Effects of carbon source type and dosage on the synthesis of Al2O3–AlN composite powders by the carbothermal reduction–nitridation method

Al2O3–AlN composite powders were synthesised in N2 by the carbothermal reduction–nitridation method with Al(OH)3 and different carbon sources (i.e. carbon black, graphite and starch) as starting materials. The effects of the carbon source type, carbon source dosage and reaction temperature on the synthesis performance of the Al2O3–AlN composite powders were investigated. The dried precursors and their synthesised products were characterised by X-ray diffractometer, comprehensive thermal analysis instrument and scanning electron microscope. The results showed that when the denoted mass ratio of Al2O3/AlN is 7:3, the optimum conditions for the synthesis of Al2O3–AlN composite powders with carbon black and starch as carbon sources are 1500°C for 2 h and 1600°C for 2 h, respectively. In addition to generating elemental carbon and gaseous H2O, the single-phase starch raw material produces gaseous CxHy during heating. The actual mass loss rate generated in the system is consequently significantly higher than the theoretical mass loss rate. The Al2O3–AlN composite powder samples synthesised at 1500°C with carbon black as the carbon source are mainly composed of approximately hedgehog-shaped aggregates, which consist of a mixture of flakes and nearly spherical particles (100–300 nm). The powder samples synthesised at 1500°C with graphite as the carbon source form diverse microstructures composed of spherical, flaky and rod-like particles. When starch is used as the carbon source, the encapsulated structure particles formed at 1500°C tend to increase gradually with decreases in the Al2O3/AlN mass ratio.