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.     

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.     

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.     

Formation and Crystallization in the Yttrium Aluminosilicate Glasses Containing Zinc Oxide

Formation of yttrium aluminosilicate glasses containing zinc oxide from batches melted at 1550°C was investigated. Densities, thermal expansion coefficients, and Vickers hardnesses were measured for some glasses. In a specific compositional region, crystals with a convex and pyramidal habit were observed on the glass surface. The crystal was identified as ZnAl₂O₄ (gahnite) which has a Moh's hardness number of ∼8.     

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.     

Reduction in Aluminum Alloy Attack on Aluminosilicate Refractories by Addition of Rare-Earth Oxides

Several aluminosilicate compositions were tested for molten 7075 aluminum alloy attack with and without the addition of 10% Na₂CO₃. The extent of corrosion was proportional to the silica content of the refractory and especially of the matrix phase. The addition of rare earths up to 15% by weight to the aluminosilicates virtually eiiminated corrosion. Bastnasite, a rare-earth concentrate, was found to be a more effective additive at low concentrations than either CeO₂ or La₂O₃ alone in rendering the aluminosilicates corrosion resistant.     

Rare-Earth Aluminogermanate Glasses

The present study is a comparison of the properties of rare-earth aluminogermanate and rare-earth aluminosilicate glasses. Several properties have been measured, including density, transformation temperature, softening point, thermal expansion, Vickers hardness, magnetic susceptibility, Verdet constant, and IR transmission. The property data are discussed in relationship to the structure of these glasses and the field strength of the rare-earth ions. The Vickers hardness numbers of the glasses are discussed using a unique theory of hardness which involves the relationship between hardness and atom/ion packing in material structures.     

New Composite Materials Based on Nanoporous Glasses Containing Manganese Oxides

Glass Physics and Chemistry - A technique is developed and new composite materials containing manganese oxides MnxOy (x = 1, 2, 3; y = 2, 3, 4) are synthesized based on high-silica nanoporous...     

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.     

Vaporization of Rare-Earth Oxides

A study of the vaporization of La₂O₃, Nd₂O₃, and Y₂O₃ at high temperatures has been carried out by the Knudsen effusion technique. The methods employed, the results of the measurements, and the low-temperature heat capacities of these materials, which were determined for the purpose of calculating thermal functions of the oxides, are discussed. All the foregoing oxides react with tantalum, forming gaseous tantalummonoxide as a principal product. Cubic tantalates of lanthanum and neodymium are also formed in these reactions.     

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.     

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。     

Sintering Characteristics of Rare-Earth Oxides

The sinterability of europium, samarium, gadolinium, and dysprosium pure oxides was investigated at various temperatures under both oxidizing and reducing conditions as well as hot pressing. Data are presented on the density, grain size, thermal expansion, resistance to water corrosion, and the microhardness of these oxides. Photomicrographs showing grain growth and microstructure are included. The results indicate that dysprosium oxide is the most stable of the four oxides investigated. It sinters with small grain size, is similar to alumina in coefficient of thermal expansion, and does not undergo a phase transformation.     

Structural and Luminescence Studies on Barium Sodium Borosilicate Glasses Containing Uranium Oxides

Barium sodium borosilicate glasses containing different amounts of uranium oxides were prepared by conventional melt quench method and investigated for their structural aspects by ²⁹Si and ¹¹B MAS NMR technique combined with steady‐state luminescence and lifetime measurements. Based on MAS NMR studies, it is confirmed that uranium ions act as network modifier up to 15 wt% and beyond which a separate uranium containing phase is formed. From the luminescence studies, it is inferred that uranyl species is in a highly distorted environment. For more than 15 wt% uranium oxide incorporation, weaker U–O–U linkages are formed at the expense stronger U–O–Si/B linkages, as suggested by the excited state lifetime value of the uranyl species as well as red shift in emission peak maximum. For glass samples containing more than 25 wt% uranium oxides, crystalline barium uranium silicate gets phase separated from glass matrix as confirmed by XRD studies.     

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   

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.     

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.     

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.     

Degree of Polymerization of Aluminosilicate Glasses and Melts

This paper presents the results of analyzing the data available in the literature on the structure and properties of silicate glasses and melts that contain Ti⁴⁺, Al³⁺, and Fe³⁺ cations in addition to alkali and alkaline-earth cations. It is established that the aforementioned multivalent cations in glasses and melts have a coordination number of four and play the role of network-formers. Aluminosilicate glasses and melts with the mole fraction ratio Al₂O₃/M ₂(M)O = 1 are of special interest. For these glasses, the structure is considered to be completely polymerized and, contrary to traditional concepts, their properties depend on the concentration ratio Al₂O₃/SiO₂. Taking into account that the structure of aluminosilicate glasses involves unusual structural units (such as triclusters) and a certain number of nonbridging oxygen atoms, a formula is proposed for calculating the degree of polymerization. The proposed formula is used to calculate the degree of polymerization for a number of Na₂O · Al₂O₃ · mSiO₂ glasses and the CaO · Al₂O₃ · 2SiO₂ glass. It is demonstrated that the calculated degrees of polymerization correlate with the experimentally measured viscosities of the relevant melts.