Influence of charge treatment with calcium chloride on the morphology, purity, and reactivity of calciothermic zirconium powder

Abstract: Problem. Calciothermic reduction of zirconium dioxide is one of the promising methods for producing zirconium powders. To reduce the synthesis temperature and modify the product morphology, calcium chloride is often introduced into the charge; however, its influence on phase formation and the final powder characteristics is insufficiently studied. Aim. To investigate the influence of calcium chloride introduced into the charge during the calciothermic reduction of zirconium dioxide on the phase composition, morphology, dispersity, and reactivity of the resulting zirconium powder. Methods. A comparative analysis was performed on two series of samples obtained with and without flux (CaCl₂). Chemical composition was determined by arc atomic emission analysis; phase composition – by X-ray diffraction analysis; particle size distribution – by laser diffraction; specific surface area – by the BET method; particle morphology – by scanning electron microscopy; and active zirconium content – by gravimetric method. Results. It was shown that the addition of calcium chloride to the charge by wetting in an alcohol solution increased the specific surface area of the powder from 0.56 m²/g (without CaCl₂) to 2.9 m²/g (with CaCl₂) while maintaining the average particle size (d50 ~5 μm). However, this was accompanied by the retention of the calcium zirconate (CaZrO₃) phase in the product, which was not removed during standard hydrometallurgical processing, leading to an increased residual calcium content (1.10 wt.% vs. 0.05 wt.%) and a decrease in active zirconium content (64.7 % vs. 96.9 %). Conclusions. The obtained results indicate the need to optimise process parameters when using CaCl₂ as a flux. The calciothermic method without flux additives made it possible to produce a powder with characteristics comparable to literature data.