Papers by Author: Qiang Xu

Abstract: Sm1.9Ca0.1Zr2O6.95 ceramic was sintered at 1600°C for 10 h in air by solid-state reaction method. The phase structure and thermal expansion coefficient were measured by XRD and a high-temperature dilatometry, respectively. The results show that the crystal structure of Sm1.9Ca0.1Zr2O6.95 ceramic is still pyrochlore. The doping with calcium cation leads to a shift of the X-ray spectrum of Sm1.9Ca0.1Zr2O6.95 ceramic to lower 2θ values. The experiments also show that the thermal expansion coefficients of Sm1.9Ca0.1Zr2O6.95 ceramic are higher than those of Sm2Zr2O7 ceramic. These results are related to the vacancy induced by doped calcium cation in the samarium lattice.

Abstract: Three rare earth zirconates (Sm2Zr2O7, Gd2Zr2O7 and Er2Zr2O7) were prepared by solid state reaction. The crystal structure and ionic conductivity of these zirconates were characterized by X-ray diffraction (XRD) and complex impedance spectroscopy. The results show that Sm2Zr2O7 exhibits single-phase pyrochlore structure and Er2Zr2O7 exhibits single-phase fluorite structure, while Gd2Zr2O7 has pyrochlore and fluorite structure. Among three zirconates, the ionic conductivity of Sm2Zr2O7 is highest, while that of Er2Zr2O7 is lowest.

Abstract: Titanium diboride nanoparticles reinforced copper matrix composite by combustion synthesis technology from titanium, boron and copper powders without other activated methods. Thermodynamics of the system was calculated theoretically. It was found that TiB2 was stable phase in the composite and TiCu interphase compound can convert into stable phase. The phases of the synthesized product were identified using X-ray diffraction and the results showed that only TiB2 and Cu phases, no other phases existed in the product. It is consistent with the calculated result of thermodynamics. SEM microstructural characterization showed that a homogenous distribution of the titanium diboride nanoparticles in the copper matrix.

Abstract: Silicon carbide whiskers (SiCw) as a kind of high strength fibrous material are widely used in the reinforcement of metal, ceramic and polymer. In this paper preparation of Silicon carbide whiskers by carbon thermal reduction reaction from the mixture of Silica and carbon was investigated with an emphasis on the study of the effect of catalyst. Fe, Co, Ni and their compounds were used as catalyst in this study. Since vapor–liquid–solid (VLS) mechanism was found to be responsible for the growth of whiskers, the formation of catalyst and its subsequent evolution on whisker nucleation, growth and appearance was a subject of extensive research. The catalyst that has the best effect among iron, nickel, cobalt and their compounds was made certain by comparing the products.

Abstract: SiO2/ SiO2 nanocomposites dipped with silicon resin was ablated and the physical state and phase transformation were characterized. Trace impurity in raw material and compound obtained by chemical reaction were analyzed. Moreover, the high-temperature dielectric properties were investigated. On the basis of above, it is found that the impurity carbon and silicon carbide are the key factors influencing dielectric properties.

Abstract: Rare earth Gd2Zr2O7 ceramic was prepared by spark plasma sintering from Gd2O3 and ZrO2 powders. The powders were sintered at 1400°C for 10min. The synthesized ceramic was annealed at 800°C for 2h under air atmosphere. XRD structural and SEM microstructural characterization showed the formation of a single phase material with pyrochlore crystal structure. The relative density of Gd2Zr2O7 ceramic was measured by the Archimedes method with an immersion medium of water and the results revealed that the relative density of the ceramic was 92%. The thermal conductivity of the ceramic was tested by laser flash method from room temperature to 700°C. The result shows the thermal conductivity of Gd2Zr2O7 ceramic is lower than that of 7YSZ.

Abstract: Rare-earth zirconate ceramics (Gd2Zr2O7, Sm2Zr2O7, Nd2Zr2O7, Dy2Zr2O7, Er2Zr2O7 and Yb2Zr2O7) were successfully prepared by pressureless sintering at 1550oC for 10 hours. The thermal conductivities of these ceramics were measured and the results indicated that the thermal conductivities of rare-earth zirconates were much lower than that of YSZ in the temperature range 20-800oC.

Abstract: The increase of the efficiency for gas turbines leads to the increasing combustion-chambertemperatures. Rapid degradation of the conventional yttria-stabilized zirconia coatings does not fulfill therequirements at these temperatures for a reliable thermal barrier coatings (TBCs) due to the phasetransformation of zirconia and the sintering behaviour. Therefore, it is very important to develop novelceramic materials for TBCs with low thermal conductivity and long-term stability at high temperatures.In this paper, the developments of potential novel ceramic materials for TBCs with low thermalconductivity are reviewed.

Abstract: Large-scale (Ti,Cr)B2-Cu composite from Ti, Cr, B and Cu powders was produced by combining combustion synthesis with Pseudo Hot Isostatic Pressing. The diameter of the synthesized product is 240 millimeter. The product was identified using X-ray diffraction and the result showed that only (Ti,Cr)B2 and Cu phases, without other phases, existed in the product. The analysis of the microstructure indicated that the skeletal structure had been formed in the (Ti,Cr)B2 solid solution phase. Fine (Ti,Cr)B2 reinforcement grew in near equivalent axis-like shape and some sintering neckings were found between the solid solution phases. The relative density of the synthesized product was 93.6% because the skeletal structure baffled the densification of the composite. The bending strength and fracture toughness of the product were 476 MPa and 6.8 MPa·m1/2 respectively.

Abstract: TiB2-Cu matrix composites from titanium, boron and copper powders were in-situ fabricated by exothermic reaction. The effect of the applied pressure on the mechanical properties of the composite was investigated. The results showed that when the applied pressure increasing, the relative density, bending strength, fracture toughness and hardness of the composites were on the increase due to the formation of fine microstructure and the improvement of densification with the pressure increasing. The high pressure is beneficial to the better mechanical properties.