졸-겔법으로 제조한 ZrO₂ㆍSiO₂계 결정화 유리의 결정화 및 파괴인성에 관한 연구

A Study of Crystallization and Fracture Toughness of Glass Ceramics in the ZrO₂ㆍSiO₂ Systems Prepared by the Sol-Gel Method

Precursor gels with the composition of xZrO₂ㆍ(100-x)SiO₂ systems (x=10,20 and 30mol%) were prepared by the sol-gel method. Kinetic parameter, such as activation energy, Avrami’s exponent, n, and dimensionality crystal growth value, m, have been simultaneously calculated from the DTA data using Kissinger and Matusita equations. The crystallite size dependence on tetragonal to monoclinic transformation of ZrO₂ was investigated using XRD, in relation to the fracture toughness. The crystallization of tetragonal ZrO₂ occurred through 3-dimensional diffusion controlled growth(n=m=2) and the activation energy for crystallization was calculated using Kissinger and Matusita equations, as about 310~325±10kJ/mol. The growth of t-ZrO₂, in proportion to the cube of radius, increased with increasing heating temperature and heat-treatment time. It was suggested that the diffusion of Zr4+ions by Ostwald ripening was rate-limiting process for the growth of t-ZrO₂ crystallite size. The fracture toughness of xZrO₂ㆍ(100-x)SiO₂ systems glass ceramics increased with increasing crystallite size of t-ZrO₂. The fracture toughness of 30ZrO₂ㆍ70SiO₂ system glass ceramics heated at 1,100℃ for 5h was 4.84 MPam1/2 at a critical crystaliite size of 40 nm.