Synthesis and optimization of tantalum monoboride (TaB) ceramics were investigated to address a gap in the literature where TaB‐based bulk ceramics are underexplored despite their predicted excellent mechanical properties. The main focus was put on evaluating influence of extra boron (0.85–1.5 at%), silicon carbide (3–15 wt%), and silicon nitride (1–15 wt%) additions on densification, phase purity, microstructure, and mechanical performance of the TaB ceramics. In the study, a Ta+B powder mixture for stoichiometric TaB was consolidated via reaction reaction hot pressing (RHP) at 1800°C and 1900°C under 30 MPa for 1 h. Because it yielded poor densification (∼62% relative density) and undesirable impurity phases, various processing routes were tried to obtain the desired TaB ceramic, the methods including (i) using B additive and C (introduced as impurity by wear of milling ball coating) to eliminate the minor oxygen‐related impurities TaC and Ta 2 O, (ii) using SiC/Si 3 N 4 to deoxidize the reaction system and reinforce the TaB composites, and (iii) using RHP versus spark plasma sintering (SPS) to compare effects of sintering temperatures and time. Thermodynamic analysis was done to facilitate understanding phases formation. The results showed that densification was improved by additions of 0.85–1.5 at% extra B in combination with SPS at 2100°C under 40 MPa for 10–30 min, but the minor impurity phase TaC or Ta 2 O remained. Additions of Si 3 N 4 at 3 wt% and above emerged as effective, achieving near‐full density (>97% relative density) and good mechanical properties, with Vickers hardness, flexural strength, and fracture toughness reaching 26.1 ± 1.3 GPa, 705 ± 45 MPa, and 4.40 ± 0.19 MPa·m 1/2 , respectively. Residual oxygen seemed to have been collected in Si 3 N 4 ‐Si 2 N 2 O aggregates due to the formation of minor Si 2 N 2 O, a beneficial situation, leaving clean TaB grain boundaries for possible better mechanical performance of the TaB‐Si 3 N 4 composites at high temperatures. In contrast, SiC addition cannot be recommended because it promoted impurity phases (e.g., TaC, TaSi 2 , Ta 5 B 6 , and Ta 3 B 4 ) and failed to enhance densification (RHP at 1800°C under 30 MPa for 1 h) at low content of SiC additions <5 wt%, while the aimed TaB was completely missed at 5–15 wt% SiC additions.

Synthesis and optimization of tantalum monoboride (TaB) ceramics were investigated to address a gap in the literature where TaB-based bulk ceramics are underexplored despite their predicted excellent mechanical properties. The main focus was put on evaluating influence of extra boron (0.85-1.5 at%), silicon carbide (3-15 wt%), and silicon nitride (1-15 wt%) additions on densification, phase purity, microstructure, and mechanical performance of the TaB ceramics. In the study, a Ta+B powder mixture for stoichiometric TaB was consolidated via reaction reaction hot pressing (RHP) at 1800 degrees C and 1900 degrees C under 30 MPa for 1 h. Because it yielded poor densification (similar to 62% relative density) and undesirable impurity phases, various processing routes were tried to obtain the desired TaB ceramic, the methods including (i) using B additive and C (introduced as impurity by wear of milling ball coating) to eliminate the minor oxygen-related impurities TaC and Ta2O, (ii) using SiC/Si3N4 to deoxidize the reaction system and reinforce the TaB composites, and (iii) using RHP versus spark plasma sintering (SPS) to compare effects of sintering temperatures and time. Thermodynamic analysis was done to facilitate understanding phases formation. The results showed that densification was improved by additions of 0.85-1.5 at% extra B in combination with SPS at 2100 degrees C under 40 MPa for 10-30 min, but the minor impurity phase TaC or Ta2O remained. Additions of Si3N4 at 3 wt% and above emerged as effective, achieving near-full density (>97% relative density) and good mechanical properties, with Vickers hardness, flexural strength, and fracture toughness reaching 26.1 +/- 1.3 GPa, 705 +/- 45 MPa, and 4.40 +/- 0.19 MPam(1/2), respectively. Residual oxygen seemed to have been collected in Si3N4-Si2N2O aggregates due to the formation of minor Si2N2O, a beneficial situation, leaving clean TaB grain boundaries for possible better mechanical performance of the TaB-Si3N4 composites at high temperatures. In contrast, SiC addition cannot be recommended because it promoted impurity phases (e.g., TaC, TaSi2, Ta5B6, and Ta3B4) and failed to enhance densification (RHP at 1800 degrees C under 30 MPa for 1 h) at low content of SiC additions <5 wt%, while the aimed TaB was completely missed at 5-15 wt% SiC additions.

