Preparation of Ultra-fine NdB6 Powders by Combustion Synthesis and Its Reaction Mechanism

Ultrafine powders NdB6 were prepared by combustion synthesis with B2O3, Nd2O3 and Mg as raw materials. The effects of reaction atmosphere, sample pressure and raw materials ratio on the reaction product morphology and phases were studied. Characterizations by XRD and SEM show that the products consist of NdB6, MgO and a little amount of Mg3B2O6 and Nd2B2O6. After reaction with sulphuric acid at low concentration to eliminate the latter three components, the pure NdB6 is obtained (purity 99.1%). As the preparation pressure increases, the NdB6 particle sizes become small. When the sample pressure is 20 MPa, the average particle size is less than 500 nm. The preparation reaction process is as follows: firstly, Mg reduces Nd2O3 to generate Nd and MgO; and then, the reaction between Mg and B2O3 are ignited to generate B and MgO; at the same time, the generated Nd and B are reacted to produce NdB6. The apparent activation energy of the reaction is 691.59 kJ/mol and the reaction order is 3.2.