Akun Liang,Yinjuan Liu,Hao Liang,Fangming Liu,Cong Fan,Jiawei Zhang,Jinjun Wu,Ji Chen,Duanwei He
The thermal insulation performance of cubic ZrO2–CaO solid solution (CSZ) (16 mol % CaO) and monoclinic ZrO2 (MZ) was investigated in a two-stage multi-anvil press under a pressure of 10 GPa and temperatures up to 1800°C through in situ temperature measurements with the same cell assembly. The results show that the cell temperatures with CSZ as the thermal insulator were always higher than that when thermal insulator was MZ at the same heating power, and the maximum deviation value was 600°C (50% higher) within the measurable range. These two materials were analyzed using X-ray diffraction (XRD), thermal conductivity measurement and scanning electron microscopy. It revealed that the point defects existed in CSZ dominated the thermal insulation performance at high pressure, the same as what at normal pressure. It was also found that the heating process was more controllable when using CSZ as thermal insulator under high pressure.
Lu Youjun,Yuan Zhenxia,Shen Hongfang,Huai Xiaochen,Huang Zhenkun
Zirconium nitride (ZrN) ceramics were prepared via hot pressed sintering (HP) at 1750 °C in N 2 atmosphere with ZrO 2 –Y 2 O 3 as sintering additive. X-ray diffraction was applied to analyze the phase composition of the as-prepared ceramics to study the high temperature phase relation in ZrN–ZrO 2 –Y 2 O 3 ternary system and establish ZrN–ZrO 2 –Y 2 O 3 ternary phase diagrams. The results show that ZrN and tetragonal ZrO 2 (t-ZrO 2 ) solid solution, face-centered cubic ZrO 2 (c-ZrO 2 ) solid solution, body-centered cubic Y 2 O 3 (c-Y 2 O 3 ) solid solution coexist in the system of ZrN–ZrO 2 –Y 2 O 3 .
The tetragonal ZrO 2 nanopowders stabilized with 3 mol% Y 2 O 3 (3YSZ) were synthesized using a polyacrylamide gel method. The mean particle size of the 3YSZ nanopowders was found to decrease with increasing molecular ratio of monomer to the precursor salt. The 3YSZ nanopowders with mean particle size of 12 nm can be densified in 1 h at 800 ∘ C, by the application of a d.c. electrical field. Under a constant d.c. electrical field, the current density through the specimen of 3YSZ rose rapidly when the temperature increased to a certain value. In the sintering process, the current density was restricted when the sharp increase occurred. By limiting current density to different values for one hour, it was found that current density was the most important factor in electrical field-assisted sintering process. The grain size of 3YSZ bulk increased with the enhanced current density. The stable stage of electrical field-assisted sintering process can be explained by Joule heating. Corresponding real temperature of specimens is estimated by applying black body radiation theory.
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