In this study, ZTA (3Y-TZP/Al2O3) ceramic composites with added SrO sintering aid from SrCO3 and Sr(NO3)2 precursors were prepared by means of pressureless sintering and hot isostatic pressing sintering (HIPing). The microstructure and mechanical properties of the ZTA ceramic composites with added SrCO3 and Sr(NO3)2 were examined, respectively. It was found that SrO incorporation inhibited grain growth and induced the in situ formation of SrAl12O19 platelets. As the SrO content increased, the fracture toughness of the ceramic composites improved; additionally, the hardness and flexural strength initially increased and then decreased. Compared to ZTA ceramics with SrCO3 addition, the samples with Sr(NO3)2 had finer grains with a more uniform platelet distribution. ZTA ceramic composites with the addition of Sr(NO3)2 exhibited a maximum hardness, four-point flexural strength, and fracture toughness of 18.46 GPa, 887 MPa, and 6.97 MPa m1/2, respectively.
X-ray computed tomography (XCT) was utilized to perform quantitative and qualitative characterizations of aqueous-oxygen corrosion evolution in SiCf/SiC composites under pre-and post-oxidation conditions. The results indicate that the SiC matrix formed with the precursor impregnation and pyrolysis (PIP) method is located mainly in the inter-bundle region, which experiences significant oxidation after 160 hours of oxidation. This oxidation results in the formation of SiO2 that fills the inter-bundle pores, leading to a decrease in porosity from an initial 10.9 % to 6.8 %. The interconnected inter-bundle pore network facilitates the ingress of oxygen, resulting in corrosion damage that is initiated preferentially at pore periphery regions. Progressive aqueous-oxygen corrosion leads to pore channel narrowing with surface smoothening, accompanied by the formation of vesicular porosity along the specimen periphery. A connected sheet-like and layered oxide skeleton structure forms finally because of the corrosion of matrix in the inter-bundle region.
An innovative electrodeposition method was developed to fabricate Ni-ZnO composite coatings on high-carbon stainless steel substrates for industrial cutting applications. In this study, key deposition parameters including current density (ranging from 2 to 8 A/dm2), bath pH (optimally maintained at 10), temperature (45 degrees C), and stirring rate (250 rpm) were systematically optimized to enhance coating properties. The integration of ZnO nanoparticles resulted in a refined microstructure, reducing the average grain size from 0.72 & micro;m to 0.56 & micro;m, while the coating thickness increased from 11.1 & micro;m at lower current levels to 24.1 & micro;m at 8 A/dm2. Under optimal conditions at 6 A/dm2, the deposition efficiency reached approximately 85 %. Electrochemical evaluations demonstrated a substantial improvement in corrosion resistance; charge transfer resistance increased from 452 !c m2 for uncoated substrates to 2 370 !c m2 for pure nickel coatings and further to 5 515 !c m2 for the composite, while corrosion current density was reduced from 30 & micro;A/cm2 to 7.9 & micro;A/cm2. Mechanical testing revealed that the composite coating exhibited a hardness of 4.8 GPa and a Young's modulus of 88 GPa, in contrast to 2.9 GPa and 52 GPa for pure nickel layers. Additionally, abrasion tests indicated a decrease in weight loss from 66 mg to 27 mg over a 35 km sliding distance. Overall, the findings confirm that the strategic incorporation of ZnO nanoparticles significantly enhances both the structural integrity and protective capability of the coating, offering a robust and cost-effective solution for prolonging the service life of industrial components. These promising results pave the way forward.
Silicon carbide (SiC) ceramics are a novel packaging material that has demonstrated significant potential in the field of electronic packaging in recent years. In this study, SiC composite ceramics were prepared using a pressureless liquid-phase sintering method with Al2O3-Y2O3-MgO-BN as sintering additives. The influence of the BN content on the thermal properties of SiC composite ceramics was investigated, with the aim of exploring the performance advantages of SiC composite ceramics in packaging applications. The results indicate that the main crystalline phase of all samples is 6H-SiC, with a relatively uniform grain size distribution ranging between 0-2 lm. The sample with a mass ratio of 90%SiC:2%Al2O3:3%Y2O3:2%MgO:3%BN (labeled as M2B3) exhibited a hardness of 340.22 N/mm2, thermal expansion coefficient of 3.35 & times; 10-6 K-1, dielectric constant of e = 486.211, and dielectric loss of tan d = 0.507. These properties meet the requirements for high hardness, low dielectric loss, and well-matched thermal expansion coefficient, making SiC composite ceramics a promising candidate for next-generation high-performance electronic packaging materials.
