Effect Of Na₂O And CaO On Crystallization Of Fluoramphibole Glass-ceramics

Fluoramphibole glass-ceramic is one of important derivatives of glass-ceramics, consists of massive micro-crystal phase and glass-phase, often is prepared by heat treatment of specific composition parent-glass with a crystallization control process.fluoramphibole crystal belongs to chain structures, like fluormica, it can be easily split along the interface between chains under forces for its poor boding which makes fluoramphibole glass-ceramics easily machinable. Fluoramphibole glass-ceramic has been widely used in the fields of engineering, electronics and biomedicine with a promising future for its low heat expansibility and machinability.Melting-crystallization method was adopted to prepare fluoramphibole glass-ceramic for a long time. Firstly, a special fluorosilicate glass was melted and then fluoramphibole was precipitated by heat treatment. In order to obtained crystalline phase, the composition of base glasses should be composed of the chemical formula of precipitated crystal or its solid solution. The stable crystalline phases in the glass-ceramic were not precipitated straightly form glass but transited from a intermediate phase.A novel technique based on sinter-reactive crystallization is developed to prepare fluoramphibole glass-ceramic, using the soda lime glass powder as main raw material, adding fluormica crystal powders to the glass powder and then sintering, fluoramphibole being formed by a reaction between fluormica and glass instead of by a direct precipitation from the base glass, therefore, the fabrication of fluoramphibole glass-ceramic dose not require a particular formulated fluorosilicate glass by the technique which has advantages of simple process and low-cost, and is a bran-new process for the fabrication of glass-ceramics.The composition of the glass has a great effect on the sintering and precipitation of glass-ceramics. Studying the influence of the content change of Na2O and CaO in soda lime glass on the sintering and reactive crystallization of the fluoramphibole glass-ceramics can not only enrich the mechanism the reactive crystallization of glass, but also be likely to get an advanced formulation of glass and provide a new approach for the solution to overcome the present lower density and strength of glass-ceramics prepared by waste glasses, which has a valuable significance in theory and practice.In order to determine the effect of Na20 and CaO on crystallization of fluoramphibole glass-ceramics, three group experiments were carried out. The XRD results show that, when the content of Na20 is below 6%, diopside and enstatite developed as main phases in glass-ceramics with increasing content of Na2O in glass, when the content of Na2O excesses 6%, fluoramphibole was obtained; the sample with increasing content CaO was mainly consist of diopside and forsterite phase, and fluormica was still existed. The SEM shows the sample with 9% Na2O was highly sintered, and the micro-structure was made of glassy phase and rod-like fluoramphibole crystallites.