Crystallization of a Lithium Silicate Glass-Ceramic under Pressure

A lithium silicate glass has been crystallized under increasing pressure using a constant thermal cycle in a hot isostatic press. As pressure increases, the amount of cristobalite that crystallizes decreases, the amount of quartz increases, and the total volume fraction of crystalline phases increases. Crystallization without added pressure gives a mixture of lithium metasilicate, lithium disilicate, cristobalite, and residual glass; quartz is not normally observed with atmospheric-pressure crystallization. The threshold pressure for the appearance of quartz is about 50 MPa, which is in qualitative agreement with the value obtained from thermodynamic calculation. In this glass-ceramic, quartz is favored over cristobalite at high pressures because it is more dense.     

Crystallization Kinetics of a Complex Lithium Silicate Glass-Ceramic

Volume crystallization of this glass is nucleated by Li₃PO₄. On heating from room temperature, Li₂SiO₃ appears around 650°C and then converts to Li₂Si₂O₅ around 850°C by reaction with SiO₂ from the melt. Preheating the glass at 1000°C forms larger Li₃PO₄ nuclei that promote additional crystallization of cristobalite in the 650° to 850°C range. Crystallization activation energies calculated from scan-rate dependence of DTA peaks are 270 kJ/mol for Li₂SiO₃ and 360 to 570 kJ/mol for Li₂Si₂O₅.     

硅酸铝锂组成的玻璃陶瓷烧结和结晶机理的研究

以硅酸铝锂组成的玻璃陶瓷为例，确定了在烧结过程中由结晶的无定形粉末形成的物料烧结机理，计算了该过程的活化能，同时揭示了烧结粉末的结晶机理。     

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.     

锂铝硅玻璃的研究进展

与传统的钠钙硅玻璃和高铝玻璃相比,锂铝硅玻璃具有网络结构致密、弹性模量较高和适宜两步法化学钢化等特点,被视为第三代高强玻璃基板,可用作电子信息产品盖板、航空透明器件以及舰船、特种车辆的观察窗口等。目前,锂铝硅玻璃的研究主要涉及:(1)探究锂铝硅玻璃的“组成-结构-性能”本构关系,为设计优化高性能锂铝硅玻璃提供理论指导和性能预测;(2)改进现有溢流和浮法成型方法和装备,满足大尺寸、多厚度和高尺寸精度锂铝硅玻璃成型需要;(3)研究锂铝硅玻璃的两步法化学增强方法,解决表面压应力和应力层深度同步提升难题,显著提高玻璃强度、硬度和抗跌落性能。本文基于上述三个方面综述了锂铝硅玻璃的国内外研究进展。     

锂铝硅透明微晶玻璃析晶动力学研究

本文利用经典方程(Johnson-Mehl-Avrami)分析了非化学计量的锂铝硅Li₂O-Al₂O₃-SiO₂-ZrO₂-P₂O₅透明微晶玻璃的析晶动力学,采用DSC、XRD和SEM研究了晶化温度对玻璃析晶行为的影响。结果表明:在较低的起始析晶温度下Li₂Si₂O₅和Li₂SiO₃析出,随晶化温度的升高,主晶相转变为LiAlSi₄O₁₀,Li₂SiO₃晶相消失,晶体尺寸变小,在550 nm处微晶玻璃透过率由89.3%升高到90.6%;利用Kissinger方法计算出的Li₂Si₂O₅和LiAlSi₄O₁₀的析晶活化能分别为349.5 kJ/mol和184.2 kJ/mol,平均晶体生长指数分别为3.05和1.42。     

Effect of P2O5 on the Nonisothermal Sinter‐Crystallization Process of a Lithium Aluminum Silicate Glass

Dense (~98.5%), lithium aluminum silicate glass‐ceramics were obtained via the sinter‐crystallization of glass particle compacts at relatively low temperatures, that is, 790–875°C. The effect of P₂O₅ on the glass‐ceramics' sinter‐crystallization behavior was evaluated. We found that P₂O₅ does not modify the surface crystallization mechanism but instead delays the crystallization kinetics, which facilitates viscous flow sintering. Our glass‐ceramics had virgilite (Li_xAl_xSi_3‐xO₆; 0.5 < x < 1), a crystal size <1 μm, and a linear thermal expansion coefficient of 2.1 × 10^?6°C^?1 in the temperature range 40–500°C. The overall heat treatment to obtain these GCs was quite short, at ~25 min.     

锂铝硅酸盐玻璃陶瓷抗侵蚀性的研究

列出采用三种独立的方法对锂铝硅酸盐型玻璃陶瓷(OTM-357型材料)抗侵蚀性介质作用的研究数据,表明其结果近似,而且材料的抗化学侵蚀性极高,从而使其应用范围扩大。     

硅酸铝锂组成的玻璃陶瓷强度的提高

根据研究可以得出结论，以硅酸铝锂组成的玻璃陶瓷通过在NaNO3溶液中进行离子交换可以使制品的强度得到提高。该玻璃陶瓷系按照陶瓷生产工艺，利用高浓度悬浮液以泥浆浇注法在多孔模里浇注成型，随后按照规定的热处理制度对坯体进行烧结和冷却。选择了通过离子交换使制品强度得到提高的最佳的温度—时间制度。     

Influence of Al2O3 and B2O3 on Sintering and Crystallization of Lithium Silicate Glass System

This article reports on the effect of Al₂O₃ and B₂O₃ added as dopants on the preparation of glass‐ceramics (GCs) belonging to the lithium silicate glass system. The GCs are prepared by sintering route using glass powders. The reasons for the crystallization of the metastable crystalline phase lithium metasilicate (LS) are discussed and the impact of the dopants on the thermodynamics and kinetics of crystallization is investigated. The addition of dopants modifies the thermodynamic equilibrium of the system and this change is mainly entropy driven and also slowdown the kinetics of crystallization. Differential thermal analysis and hot‐stage microscopy are employed to investigate the glass‐forming ability, sintering, and crystallization behavior of the studied glasses. The crystalline phase assemblage studied under nonisothermal heating conditions in the temperature range of 800°C–900°C in air. Well sintered and dense glass‐ceramics are obtained after sintering of glass powders at 850°C–900°C for 1 h featuring crystalline phase assemblage dominated by lithium disilicate (LS₂).     

