Synthesis of ZrN powders by aluminum-reduction nitridation of ZrO2 powders with CaCO3 additive

Abstract

ZrN powders were synthesized from mixtures of ZrO2 and Al metal powders using CaCaO3 as an additive. The effects of various heating temperatures, nitrogen pressures and amounts of CaCO3 additive on the phase assemblage and morphologies of the final products were investigated using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Impurity contents and particle sizes of the final powders were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), oxygen gas analysis, Energy Dispersive Spectroscopy (EDS) and ImageJ software. The results show that without adding CaCO3, the products were mostly composed of ZrN and ZrAl3O3N, and a small amount of other ZrOxNy phases. However, both of the ZrAl3O3N and ZrOxNy were stable in acid, and it was not possible to separate the ZrN powders. Suitable CaCO3 concentration, heating temperature and nitrogen gas pressure were employed to avoid the formation of ZrAl3O3N and ZrOxNy and resulted in powders composed of ZrN, calcium-aluminates and calcium-zirconate phases. The by-products, calcium-aluminates and calcium-zirconate were subsequently dissolved by HCl acid to obtain single phase ZrN. The impurity elements contents are less than 2% and the mean particle size is around 0.96µm. The optimum parameters for synthesis of ZrN were: CaCO3 concentration of 26.83 ~29.53wt%, heating temperature of 1400°C and nitrogen gas pressure of 0.4MPa.