Photoelastic Effects in Silicate Glasses

The photoelasticity of R_nO_mSiO₂(R_nO_m=Li₂O, Na₂O, K₂O, and ZnO), Li₂O-Al₂O₃-SiO₂, Na₂O-Al₂O₃-SiO₂, and Na₂O-ZnO-SiO₂ glasses was analyzed on the basis of the following equation relating the stress-optical coefficient and the strain-optical coefficient:
where C is the stress-optical coefficient, n is the refractive index, G is the shear modulus, pI2and pI1are the Pockels strain-optical coefticients, and p and q are the Neumann strain-optical coefficients. No simple relation was found between the stress-optical coefficient and the shear modulus, and the factor (p−q) was found to be an essential factor deter- mining the stress-optical coefficient of silicate glasses. It was found that (p−q) decreases markedly with increasing content of modifier oxide, and that the change of (p − q) with composition is governed by the change of the atomic effect, while the lattice effect does not change as much. It is argued that the bridging oxygen with covalent bonds increases the atomic effect and the nonbridging oxygen with ionic bonds reduces the atomic effect.     

Bismuth Phosphate Glasses

Homogeneous glasses are formed in the Bi₂O₃-P₂O₅ system up to 35 mol% (63.8 wt%) Bi₂O₃. In property vs composition plots, the thermal expansion coefficient and tan δ exhibit minima, and hardness and activation energy for conduction show maxima at about 20 mol% Bi₂O₃. The deformation temperature of the glasses also increases abruptly at this composition. This anomalous behavior is interpreted in terms of a change in the function of Bi³⁺ ions from network formers to network modifiers.     

Compositional Trends in Photoelastic Constants of Borate Glasses

The stress-optical coefficients of binary and ternary borate glasses were measured and the factor ( p·q ), where p and q are the Neumann strain-optical coefficients, was determined. As a modifier oxide was added to B₂O₃ glass, the stress-optical coefficient decreased monotonically. It was found that the stress-optical coefficient is determined mainly by the elastic modulus, but the factor ( p·q ) becomes significant when the content and polarizability of the modifier cation are high. It was also found that the factor ( p·q ) decreases when the content and polarizability of the modifier cation increase. The ( p·q ) was divided into the lattice effect and the atomic effect, and their compositional dependences were discussed.     

Constitution of Mixed-Alkali Phosphate Glasses: Constitution of Lithium-Rubidium Phosphate Glasses

In a previous study of the constitution of lithium-sodium-potassium phosphate glasses slight but definite cationic effects were observed. The constitution of lithium-rubidium phosphate glasses with , the number average chain length, varying from 1.25 to 9.00 was determined by paper chromatographic methods to follow the effect of substituting the rather large rubidium ion (1.47 A) for the small lithium ion (0.68 A). Systematic changes were observed; these changes, however, were numerically small. With the increase in the rubidium substitution for lithium the pyrophosphate content of the glass decreased and the tripolyphosphate content increased. Glasses with values as low as 1.5 (Li/Rb = 1/1) could be made by quenching the platinum crucible containing the melt in water. The = 1.25 glass, however, devitrified when thus made. It could be prepared only by the new copper-block-cooled strip furnace technique.     

Thermochromism in Reduced Phosphate Glasses

Coloring and bleaching of reduced phosphate glasses in the systems K₂O-B₂O_r Al₂O₃-P₂O₅ and K₂O-Al₂O₃-P₂O₅, containing no silver halide, were studied. The as-cast glasses, which are colorless and transparent, become tinged with red when they are reheated at high temperatures for long times. The bleached specimens (PTC-RP glass) are obtained by heating at >600°C, then quenching. The PTC-RP glasses exhibit coloring phenomena by irradiation of light or by heating above 200°C; the colored glasses are again bleached thermally. Coloring of the glasses by heating is described in this paper in terms of phase change within the colloidal phosphorus formed in the glasses. The apparent activation energy for the thermocoloring is estimated to be ∼15×10⁴ J/mol (35 kcal/mol).     

Ionic Conduction in Phosphate Glasses

Ionic conductivity in phosphate glasses has been known for almost 30 years. Recently these glasses have been shown to exhibit some of the highest ionic conductivities ever reported. In many cases, because of their ease of preparation, low melting points, strong glass-forming character, and simple composition, phosphate glasses have been studied more than any other ionically conducting glasses. However, no single review has ever been made of these glasses with the purpose of correlating the apparent widely disparate values of conductivity that these glasses exhibit. In this review, the conductivities of phosphate glasses are examined considering new structural studies of them. A systematic comparison of the dependence of the conductivity on glass chemistry reveals that, similar to other glass families (silicates and borates for example), the conductivity maximizes when the cation environments in the glass are minimized in their charge density and maximized in their site proximity.     

