Copper ⇌ Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Copper-Containing Molten Salt: II, Divalent Copper Salts, CuCl2 and CuSO4

The ion-exchange mechanism between copper and alkali ions, when 20R₂O · 10Al₂O₃· 70SiO₂ (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl₂, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl₂ decomposes into CuCl and Cl₂ at 550°C and the Cu⁺ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl₂ acts as an oxidizing agent just like oxygen. In the case of molten CuSO₄─₂SO₄, a small amount of Cu⁺ which is present in the molten state plays a primary role in the Cu ⇌ R⁺ ion exchange process, although the contribution of direct Cu²⁺⇌ 2R⁺ ion exchange cannot be ignored.     

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.     

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.     

Influence of Strain Energy on Kinetics of Ion Exchange in Glass

The kinetics of the K⁺⇌ Na⁺ exchange in Na₂O·3SiO₂ glass at 350°C were studied. The distribution of K in the glass specimens after exchange in molten KNO₃ was determined with an electron microprobe. The calculated interdiffusion coefficients, which varied with the local composition in the glass, were compared with those obtained using the Nernst-Planck equation and Fleming and Day's self-diffusion data for xNa₂O. (1-x)K₂O·3SiO₂ glasses. Deviations of the observed interdiffusion coefficient from the Nernst-Planck formula were noted. These deviations are explained on the basis of changes in the average size of the alkali ion sites and in the strain energy that occur during ion exchange.     

Thermochemistry of Charge-Coupled Substitutions in Silicate Glasses: The Systems Ml/nn+ AlO2-SiO2 (M = Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Pb)

Enthalpies of solution of framework aluminosilicate glasses x M_{l/ n} ^{n +} AlO₂-(1- x )SiO₂ (M = Cs, Rb, K, Na, Li, Ba, Pb, Sr, Ca, Mg) in molten 2PbO.B₂O₃ near 973 K were measured. The sequence above represents increasing ability of the nonframework cation M to bond to the bridging oxygen. In that sequence, the enthalpy of the substitution Si⁴⁺→+ Al³⁺+ 1/ n M ^{n +} in the glass becomes less exothermic, the enthalpy of vitrification increases, and the tendency toward glass-glass immiscibility becomes more pronounced. These parameters correlate smoothly with the ionic potential, z/r , of the substituting cation.     

Ultraviolet Absorption of Pentavalent Vanadium in Binary Alkali Borate Classes

The ultraviolet absorption of vanadium(V) in R₂O-B₂O₃ glasses (R represents Li, Na, or K) and in aqueous buffer solutions was investigated. In glasses of variable R₂O:B₂O₃ ratio, a change in the absorption spectra similar to the [VO₄]³- → [VO₃(OH)]^2- change in aqueous solution was observed. It is suggested that vanadium(V) in these glasses may be present as either [VO₄]^3- or [VO₃O_1/2]^2- (O_1/2 indicates a bridging oxygen ion), depending on the basicity of the melt. The critical R₂O concentration, above which this change in vanadium(V) environment occurs with increasing alkalinity, is 24, 26, and ≅30 mol%, for K₂O, Na₂O, and Li₂O, respectively.     

Spectroscopic Analysis of the Structure of Silicate Glasses along the Joint xMAlO2-(1–x)SiO2(M = Li, Na, K, Rb, Cs)

Infrared spectroscopic studies of charge-coupled substitution in silicate glasses and crystals along the joints x MAlO₂(1 – x )SiO₂ (M = Li, Na, K, Rb, and Cs; 0.10 ≤ x ≤ 0.60) were carried out in the range 2000 to 200 cm⁻¹ Three major absorption bands appeared in the 1100-, 800-, and 500-cm⁻¹ regions. For a specific value of x, the observed changes in frequency, intensity, and bandwidth decreased in the order Li > Na > K > Rb > Cs and the apparent disorder in the glass structure caused by the substituted aluminum increased in the direction K < Na < Li. The 800-cm⁻¹ band splits at SiO₂≃ 0.75 mol, which has been interpreted in terms of the number of AlO₄ tetrahedra in the structure. Most of the substituted aluminum in the glasses and the crystals was found to be in the fourfold coordination.     

