Visible Spectroscopy of Irradiated High-Alkali Borate and Mixed-Alkali Phosphate Glasses

Expectations of increased stability for trapped electrons in high-alkali glasses, based on extrapolations from observations on low-alkali borate glasses, are not borne out. In 69Na₂O-31B₂O₃ glass, electron centers have approximately the same thermal stability as in Na₂O·2B₂O₃ glass. In Na₂Oplus;P₂O₅ glasses the lifetimes, 3 · 0.5 μS, of transiently trapped electrons as well as their absorption spectra prove to be independent of increase of Na₂O content from 50 to 60 mol%. The same composition change destabilizes "permanent" hole centers. Exchange of Na₂O with K₂O in the metaphosphate glass also has no effect on the trapped electron lifetime. Small linear shifts in the trapped-hole absorption peak wavelengths are observed in the latter case. The most important positive finding in the phosphate glasses is a pronounced mixed-alkali effect on the yield of transiently trapped electrons and holes and of permanently trapped holes. The yield is a minimum at Na:K=1:1, due either to the elimination of trap sites or to the reduction of alkali ion mobilities which play a role in trap formation.     

Sodium Transport in the Na2O-H2O-SiO2 Glass System

The variation with water content of dc conductivity and Na diffusion coefficient for the Na₂O · 4siO₂ and Na₂O · 2SiO₂ glass systems was found to be similar to that of the Na₂O.3SiO₂ series reported earlier. The conductivity was estimated for the ternary system Na₂O-H₂O-SiO₂ by combining the present results with the previous data on the Na₂O · 3SiO₂ system. When the conductivity of those glasses with a constant [Na₂O] + [H₂O] content was plotted against water content, a pronounced mixed "alkali" effect was demonstrated. The Haven ratio, calculated by comparison of the dc conductivity to the Na diffusion coefficient at 100°C for each of the three glass systems, was found to increase toward unity with increasing water content. This suggests that the addition of water reduces the number of sodium charge carriers. The subsequent increase in conductivity beyond the minimum with the introduction of larger amounts of water is, probably, due to an increase in the mobility of the Na⁺ ions.     

Influence of Al2O3, ZnO, and K2O on the Opacity of Fluoride-Opacified Glasses

In the glass SiO₂ 71, Na₂O 17, CaO 12% with 7.5 parts per hundred of fluorine added to the batch, substitution of up to 6% ZnO for CaO produced a great increase in the opacity; substitution of Al₂O₃ for SiO₂ or of K₂O for Na₂O produced much smaller effects, which were dependent on the composition and were inappreciable in the presence of 6% ZnO. Despite the differences in opacity, no differences in fluorine content were detected. No support was found for the belief that Al₂O₃ is essential to the successful opacification of a glass by means of fluorides.     

Melting Reactions of Soda-Lime-Silicate Glasses Containing Sodium Sulfate

Various Na₂SO₄-Na₂CO₃-CaCO₃-SiO₂ combinations were studied by differential thermal analysis to elucidute the role of Na₂SO₄ in soda-lime-silica glassmelting reactions. It was found that Na₂SO₄ encourages the formation of wollastonite at 850° to 900°C. The solid-state reaction of Na₂Ca(CO₃)₂ occurs very readily at temperatures in the vicinity of 400°C. The Na₂Ca(CO₃)₂ must therefore be considered a major constituent in glass batches containing both soda ash and limestone .     

Effect of Na2O Additions in the Crystallization of Barium Ferrite from a BaO-B2O3-Fe2O3 Glass

A glass crystallization method was utilized to synthesize nanosized BaO-6Fe₂O₃ platelets from a 0.412BaO-0.258B₂O₃-0.330Fe₂O₃ batch composition. Quenched ribbons were inhomogeneous, showing microclustering and ∼1 μm hematite crystals. Na₂O substitutions for BaO greatly enhanced the glass-forming tendency of quenched ribbons, though quenched-in ∼0.5 μm barium ferrite crystals were infrequently present. The improved homogeneity with Na₂O substitution was attributed to lower vapor pressure of BaO during batch melting, which increased its retention in the as-quenched ribbons. Quantities of BaO equal to or in excess of Fe₂O₃ allowed iron ions to adopt stable network positions in the glass melt. With Na₂O substitution, devitrification of dispersed ∼40 nm barium ferrite particles from phase-separated regions occurred after secondary heat treatment. 5 mol% Na₂O batch substitution showed the lowest crystallinity in the as-quenched ribbons, and the highest crystallinity after secondary heat treatment. After optimum devitrification, the maximum values of saturation magnetization and coercivity were 21.22 emu/g and 2.82 kOe, respectively.     