磷酸盐玻璃中稀土离子的发光浓度效应研究

磷酸盐玻璃中稀土离子的发光浓度效应研究王民权，马立新，樊先平（浙江大学材料科学与工程系３１００２７）（南京航空航天大学）ＳｔｕｄｙｏｎＣｏｎｃｅｎｔｒａｔｉｏｎＥｆｆｅｃｔｓｏｆＲａｒｅＥａｒｔｈＩｏｎｓｉｎＰｈｏｓｐｈａｔｅＧｌａｓｓｅｓ￥Ｗａｎｇ...     

Constitution of Mixed-Alkali Phosphate Glasses: IV, Constitution of Lithium-Cesium Phosphate Glasses

The constitution of lithium-cesium phosphate glasses was determined by paper chromatographic techiques. Because of the rather high hygroscopicity, glasses with M/P ratio >1.33 could not be prepared. With increase in cesium/lithium ratio, the tripoly and tetrapoly fractions increased, indicating a definite cationic effect. The significance of the results is discussed.     

Free Volume of Phosphate Glasses

Free volume (V_f), defined by Simha and Boyer, was measured for glasses in the system MO-P₂O₅ (M=Be, Mg, Ca, Ba, Zn) and (1-x)MO·P₂O₅-xAl₂O₃·3P₂O₅ (M = Mg, Ca, Ba). Experimental V_f of the glasses was ∼0 to 0.3. These results indicate that V_f is not a universal constant (∼0.1) for all glasses as previously reported, but that V_f depends on the glass backbone structure.     

Constitution of Soluble Phosphate Glasses

Filter-paper chromatographic methods have been developed which permit the separation and de- termination of condensed phosphate anions containing up to four phosphorus atoms per ring and of linear structures containing from one to nine phosphorus atoms per chain. These methods have been used to study the anions produced when soluble sodium phosphate glasses of a range of compositions and methods of preparation are dissolved in water. The analyses are in qualitative agreement with the structure of phosphate glasses proposed by Van Wazer. X-ray and other evidence is presented which indicates, for the range of compositions studied, that the structures of condensed phosphate anions found in solution correspond to similar structures of condensed phosphates in the glass before dissolution and do not arise during the solution process. The study thus supports the polymer approach to the constitution of glasses for the range of com- position studied.     

Role of Iron in Calcium Phosphate Glasses

Some physical properties okf phosphate glasses con-taining up to about 26 mol% Fe₂O₂ were studied. Pronounced changes in properties were observed at compositions containingabout 6, 10, and 13 mol% Fe₂O₃. The X-ray diffraction spectra of devitrified (heat-treated) samples showed new compounds near these compositions. Electron spin resonance and optical studies confirmed the presence of Fe³⁺ and Fe²⁺ in both 4- and 6-coordination. An increase in total iron in these samples was associated with a decrease in the ratios Fe²⁺ 4-coordinated/Fe³⁺ 6-coordinated 6-coordinated and Fe³⁺ 4-coordinated/Fe³⁺ 6-coordinated up to about 2.0 mol% Fe₂O₃, as shown by the intensity of the optical absorption bands at about 2.0 and 1.0 μm and by the intensity of the ESR lines at g⋍4.2 and 2.0, respectively. Samples containing up to 4.3 mol% Fe₂O₃ showed an increase in Fe³⁺ concentration and a decrease in Fe²⁺ concentration after gamma irradiation. The electrical conductivity and activation energy decreased sharply with increasing Fe₂O₃ content.     

Constitution of Mixed-Alkali Phosphate Glasses: II, Constitution of Variable Lithium Constant Sodium-Potassium Phosphate Glasses

In order to study the cationic influence of lithium, if any, the constitution of variable lithium constant sodium-potassium phosphate glasses was determined using paper chromatographic methods. It was possible to prepare glasses with very low ñ, the number average chain length value. Glasses with ñ values of 2, 1.75, and 1.5 could be prepared for glasses with Li:Na:K atomic ratios of 1:1:1 and 2:1:1. Attempts to prepare a glass with ñ= 1.25 were unsuccessful. At higher lithium concentrations, it was not possible to prepare glasses with low ñ values. The constitution of lithium phosphate glasses was reinvestigated. A comparison of the constitutions of mixed-cation phosphate glasses and lithium glasses indicates a small but definite cationic effect. The significance of these results in relation to Van Wazer's polymer theory and distribution laws is discussed.     

