Mechanical Relaxations in Mixed Alkali Silicate Glasses: II,Discussion*

The internal friction of mixed Li-Na, Li-K, Li-Rb, Li-Cs, Na-K, Na-Rb, Na-Cs, and K-Rb silicate glasses is interpreted on the basis of the various explanations proposed for the mixed alkali effect. A direct correlation was found between the mechanical loss peak due to the stress-induced movement of the alkali ions, i.e. the alkali peak, and the electrical loss properties. The large mechanical loss peak appearing when the alkalis are mixed was attributed to an interaction between dissimilar alkali ions such that an elastic dipole is formed. The absence of a comparable electrical loss peak was interpreted as indicating that the elastic dipole is electrically inactive. In glasses containing equimolar quantities of two alkalis, the activation energy and height of the new loss peak, i.e. the mixed peak, were more closely related to the size difference than to the mass difference of the alkali ions.     

Structure Transition in Alkali Silicate Glasses

The logarithm of measured high-temperature fluidities is related to the square of the calculated probability of finding a nonbridging oxygen in a randomly chosen SO4 group. This is interpreted in terms of a flow mechanism (gliding) dependent on juxtaposition of two such oxygens. A theory of the glass transformation is developed. On cooling, the coordination number of nonbridging oxygens increases until, ideally, at T , each touches three oxygens of an external Si04 group (stabilization). Below this temperature, thermal expansion/contraction contains no coordination change component. These changes constitute a second-order transition. Observed volume data are in agreement with hypothesis. On this view, stabilization creates vacant tetrahedral environments adjacent to existing ones. Migration of glass-forming ions to these empty sites can unlock the structure and permit the operation of a new set of flow processes. The coordination requirements for stabilization severely restrict the types of local arrangement possible at high silica contents, and therefore reduce the configurational entropy and induce unmixing. The overall transformation is composite in character. Rather extensive bond rearrangement and unmixing (when present) are features of first-order kind.     

Manganous-Manganic Equilibrium in Alkali Borate Glasses

The manganous-manganic equilibrium was studied in potassium, sodium, and lithium borate glasses. The glasses were analyzed chemically for total and trivalent manganese. The manganese equilibrium shifts more toward the oxidized state when the alkali concentration in the glass is increased and/or when the molar equivalent of lithia is replaced by soda and soda is replaced by potash. A linear relation between log (Mn³⁺/Mn²⁺) and mole percent alkali oxide was observed. Straight lines were obtained for lithium, sodium, and potassium borates. The disadvantages of using a concentration equilibrium constant where the glass composition is varied are discussed.     

Effect of Cerium on the Ion-Exchange Parameters in Alkali Silicate Glasses

Alkali gallosilicate glasses containing 1–8 mol % CeO₂ after ion-exchange treatment in a NaNO₃ melt at different temperatures are studied. The refractive index distributions in glasses with different cerium oxide contents are obtained, and the profiles of the Na₂O concentration distribution in the samples containing 2 mol % CeO₂ after ion-exchange treatment at temperatures T = 500–550°C are determined. It is revealed that, as the cerium oxide content increases, the interdiffusion coefficient decreases, whereas the refractive index increment increases. The results obtained are analyzed within the framework of the model of dopant segregation, according to which cerium undergoes selective incorporation and concentration displacement into polar microregions of the glass.     

氟锆酸盐玻璃的混碱效应

４８Ｚｒｆ４－２４ＢａＦ２－８ＡｌＦ３－２０ＲＦ（ＲＦ＝ＬｉＦ－ＮａＦ和ＮａＦ－ＫＦ）玻璃中引入不同比例的碱金属离子。利用ＤＴＡ研究玻璃的成玻性,并测定玻璃的化学稳定性和折射率。讨论了各理化性能的混碱效应。结果表明,混碱氟锆酸盐玻璃的成玻性和化学稳定性均优于单碱玻璃。当ＲＦ为ＬｉＦ－ＮａＦ且ＬｉＦ：ＮａＦ为１：３时有最佳的成玻能力,ＬｉＦ：ＮａＦ为１：１时玻璃有最好的化学稳定性。     

Mixed Intermediate Effect in Calcium Alumino/Galliosilicate Glasses

Glasses in the calcium alumino/galliosilicate system were prepared. All glasses contained 30 mol% CaO. The density, refractive index, and infrared spectra were measured. These glasses exhibited additive behavior in all properties, which implies that Al and Ga play isostructural roles in the glass network. These results agree with those reported previously for lithium alumino/galliosilicate glasses.     

Property Variation in Alkali Alkaline-Earth Metaphosphate Glasses

Coefficients of helium migration, coefficients of thermal expansion, and glass-transition temperatures were measured for several series of alkali alkaline-earth phosphate glasses. The helium permeability decreases with the field strength of alkali or alkaline-earth ions in the order Na⁺ > Li⁺ and Mg²⁺ > Ca²⁺ > Ba2+. The glass-transition temperature increases and coefficient of thermal expansion decreases with increasing field strength of alkali or alkaline-earth ions. The relationship of lower molar volume, corresponding to decreased coefficients of helium diffusivity reported for other glass-forming systems, occurs in the phosphate glasses.     

Impurity Alkali Diffusion in Sodium-Cesium Silicate Glasses

The tracer diffusion coefficient of ⁸⁶Rh was measured as a function of Cs/Na ratio in (Na, CS)₂O:3SiO₂ glasses. A comparison of the compositional dependence of this impurity alkali diffusion with the self-diffusion coefficients of ²²Na and ¹³⁷Cs suggests that the alkali-ion pair concept in the weak-electrolyte model is not sufficient to explain the mixed-alkali effect.     

