Development of SiC-Whisker-Reinforced Lithium Aluminosilicate Matrix Composites by a Mixed Colloidal Processing Route

Based on the surface properties of aqueous silica, boehmite, and SiC-whisker dispersions, SiC-whisker-reinforced lithium aluminosilicate (LAS) matrix composites were fabricated by a mixed colloidal processing route. The composites were characterized by a uniform spatial distribution of SiC whiskers throughout the matrix. The fracture toughness increased from 1.3 MPa.m^1/2 for the LAS specimen to 5.0 MPa.m^1/2 for the hot-pressed composite (950°C and 20 MPa for 20 min) containing 20 wt% SiC whisker. The increase in fracture toughness appears to result mainly from crack deflection and crack bridging by whiskers with some additional toughenings from load transfer and whisker pullout.     

Fracture Behavior of SiC-Whisker-Reinforced Barium Aluminosilicate Glass-Ceramic Matrix Composites

Barium aluminosilicate (BAS) glass-ceramic composites reinforced with various volume percents (0, 10, 20, 30, 40 vol%) of SiC whiskers were fabricated by hot pressing. The microstructure, the whisker/matrix interface structure, the phase constitution, and the mechanical properties of the composites were systematically studied by means of SEM, TEM, and XRD techniques as well as by indentation crack microfracture and single-edge-notched-beam bend testing. It was demonstrated that the incorporation of SiC whiskers could significantly increase the flexural strength and fracture toughness of BAS glass-ceramic matrices. The addition of active Al₂O₃ to the BAS matrix reduced the amount of SiO₂ in the matrix, forming needlelike mullite, which further improved the mechanical properties.     

Internal Friction in Lithium Aluminosilicate Glass-Ceramics

This paper describes the results of an investigation of the anelastic behavior of two glass-ceramic materials with similar compositions, one nucleated with TiO₂ and the other with ZrO₂. The influence of the grain size, residual glass fraction, and composition was examined. A low-frequency torsion pendulum was constructed for this purpose. The as-received TiO₂-nucleated. Corning Code 9608 ceramic exhibits an attenuation peak at about 750°C; when heat-treated at 1200°C for 167 h, the attenuation peaks at approximately 850°C. The ZrO nucleated glass-ceramic showed no such peak. Our results indicate that this anelastic behavior is due to grain boundary sliding, but the rates and magnitude of sliding are strongly dependent on boundary chemistry.     

Intensified Sintering of Lithium Aluminosilicate Ceramics

Experimental data are presented showing that the sintering of lithium aluminosilicate-based glass ceramics, produced by ceramic technology, can be accelerated by adding 0.1 – 0.7% Cr₂O₃, without detriment to the product quality.     

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...     

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.     

Fatigue Resistance of a Lithium Aluminosilicate Glass-Ceramic

The resistance to delayed failure of a lithium aluminosilicate glass-ceramic was measured by dynamic fatigue experiments on abraded samples in the as-formed glassy state and after various stages of heat treatment. Heat treatment was varied in a controlled manner to give microstructures of high quartz and keatite with small and large grain size. The glassy state was most susceptible to delayed fatigue, and the keatite state the least. The increase in fatigue resistance of the ceramic phases is attributed to the crystalline structure having a lower reactivity with water.     

Alumina Region of the Lithium Aluminosilicate System: A New Window for Temperature Ultrastable Materials Design

Revisiting classic phase diagrams and chemical phase relations in the solid state of a very well‐studied oxide system, such as the lithium aluminosilicate (LAS) system, can open a new window for the design of new advanced materials with improved properties. Crystal chemistry and phase equilibria are used to demonstrate the ability to design materials with particular desired properties in the alumina‐rich corner of the LAS phase diagram. The experimental results demonstrate the alumina and β‐eucryptite solid‐state compatibility.     

Mechanism of Oxide Nucleation in Lithium Aluminosilicate Glass-Ceramics

A commercial lithium aluminosilicate glass-ceramic material is investigated by high-resolution transmission electron microscopy after different heat treatments. Evidence is presented that epitaxy of β-quartz crystals on ZrTiO₄-type crystallites is the critical step initiating silicate crystallization.     

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.     

Mechanical Properties of a Lithium Disilicate Strengthened Lithium Aluminosilicate Glass‐Ceramic

A glass composition in the Li₂O–Al₂O₃–SiO₂ (LAS)‐ternary phase diagram is presented, which enables the crystallization of Li₂Si₂O₅ as well as LiAlSi₂O₆ upon a well‐defined heat treatment. Li₂Si₂O₅ is the minor crystalline phase in the glass‐ceramic and generates through the bulk strengthening of the LAS glass‐ceramic. A flexural strength as higher as 400 MPa is measured in the proposed glass‐ceramic formulation, thus outperforming conventional LAS‐glass‐ceramics. A combination of the presence of those two crystalline phases of very different mechanical properties and coefficient of thermal expansion as well as the microstructure are believed to contribute largely to the enhancement of the measured properties.     

