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.     

Polarization-Dependent Birefringence in Lithium Aluminosilicate Glass

Glass and Ceramics - The formation of polarization-dependent birefringence, apparently due to the formation of nanogratings, in the bulk of lithium silicate and lithium aluminosilicate glasses...     

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   

铝硅酸盐玻璃中澄清剂的使用研究

主要针对铝硅酸盐玻璃熔化温度高、黏度大、表面张力大、澄清困难等特点,通过试验研究,探讨了适合铝硅酸盐玻璃熔制的最佳澄清剂及澄清剂的比例,对铝硅酸盐玻璃的生产具有指导性的意义。     

Molecular Dynamic Calculations of A Sodium Borosilicate Glass Structure

The structure of seven sodium borosilicate glasses was calculated using molecular dynamics. Consistent with Zachariasen's rules of glass formation, silicon and boron were found to form a continuous near-random network of SiO₄, BO₃, and BO₄ polyhedra linked to each other at corners, whereas sodium ions occupied interstitial sites only. The most probable coordination of oxygen around sodium was five. There were roughly six oxygen atoms around an oxygen, nearly independent of the glass composition. The trigonal to tetrahedral conversion of boron with the addition of sodium agreed with the NMR results. The glasses studied showed no tendency to form boroxol groups.     

无碱铝硅酸盐玻璃的应用研究

无碱铝硅酸盐玻璃是一种应用范围较广的特种玻璃。介绍了该种玻璃在高压液位计、卤素灯及无碱基片方面的应用,提出了应用中存在的问题及发展趋势。     

Nucleation and Crystallization of a Lithium Aluminosilicate Glass

An aluminosilicate glass of composition 61SiO₂6Al₂O₃10MgO6ZnO·12Li₂O·5TiO₂ (mol%) has been prepared by a melting process and investigated as far as crystallization is concerned. Glass-ceramic is easily obtained because glass shows a high tendency to crystallize starting from 700°C. The crystalline phases evolve with temperature, showing the aluminosilicates to be the main phase up to 1050°C, followed by metasilicates and silicates, some of which have lower melting points. The titanates of Mg and Zn develop from the phase-separated glass, soon after T _g, and grow to form nucleation centers for the other crystalline phases. The evolution from phase-separated glass to glass-ceramic has been followed by many thermal, diffractometric, spectroscopic, and microscopic techniques.     

Nature of Alumina in Phosphate Glass: II, Structure of Sodium Alurninophosphate Glass

We have used ²⁷Al and ³¹P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to describe quantitatively the relationships between the composition, structure, and properties of glasses in the Na₂O.Al₂O₃.P₂O₅ (NAP) system. In general, the glass properties (evaluated in part I) are most sensitive to changes in Al coordination. ²⁷ Al MAS NMR spectra reveal that octahedrally coordinated Al is most abundant in glasses with O/P ratios less than 3.5, the pyrophosphate structural limit. Tetrahedrally coordinated Al is most abundant in glasses with O/P greater than 3.5. Decreasing Al(OP)₆/Al(OP)₄ ratio generally correlates with decreasing glass transition temperature and refractive index. The compositional dependence of glass structure and properties can be qualitatively understood using a crystal chemical model based on oxygen charge balancing by the different Al and P moieties.     

Microscopic Origins of Compositional Trends in Aluminosilicate Glass Properties

Revealing and understanding the microscopic origins of the macroscopic properties of aluminosilicate glasses is important for the design of new glasses with optimized properties. In this work, we study the composition‐structure‐property relationships in 20 MgO/CaO sodium aluminosilicate glasses upon Al₂O₃‐for‐SiO₂ and MgO‐for‐CaO substitutions. We find that some properties (density, molar volume, Young's modulus, and shear modulus) are linear through the investigated range of Al₂O₃ compositions, while others (refractive index, coefficient of thermal expansion, Vickers hardness, isokom temperatures, and liquid fragility index) exhibit a change in the slope around the composition with [Al₂O₃] = [Na₂O], which is especially pronounced for the glasses containing MgO. We discuss these phenomena based on structural information obtained by NMR spectroscopy and topological considerations.     

