Research On Structure And Properties Of R₂O-CaO-SiO₂-F System Glass-ceramics

In this paper, the research background, classification, preparative technology and application of glass-ceramics (especially about a glass-ceramics consisting of the R2O-CaO-SiO2-F system) were systematically reviewed. The influence of heat treatment and composition on structure and properties of the glass-ceramics based on R2O-CaO-SiO2-F system were investigated. The relationships among composition, heat treatment, crystallization and properties were studied to attain some results about reasonable composition and heat treatments and high-performance glass-ceramic substrate.Firstly, the influence of K2O, CaO, F and Al2O3 content on crystallization and properties of glass-ceramics was investigated. The results showed that the increase of K2O addition resuled in the reduction of the glass transition temperature and the enhancement of the crystallization temperature. Moreover, the crystalline phase was granular CaF? and cylindrical cuspidate and the crystalline were 15% with 5wt% K2O. However, the crystalline phase were transformed to bulk radial A-canasite and CaF2 and the crystallinity were up to 40% when the addition of K2O increased from 6wt% to 8wt%.With the CaO content was added from10.8 wt% to 16.8 wt%, the crystalline phases were disordered. The canasite transited to others Crystalline phases. Excess CaO acted as speed up the rate of crystallization, caused coarse crystallite and low flexure strength. And as the F content was added from 3.4 wt% to 6.4 wt%, the canasite or A-canasite crystalline phase was promoted. With appropriate F content, the flexure strength of sample was perfect. However excess F acted as speed up the rate of crystallization, caused coarse crystallite and low flexure strength.The addition of Al2O3 would strengthen the glass network. Moreover, the crystal phases became CaF2 and canasite if the mass fraction of alumina was 2.5%. However, the crystal phases were transferred into CaF2and xonotlite when the mass fraction of alumina was 3.5% and 4%. When the mass fraction of alumina increased up to 4.5%, the CaF2, A-canasite and xonotlite were precipitated.Secondly, we investigated the influence of heat treatment on the phase transition, study the processes of phase transition and try to explain the result by analysis of thermodynamic theory further. The result shows that the growth rate of canasite or A-canasite (frankamenite) was higher than xonotlite at high temperature for the vantage of thermodynamic drive force. The kinetic analysis indicated that the precipitation of canasite or frankamenite needs to overcome more activation energy of particles diffusing then xonotlite. So Therefore, the precipitation of xonotlite litter is earlier than canasite or frankamenite at low temperature. The phase transition between xonotlite and canasite or frankamenite does correspond agreed with the thermodynamic theoretical expectations. Which demonstrate that although the phase evolution is was a complex procedure in canasite-based glass-ceramic, we can still get some its general principle through theoretical analysis.