Silicon Carbide/Calcium Aluminosilicate: A Notch-Insensitive Ceramic-Matrix Composite

Tension experiments performed on a 0/90 laminated silicon carbide/calcium aluminosilicate composite at room temperature establish that this material is notch insensitive. Multiple matrix cracking is determined to be the stress redistribution mechanism. This mechanism is found to provide a particularly efficient means for creating local inelastic strains, which eliminate stress concentrations.     

锂铝硅透明微晶玻璃的发朦现象研究

锂铝硅透明微晶玻璃的发朦现象研究陈建华，孙方明（盐城工业专科学校２２４００３）（华东理工大学２００２３７）ＳｔｕｄｙｏｎＨａｚｅｄＳａｍｐｌｅｓｏｆＴｒａｎｓｐａｒｅｎｔＬｉｔｈｉｕｍＡｌｕｍｉｎｏｓｉｌｉｃａｔｅＧｌａｓｓ－Ｃｅｒａｍｉｃｓ￥Ｃｈｅ...     

SiC晶须加强的高铝质耐火材料

叙述了在采用SiC晶须加强的高铝质耐火材料生产过程中的处理参数。通过修改处理参数，诸如铝矾土的平均粒度、SiC晶须的含量以及在成型期间施加的压力可以提高断裂韧性。     

新型铝硅酸盐基多孔陶瓷材料合成工艺研究

以粉煤灰、固体燃料以及少量黏结剂为主要原料,采用KAl(SO4)2·12H2O和碱性激发剂作为Al2O3的前驱体,通过溶胶-凝胶法对粉煤灰粉体进行表面包覆改性,在原灰表面形成无定型态Al(OH)3溶胶提高了原粉煤灰的表面活性,由于降低了原灰颗粒的表面能,从而降低了样品烧结温度.借助Zeta电位分析仪(Brookhaven Instruments Corp,USA)分析粉煤灰改性前后表面所带电荷(ξ电位)随pH值变化情况,确定了改性处理化学反应体系最佳pH范围是7.8～8.1;探讨了制备工艺对改性后粉煤灰颗粒表面ξ电位和分散体系性能的影响.借助TGA-DSC分析和XRD分析研究了粉体热处理过程中的相变化,确定了改性粉煤预处理制度以及粉煤灰制备样品的热处理制度.     

Crystallization Kinetics and Mechanism of Low-Expansion Lithium Aluminosilicate Glass-Ceramics by Dilatometry

The crystallization kinetics and mechanism of a precursor glass of lithium aluminosilicate (LAS)-based commercial low-expansion glass-ceramics were investigated using a dilatometer. The isothermal crystallization behavior of β-quartz solid solution (ss) was found to obey the Avrami equation. Nonisothermal crystallization data were analyzed by the Ozawa method and modified Kissinger equation. The value of the Avrami exponent ( n ) was ∼1.5, and the apparent activation energy ( E _a) was ∼500 kJ/mol, which was close to that of the diffusion of silicon and aluminum ions as well as metal–oxygen bond strengths, suggesting a three-dimensional (3D) diffusion-controlled reaction mechanism.     

氧化锆对锂铝硅酸盐玻璃化学强化性能的影响

采用熔融淬冷法制备了含不同摩尔分数Zr O₂的锂铝硅酸盐玻璃,通过两步化学强化法对玻璃样片进行了化学强化,研究了Zr O₂对玻璃的稳定性、硬度和化学强化效果的影响。结果表明:随着Zr O₂的摩尔分数从0增加至5%,玻璃化转变温度随之升高,玻璃稳定无析晶现象。引入适量的Zr O₂会促进Li⁺-Na⁺离子交换,提高应力层深度,表面压应力随着Zr O₂浓度的增加而增加,并在摩尔分数为4%时达到最大值,为1 055.6 MPa。中心张应力随着Zr O₂浓度的增加先增加后缓慢减小,表明该系列样品具有较好的抗冲击能力。Zr O₂的浓度变化对强化后玻璃的硬度影响较小,在引入Zr O₂后其抗裂性有所降低,但仍具有较好的抗裂能力。     

零膨胀锂铝硅透明微晶玻璃的研究与应用现状

外界温度的剧变,易在材料中产生热应力,导致材料失效.零膨胀锂铝硅透明微晶玻璃卓越的热学性能,优良的光学和机械性能使之成为不可或缺的综合材料.主要介绍零膨胀LAS系透明微晶玻璃的主要形态和结构特征,热学、光学性能以及应用现状,并提出了研究中存在的问题及今后发展的方向.     

超低膨胀锂铝硅透明微晶玻璃的研究与应用现状

环境温度的变化,会引起材料的膨胀与收缩,在材料中产生热应力,会影响材料使用。零膨胀锂铝硅透明微晶玻璃卓越的热学性能,优良的光学和机械性能使之成为不可或缺的综合材料。本文主要介绍了零膨胀LAS系透明微晶玻璃的主要形态和结构特征,热学、光学性能以及应用现状,并提出了研究中存在的问题及今后发展的方向。