States of Sulfur in Alkali Borate Glasses

Simple binary alkali borate glasses of differing alkali content (alkali = Li, Na, or K) containing sulfur were prepared and their absorption spectra were measured in the range of 200 to 700 nm. The absorption bands obtained were used to determine the stable states of sulfur in these glasses by directly comparing them with published data. The following states of sulfur were identified and their ranges of stability were determined: the S₂ molecule in glasses containing at least 15 mol% alkali oxide, the S₃⁻ and S₂⁻ in glasses containing 20 to 30 mol% Na₂O or K₂O, and the polysulfide ion (S x ²⁻) in glasses of 30 to 35 mol% Na₂O or K₂O.     

Durability and Properties in Alkali Aluminofluorophosphate Glasses

Glass-forming and properties of glasses in the systems AI-Li-Na-K-P-O-F are presented. Useful durability, which is defined as a weight less in deionized water at 95°C of <1 mg/cm².h, limits the range of properties available. These boundaries are represented by T_gs of 305°±25°C, density of 2.63±0.02 g/cm³, and refractive indices of 1.46±0.01.     

Thermal Expansion of Alkali Borate Glasses

The thermal expansion behavior of lithium, sodium, potassium, and rubidium borate glasses was measured. The results indicate that the "borate anomaly" in the thermal expansion coefficient occurs at ∼20 mol% alkali oxide. A maximum in the glass transformation and dilatometric softening temperatures also occurs at ∼27 mol% alkali oxide. No evidence for phase separation was observed in this study. These effects are related to the structural changes reported for these glasses by Bray and coworkers.     

Elastic Properties of Alkali Phosphomolybdate Glasses

Ultrasonic velocities at 10 MHz have been measured in two series of lithium, sodium, and potassium phosphomolybdate glasses with two fixed P₂O₅ concentrations. Elastic moduli, Poisson's ratio, and Debye temperature have been calculated. The composition dependence of most of the properties of lithium glasses exhibits a trend opposite to that of potassium glasses. Properties of sodium glasses lie between the other two alkali systems. Alkali oxide modification is suggested to be accompanied by ring reformation in lithium and sodium glasses. Ring size effects have been shown to account for all of the composition dependence.     

Spontaneous Bubble Formation in Silicate Melts at High Temperatures: II, Effect of Wet Atmospheres and Behavior of Mixed Alkali Glasses

Earlier work with alkali silicates was extended. Time and temperature for originally melting the glass had little influence on bubble or foam formation. Water vapor in the furnace atmosphere lowered foaming temperature considerably. Mixed alkali glasses showed complex and unexpected behavior. Nucleation and growth of foam bubbles as well as foam stability are discussed.     

Ionic Conduction in Alkali and Thallium Silicate Glasses

Electrical conductivities of binary alkali and thallous silicate glasses have been measured as a function of composition, temperature, and frequency. The best approximation to the activation energy for dc conduction can probably be obtained by extrapolating its frequency dependence to zero frequency, although values obtained at frequencies below 2500 hz do not differ greatly from the dc values. The plot of activation energy for conduction against modifier content consists of two straight lines of different slope. For all the alkali silicate glasses the break in slope occurs near 25 mole % alkali oxide and at an activation energy near 14.7 kcal/mole. The slope of the line below 25 mole % alkali oxide is proportional to the alkali ion radius. The behavior of thallous silicate glass is similar but not identical to that of the alkali silicates. It is concluded that (1) the reported conduction behavior does not result primarily from phase separation, (2) the principal contribution to the activation energy is probably the work required for a mobile ion to pass through the glass network rather than to leave its initial position, and (3) a structural change independent of the nature of the modifier cation occurs near a modifier content of 25 mole %.     

Equilibrium Studies of Fe in Alkali Phosphate Glasses

The Fe²⁺-Fe³⁺ equilibrium in binary Na₂O-P₂O₅, glasses was studied by equilibrating glass melts at different temperatures in air. The enthalpy change (δH) of the reaction 1/2Fe₂O₃⇌FeO+1/4O₂ was calculated for 4 glasses. The results indicate that (1) the equilibrium shifts toward the oxidized state as the Na₂O content of the glass increases (plots of log ([Fe²⁺]/[Fe³⁺]) vs mol% alkali were linear) and (2) Δ H values for glasses of different composition are nearly equal but differ from the standard (calculated) value for the reaction. The experimental ΔH values were nearly equal to that for the reaction FePO₄→1/3 Fe₃(PO₄)²+ 1/6P₂O₅+1/4O₂, indicating that Fe forms phosphate or polyphosphate configurations in the Na₂O-P₂O₅ glasses. In certain of the glasses studied a faint-pink solid precipitated; its X-ray diffraction pattern indicated that its principal component is crystalline Na₂Fe¹¹¹P₃O₁₀.     

Heat of Annealing in Simple Alkali Silicate Glasses

The enthalpy changes associated with annealing of glass were studied in simple and mixed alkali silicate glasses. The data indicate that during prolonged annealing the glass comes to a metastable equilibrium state and has a unique heat of solution which depends on its fictive temperature. The heats of solution of these glasses show a linear dependence on fictive temperature, and the magnitude of this dependence is related to the molar volume of the glass. The significance of these heat effects is discussed. The maximum heat effects which can occur on annealing sodium silicate glasses were measured and were approximately half as large as the enthalpy changes associated with the structural arrangements that occur during crystallization of these glasses.