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.     

Na+浓度对化学增强钠铝硅酸盐玻璃性能的影响

熔盐中少量的Na⁺并不会对玻璃的离子交换效果产生明显影响,但当熔盐中Na⁺浓度不断增大时,化学增强钠铝硅酸盐玻璃的性能开始受到影响。本文采用一步法离子交换工艺研究了熔盐中Na⁺浓度对不同厚度化学增强钠铝硅酸盐玻璃表面压应力、应力层深度和弯曲强度等性能的影响。研究表明:熔盐中Na⁺浓度不断增大时,化学增强钠铝硅酸盐玻璃的表面压应力、弯曲强度下降;弯曲强度下降最多可达175 MPa,此时玻璃的表面压应力下降了57.4 MPa;熔盐中Na⁺浓度变化未对化学增强钠铝硅酸盐玻璃的应力层深度和可见光透过率产生明显影响。     

Structure of Rhenium-Containing Sodium Borosilicate Glass

A series of sodium borosilicate glasses were synthesized with KReO₄ or Re₂O₇, to 10,000 ppm (1 mass%) target Re, to assess effects of large concentrations of rhenium on glass structure and fto estimate solubility of ⁹⁹Tc, a radioactive component in low active waste nuclear glasses. Rhenium was used as a surrogate for ⁹⁹Tc for laboratory testing, due to similarities in chemistry, ionic size, and redox. Magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, and Raman spectroscopy were performed to characterize the glasses. Si was coordinated in Q² and Q³ units, Al was four-coordinated, and B was mostly three-coordinated. The rhenium additions did not have significant effects on the glass structure up to approximately 3000 ppm Re by mass, the maximum concentration that remained dissolved in glass. Rhenium likely exists in isolated anions in the interstices of the glass network, as evidenced by polarized Raman spectrum of the Re glass in the absence of sulfate. Analogous to in similar glasses, is a network modifier and above solubility forms alkali salt phases on the surface and in the bulk. Comparisons of phase separation and crystallization in containing borosilicate glasses can also be made to containing glasses.     

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...     

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。     

高铝硅酸盐玻璃的复合澄清剂研究

通过高温观测系统,研究了澄清剂SnO2、CeO2和Na2SO4在高铝硅酸盐系统中的作用温度,并根据高温观测研究结果选用两组复合澄清剂进行对比,讨论了复合澄清剂对澄清效果的影响,分析了玻璃澄清过程中气泡数量和尺寸的变化规律.结果显示:三种澄清剂在高铝玻璃中的作用温度均略低于普通钠钙硅,采用SnO2和Na2SO4作为复合澄清剂时形成的梯度澄清比SnO2和CeO2组合形成的协同澄清作用更明显,澄清效果良好.     

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   

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.     

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.     

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.     

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.     

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.     

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%.     

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.