Materials Science Forum Vols. 745-746

Abstract: Reticulated silicon carbide porous ceramics was fabricated through organic foam infiltration process by using silicon carbide slurry prepared from silicon carbide, alumina and clay and other raw materials. The effect of solid content on the viscosity and Zeta potential of the slurry were investigated. The results showed that the viscosity of slurry increased with the increase of the solid content. The absolute value of Zeta potential increased with the increase of pH value of the slurry from acid to alkaline aptitudes, and it became smaller with the further increase of the pH value. The maximum was reached at the pH around 10. The viscosity of slurry in the range of 4000mPas ~ 5000mPas was appropriate to prepare reticulated silicon carbide porous ceramics. The sintered body collapsed or cracked apparently, when the viscosity was too low. On the other hand, the viscosity could not be too high because its hard for slurry to impregnate foam. The performance of the samples coated once and recoated was compared. The porosity of the sample with one layer was higher than that of the samples with two layers. However, the recoating process improved the compressive strength and flexural strength of the reticulated silicon carbide porous ceramic.

Abstract: In this paper, Mechanical alloying (MA) and field activated and pressure assisted synthesis (FAPAS) were used for preparing the ultra-hard, super-abrasive AlMgB₁₄-xTiB₂ composite ceramic. The samples were fabricated at 1500 under a pressure of 60 MPa. The microstructures and compositions of samples were observed and determined by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD). It was indicated that addition of TiB₂ was effective for increasing both quantities. A maximum Vichers hardness of 38.5GPa and a fracture toughness of 3.85MPam^½ of AlMgB₁₄ reinforced with 70 wt.% of TiB₂ were achieved. Abrasion wear tests showed that adding TiB₂ would improve the wearability obviously.

Abstract: Compact short carbon fiber and silicon nitride particles co-reinforced BAS (barium-aluminosilicate) composites were synthesized by hot-pressed. Phase compositions and microstructures of these composites were characterized by means of XRD and SEM methods. The results showed that BAS was benefit to the densification and partially realize the αβ-Si₃N₄ phase transformation. Definite orientation of the carbon short fibers was observed in the BAS matrix.

Abstract: SiC whiskers are the common reinforced phases in alumina carbon refractories. In this paper, the effect of transition metal catalyst on the evolution of matrix phase and the formation of β-Si₃Al₃O₃N₅ whiskers were studied. It was found that the whiskers of both SiC and β-Si₃Al₃O₃N₅ in alumina carbon materials with the catalyst in reducing atmosphere were generated. The existence of catalyst can promote the nitriding process of Si metal and facilitate the formation of β-Si₃Al₃O₃N₅ whiskers. The growth mechanism of both SiC and β-Si₃Al₃O₃N₅ whiskers agrees with the vapor-liquid-solid model.

Abstract: Porous TiN ceramics with high porosity and uniform pore structure was prepared following the carbothermal reduction reaction between TiO₂ and carbon. Influences of sintering additives and particle size of TiO₂ on the microstructure and mechanical properties of porous TiN ceramics were investigated. Microstructure and mechanical properties of porous TiN ceramics were studied by XRD, SEM and three-point bending measurement. XRD analysis proved that the TiN phase has completely formed after reaction. In addition, SEM analysis showed that the resultant porous TiN ceramics were composed of fine grains with uniform pore structure. The addition of La₂O₃ not only accelerated the densification of porous TiN ceramics, but also decreased the porosity and increased the flexural strength. With a decrease in TiO₂ particle size, the linear shrinkage increased and the porosity decreased accordingly.

Abstract: Aluminum titanate (Al₂TiO₅) powder has been synthesized at low temperature via nonhydrolytic sol-gel method by using aluminum powder as aluminum source, titanium tetrachloride as titanium source, anhydrous ethanol as oxygen donor with different catalysts. The phase transformation of aluminum titanate xerogel powder during heat treatment and the influence of the mixing orders of raw materials, catalyst kinds on the synthesis of aluminum titanate were investigated by means of differential-thermal analysis (DTA-TG), X-ray diffraction (XRD), transmission electron microscope (TEM). The results indicated that aluminum titanate powder was easily synthesized at 750 °C by using AlCl₃ as catalyst with a mixing order of adding TiCl₄ before AlCl₃ into aluminum alcohol mixture. The catalytic order of the different catalysts in the preparation process of aluminum titanate is: FeCl₃> AlCl₃> MgCl₂. The catalyst promoted the activation of metal aluminum powder and played a major role in the synthesis of aluminum titanate powder at low temperature via nonhydrolytic sol-gel method.

Abstract: Lead-free (1-x-y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yK_0.5Na_0.5NbO₃ (BNT-BT-KNN) ceramics were fabricated by traditional sintering method. The X-ray diffraction patterns showed that the ceramics are all crystallized into a perovskite structure phase. Measurements of temperature-dependent dielectric constants showed the two typical shoulders observed in the BNT-BT binary system, indicating that the ceramics are also of relaxor anti-ferroelectric nature. Moreover, it was observed that the dielectric constants decreased sharply with the increase of KNN addition, while maintained the same level when the BNT/BT ratio changed. The P-E hysteresis loops showed that the saturated polarization and the remnant polarization both decreased with the increasing addition of KNN, while the reduction of the BNT/BT ratio enhancesd the saturated polarization. The energy-storage density calculated from the P-E loops also increased with the decrease of KNN addition and BNT/BT ratio, which further demonstrated that the key for improving the energy density of BNT-BT-KNN ceramics is relatively low addition of KNN and low BNT/BT ratio.

Abstract: Antimony-doped tin oxide (ATO) nanoparticles with controlled doping level were prepared by a nonaqueous solution route, using alcohol as the solvent, citric acid as an agent, tin (IV) tetrachloride as tin source and antimony (III) chlorideas as antimony sources. As-synthesized samples were characterized by Thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), transmission electron micrographs (TEM), N₂ adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The results showed that the content of citric acid was the most important processing parameter which was largely governing the reaction course and the complete incorporation of Sb. When the citric acid to metal mol ratio was 2, the particles were the highly crystallized ATO nanoparticles of about 20nm and the Sb atoms were indeed incorporated into the SnO₂ crystal structure (cassiterite SnO₂).

Abstract: Aluminium titanate (AT) ultrafine powder was prepared via hydrolytic sol-gel (HSG) method using aluminium nitrate (Al (NO₃)₃·9H₂O) and titanium tetrachloride (TiCl₄) as precursors as well as ethanol as solvent. Water required for hydrolysis reaction was supplied by the crystal water of aluminium nitrate itself. The effect of gelation processes, i.e. reflux and solvothermal treatment, on synthesis of AT powder was investigated by means of DTA-TG, XRD, SEM, and TEM, etc. The result shows that the gelation process has significant effect on the synthesis of AT powder. By reflux process, AT powder was synthesized at 1350 °C with average particle size above 1μm and serious agglomeration. Through solvothermal treatment process, however, AT powder with average particle size less than 150 nm was prepared at 1050 °C at a relatively high synthesis rate, which is due to the refinement reactants by the solvothermal treatment.

Abstract: SiC-Ti functionally graded material (FGM) was prepared by polymer-derived method in order to resolve connection problem between the ceramic matrix and its composite materials, as well as metal at high-temperature. Gradient materials were fabricated successfully by polymer-derived method combined with hot-press sintering process at 1300. The microstructure of the prepared samples was studied, and the results revealed that this FGM had a compact structure, without obvious interface between different layers. The distribution of elements was gradient according to the SEM and EDX results.