Estimated immiscibility isotherms of the Li2O-Al2O3-SiO2 system

Using the immiscibility temperature estimation method, recently developed by the present author and Tomozawa, immiscibility isotherms of the Li₂O-Al₂O₃-SiO₂ system were estimated. High reliability of the estimated immiscibility isotherms was confirmed by observing the morphologies of phase-separated glasses, and also by comparing the estimated and observed immiscibility temperatures at several compositions. The determined immiscibility isotherms revealed that, in the Li₂O-Al₂O₃-SiO₂ system, only composition regions near the Li₂O-SiO₂ and Al₂O₃-SiO₂ binary edges are phase-separable. In composition regions where base glasses for commercial glass-ceramics are located, the immiscibility temperatures were much lower than the glass transition temperatures, implying that no phase separation actually occurs. Accordingly the phase separation in practical glasses for producing glass-ceramics may be attributed to increased immiscibility resulting from various additives.     

CaO-Al2O3-SiO2系黑色装饰微晶玻璃的研究

为了研究制备黑色装饰微晶玻璃,使用Fe2O3、Ni2O3、Co2O3等着色剂,研究了其对微晶玻璃装饰板材的颜色、烧结和晶化性能的影响规律,确定合理的着色剂种类、含量以及热处理制度,并利用XRD与SEM等技术研究了黑色装饰微晶玻璃的结构.研究表明:以Fe2O3、Co2O3组合和Fe2O3、Co2O3、Ni2O3的组合都可制得黑色系列玻璃与花纹清晰的黑色微晶玻璃;100g玻璃配合料中,较合理的着色剂用量为:Fe2O33～5g,Co2O30.15～0.25 g,Ni2O30.2～0.4 g.     

亚微米Li2O-Al2O3-SiO2微晶玻璃制备

本文利用DTA、XRD和SEM对Li2O-Al2O3-SiO2(以下简称LAS)微晶玻璃核化晶化热处理制度及氟离子在该玻璃体系中的作用进行研究.通过分析得出:含氟LAS玻璃核化温度和晶化温度分别为620℃和710℃,比相同组份的不含氟Li2O-Al2O3-SiO2玻璃核化、晶化温度分别降低了40℃和160℃左右;引入氟离子明显降低LAS玻璃析晶温度,系统的活化能降低约54kJ/mol,当含氟LAS玻璃的核化时间为1h、晶化时间为4hrs,平均微晶颗粒尺寸在50nm左右.     

The crystallisation of glasses based on eutectic compositions in the system Li2O-Al2O3-SiO2

Structural transformations have been studied in glasses related in composition to the binary eutectic between lithium metasilicate and -spodumene. Crystallisation processes and changes in microstructure during the controlled heating of the glasses have been followed using X-ray diffraction, electron microscopy, high temperature microscopy, thermal analysis and electron spin resonance spectroscopy.The influence exerted by titanium dioxide on the phase relationships, crystal growth rates and micromorphology of the polycrystalline products of heat-treatment has been investigated and the findings used as a basis for proposals on the rôle of TiO₂ during nucleation and crystal growth.     

B2O3-Al2O3-SiO2系微晶玻璃析晶动力学研究

采用差示扫描量热（DSC）分析法对B2O3-Al2O3-SiO2系统微晶玻璃的析晶动力学参数进行了测定，研究了该系统微晶玻璃的析晶动力学。结果表明：随着B2O3/SiO2比的降低，该系统玻璃的析晶活化能E呈先升高后降低的变化趋势，当B2O3/SiO2比为11：5时，析晶活化能最小，Emin=375．4kJ／mol，晶化指数n则先减小后增大，但均〉4，表明该系统玻璃可整体析晶。     

B2O3-Al2O3-SiO2透明玻璃陶瓷研究

玻璃陶瓷属于一类多晶陶瓷材料.通过调整玻璃基质和晶相组成可以制备出具有良好的力学、热学、电学和光学性能的玻璃陶瓷材料.采用传统的熔融和退火技术制备出含B2O3-Al2O3-SiO2-Li2O-K2O组分的硼铝硅玻璃,并通过成核和长晶工艺最终制备出透明玻璃陶瓷.配合料在铂金坩埚中于1450℃下熔融2h,然后经两步热处理制度控制晶核的生成和晶粒的长大.采用差热分析技术确定成核和长晶温度.采用X射线衍射技术对不同热处理制度下的玻璃陶瓷样品进行分析,以确定最佳成核和长晶条件.采用扫描电子显微镜分析玻璃陶瓷形态,晶粒尺寸及其在残余玻璃相中的分布.采用UV-Vis-Nir分光光度计测定玻璃陶瓷样品的透过率.     

The crystallisation of glasses based on the eutectic compositions in the system Li2O-Al2O3-SiO2

A study has been made of the crystallisation of glasses based on the eutectic between lithium metasilicate and-eucryptite and of the rÔle of TiO₂ in promoting fine-grained crystallisation. The hypothesis advanced in part 1 of this work is extended to a semi-quantitative measure of the effect of TiO₂.Characteristics of two metastable phases are described in an appendix.     

