in strength retrogression during 14-28 d of curing. Conclusions This study was to propose a formula for calculating the gypsum coefficient M-value in sulphosilicate cement,i.e.,CG=0.13×M×(Y-A×2.24-T×1.27)/Sg,establishing the relationship between gypsum dosage and cement performance,while elucidating the influence of M-values on the mechanical properties and hydration mechanisms.The experimental results demonstrated that within the optimal M-range of 0.9-1.8,cement could achieve continuous strength development for all curing ages.Higher M-values(2.7-3.6)enhanced mid-term strength but induced strength regression at 28 d.Increasing M-values effectively suppressed early-age shrinkage and induced progressive expansion,and expansion rates were positively correlated to M-values at all hydration stages.Hydration products primarily consisted of AFt,AH3,and C-(A)-S-H gel.At M0 and M0.9,AFm phases formed during early hydration,followed by C2ASH8 in later stages.Conversely,M-values of≥1.8 accelerated C4A3$ hydration but inhibited both C5S2$ dissolution and C2ASH8 formation.Microstructurally,M0.9 specimens exhibited pore refinement and reduced porosity through gel-phase densification,enhancing strength development,whereas M3.6 samples suffered from coarse pore proliferation due to excessive anhydrite content promoting oversized AFt crystals,ultimately degrading 28-d strength.At the M-value of 0.9-1.8,the system achieved balanced high strength and minimal volumetric deformation,making it suitable for general engineering applications.Elevating the M-value to 1.8-2.7 induced a controlled expansion behavior,enabling targeted use in shrinkage compensation scenarios.However,at the M value of 3.6,delayed strength retrogression and microstructural deterioration could occur,thus establishing 3.6 as a critical upper limit for M-values.
Introduction Magnesium silicate hydrate(M-S-H)cementitious material is regarded as a potential alternative to conventional Portland cement due to its excellent sulfate erosion resistance,heavy metal ion solidification performance,and low pH value during hydration.However,the industrialization process of M-S-H cementitious materials is currently restricted due to the high cost and unstable supply of traditional silicon sources that rely on industrial by-products(such as silica fume,fly ash,and slag).Natural layered silicates such as montmorillonite and kaolin have a similar tetrahedral-octahedral stacking unit structure to M-S-H,and can exhibit a good pozzolanic activity after mechanical or thermal activation.Exploring the use of calcined montmorillonite and kaolin as alternative silicon sources to partially or completely replace silica fume broadens the source of raw materials for M-S-H cementitious materials and reduces production costs.This work was to investigate the effects of partial or complete replacement of silica fume by calcined montmorillonite(MT)and calcined kaolin(KL)on the structure and strength of M-S-H cementitious materials,clarifying the action mechanism of aluminum in the two clay minerals on the M-S-H hydration process and layered structure. Methods Light-burned magnesia(LM)was used as a magnesium source and silica fume(SF)as a reference silicon source.Montmorillonite and kaolin were calcined in a muffle furnace at 750℃for 1 h at a heating rate of 10℃/min to obtain calcined montmorillonite and calcined kaolin.The reference sample was prepared via mixing MgO and silica fume at a mass ratio of 4:6.On this basis,different mass fractions(i.e.,10%,30%,50%,70%,and 100%)of calcined montmorillonite and kaolin were used to replace silica fume,and the samples were named as MT-10～MT-100 and KL-10～KL-100,respectively according to the replacement ratio.The mortar strength specimens were prepared with the samples above,superplasticizer,tap water,and standard sand,and the compressive strength was tested according to the standard GB/T 17671-1999"Methods of testing cement-Determination of strength".The paste was prepared at a water-to-solid ratio of 0.5 and 0.7%superplasticizer based on the total mass of solids,cured in sealed glass tubes with liquid paraffin,and terminated hydration with isopropanol at a certain age,then dried in a vacuum oven at 40℃for 48 h.The mineral phase,thermal behavior,functional groups,microstructure,and element distribution of the samples were characterized by X-ray diffraction(XRD),thermogravimetric analysis(TGA),Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),and solid-state 29Si and 27Al magic-angle spinning nuclear magnetic resonance(MAS NMR). Results and discussion Calcined kaolin exhibits a great early strength enhancement effect,and its compressive strengths at 3 d and 7 d have a positive correlation with the dosage(i.e.,correlation coefficients are 0.996 and 0.905,respectively).At the dosage of calcined kaolin of 70%,the strength at 3 d reaches 39.37 MPa and the strength at 7 d reaches 49.58 MPa,which are 464.0%and 400.3%higher than those of the reference sample,respectively.In contrast,the strength enhancement effect of calcined montmorillonite is weak.The strengths at 3 d and 7 d increase slowly with the increase of montmorillonite dosage.At the montmorillonite dosage of 70%,the strength at 3 d is only 8.94 MPa and the strength at 7 d is 14.28 MPa,which are 36.5%and 53.7%higher than those of the reference sample,respectively.The strength increases slowly in the montmorillonite dosage range of 10%-50%. The microscopic analysis shows that calcination at 750℃causes more thorough damage to the crystal structure of kaolin than that of montmorillonite.The XRD diffraction peaks of kaolin disappear completely after calcination,and the layered structure collapses completely,resulting in a higher pozzolanic activity.After calcination,the interlayer spacing of montmorillonite decreases,and some characteristic diffraction peaks are still retained,indicating that its crystal order is not completely destroyed and the pozzolanic activity is lower than that of calcined kaolin.The FTIR and NMR analysis further confirms that the structural hydroxyl groups of calcined kaolin are completely removed,and a large number of active Al and Si sites are exposed.Although montmorillonite also undergoes dehydroxylation and structural damage after calcination,the degree of disorder is lower than that of kaolin. Aluminum in both calcined montmorillonite and kaolin can enter the M-S-H phase in the early stage of hydration,and form magnesium aluminosilicate hydrate(M-S-A-H)gel via substituting Si4+in the silicate tetrahedron or Mg2+in the magnesium-oxygen octahedron,which significantly improves the polymerization degree of the product.The formed M-S-A-H is external hydration products,mainly formed through element diffusion between particles.The analysis by the XRD,FTIR,and DTG shows that Mg-Al layered double hydroxide(Mg-Al LDH)is generated within the first 28 d of hydration in both raw material systems.The enhancement of cementitious material strength by calcined kaolin and montmorillonite is related to the formation of M-S-A-H.The strength improvement effect of calcined kaolin is higher than that of calcined montmorillonite due to the more thorough destruction of the crystal structure,higher degree of network disorder,more active Al and Si sites,and higher content of Al(V). Conclusions Calcined kaolin and montmorillonite could be used as alternative silicon sources for M-S-H cementitious materials.Calcined kaolin had a great early strength enhancement effect,and its compressive strength had a positive correlation with the dosage.At the dosage of 70%,the compressive strength at 7 d was increased by more than 400%,compared with the sample prepared with pure SF.The strength enhancement effect of calcined montmorillonite could be weak,and the strength was only increased by 53.7%at the same dosage and age.The difference in strength enhancement effect between calcined kaolin and montmorillonite could be due to the fact that the calcination at 750℃caused more thorough damage to the crystal structure of kaolin than that of montmorillonite,resulting in a higher pozzolanic activity.Aluminum in both calcined montmorillonite and kaolin could enter the M-S-H phase in the early stage to form M-S-A-H gel,significantly improving the polymerization degree of the product.The formed M-S-A-H were external hydration products,and Mg-Al LDH was generated within the first 28 d of hydration.
Introduction The hydration of binder is an exothermic reaction,which results in an obvious temperature increase in concrete in the early hydration period.The shrinkage of hardened concrete due to the temperature drop is a main cracking trigger of concrete.A kind of temperature rising inhibitor is developed to decrease the hydration heat of binder in early hydration age,which can reduce the cracking risk of concrete.Cyclodextrin is a main functional composition of the temperature rising inhibitor.C3A is an important clinker mineral influencing the early exothermal characteristics of Portland cement.In this paper,the effect of cyclodextrin on the hydration of tricalcium aluminate-gypsum(C3A-CaSO4·2H2O)was investigated.This work could favor understanding the action mechanism of the temperature rising inhibitor to reduce the cracking risk of concrete structures. Methods Pure C3A was calcined,the chemical pure gypsum and cyclodextrin was used.The hydration exothermal curves of C3A-CaSO4·2H2O pastes containing different dosages of cyclodextrin were measured.The hydration products of C3A-CaSO4·2H2O pastes containing different dosages of cyclodextrin in different ages were in-situ determined by quantitative X-ray diffraction(QXRD).The morphology of hydration products on the surface of C3A particles immersed in different solutions was characterized by scanning electron microscopy(SEM).The etching situation on the surface of C3A particles washed by different solutions was determined by three-dimensional white light interferometric surface profilometry. Results and discussion The beginning time of second hydration of C3A moves up and its exothermic rate decreases,but its reacting time prolongs with the increase of cyclodextrin dosage.The heat output of C3A during its second hydration stage varies little.The consumption of C3A and CaSO4·2H2O increases continuously and the exhausting time of gypsum reduces with the increase of cyclodextrin dosage.The forming quantity of ettringate in the paste containing cyclodextrin is greater than that in controlling paste.The transformation of ettringate to AFm is suppressed after the exhaust of gypsum.Cyclodextrin can expedite the dissolution of C3A in CaSO4 solution to form more deeper etch pits on the surface of C3A particles,which speeds up the hydration of C3A.Needle-like ettringite changes to stick-like one,and the transformation of ettringite to AFm restrains when cyclodextrin exists in pastes. Conclusions Cyclodextrin could promote the initial hydration of C3A to move up the beginning of the second hydration of C3A.The consumption of C3A and CaSO4·2H2O increased continuously in the first hydration stage and the exhausting time of gypsum reduced with the increase of cyclodextrin dosage.Cyclodextrin reduced the reaction speed and prolonged reacting time of C3A during its second hydration stage,its heat output changed little.Cyclodextrin could enhance the dissolution of C3A in gypsum solution to form more deep etch pits on the surface of C3A particles,speeding up the hydration of C3A.Cyclodextrin could change needle-like ettringate to stick-like one and suppress the transformation of ettringate to AFm.
