Mixed-Alkali Effect on Rayleigh Scattering in K2O–Na2O–MgO–SiO2 Glasses

The Rayleigh scattering of the mixed-alkali glass system K₂O–Na₂O–MgO–SiO₂ (KNMS) was investigated, both experimentally and theoretically. The lowest Rayleigh scattering coefficient (38% of that for pure SiO₂ glass) was obtained when the glass composition was 22K₂O–8Na₂O–10MgO–60SiO₂ (in mol%). These values are equal to or less than the minimum values reported for the ternary sodium silicate glass Na₂O–MgO–SiO₂. The Rayleigh scattering caused by concentration fluctuation was believed to have been reduced greatly in this KNMS glass, because the mobility of the alkali-metal ions was reduced by the mixed-alkali effect.     

Glass Formation and Recrystallization in the Lithium Metasilicate Region of the System Li2O–Al2O3–SiO2

The stability of the vitreous state in the lithium metasilicate region of the system Li₂O–Al₂O₃–SiO₂ was found to be a function of the concentration of lithia. The higher the lithia content, the less stable was the glass. The devitrification of glasses in this system was studied. In addition to the phases present at or near the liquidus, it was found that the β -eucryptite– β -quartz solid solution phase was metastable over most of the region. The Li₂O–SiO₂, β -Li₂O–Al₂O₃–4SiO₂ solid solution, β -Li₂O–Al₂O₃–2SiO₂ solid solution triple point was estimated to be near 62.5% SiO₂, 17% Al₂O₃, and 20.5% Li₂O (by weight). The thermal expansions of bodies in this region were measured and the values obtained are explained in terms of the phases present.     

Equilibrium Compressibilities and Density Fluctuations in K2O–SiO2 Glasses

The density fluctuations contributing to light scattering in a glass are governed by the flctive temperature of the glass and the equilibrium compressibility of the melt. Using ultrasonic velocity data for K₂O–SiO₂ melts, these compressibilities were evaluated, and the magnitude of the density fluctuations were calculated. In this system, the mean–square amplitude of the fluctuations reaches a minimum value (about half that of pure SiO₂) for a composition of ∼20 mol% K₂O. By extrapolating the equilibrium compressibilities to zero K₂O content, the density fluctuations can be calculated for pure SiO₂ glass; this calculation agrees well with the result obtained from light–scattering measurements.     

Influence of TiO2 on Properties of Glasses in the System K2O–PbO–SiO2–TiO2 and Its Relation to Structure

By a progressive weight percent substitution of TiO₂ for SiO₂ at various rations of concentration of K₂O and PbO, the entire region of glass formation in the quaternary system K₂O–PbO–SiO₂–TiO₂ was covered with 51 glass compositions. The properties of these glasses were determined and studied with respect to the role of TiO₂ in the system. The results indicated that the dielectric constant increased progressively with increasing TiO₂ concentration whereas the dissipation factor showed an overall decrease, when measured at 1 Mc and 25°C. Density and the refractive index increased progressively with increasing TiO₂ concentration but deviated from the additive relation. Chemical durability, expansivity, and softening temperature vs. composition curves showed definite inflections. The effect of TiO₂ on oxygen packing indicated that Ti⁴⁺ strengthens the network in lower concentrations and weakens the network in higher concentrations in this system. It appears to be likely that Ti⁴⁺ changes its coordination number form 4 to 6.     

Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass-Ceramic

The devitrification kinetics and mechanism of a low-dielectric, low-temperature, cofirable K₂O–CaO–SrO–BaO–B₂O₃–SiO₂ glass-ceramic have been investigated. Crystalline phases including cristobalite (SiO₂) and pseudowollastonite ((Ca,Ba,Sr) SiO₃) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami-like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.     

