The raw materials used in this work include high-purity, ultrafine Al2O3 powder and nano carbon black powder, purchased in China National Pharmaceutical Industry Corporation Ltd. Characteristics of the two types of powders are shown in Table 1. The organic binder used in this study was analytically pure, also purchased in China National Pharmaceutical Industry Corporation Ltd.
The Al2O3 powder and nano carbon black powder were blended at a mass ratio of 1:3.5 and dry-milled for 5 h in a planetary ball mill at a speed of 300 rounds/min. Both the jar and milling balls were made of 99.9 wt% corundum ceramics. 5 wt% organic binder was poured into the powder mixture and then uniformly stirred into plasticine. Next, the plasticine was extruded into short rods, and finally, the plasticine rods were placed in an atmosphere protecting furnace and annealed at 360 °C for 2 h at a rate of 120 °C/h. The adhesive-discharging process was carried out in a 99.99 vol% high-purity N2 atmosphere at a gas flow rate of 15 L/min.
After that, the synthesis precursors of AlN powder were prepared. The precursor rods were shifted into a high temperature synthesis furnace with a batch capability of 5 kg AlN powder per hour. The precursors were calcined at 1700 °C for 12 h at a heating rate of 100 °C/h. After that, the furnace was cooled to 300 °C at a rate of 100 °C/h and then naturally cooled to room temperature. The calcination process was carried out under the protection of the 99.99 vol% high purity N2 gas at a gas flow rate of 250 L/min. The short rod-shaped AlN calcined products were then placed in a decarburization furnace and annealed at 700 °C for 2 h in air at a heating rate of 100 °C/h. After that the furnace was cooled to 300 °C at a rate of 100 °C/h and then naturally cooled to room temperature. After pulverizing, the AlN powder final product was achieved.