To assess the influence of surface conditioners, i.e. hydrofluoric acid (HFA), Er: YAG laser, and Radachlorin-activated low-level laser therapy (LLLT), on the contact angle (CA), surface topography, and shear bond strength (SBS) of lithium disilicate ceramics (LDC) and resin-based ceramics (RBC). RBC Lava Ultimate (Group A) and IPS Emax (Group B) were used to obtain forty-five discs in each case. Each group was further divided into subgroups based on the conditioning protocol used. Group 1: HFA, Group 2: Er: YAG laser, and Group 3: LLLT (RD). CA (n =2) and surface topography analysis (n =3) were performed using a goniometer and scanning electron microscope. Resin cement was built on ten discs from each group, followed by the evaluation of the SBS by means of a universal testing apparatus. A one-way ANOVA and Tukey test were utilized to conduct a comparative analysis of CA and bond strength values. The lowest CA was exhibited by Group 1A (HFA + LDC) with the highest bond strength. Whereas Group 3B (RDLLLT+RBC) presented the highest CA and lowest SBS. The Er: YAG laser can be considered as a suitable alternative to HFA for enhancing the contact angle and bond integrity of adhesive cement. LDC and RBC exhibited comparable contact angle and bond strength outcomes, except in the hydrofluoric acid group.
The influence of hydrofluoric acid (HFA), Er, Cr: YSGG laser (ECL), Nd:YAG laser (NdYL) on the surface roughness (Ra), characterization, and shear bond strength of lithium disilicate ceramics (LDC) bonded to light cure (LC) and dual-cure (DC) resin cement was studied. 78 LDC discs were fabricated with the CAD-CAM technique. Samples were categorized into cohorts based on conditioning protocol: Group 1-HFA, Group 2-ECL, and Group 3-NdYL. Assessment of Ra and surface characterization was conducted using a profilometer and SEM. Twenty samples from each group were subdivided into two subgroups. Light-cure (LC) (A) and dual-cure (DC) resin cement (B) were built on the LDC, and this was followed by thermocycling. A universal testing machine and stereomicroscope were used for SBS and failure mode assessment. Ra and SBS were evaluated via ANOVA with post hoc multiple comparisons. The highest Ra was exhibited by Group 1-HFA. Group 3-NdYL-conditioned samples demonstrated the lowest Ra. The maximum bond integrity score was recorded for HFA+DC resin cement. The minimum bond strength was noted for NdYL+LC cement. LDC can be effectively conditioned with HFA and bonded with DC resin cement. Due to the drawbacks associated with HFA, it is advisable to seek a superior alternative for the surface conditioning of LDC.
This study investigates the influence of as-cast c-Al2O3 nanoparticles on the dynamic recrystallization and mechanical properties of an Mg-10Gd-3Y alloy. Alumina nanoparticles (--35 nm), synthesized via a green method using Mentha pulegium extract, were incorporated into the Mg alloy by means of stir-casting followed by extrusion. Microstructural characterization revealed uniform nanoparticle dispersion and grain refinement from 10.2 & micro;m to 6.1 & micro;m, accompanied by weakened basal texture. X-ray photoelectron spectroscopy confirmed strong interfacial bonding, with Al2O3-related peaks at 74.8 eV and O 1s components at 531-532.5 eV. Mechanical testing demonstrated that 2 wt% Al2O3 increased the yield strength from 280 MPa to 320 MPa and ultimate tensile strength from 350 MPa to 380 MPa, while improving ductility to 20 %. Microhardness rose from 81 HV to 102 HV with increasing nanoparticle content. Dynamic recrystallization (DRX) analysis via EBSD and hot compression revealed accelerated DRX kinetics, achieving-- 60 % recrystallized grains at a true strain of 0.2 at 450 degrees C. Process maps identified optimal hot working conditions at 400 degrees C and strain rates of 0.01-0.1 s-1, with dissipation efficiency g reaching 0.5. Fractography showed ductile failure with uniform dimples and no evidence of particle debonding. The synergy between Al2O3 nanoparticles and LPSO phases enhances grain boundary nucleation and suppresses flow localization. These findings demonstrate that nanoparticle reinforcement offers a viable strategy to improve strength-ductility balance and high-temperature formability in RE-containing Mg alloys.
