Research On The Structure And Performance Of Low Cost CAS Glass-ceramics

Sintering CaO-Al2O3-SiO2 glass-ceramics are high-grade building decorative materials, which have wide market prospect and considerable economic benefit, therefore many researchers of glass and companies compete for it's investigations and product development. In recent years, for the price growth of ZnO, which is the essential component of this system glass-ceramics, the production cost is raised, it is a major breakthrough point for my subject study that seeking reasonable substitutes of ZnO and creating a more cost-effective glass-ceramics, which have unaltered process parameters.In the paper, based on CAS system glass-ceramics, by adjusting the components, emphasis is laid on the study of the influence of ZnO,Na2O,Li2O,K2O,MgO content on sintering crystallization process, structure and properties of glass-ceramics, in order to determine more reasonable components. The influence of different oxides content on sintering crystallization process and heat treatment were studied by DTA and gradient temperature furnance experiment; the influence of different oxides content on crystallization property and internal structure were investigated by XRD, SEM, etc; the effect of composition and structure on properties were analysised by performance tests; the sintering kinetics of CAS glass-ceramics was studied in order to investigate the sintering process of glass particles and discuss the major factors on sintering densification in different stages.In the paper, components of low cost sintering CAS glass-ceramics was determined (wt%):SiO260-70%, A12O33-8%, CaO 13-18%, ZnO 1-5%, BaO3-5%, Na2O 3-6%, B2O31-1.5%, MgO0-4%, K2O0-2%, Li2O0-4%, Sb2O30.5%. The main conclusions show that:With decreasing ZnO, the flattening temperature increases, the quantity and size crystal both decrease, the compactness of crystal arrangement reduce, and the flexcural strength become lower. With increasing Na2O, the flattening temperature, crystallization property and quantity of crystal decrease, the overall structure become looser, so the Tg, Tf and flexcural strength of glass-ceramics both decrease, and the thermal expansion coefficient increase. The sintering crystallization process of glass can be improved with adding Li2O, which has dual function of promoting crystallization and crystal melting, the optimum Li2O content was between 1.0%-1.5% at flattening temperature 1120℃. With increasing Li2O, the major crystal phase is stillβ-wollastonite, the quantity of crystal increase first and then decrease, the crystal size become larger, and the flexcural strength of glass-ceramics maximize when Li2O content is 1.5%. Simultaneously, the glass-ceramics, which are prepared by using lepidolite and lithium feldspar, have flexural strength higher than national standard(JC/T872-2000), and well-formed glass-ceramic structure. It's practical that lepidolite and lithium feldspar can be the raw material of CAS glass-ceramics in industrial production.An appropriate increase of K2O and MgO content is conducive to sintering densification processing, optimize the sintering crystallization process in some extent. The main crystal phase isβ-wollastonite, but with increasing K2O the proportion of crystal phase decrease significantly, with increasing MgO that increase. Therefore with the addition of K2O for improving sintering process, MgO can be introduced to enhance the crystallization propertyThe sintering densification processing of CAS system glass-ceramic occurs mainly in prophase and metaphase of sintering of glass particles, while the higher temperature and the wider temperature range are favorable for sintering densification. The higher completeness of sintering, the lower porosity finished product have. For the glass particles which have low sintering activity, unsatisfactory of prophase sintering densification can be made up through high-temperature sintering in the metaphase. For the glass particles which have higher sintering activity, though it has a satisfactory prophase sintering densification, fast crystallization in the metaphase will stop sintering ahead of time. Li2O can decrease sintering activity energy, improve the sintering activity of the glass. When the content of Li2O is 1%-1.5%(wt%), glass particles have lower sintering activity energy and can be sintered in higher temperature, the change of shrinkage ratio is more reasonable, and there is a wider temperature range of sintering shrinkage, which is favorable to sintering densification and effectively decrease the porosity of glass-ceramic.