Leachability of Molybdenum from Ternary Phosphate Glasses

With a view to use glasses as a source of molybdenum, which is one of the micronutrients required by plants, a systematic study of the leachability of molybdenum from ternary phosphate glasses having molar compositions of 25MoO₃-25X50P₂O_s (where X = Li₂O, Na₂O, K₂O, CaO, B₂O₃, or SiO₂) was carried out. Leaching of molybdenum ions has been studied as a function of pH, which shows that leaching increases with increasing pH of the solutions. The concentration of molybdenum ions in the leachate decreases with increasing bond strength between nonbridging oxygen ions and the cations in glasses. Leaching increases with an increase in leaching time and decreases with an increase in the particle sizes of the glasses. P₂O₅ was also leached along with MoO₃. The leaching characteristics of P₂O₅ from the glasses are also reported.     

Thermal Expansion and Chemical Durability of Phosphate Glasses

The thermal expansion coefficient and aqueous dissolution rate were measured for alkali phosphate glasses containing a third and fourth component. For a given series, both properties increased monotonically as the radii of the alkali ions increased. The observed expansion coefficients were in the range 99 to 286 × 10⁻⁷°C⁻¹. A small mixed-alkali effect was observed for both properties.     

Temperature-Induced Structural Modifications Between Alkali Borate Glasses and Melts

High-temperature neutron diffraction and Raman spectra have been obtained on M₂O–2B₂O₃ (M=Li, Na, K) glasses and melts. Both techniques indicate a coordination change of boron atoms: the tetrahedral boron sites present in the glasses are converted into triangular boron sites. These changes of the borate network yield modifications of the alkali environment, as assessed for Li using the isotopic substitution technique. We observe that Li atoms are in a charge-compensating position in the glass and in a modifying position in the liquid. These structural modifications have important implications toward understanding the physical properties of borate melts.     

Optical, Structural, and Chemical Characteristics of Lead-Indium Phosphate and Lead-Scandium Phosphate Glasses

Two new glass systems based on a range of lead-indium phosphate and lead-scandium phosphate compositions have been developed and characterized. These glasses have a relatively high index of refraction ( n = 1.75 to 1.83) in the visible region and exhibit moderate dispersion (Abbe number ∼30). The ultraviolet absorption edge occurs near 300 nm and the glasses strongly absorb in the infrared at wavelengths greater than 2800 nm. Both glass types can be prepared at relatively low temperatures (900° to 1000°C) and are easily poured down to ∼800°C because of their low melt viscosities. The glasses exhibit good chemical durability and resistance to both weathering and intense γ-radiation. These materials have a glass transition temperature of about 430°C, a softening point of about 460°C, and thermal expansion coefficients in the range of 10.8 × 10⁻⁶ to 12.0 × 10⁻⁶/°C. The structure of these phosphate glasses is shown to consist of a distribution of chains of PO₄ tetrahedra held together by bonding between the non-bridging oxygens of the tetrahedra and the metal cations. The polyphosphate chain length distribution was determined by a liquid chromatographic technique. Potential aqueous corrosion mechanisms are discussed and some general guidelines for forming a chemically durable phosphate glass are given.     

Structural and Thermal Expansions in Alkali Silicate Binary Glasses

Two volume-changing processes that should be considered in detail are (1) distention of networks by added oxides which may swell glass volumes in proportion to the added oxide volumes and (2) angular change in intertetrahedral bonding which may take place at and above annealing temperatures in proportion to the number of metal ions introduced by the modifications. Accordingly, the partial molar volumes of modifiers, ν _R , are assumed as those of their crystal or liquid states and the partial molar volumes of silica are computed from (1/ν_S) = 2.20 + 0.00057 ( r_m – 0.12) (1723 – t ). Tentative glass volumes are then computed as V_g= S_mν_S+ r_mν_R by use of the mole fractions S_m and r_m for silica and nonsilica, respectively. The excess of computed glass volumes, V₀ , over V as derived from observed densities is taken as a measure of the penetration of modifiers into the network cavities without corresponding distention of the network. By using the computed density of 1.95 for vitron, the value 2.20 for silica glass, and 2.30 as reported for irradiated silica, one can estimate that silica glass consists of 28% vitron and 72% disordered silica in the intervitron tissues. The values of V_g , – V mentioned are found to be in fair accord with expectations computable from the vitron theory.     

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.     

Modifications of Unpromoted and Cobalt-Promoted MoS2 During Thermal Treatment by Dimethylsulfide

Previous results have shown that the active surface in stabilized active sulfide catalysts is carbided. This fact led us to reconsider the influence of organosulfide agents in the activation of hydrotreatment catalysts. Structural and morphological consequences of dimethylsulfide treatment of (Co)/MoS₂-based solids were studied. Results suggest that the electronic promotion of Mo by Co substantially influences the carbon replacement of sulfur atoms at the edges of molybdenum sulfide layers.     

