Study On Diopside Glass-Ceramics Derived From Waste Glass By Direct Sintering Process

Diopside glass-ceramics is a kind of material with excellent physical and chemical properties,which has broad application prospects in many fields.However,at present,melting method and sinter-crystallization method are mainly used in the preparation process.Both of them involve the high-temperature melting process of basic glass.Therefore,there are many defects,such as being complicated,high energy consumption and high cost.How to reduce the production cost of diopside glass-ceramics has become the key to its wide application.As a kind of solid waste,waste glass can promote sintering and crystallization in the preparation of glass-ceramics.Therefore,the preparation of glass-ceramics using waste glass has positive significance for reducing energy consumption and realizing the recycling of waste.At the same time,the one-step preparation of glass-ceramics can be realized by using the ceramic preparation process-direct powder sintering method,which has the characteristics of simple production process and energy saving.In view of this,the diopside glass-ceramics with good properties were successfully prepared by using waste glass as the main raw material and powder direct sintering process.The effects of kaolin,MgO and the corresponding sintering schedule on the crystallization and properties of the glass-ceramics were systematically studied.Meanwhile,the crystallization mechanism of diopside crystalline phase in the system was deeply investigated by means of crystallization kinetics calculation and EDS test analysis.The conclusions are as follows:(1)The addition of kaolin can promote the precipitation of diopside crystalline phase during the sintering process of waste glass powder,and its crystallization amount initially increases and then decreases with the increase of kaolin addition.Increasing the sintering temperature of the sample is more in favor of the formation of diopside crystalline phase.With the extension of sintering time,the crystalline phase in the sample precipitates in the order of cristobalite-sodium aluminum silicate-diopside.The results show that the crystal phases of quartz and sodium aluminosilicate formed in the sample are unstable in the system.With the increase of sintering temperature or sintering time,the precipitation decreases gradually after reaching the highest point,while the diopside crystal phases increase continuously.The optimum addition of kaolin is 25%.The bulk density and flexural strength of glass-ceramics sintered at 825?for 2 h reach the maximum values of 2.484 g/cm~3 and 114.9 MPa,respectively.(2)The addition of MgO can significantly promote the precipitation of diopside crystalline phase in waste glass-kaolin binary system during sintering.Increasing the sintering temperature of the sample is beneficial to the continuous growth of diopside grain,and its crystal morphology changes from granular to short columnar.The results show that increasing sintering temperature or prolonging sintering time can promote the decomposition and disappearance of crystal phases such as cristobalite,sodium aluminum silicate and nepheline in the samples,which is conducive to the formation of a single diopside crystal phase structure.The optimum MgO content is 4%.The bulk density and bending strength of the glass-ceramics sintered at 975?for 2 h reach the maximum values of 2.395 g/cm~3 and 102.1 MPa,respectively.(3)The crystallization kinetics calculation shows that the activation energy and crystallization coefficient of diopside are 345.04 kJ/mol and 2.80 respectively for the samples consisting of 75%waste glass powder and 25%kaolin,which indicates that diopside crystalline phase in the system precipitates in form of volume crystallization.The crystallization activation energy of diopside decreases with the addition of MgO,and the crystallization coefficient of diopside decreases to 1.69.This indicates that the addition of MgO will make the precipitation of diopside easier and the crystallization mechanism gradually change from bulk crystallization to surface crystallization.Combined with the results of EDS test analysis,the crystallization mechanism of diopside in waste glass-kaolin binary system is explained as follows:the addition of kaolin makes Na~+in the surrounding glass phase diffuse to the side of kaolin,resulting in the formation of sodium aluminum silicate phase.At the same time,the content of Na~+in the glass phase decreases,which is conducive to the formation of diopside nuclei in the glass phase and grows along the direction of Na~+ diffusion.