The crystal structure, microstructure, and microwave dielectric properties of B2O3-V2O5 co-doped (Mg1-xCux)2SiO4 (x=0.05-0.20) ceramics were investigated. The sintering temperature was successfully reduced to about 1250 degrees C/4 h for the B2O3-V2O5 co-doped (Mg1-xCux)2SiO4 specimens. The (Mg0.95Cu0.05)2SiO4 with 6 wt% B2O3-6 wt% V2O5 ceramics sintered at 1250 degrees C for 4 h achieved excellent microwave dielectric properties of er = 6.55, Q center dot & fnof; = 37 500 GHz and a s & fnof; of-35.65 ppm/K.
Evaluating the effect of airborne particle abrasion (APA), Nd: YLF laser, hydroxyapatite nanoparticles (Nano-HAp) on surface roughness (Ra), topography, and repair bond strength (RBS) of different-viscosity composites bonded to hybrid ceramic (HBC). 78 CAD/CAM HBC discs were prepared and divided into three groups based on surface treatment (n = 26). Group 1: APA, Group 2: Nd: YLF laser, and Group 3: Nano-HAp coating. A surface profilometer measured the Ra scores (n = 5 each). SEM was used for surface topography (n = 1 each). On the remaining samples, an adhesive was applied and cured. Twenty samples from each group were further categorized into two subgroups based on the composite viscosity. Bond strength and failure mode were assessed. A one-way ANOVA and a Tukey test were conducted to identify significant differences among groups. The highest mean Ra score was exhibited by Group 2 (Nano-HAp). Group 3 (Nd:YLF laser)-conditioned samples demonstrated the lowest Ra. Maximum RBS values were observed for Group 2B (Nano-HAp+Injectable). The minimum bond strength was noted for Nd: YLF laser+Microhybrid. Lower-viscosity composite displayed better performance than conventional composite. The most successful method for surface preparation of HBC involves pretreating with Nano-HAp coating. The use of a low-viscosity injectable composite as the repair material results in enhanced bond strength.
AIMS To investigate the effect of different conditioning regimes, that is diamond bur (DB) grinding, sandblasting (SB), and Er, Cr: YSGG laser (ECL) at different pulse modes (long and short), on the surface roughness (Ra) and repair bond strength (RBS) of resin nanoceramics (RNCs) to different viscosity composites. METHODS 104 RNC discs were prepared and classified into four groups based on the surface pretreatment protocol (n = 26) Group 1 DB, Group 2 SB, Group 3 (ECL-short pulse), and Group 4 (ECL-long pulse). Five discs from each group underwent Ra assessment. SEM was used to assess the surface topographic changes. Twenty samples from each cohort were divided into two subgroups based on the composite types: micro-hybrid composite and low-viscosity injectable composite. ANOVA and Tukey HSD test were used to analyze the statistical difference among different groups tested for Ra and RBS. RESULTS The highest value for Ra was observed in the SB group. The lowest Ra was indicated in the ECL-long pulse group. Maximum RBS was observed in Group 2B (SB+Injectable). The lowest scores were displayed by Group 4A (ECL (long pulse)+micro hybrid) CONCLUSION SB and ECL along with low-viscosity injectable composite can be considered suitable surface conditioners and restorative materials for repairing fractured resin nano-ceramic.
