Analysis of Thermal Explosion Process for Preparing Ferromagnetic Al2O3-based Cermets

Ferromagnetic Al2O3-based cermets characterized by homogeneous dispersion of Co-Ni alloy particles were successfully prepared via thermal explosion. The differential scanning calorimeter (DSC) analysis was employed to investigate the reaction process of Al-CoO-NiO system. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis on water-quenched samples were carried out for phase identification and microstructure observation, respectively. The results show that a solid state reaction between Al and CoO (NiO) occurs at about 939K and the reaction of Al melt and CoO (NiO) leads to the ignition of thermal explosion. The Al2O3 initially added into the compact cannot only prevent the as-synthesized product from splashing under high combustion temperature, but also react with CoO (NiO) to form intermediate spinel phase (Co, Ni)Al2O4. The measured saturation magnetization and coercive force of synthesized ferromagnetic (Co, Ni)-Al2O3 cermets are 29 emu/g and 31 Oe, respectively.