alpha-SiAlON as a solid solution of alpha-Si3N4 incorporates alien cations (namely Al3+ and REv+, RE = Li, Mg, Ca, and most rare earths) and anion O2- in the Si3N4 lattice. While effects of the cations on phases, microstructure and mechanical properties of the alpha-SiAlON ceramics have been well established, possible incorporation of another anion rather than O2- and its effects are not clear. In this work, Y-doped alpha-SiAlON ceramics with a nominal composition of Y0.4Si9.6Al2.4O1.2N14.8 were synthesized by hot pressing. Y2O3 in the powder mixture of Si3N4, AlN, Al2O3 and Y2O3 for synthesis of Y-SiAlON was partially substituted by 2YF3 to investigate effects of the substitution of F- for O2-. Density measurement, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Vickers hardness and three-point bending test were performed to characterize the Y-SiAlON ceramics. Thermodynamics of reactions involving YF3 was also assessed. The results showed that the compositions with 1-50 % 2YF3 substitution could reach full density, while the 75-100 % 2YF3 compositions were porous. The SiO2 impurity present on the Si3N4 particle surface could be eliminated by reaction with YF3. When YF3 was overdosed, formation of YOF liquid would replace the low temperature Al2O3-Y2O3-SiO2 ternary eutectic liquid to hinder alpha-SiAlON formation, leaving residual Al-O, Al-N, Y-O and Y-F species to form a variety of crystalline intergranular phases. Thin Y-O-F films existed along grain boundaries to impart good corrosion resistance against molten NaOH and better toughening effects to the SiAlON ceramics.

TaB2-SiC composites with 0-20 wt% SiC contents were prepared by reaction hot pressing using Ta, B and SiC powders as starting materials. Densification, constituent phases, microstructure and mechanical properties, namely Vickers hardness, fracture toughness and flexure strength, were evaluated by means of inspection of sintering shrinkage, density measurement, XRD, SEM, TEM, HRTEM, EDS, SAED, indentation and three-point bending tests. Phase formation, including dominant (TaB2, SiC) and minor (TaC, glassy SiO2) phases, was checked by thermodynamic assessment relevant with Ta2O5 and B2O3 impurities introduced into the reaction system by the starting powders. The results showed that mixtures of Ta, B and SiC powders would initiate self-propagating combustion synthesis (SPCS) at about 900 degrees C; a transient hold at 800 degrees C for 1 h could suppress this reaction. Volatilization of B2O3 impurity in association with local high temperature due to SPCS helped reduce the TaC and glassy SiO2 minor phase formation. TaB2-SiC composites could reach 99 % relative densities with 3 wt% SiC addition and above. Compositions with <7.5 wt% SiC additions showed uniform dispersion of SiC particles at multi-TaB2 grain junctions while compositions with higher SiC content revealed SiC segregation. Bending strength of 503 MPa and fracture toughness of 6.69 MPa & sdot;m(1/2) could be reached with 7.5-20 wt% SiC addition.

Three multi-phase tantalum carbide composites (TaCz-Ta5Si3) were fabricated by Spark plasma Sintering (SPS) using Ta, TaC and SiC powders. SiC was added to control the C:Ta ratio (z = 0.6, 0.74, 1.0), regulating the phase composition and grain morphology while also serving as a deoxidizer. Composite TaC0.6-Ta5Si3 had Ta2C as the major phase and contained Ta4C3_x, TaC and Ta5Si3. It exhibited an excellent combination of high flexure strength (714 +/- 21 MPa) and toughness (13.9 +/- 0.2 MPa center dot m1/2), despite a low Ta4C3_x fraction, a phase known to have very high toughness. The outstanding performance was attributed to the elongated Ta2C grain morphology, highly laminated intra-granular Ta4C3_x laths, and the refined Ta2C grain size. Composite TaC0.74-Ta5Si3, characterised by equiaxed grain morphology, exhibited good flexure strength (571 +/- 36 Mpa) and toughness (7.6 +/- 1.1 MPa center dot m1/2) due to the presence of Ta4C3_x laths in the c-TaC. Lastly, composite TaC1.0-Ta5Si3, composed of c-TaC and Ta5Si3, exhibited moderate strength (545 +/- 25 MPa) and toughness (5.3 +/- 0.1 MPa center dot m1/ 2).

