Papers by Author: Xiao Lei Li

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.