Introduction Solid oxide fuel cells(SOFCs)are high-efficient solid-state energy conversion devices.However,all-ceramic self-supported SOFCs face several challenges such as high brittleness,difficulty in mechanical processing,poor thermal shock resistance,and limited weldability,which result in high manufacturing costs and restrict the applications in mobile power systems.In contrast,metal-supported SOFCs(MS-SOFCs)with metal materials as the external structural support,exhibit remarkable mechanical strength,low cost,and rapid start-up capability,making it highly promising for mobile applications.The anode is a critical component of MS-SOFCs,serving as the site where fuel oxidation occurs to generate electrons.Its microstructure significantly influences the density and effectiveness of the triple-phase boundaries(TPB),where the gas phase,the ionic phase,and the electronic phase intersect.The TPB density largely determines the polarization resistance,with its low-frequency component being inversely related to anode gas diffusion.A common strategy to enhance gas transport is the incorporation of pore-formers,such as graphite,into the anode raw materials.Most studies focus on the type,particle size,and content of pore-formers,which directly affect the pores number,size,and distribution.In this work,atmospheric plasma spraying(APS)was employed to fabricate three types of anodes and corresponding cells.APS reduces thermal input to the metal substrate,effectively preventing oxidation,deformation,and elemental interdiffusion between the metal support and the anode at high temperatures.This study systematically investigates the influence of graphite incorporation methods on the microstructural evolution of the anode and the resulting cell performance,providing important theoretical insights into the operational mechanisms of SOFC anodes. Methods Porous 430L stainless steel substrates were used as supports.Three different NiO-GDC(Gd0.2Ce0.8O1.9)anode powders were prepared.C1 is the baseline without a pore-former.C2 contains 40%(in volume fraction)graphite,which is mixed by spray granulation process to produce composite particles.C3 is made by mechanically mixing 40%of the same graphite with C1 powder.All powders are spherical with good fluidity.Anode layers were deposited via APS.Subsequently,the C2 and C3 anodes were heat-treated in air to remove the graphite pore-former at 750℃for 2 h.A ScSZ(Sc2O3-ZrO2)electrolyte and an LSCF(La0.6Sr0.4Co0.2Fe0.8O3-δ)cathode were subsequently deposited by APS to build single cells.The microstructure and porosity of the anodes were characterized using scanning electron microscopy(SEM)and image analysis software.The surface roughness was measured by profilometer.The electrochemical performance,including the open-circuit voltage(OCV),current-voltage-power(I-V-P)and electrochemical impedance spectroscopy(EIS),were evaluated in the range of 600-750℃using humidified H2 as fuel and air as oxidant.The equivalent circuit fitting of EIS data is carried out to quantitatively analyze the contribution of charge transfer,surface adsorption/dissociation and gas diffusion in polarization impedance. Results and discussion The incorporation of graphite pore-former significantly modified the pore size distribution and total porosity within the anodes.The measured porosity of C1,C2,and C3 was 26%±2%,37%±3.1%,and 42%±2.3%,respectively.The C1 anode featured a relatively dense structure with uniformly distributed pores,which primarily consisted of submicron cracks and fine pores originating from the thermal stress inherent to the APS process.In contrast,the C2 anode showed a notable increase in both the number and size of pores,which were homogeneously dispersed without significant agglomeration.The C3 anode,however,contained a substantial amount of large pores,mostly～5 μm in diameter,attributed to the agglomeration of graphite particles during mechanical mixing,resulting in coarse and irregular pore structures after heat treatment.Furthermore,the addition of graphite modified the thermal response characteristics of the agglomerated powder during the spraying process,promoting the formation of a more uniformly melted microstructure in the anode layer.The average surface roughness(Ra)values for C1,C2,and C3 were 6.64,7.06 nm,and 7.66 μm,respectively,indicating that graphite addition increased anode surface roughness.This phenomenon is due to the thermal decomposition of graphite during the plasma spraying process,where high temperatures cause partial oxidation of graphite in the open atmosphere,thereby generating CO2 gas.The release of this gas from the incompletely solidified anode surface etches irregular pits and protrusions,ultimately leading to increased surface roughness.The cell without graphite pore-former(C1)consistently demonstrated the highest OCV and maximum power density,reaching 1.0 V and 957 mW·cm-2 at 750 °C,respectively.EIS analysis revealed that the anodes with graphite pore-former(C2 and C3)exhibited improved charge transfer capability,thereby reducing the high-frequency polarization resistance.Despite this,the overall output performance of C2 and C3 did not show effective enhancement,which is attributed to their increased ohmic resistance(Ro)and lower OCV.The elevated surface roughness and inherent porosity in the C2 and C3 anodes adversely affected the quality of the subsequently sprayed electrolyte layer,introducing microcracks and gas permeation pathways.This resulted in increased Ro and reduced OCV,ultimately weakening the benefits gained from the reduced polarization resistance. Conclusions The method of graphite pore-former addition significantly affects the anode microstructure and overall cell performance.Compared with mechanical mixing,spray granulation produces a superior and uniform pore structure.However,contrary to conventional expectation,the introduction of graphite pore-forming agent into the APS anode reduces overall cell performance due to induced electrolyte defects,which elevated Ro and lowered OCV.Future optimization should focus on strategies to reduce anode surface roughness and refine pore structure without affecting the quality of electrolyte deposition.It is anticipated that this will further enhance the output performance of MS-SOFCs.
Introduction With the continuous pursuit of higher efficiency and larger thrust-to-weight ratio in aero-gas-turbine engines,the turbine inlet temperature has already exceeded 1300℃,imposing increasingly stringent requirements on the thermal resistance and protective capability of hot-section structural materials.Environmental barrier coatings(EBCs)have become a crucial technology to ensure efficient and reliable service of ceramic matrix composite(CMC)turbine components under such extreme working conditions.However,the service environment of EBCs is exceptionally complex.Coatings are continuously exposed to corrosive gaseous species within combustion products,among which the ingression and reaction of molten calcium-magnesium-aluminum-silicate(CMAS)deposits represent one of the most detrimental degradation mechanisms. To mitigate CMAS-induced deterioration,numerous strategies have been proposed,including compositional modification(doping,high-entropy ceramics),structural design optimization(multilayer or graded coatings),and surface engineering(laser or ion beam treatments).Although these approaches can improve corrosion resistance to some extent,most of them inevitably alter the coating chemistry or structural system,which tends to induce thermal expansion mismatch with the substrate and promotes premature failure during thermal cycling.Therefore,how to enhance CMAS-corrosion resistance while maintaining thermomechanical compatibility remains a critical challenge. Laser glazing(LG)is a surface-modification technique that locally melts and rapidly solidifies the coating surface to form a dense glaze layer.It improves surface compactness and seals microdefects without altering the coating composition,thereby presenting a promising method for improving CMAS-corrosion resistance.In this work,laser glazing is introduced to enhance the CMAS-resistance of EBCs,and the CMAS-corrosion behavior together with the underlying improvement mechanisms are systematically investigated. Methods SiC ceramic substrates were purchased from Fuzhou Pengkun Optoelectronics Co.,Ltd.The samples were cylindrical(diameter 25.4 mm,thickness 3 mm)and mechanically grit-blasted prior to coating deposition.Yb2Si2O7/Si(YbDS)EBCs were deposited on the substrates by atmospheric plasma spraying(APS).Commercial Yb2Si2O7 and Si powders(Shanghai Shuitian Materials Technology Co.,Ltd.)were used,and the bond coat consisted of 90%(in mass fraction)Si and 10%Yb2Si2O7. A picosecond ultraviolet pulsed-laser system was subsequently applied to modify the surface microstructure of APS YbDS coatings.Four sets of parameters(L1-L4)were obtained by adjusting the laser power(6 W or 20 W)and scanning speed(100-300 mm/s).CMAS bulk material was synthesized by high-temperature melting.CMAS powder was mixed with ethanol and uniformly brushed onto the coating surface,followed by drying to achieve a coating mass of 5 mg/cm2.The coated samples were exposed at 1350℃for 10,60 h,and 120 h.After corrosion,the evolution of microstructure and phase composition was analyzed to reveal the degradation behavior. Results and discussion The APS-prepared YbDS coating exhibited a surface roughness of～3.7 μm and a porosity of～4.87%,with typical APS defects such as pores,unmelted particles,and microcracks.After laser glazing,four modified surfaces were obtained.Among them,sample L2 demonstrated the most favorable structural morphology and was selected for subsequent corrosion tests.The L2 coating showed a reduced surface roughness of～1.824 μm and a homogeneous,dense glaze layer of～9.6 μm thickness.Moreover,the glazed surface phase completely transformed from Yb2Si2O7 to Yb2SiO5. During CMAS corrosion,the YbDS coating surface was continuously covered by a loose mixture of Ca2Yb8(SiO4)6O2 and CMAS residual glass.In contrast,the laser-modified L2 coating was covered by a compact Ca2Yb8(SiO4)6O2 reaction layer.After corrosion,both coatings displayed Ca2Yb8(SiO4)6O2 and secondary Yb2Si2O7 phases;however,their structural evolution differed significantly.After 120 h of corrosion,the YbDS coating suffered severe structural degradation,including interfacial delamination and partial spallation in cross-sectional observations.Conversely,the L2 coating maintained structural integrity,and its corrosion depth was consistently lower under the same conditions. The improved CMAS resistance of the L2 coating can be attributed to three synergistic mechanisms:Surface densification,Laser glazing produced a dense,continuous glaze layer that sealed APS-induced pores and cracks,effectively delaying CMAS infiltration pathways;Protective reaction-layer formation,The Yb2SiO5 glaze reacted with CMAS to form a dense Ca2Yb8(SiO4)6O2 layer,which further hindered molten-salt penetration;Enhanced non-wettability,Laser glazing significantly reduced surface roughness and improved hydrophobicity.As a result,molten CMAS appeared as aggregated hemispherical droplets rather than fully spreading,making it more easily removed by high-velocity gas flow during service. Conclusions The findings of this study demonstrate that laser glazing effectively enhances the CMAS-corrosion resistance of YbDS coatings.The improvement originates from the combined effects of surface densification,pore/crack sealing,phase transformation to Yb2SiO5,and subsequent formation of a compact Ca2Yb8(SiO4)6O2 reaction layer during corrosion.Additionally,the smoother and less wettable glazed surface reduces the adhesion and spreading tendency of CMAS,enabling molten deposits to be removed more easily under aerodynamic forces.As a result,the degradation rate of the coating is substantially suppressed,delaying the propagation of corrosion-induced cracks and maintaining structural integrity over prolonged exposure.Moreover,the laser-induced modifications do not alter the coating architecture or introduce thermal expansion mismatch,making the technique compatible with existing EBC design frameworks.Overall,laser glazing represents a promising strategy for improving the durability and service lifetime of EBC systems in next-generation high-temperature aero-engine applications.
