Anisotropic mullitization in CuO-doped oxide mixture activated by high-energy ball milling

Mullite phase formation and grain growth, in a CuO-doped Al2O3and silica mixture, has been investigated. The oxide mixture was activated with both stainless steel and tungsten carbide milling media. The milled powders demonstrated a much lower mullite formation temperature when compared to the conventional solid-state reaction process. Anisotropic grain growth was observed in the powders milled with stainless steel media, while well-shaped mullite whiskers were produced in the WC milled samples. The lowered mullitization temperature together with the anisotropic grain growth behavior was attributed to the refined microstructure of the powders as a result of the high-energy ball milling process.