The Study About Highly Crystalline Soda-Lime-Silica Glass-Ceramics

Glass-ceramics is based on controlling the nucleation and crystal growth of certain glass.Compared with ceramics traditionally obtained by powder sintering,glass-ceramics have the advantages of low or zero porosity,microstructure uniformity and reproducibility.In general,the increase of crystalline phase in some glass matrix will change its properties.For example,it will cause low coefficient of thermal expansion,high chemical and thermal stability,high mechanical strength,etc.In this paper,we mainly research the common sodium-calcium-silicon system glass,using basic glass heat treatment method to prepare glass-ceramics,and explore the influence of composition,temperature and time on glass crystallization by changing the basic glass composition,heat treatment temperature and heat treatment time.The main findings are as follows:?1?The basic Na₂O-Ca O-Si O₂-Al₂O₃ system glass with different Al₂O₃ content was prepared by the melting method,the basic glass was heat-treated in two steps.And then the rheological and crystallization behavior of 20Na₂O-29Ca O-51Si O₂?wt/%?glasses with high crystallinity were investigated using DSC,XRD,FTIR and viscosity test methods after introducing Al₂O₃.Specially,the influence of Al₂O₃ content on the nucleation sites and crystal species were studied in glass compositions.The results show that with the introduction Al₂O₃,the viscosity???values,glass transition temperature?T_g?and crystallization temperature?T_c?of glass gradually increase.At the same time,the activation energy for viscous flow?_????increases significantly,which means the mobility of crystal forming ions decreases,in other words,the ion mobility required for crystal growth is reduced.For crystallization behavior,the introduction of Al₂O₃ leads to a transformation from bulk crystallization to surface crystallization.IR spectroscopy shows that Al³⁺ions mainly exist as[Al O₄]^-tetrahedrons in this system glass,and other low field strength cations(such as Na⁺and Ca²⁺)charge compensate it,which leads to a decrease in non-bridged oxygen concentration in the glass.In other words,the glass network is strengthened due to addition of Al₂O₃ in this glass system,and the bulk diffusion of ions is suppressed,thus causing surface crystallization?2?The 50.2 Si O₂-19.2Na₂O-30.6Ca O?mol%?based glass containing trace Ni O?0.1wt%?was prepared by melting method,and the base glass was heat-treated in one step.Using DSC,XRD,SEM and FTIR test methods and the classic nucleation and crystal growth theory to study the effect of 0.1 wt%Ni O addition on the rystallization behaviort isochemical soda-lime-silicate glass system around glass transition temperature.The results show that after the introduction of Ni O,the mobility of structural unit forming crystals increases,resulting in the acceleration of the crystal growth rate in the early stage of crystallization.In the later period of crystallization,Ni element mainly exists in the residual glass phase,which causes density mismatch effect with the remaining glass phase around it,thereby generating stress energy??,which causes the crystal growth to stop.In addition,after the introduction of Ni O,the time-lag for nucleation is prolonged and the steady-state nucleation rate is reduced,resulting in a wider crystal size distribution.IR spectrum shows that the basic glass samples with undoped and doped Ni O have similar spectral characteristics.In other words,the influence of trace Ni O on the structure of sodium-calcium-silicon glass is small,which is not enough to affect its crystallization behavior.?3?Based on the composition of 20Na₂O-29Ca O-51Si O₂?wt/%?glass,water quenched-glass?HQ glass?and bulk glass?bulk glass?were prepared respectively by melting method,and then these two kinds of base glass were treated with low temperature heat treatment?0.85T_g?T_g?.The influence of sub-T_g enthalpy relax on glass transition and crystallization behavior above the glass transition temperature was studied by DSC.The results show that when HQ glass samples are heat-treated at 0.85T_g,the pre-endothermic peak appears after about 10 hours.And with the extension of time,the pre-endothermic peak moves to the glass transition peak,and the enthalpy also gradually decreased,resulting in slow-?and?relaxation.When the HQ glass sample was heat-treated at0.96T_g,the pre-endothermic peak overlapped with the glass transition peak,resulting in an increase in peak strength.And with the extension of time,the glass transition peak moved slightly to a higher temperature,which means that the slow-?and?relaxation were not only completed quickly,but also excessively relaxed.In other words,the higher the heat treatment temperature of the glass,the faster the relaxation and the shorter the time required.Secondly,the sub-T_g enthalpy relaxation of glass will be accompanied by the formation of ordered domains,which will lead to the decrease of the overall thermal stability.During the second heating,the crystallization will become easier,that is,the sub-T_g enthalpy relaxation will affect the glass transition temperature and promotes crystallization above the glass transition temperature.In addition,the faster the cooling rate during the glass forming process,the shorter the relaxation time.