Introduction Cement production accounts for approximately 12%of China's total CO2 emissions,having a significant challenge to achieving the national"dual carbon goals".Carbon capture,utilization,and storage(CCUS)represent a pivotal innovative technology for mitigating these emissions.However,conventional amine-based CO2 capture requires an energy-intensive high-temperature desorption,hindering its industrial implementation in cement plants.Also,the limited utilization pathways for captured CO2 pose another challenge for cement CCUS.Diethanolamine(DEA)offers a promising solution as it functions both as a CO2 absorber and a cement additive.This dual capability enables a potential carbonation utilization of CO2 absorbed DEA solutions without requiring the desorption step within cementitious systems.This study was thus to investigate the effect of CO2-absorbed diethanolamine(DEAC)on the early hydration behavior and strength development of cementitious systems.The findings could propose a novel approach for low-energy CO2 capture coupled with efficient in-situ utilization within cement industry. Methods Cement mortars with a water-to-cement ratio(W/C)of 0.50 were prepared with P·I 42.5 Portland cement(GB 8076)and ISO standard sand.The specimens were designated as REF,D0.1%C0%,D0.1%C0.02%,D1.0%C0%,and D1.0%C0.22%,respectively.DEA and its equivalent CO2 admixture were added as percentages of cement mass.All associated cement paste mixtures were prepared at a W/C ratio of 0.3.DEAC was prepared by continuously bubbling CO2 gas(≥99%purity)at a flow rate of 200 mL/min through a 5 mol/L DEA solution maintained at 40℃until saturation was achieved.An eight-channel microcalorimeter recorded the hydration heat of cement paste specimens at 25℃for 72 h.The phase composition of hardened cement pastes was determined by X-ray diffraction(XRD).The contents of bound water,CH,and CaCO3 were analyzed by thermogravimetric analysis(TGA).The cumulative porosity and pore size distribution of hardened paste samples at 7 d were characterized by mercury intrusion porosimetry(MIP).The compressive strength was measured on mortar specimens at 1,3 d and 7 d of curing in accordance with the standard GB/T 17671. Results and discussion The hydration calorimetry results demonstrate that D0.1%C0.02%and D0.1%C0%both accelerate the hydration rate of silicate phases,as evidenced by an increased second exothermic peak rate,while leaving the induction period duration unaffected.Conversely,D1.0%C0%and D1.0%C0.22%significantly reduce the second exothermic peak rate.D1.0%C0.22%extends the hydration induction period to 240 min,while D1.0%C0%has a negligible effect on its duration.The XRD patterns and TG analyses reveal that the impact of DEAC on the cement hydration depends critically on its specific DEA and CO2 dosage.At a low dosage(i.e.,D0.1%C0.02%),a mild carbonation promotes a concurrent hydration of silicate and aluminate phases.However,a high dosage(i.e.,D1.0%C0.22%)substantially inhibits early hydration of silicates.The MIP results indicate that DEAC and DEA both refine the pore structure of hardened cement paste.The pores below 20 nm are significantly reduced in D0.1%C0%and D0.1%C0.02%systems,aligning with their enhanced early hydration kinetics.This refinement also occurres in D1.0%C0%and D1.0%C0.22%systems despite inhibited silicate hydration.The results of compressive strength tests show that D0.1%C0.02%and D0.1%C0%can enhance mortar strengths at 1,3 d,and 7 d,respectley.The strengths of D0.1%C0.02%systems can be increased by 8.4%,10.2%,and 16.8%at these ages,respectively,primarily due to the DEA component with the weak carbonation contributing minimal additional enhancement.The 3-day and 7-day strengths of D1.0%C0.22%and D1.0%C0%systems both are increased(more significantly in the carbonated system),indicating a synergistic hydration-carbonation effect.However,the 1-day strength of D1.0%C0.22%system drastically is reduced by 52.2%,with silicates hydration inhibition by D1.0%C0%identified as a primary factor underpinning early strength reduction.According to the analysis of bound water content,calcium hydroxide(CH)content,porosity,and compressive strength relationships,a linear correlation between CH content and mortar strength is proposed.This demonstrates that silicate phase hydration kinetics can be modulated differently by DEAC and DEA formulations-fundamentally governed compressive strength development. Conclusions The addition of 0.1%DEA with 0.02%CO2(D0.1%C0.02%)as DEAC enhanced the flexural and compressive strengths of cement mortar at 1,3 d,and 7 d.In contrast,the addition of 1.0%DEA with 0.22%CO2(D1.0%C0.22%)significantly reduced the 1-day strength.In D0.1%C0.02%system,the CO2 component reacted with dissolved Ca2+released from cement minerals to precipitate CaCO3.This reaction promoted cement hydration,refined the pore structure of the hardened paste by reducing the volume of harmful pores,and facilitated a synergistic enhancement of hydration and carbonation.D1.0%C0.22%addition significantly retarded cement hydration within the first 24 h,primarily by inhibiting the dissolution of silicate phases and extending the induction period,leading to the reduced early strength.Although carbonation exacerbated the retardation of silicate phase hydration via DEA interaction,the hydration process recovered normal kinetics after 7 d.
Introduction Polymer-derived ceramics are prepared via forming precursors through the polymerization of tiny molecules and cracking at high temperatures.Compared to conventional ceramics,their advantage lies in an ability to precisely control the microstructure and crystalline phase composition through the design of the molecular structure and elemental composition of the precursor and subsequent thermal treatment,thereby producing the optimal final properties.Among these,SiBCN ceramics stand out within the polymer-derived ceramics due to their flexible molecular structure designability.This enables the in-situ formation of multi-phase synergistic loss systems incorporating SiC,BN and graphitic carbon,coupled with a unique oxidation resistance mechanism,which excel particularly within polymer-derived ceramic systems.However,SiBCN ceramics primarily exist in an amorphous state at lower temperatures(i.e.,<1400℃),thus limiting their application in electromagnetic wave absorption.The paper was to introduce Ti nanopowder during the ceramicization process to catalyze the formation of nano-dielectric crystals such as SiC,TiC,and crystalline graphite.These crystals could enhance the dielectric imaginary part of SiBCN ceramics,thereby strengthening their electromagnetic wave attenuation capabilities. Methods For the synthesis of polymer precursor,tetrahydrofuran(THF)-methylvinyl dichlorosilane and borane dimethyl sulfide complex were mixed into a three-neck flask and conducted in argon for 24 h.Also,methyl dichlorosilane and hexamethyldisilazane were introduced,and the reaction was continued at the ambient temperature for 24 h.Subsequently,the mixture was then heated from room temperature to 170℃for amide copolymerization reaction.After holding at this temperature for 3 h,vacuum distillation was performed,and filtrated for three cycles,thus producing a pale yellow polyborosilazane(PBSZ).For the synthesis of SiBCN ceramibs,polyborosilazane(PBSZ)was placed in a tube furnace and heated to 280℃for 2 h to fully cure the precursor.The cured sample was subjected to ball grinding.The resultant ground powder was mixed with Ti nanopowder at different Ti mass contents(i.e,0%,5%,10%,and 15%),and then was ground to produce different composite powders,.The composite powders were pressed into discs with the diameter of φ20 mm.The discs were heat-treated in a vertical tube furnace(i.e.,firstly heating at 800℃for 1 h,and thenheating at 1000℃for 2 h)to allow enough molecular diffusion for TiC crystal formation,resulting in SiBCN ceramics. Results and discussion The analysis of the four-component doped ceramics reveals that Ti nanoparticles doping positively affects both the phase composition and dielectric properties of SiBCN ceramics.The XRD patterns indicate that pure SiBCN ceramics remain amorphous after heat treatment at 1000℃,whereas the addition of Ti nano-particles promotes the formation of TiC crystals within the ceramics,thereby enhancing their crystalline properties.The SEM and TEM images demonstrate that varying the nano-Ti doping content alters the microstructure of SiBCN ceramics.Nano-Ti addition promotes the formation of a porous structure within the ceramics and facilitates the growth of crystals such as TiC and carbon nanotubes,enriching the phase composition of the ceramics.Varying Ti nanoparticles doping contents alters SiBCN's electromagnetic wave absorption and loss capabilities.Compared to pure SiBCN ceramics,Ti nanoparticles doping confers higher electromagnetic parameters and lower reflection loss,and 10%Ti nanoparticles-doped SiBCN exhibits the optimum electromagnetic wave absorption performance.The incorporation of Ti nanoparticles optimizes the ceramic structure,with synergistic interactions among various crystals and structural components,thus enhancing the overall performance. Conclusions This study demonstrated that doping Ti nano-particles into SiBCN ceramic could enhance the ceramic dielectric loss and impedance matching qualities.Ti nano-particles enhanced the low-temperature crystallization property of SiBCN.The crystallinity and microstructure of SiBCN ceramics could be adjusted by varying the nano-Ti doping content.The ceramics heat-treated at 1000℃could develop porous architectures,TiC,and crystalline phases such as crystalline carbon.Ti nanoparticles improved the electromagnetic wave attenuation properties of SiBCN.The formation of TiC and carbon nanotubes,along with the heterogeneous interfaces formed with the amorphous matrix,could boost the electromagnetic wave attenuation performance of SiBCN ceramics.The crystallinity of SiBCN ceramics and the presence of abundant atomic defects resulted in a significant polarization loss,thereby enhancing the ceramic's electromagnetic wave absorption capability.At Ti nanoparticles content of 10%,the RLmin value of SiBCN ceramics at 6.24 GHz achieved-44.5 dB,with an EAB as high as 3.43 GHz,indicating that adding Ti nanoparticles could effectively enhance the electromagnetic wave absorption capacity of low-temperature heat-treated SiBCN ceramics.
