Two-Step Gradient Reduction of Zirconia for Making High-Purity Zirconium Powder
Ultra-high pure metallic zirconium powder was successfully obtained through a two-step gradient reduction of nano-ZrO 2 in Ar atmosphere. The first reduction by Mg was to remove ~ 85% oxygen, followed by a heat-treatment step to control the particle size and specific surface area of the powder, and the final reduction by calcium was to further purify the powder and decrease oxygen to an extremely low level (0.068 wt.%). The oxygen level in the final powder meets the standard specification of Zr sponge (ASTM B349/B349M-16). Processing parameters, including the reduction temperature, the amount of Mg and MgCl 2 and the heat treatment temperature, were investigated. Thermodynamic modeling with the assistance of HSC Chemistry software was carried out to understand the reduction reaction. This study offers a novel process for producing ultra-high pure metallic zirconium powder with the potential to replace the conventional Kroll process.
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