Study And Prediction Of Physical Properties Of Glass Via The Phase Diagram Approach

The glasses have been widely used in many fields including daily life,building,energy and military filed due to their various types and multiple functional properties.After a development of around one century,the glass science is still a discipline depending much on the experiment.Exploring new type glass with unique properties needs a long term investigation together with a large amount of manpower and material resources.Therefore,it is of great importance to establish a simple and accurate structural model which can be used to predict the physical properties of glass and explanation of the glass structure.This dissertation includes five chapters.The first chapter presents an introduction to the theory of glass structure and recent advances in glass field.The association between the glass structure and physical properties of glass including density refractive index,thermal expansion coefficient,elastic modulus and shear modulus were reviewed as well as the influence factors on these poperties.The second chapter presents a detailed description of the phase diagram structure model of glass and summary of the experimental test methods which were used in this dissertation such as Raman spectrum,Fourier infrared spectrum,and X-ray diffraction.In the third chapter,the physical properties of oxide glass were calculated by using the phase diagram model,including density,refractive index,thermal expansion coefficient,elastic modulus and shear modulus.The physical properties on the glass composition in silicate and tellurite glass systems were studied,showing a linear change for these glasses with the addition of metal oxides.However,the physical properties of borate and germanate glasses show a different tendency in this process,namely,an initial increase with afterward decrease or vice versa for the physical properties.The error in the use of phase diagram structure model of glass showed that the borate glass has a larger error in comparison with other oxide glass systems,and the density and refractive have higher calculation accuracy than thermal expansion coefficient,elastic modulus and shear modulus.Moreover,the calculated result based on phase diagram model had larger error when the glass contained ion with high polarizability such as Pb²+.The mechanism of structure about borate anomaly and germanate anomaly was investigated by phase diagram model.The predicted values of borate and germanate glass are in good agreement with experimental data which suggests the existance of a compound for the composition at “anomaly point”.The fourth chapter gives the calculation results of the physical properties of non-oxide glass using the phase diagram model,showing different change rule of physical properties with tuning composition for chalcogenide glass system.For the As-Se and As-S glass systems,the density increases firstly with the addition of As and then decreases when the content of As is more than 40%,while the thermal expansion coefficient shows an opposite change tendency.For the GeS2-Ga₂S₃ glass system,the physical properties shows a linear change on glass composition.The results indicated that the phase diagram model can also be used to chalcogenide glass despite of a relatively higher error than the oxide glass,which may be resulted from the critical preparation process of chalcogenide glass.These results indicated that phase diagram approach play a critical role in guiding the theoretical research and practical application.In the fifth chapter,the structural mechanism of germanate anomaly was studied deeply.The structure and coordination of sodium and potassium germanate glasses were analyzed by the phase diagram model.In the Na₂O-GeO₂ glass,when the Na₂O is less than 18 mol% in content,the [GeO₄] and [GeO₆] coexist in the glass and the four-membered ring transform into three membered ring occurs with the continuous addition of Na₂ O,forming a corner with two [GeO₆] and one [GeO₄] unites.However,for the K₂O-GeO₂ glass,there are only [GeO₄] and [GeO₅] exist in the glass when the K₂O is less than 11 mol%.When the content of K₂ O is between 11 and 18 mol%,three Ge-structural units?[GeO₄],[GeO₅] and [GeO₆]?coexist in the glass structure.Meanwhile,some of the four-membered rings would also convert into the six-membered rings which were formed by four [GeO₄] and two [GeO₆] unites.When the K₂O is more than 20 mol%,there were only [GeO₄] and [GeO₆] in the glass.The K₂O_·8GeO₂ compound should be assigned to an congruent compound in the K₂O-GeO₂ phase diagram in accordance with the phase diagram model.