Wang Mingzhi

Cubic BN Sintered with Al under High Temperature and High Pressure

Sintering of cubic boron nitride (cBN) with addition of Al is carried out in the temperature range 1300–1500°C and under the pressure 5.5 GPa. When sintered at 1300°C, a weak diffractive peak of hexagonal BN (hBN) is observed in the Al-cBN sample, indicating the transformation from cBN to hBN. No nitrides or borides of Al are observed, which indicated that Al does not react with cBN obviously. When the sintering temperature is increased to 1400°C, the diffractive peak of hBN disappears and new phases of AlN and AlB2 are observed, due to reactions between Al and cBN. When the sintering temperature is further increased to 1500°C, the contents of AlN and AlB2 phases increase and the Al phase disappears completely.

Effects of Raw Material Content on Efficiency of TiN Synthesized by Reactive Ball Milling Ti and Urea

Ti and urea mixed according to the molar ratios of 2:1, 3:1 and 4:1 are milled under the same condition. The structures of the as-synthesized powders are analyzed by an x-ray diffractometer (XRD). The decomposed temperature of the urea and the products decomposed are characterized by differential scanning calorimetry (DSC) and thermogravimetry analysis-Fourier transform infrared (TG-FTIR) spectrometry. The results show that the reaction progress is a diffusion reaction. The efficiency of TiN synthesized by reactive ball milling can be increased by increasing the content of Ti. The reactive ball milling time decreases from more than 90 h to 40 h corresponding to the content ratio between Ti and urea increasing from 2:1 to 4:1. Ammonia gas (NH3) and cyanic acid (HNCO), the decomposed products of urea, react with the refined Ti to form TiN. The grain refinement of Ti has a significant effect on the efficiency of reactive ball milling.