Constitution of Mixed-Alkali Phosphate Glasses: I, Constitution of Constant Lithium Variable Sodium-Potassium Phosphate Glasses

By the use of a mixture of alkali cations, Li, Na, and K, it has been possible to prepare phosphate glasses with higher M₂O/P₂O₅, ratio than was possible by the use of a single alkali cation. Variation of the Na:K ratio over a wide range has no effect on the distribution of polyphosphates in the composition range studied (Li: Na: K = 1:5:1 to 1:1:5). Glasses with × values of 2 or less contain an appreciable amount of orthophosphate ion. The significance of these results is discussed.     

Raman Spectra of Rare-Earth Phosphate Glasses

Raman spectra have been recorded for glasses in the binary systems CeO₂-P₂O₅ and Pr₂O₃-P₂O₅. The cerium phosphate glasses were prepared having different concentrations of CeO₂ and the praseodymium phosphate glasses with different ratios of Pr³⁺ to Pr⁴⁺. The spectra indicate that both cerium and praseodymium enter the glass in modifying sites. We see no changes in the Raman spectra with Pr³⁺/Pr⁴⁺ ratio. Measurements of the density and glass transition temperature are also reported.     

Electret Properties of Radiation-Charged Phosphate Glasses

The process of formation of a surface charge in phosphate glasses depending on polarization conditions is investigated. A relationship is established between the chemical composition of glass and its capacity for forming internal electric fields under radiation for glasses of type 0.50P₂O₅ – 0.45RO – 0.05R₂O₃.     

Correlation of Structure and Photoelastic Response in Tin Phosphate Glass

Recently an empirical model was established to predict the photoelastic response of a glass based on its composition and the crystalline structure of its constituents. In the present work the model was tested in detail by comparing the local structure assessed by a combination of nuclear magnetic resonance and Mössbauer spectroscopy with the model predictions and the measured photoelastic response. The system investigated was (SnO)_x(P₂O₅)_1−x. It was found that while the original simple model based on data on the pure components predicted the composition of the zero stress-optic glass to within about 15 mol%, inclusion of data on mixed systems, more reflective of the true glass structure, gave substantial improvement of the prediction. This finding further confirms the relation of local bonding structure to the photoelastic response of glass.     

Conversion of Tetranary Borate Glasses to Phosphate Compounds in Aqueous Phosphate Solution

In our earlier work, it was found that particles of a ternary alkali-borate glass, containing either CaO or BaO, converted completely to a crystalline phosphate of calcium or barium when reacted in an aqueous phosphate solution at 37°C. The present work is an extension of our earlier work to investigate the conversion of tetranary borate glass with the composition 10Li₂O·10CaO·10(AeO or T₂O₃)·60B₂O₃ (weight percent), where Ae is the alkai-earth metal Mg or Ba, and T is the transition metal La, Sm, or Dy. In the experiments, particles of each glass (150–300 μm) were reacted in 0.25 M K₂HPO₄ solution with a starting pH of ∼9.0 at 37°C. Weight loss and pH measurements indicated that the reaction was complete after 30–50 h, yielding an amorphous product. X-ray fluorescence showed that the as-formed product consisted of a calcium phosphate phase that contained the alkali-earth metal or transition metal present in the starting glass. Heating the as-formed material for 8 h at 600°–700°C produced a mixture of two crystalline phosphates: calcium phosphate and an alkali-earth or transition metal phosphate. The kinetics and mechanism of converting tetranary borate glass to phosphate materials are discussed and compared with data from earlier work for the conversion of ternary borate glass.     

XAFS Investigation of Platinum Impurities in Phosphate Glasses

The coordination environments of Pt impurities in a ternary K-aluminophosphate (KAP) glass and commercial K,Mg-aluminophosphate (KMAP) laser glasses have been investigated by Pt L _III-edge X-ray absorption fine structure (XAFS) spectroscopy. Pt valence in the KAP glass depends on the melt preparation atmosphere. Pt⁴⁺ ions form in melts that are bubbled with oxygen, whereas metallic Pt particles form when these same samples are remelted in air. Residual chlorine in KMAP glasses has an effect on Pt bonding. In chlorine-free samples, Pt⁴⁺ ions are coordinated with ∼5.4 (8) oxygen atoms with an average distance of 2.02 (1) Å. For glasses with low chlorine contents (<200 ppm Cl), the Pt⁴⁺ ions have both O and Cl atoms in the first coordination shell. As the Cl concentration increases, the number of O nearest neighbors decreases and for Cl:Pt > 5, only Cl nearest neighbors are observed. Pt⁴⁺ ions in these latter glasses are coordinated by ∼5.5 (8) Cl atoms at an average distance of 2.27 (2) Å.     

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.     

部分稀土掺杂磷酸盐玻璃发光性质分析

磷酸盐玻璃中单掺杂镱（Yb）、铒（Er）、钕（Nd）等稀土元素,对其光谱特性,荧光寿命,低温特性等将产生重要影响。也会改善杂质对磷酸盐玻离性能的影响。