In this study, lotus-root-inspired honeycomb alumina ceramics were fabricated using digital light processing (DLP) 3D printing technology, and a systematic investigation was conducted to determine the rheological characteristics of the alumina slurry and the mechanical properties of the sintered ceramics. Their potential applications in oil-water separation and cigar smoke filtration fields were explored. The experimental results showed that the viscosity of the 82 wt% Al2O3 ceramic slurry was 2 615 mPa & sdot;s at a shear rate of 30 s-1, and the alumina ceramics sintered at 1750 degrees C can resist high temperature with excellent mechanical properties: the three-point bending strength was 236 MPa, the compressive strength was 595 MPa, the Vickers hardness was 14.7 GPa, and the density was 3.77 g/cm3. In the oil-water separation experiment, the surface-modified honeycomb alumina ceramics were able to separate the oil-water mixture with high efficiency. When acting as one part of the cigar smoke filtration, the honeycomb ceramic provided support and sieved large particles out of the smoke. The filtration efficiencies for nicotine, total particulate matter, and tar reached 93.4 %, 91.7 %, and 89.7 %, respectively. In summary, high-performance honeycomb alumina ceramics were successfully prepared with 3D printing and showed broad application prospects in the separation field.
Borate-based bioglass has attracted keen interest as a bone repair material owing to its good machinability and degradability, but the quick release of boron can lead to cytotoxicity and this is an issue that needs to be taken into consideration. In this paper, borate-based bioglass scaffolds substituted with 0 - 9 mol% strontium with a porous microstructure were prepared by means of a polymer foam replication technique. The effect of the strontium substitute on the bioactive properties and structure of the scaffolds was investigated by means of XRD, SEM, MTT, FTIR and MAS-NMR testing. The results showed that the as-made bioglass was amorphous and had a porous microstructure similar to human trabecular bone. The in vitro bioactivity of the glass was observed based on the conversion of the glass surface to a nanostructured hydroxyapatite layer in SBF. The substitution of strontium in borate-based bioglass keeps the concentration of B3+ ions in a more acceptable[GS1] range. According to the Fourier transform infrared and MAS-NMR spectra, when the strontium increased, part of the silicate network structure in the glass is destroyed. Meanwhile, the layer structure containing [BO3] is gradually replaced by the framework structure containing [BO4], this is the basic reason why the bioactive properties of the borate-based glass changed with the strontium substitution.
This study examined the influence of a hydrogen-containing atmosphere on cement-bonded refractory castables. Two series of tests were conducted using different materials, a fireclay and a high-alumina castable with SiC. Each test series consisted of three samples exposed in a tube furnace at temperatures of 1 100 degrees C and 1500 degrees C for 24 and 72 hours. The temperature of 1 100 degrees C represents the upper temperature limit of a direct reduction plant, while 1500 degrees C should provoke corrosion. An optical examination revealed a change in colour, due to the formation of oxygen vacancies. At 1 100 degrees C, there were only minor changes, with no significant loss of mass or change in porosity. At 1 500 degrees C a greater loss of mass was observed, particularly at the gas inlet, and an increase in porosity was determined. The chemical composition of the high-alumina material undergoes a transformation, with the loss of SiO2, SiC, and alkalis. Depending on the temperature and holding time, non-oxide agglomerates of iron and phosphorus, form on the surface. Similarly, agglomeration occurs in the castable with a high alumina content and SiC. In contrast to the other test series these agglomerates do not consist of iron and phosphorus, but of iron and silicon.
MgO-C refractories are extensively utilized in the steel industry, particularly in steel ladles, basic oxygen furnaces, and electric arc furnaces. These materials are subjected to intense mechanical and thermal stresses, as well as aggressive interactions with corrosive agents. The most severe wear typically occurs upon contact with slag or molten metal; therefore, the use of high-purity raw materials is essential to ensure durability under such conditions. To enhance the thermomechanical performance of MgO-C refractories, antioxidants are commonly incorporated, leading to the formation of high-temperature ceramic phases (e.g. MgAl2O4, AlN, SiC) that reinforce the material's structure. However, alternative additives may also be considered to further improve their performance in demanding environments. Raw materials containing CaO and MgO-bearing aluminates not only enhance slag resistance but are also considered among the most promising solutions for stabilizing steel ladle linings. Laboratory tests involving the addition of various grain sizes of CMA additives to MgO-C refractories demonstrated improved slag resistance through the formation of a protective contact layer. Furthermore, these modifications enabled better control over dimensional changes after heating, as well as thermal expansion behavior. The study also investigated the feasibility of incorporating recycled raw materials in combination with aluminates. The obtained results enabled the design of a complete ladle lining system optimized for use in silicon-killed steel processes and environments subjected to high thermomechanical stress in secondary metallurgy. Microstructural analysis of post-mortem samples using SEM/EDS methods provided insight into the influence of aluminates on slag attack resistance and thermal stress behavior, particularly through reinforcement of joint areas. The corrosion study was further supported by thermodynamic calculations.