A new route based on HfO2 + B4C + C & RARR; HfB2 + HfC + CO reaction was developed to synthesize HfB2-HfC hybrid powders. X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and transmission electron microscopy were used to evaluate the powder products. The effects of excess additions of B4C and C on the phase constituents of the powder products were investigated. Thermodynamics of relevant reactions for the synthesis of the hybrid powders were calculated to guide the selection of compositions and processing parameters. The results indicated that HfB2-HfC hybrid powders were obtained by reaction at 1750 & DEG;C for 1 h. HfB2:HfC phase content ratios showed a dependence on B4C and C additions. The obtained hybrid powders exhibited good oxidation resistance with an oxidation activation energy of 303 kJ/mol. Good sinterability of the powder products was demonstrated by spark plasma sintering at 2100 & DEG;C. The consolidated ceramics based on them measured good Vickers' hardness values (>26.0 & PLUSMN; .5 GPa) and fracture toughness (>3.78 & PLUSMN; .27 MPa & BULL;m(1/2)).

Although significant increase in mechanical properties has been achieved in ?-SiAlON ceramics by introducing self-toughening bimodal microstructure, the bimodal microstructure may not always result in better cutting performance of ?-SiAlON tool inserts. Herein Dy-?-SiAlON ceramics were prepared by hot-pressing at 1900?C under 30MPa. Diameter and aspect ratio of the large elongated ?-SiAlON grains pivotal to formation of bimodal microstructures were regulated by using 0-5wt.% Dy2O3 as a sintering additive. Mechanical properties and cutting performance of ?-SiAlON tool inserts were evaluated. The results showed good Vickers hardness (19.0-19.7GPa) and fracture toughness (3.61-4.18MPa?m1/2) increasing with crack propagation length. However, transverse section of the large elongated grains was revealed as critical crack to cause premature fracture of the ?-SiAlON ceramics. Fracture rather than attrition wear was recognized as dominant mechanism for tool failure, indicating that for better cutting performance of the ?-SiAlON tool inserts a selftoughening microstructure consisting of thinner grains with large aspect ratio is required.

以TaC、Ta和Ni粉为原料,采用热压法制备名义成分为TaC0.3-20％(体积分数)Ni的复合材料,研究热压温度在1 100～1 900℃范围内变化对TaC+Ta反应进程、物相、显微组织和力学性能的影响.根据压头位移,致密化过程可分为四个阶段,反应致密化主要发生在第二阶段950～1 700℃,充分反应后,生成平衡物相Ta2C和Ni3Ta相.在1 600℃/30 MPa/30 min条件下热压,材料能够完全致密,并形成均匀的细晶组织(平均晶粒尺寸小于5 μm),测量的抗弯强度和断裂韧性分别为(689±71)MPa和(5.72±0.57)MPa·m1/2.当热压温度超过Ni3Ta熔点(约1 500℃)较多时(例如T=1 700℃),熔化的Ni3Ta被挤出而获得几乎单相的Ta2C陶瓷材料.1 900℃条件下制备的复合材料中晶粒长大到40～50μm,虽然断裂韧性值可达到(6.96±0.38)MPa·m1/2,但粗大晶粒作为结构缺陷诱发裂纹扩展,使抗弯强度略降低到(546±44)MPa.