Basic magnesium sulfate cement(BMSC)is a new type of magnesium-based cementitious material modified by the chemical additive such as citric acid or boric acid on the basis of magnesium oxychloride cement.BMSC has the abundant mineral resource for the raw material,low energy consumption of production,and high utilization rate of the solid waste.BMSC has the green and environmental advantages,such as the conservation of energy,material,land,and low-carbon emissions.The systematic research on the durability of BMSC is still needed if BMSC are applied to the special environment such as the ocean and saline soil area.The main progress of the durability of BMSC material in past ten years is summarized in this paper,which includes the water resistance,carbonization and resistance of seawater,salt brine,freeze-thaw of BMSC material.and the influencing factors,the evolution law of corrosion and mechanical properties of internal steel bars,the mechanical properties of BMSC components under the natural exposure condition for 869 days.The relative dynamic modulus of the elasticity and mass change,corrosion products,and the microstructural changes of BMSC in the harsh environment is studied.The analysis of mechanism is also conducted on the durability of BMSC.The durability performance of the BMSC material is related to the composition and microstructure of BMSC.It can be found that the stable and abundant formation of 5·1·7 phase,which is the main hydration product in BMSC,is the fundamental reason for the good durability and high mechanical properties of BMSC-based material.BMSC concrete is not prone to carbonation and the internal steel reinforcement is not easily corroded in the atmospheric environment.The main changes in the microstructure of the carbonized zone on the surface of BMSCs during the carbon dioxide curing are the transformation of some hydration product Mg(OH))2 into MgCO3.The long-term retention rate of the compressive strength of BMSC concrete is closely related to its initial strength before the immersion in the seawater.The polarization resistance Rp decreases with the prolonged exposure time in the environment of seawater immersion.BMSC concrete with the compressive strength of C40 or above,BMSC mixed with KLJ rust inhibitor or the steel bar coated with epoxy resin are recommended to be used in the environment of seawater immersion.The freeze-thaw life of BMSC concrete exceeds 40 times,far exceeding that of Portland cement concrete.Compared to PCC components,the BMSC beams and columns under the coupling effects of the acid rain and freeze-thaw have less degradation of mechanical performance,lower rate of the internal steel corrosion,and higher enhancement effect of cracking load.The effective additive,suitable activity of MgO,appropriate addition of polymers,5·1·7 crystal seed,slag(or fly ash),and solution immersion of KH2PO4 or NH4H2PO4 can optimize the composition of hydration product of BMSC,increase the stability of the 5·1·7 phase of hydration product,effectively improve the microstructure of BMSC,and enhance the durability of BMSC-based material in the harsh environment.The prospect for the application of BMSC material is discussed.Due to the advantages of BMSC,such as resistance to carbonization,salt brine corrosion,low transmission,and reinforcement protectio,it can be found that the BMSC material can be used in the area with harsh environment such as the ocean,western saline soil,and Qinghai Tibet Plateau after KLJ rust inhibitor being added.The military engineering,pavement repair of cement concrete,crack repair in the brick and stone masonry of ancient building and prefabricated construction have good application prospects in the harsh environments such as the Qinghai Tibet Plateau and saline soil area.Finally,the problems of durability are discussed as follows:the mechanism of microstructure formation and evolution of BMSC-based material under the harsh environment,the corrosion resistance of BMSC concrete to sulfate,magnesium,and chloride salt under the wet dry and freeze-thaw cycles,mechanism of corrosion resistance of 5·1·7 phase and BMSC concrete,the dynamic evolution and mechanism of intrinsic degradation of the interfacial bonding performance between BMSC repair material and the old material under the harsh service condition,the structural damage,disasters,and life extension and toughening under the interaction response of permafrost and engineering in the high-altitude environment,the stress damage,degradation of structural performance,identification of field effects and long-term performance,and design for the expected lifespan of BMSC in the harsh environment such as the ocean and saline soil,the mechanism of transport and failure of BMSC concrete in the harsh environments,the reinforcement and long-term protection system of the surface of BMSC concrete,the model of the rapid life prediction for BMSC-based material.This paper can provides the theoretical basis for the application,durability evaluation,and engineering design of BMSC in the harsh environment.
Introduction As a type of energy-saving and environmental protection building system,steel structure building is widely used in engineering construction in recent years,and its fire protection measures are particularly important.At present,the commonly used fire retardant coatings are mainly divided into two categories,i.e.,organic intumescent and inorganic non-intumescent coatings.Although organic intumescent coatings exhibit a good fire resistance in the initial stage,their duration of protection is relatively short,and they may release toxic and corrosive gases during combustion,posing certain safety risks.In contrast,inorganic non-intumescent fireproof coatings have advantages such as high thermal resistance,strong durability,good wear resistance,and low cost,making them considered as an ideal fire protection material for steel structures.However,some issues such as insufficient adhesion and poor overall durability seriously limit its widespread application in practical engineering.Magnesium phosphate cement(MPC)is regarded as a fireproof material with an application potential due to its high strength,high-temperature resistance and excellent interfacial bonding performance with steel.However,the conventional raw material for MPC like dead-burned magnesia has a high density and carbon emissions,which is unfavorable for its green and sustainable development.To address the above issues,this study was to select a low-grade natural brucite powder as a complete substitute for dead-burned magnesia to prepare magnesium phosphate cement,and optimize the physical,mechanical,and fire insulation properties of brucite-based magnesium phosphate steel structure fireproof coatings(BMPC)via introducing modified expanded perlite. Methods The raw materials for the preparation of BMPC included natural brucite powder,ammonium dihydrogen phosphate,analytical grade borax,and expanded perlite.Expanded perlite was divided into two types,i.e.,untreated(EP)and water absorption pretreatment(HEP)according to different treatment methods.Under the condition of fixed process parameters(i.e.,M/P mass ratio of 2.5,borax content of 15%,water-cement ratio of 0.17,and expanded perlite content of 0-20%of the total mass of brucite powder and ammonium dihydrogen phosphate),the BMPC slurry was prepared. The dry density and surface drying time of the BMPC coating under natural curing conditions were tested in accordance with the standard GB 14907-2018.The compressive strength and adhesive strength tests were conducted on the specimens after 3-d,7-d and 28-d curing,respectively.The thermal conductivity of BMPC was determined by a transient plane source method.The fire resistance limit was tested according to the standard GB/T 9978.1-2008.The internal pore structure of BMPC samples was analyzed by an industrial computed tomography system,and its microstructure was analyzed by field emission scanning electron microscopy.The phase change of BMPC coating before and after fire test was analyzed by X-ray diffractometry,and its thermal stability in the range of 30-1000℃was analyzed by thermogravimetric analysis. Results and discussion The expanded perlite(HEP)after water absorption treatment has a more open pore structure and a higher surface roughness rather than the untreated expanded perlite(EP).In the BMPC system,the HEP has a relatively small effect on the mechanical properties,especially under low density conditions,it can still maintain high compressive strength and adhesive strength.At the HEP content of 20%,the microporous structure inside the material significantly reduces the thermal conductivity and thermal diffusion coefficient.This is mainly since the HEP acts as a low thermal conductivity filler,and the air layer retained in its pores(i.e.,thermal conductivity of 0.026 W/(m·K))effectively blocks heat transfer.Also,the introduction of HEP optimizes the pore structure,reduces the proportion of large pores,makes the heat conduction path more complex,delays the diffusion process of heat into the substrate,and significantly slows down the flame propagation rate and thermal decomposition process.The results of fire resistance test and pore structure show that the porosity of BMPC-HEP sample is higher than that of the control group,and the standard deviation of pore fluctuation increases from 4.0%to 5.1%,indicating that HEP forms a lightweight porous structure at a high temperature,further improving the thermal insulation performance and thermal stability of the material.The addition of HEP has a significant effect on the microstructure of BMPC at a high temperature.Some struvite and unreacted raw materials absorb a large amount of heat during pyrolysis,which plays a role in delaying temperature rise and enhancing thermal buffering,and provides an important support for the thermal insulation protection mechanism of fire retardant coatings. Conclusions The expanded perlite after water absorption treatment had little effect on the mechanical properties of BMPC system.When the density reduced from 1062 kg/m3 to 647 kg/m3,the 28-d compressive strength and adhesive strength were only reduced by 26.5%and 17.7%,respectively.At the content of HEP of 20%,the thermal conductivity and thermal diffusivity of BMPC were 49.3%and 44.0%lower than those of BMPC without HEP,respectively.The significant improvement of this thermal performance could be mainly attributed to the fact that HEP itself had low density and low thermal diffusion characteristics,effectively slowing down the heat transfer rate in the process of temperature change,and thereby improving the thermal insulation performance of the material.The fire resistance limit of BMPC-HEP system reached 206 min,which was significantly better than that of the control sample.Its excellent fire resistance was mainly attributed to the synergistic effect of porous structure,low thermal conductivity filler and microstructure stability at a high temperature,indicating that it could have a promising application potential in the field of fire retardant coatings for steel structures.