Thermal, Structural, and Dielectric Properties of Cu-Doped Ge-S Glasses

Glasses of GeS_1.5+y at.% Cu and GeS 1.375 +z at.% Cu were analyzed by DTA. For concentrations y ≊2.5 and z ≊4, new exothermic transformations and an initial small endothermic effect appear. All these transformations occur below the glass transition temperature of the original Ge:S glass, Analysis by X-ray and electron diffraction showed that this devitrification process is connected with crystallization of a Cu₂GeS₃ phase. Electron transmission microscopy showed that this crystalline phase is dispersed in a glassy matrix as disconnected aggregates with irregular symmetry. Near the maximum copper concentration y ≊5, z ≊6) at the boundary of the glass-forming region, there is one additional exothermic transformation in the system GeS_1.5+y at.% Cu and two in the system GeS_1.375+z at.% Cu, one of them corresponding to crystallization of the Cu₃GeS₄ phase. X-ray diffraction patterns of the crystalline phases are shown. The spectrum of ionic thermocurrents in such glassyceramic material shows a new peak at 120 K which is probably related to interfacial polarization associated with the crystalline phase-glassy matrix boundary.     

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.     

热处理针铁矿的结构与色度演化

利用X射线粉末衍射仪、透射电子显微镜、比表面积分析仪、漫反射光谱仪等研究了针铁矿在空气气氛中的热结构演化和色度变化规律,并以红度、黄度、橙度和总反射率表征色度变化。结果表明:煅烧温度低于200℃时,针铁矿未发生相变,比表面积约为12.0m2/g,样品颜色为橙黄色,总反射率、红度、橙度、黄度变化不明显;高于200℃时,针铁矿开始转变成赤铁矿,并形成纳米孔结构,比表面积呈现先增加后减小的变化,在250℃达到最大值97.4m2/g,颜色由橙黄色变成赤红色,总反射率、橙度和黄度降低,红度升高;且随着煅烧温度升高,针铁矿相变形成的颗粒内部纳米孔孔径逐渐增大,比表面积急剧减小,煅烧产物的颜色略有变化,总反射率、橙度、黄度和红度变化不明显;当温度大于750℃时,纳米孔消失,温度为900℃时,比表面积降至2.8m2/g,产物颜色从赤红色向暗红色转变,总反射率和红度降低,橙度与黄度未变。     

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.     

天然针铁矿热处理产物的结构特征

采用X射线粉末衍射仪、热重分析仪、透射电子显微镜、比表面积分析仪等研究空气中热处理铜陵新桥天然针铁矿的结构演化。热分析结果表明:针铁矿在154.5℃开始脱羟基向赤铁矿转变,在300℃时相转变完全。煅烧温度250~700℃之间,虽然产物都是赤铁矿,但都保持针铁矿原有的形貌特征,且产物的比表面积和孔结构随煅烧温度变化有明显差异。300℃煅烧产物由于脱羟基水,针铁矿假象颗粒内部出现1~5μm大小的孔,且具有最大的比表面积(107.8m2/g);随着煅烧温度升高,由于赤铁矿晶体生长变大,赤铁矿晶体间空隙变大,比表面积逐步降低;煅烧温度大于700℃时,由于赤铁矿晶粒生长开始出现颗粒间烧结现象,针铁矿假象颗粒内部和外部空隙进一步减少,当煅烧温度达到900℃时,针状形貌变成粗短圆柱状,此时比表面积降至最小值为4.8m2/g。结果表明:铜陵新桥针铁矿可以在300~400℃空气中煅烧获得高比表面积的纳米孔材料,在环境保护领域具有很大的潜在应用价值。     

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.     

Preparation and Properties of Nitrogen-Doped Phosphate Glasses

Techniques for preparation and the properties of phosphorus oxynitride glasses produced from sodium metaphosphate and nitride compounds are reported. Properties reported include nitrogen content, dissolution rate in water, thermal expansion coefficient, softening point, glass transformation temperature, density, refractive index, microhardness, and infrared absorption.     

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.     

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.     

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.     

Magnetic Behavior and Microstructure of Vanadium Phosphate Glasses

The magnetic properties and microstructures of the vanadium phosphate glass system over the composition range 60 to 90 mol% V₂O₅ were investigated to study magnetic ordering in the glass and the effect of microstructure on its magnetic properties. Direct antiferromagnetic coupling between V⁴⁺ ions in the glassy matrix exists, and a transition temperature near - 70°C was observed. As-cast glasses with high V₂O₅ concentrations separated into two glassy phases; this separation increased the ESR line width as a result of inhomogeneity broadening. The separation, which concentrated the vanadium ions in a vanadium-rich phase, caused a hysteresis in the plot of ESR line intensity vs temperature at the transition temperature. Reduction of the vanadium ions by dextrose added to the melt enhanced phase separation and resulted in weak antiferromagnetic transitions at +70° and -120°C, the Neel temperatures of VO₂ and V₂O₃, respectively.     

Dielectric Studies of Some Borate and Phosphate Glasses

Some borate glasses, with sag points of 350° to 500°C., of high specific resistance and low power factor have been prepared. The power factor of the glasses has been measured to 250° C., and the resistivity has been measured up to temperatures approaching the transformation region. Borate glasses have higher resistivities and power factors than phosphate glasses. An increase in sag point of lead borate glasses by substitution of PbO with BaO, Al₂O₃, or SiO₂ improves their dielectric properties. Depending on the type of glass, the dielectric constant varies linearly with the density of the glass.