Silicon carbide (SiC)/graphene nanoplatelets (GNPs) ceramic composites with additions of 0,1,2,4,6,8 wt.% GNPs were fabricated by spark plasma sintering (SPS). Effects of GNPs addition on densification, microstructure and mechanical properties of the SiC/GNPs composites were investigated. As GNPs content increased, relative density of the composites decreased slightly from 99.0% for monolithic SiC to 98.3% at 8 wt.% GPNs. Uniform distribution of GNPs in the microstructure was exhibited. A small portion of SiC grains was assumedly wrapped by thin-layered GNPs, which could explain microstructural refinement of the composites with CNPs additions. Vickers hardness was increased by 7% (25.4 GPa) in the 1 wt.% GNPs composition relative to monolithic SiC (23.5 GPa) while fracture toughness of the SiC/GNPs composites showed a minimum at 1, 2 wt.% GNPs additions. The mechanical property changes indicated different states of GNPs existence in the SiC/GNPs composites, among which thin-layered GNPs wrapping SiC grains could benefit Vickers hardness relative to agglomeration of GNPs.

将金属Zr块埋在B粉末中在800～1500℃温度下反应2～16 h,使用XRD法研究金属Zr块表面反应产物的物相构成，使用SEM观察抛光截面的产物层形貌，采用EDS分析Zr、B元素分布，测量产物层厚度，根据菲克第二定律采用线性拟合法计算B向金属Zr中反应扩散动力学。研究结果表明：在800℃2 h条件下进行反应，金属Zr块表面生成少量ZrB 2 ,抛光截面上未观察到明显的产物层生成。当温度升高到1 200～1 500℃反应时间延长到4～16 h时，抛光截面上生成了厚度均匀连续的ZrB 2 产物层，其厚度随反应温度升高和反应时间延长而增加。计算得出产物层增厚的时间指数n=0.434,B元素扩散激活能Q=152.0 kJ/mol,扩散系数指前项D 0 =1 743.4×10 -12 m~2/s。

Generating oxygen vacancies is an effective way to improve the lithium-ion storage performance of V2O5. However, the mechanism has not been theoretically investigated. In this study, first-principle calculations were performed to study the effect of oxygen vacancy on electrochemical properties of γ-V2O5 as cathode material for lithium-ion batteries. γ-V2O5 with oxygen vacancy mole fraction of 1.67% shows an open circuit voltage about 0.1 V lower than that of the perfect γ-V2O5. Oxygen vacancies generates gap states, which is beneficial to the electronic conductivity of γ-V2O5 and γ-LiV2O5. In addition, the activation energies for lithium-ion diffusion along [010] in both γ-V2O5 and γ-LiV2O5 are increased by oxygen vacancy, which might lead to the decrease of diffusion coefficient. Our results will provide guidance for further improving the lithium-ion storage performance of γ-V2O5.

ZrB2-20%volSiC composites were hot pressed with ZrB2 and SiC powders and the effect of temperature and friction couples (WC or Al2O3) on the tribological properties of these composites was investigated. The results show that the coefficient of friction (CoF) of ZrB2-SiC composites coupled with WC or Al2O3 was almost constant with respect to temperature (0.5-0.6). Meanwhile, their wear rates (WRs) were of the order of 10(-4) mm(3) N-1 m 1. Either discontinuous (with WC) or continuous (with Al2O3) tribo-layers were found to have been formed on the worn surfaces of the composites and these tribo-layers did not exhibit any lubricious or anti-wear effects. At temperatures of 25-400 degrees C, the wear mechanism of the composites coupled with WC and Al2O3 included abrasion, tribo-oxidation, and adhesion. At higher temperatures (600-800 degrees C), the wear mechanism of both tribo-pairs included tribo-oxidation and adhesion.

Samples in Si-Al-R-O-N (R = Y, Gd, Yb) systems were prepared by solid-state reactions using R2O3, Al2O3, SiO2 and Si3N4 powders as starting materials. X-ray diffraction was done to investigate RAM-J(R) solid solutions [RAM = R4Al2O9, J(R) = R4Si2N2O7] formation and their equilibrium with RSO (R4Si2O10). Phase relations between RAM, J(R) and RSO at 1700 degrees C were summarized in a phase diagram. It was determined that a limited solid solution of RAM and RSO could be formed along RAM-RSO tie-line, while RAM and J(R) form a continuous solid solution along RAM-J(R) tie-line. In RAM-J(R)-RSO ternary systems, the RAM-J(R) tie-lines were extended towards the RSO corner to form a continuous solid solution area of JRAMss (R = Y, Gd, Yb). The established phase relations in the Si-Al-R-O-N (R = Y, Gd, Yb) systems may facilitate compositional selections for developing JRAMss as monolithic ceramics or for SiC/Si3N4 based composites using the solid-solutions as a second refractory phase.