Lightweight aggregates and castables are of great significance for energy saving and the reduction of emissions. In this work, lightweight aluminosilicate aggregates were produced using high-quality kaolin and porogenous material by means of high-temperature processing and investigated in terms of XRD mineralogy, bulk density, open porosity, and microstructure. In addition, the influence of the lightweight aggregates on the bulk density, cold crushing strength, microstructure, thermal properties and thermal shock resistance of refractory castables was investigated in detail. For this reason, lightweight castables with different particle size distribution, as per the Dinger and Funk model, were designed to attain very good flow consistency, cast, cured and heat-treated at temperatures between 110-1 200 degrees C. The lightweight castables with chamotte aggregates presented improved performance, exhibiting bulk density of 1.64 g/cm3 to 1.77 g/cm3, cold crushing strength of 30.3 MPa to 54.8 MPa and thermal conductivity of 0.66 to 0.74 W/m & sdot;K measured at room temperature, depending on the firing temperature (850 degrees C-1200 degrees C) and lightweight aggregates content. The results underscore that the use of microporous aggregates instead of traditional dense aggregates enabled the design of semi-insulating castables for the working lining of kilns and furnaces with improved properties, eliminating the need for porogenic agents.
Cement-free binders have recently attracted significant attention due to their rapid drying and superior high-temperature performance, including enhanced thermo-mechanical properties, refractoriness under load, and corrosion resistance, compared to low-cement castables (LCCs). Despite these advantages, conventional no-cement castables (NCCs) exhibit limited mechanical strength at intermediate temperatures (600 to --1000 degrees C). This study aims to develop innovative binder systems for NCCs, specifically targeting intermediate temperature applications, while also being suitable for high temperatures (>1 300 degrees C). The research evaluated the flowability, setting behavior, and mechanical strength of NCCs incorporating novel cement-free binders, in comparison to conventional NCCs and LCCs. Additionally, hot properties such as hot modulus of rupture (HMOR), hot abrasion resistance (HAR), and refractoriness under load (RUL) were assessed. The results demonstrated that the novel binder system provided superior mechanical strength and improved hot properties at intermediate temperatures, surpassing conventional NCCs, while maintaining comparable performance at elevated temperatures. Notably, RUL results indicated that the novel binder facilitated sintering and/or mullite formation at a lower temperature (-- 800 degrees C) compared to the reference NCC (--1300 degrees C), with reduced shrinkage after maximum expansion. Scanning electron microscopy (SEM) analysis confirmed that the novel binder influenced both the temperature and morphology of mullite formation, contributing to the observed improvements.
Beside the coarse and medium grain size distribution, the matrix components play a central role in the performance of refractory castables. On the basis of practical experience, it is evident that the particle size distribution (PSD) and the resulting specific surface area of the ceramic matrix exert a significant influence on the processing, setting and sintering properties of refractory castables, which in turn influence each other. However, there is a lack of detailed highly systematic studies regarding the extent to which the properties of refractory castables are influenced by changes in the PSD or specific surface area of the raw materials in the matrix. The objective is to gain a general understanding of this. To shed more light on this issue, the ceramic matrices were varied, resulting in model castables with gradations in the specific surface area of the matrix. The refractory castables were dispersed using three different dispersing agents with different mechanisms of action (electrosteric and steric) at graded concentrations. The findings of this study demonstrate that refractory model castables with variations in the specific surface areas of the ceramic matrix and different dispersing agents and their concentrations necessitate substantial differences in the required mixing energy. Castables with matrices containing larger quantities of highly sintered and (very) finely ground alumina raw materials (with high specific surface areas) require less mixing energy than mixtures with lower specific surface areas. An increase of the dispersing agent content also results in a reduction in the required mixing energy and lower temperature evolution, with due consideration of the respective water content. A clear correlation can be established between the mixing energy introduced and the temperature increase during mixing. Castables with higher specific surface areas of the matrix require less mixing energy and therefore heat up less during the mixing process than castables with lower specific surface areas. The findings of the measurements of the dynamic viscosity of matrix suspensions in high shear rate ranges support these observations.