La3+、Nd3+稀土离子掺杂对电路基板用锂铝硅微晶玻璃性能的影响

通过烧结法制备La3+和Nd3+掺杂的锂铝硅微晶玻璃,结合DSC、密度、热膨胀、SEM等检测技术研究了热处理和稀土离子掺杂对LAS微晶玻璃力学和电学性能的影响。结果表明:在640℃核化保温30min、940℃晶化保温2.5h可得到晶粒细小、力学强度和介电性能优良(ε=5.1～7.0,tanδ<0.005,10MHz),的微晶玻璃。同时稀土离子的加入产生的钉扎作用可以细化晶粒,进一步优化提高微晶玻璃的力学性能。     

Novel low-temperature synthesis of glasses and glass-ceramics in the B2O3-SiO2-P2O5 system

In recent years considerable progress has been made in electronic packaging substrate technology. The future need of miniaturization of devices to increase the signal processing speed calls for an increase in the device density requiring the substrates to be designed for better thermal, mechanical and electrical efficiency. Fast signal propagation with minimum delay requires the substrate to possess very low dielectric constant. Several glasses and glassceramic materials have been identified over the years which show good promise as candidate substrate materials. Among these, borophosphate and borophosphosilicate glass-ceramics have been recently identified to have the lowest dielectric constant (3.8). Sol-gel processing has been used to synthesize borosilicate, borophosphosilicate and borophosphate glasses and glass-ceramics using inexpensive boron oxide and phosphorus pentoxide precursors. Preliminary results of the processing of these gels and the effect of volatility of boron alkoxide and its modification on the gel structure are described. X-ray diffraction, differential thermal analysis and Fourier transform-infrared spectroscopy have been used to characterize the as-as-prepared and heat-treated gels.     

High-temperature glass-ceramics of the BaO-Al2O3-SiO2-Ta2O5 system and molybdenum metal composites

Glass-ceramics which consist of tantalum pentoxide (Ta₂O₅), hexacelsian (BaO·Al₂O₃· 2SiO₂), and aluminium tantalate (Al₂O₃·Ta₂O₃) are described. These glass-ceramics can form refractory composites up to 1400° C with molybdenum metal. The glass-ceramics and metal have compatible physical and chemical properties which allow close thermal expansion and excellent bonding.     

F-离子对Li2O-Al2O3-SiO2系微晶玻璃晶化的影响

采用差热分析(DTA),X射线衍射分析(XRD),扫描电镜(SEM等分析手段研究了F-离子对Li₂O-Al₂O₃-SiO₂系微晶玻璃形核和晶化的影响.结果发现,引入F^-离子使得玻璃的析晶峰值温度降低,玻璃的析晶活化能E降低,晶化指数n加大.引入F^-离子后,一方面促进了玻璃析晶和晶化,Li_xAl_xSi_1-xO₂固溶体析出以及Li_xAl_xSi_1-xO₂固溶体向β-锂辉石固溶体转变加快,晶化后的晶粒尺寸加大,析晶活化能E,晶化指数n与扫描电镜(SEM)分析一致.表明F-离子促进了玻璃晶化和离子扩散.     

Toughened glass-ceramics in the ZrO2-Al2O3-SiO2 system prepared by the sol-gel process

Monolithic glass-ceramics containing Al₂O₃ or TiO₂ were prepared in the ZrO₂-SiO₂ system by the sol-gel process from metal alkoxides. Tetragonal ZrO₂ was precipitated by heat treatment at 900–1200 °C and its crystal growth was increased by adding TiO₂ or Al₂O₃. Further heating at higher temperature resulted in the precipitation of zircon and monoclinic ZrO₂ which was transformed from tetragonal ZrO₂. The addition of Al₂O₃ had less effect on both the tetragonal-to-monoclinic ZrO₂ transformation and the precipitation of zircon. The fracture toughness increased as the size of tetragonal ZrO₂ particles increased and then decreased with the appearance of monoclinic ZrO₂ or zircon. The fracture toughness of the glass-ceramics was measured in the glass-forming regions of the ZrO₂-Al₂O₃-SiO₂ system. The fracture toughness was sensitively dependent on both Al₂O₃ and ZrO₂ content, of which the highest value achieved was 9 MPa m^1/2 for the 50ZrO₂·10Al₂O₃·40SiO₂ composition.     

Preparation and crystallization of ultrafine Li2O-Al2O3-SiO2 powders

Ultrafine powders of Li₂O-Al₂O₃-SiO₂ (LAS) glass-ceramic were prepared by the sol-gel process using tetraethoxysilane, titanium butoxide, lithium, magnesium, aluminium (and zinc) inorganic salts as starting materials. The effect of pH on the sol-gel transition and particle sizes of the Li₂O-Al₂O₃-SiO₂ system was studied. The nucleation and crystallization process of LAS powders were also investigated by differential thermal analysis and X-ray diffraction. The results show that a surface nucleation process occurs for ultrafine LAS powders. The LAS glass-ceramics fabricated from ultrafine LAS powders have a low thermal expansion coefficient, <10×10^–7 °C.     