To achieve the 2050 carbon neutrality vision,it is necessary to promote research and development of efficient and economically beneficial green hydrogen production technologies.In the process of global transition to a low-carbon energy system,hydrogen as a key zero carbon energy carrier continues to attract much attention.This review provides a comprehensive evaluation of high-temperature solid oxide electrolysis cell technology,focusing on analyzing some related challenges and potential pathways for large-scale application. Compared to low-temperature alternatives such as alkaline and proton exchange membrane electrolysis,SOEC has unique advantages due to its high-temperature operation,It uses ceramic materials without precious alloys and can operate at 650-1000℃,and it can improve the electrochemical performance,resulting in an energy conversion efficiency of>80%,These characteristics make SOEC a promising solution for low-cost production of green hydrogen gas,The existing domestic technology is still in demonstration stage with project scales typically ranging from tens to hundreds of kilowatts.Commercial deployment needs to overcome challenges of"three highs and one low".A key is to improve power density of battery stack,increase its service life,improve system integration,and reduce costs.To solve this problem,collaborative progress is needed in fields of material innovation,structural design,and system integration. Collaborative design approach involving electrodes,electrolytes,and sealing components is crucial in development of materials and structures.For precise microstructure control and interface optimization,battery pack can operate stably at a high current density of 2 A/cm2,while controlling attenuation rate of<1mV/h,and significantly extending actual service life. Optimizing multi energy data collaboration system is equally crucial,and SOEC can leverage industrial waste heat and renewable energy resources to utilize medium to low temperature thermal energy(i.e.,200-300 ℃),thereby reducing external power consumption by approximately 30%and improving overall energy utilization efficiency,It is also necessary to build a regional supply chain that covers entire process from raw material and battery preparation to integrated assembly and system integration.The integration cost should be controlled within RMB 2500 kilowatt hours,and the design life should reach 50 000 h.A key is to lay a foundation for widespread application. The widespread promotion of SOEC still faces several constraints,i.e.,loss of electrode materials under high temperature and high humidity conditions,stability challenges caused due to power input fluctuations,and relatively high initial costs.Future research should focus on developing more durable electrode materials,establishing intelligent management systems that adapt to changes in renewable energy,and promoting standardization and cost control throughout entire industry chain to achieve technological popularization. The combination of wind and solar energy with water electrolysis can build a more adaptable clean energy resource system,Integration helps alleviate grid stability issues related to intermittent renewable energy resources and significantly reduces electricity cost of hydrogen production.Hybrid wind and solar energy system can increase hydrogen production,while reducing costs.A key is that when SOEC is matched with fluctuating power sources,oxygen electrode/electrolyte interface will degrade under frequent thermal cycles,which is an important factor affecting long-term stability of system.In global,green hydrogen production driven by renewable resources is gradually known as a key approach of reducing greenhouse gas emissions.Electrolytic hydrogen can utilize local wind and solar energy to decompose water into hydrogen and oxygen,reducing production costs.Moreover,solar and wind energy are widely distributed and naturally compatible with electrolysis equipment.Excess electricity can be chemically stored as hydrogen,efficiently regulating spatial and temporal imbalance of energy supply and demand.Therefore,generated hydrogen and oxygen can be directly applied in transportation and industrial fields without conversion,making hydrogen both a primary energy source and a data carrier. Compared with conventional methods,the SOEC technology has a better hydrogen production efficiency and a lower unit energy consumption,and its commercialization key lies in increasing lifespan of fuel cell stack from less than 104 h to 5 × 104 h,reducing cost of hydrogen to below $1.5/kg.The current costs of photovoltaics and wind power continue to decline.In combination with growing demand for green hydrogen in industries such as chemical metallurgy,the SOEC is expected to achieve large-scale applications in"electricity hydrogen ammonia/methanol"integrated system,distributed energy network,and sustainable financing model.Its core position lies in serving as a fundamental supporting technology for carbon neutrality goals. Summary and Prospects In transition towards a decarbonized energy system globally,hydrogen plays a crucial role as a zero carbon energy carrier.In this context,solid oxide electrolysis cell(SOEC)technology with its advantages in high-temperature operation significantly reduces material costs and improves overall system energy efficiency,compared to low-temperature solutions such as alkaline and proton exchange membrane electrolysis.SOEC system adopts a non-precious metal ceramic structure.When operating at 650-1000℃,electrochemical kinetics acceleration mechanism achieves a conversion efficiency of>80%,providing a feasible approach to reduce cost of green hydrogen leveling.The existing domestic demonstration projects are limited to a scale of tens to hundreds of kilowatts,and the commercial implementation needs to break through bottleneck of"three highs and one low",thus increasing power density of fuel cell stack,extending its service life,and optimizing system integration,while reducing assets and operation and maintenance costs.Solving these obstacles requires collaborative efforts in three major fields,and innovation in materials and structures must break through conventional design framework of electrodes,electrolytes,and sealing glass. With precise microstructure design and interface stress control,system can maintain a high current density of 2 A·cm-2,while controlling degradation rate at 1 mV per thousand hours,significantly extending lifespan of battery pack.Multi-energy coupling optimization is crucial,which requires integrating the SOEC with industrial waste heat and renewable resources,thus utilizing low-grade thermal energy(i.e.,200-300℃),efficiently offsetting internal heating demand,reducing external electricity consumption by approximately 30%,and comprehensively improving energy utilization efficiency.For those localized supply chains,establishing a complete domestic production capacity from precursor powder to single cell manufacturing,stacking and assembly to system integration is particularly crucial.The goal is to control stacking cost at RMB 2500 per kW and achieve an operating life of 5×104 h,laying a foundation for large-scale applications.At present,although the SOEC has significant energy efficiency advantages,its promotion and application still face multiple constraints,i.e.,gradual decay of oxygen electrodes under high temperature and high vapor partial pressure,mechanical and electrochemical damage caused by power fluctuations,and daunting initial capital investment. Subsequent exploration should focus on preparing new electrode materials with a higher stability,establishing flexible thermoelectric synergistic regulation mechanisms to adapt to fluctuating renewable energy,and promoting standardization and cost reduction and efficiency improvement throughout entire industry chain.The cost of photovoltaic and wind power continues to decrease,coupled with increasing demand for green hydrogen in chemical and metallurgical fields.Solid oxide electrolysis cell technology is expected to be widely applied in"electricity hydrogen ammonia/methanol"integrated system,distributed energy system,and sustainable refining scenarios.This technology will undoubtedly become a key pillar technology supporting the dual carbon goals in China.
ZrB2-based multiphase ceramics are representative ultra-high temperature ceramics(UHTCs).Their service temperature significantly exceeds the sintering temperature,often requiring substantial amounts of SiC as a sintering aid to achieve the densification and enhance the oxidation resistance.The transition metal carbides(MCs)are superior sintering aids for UHTCs,effectively removing the oxygen-impurity and improving high-temperature strength.From some projects supported from the National Natural Science Foundation of China,our studies focus on the effect of MC on controlling the multiphase microstructure of UHTCs.The results obtained reveal the reactive-sintering mechanism engaging the high-viscous liquid-phase and explore the mutual-solution behavior in multiphase ceramics along with the structure-property relationship.The quantitative characterization for microstructures indicates the dominance of bora-carbide sintering-melts on reactive-sintering and densification,and on regulating the multi-level evolution of high-solution microstructures.MC additives are transformed into ZrC grain boundary phases via the sintering-melt,and its exchange-reaction with the primary phase governs the multiphase relationship.The melt as a transient liquid enables a bi-solubility of M to create prevalent core-rim structures.In the later stages of sintering,ZrC second-phase precipitates with a higher solubility of M. Summary and Prospects The multi-levelled control of multiphase microstructures by the reactive-melt is analogous to"dissolution-reprecipitation"process for liquid-phase sintering in the transformable microstructures of silicon-based ceramics,with silicate-melts and glassy phases at grain boundaries.In contrast to the monolithic ceramics of high-entropy MB2 and MC,the multi-levelled solid-solutions and the associated multiphase microstructures of MIB2-MIIC UHTCs offer ample and novel routes for comprehensive control,better optimization and further enhancement in high-performance UHTCs.The coherent hetero-interfaces created from the multi-levelled solutions via solid-state phase-separations and their interconnected dislocation networks can further improve the high-temperature strength,and those phase-boundaries,grain-boundaries,and solute-segregates allow a precise control over the multiscale semi-coherent microstructures.The research on this synergistic evolution of intergranular phases and sintering-melts at high temperatures along with the multiphase transformation has a promising potential for future advancements in ceramic genomes and levelled structure-property relationship for multiphase UHTCs governed by solid-solutions as enthalpy-regulation.
Introduction With the continuous expansion of infrastructure construction in alpine regions,a demand for concrete construction under sub-zero temperatures increases significantly.However,conventional low-temperature construction methods suffer from high energy consumption and complex operational processes.Although sulfoaluminate cement(SAC)exhibits excellent low-temperature adaptability,and calcium chloride(as an antifreeze agent)can effectively lower the freezing point and maintain a liquid-phase environment,the hydration kinetics of the simple SAC-calcium chloride composite system under fully cold construction conditions(≤-15℃)are severely inhibited at sub-zero temperatures,leading to an insufficient early-age strength development,which fails to meet the rapid construction requirements of engineering projects.Consequently,there is an urgent need to optimize this composite system to fully exploit its rapid hardening and early-strength characteristics under fully cold conditions at-15℃. Anhydrite as a key component of SAC critically regulates the composition of hydration products,microstructure,and macro-scale performance of the cementitious system.However,the existing studies on the effect of anhydrite dosage primarily focus on ambient temperatures or relatively mild sub-zero conditions(e.g.,>-5℃).Systematic investigations into how anhydrite dosage governs the hydration product evolution,microstructural formation,and mechanical-deformation properties(particularly early-age performance)of the SAC-calcium chloride composite system under extreme low-temperature conditions(-15℃)and fully cold construction processes remain largely unexplored. This study was to systematically reveal the critical regulatory effects and intrinsic mechanisms of anhydrite dosage on the low-temperature hydration and hardening behavior of the SAC-calcium chloride composite system under fully cold construction conditions at-15℃,simulating the harsh environments encountered in real-world engineering.The findings could be expected to expand the application potential of SAC in extreme environments,particularly in remote regions lacking thermal energy supply. Methods Under fully cold construction conditions(chilled materials,mixing,and curing)at-15℃,a composite system was designed with SAC clinker and anhydrite as binders and a 20%calcium chloride solution as a mixing medium.Anhydrite dosage gradients were set at 0%,5%,10%,15%,20%,25%,and 30%,respectively. The mortar specimens(40 mm×40 mm×160 mm)were prepared at a water-to-binder ratio of 0.37 based on the standard GB/T 17671-2021 Test Method for Cement Mortar Strength(ISO Method)for strength evaluation.The shrinkage specimens(40 mm×40 mm×160 mm)were prepared based on the standard JGJ/T70-2009 for Test Methods of Basic Properties of Construction Mortar. Cement paste specimens were formulated at a water-to-binder ratio of 0.32.The calcium chloride solution and cement were sequentially poured into a mixer,stirred at a low speed for 120 s,paused for 15 s,and then stirred at a high speed for 120 s.The resultant mixture was cast into molds and compacted by a vibrating table for 60 cycles.All the specimens were cured on racks under uncovered conditions at-15℃. After reaching specified curing ages,the mortar specimens underwent macroscopic tests.Cement paste specimens were crushed on-site,submerged in anhydrous ethanol to terminate hydration at room temperature for≥7 d,and then vacuum-dried at 40℃and-0.08 MPa for≥24 h.The dried samples were subjected to the microstructural analyses to investigate the phase composition and hydration mechanisms. Results and discussion Under fully cold construction conditions at-15℃,the incorporation of 10%anhydrite dosage enables the SAC-calcium chloride composite system to achieve the 1-d and 3-d compressive strengths of 20.1 MPa and 38.0 MPa,respectively,representing approximately 100%enhancement,compared to the pure clinker group.At an anhydrite dosage of 15%,the peak hydration temperature increase reaches 18.9℃(33.9℃relative to ambient temperature),effectively addressing the challenges of delayed early hydration kinetics and insufficient strength in sub-zero environments. Anhydrite significantly suppresses a shrinkage via promoting the formation of expansive AFt phases.At the dosage of 5%,the 3 d shrinkage rate reduces to 0.100%(i.e.,47.4%reduction),while at the dosage of 25%,the 28 d shrinkage rate decreases to 0.237%(i.e.,35.1%reduction),offering a graded solution for a low-temperature shrinkage control. The microstructural analyses reveals that anhydrite regulates the types and morphology of hydration products.In the 28 d hydrated pure SAC clinker,unstable petal-like Friedel's salt crystals occur.Anhydrite optimizes the Cl/S ratio of the system,promoting AFt formation,while suppressing Friedel's salt generation.At the optimal dosage of 10%,needle/rod-shaped AFt crystals form a dense interlocking network,which is pivotal for early-age strength enhancement.However,the excessive dosage(>10%)leads to unreacted anhydrite enrichment and short rod-shaped AFt aggregates with localized bridging,resulting in the strength regression at later ages. Conclusions Under fully cold construction conditions at-15℃,anhydrite significantly enhanced the hydration activity and early-age strength of the SAC-calcium chloride composite system.An appropriate anhydrite dosage of 10%promoted the hydration process of calcium sulfoaluminate in the system and accelerated the nucleation and growth rate of AFt,thereby forming a denser microstructure of early hydration products.However,the excessive anhydrite disrupted the sulfate phase equilibrium in the reaction system,inhibited the continuous formation of AFt,and induced anhydrite enrichment,ultimately degrading the mechanical properties due to structural loosening. At early ages,the anhydrite dosage of 5%approached the optimal sulfate balance required for hydration,effectively compensating for plastic shrinkage and chemical shrinkage.In contrast,the dosage of 25%provided sufficient SO42-ions during later hydration stages,ensuring sustained AFt formation and suppressing drying shrinkage over time. Anhydrite optimized the Cl/S molar ratio in the system,facilitating the formation of a dense network of needle-bar Aft,while inhibiting the formation of the unstable Friedel's salt phase.The excessive anhydrite,however,led to interconnected short-rod AFt and gypsum enrichment,further compromising the structural integrity.