Influence of Particle Size on Nonisothermal Crystallization in a Lithium Disilicate Glass

In this study, lithium disilicate (LS₂) glass samples with different particle sizes ranging from less than 105 to 850 μm were prepared. These specimens were inserted in a Pt‐Rh DSC crucible and heated to 850°C at different rates (? = 0.5–30 K/min) to identify their crystallization peaks. The activation energies for the overall crystallization (E) and the Avrami coefficient (n) were evaluated using different nonisothermal models. Specifically, n was evaluated using the Augis–Benett model and the Ozawa method, and E was evaluated using the Kissinger and Ligero methods. As expected, the coarse particles mainly crystallized in the volume, while surface crystallization was predominant in the samples with particle sizes of less than 350 μm. This result was confirmed through SEM analysis of the double stage heat‐treated samples. In contrast with previous studies, our results demonstrated that the activation energy decreased as the particle size increased. In addition, no clear correlation between the peak intensity (δT_p) and the particle size was observed.     

Surface Nucleation and Crystal Orientation in Lithium Silicate Glass Fibers

The effect of inorganic surface treatments on the orientation of lithium disilicate crystals formed in Li₂O·2.75SiO₂ glass fibers was studied. Glass fibers 0.5 mm and 9μ in diameter were subjected to various surface treatments at room temperature and then heated between 550O and 800°C. It was observed that metal salt solutions applied to the fiber surfaces at room temperature decreased the degree of orientation during heating only if the metal entered the glass and formed nucleation sites within the fibers. Orientation could also be decreased by removing lithium from the glass surfaces. Comparison of the crystallization characteristics of untreated and AgNO₃-treated fibers indicated that the crystallization behavior was controlled by either a growth process or a nucleation process, depending on whether the temperature was below or above 625°, respectively.     

Microstructural Studies of the Interfacial Zone of a SiC-Fiber-Reinforced Lithium Aluminum Silicate Glass-Ceramic

Transmission electron microscopy studies have been conducted on interfaces in a lithium aluminum silicate/SiC-fiberreinforced composite. In the as-processed state, interphases of amorphous C and carbides of Nb have been confirmed, with circumferential thermal debonds evident in the C layer. After heat treatment in air at 800°C, the C is found to be replaced by amorphous SiO₂, and the carbides of Nb replaced by oxides. The SiO₂ thickens with exposure time and typically contains circumferential separations. Some Mg and Al diffusion also accompanies the heat-treatment process and eventually leads to the formation of MgO and Mg silicates in the interfacial zone.     

Nanoscale Phase Separation in Lithium Niobium Silicate Glass by Femtosecond Laser Irradiation

Understanding the phase transformation in glass and the morphology of related nanostructure after femtosecond laser irradiation is of great importance for fabricating functional optics, in which glass crystallization is involved to obtain nonlinear optical properties. We report on the crystallization inside lithium niobium silicate glass induced by fs laser irradiation. Energy‐dispersive X‐ray spectroscopy coupled to scanning transmission electron microscopy (STEM/EDS) and transmission electron microscopy confirm a nanoscale phase separation whereby LiNbO₃ crystals are embedded in lamella‐shaped frames of amorphous SiO₂. The obtained nanostructure may have applications in fabricating second‐order nonlinear optical devices.     

Kinetic Studies of Crystallization of Synthetic Mica Glass

The mechanism of crystallization of a synthetic mica glass was studied on the basis of microstructures and reaction kinetics. Uniform crystallization of this glass was found to occur by a two-stage process. The glass first transformed to an intermediate pseudocrystalline phase from which mica crystals subsequently were formed. The kinetics of the reaction leading to this intermediate pseudocrystalline phase were studied quantitatively by microscopic methods. The nucleation of this intermediate phase was found to be heterogeneous. The growth of the rim of the plate-shaped intermediate phase was an interface-controlled process having an activation energy of 84 kcal per mole. The rate of growth of the intermediate phase was found to be consistent with previous relations that describe the kinetics of growth of crystals from a glass. The final mica phase initially formed at the interfaces of the intermediate phase and parent glass phase; later it progressively formed within the intermediate phase.     

硅酸盐激光玻璃

结合硅酸盐激光玻璃的最新进展和应用,系统、全面地介绍了硅酸盐激光玻璃的基本结构、性质、制备和研究方法等一系列问题,总结了近年来硅酸盐激光玻璃工业发展的理论和实验基础性研究,对硅酸盐激光玻璃可能的发展方向进行了展望.     

Surface Crystallization of a Fluoride Glass

Growth of crystals on the surface of a Zr-Ba-La fluoride glass was observed by optical and scanning electron microscopy. Small, dark crystals nucleated rapidly and grew to a size of ∼10 μm; then they stopped growing, and wrinkled regions emerged, covering the entire crystal surface .