| CaO-MgO-Al2O3-SiO2 glass-ceramic system is an important glass-ceramics system. The crystals like diopside [CaMgSi2O6], anorthite [CaAl2Si2O8] and cordierite [Mg2Al4Si5O18] can precipitate in the CMAS glass-ceramic, therefore the corresponding CMAS glass-ceramics have excellent mechanical properties, high abrasive resistance and good chemical resistance and are good candidates for decorative materials in construction field. However, the crystallization of CMAS glass-ceramics prepared by bulk crystallization process is very difficult and hard to control; while the sintering process can lower the properities of CMAS glass-ceramics, these factors seriously restricts the research and application of CMAS glass-ceramics. In this paper, the effects of the compositions, additives, preparation process on the crystallization of CMAS glass-ceramic were studied and optimized to improve the crystallization ability, mechanical properties and chemical durability, and to expand its scope of application.On the basis of CMAS glass system, the CMAS glass-ceramics containing disopide and anorhite as major phases were prepared by bulk crystallization process, and the effects of the mass ratio of CaO to MgO and fluxing agent on devitrification of glass-ceramics were investigated. Keep the total weight percentage of CaO and MgO was 24wt%, it was found that when the m(CaO)/m(MgO)=3 and 1.4, the corresponding glass-ceramics can devitrify better than other samples; and the sample with m(CaO)/m(MgO)=1.4 containing more diopside, while the best pre-nucleating temperature and crystallization temperature of it were 660℃and 936.2℃respectively. The fluxing agent Na2O+K2O can promote the crystallization of glass-ceramic while B2O3 inhibited it.The effects of mixed nucleation agents (fluoride+oxide) on the crystallization of glass-ceramics were investigated by using crystallization kinetic theory. The CaF2+Ti02 could reduce the activation energy of glass to 330±10kJ/mol and accelerate the growth of crystalline phases, while the CaF2+P2O5 can improve the Avrami parameter to 2.9±0.03 and boost more crystal nucleus form in the glass.Two kinds of inital glasses which can precipitate diopside and cordierite respectively were mixed to prepare diopside/cordierite based glass-ceramics by sintering process. The obtained glass-ceramics can’t precipitate diopside and cordierite phases together in one glass-ceramic. By contrast, the glass-ceramic with cordierite as main crystalline phase had high Vickers hardness greater than 8.0GPa, while the values of bending strength and chemical resiatance of it are closed to diopside based glass-ceramic. |
PDF Full Text Request