Effect of Small Additions of Al2O3 and Ga2O3 on the Immiscibility Temperature of Na2O-SiO2 Glasses

Alumina and gallia were substituted separately for Na₂O in amounts of 0.2, 0.5, 1.0, 1.5, 2.0, and 3.0 wt% in three Na₂O-SiO₂ glass compositions (82, 84, and 86 wt% SiO₂) within the immiscibility region. The immiscibility regions for each system extend to ∼1.5 mol% of the added oxide. In general, the addition reduced the immiscibility temperature ( T _m), but at the edge of the immiscibility region (82% SiO₂) the Na₂O loss effect initially increased T _m. A structural model of the miscibility of Al₂O₃ added to silicate glasses is presented.     

Infrared Spectroscopy of Wide Composition Range xNa2S + (1 –x)B2S3 Glasses

Wide composition range studies of the IR spectra of x Na₂S + (1 – x )B₂S₃ glasses are reported for the first time. Glasses can be prepared in two composition regions: 0 x 0.33 in a low-alkali region and 0.55 x 0.80 in a highalkali region. The structures of glasses in the former region are dominated by the creation of tetrahedral boron units similar to those observed in the alkali borate glasses. For pure B₂S₃, a large fraction of six-membered rings is found, as in glassy B₂O₃. As alkali is added, the vibrational frequency of the six-membered ring mode decreases, but not the intensity, and a new band grows in which is used to propose, by analogy with the alkali borate glasses, that the fraction of tetrahedral borons increases with alkali sulfide content. These observations suggest that isolated six-membered rings persist even in the presence of tetrahedral borons. For the high-alkali glasses, both the six-membered rings and tetrahedral boron structures are destroyed in preference to the formation of isolated orthothioborate groups, Na₃BS₃. The IR spectra of the high-alkali glasses show a monotonic increase in symmetry and simplicity, indicating an increase in structural simplicity as the orthothioborate composition is approached. For the orthothioborate composition, both glass and polycrystal can be prepared. The IR spectra of the two phases are very similar, with the glass exhibiting a broadened absorption envelope.     

Phase Formation in the System Na2O · Al2O3-CaO · A12O3-Al2O3 at 1200°C in Air

Phase relations in the system Na₂O_· Al₂O₃-CaO· Al₂O₃-Al₂O₃ at 1200°C in air were determined using the quenching method and high-temperature X-ray diffraction. The compound 2Na₂O · 3CaO · 5Al₂O₃, known from the literature, was reformulated as Na₂O · CaO · 2Al₂O₃. A new compound with the probable composition Na₂O · 3CaO · 8Al₂O₃ was found. Cell parameters of both compounds were determined. The compound Na₂O · CaO-2Al₂O₃ is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na₂O · Al₂O₃ up to 38 mol% Na₂O at 1200°C. The compound Na₂O · 3CaO · 8Al₂O₃ is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al₂O₃ is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β "-Al₂O₃ make it very difficult to determine equilibrium phase relations in the high-Al₂O₃ part of the diagram. Conclusions as to lifetime processes in high-pressure sodium discharge lamps can be drawn from the phase diagram.     

Effect of Poling Temperature on Optical Second-Harmonic Intensity of Lithium Sodium Tellurite Glass

Second-harmonic generation has been observed in poled 10Li₂O10Na₂O80TeO₂ glass. The effect of poling temperature on the second-harmonic intensity has been examined. The second-harmonic intensity increases, attains a maximum, and then decreases as the poling temperature increases. In other words, an optimum poling temperature that results in a maximum second-harmonic intensity exists. The optimum poling temperature linearly increases as the glass-transition temperature increases for several types of tellurite glasses, including the present 10Li₂O10Na₂O80TeO₂ glass. This fact suggests that the process to create a polarization that results in the second-harmonic generation is affected by the structural relaxation at the glass-transition range. The thermal stability of 10Li₂O10Na₂O80TeO₂ glass is higher than that of 18Na₂O82TeO₂ (30NaO_1/270TeO₂) glass, as revealed via differential scanning calorimetry. As a result, the temperature range within which the poling is effective is wider for the former glass.     

Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er³⁺-doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO₂·0.3Al₂O₃)· x Na₂O·8.2La₂O₃· 0.6Er₂O₃·0.2Yb₂O₃·1Sb₂O₃ (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω _t ( t = 2, 4, 6) decreases with increasing Na₂O. Ω₂ decreases rapidly with increasing Na₂O while Ω₄ and Ω₆ decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na₂O. Fluorescence spectra of the ⁴ I _13/2 to ⁴ I _15/2 transition have been measured and the change with Na₂O content is discussed. It is found that the full width at half-maximum decreases with increasing Na₂O.     

Growth of α-Al2O3 Crystals by Na2O Evaporation

A technique for growing α-Al₂O₃ crystals is described in which Na₂O·11Al₂O₃ is dissolved in a liquid of composition Na₂O·4TiO₂·3Al₂O₃. Alpha Al₂O₃ is precipitated as Na₂O evaporates from the system; Na₂O·11Al₂O₃ serves as a source of Al₂O₃, and Na₂O in the liquid. The content of solids in the mixture is always such that it does not melt completely. The size of the α-Al₂O₃ crystals grown is related to the Na₂O content of the composition. Crystals as large as 4000 by 3000 μm in the α-axis direction and 500 μm in the c -axis direction have been grown.     

Viscosity of Molten Na2O─B2O3 Slags

The viscosity of sodium borate slags at high Na₂O concentrations (37.3 to 49.4 mol%) and high temperatures (1000° to 1300°C) follows an Arrhenius-type relationship. This relationship was also observed for sodium borate slags (mass% Na₂O/mass% B₂O₃= 0.86) containing CaO and CaF₂ for the same temperature range. There has been a reduction in viscosity of the sodium borate slags (mass% Na₂O₃mass% B₂O = 0.53 to 0.86) with increase in Na₂O concentration. On adding CaO (10 to 50 mass%) to the sodium borate slag (mass% Na₂O/mass% B₂O₃= 0.86), the viscosity increased considerably, while an addition of CaF₂ (S to 15 mass%) to the slag (30.9 mass% Na₂O₃ 35.8 mass% B₂O₃, 33.3 mass% CaO) decreased the viscosity. The average activation energies of Na₂O─B₂O₃, Na₂O─B₂O₃─CaO₃ and Na₂O─B₂O₃─CaO─CaF₂ slag systems have been estimated as 14.6, 124.7, and 41.4 kJ/mol, respectively, for the given composition ranges and 1000° to 1300°C temperature range.     

Conductivity Activation Energy Relations in High-Sodium-Content Borate and Aluminoborate Glasses

Glasses were prepared having compositions x Na₂O + (1 − x )B₂O₃ and x Na₂O + (1 − x )( n B₂O₃·Al₂O₃) where n = 4.0 and 6.7, and their conductivities and activation energies were determined up to 70 mol% Na₂O. Below 50 mol% Na₂O, the conductivity activation energy decreases with Na₂O content, which is attributed to a decreasing cation jump distance. Above 50 mol% Na₂O, however, the activation energy increases with Na₂O content. These measurements are the first to clearly show a conductivity activation energy increasing with alkali oxide content, an effect which is not yet explained by any of the current models of ionic conduction in glass.     

Mixed-Alkali Effect in Low-Alkali Germanate Glasses

Direct-current conductivities of mixed-alkali Na₂O-K₂O-GeO₂ glasses with ∼0.02 mol% total alkali were investigated. No minima in conductivity isotherms were indicated as K₂O is substituted for Na₂O. However, a conductivity-suppressing effect with the-addition of K₂O to Na₂0-GeO₂ glass was demonstrated, from the comparison with the conductivity ofNa₂O-GeO₂ glasses of varied sodium content (0.0079∼0.30 mol% Na₂O.     

Phase Equilibria in the System Na2O – Nb2O5

Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na₂O-Nb₂O₅. Five compounds corresponding to the formulas 3Na₂O.1Nb₂0₆, lNa₂O. 1Nb₂O₅, lNa₂O 4Nb₂O₆, lNa_zO.7Nb₂O₅, and lNa₂O. 10Nb₂O₆ have been found. The compound 3Na_z0.lNb₂O₅ melts congruently at 992°C. The compounds 1Na₂O. 4Nb₂O₆, lNa₂O.7Nb₂O, and 1Na₂O. 1Onb₂O₅ melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO₃ was found to melt congruently at 1412°C. The transition temperatures in NaNbO₅ were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO₃ could be preserved to room temperature by very rapid quenching.     

