Formation of β-zirconia and γ-zirconia nano-particles from α-zirconia by mechanical activation

The phase transformation of zirconia and formation of β-zirconia and γ-zirconia nano-particles from α-zirconia by mechanical activation were studied. α-zirconia powder (with monoclinic structure) for 2-150 h and 40:1-60:1 ball-to-powder weight ratio (BPWR) was ball milled. The effect of milling variables on this process such as BPWR and milling duration was also investigated. Structural evaluations were analyzed using X-ray diffraction and a scanning electron microscope (SEM). Results showed, however the phase transformation of α-zirconia to β-zirconia (with tetragonal structure) at 1250 °C after eight hours was not performed, β-zirconia and γ-zirconia (with cubic structure) could be achieved by ball milling of α-zirconia at room temperature. Results shown that α to β phase transformation began after two hours milling and completed after 48 h. Moreover, α to γ phase transformation completed after 150 h milling with 40:1 BPWR. In addition, using Williamson-Hall equation indicated that the particle size of zirconia powder was reduced down to 30 nm and obtained the equilibrium point after 48 h milling.