TaCx (x = 0.5, 0.55, 0.6 and 0.7) ceramics with 20 mol% Al addition were prepared by hot pressing TaC, Ta and Al powder mixtures. Effects of the overall C:Ta ratios and the Al addition on constituent phases, microstructures and mechanical properties of the consolidated materials were examined. Results showed that O impurity contained in the starting powders was collected in form of Al2O3 due to strong affinity of O with Al. The TaCx-Al composites were easy to densify due to presence of molten Al at its melting point (T-m = 660 degrees C) and a transient Al-Ta eutectic liquid at higher temperatures. After densification, the metallic liquids were eliminated ultimately by formation of refractory Ta4AlC3 via reaction of Al, Ta and TaC. Reactions between the remnant Ta and TaC after Ta4AlC3 formation resulted in zeta-Ta4C3-z or h-Ta2C depending on the initial C:Ta ratio. The Ta4AlC3 compound was compatible with the tantalum carbides. Microstructures of the TaCx-Al (x = 0.5-0.7) composites were consisted of zeta-Ta4C3-z, and Ta4AlC3 fine lamellar grains to benefit the mechanical properties of the composites. The TaC0.7 -20mol% Al composition had satisfying mechanical properties (flexural strength 613 +/- 28 MPa and fracture toughness 11.2 +/- 0.8 MPa m(1/2)). TG-DSC evidenced an increase in oxidation resistance of the TaCx ceramics by the addition of 20 mol% Al.

(Ti,Ta)(B,C)-(Ta,Ti)C composites were synthesized by reactive hot pressing using commercial TaB2 and TiC powders as starting materials. The reaction process and effects of TiC contents in the starting batches on the microstructure and mechanical properties of the resultant composites were reported. The microstructure of the composites was refined due to reaction and solid solution coupling effect. A core-rim structure was observed in the (Ti,Ta)(B,C) grains. Vickers hardness, flexural strength and fracture toughness of the composites increased with increasing the TiC content. The TaB2-70 mol.% TiC sample (starting batch composition) prepared by hot pressing at 2000 degrees C for 1 h had a super high Vickers hardness value of 30.5 GPa (indented under 9.8 N, 15 s) approaching that of B4C-based composites. Good flexural strength (714 MPa) and fracture toughness (5.4 MPa m(1/2)) were also found.

TaCx (x = 0.5, 0.55, 0.6, 0.7) ceramics with 20 mol% Fe, Co or Ni addition were prepared by hot pressing TaC and Ta powder mixtures at 1800 degrees C. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, X-ray energy dispersive spectroscopy and selected area electron diffraction were used to investigate the constituent phases and microstructures of the composites. Vickers hardness, flexural strength and fracture toughness were measured. Intermetallic compounds Fe7Ta3, Co2Ta and Ni3Ta were formed due to reactions of Fe, Co and Ni with Ta. The remaining TaC and Ta reacted to form hexagonal Ta2C, rhombohedral zeta-Ta4C3-z or cubic TaCy depending on the overall C:Ta ratios. The microstructure of the TaC0.5-20 mol% Fe, Co, Ni compositions (where C:Ta = 0.5) were composed of intermetallics and fine anisotropic Ta2C and zeta-Ta4C3-z grains. As the C:Ta ratio increased to 0.55-0.7, the zeta-Ta4C3-z and TaCy grains were enlarged in size and equiaxed in the TaC0.55-, TaC0.6-, and TaC0.7-20 mol% Fe, Co, Ni compositions. Addition of Ni instead of Fe and Co benefitted to refine microstructures of the composites. The TaC0.5-20 mol% Fe, Co, Ni compositions had good flexural strength (580-650 MPa) and fracture toughness (9.3-9.5 MPa.m(1/2)) due to growth of fine lamellar grains, despite the high Ta2C content.