Studies in Germanium Oxide Systems: II, Phase Equilibria in the System Na2O—GeO2

Phase equilibrium relations in the system Na₂O-GeO₂ have been determined using standard quenching techniques supplemented by differential thermal analysis. Two congruently melting compounds, Na₂O·GeO₂ and 2Na₂O·9GeO₂, exist; the melting points are 1103°± 15°C and 1073°± 3°C, respectively. The eutectic temperature between GeO₂ and 2Na₂O·9GeO₂ is 950°±f 10°C at 94.5 wt GeO₂. The eutectic temperature between 2Na₂O · 9GeO₂ and Na₂O·GeO₂ is 790° f 10°C at about 75 wt% GeO₂. Both the refractive index and the density of glasses in the system Na₂O-GeO₂ exhibit maximum values at about 16 to 18 mole % Na₂O. The Ge-O-Ge absorption band at 890 cm⁻¹ shifts toward lower wave numbers with the addition of Na₂O.     

Conductivity Maximum in Sodium Aluminoborate Glass

By taking advantage of an exceptionally wide range of glass formation made possible by adding Al₂O₃ to the Na₂O-B₂O₃ binary system, the presence of a maximum in specific conductivity, not predicted by weak-electrolyte models, was demonstrated at –55% Na₂O. The decoupling of conducting modes from viscous modes in the supercooled liquid, assessed at T_g, reaches a maximum at 45% Na₂)O. A second regime of increasing conductivity at >60% Na₂O seems to be associated with incipient compound crystallization.     

Bioactivity of Na2O-CaO-SiO2 Glasses

Bioactivities of Na₂O-CaO-SiO₂ glasses were evaluated by examining the formation of bonelike apatite, which is responsible for their bonding to living bone, on their surfaces in a simulated body fluid, using thin-film X-ray diffraction and Fourier-transform infrared reflection spectroscopy. It was found that glasses in a wide compositional region in the P₂O₅-free Na₂O-CaO-SiO₂ system can show bioactivity, as those in the P₂O₅-containing system. The rate of apatite formation on the surfaces of glasses varied largely with the composition of the glasses. Under a constant SiO₂ content of 50 mol%, a glass containing equimole of Na₂O and CaO showed the highest rate of the apatite formation. Variation in the rate of apatite formation with the glass composition corresponded well with the rate of increase in the degree of the supersaturation of the simulated body fluid with respect to the apatite due to dissolution of sodium and calcium ions from the glasses. Little difference was observed in the rates of ion dissolution and of apatite formation between P₂O₅-containing Bioglass 45S5-type and a corresponding P₂O₅-free Na₂O-CaO-SiO₂ glass. It is believed that P₂O_s-free Na₂O-CaO-SiO₂ glasses also show bioactivity as high as that of Bioglass.     

Ionic Conductivity and Sinterability of NASICON-Type Ceramics: The Systems NaM2(PO4)3+yNa2o (M = Ge, Ti, Hf, and Zr)

Sodium-rich NASOCON-type ceramics, the NaM₂(PO₄)₃+_yNa₂O (M = Ge, Ti, Hf, Zr) system, were investigated in order to obtain a material having a high Na⁺ conductivity and high density. The ionic conductivity and the sinterability were greately improved by an increase in the valve of y for all of the system examined. Added Na₂O was not souble in teh NASICON-type skeletton, sice the lattice constants and teh X-ray diffraction patterns were not changed by the Na₂O addintion in all of the samples. Na₂O acts as a flux for obtaining highly dense ceramics and highly conductive grain boundaries. Partial A₂ site insertion by Na⁺ ions is effective for the enhancement of conductivity, because the conductivity for Na_1.5M(III)_0.5Zr_1.5(PO₄)₃ (M = In or Y) is about 1 order of magnitude higher than the maximum conductivity of the NaZr₂(PO₄)₃+_yNa₂O system.     

Disproportionation of SO2 in Bubbles Within Soda-Containing Glasses

Deposits of S⁰; and Na₂SO₄ together in bubbles within production float glass are generated by disproportionation of SO₂, derived from dissolved SO₃, in company with Na₂O from the interior bubble surfaces. This reaction proceeds rapidly in molten glass and also at temperatures well below T_g.