Molecular Dynamics Simulation of the Structure and Hydroxylation of Silica Glass Surfaces

The surface structure of silica glasses has been simulated using molecular dynamics. The surface hydroxyl concentration was estimated to be 4.5/nm², based on surface defect statistics. Hydroxyl-silica potentials were developed and used to study the hydroxylation of silica surface. It is found that the energy of chemisorption of water declines in the sequence: three coordinated silicon (Si³) and non-bridging oxygen (NBO) on separate sites, Si³ and NBO on combined sites, two- and three-membered rings. Partial hydroxylation of the most reactive sites, which leads to an OH coverage of 2.5/nm², was studied. Structural relaxation after hydroxylation was observed.     

Identification of Float Glass Surfaces

Methods for identifying the lower (contacting with tin melt) and the upper (contacting with gaseous atmosphere) surfaces of float glass are considered.     

Liquid-Phase Sintering of Alumina Coated with Magnesium Aluminosilicate Glass

Densification of alumina coated with a MgO-Al₂O₃-SiO₂ (MAS) glass was investigated from 1400° to 1460°C. Spinel was observed to form at the liquid-alumina interface, whereas mullite crystallized uniformly in the liquid. Spinel and mullite crystallization kinetics were accelerated by smaller alumina particle size. Mullite and spinel crystallization retarded densification by forming a percolating network. Boron doping suppressed spinel formation, and thus alumina sintered to higher densities at low temperature. The concept of glass basicity is proposed as a useful guide for selecting dopants for low-temperature sintering.     

A Technology for Accelerated Calcination of Lithium Aluminosilicate Glass Ceramics

The results of a study of the processes of sintering and crystallization of Li-aluminosilicate glass ceramics have shown a route towards saving heat-treatment time (by a factor of 2.5 – 3.0) and power consumption without detriment to the major physicomechanical characteristics of the components produced.     

Tensile and Fatigue Behavior of Silicon Carbide Fiber-Reinforced Aluminosilicate Glass

The onset of damage accumulation in ceramic-matrix composites occurs as matrix microcracking and fiber/matrix debonding. Tension tests were used to determine the stress and strain levels to first initiate microcracking in both unidirectional and cross-ply laminates of silicon carbide fiber-reinforced aluminosilicate glass. Tension–tension fatigue tests were then conducted at stress levels below and above the matrix cracking stress level. At stress levels below matrix microcracking, no loss in stiffness occurred. At stresses above matrix cracking, the elastic modulus of the unidirectional specimens exhibited a gradual decrease during the first 10 000 cycles, and then stabilized. However, the cross-ply material sustained most of the damage on the first loading cycle. It is shown that fatigue life can be related to nonlinear stress–strain behavior of the 0° plies, and that the cyclic strain limit was approximately 0.3%.     

铝硅准二元玻璃硬度和抗碎裂性演化的结构起源

为探究准二元铝硅玻璃硬度和抗碎裂性随组分变化的结构起源,采用激光加热气动悬浮技术,制备了组分为xAl2O3·(100–x)SiO2(30≤x≤63,摩尔分数)的系列玻璃样品.利用显微维氏硬度仪对玻璃的硬度、抗碎裂性进行了详细表征.结果表明:随着Al2O3含量增加,玻璃硬度逐渐升高,于x=63时硬度最大(8.94 GPa...     

Adhesion of Nanoparticles Fouling Glass Surfaces

The fouling of glass surfaces by nanoparticles formed from corroding iron was studied. Simple experiments demonstrated that adherent films of nanoparticles were deposited by corrosion of iron particles on a glass surface and by flowing water past corroding particles and then onto a glass surface. The water collected from this experiment was found to contain about 2 parts per million (ppm) of particles 500 nm in diameter when tested by photon correlation spectroscopy. However, electron micrographs showed that the primary particles in the fouling film were 20 nm in diameter. This discrepancy was explained by a new theory of nucleation of the fouling films. The theory was confirmed by measuring the particle size of ferric hydroxide dispersions as a function of concentration and pH. It was shown that the 20 nm primary nanoparticles nucleated much larger stable aggregates (defined as nucleags), which were sensitive both to pH and to magnetic fields. In particular, as the pH rose above 6, flocculation occurred, and large unstable agglomerates were observed. The conclusion was that three types of particle could exist in the corrosion product of iron and water: nanoparticles, nucleags, and flocs.