Effects of Mechanically Activated Millin

The purpose of this paper was to investigate the effect of a high-energy milling (HEM) process on the particle morphology and the correlation between a thermal treatment and tetragonal/monoclinic nanostructured zirconia powders obtained by a precipitation process. To eliminate chloride residue ions from hydrous zirconia, a modified washing method was used, which proved effective in removing chloride from the precipitated gel. It was found that the particle size of Zr(OH)4 after HEM milling with distilled water reduced to 100–150 nm, in contrast to the fresh Zr(OH)4 powder without pre-milling, which exhibited a larger and irregular size of 100 nm–1.5 μm. A modified heat treatment process was proposed, resulting in nano-sized zirconia with a pure monoclinic phase. The two-step calcining process effectively eliminated the tetragonal phase, yielding a small average particle size of ~100 nm with good uniformity, while the single-step process resulted in ~300 nm particle sizes with irregular shapes and broad distributions. This modified method emerges as a promising process for producing nano-sized zirconia with a fully monoclinic phase.