Rare-Earth Aluminosilicate Glasses

Rare-earth aluminosilicate glasses of the general formula 20R₂O₃· 20Al₂O₃· 60SiO₂ have been formed for 10 of the 14 possible rare-earth oxides. Two series of "mixed-rare-earth" glasses were also formed (Nd/Er and Nd/Y). These glasses exhibit exceptionally high glass transformation temperatures, moderate thermal expansion coefficients, and refractive indices of approximately 1.65. The glass transformation temperature and thermal expansion coefficients vary linearly with the field strength of the rare-earth ion. No evidence of a "mixed-rare-earth effect" was observed. MAS-NMR indicates that the aluminum ions are tetrahedrally coordinated in at least some of these glasses.     

Structure of Sodium Aluminosilicate Glasses

A series of sodium aluminosilicate glasses composed of varying ratios ( R ) of Al₂O₃/Na₂O (0.25 R 2.0) has been simulated with the molecular dynamics technique using a tetrahedral form of a three-body interaction potential. Extrema in the activation energies for sodium diffusion and in the diffusion constants for all of the atomic species were observed for glasses with equal concentrations of Al₂O₃ and Na₂O ( R = 1.0). These changes corresponded to the minimum observed experimentally in the activation energy for electrical conductivity and to the maximum observed in the viscosity for glasses with compositions of R = 1.0. The coordination of aluminum remained 4 over the entire compositional range, negating the need to invoke a coordination change of aluminum to explain the changes in the physical properties. The changes to the simulated physical properties as R passed through the equivalence point were attributed to the elimination of nonbridging oxygen, to the introduction of oxygen triclusters, and to changes in the distribution of ring structures within the glass networks.     

Electrical Conductivity in Mixed-Alkali Aluminosilicate Melts

The mixed-alkali effect in ac electrical conductivity has been investigated in 25R₂O(Na₂O+K₂O)- y Al₂O₃-(75- y )SiO₂ melts, with y = 0, 5, 7.5, and 10 mol%, at temperatures of 1000°-1400°C. The results for the molten state show a typical mixed-alkali effect, similar to that exhibited below the transformation temperature. These results imply that the interaction between two different alkali ions is maintained in the molten state. However, the mixed-alkali effect increases as the Al₂O₃ content increases (in other words, with decreasing nonbridging oxygen content). Such results can be explained in terms of the binding state of AlO₄-R⁺ and -O^--R⁺, based on the conductivity behavior of alkali aluminosilicate melts.     

Alkali-Resistant Magnesium Aluminosilicate Oxynitride Glasses

Glasses containing up to 3.3 wt% nitrogen were prepared in the system MgO─Al₂O₃─SiO₂─AIN─Si₃N₄. GlasGlass transition temperature, density, and elastic properties increased with increasing nitrogen content. Resistance against aqueous alkaline solutions was determined by weight loss measurements, solution and surface analysis. The good durability of both oxide and oxynitride glasses is caused by a protective surface layer. The introduction of nitrogen decreases the alkaline attack. The data suggest that nitrogen is incorporated as Si─N boxhs.     

Formation and Properties of Calcium Aluminosilicate Glasses

The glass-forming region for calcium aluminosilicate glasses has been determined. A number of properties of these glasses (thermal expansion coefficient, glass transformation and dilatometric softening temperature, and refractive index) have been studied. The results of these measurements suggeq that the structures of these glasses may not as closely resemble those of alkali aluminosilicate glasses as is commonly assumed. Evidence is presented which suggests that the binary calcium aluminate glasses may be phase separated.     

超薄铝硅玻璃离子交换工艺研究

高强度超薄盖板玻璃是电子信息产品的重要组成部分,化学强化(离子交换)是提升超薄盖板玻璃力学性能的主要技术途径。在离子交换过程中,玻璃易产生应力弛豫等现象,导致化学强化玻璃难以具备较高的表面压应力、较大的应力层深度与较高的维氏硬度。本文采用两步法离子交换工艺,研究了熔盐、离子交换温度与时间等因素对强化后超薄铝硅玻璃应力层分布及维氏硬度等性能的影响。结果表明,本文所研发的两步法离子交换工艺,可以使玻璃兼具较高的表面压应力、较大的应力层深度与较高的表面维氏硬度。离子交换后,铝硅玻璃的表面压应力可达900 MPa以上,应力层深度可达70 μm以上,同时表面维氏硬度达7.2 GPa以上。     