Deposition and Characterization of Li2O–SiO2–P2O5 Thin Films

Amorphous lithium electrolyte thin films, xLi₂O·ySiO₂·zP₂O₅, were deposited by rf magnetron sputtering of pure and mixed-phase lithium silicate, lithium phosphate, SiO₂, Li₂O, and Li₂CO₃ targets, and their compositions were determined using proton-induced y -ray emission spectroscopy, energy-dispersive X-ray analysis, Rutherford backscattering spectrometry, and atomic-emission spectroscopy. The deposition conditions were chosen to assure thermalization of the sputtered flux, which proved to be necessary in order to obtain a homogeneous distribution of Si and P in the films. Optical absorption and ac impedance measurements showed that glass-in-glass phase separation occurred in a large SiO₂-rich domain of the composition diagram. In contrast to bulk glasses, all of the Li₂O–SiO₂ films were phase-separated, including those with lithia contents larger than lithium disilicate. High-performance liquid chromatography measurements revealed that, analogous to bulk glasses, the addition of SiO₂ to Li₂O-P₂O₅ compositions reduced the number of phosphate anion dimers, trimers, and higher anion polymers in the films through the formation of -Si-O-P-bonds. However, in contrast to bulk glasses, the distribution of phosphate anion polymers followed closely the Flory distribution, with the fraction of anion polymers decreasing monotonically with increasing chain length.     

Cassiterite Solubility in High-Silica K2O-Al2O3-SiO2 Liquids

The saturation surface of cassiterite, SnO₂, was determined for liquids in the system K₂O–Al₂O₃–SiO₂ as a function of bulk composition and temperature. At fixed K₂O/Al₂O₃ cassiterite solubility varies weakly with SiO₂ concentration (76 to 84 mol%), temperature (1350° to 1550°C), and log ( f _O2) (−0.7 to −5.3). Cassiterite solubility is also approximately independent of composition in liquids with molar ratios of K₂O/Al₂O₃ lessthan equal to 1 (peraluminous liquids). As K₂O/Al₂O₃ increases from 1 (peralkaline liquids), however, cassiterite solubility increases steeply and approximately linearly with K₂O in excess of Al₂O₃. It is proposed that potassium in excess of aluminum combines with Sn⁴⁺ to form quasi-molecular complexes with an effective stoichiometry of K₄SnO₄.     

Rayleigh and Brillouin Scattering in K2O–SiO2 Glasses

The intensity and spectral distribution of light scattered by K₂O-SiO₂ glasses (K₂O content up to 40 mol%) were measured. The transverse and longitudinal sound-wave velocities and the photoelastic constants were evaluated from the results. The total intensity of the scattering (and therefore the attenuation caused by it) exhibited a minimum at a concentration of ∼25 mol% K₂O. For this composition the attenuation is ∼2/2 of that in pure SiO₂. This behavior results from the existence of anomalously small concentration fluctuations in the melt of K₂O·3SiO₂ glass. A qualitative explanation of this result, involving low-temperature immiscibility regions, is presented.     

The System KAlSiO4–Mg2SiO4–KAlSi2O6

Schairer's study (1954) on phase relations in the system KalSi₂O₆–Mg₂SiO₄–SiO₂ was extended to include the system KalSiO₄–Mg₂SiO₄–KalSi₂O₆. It is shown that this join is ternary; however, the relatively high vapor pressure of the condensed phases prohibits study by the usual quenching techniques. The apparent intersection of the (KalSiO₄–Mg₂SiO₄–SiO₃) join with the primary phase volume of spinel is attributed to loss of the alkali-silicate constituents by vapor transport. This results in the effective bulk composition being moved away from this join toward the primary phase volume of spinel in the system K₂O–MgO–Al₂O₃–SiO₂.     

The System K2O-BaO-SiO2

Phase equilibrium studies of compound formation and liquidus and solidus surfaces of the system K₂O-BaO-SiO₂ are presented. The system contains 3 ternary compounds: K₄BaSi₃O₉, K₈BaSi₁₀O₂₅, and K₂Ba₃Si₈O₂₀. Both high and low polymorphs of the third have fields on the ternary liquidus surface. Solid solution with SiO₂ depresses the high-low inversion from 1030°C at K₂Ba₃Si₈O₂₀ to 835°C at 70.2 mol% SiO₂. Data for 20 liquidus invariant points were found; 8 are thermal maxima and 12 are eutectics or peritectics. The isofracts of quenched glasses were determined.     

