Papers by Author: Xiao Peng Jia

Abstract: Large volume cubic anvil (LVCA) have been widely used in cubic high pressure apparatus, which can accommodate a large sample volume (the largest volume of compressed cell is 422 cm3), but they are limited by shorter lifetime (£143000 times) and lower cell pressure (£146 GPa). In this paper, we have designed of a double radius type LVCA, which has three advantages. Firstly, the rate of cell pressure transmitting and the pressurized seal stability of the sample cell can be maintained, which is often sacrificed with optimum the geometrical condition of the anvil. Secondly, the lifetime of double radius type LVCA can be increased about 19.86 % than that of traditional anvil. Thirdly, the cell pressure can be increase about 13.45 % after the modification of the anvil. This work makes an effective solution for solve the choke points of LVCA and would be used widely in other types of Multi-anvil apparatuses.

Abstract: Polycrystalline filled Skutterudite compounds Ba_xCo₄Sb₁₂ (0-x-0.5) are synthesized by high pressure and high temperature （HPHT） technique. The thermal conductivity for CoSb₃ is depressed significantly by Ba-filling combined HPHT technique. The value of 1.25 Wm^-1 K^-1 for Ba_0.372Co₄Sb₁₂ is obtained at 633K. The dimensionless thermoelectric figure of merit ZT, increases with temperature increasing and reaches a maximal value of 1.01 at 663 K.

Abstract: In this paper, industrial diamonds using pure Fe powder catalyst with additive Si has been synthesized by HPHT method. Optical microscope, XRD and SEM were utilized for observation and detection. The influences of additive Si on the synthesis have been investigated from several aspects such as the diamond-forming conditions, the composition of synthesized sample and inclusions in diamond, and the morphology character of diamonds etc. The results indicate that the formation of SiC, which should have been in a solid state during the synthesis.

Abstract: With adopting Al as the nitrogen getter in Ni70Mn25Co5 or Fe55Ni29Co16 catalyst, High-quality type-Ⅱa large diamonds have been grown under the conditions of about 5.5GPa and 1580K by using the temperature gradient method. While Al(2.0wt%) is added in the Fe55Ni29Co16, the nitrogen concentration(Nc) in the diamond is less than 1ppm. While Al(4.0wt%) is added in the Ni70Mn25Co5, the Nc in the diamond is highly arrived at 48ppm. The different of solubility of nitrogen in both catalyst at high pressure and high temperature is the basic reason of the different effect of eliminating nitrogen of Al. It can be shown in experamentals that Al is a less efficient nitrogen getter in Ni70Mn25Co5 than in Fe55Ni29Co16. While Al(2.0wt%) is added in the Fe55Ni29Co16, the high-quality type-Ⅱa large diamond, in which nitrogen is less than 1ppm and which the size was arrived at 3.3mm, had grown by decreasing the growth rate of diamond.

Abstract: Heat treatment is an effective means of structural adjustment and performance improvement of AlN ceramics. AlN ceramics prepared at high pressure with Y2O3 as a sintering aids were heat treated in a nitrogen flow atmosphere. The effects of heat treatment on microstructure and thermal conductivity of AlN ceramics were studied. The results show that the grain size of the AlN ceramics heat-treated at 970 °C for 2 h is significantly increased, the actual crystal morphology is realistic and the second phases are almost present at the grain boundaries or triple pockets compared with the samples without heat treatment, which thermal conductivity has reached 156.7 W/(m·K) from 77.3 W/(m·K). However, the pore size of AlN ceramics is increased and there is the phenomenon of anti-densification while the heat treatment time is extended to 4 h. The thermal conductivity of AlN ceramics heat-treated at 970 °C for 4 h is reduced to 92.6 W/(m·K).

Abstract: High-density AlN ceramics were fabricated without sintering additives at high pressure (5.0 GPa) and temperature (1300-1700 °C). The sintered bodies were characterized by XRD and micro-Raman spectroscopy (MRS). The values of residual stresses due to the distortion of the AlN lattice were assessed using the Micro-Raman Spectroscopy (MRS). Residual compression stress of the AlN ceramics sintered at 5.0 GPa and 1700 °C for 125 min is -2.0 GPa. The residual compression stress increased according to the extension of the sintering time.