TaC ceramics with 0-0.237 wt% B addition were prepared by hot pressing. The effect of B addition on the phase constitution, interfacial chemistry/bonding and mechanical properties of the TaC ceramics were investigated. Upon B addition, the elimination of O impurity and segregation of B at grain boundaries were evidenced, accompanied by an increase in bonding strength of the TaC grains, to result in a fracture mode change from intergranular to transgranular and a reduced fracture toughness. Addition of excessive B resulted in the formation of TaB2 and C within TaC ceramics. Further, TaC-TaB2-SiC composites were prepared by Si addition. Coherent bonding between TaB2 and TaC was preserved in the TaC-TaB2-SiC composites, and residual stresses due to thermal expansion mismatch of the different phases increased flexural strength and fracture toughness of the composites.

Cu alloys with compositions of Cu-3.2Ni-0.7Si (wt. %) and Cu-2.8Ni-0.7Si (wt. %) were prepared by melt spinning. Effects of composition, spinning rate, aging temperature and time on microstructure, precipitation of reinforcing phases, mechanical and electrical properties of Cu-Ni-Si alloys were investigated. Melt spinning could produce continuous Cu alloy ribbons with thickness and width of the ribbons mainly dependent on the cooling rate. Columnar grains of super-saturated Cu-Ni-Si solid solutions grew in the ribbons. The melt-spun Cu-Ni-Si alloys had a faster aging kinetics in comparison with commercial alloys of similar compositions. Peak-aging of the melt spun alloys appeared after heating at 400 to 550 degrees C for 1 to 2 h to show maximum tensile strength of 650 to 700 MPa. Prolonged heating resulted in large precipitates on the grain boundaries and formation of precipitation-free zones around each grain with sharp drop of tensile strength. Precipitation of nano delta-Ni2Si rather than other phases was the main reason for the enhanced mechanical properties at peak-aging. The peak- and slightly over-aged ribbons had a good electric conductivity up to 55% IACS.

In direct borohydride fuel cell (DBFC), there is a contradiction between catalytic activity and specific discharge capacity (SDC) owing to the dual catalytic effects of most anode catalysts on both bomhydride oxidation reaction (BOR) and borohydride hydrolysis reaction (BHR). To overcome this problem, a facile method to fabricate an ultrathin tin dioxide (SnO2) supported cobalt oxide (Co3O4) composite material (u-SnO2/Co3O4) as DBFC anode catalyst was developed. Both catalytic ability for BOR and specific discharge capacity of the DBFC using the uSnO(2)/Co3O4 (DBFC-u-SnO2/Co3O4) with 5-10 nm thick two-dimensional (2D) SnO2 were improved. The maximum power density (52.5 mW cm(-2)) and SDC (1380 mAh g(-1)) of DBFC-u-SnO2/Co3O4 were respectively increased by 105% and 1740% in comparison with those of DBFC with Co3O4 as anode catalyst (DBFC-Co3O4). The u-SnO2/Co3O4 has higher specific surface area, electron donation ability, and the rate of desorption of intermediate product (such as BH3OH-, H-ads) which may account for the excellent catalytic performance of uSnO(2)/Co3O4 for BOR.

In previous works, it was found hard to synthesize "phase pure" zeta-Ta4C3-z at relatively low temperatures even by prolonged heating, though zeta-Ta4C3-z was believed stable till decomposition at similar to 2130 degrees C. When the samples were subjected to TEM, vast richness of locally disordered structures in close relation with stacking of the close-pacted Ta-atom planes was observed. Although kinetic factors including diffusion of C atoms/vacancies and re-stacking of the Ta-atom planes explain the densely disordered structures, the richness of local disorders is a scenario that shows cohabitant of the cubic, rhombohedral, and hexagonal structures in a single grain, i.e. formation of a "hybrid grain" consisted of the three symmetries, indicating a transitional or intermediate stage before complete formation of the final phase of rhombohedral zeta-Ta4C3-z. This time tantalum carbide ceramics TaCx with C:Ta atomic ratios x = 0.66 and 0.7 were prepared by reaction hot pressing of TaC and Ta powder mixtures. 5-30 mol % Cu/Ag additives and heat treatments were used to reproduce "hybrid grains" to facilitate further TEM and HRTEM observations on the disordered hybrid grains to argue for the transitional/intermediate stage. The cohabitant cubic, rhombohedral, and hexagonal structures in single grains may also help explain the difficulty in identification of the various phases by XRD in the transitional/intermediate stage of zeta-Ta4C3-z reaction. Microstructural evolution and fracture toughness of the composites were also investigated.