Effect of Molybdenum on the Structure and on the Crystallization of SiO2–Na2O–CaO–B2O3 Glasses

Crystallization of the poorly durable Na₂MoO₄ phase able to incorporate radioactive cesium must be avoided in SiO₂–Al₂O₃–B₂O₃–Na₂O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B₂O₃ and MoO₃ were added to a SiO₂–Na₂O–CaO glass, and crystallization tendency was studied. Na₂MoO₄ crystallization tendency decreased with the increase of B₂O₃ concentration whereas the tendency of CaMoO₄ to crystallize increased due to preferential charge compensation of BO₄⁻ entities by Na⁺ ions. ²⁹Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd³⁺) were shown to enter into CaMoO₄ crystals formed in glasses.     

Structure and Properties of Low Phonon Antimony Glasses in the K2O–B2O3–Sb2O3–ZnO System

The monolithic glass-forming region of the low phonon and low softening point antimony glasses containing high Sb₂O₃ (40–75 mol%) in the novel quaternary K₂O–B₂O₃–Sb₂O₃–ZnO system has been found with the help of X-ray diffraction (XRD) analysis. The structure of a series of glasses with the general composition of (mol%) 15K₂O–15B₂O₃–(70− x )Sb₂O₃– x ZnO (where x =5–25) has been evaluated by infrared reflection spectral (FT-IRRS) analyses. All the glasses are found to possess a low phonon energy of around 600 cm⁻¹, as revealed by FT-IRRS. Their softening point ( T _s), glass transition temperature ( T _g), and coefficient of thermal expansion (CTE) have been found to vary in the ranges of 351°–379°C, 252°–273°C, and 195–218 × 10⁻⁷ K⁻¹, respectively. These properties are found to be controlled by their fundamental property, like the covalent character of the glasses, which is found to increase with an increase in Sb₂O₃ content. In addition, the devitrified glasses have been characterized by XRD and field emission scanning electron microscopy, which manifests the presence of nanozinc antimony oxide crystals with sizes of 21–43 nm. The exhibited properties have revealed that they are a new class of versatile materials.     

Studies in Lithium Oxide Systems: VII, Li2O–B2O2–SiO2

Phase relations in the system Li₂O–B₂O₃–SiO₂ were studied by quenching and solid-state reactions. No ternary compounds were detected in the portion of the system containing less than 53% Li₂O. Compatibility triangles were formed from the binary borate and silicate compounds. Liquidus data obtained by quenching are reported for four joins, Li₂O·2SiO₂–Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·B₂O₃, and Li₂O·2B₂O₃-SiO₂. The last join cuts across the two-liquid region and is not a true binary system. Some probable ternary invariant points were located in the portion of the system which was quenchable to glass and adjacent to the two-liquid region. Further data on the previously reported immiscible liquid formation are given and the significance is discussed. Data on the thermal expansion behavior of certain glasses are presented.     

Dielectric Properties of Glasses in the System Nb2O5–Na2O–SiO2

The effect of niobia on the dielectric properties of glasses in the system Nb₂O₅–Na₂O–SiO₂ has been studied from 100 to 10¹⁰ cps. The dielectric constant is high even at frequencies up to 10¹⁰ cps. The Nb⁵⁺ ion, with its small ionic radius and high charge, reinforces the network and raises the dielectric constant.     

Differences in Surface Behavior of Alkali Ions in Li2O ·3SiO2 and Na2O · 3SiO2 Glasses

The molecular dynamics computer simulation technique was used to determine the short-time dynamics behavior and resultant structures of ions at the surface of Li₂0·3SiO₂ and Na₂O-3SiO₂ glasses. Room temperature and elevated temperatures were used. Results are compared with similar studies of the K₂O·3SiO₂ glass surface and with recent experimental ion-scattering-spectroscopy data. The simulations indicate that a localized surface rearrangement occurs within picoseconds after formation of the free surface, creating a surface excess of alkali in the Na (and K) case, but not in the Li case. Elevated temperatures, even for brief times, enhance the observed surface excess of Na and K. The results correspond to those obtained from the ion-scattering-spectroscopy studies.     