In the information era,conventional silicon-based chips face significant challenges to meet the demands of real-time data processing,device miniaturization,and low-power operation due to the short-channel effects,leakage current control,and quantum effects.The von Neumann architecture,with its separation of computing and storage units,leads to a bottleneck that the massive data transfer between units consumes a substantial energy and reduces a system efficiency.To address these issues,neuromorphic computing systems based on memristors have attracted much attention.These systems integrate storage and computing together,thus enhancing a computational efficiency and reducing an energy consumption.Two-dimensional(2D)materials,with their atomic-scale thickness,free of dangling bonds on the surface,and tunable properties,emerge as promising candidates for key materials in neuromorphic computing. This review provides a comprehensive overview on the applications of 2D materials in neuromorphic computing.The synthesis methods of 2D materials and their heterojunctions are introduced,and then various architectures and operating principles of 2D neuromorphic devices are discussed.The review also represents the unique advantages of 2D materials,such as their high carrier mobility and excellent mechanical flexibility,which make them suitable for a wide range of applications,including wearable devices,biosensors,and implantable medical devices.In terms of device structures,the review mainly covers two-terminal memristors and three-terminal synaptic transistors.Two-terminal memristors,with their simple structure and high scalability,are ideal for high-density memristor crossbar arrays.Three-terminal synaptic transistors offer a more controllable performance and a better stability.The review explores emerging multi-terminal heterosynaptic devices,which can simulate more complex synaptic behaviors. This review further examines the integration of 2D materials into neuromorphic systems,including in-memory computing architectures and sensory-processing-computing integrated systems.In-memory computing architectures,such as memristor crossbar arrays,leverage the non-volatile storage and multi-resistance states of memristors to directly simulate neural network node weights and perform parallel matrix operations.Sensory-processing-computing integrated systems utilize the unique response properties of 2D materials to collect environmental signals,such as light,gas,and sound,as well as integrate sensing modules with in-memory computing to achieve efficient data processing. This review addresses the challenges of applying 2D materials to neuromorphic computing,including material preparation,device design,and system integration.While laboratory-scale preparation methods like mechanical exfoliation can yield high-quality 2D materials,they are not suitable for large-scale integration.Wafer-scale growth methods,such as chemical vapor deposition(CVD)and molecular beam epitaxy(MBE),offer a better scalability but face some challenges in controlling the number of layers,achieving a uniform thickness or a high production efficiency.In terms of device design,2D neuromorphic devices exhibit diverse architectures and operating principles,such as conductive filaments,phase changes,and defect engineering.However,further efforts are needed to reduce power consumption and improve cyclic stability. Summary and Prospects The review outlines future research directions,such as the development of large-area material growth and transfer techniques,the design of novel device structures,and the integration of multi-functional systems.2D materials are expected to play a crucial role in the advancement of neuromorphic computing through interdisciplinary collaboration and continuous innovation,paving a way for the development of artificial intelligence,the Internet of Things,and big data technologies.
Introduction Conventional concrete suffers from its inherently low tensile strength.To address this drawback,researchers propose steel fiber reinforced concrete(SFRC)as a novel material that significantly improves tensile properties and exhibits outstanding performance in cracking resistance,toughness,and durability.However,the incorporation of steel fibers makes the mechanical behavior of SFRC more complex.To ensure its safe application in structural engineering,an accurate prediction of its mechanical properties is essential. Artificial intelligence technologies are widely applied to accurately evaluate the mechanical properties of concrete.However,the existing machine learning models for SFRC are typically trained on a limited number of samples(i.e.,fewer than 300),which restricts their generalization capability.Moreover,these models often lack interpretability,undermining their credibility and limiting their practical application in engineering projects. This study was to establish a database for the compressive and splitting tensile strengths of SFRC,develop corresponding machine learning prediction models,and evaluate their predictive performance.Furthermore,the interpretability of the models was analyzed.The findings of this study could offer some insights into the development of high-precision machine learning models for SFRC and their interpretability analysis,thereby promoting their application in engineering practices. Methods In this study,a total of 636 experimental data points on SFRC were collected from 24 independent studies to establish a comprehensive database,including 419 data points for compressive strength and 217 for splitting tensile strength.Each data entry contains a mix-related information such as the water-to-binder ratio,sand ratio,aggregate-to-binder ratio,maximum size of coarse aggregate,fiber shape factor,fiber aspect ratio,fiber volume fraction,and the corresponding compressive or splitting tensile strength. Based on this database,five machine learning models(i.e.,Random Forest(RF),Gradient Boosting Regression Tree(GBRT),Extreme Gradient Boosting(XGB),Light Gradient Boosting Machine(LGBM)and Bayesian Neural Network(BNN))were proposed.The predictive performance of these models was evaluated using the coefficient of determination(R²),mean absolute percentage error(MAPE),and root mean square error(RMSE),in order to identify the most effective prediction model. For the selected model,the SHAP(SHapley Additive exPlanations)method was employed to analyze the trends and contribution of each input parameter on the compressive and splitting tensile strengths of SFRC.In addition,the Partial Dependence Plot(PDP)and Individual Conditional Expectation(ICE)methods were also used to quantitatively investigate the variation patterns of predicted values with respect to individual input parameters. Results and discussion All the models proposed demonstrate a great predictive performance.The R2 for the test set ranges from 0.84 to 0.90,while for the training set it ranges from 0.80 to 0.90.A small difference between them(i.e.,both being>0.75)indicates a good predictive accuracy and a generalization ability.For the overall performance across R²,MAPE and RMSE metrics,the LGBM model shows the optimum prediction performance. The SHAP analysis reveals that the compressive and splitting tensile strengths of SFRC decrease with increasing water-to-binder ratio and aggregate-to-binder ratio,while the strengths both increase at a higher sand ratio and a greater fiber reinforcement factor.In addition,as the maximum size of coarse aggregate increases,the compressive strength decreases,whereas the splitting tensile strength increaseds.These results are consistent with the practical observations.Based on the mean absolute SHAP values,the input parameters influencing the compressive strength in a descending order are water-to-cement ratio,sand ratio,fiber reinforcement factor,aggregate-to-cement ratio,and maximum coarse aggregate size.For splitting tensile strength,the order is fiber reinforcement factor,sand ratio,water-to-binder ratio,aggregate-to-binder ratio,and maximum coarse aggregate size. The influence and parameter importance rankings obtained through the PDP and ICE analysis are in a reasonable agreement with those derived from SHAP,further validating the interpretability and reliability of the model. Conclusion A large-scale database containing 636 data entries was established for the compressive and splitting tensile strengths of SFRC.Based on this database,five machine learning prediction models(i.e.,RF,GBRT,XGB,LGBM and BNN)were proposed.All the models exhibited good predictive performance and generalization ability,significantly outperforming the existing prediction methods.Among them,the LGBM model showed the optimum overall performance.The SHAP,PDP and ICE techniques were employed to analyze the influence and importance of each input parameter on the compressive and splitting tensile strengths.Based on the variable contribution analysis,the main factors affecting the compressive strength were the water-to-cement ratio,sand ratio,fiber reinforcement factor,aggregate-to-cement ratio,and maximum coarse aggregate size.In contrast,the key determinants of splitting tensile strength were the fiber reinforcement coefficient,sand ratio and water-to-cement ratio.
