Growth Of ZrO2 Research Articles

ZrO<sub>2</sub> Transformation of Glass-Ceramics in the System ZrO<sub>2</sub>-SiO<sub>2</sub> Prepared by the Sol-Gel Process from Metal Alkoxides

Crystal growth of ZrO2 and crystallite size dependence of tetragonal to monoclinic ZrO2 transformation were investigated in relation to the fracture toughness of glass-ceramics. Glasses of 2ZrO2⋅3SiO2, ZrO2⋅SiO2 and 3ZrO2⋅2SiO2 in molar ratio, prepared by the sol-gel process from metal alkoxides, were heat-treated to precipitate tetragonal (t-) ZrO2 crystals. Tetragonal-ZrO2 crystals grew in proportion to the cube-root of heat-treatment time, and the growth rate increased with increasing ZrO2 content. Crystals of t-ZrO2 larger than a critical size transformed into monoclinic (m-) ZrO2 during cooling. Transmission electron microscopy revealed that the m-ZrO2 particles showed twinning associated with t- to m-ZrO2 transformation. Tetragonal to m-ZrO2 transformation temperature was found proportional to the reciprocal ZrO2 crystal size, which was consistent with Garvie's transformation equation. The critical sizes corresponding to the transformation temperature of 273K were estimated to be 90, 56 and 40nm for 2ZrO2⋅3SiO2, ZrO2⋅SiO2 and 3ZrO2⋅2SiO2 glass-ceramics, respectively. The interfacial and strain energies for the transformation calculated from Garvie's equation increased with decreasing ZrO2 content. The fracture toughness (KIC) of these glass-ceramics increased in proportion to the cube of t-ZrO2 crystal size. From the critical crystal size of t-ZrO2 in the glass-ceramics, the maximum KIC was estimated to be 4.7, 4.7 and 5.0MN/m3/2 for 2 ZrO2⋅3SiO2, ZrO2⋅SiO2 and 3ZrO2⋅2SiO2, respectively. After reaching the maximum, KIC decreased abruptly on further heating, which was attributed to the occurrence of m-ZrO2 crystals in the glass-ceramics.

Coupled Grain Growth Effects in Al2O3/10 vol% ZrO2

Coupled crystallization has been observed in the Al3O3/10%‐ZrO2 system by heating an amorphous precursor Al /Zr copolymerized alkoxide network structure. A finely divided two‐phase material results which stabilizes tetragonal ZrO2 to 1700°C and exhibits an unprecedented microstructure. During crystallization, the grain growth of ZrO2 is coupled to the γ→α phase transformation of Al2O3.

Crystallisation of titanium, zirconium and hafnium oxides and some titanate and zirconate compounds under hydrothermal conditions

Crystallization of titanium, zirconium and hafnium oxides in KF, NaF, NH 4F solutions was studied at 450–700°C and 800–3000 atm. Under otherwise identical conditions the quantity of carrying substance decreases from TiO 2 to ZrO 2 and HfO 2, and increases in NaF<KF<NH 4F solutions. The substance is transferred from the hot to the cold zone of the autoclave in KF, NaF solutions, and is transferred in a reverse direction in a NH 4F solution. The spontaneous crystallization of rutile and its growth on seed crystal was studied. The growth rate of the faces {110} and {100} was 0.2–0.3 mm/day at 550–600°C and Δ T= 20–35°C. The growth of ZrO 2 and HfO 2 was realized in a horizontally placed vessel under analogous conditions (550–600 °C, Δ T = 15–30°C). Crystallization of some titanates and zirconates of lead was brought about in a KF solution. PbTi 3O 7 · K 2O· 0.5 PbO · 7 TiO 2, PbTiO 3 and PbZrO 3 were obtained at 450–700 °C and 800–3000 atm. Vigorous crystallization of PbTiO 3 and PbZrO 3 takes place above 550 °C. Recrystallization of mixed Pb(Ti 0.5 Zr 0.5)O 3 crystals resulted in Pb(Ti,Zr)O 3 with TiO 2 concentration up to 25%.