Research On The Preparation Of Cordierite Glass-ceramics Using Blue Stone Powder

Bluestone powder is solid waste produced during the production of bluestone,which mainly consists of SiO2 and Al2O3,and the total mass fraction of the two components accounts for more than 80%.Besides,bluestone powder also contains MgO,Fe2O3,K2O and Na2O in small quantities.Due to the relative low value,the open storage method is adopted to process bluestone powder currently,which not only wastes large amounts land resources but also has a significant influence on the environment.In this paper,bluestone powder powder is used as raw material to prepare cordierite-based glass-ceramic with outstanding property by melting method,which also provides an innovative method to realize the solid waste resource recycling efficiently and securely.In this paper,the FactSage7.1 thermodynamic calculation,differential thermal analysis(DTA),X-ray diffraction analysis(XRD),scanning electron microscope analysis(SEM),Fourier transform infrared spectroscopy(FTIR)and other methods are used to investigate the effects of non-main crystal phase impurities Fe2O3,K2O and Na2O in bluestone powder on cordierite glass-ceramic system firstly.Then,the influence of bluestone powder blended ratios on the thermodynamics,crystallographies,phase components,crystal microstructures and dielectric properties of bluestone powder glass-ceramics are explored systematically.Moreover,the effects of heat treatment conditions on the devitrification of glass-ceramics and product properties are also explored,aiming to obtain rational heat treatment parameters.The main research contents and conclusions are as follows:First,the influence of main impurities Fe2O3,K2O and Na2O in bluestone powder on cordierite glass-ceramics are explored systematically.The introducing of Fe2O3 is conducive to the crystallization of the base glass,thereby decreasing the nucleation temperature Tg,crystallization temperature Tp and stability.Correspondingly,the crystallization activation energy Ec decreased from 464.79 kJ/mol to 396 kJ/mol of the base glass.In addition,the crystallization ability would be improved of the system,and the crystal microstructure of the crystallized glass transformed from ring growth to network barrier growth.The introducing of K2O could reduce the crystallization ability of the base glass,restrain the crystallization of the system,and increase the nucleation temperature Tg,crystallization temperature Tp.Correspondingly,the crystallization activation energy Ec increased from 464.79kJ/mol to 487.90 kJ/mol.Under this conditions,the crystal growth mode is surface crystallization and the crystal microstructure of the crystallized glass transformed to granular disordered agglomeration.Simultaneously,the segregation and aggregation would occur in the system and suppress the growth of the crystal.The influence mechanism of Na2O is similar to that of K2O.However,the suppress effect of K2O on the crystallization of the system is much stronger than that of K2O.The crystallization activation energy Ec of the base glass increased from 464.79 kJ/mol to 567.32 kJ/mol.Similarly,the crystal growth mode is surface crystallization.In addition,the introducing of Fe2O3,K2O and Na2O could suppress the precipitation of ?-cordierite phase in the base glass,and promote the precipitation of ?-cordierite phase,which benefits the preparation of single ?-cordierite phase glass-ceramic.According to the stoichiometric ratio of cordierite(SiO2:MgO:Al2O3=5:2:2),the cordierite glass-ceramics are prepared with bluestone powder instead of some purification reagents to explore the effect of bluestone powder blended ratio on the glass-ceramics.With increasing the bluestone powder ratio from 40%to 70%,the content of impurities and the crystallization ability of the system continue to increase,and the melting point and the integrity of the basic glass structure continues to decrease gradually.Besides,the Tg and Tp of the base glass keep decreasing,resulting in the crystallization activation energy gradually decreases from 463.52 kJ/mol to 432.77 kJ/mol.The crystal growth index n is all higher than 3,and the crystallization mode is volume crystallization.The crystallinity of the obtained glass-ceramic samples increases from 49%to 64%,and the microstructures show that the crystals grew up in granular agglomeration.The property tests of glass-ceramic shows the density increases from 2.75 g/cm3 to 2.89 g/cm3,the Vickers hardness increases from 723.41HV to 813.23HV,and the dielectric constant gradually decreases from 15.47 to 16.65.The most suitable isothermal heat treatment system for sample Q70 is explored.Specifically,the temperature is raised to 720? at a heating rate of 10?/min,and then to the crystallization temperature of 970? at a heating rate of 5?/min.After holding for 1.5 hours,the samples are cooled to room temperature in the furnace.Further,the crystal growth behavior and products properties of the glass-ceramics prepared under different heat treatment conditions were analyzed and compared.The dielectric constant of the sample prepared by isothermal heat treatment at 10MHz is 18.79,which is inferior to the sample prepared by step heat treatment(16.65).In conclusion,both heat treatment methods could produce glass-ceramic samples with excellent crystallization conditions,and the performance of glass-ceramics prepared under step heat treatment conditions is better.