Introduction Tricalcium silicate(C3S)is one of Portland cement clinker minerals whose proportion is over 50%.It hydrates quickly and releases lots of heat in early hydration period.The reaction rate and degree of C3S in early hydration period are the chelloef constituent to determine the exothermal and mechanical performance of Portland cement;as well as the cracking risk of concrete.One of concrete additive,temperature rising inhibitor,was created to suppress the heat release of binder and decrease its exothermic rate.Cyclodextrin(CD)is the main functional composition of temperature rising inhibitor.It is studied that the effect of CD on the early hydration process of C3S.This work is helpful to understand the action mechanism of temperature rising inhibitor. Methods Pure C3S was calcined,chemical pure CD was used.C3S paste with w/c=0.5 was prepared.The CD dosage in paste is 0%,0.05%,0.10%and 0.20%separately.Dilute C3S solution with the solid content of 10-4 and containing 0,2 mmol/L and 4 mmol/L CD solution was prepared to measure the dissolving rate of C3S in the induction period of hydration.Pore solution of C3S was obtained using centrifugal extraction for fresh paste or press method for hardened C3S paste.The hydration exothermal curves of C3S pastes containing different dosages of CD were measured using isothermal calorimetry.The time-depended concentration variation of Ca and Si in dilute C3S solution and pore solution was measured by ICP-AES.SEM was used to investigate the formation of hydrate nucleus on the polished surface of C3S particles etched by CD solution or pure water.The ion activity product of pore solution relative to C3S was calculated. Results and discussion There is not obvious induction period during the hydration of pure C3S.The induction period of C3S hydration prolongs with the increase of CD dosage in paste.The accumulate heat release of C3S is proportional with its hydration degree.The hydration degree of C3S paste containing CD is higher than blank one at the point of maximal exothermic rate.The accumulate heat release of C3S paste with or without CD is almost same at the end of induction period.The addition of CD decreases the early hydration speed,but does not negatively influence the final hydration degree.CD inhibits momentarily the dissolution of C3S in early hydration period,but does not affects the hydration of C3S in long period.The Ca and Si concentration in pore solution increases with the increase of CD dosage in induction period of hydration.The ion activity product of pore solution relative to C3S is changed when Cd is added into C3S paste.CD is adsorbed at the etch pits on the surface of C3S particles to increase the barrierΔGcrit of the etch pit expansion model and decrease the growing speed of etch pit.There are lots of etch pit on the polished surface of C3S particle after 1 h immersion in pure water.There are few etch pit on the polished surface of C3S particle after 1 h immersion in 1 mmol/L CD solution. Conclusions CD prolongs the induction stage and the main reaction stage of hydration,decreases the reaction rate of C3S.This effect is very intense when the dosage of CD increases to 0.2%.The hydration degree of C3S paste increases in some extent at the peak reaction rate due to the prolongation of the main reaction period of C3S paste containing CD.The ultimately hydration heat release of C3S paste containing CD does not decrease due to the delay of hydration.CD is absorbed on the etch pit of C3S particles in the initial hydration stage to elevate the energy barrier ΔGcrit of the etch pit expansion model.It decreases the dissolving rate of C3S and prolongs the induction period of hydration.In the induction period the exist of CD results in an increase of Ca and Si concentration in pore solution and higher degree of supersaturation relative to Ca(OH)2 and C-S-H.The formation of C-S-H nucleus is inhibited to hinder the acceleration of C3S hydration.
Introduction The issue of electromagnetic pollution has become increasingly severe with the development of the electronic communication technology.The excessive electromagnetic waves pose risks to the national security and the human health in daily life.Consequently,wave-absorbing materials have gradually garnered public attention.Biomass,with its inherent network structure,can be used to produce porous carbon for addressing electromagnetic pollution.Among various biomass sources,coconut shells are widely distributed in China and have long been treated as agricultural by-products or waste.Recycling and utilizing coconut shells to prepare wave-absorbing materials not only helps mitigate electromagnetic pollution but also offers a new approach for the high-value application of agricultural by-products such as coconut shells. Methods The experimental materials included coconut shells purchased from Hainan Wenchang Coconut Shell Co.,Ltd..Potassium hydroxide(KOH),calcium carbonate(CaCO3),hydrochloric acid(HCl),and paraffin wax(C25H52)purchased from Shanghai Titan Scientific Co.,Ltd.The coconut shells were processed into 1-2 cm pieces,cleaned,and dried at 80 °C for 24 h.The dried pieces were then ground into powder using a pulverizer and sieved through a mesh with an aperture of 250-300 μm.The coconut shell powder was mixed with CaCO3 and KOH at mass ratios of 1.0∶1.0∶0.5,1∶1∶1,1∶1∶2,and 1∶1∶3,respectively.The mixtures were uniformly ground in a pulverizer to obtain alkalized coconut shell powder,which was subsequently dried.The dried alkalized powder was placed in a tube furnace,which was purged with nitrogen gas(N2),and then carbonized at 700 °C for 2 h.The resulting product was neutralized with hydrochloric acid(HCl)under magnetic stirring for 12 h,washed with deionized water until neutral,and finally dried at 80 °C for 24 h,then the coconut shell-based porous carbon was obtained. Results and discussion In this study,coconut shell was utilized as the carbon source,based on its inherent multi-level network structure and high carbon content.Using KOH and CaCO3 as dual activators,a one-step carbonization method was employed to prepare coconut shell-based carbon wave-absorbing materials with superior microwave absorption performance.Compared to pure coconut shell carbon and coconut shell carbon activated solely with an equal mass of KOH,the sample prepared with dual activators exhibited more uniform surface pore distribution and hierarchical structure.This specific structure played a critical role in enhancing the electromagnetic wave absorption performance.Consequently,the dual-activator method offered a novel approach for preparing porous carbon materials with complex three-dimensional micro/mesoporous structures.At 700℃,the gradual addition of activator resulted in enlarged pores and increased defects in the porous carbon structure,ultimately causing pore collapse.Higher activator concentrations led to larger pore diameters,which reduced electromagnetic wave reflection efficiency and consequently diminished microwave absorption performance. Conclusions A coconut shell-based porous carbon material with excellent wave-absorbing performance was successfully prepared via a one-step carbonization method combined with a dual-activator(KOH and CaCO3)activation process.By adjusting the mass ratios of KOH to CaCO3,the pore structure of the resulting carbon material was modulated,leading to varied electromagnetic wave absorption properties.The optimal absorption performance was achieved under the conditions of a carbonization temperature of 700℃and a mass ratio of coconut shell powder:CaCO3∶KOH=1∶1∶1.The material obtained under these conditions exhibited a minimum reflection loss(RLmin)of-45.79 dB at a sample thickness of 5.0 mm and a frequency of 5.12 GHz.This study utilized a simple one-step carbonization process to produce effective wave-absorbing materials with abundant coconut shell waste,providing valuable theoretical guidance for the development of high-performance absorbers and significantly broadening the application prospects for biomass-derived wave-absorbing materials.
Introduction Crystallization control is crucial during glass production.In glass crystallization theory,it has been hypothesized that there is a direct relationship between glass-crystal interfacial energy and nucleation rate.Since it is difficult to measure interfacial energy directly,classical nucleation theory is used to obtain it.However,the estimation process is complex;various measurement data such as the nucleation rate,viscosity,and Gibbs free energy barriers between the glass and crystal are required.Overall,estimating the glass-crystal interfacial energy is time-consuming.In this regard,the interfacial energy can be directly obtained using molecular dynamics(MD)simulations.In this study,we implemented an interface model to estimate the glass-crystal interfacial energy based on the theory of Tielemann et al.,which was recently introduced to generate crystal orientation planes using minimum-energy cuts.To the best of our knowledge,this is the first work in which the crystal orientation plane determined based on a minimum-energy cutting process has been used to build a glass-crystal interface in a more realistic environment(i.e.,hypothesizes that a minimum-energy structure may occur during crystal nucleation)and calculate the interfacial energy.To achieve this,we considered stoichiometric alkali(Li,Na,and K)disilicate(2SiO2)glasses and crystals,as some early-stage experimental data have been reported,which are highly beneficial for validating the MD results.The effects of different potential models were also investigated and found that they had a significant impact on the reproduction of the experimental trend. Methods Simulations were performed using the LAMMPS package.The temperature and pressure were controlled with the Nose-Hoover thermostat and barostat,respectively.After setting up the glass-crystal interface using NPT,we ran MD simulations with NVT for another 200 ps to calculate the interfacial energy.The MD simulations were performed with a time step of 1 fs.Periodic boundary conditions were applied in all directions.Cutoff distances were applied according to references.We used three interatomic potential(SHIK,Du,and Pedone)models to estimate the interfacial energies of Li2O-2SiO2 glass-Li2O-2SiO2(001),Na2O-2SiO2 glass-Na2O-2SiO2(010),and K2O-2SiO2 glass-K2O-2SiO2(001).All three of these potential functions are widely used.The glass structure was fabricated from the crystal structures by simulating a melt-quenching process.First,the Li2O-2SiO2(001),Na2O-2SiO2(010),and K2O-2SiO2(001)crystal structures were prepared.Half the crystal was kept fixed,while the other half was melted at 3500 K with a canonical ensemble(NVT)for 300 ps and then quenched to 300 K at a cooling rate of 5 K/ps.After the melt-quenching process,the crystal part was unfixed and relaxed for 200 ps with a glassy structure using an isobaric-isothermal ensemble(NPT)at a temperature of 300 K.An interfacial model was developed by the theory of Tielemann et al,where the crystal plane was determined through the minimum energy cut in the crystal structure. Results and discussion We first evaluated the glass density by calculating the local density profile along the z-direction of Li2O-2SiO2 glass-Li2O-2SiO2(001),Na2O-2SiO2 glass-Na2O-2SiO2(010),and K2O-2SiO2 glass-K2O-2SiO2(001).The glass structures show density results comparable to the experimental data. The calculated interfacial energy values using the SHIK potential show a similar experimental trend,while the Du and Pedone potentials are unable to reproduce the experimental trend.However,the potentials of Du and Pedone show better values of interfacial energy for the glass-crystal interface of Li2O-2SiO2 than the SHIK.Our MD results demonstrate that among the potential models,SHIK is a good candidate for calculating interfacial energy in terms of experimental reproduction. We analyzed the interfacial coordination number(i.e.,cation-anion)in the contact area between the glass and crystal surfaces.These coordination numbers are difficult to estimate experimentally.Typically,the coordination number is determined in the bulk region of a glass or crystal structure.We found that the interfacial coordination number varies significantly at the glass-crystal interface of Li2O-2SiO2,Na2O-2SiO2,and K2O-2SiO2.Among the interfacial systems,coordination number values of two,three,four,and five were observed,the most frequently observed value was one.The values were significantly lower at four and five for K2O-2SiO2 and Na2O-2SiO2,respectively.Our MD results demonstrated that the cation(Li,Na,and K)-anion environments were not the same in the interfacial domain.For further evaluation,we calculated the bond strength-coordination number. The bond strength-coordination number has been reported for chalcogenide glasses.In the present work,the bond strength-coordination number is introduced for glass-crystal interface systems.The calculated results of bond strength-coordination number show a decreasing trend in the order Li>Na>K,which is similar to interfacial energy.Overall,analysis revealed that the alkali(Li,Na,and K)—O bond plays a crucial role in the interfacial strength. Conclusion We developed an interface model using molecular dynamics simulations based on the minimum energy cut of crystals with glassy structures.The minimum energy cut of the crystal was determined by applying Tielemann theory.The modeled interfaces were between glass and crystals in stoichiometric alkali(Li,Na,and K)disilicates.The interface model reproduced the experimental interfacial energy trend of Li>Na>K;the interatomic potential model was found to have a significant effect on reproduction.The MD results indicate that the SHIK-based MD model could reproduce the experimental results better than the other potential models.In addition,the interfacial coordination number was also calculated,which varies depending on the alkalinity of Li,Na,and K.Using the interfacial coordination number,the bond strength-coordination number was estimated,and found that the interfacial energy trend Li>Na>K is related to the bond strength-coordination number.