Microstructure and grain growth in Li2O-Al2O3-SiO2 glass ceramics

Microstructure and grain growth were studied in two glass ceramics of the Li₂O-Al₂O₃-SiO₂ system, one an experimental material of basic composition Li₂O-Al₂O₃-4SiO₂ and the second a commercial material of approximately 0.7Li₂O-Al₂O₃-6SiO₂ composition with small amounts of other oxides. There was evidence from transmission electron microscopy that the commercial material contained residual glass at grain-boundary triple points and glass layers at some but not all grain boundaries. No definite evidence was found for residual glass in the experimental material. The composition of secondphase regions in the commercial material was studied by STEM microanalysis. Al-rich regions of irregular morphology were found but there was no evidence that residual glass was SiO₂-rich, as has been previously suggested for this type of glass-ceramic. Grain growth showed a fairly similar time dependence in the two materials with growth more rapid in the commercial material at a given temperature. It is suggested that grain growth is controlled by precipitate particles rather than by residual glass phase.     

The dielectric properties of certain ZnO-Al2O3-SiO2 glass-ceramics

An original study has been made of the influence of additions of alkaline-earth metal oxides (CaO, SrO, BaO) at the expense of ZnO on the dielectric properties of certain ZnO-Al₂O₃-SiO₂ glass-ceramics. Tests were carried out at 20° C at frequencies of 10⁵ to 10¹⁰ Hz and at temperatures up to 400° C at a frequency of 9.37 × 10⁹ Hz. X-ray diffraction analysis showed that the major crystalline phase in all cases was Zn₂SiO₄ and this was little changed in proportions or lattice parameters by the additions. Some changes in secondary crystal phases were noted but no positive identification of crystals containing Ca²⁺, Sr²⁺ or Ba²⁺ was made. It is concluded that the alkaline-earth metal ions are essentially contained in the residual glassy phase and that the major contribution to the dielectric losses is by the residual glassy phase. Increase in the BaO content causes a loss peak to move to lower frequencies (in the range > 10¹⁰ to 10⁸ Hz) and this is believed to be partly due to the BaO additions rendering the network of the residual glassy phase more open, and partly due to the heavy mass of the Ba²⁺ ions. A similar effect was not observed for additions of CaO and SrO. Furthermore, it appears that the alkaline-earth metal oxide additions are restricting deformation of the network of the residual glassy phase.     

Na_2O－Al_2O_3－SiO_2系统霞石微晶玻璃机械强度的研究

霞石微晶玻璃是一种高强度的新型无机非金属材料．本文以Ｎａ２Ｏ－Ａｌ２Ｏ３－ＳｉＯ２系统为基础，引入晶核剂和复合澄清剂，经高温熔制和两步热处理制备的霞石微晶玻璃，具有较高的抗压和抗折强度．结果表明，霞石微晶玻璃的机械强度与霞石晶体及试样的结构有关，也与微晶化热处理的时间有关。     

形核剂对Li2O-Al2O3-SiO2系微晶玻璃晶化过程的影响

采用差热分析(DTA),X射线衍射分析(XRD),扫描电镜(SEM)等分析手段研究了 TiO₂和TiO₂+ZrO₂两种形核剂对Li₂O-Al₂O₃-SiO₂(LAS)系微晶玻璃的形核和晶化的影响. 结果发现,样品经过不同温度的预形核处理后,采用TiO₂单一形核剂,晶化峰值温度和晶化峰 高度的变化较大,而采用TiO₂+ZrO₂复合形核剂,晶化峰值温度和晶化峰高度的变化较小. 当形核时间为2h,两种形核剂样品的最佳形核温度分别为745和760℃.晶化后均可得到纳米 结构的β-石英石固溶体晶相,其中采用TiO₂+ZrO₂复合形核剂样品的晶粒更细小.研究表 明采用复合形核剂的LAS微晶玻璃的形核过程对温度的敏感性小,有利于对形核过程进行控 制,同时形核效率高.     

Microstructural characterization of grain-oriented glass-ceramics in the system Ba2 TiSi2O8-SiO2

In polycrystalline fresnoite, advantage of the piezo- and pyroelectric properties can be taken only if texturing along its polar [0 0 1]-axis can be achieved. We report on a novel technique to prepare grain-oriented glass-ceramics in the system fresnoite-SiO2 by electrochemically induced nucleation. Optimum conditions for grain orientation were determined by characterizing the microstructure of glass-ceramics prepared at 1150, 1200 and 1350 °C using electron microscopy and X-ray texture goniometry. At 1150 °C—due to the smallest crystal growth rate and highest nucleation rate—the most distinct orientation is obtained. The solidification of the glass-ceramic consist of three subsequent steps. First, dendritic fresnoite crystallizes most rapidly along its [0 0 1]-axis with [1 1 0] facet planes. Due to growth selection, the polar {c}-axes become oriented. Secondly, within the interdendritic areas, the pseudo-binary eutectic fresnoite-silica solidifies lamellarly. Finally, in the middle of the interspaces, a crystalline barium silicate coexisting with glassy silica is formed at 1200 °C and 1350 °C. At 1150 °C, however, a glass with the composition of the melt solidifies.