Currently, the main purpose for obtaining alternative binders for use in taphole clay is to reduce the exposure to harmful polycyclic aromatic hydrocarbons (PAH) associated with conventional coal tar (CTht) binders. Some advances have been made such as using lower-PAH alternative binders or phenolic resole resins (resin-bonded) in taphole clays. The use of non-toxic binders has become exceedingly difficult due to the versatility of CTht in taphole clay. This study investigated a combination binder system that consisted of a sugar alcohol (research-grade glycerine) and phenolic resole resin as a potential non-toxic binder for use in platinum smelting taphole clay. The binder system was characterized according to its composition by means of Fourier-transform infrared spectroscopy and the PAH content (16-EPA-PAH) was determined using targeted gas chromatography mass spectroscopy. Flow behaviour of the binder was determined based on rotational rheology, and the volatilization and rheological thermal stability of the binders were assessed by means of thermogravimetric analysis and thermorheology, respectively. The effect of mixing these binder constituents on the cross-linking behaviour of the phenolic resin was evaluated using differential scanning calorimetry. The combination binder had a higher average mass loss and lower carbon yield compared to conventional CTht, but with a lower total PAH content, making it a more health-friendly alternative.
While calcium aluminate cements have become established as a "workhorse" for refractory castables (reliable and cost-effective), they nonetheless have certain drawbacks (high risk of explosive spalling during drying, limited resistance to acidic slags and ashes) and, after years of optimization, only limited potential remains for further improvements. By contrast, colloidal suspensions (sols) are increasingly used as bonding solutions in the industry (silica sols) and, despite their current limitations (providing low green strength and limited refractoriness), they have much to offer. Especially alternative sols, such as mullite and spinel sols, are attracting attention for improving the refractoriness and resistance to corrosion of sol-bonded castables, but studies regarding their performance at high temperature are extremely sparse. The thermomechanical and thermochemical behaviour of silica- and spinel-sol-bonded high-alumina refractory castables was investigated using wedge splitting measurements, high-temperature thermal shocks and induction furnace tests. Silica-sol-bonded high-alumina refractory castables are rather weak when compared to high-alumina refractory bricks, but they are able to develop more ductility before weakening and exhibit improved resistance to high-temperature thermal shocks. The use of spinel sols considerably improved the high-temperature mechanical and fracture resistance of the sol-bonded high-alumina refractory castables without degrading their resistance to thermal shocks. The spinel sols even slightly improved the resistance of the castables to corrosion.
In this work, we studied the effect of small additions of titania and three carbon sources on the spinelization of magnesia alumina castables. Compared to additive-free reference samples, titania-containing magnesia alumina castables were found to exhibit improved sinterability and higher cold crushing strength after firing. In parallel, significantly higher amounts of spinel formed during heat treatment when titania had been added to the castable. For the carbon-containing samples, the grain size of the carbon source proved to be an important parameter controlling the influence on spinelization. While the addition of carbon black (particle size d(90) < 1 m) clearly facilitated the spinel formation at a temperature of 1 200 degrees C, the influence of small-flake graphite (particle size d(90) similar to 75 mu m) was less pronounced. The use of large-flake graphite (particle size d(90) similar to 180 mu m) ultimately even hampered the spinelization reaction at this temperature. This latter effect is attributed to the presence of large graphite flakes which presumably inhibit the chemical reaction in the sample by blocking the direct contact between alumina and magnesia grains.
