Fast synthesis of MgAl2O4‒W and MgAl2O4‒W‒W2B composite powders by self-propagating high-temperature synthesis reactions

MgAl2O4‒W and MgAl2O4‒W‒W2B composite powders were obtained rapidly in a single step by self-propagating high-temperature synthesis of WO3‒Mg‒xAl2O3 and WO3‒B2O3‒Mg‒yAl2O3 systems. The addition of various Al2O3 contents (x and y-values) to the starting materials was considered as the main synthesis parameter. Thermodynamic calculations revealed that the adiabatic temperature of both systems was decreased with increasing Al2O3 content. The XRD results indicated that after acid leaching of the WO3‒Mg‒xAl2O3 combustion products, W and MgAl2O4 were formed as the main phases and WO2, MgWO4 and Al2O3 as the minor constituents in the final composite. On the other hand, MgAl2O4‒W composites were synthesized in the WO3‒B2O3‒Mg‒yAl2O3 system at y<1.4 mol. By increasing the y-value to 2.1 mol, W2B was formed as a new product leading to production of MgAl2O4‒W‒W2B composite. The formation of spinel was confirmed by the Fourier transformed infrared spectroscopy analysis. Microstructure observations represented the uniform distribution of MgAl2O4 blocks within the fine spherical W particles. The melting of Al2O3 was found as a vital step for rapid synthesis of MgAl2O3 by the SHS route. Finally, the possible formation mechanism of MgAl2O4 during the combustion synthesis was proposed.