Stannous-Stannic Equilibrium in Molten Binary Alkali Silicate and Ternary Silicate Glasses

The stannous-stannic equilibrium in binary alkali silicate and ternary silicate glasses was studied by equilibrating glassmelts with air at 1400°C. The Sn²⁺-Sn⁴⁺ equilibrium shifts more toward the oxidized state with increasing ionic radii of the alkali ions or with increasing concentration of the alkali ions in the same series of glasses. The slope of the straight lines obtained on plotting log (Sn⁴⁺)/(Sn²⁺)( pO₂ )^n/2 vs mol% R₂O increased in the order Li→Na→K. In ternary silicate glasses having the base glass composition 20Na₂O·10RO·70SiO₂, the Sn²⁺-Sn⁴⁺ equilibrium shifts more toward the reduced state, with increasing bond strength between the divalent cations and the nonbridging oxygens. With increasing temperature, the equilibrium shifts more toward the reduced state.     

Nonlinear Optical Properties of B2O3-Based Glasses: M2O-B2O3(M = Li, Na, K, Rb, Cs, and Ag) Binary Borate Glasses

The third-order nonlinear optical susceptibilities χ⁽³⁾ of M₂O-B₂O₃ (M = Li, Na, K, Rb, Cs, and Ag) binary borate glasses have been measured by the third harmonic generation (THG) method. It is found that the enhancement of χ⁽³⁾by the structural change of BO₃ units to BO₄ units is small, while the enhancement of χ⁽³⁾ due to the formation of non- bridging oxygen is rather significant. The effects of alkali cations on the χ⁽³⁾ of alkali borate glasses are discussed in terms of the M-O bond character, focusing on the covalency of Li₂O-B₂O₃ glasses. Comparison of the χ⁽³⁾ values for Cs₂O-B₂O₃ and Ag₂O-B₂O₃ glasses which contain cations of comparable polarizability reveals that the χ⁽³⁾ value is much greater for Ag₂O-B₂O₃ glasses than for Cs₂O-B₂O₃glasses, which is possibly due to the great contribution of Ag(4 d_z2 + 5 s + 5 p_z ) hybrid orbitals to the nonlinear optical response.     

Infrared Spectra of Rapidly Quenched Glasses in the Systems Li2O-RO-Nb2O5 (R=Ba, Ca, Mg)

Twin-roller quenching produced wide ranges of glass formation in the systems Li₂O-RO-Nb₂O₅ (R=Ba,Ca,Mg). The glass-forming ability is improved with an increase in the ionic radius of R²⁺ ions. The crystallization temperature is increased as Li₂O is replaced by RO or the ionic radius of R²⁺ ions is increased. Infrared spectra revealed that the glass LiNbO₃ (=50Li₂O-0Nb₂O₅) was composed of six-coordinated NbO₆ octahedra, which were joined together by corner-sharing only. In the Li₂O-RO-Nb₂O₅ glasses there exist edge-shared as well as corner-shared NbO₆ octahedra. The edge-shared NbO₆ octahedra in the glasses are increased with an increase in the content of RO or Nb₂O₅, and also with an increase in the ionic radius of R²⁺ ions.     

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.     

Preparation and Faraday Effect of Fluoroaluminate Glasses Containing Divalent Europium Ions

Fluoroaluminate glasses containing various concentrations of Eu²⁺ were prepared under a reducing atmosphere for the present study, and the wavelength dependence of the Faraday rotation angle was examined. The magnitude of the Verdet constant (V_c) increased as the concentration of Eu²⁺ increased. In addition, the Verdet constant of glasses containing 5 cat.% Eu²⁺ was larger than that of fluoroaluminate glasses containing the same concentration of Tb³⁺ in the wavelength region from 400 to 600 nm. The effective transition wavelength, λ_t, for glasses containing Eu²+ as well as those containing Tb³+ was evaluated based on the Van Vleck and Hebb theory. Factors dominating the Verdet constant of those glasses are discussed in this report.     

Copper-Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Molten CuCl—An Ion Exchange Controlled by the Cu+→Cu2+ Oxidation Reaction in Glass

The kinetics of copper-potassium ion exchange of potassium aluminosilicate glass have been investigated in molten CuCl at 550°C in air and nitrogen. The presence of oxygen dissolved in molten CuCl has a great effect on the Cu-K ion-exchange kinetics, i.e. ion exchange in nitrogen is controlled by the interdiffusion process of Cu⁺ and K⁺ in the glass, whereas ion exchange in air seems to be controlled by the Cu⁺→Cu²⁺ oxidation reaction.     