The active-matrix light-emitting diodes(LEDs)array is a main development direction of the next-generation display technology,which requires high efficiency,wide color gamut,high contrast,high resolution,fast response,and cost-effectiveness.Perovskite CsPbX3 nanocrystals emerge as promising candidates,offering tunable emission wavelength,remarkable photoluminescence quantum yields,cost-competitiveness,and integration with diverse solution-based pixilation methods.Based on these unique properties from lead halide perovskite and nanomaterials,CsPbX3 nanocrystals demonstrate a formidable potential for active-matrix LEDs.However,the integration of perovskite LEDs with active-matrix remains a challenge.The efficiencies of both red and green perovskite LED have exceeded 28%,approaching the theoretical limit of light out-coupling efficiency for planar LED.The existing efficiency of sky-blue perovskite LED reaches 20%,while the efficiency of pure-blue perovskite LED is still lagging.Thus,improving the efficiency of pure-blue perovskite LED becomes imperative to realize full-color display.In addition,the slow electroluminescence response time caused by ion migration in perovskite under an electric field is also a critical issue,which is a limiting factor for the development of high-refresh-rate active-matrix display using perovskite LEDs. To enhance the device performance of red,green and blue quantum dot LEDs,it is crucial to control the surface structure at the nanoscale of metal halide quantum dots.Previous extensive studies carried out on the atomic composition of the surface,the types and coordination modes of surface ligands,ligand density and developed various surface reconstruction strategies and ligand application paradigms to improve the quality of metal halide quantum dot crystals and the integrity of the surface lattice.This review systematically demonstrates recent research achievements,summaries the principles and ligand functions of different reconstruction strategies,and represents single-color demo of quantum dot LEDs integrated with active-matrix,providing a reference for the further development of full-color active-matrix displays based on metal halide quantum dots. Summary and Aspects In this review,we summary various strategies for surface reconstruction of quantum dots,discuss the selection and design principles of surface and ligands for quantum dots applied in electroluminescence,and finally represent recent research progress in the integration of lead halide and its quantum dots with active-matrix displays.To further promote the realization of efficient full-color active drive LEDs,a key interim goal in the next step is to break through the pixelization technology for lead halide quantum dots,thereby achieving the integration of red,green,and blue colors onto the active-matrix TFT backplane simultaneously.Many scientific and technical issues need to be solved in this process.For instance,how to ensure that the morphology and photoelectric performance of the lead halide quantum dot film are not damaged during pixelization.The need for high resolution means that thousands of pixel points should be arranged very closely,having high requirements for the precise positioning of pixelization technology.In addition,avoiding color crosstalk caused by ion exchange between pixel points is also a technical problem that must be solved due to the easy ion exchange of halogen ions.
Introduction Cement is a fundamental material for global infrastructure.Global cement production is projected to exceed 4.5 billion tons by 2030.The cement industry contributes about 7.5%of global anthropogenic carbon dioxide(CO2)emissions.These emissions mainly come from fossil fuel combustion and limestone decomposition during the calcination process.Replacing fossil fuels with concentrated solar energy(CSE)for clinker calcination is a key pathway to achieve carbon neutrality in this sector.The CSE technology can concentrate solar radiation up to 7000 times and generate ultra-high temperatures of above 3000 K.These conditions can meet the thermal requirements for cement clinker production. The spectral mismatch between cement materials and solar radiation as a critical bottleneck limits the efficiency of solar calcination..The solar spectrum concentrates its energy in the visible(400-700 nm)and near-infrared(NIR,700-2500 nm)bands.Most cement raw materials,such as calcium carbonate(CaCO3),silicon dioxide(SiO2),and aluminum oxide(Al2O3),are wide-bandgap materials.These materials absorb mainly in the ultraviolet region and are nearly transparent to visible and NIR light.This transparency leads to a low solar-to-thermal conversion efficiency.Iron oxide(Fe2O3)and iron-bearing ferrite minerals have narrower bandgaps of 2.0-2.2 eV.These minerals offer a stronger light absorption in the solar spectrum.This study was to investigate high-ferrite cement(HFC)clinkers to use the high absorption of the iron phase for better photothermal conversion.The calcination performance in electric furnace and solar furnace was compared and the first-principles calculations were performed.The goal was to reveal the photothermal coupling mechanism that could enable low-temperature and rapid clinker formation. Methods Three high-ferrite cement raw meals were prepared with analytical-grade reagents.These samples,named HFC-16,HFC-18,and HFC-20,were designed with different mass fractions of tetracalcium aluminoferrite(C4AF,16%,18%,and 20%),respectively.All raw materials were ground and passed through a 200-mesh sieve.The sintering was carried out in a conventional electric elevator furnace and a high-flux solar simulator,respectively.The solar simulator used a xenon lamp array to mimic the solar spectrum(AM1.5).This simulator generated a peak heat flux of>1800 kW/m2 at the focal plane. For the experiments in the electric furnace,the samples were heated to 800℃and held for 30 min.The samples were then heated at 1000,1200℃,or 1375℃and held for 2 h,respectively.For the experiments in the solar furnace,the samples were rapidly heated to 800℃and held for 1 min.They were then heated to the target temperature and held for 5 min.All the samples were rapidly cooled after firing.The phase composition of each sample was analyzed by X-ray diffraction(XRD).The Rietveld refinement was used for quantitative phase analysis.The optical properties were measured by ultraviolet-visible(UV-Vis)spectrophotometry in the range of 200-2500 nm.The total solar absorptance was calculated by the AM1.5 solar irradiance distribution.The electronic structures were simulated by a software named Vienna Ab initio Simulation Package(VASP).The simulations were based on the Density Functional Theory(DFT)with the GGA-PBE functional and a Hubbard U correction for Fe 3d orbitals. Results and Discussion The UV-Vis spectra of the raw materials show that wide-bandgap oxides(i.e.,CaO,SiO2,Al2O3)have a weak absorption in the solar spectrum region.Their absorptance values are all below 20%.Fe2O3 is a main absorber among all the raw materials.Its solar absorptance reaches 71.1%.As a result,increasing the Fe2O3 content in the raw meal improves the overall light absorption.The solar absorptance of the raw meal increases from 56.6%for HFC-16 to 60.5%for HFC-20.The light absorption of the clinker minerals depends on the calcination temperature.At 1000℃,the absorptance decreases slightly.This decrease is due to the decomposition of CaCO3 into weakly absorbing CaO and the low crystallinity of intermediate phases.At 1200℃,the absorptance increases sharply.The iron phase mineral formed at 1200℃shows a solar absorptance of 83.9%.This value is greater than that of the raw Fe2O3.For the clinker sample HFC-20,the total light absorptance is 75.6%at 1375℃. The results by the First-principles calculations explain the mechanism behind this enhancement.In the high-temperature ferrite solid solution(C4AF),Fe3+ions occupy both tetrahedral and octahedral sites.This mixed coordination induces a crystal field splitting and creates diverse intermediate energy levels.The substitution of Al3+for Fe3+also introduces lattice defects.These defects create dense defect states within the bandgap.The density of states(DOS)analysis indicates that Fe 3d orbitals dominate the conduction band minimum.O 2p orbitals dominate the valence band maximum.The strong O 2p → Fe 3d transitions are responsible for the intense broadband absorption in the visible and NIR regions. The comparison between the two heat sources shows a clear photothermal coupling effect in the solar furnace.The XRD patterns indicate that the solar-calcined samples processed at a thermocouple-measured temperature of only 800℃already contain distinct silicate mineral phases(i.e.,tricalcium silicate,C3S,and dicalcium silicate,C2S).In the conventional electric furnace,these phases only form at 1200℃.This result indicates that the iron phase absorbs a high-intensity photon energy locally and lowers the formation temperature of clinker minerals by approxiamtely 400℃.The electric furnace transfers heat slowly through conduction from the surface to the interior.The solar furnace delivers energy directly to the reactive iron-bearing sites.This direct energy delivery greatly accelerates the solid-state reaction kinetics. At the final sintering temperature of 1375℃,the two methods both produce clinkers with the target mineral phases(i.e.,C3S,C2S,tricalcium aluminate C3A,and C4AF).No free CaO appears in either case.This result confirms that the solar furnace can fully sinter cement clinker.The Rietveld refinement of the XRD patterns shows that the solar-calcined clinker exhibits broader diffraction peaks than the electric furnace clinker.The rapid heating rate and the unique photothermal environment in the solar furnace likely caused this broadening.Smaller crystallite sizes or higher lattice defect concentrations are the probable reasons.These findings indicate that solar calcination saves energy and changes the microstructural evolution of the cement minerals. Conclusions Based on the UV-Vis absorption testing and XRD analysis of raw materials,raw meals,and samples calcined at different temperatures,the overall light absorption intensity of the raw meal increased significantly as the Fe2O3 content in the raw meal increased.Furthermore,the light absorption intensity of the iron phase in the clinker minerals increased with increasing the calcination temperature.At 1200℃,its light absorption rate reached 83%.The light absorption intensity of the clinker also increased with the calcination temperature,reaching 75.6%at 1375℃.More importantly,the iron phase could trigger a photothermal coupling effect when calcined in a simulated high-concentration solar furnace,significantly lowering the formation temperature of clinker minerals.The results by the XRD Rietveld refinement and hydration calorimetry indicated that,compared with the electric furnace clinker,the simulated concentrated solar calcined clinker(SF-HFC)exhibited diffraction peak broadening characteristics.This could demonstrate that the photothermal effect of the iron phase significantly reduced the calcination temperature of cement clinker and lowered the production energy consumption,providing a material design strategy for high-efficiency and low-carbon cement manufacturing.