Helium Migration in Sodium Aluminosilicate Glasses

Helium permeation, diffusion, and solubility have been measured for a number of sodium aluminosilicate glasses. The results indicate that a major change in the glass structure occurs when the alumina-to-soda ratio exceeds unity. It also appears that small substitutions of alumina (Al/Na<0.5) have a different effect on the glass structure than do larger (0.5相似文献   

Infrared Spectroscopy of Lead and Alkaline-Earth Aluminosilicate Glasses

Infrared spectroscopic studies of lead and alkaline-earth aluminosilicate glasses in the series x MO- x Al₂O₃ (1 - 2 x )SiO₂ M = Mg, Ca, Sr, Ba, and Pb; 0.05 x 0.275] were carried out in the range 2000 to 200 cm⁻¹. Three major absorption bands were observed in the 1100-, 800-, and 500-cm⁻¹ regions. The frequency and the intensity of the 1100-cm⁻¹ band varied linearly with composition. For a specific value of x , the changes in the frequency, intensity, and bandwidth of this band decreased in the order Mg > Ca > Sr > Pb > Ba and the apparent disorder in the glass structure, effected by the substitution of aluminum, increased in the direction Mg < Ca < Sr < Ba, with Pb in between Mg and Ca. The force constants and the bond orders of the Si-O and Al-O stretching vibrations in each of the glasses increased monotonically as Al/(Al + Si) decreased.     

Thermal Expansion of Substituted Copper Aluminosilicate Glasses

The effects of various components on the thermal expansion coefficient of low-expansion Cu₂O-Al₂O₃-SiO₂ glasses were examined. When a component of glass was substituted by another oxide, the expansion coefficient always increased, except for substitution of Al₂O₃ by B₂O₃. This result indicates that the essential components to maintain the low expansivity are Cu₂O, such trivalent oxides as Al₂O₃ and B₂O₃, and tetravalent oxide SiO₂. Glasses of the systems Cu₂O-Al₂O₃-B₂O₃, Cu₂O-Al₂O₃-GeO₂, and Cu₂O-Al₂O₃-P₂O₅, which were derived by replacing SiO₂ by other network-forming oxides, showed fairly low expansion coefficients compared with other conventional borate, germanate, and phosphate glasses. It was also found that the valence state of copper ions is important for the thermal expansion characteristics of these glasses; Cu⁺ ions contribute to the low expansion coefficient.     

Formation of Aluminosilicate Glasses Containing Rare-Earth Oxides

Formation of aluminosilicate glasses containing oxides of rare-earth elements, e.g. Sc, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, and Yb, was studied by melting at 1550°C and air quenching. The upper limit of the amount of rare-earth oxide which can be incorporated into the aluminosilicate glasses decreases according to the lanthanide contraction.     

New Aluminosilicate Glasses as High-Power Laser Materials

In the past few years, aluminosilicate glasses of an extremely broad compositional range have been prepared and analyzed to scan this glass type for its potential use as high-power laser material. The tested network modifier ions included Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Pb²⁺, Y³⁺, and La³⁺. Preliminary investigations have been conducted with Sm³⁺- and Eu³⁺-doped glasses; selected glass compositions have also been prepared with Yb³⁺ doping for laser testing. It has been found that low refractive indices/low average molecular weights/low densities of the glasses in most cases support relatively long fluorescence lifetimes of the doped ions. It was further concluded that the phonon energy of the molecular network of the glasses does not affect the fluorescence properties of the doped samples. The mechanical properties such as Young's modulus, Vickers hardness, and fracture toughness generally increase with increasing field strength of the network modifier ion for constant stoichiometric ratios of the glass components. The lowest potential thermal stress values were found for zinc and magnesium aluminosilicate glasses, which also have relatively high field strengths. Taking all these facts into account, a ternary lithium aluminosilicate and a mixed lithium magnesium aluminosilicate glass doped with Yb³⁺ have been prepared in high optical quality and tested with respect to their laser performance. The fluorescence lifetime values are somewhat lower than in well-established Yb³⁺-doped laser materials, such as fluoride phosphate glass or single crystalline calcium fluoride. Nevertheless, the aluminosilicate glasses show exceptionally high absorption and emission cross sections, smooth and very broad amplification profiles, as well as much better thermomechanical properties. Quantum efficiencies close to unity could be reached by consequently removing dissolved OH from the glass melt.     