Mixed Alkali Effect in Noncoventional Alkali Gallotitanate Glasses

The mixed alkali effect on electrical conductivity, that is, the reduction of conductivity due to alkali mixing, was observed in Na₂O–K₂O–Ga₂O₃–TiO₂ glasses, which are nonconventional in the sense that glass-forming oxides defined by Zachariasen are not involved. The magnitude of the reduction in conductivity of the present glasses due to alkali mixing was similar to that of corresponding mixed alkali silicate and phosphate glasses. The activation energy for electrical conduction showed a maximum around the composition Na/(Na + K) = 0.5, where the conductivity was at a minimum.     

Effect of Corrosion Processes on Subcritical Crack Growth in Glass

Crack-growth studies were conducted on soda-lime-silica, soda borosilicate, and two binary soda-silica glasses immersed in solutions of 1 M Li⁺, 1 M Cs⁺, or deionized water at different pH values. A definite effect of the Li⁺ and Cs⁺ was observed on the V-K₁ curves in all but the soda-lime glass. A plateau in crack velocity in the range 10-⁸ to 10-¹⁰ m/s was measured on the binary soda-silica glasses for K₁<0.35 MPa.m^1/2. These data are analyzed in terms of both the ion exchange and SiO₂ dissolution steps of the corrosion process. A model of crack growth in corrosive conditions is proposed.     

Optical Absorption and Oxidation States of Uranium in Alkali Aluminoborate Glasses

The optical absorption spectra of 22R₂O.13Al₂O₃.65B₂O₃ (mol%) glasses contain ing uranium indicate the presence of U⁶⁺, U⁵⁺, and U⁴⁺. The presence of U⁶⁺ in the uranyl group is favored as alkali ion (R) is replaced in the direction Li6+ coordinated diflerently from that in uranyl groups (possibly 4-coordinated). A suggestion for making use of such findings in estimating the uranium content of a sample is given.     

Redox Equilibria of Multivalent Ions in Silicate Glasses

Experimental studies were made on the compositional dependence of the redox equilibrium of Eu in synthetic silicate liquids, together with an empirical model describing the observed compositional dependence. Electron paramagnetic resonance (EPR) was used to measure the concentration ratio of Eu²⁺ to Eu³⁺ in various glasses formed by rapidly quenching silicate liquids. The compositional field studied comprised mixtures of SiO₂, TiO₂, Al₂O₃, CaO, MgO, and Na₂O. The proposed model describes the Eu²⁺/Eu³⁺ ratio over the entire compositional field in terms of parameters easily related to each glass composition. The general applicability and utility of the model is further demonstrated by its application to the Fe²⁺-Fe³⁺, Ce³⁺-Ce⁴⁺, and Cr³⁺-Cr⁶⁺ redox reactions in binary alkali oxide silicate glasses of Li, Na, and K.     

Role of Copper Ions in Low-Melting Solder Glasses

Controlled melting conditions for Cu-containing solder glasses yielded a variety of Cu⁺/Cu²⁺ ratios from a single glass starting composition. Measurements of softening point, thermal expansion, chemical durability, plus chemical analysis revealed that the well-known viscosity effect of adding copper oxide to solder glasses is caused primarily by the Cu⁺ ion; Cu²⁺ plays a minor role, if any.     

Properties and Structure of Glasses in the Systems M2O-In2O3-GeO2 (M = Li,Na,K)

The glass-forming regions in the ternary systems M₂O-In₂O₃-GeO₂ (M = Li,Na,K) were determined. The region in each of the three ternaries is less extensive than in either of the analogous systems M₂O-Al₂O₃-GeO₂ and M₂O-Ga₂O₃-GeO₂; this behavior reflects the restrictive coordination requirements of the larger In ion. The In₂O₃-containing glasses exhibit higher densities and refractive indices than the corresponding Al₂O₃ and Ga₂O₃-containing glasses. Refractive index and density maxima are observed along lines of constant In₂O₃ in each of the three alkali indogermanate systems.     

High-Temperature Energy Relations in the Alkali Borates: Binary Alkali Borate Compounds and Their Glasses

The energy relations existing between the congruently melting compounds Li₂O -2B₂O₃, Na₂O–2B₂O₃, Na₂O-4B₂O₃, and K₂O-4B₂O₃ and their glasses have been determined for the temperature range 25° to 1100°C. High-temperature heat-content, entropy, and heat of solution data are given for both the glasses and the corresponding devitrified materials. A comparison of the heats of fusion of the alkali borates on a gram atom of oxygen basis shows that they follow the order Li > Na > K. The entropy differences between the glass and the corresponding crystalline material have been determined at 25°C. The free-energy change at 25°C. for the reaction crystal → glass has been calculated for the four compounds.