Low Temperature Synthesis of Phase Pure MoAlB Powder in Molten NaCl
Cheng Liu, Zhaoping Hou, Quanli Jia, Xueyin Liu, Shaowei Zhang
Abstract
MoAlB fine powders were prepared in molten NaCl from Al, B and Mo powders. The effects of key parameters affecting the synthesis process and phase morphology were examined and the underpinning mechanisms proposed. MoAlB product particles exhibited different shapes/sizes, as follows: spherical grains (1~3 μm), plate-like particles (<5 μm in diameter) and columnar crystals with lengths up to 20 μm and diameters up to 5 μm, resultant from different reaction processes. Phase pure MoAlB was synthesised under the following optimal conditions: use of 140% excess Al and 6 h of firing at 1000 °C. This temperature was at least 100 °C lower than required by other methods/techniques previously reported. At the synthesis condition, Mo first reacted with Al and B, forming Al8Mo3 and MoB, respectively, which further reacted with excess Al to form Al-rich Al–Mo phases and MoAlB. The Al-rich Al–Mo phases further reacted with the residual B, forming additional MoAlB. The molten NaCl played an important role in accelerating the overall synthesis process.