| Summary: | 碩士 === 國立臺北科技大學 === 材料及資源工程系碩士班 === 92 === The effects of cation size and anionic structural unit on the structure and elasticity of silicate glasses have been studied by using both Raman and Brillouin scattering techniques at ambient conditions. A consideration of cation size, Z/r2 field, equilibrium, and geometry of anions has revealed that the difference in Raman intensity among a series of alkali and alkali-alkaline earth silicate glasses should be determined largely by the change of coordination number; that is, a larger cation will cause more Q3 species and thus smaller Q2/Q3 ratio in the glasses. With the addition of Na2O, the fraction of Q4 displayed a monotonically decrease, while the inverse was found for both Q0 and Q2. On the other hand, a maximum abundance was observed in both Q3 and Q1 at NBO/T of 1.5 and 2.5. An interpretation based on the equilibrium between Q species has been given for the observed phenomena. Except for abnormally low moduli for the Mg-bearing glasses, it has been found that the elastic moduli (bulk, shear and Young’s) of Na2O.MO.4SiO2 glasses (M = Ca, Sr, Ba) decrease with increasing in cation size. This result can be attributed to the competition between increase of density and lowering in the Z/r2 field of alkaline earth cations. For xNa2O.MgO.4SiO2 (x = 1~5) glasses, shear and Young’s moduli decreased with increase of Na2O content (i.e., increasing in NBO/T). However, bulk modulus for this series of glasses showed an opposite Na2O dependence, though a maximum appeared at NBO/T of 2.5. The difference between Na2O dependences of bulk and shear moduli has been ascribed to the change in the amounts of more polymerized Q species — more Q3 and Q4 in a glass will result in higher shear modulus but lower bulk modulus. Finally, it was found that the glass quenched at lower temperature shows a slightly higher elastic moduli than that quenched at higher temperature, and the glass without annealing showed a slightly lower elastic moduli than that of annealed one. The former is attributed to different extent of deviation from equilibrium (900 vs. 1200 oC); the latter is caused by slightly structural regulation during annealing.
|
|---|