Reaction Between K2O and Al2O3-SiO2 Refractories as Related to Blast-Furnace Linings

An examination was conducted to determine the mechanism of peeling of fire-clay brick in the low-temperature region of a blast furnace where 3 to 10% K₂O is the principal contaminant. In laboratory tests, as-received high-duty and superduty fire-clay brick and 70% alumina brick treated with KCl-K₂CO₃ mixtures showed no peeling at a temperature of 1600°F. Cracks were found in high-duty brick that were treated with KCN at 1500°F. under partially reducing conditions. X-ray diffraction studies of mixtures of crushed brick and K₂CO₃ indicated the formation of leucite (K₂O.Al₂O₃.4SiO₂) and kaliophilite (K₂O.-Al₂O₃.2SiO₂) at temperatures below 1700°F. These latter data, confirmed by specimens from used blast-furnace linings, showed that silica is the first constituent attacked by alkali. Since the formation of leucite and kaliophilite in fire-clay brick is the probable cause of peeling, the increased reaction of silica, in a dense Al₂O₃.SiO₂ refractory of higher silica content than fire-clay brick, should confine the alkali attack to the surface of the brick in low-temperature applications.     

Prominent Nanocrystallization of 25K2O·25Nb2O5·50GeO2 Glass

Some K₂O-Nb₂O₅-GeO₂ glasses are prepared, and their crystallization behaviors are examined. 25K₂O·25Nb₂O₅·50GeO₂ glass with the glass transition temperature T _g= 622°3C and crystallization onset temperature T _x= 668°3C shows a prominent nanocrystallization. The crystalline phase is K_3,8Nb₅Ge₃O_20,4 with an orthorhombic structure. The sizes of crystals in the crystallized glasses heat-treated at 630° and 720°3C for 1 h are °10 and 20–30 nm, respectively, and the crystallized glasses obtained by heat treatments at 620°-850°3C for 1 h maintain good transparency. The density of crystallized glasses increases gradually with increasing heat-treatment temperature, and the volume fraction of crystals in the sample heat-treated at 630°3C for 1 h is estimated to be ∼35%. The usual Vickers hardness and Martens hardness (estimated by nanoindentation) of 25K₂O·25Nb₂O₅·50GeO₂ glass change steeply by heat treatment at T _g, i.e., at around 35% volume fraction of nanocrystals. The present study demonstrates that the composite of nanocrystals and the glassy phase has a strong resistance against deformation during Vickers indenter loading in crystallized glasses.     

Solubilities of Ar, N2, CO2, and He in Glasses at Pressures to 10 Kbars

Glasses containing up to several percent of Ar, N₂, and CO₂ were prepared at 2000 to 150,000 psi and up to 950°C and retained under ambient conditions. The solubilities are presented as a function of pressure, temperature, and composition of glass. Solubilities of O, He, and H₂O were also investigated in various glass compositions, especially K₂O–4SiO₂ and B₂O₃. The evolution of the gases at atmospheric pressure was followed by electron microscopy and density measurements.     

Isothermal Section of a Cu2O–Al2O3–SiO2 Pseudo-Ternary System at 1150°C in Air

In this study, the isothermal section of a Cu₂O–Al₂O₃–SiO₂ pseudo-ternary phase diagram at 1150°C was analyzed by means of a scanning electronic microscope and powder X-ray diffraction of the quenched samples qualitatively, and the compositions of the tie-points of the tie-planes as well as their regions were determined by in situ high-temperature quantitative X-ray diffraction analysis and energy-dispersive X-ray spectroscopy. Then, the isothermal section of the Cu₂O–Al₂O₃–SiO₂ pseudo-ternary phase diagram at 1150°C was constructed; it was found that the isothermal section is composed of two single liquid-phase regions, five two-phase regions, and six three-phase regions.     

Effect of Na2O/K2O Ratio on Chemical Durability of Alkali-Lime-Silica Glasses

The chemical resistance of mixed-alkali glasses to water was measured by determining the sodium, potassium, calcium, and silicon ions extracted instead of evaluating it from the alkalinity of the mixed-alkali extracts. In glasses of the composition K₂O and Na₂O 18, CaO 10, and SiO₂ 72% the minimum extraction of alkali (maximum durability) occurred for a K₂O/-Na₂O ratio of 2.6/1.0 (by weight). Based on an ionic-composition analysis of the results, an empirical index is suggested for determining the relative degree of ion-exchange and network-breakdown modes of reactions that occur when such mixed-alkali glasses are attacked by water.