Elastic Properties and Molar Volume of Rare-Earth Aluminosilicate Glasses

The elastic properties, molar volume, and glass transition temperature ( T _g) of rare-earth-containing aluminosilicate glasses were investigated in the compositions of SiO₂–LnAlO₃ and SiO₂–Ln_3/4Al_5/4O₃, where Ln is Y, La, Nd, Eu, or Yb. The molar volume decreased with decreased ionic size of the Ln³⁺ ion, and T _g and elastic moduli increased in the same order. The Yb-containing glasses showed the highest Young's modulus among all the oxide glasses, even higher than the highest value ever known for glass containing Y₂O₃, as expected from the smaller ionic radius of Yb³⁺ than that of Y³⁺. The bulk modulus was found to be almost proportional to the inverse four-thirds power of the molar volume of glasses in each composition, indicating that Ln³⁺ ions can substitute for each other without changing the glass structure except for the size of the local structure around themselves. From the comparison of these properties, the structural role of rare-earth ions in these glasses is discussed.     

Molecular Dynamics Simulations of Silicate Glasses and Melts

The application of molecular dynamics to the modeling of glasses is reviewed. Several examples are used to illustrate the value of these computer simulations in advancing our understanding of the structure of silicate glasses. The mixed alkali effect is explained in terms of structural variations in going from single alkali to mixed alkali glasses that lead to distinct environments for each type of alkali ion and also result in the smaller alkali ion becoming more tightly bound to the network. Some recent results on the structure of silicate melts are presented, and the relationship between the structures of glass and melt are discussed.     

Bridging and Nonbridging Oxygen Atoms in Alkali Aluminosilicate Glasses

Thallium-probe ion luminescence spectroscopy and X-ray photoelectron spectroscopy were used to study the structure of sodium aluminosilicate glasses. It was demonstrated that the O1s spectral envelope for these glasses is comprised of three energetically distinct peaks, two attributed to bridging oxygen atoms (Si-O-Si and Al-O-Si) and one to nonbridging oxygen atoms (Si-O-Na). Both techniques indicate that nonbridging oxygen atoms are present in all sodium aluminosilicate glasses, for which A1 /Na is < 1.     

Formation and Crystallization of Yttrium Aluminosilicate Glasses Containing Calcium Oxide

Formation of yttrium aluminosilicate glasses containing calcium oxide from batches melted at 1550°C was investigated. Densities and thermal expansion coeflcients were measured for some glasses. In a specific compositional region, crystals with a needlelike habit were observed in the glass matrix. A crystal in the form of a tubular hexagonal prism was identified as Ca₄Y₆0(Si0₄)₆.     

Aluminum Oxide Anomaly and Structure Model of Alkali Aluminosilicate Glasses

The molar volume, Vickers hardness number, and optical basicity A(Pb²⁺/CaO = 1) were measured for alkali aluminosilicate glasses of composition (1 −χ)R₂O ·χAl₂O₃· n SiO₂ in the range 0.2 < χ < 0.7 (0.25 < Al/R < 2.33). On the basis of their composition dependences, the constitution of the glasses is discussed in terms of the formation of [RalO_4/2] units in the range Al/R < 1 and that of triclusters of AlO₄ and SiO₄ units in the range Al/R > 1. The possibility of the presence of a small amount of the tricluster is proposed in the range Al/R < 1.     

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.     

Structure of High-Alkali Aluminosilicate Melts from the High-Temperature Raman Spectroscopic Data

The Raman scattering spectra of the 30Na₂O · 70(25NaAlO₂ · 75SiO₂) (mol %) melt are measured at high temperatures. A comparison of the Raman scattering spectra of the melt and the glass is carried out. It is demonstrated that, with an increase in the temperature and upon the melt–glass transition, the aluminum distribution among the anion groups characterized by different degrees of polymerization becomes more random and the melt structure is more homogeneous compared to the glass structure.     

Ferric Iron Species in Alkali Aluminosilicate Glasses During Fusion

The luminescence spectra of Fe³⁺ in alkali aluminosilicate glasses indicate that several species of Fe³⁺ are present during early stages of melting. When the glass has been heat-treated for periods of time on the order of 20 h at 1400°C, the luminescence spectra simplify to that of a single species which is interpreted as due to Fe³⁺ in the glass-forming framework.