Structure Origin Of Evolution Of Performance For Alkaline-earth Element Containing Silicate Glasses

Silicate glass is one of the most important basic materials,due to the complex glass composition,there is considerable disagreement between certain studies on the effects of network modifiers,especially on the structural role of Mg²⁺due to the lack of unambiguous information on its local environment.In this study,SiO₂-Al₂O₃-Bi₂O₃-Fe₂O₃-Na₂O-K₂O-MeO（Me=Mg,Ca,Sr and Ba）series glasses were prepared by means of conventional melt quenching method.The density,modulus,microhardness and glass transition temperature were determined by different instruments,and the structural changes of the glasses were investigated by nuclear magnetic resonance,Raman spectroscopy,infrared spectrum and positron annihilation lifetime spectra.The structural origin of evolution of performances for alkaline-earth element containing silicate glasses was discussed.On the other hand,using viscosity and DSC method,the properties of glass melt were studied by different theoretical equation.The results showed that:Density of the glasses increases with the increase of alkaline-earth ionic radius.From GCa to GBa,elastic modulus,microhardness and glass transition temperature decreased with the increase of alkaline earth ion radius,the Mg-containing glass shows an obvious deviation.Results of NMR,IR spectra and Raman spectra showed that the non bridge oxygen of GMg decreased compared with GCa,this indicates that MgO is behaving as an intermediate oxide.Furthermore,the result of PALS showed that,from GBa to GCa,the free volume decreases with the decreasing of alkaline earth ion radius,however,the free volume of Mg-containing glass is higher than Ca-containing glass,which verifies the degree of polymerization for GMg is better than GCa.The viscosity of glass melts decreasing as the temperature rises.GMg and GCa glass melts show different responses of viscosity in high and low temperature regions.As the temperature rises,this is because the coordination number of Mg²⁺reduces as temperature decreases.VFT equation,AG equations,AM formula and MYEGA equation were used to fit the relationship between the viscosity and temperature.The configurational entropy（S_c）and liquid fragility（m）were calculated by different methods.From GBa to GCa,as the field strength of alkaline earth ions increases,the attraction to surrounding[SiO₄]was enhanced,and hence,leads a high degree of short-range order,which prevents the structure from a rapid breakdown with increasing temperature.Consequently,the configurational entropy and liquid fragility decreases from GBa to GCa.However,Mg²⁺is entering the silicate network,the lower bond strength of Mg-O compared to Si-O weakens the glass network,Mg-O bonding could be easily broken when temperature increases.As a result,the Mg-containing glass has a higher fragility and configurational entropy than the Ca-containing glass.From the conclusion mentioned above,We got the molecular origin of these variation of macroscopic features as the alkaline earth elements changed,which provides reference for guiding the production of silicate glass.