Sinterable β-Spodumene Glass-Ceramics

β-Spodumene glass-ceramic compositions were melted and studied. Compositional variations were made in the three major components as well as through minor additions of other oxides. Sintering characteristics and microstructures were studied and values for crystallization temperature, melting temperature, and crystallized thermal expansion coefficient were recorded. It was found that sinterable β-spodmene glass-ceramics could be made with a wide range of properties. Selection of an appropriate composition would be based on desired properties.     

Properties of Nitrogen-Containing Yttria—Alumina—Silica Melts and Glasses

The viscosity and solubility of nitrogen in Y₂O₃–Al₂O₃–SiO₂ melts have been systematically examined. The effects of nitrogen content on viscosity for Y-Al-Si-O-N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y₂O₃–Al₂O₃–SiO₂ melts was decreased, the solubility of nitrogen into the melts was increased with increased Y₂O₃ content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y₂O₃ content increased. The viscosity of Y-Al-Si-O-N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross-linking produced a more rigid glass network.     

Preparation of Whisker β-Spodumene Glass–Ceramics

β-spodumene glass–ceramics with a whisker-like microstructure were prepared from the following materials (in wt%): 64.5 SiO₂, 18.0 Al₂O₃, 4.2 Li₂O, 4 ZrO₂, and 8 MgF₂. Scanning electron microscope (SEM) analysis showed that phase separation in the base glass leads to the formation of a primary crystal phase of MgF₂ that promotes the formation of spherical β-spodumene. Whisker spodumene crystals surrounded by spherical crystals are observed at 720°C after 1 h, and the whisker crystals grow at the cost of spherical crystals with increasing temperature and time. The flexural strengths of the glass–ceramics reach a maximum of 228 MPa after heat treatment at 850°C for 1 h.     

Mullite–β-Spodumene Composites from Aluminosilicates

Sintering studies were conducted using kaolin, metakaolin, zeolite 4A, and various synthetic mixtures of Al₂O₃ and SiO₂ in the presence of Li₂CO₃ and LiCl as fluxing agents. Various compositions of the above were prepared, and conventional sintering studies were conducted at temperatures of 900°–1450°C with soaking periods of 1–3 h. Kaolin, metakaolin, and amorphized kaolin in the presence of Li₂CO₃ showed nucleation centers of β-spodumene as pink specks, whereas synthetic mixtures of Al₂O₃ and SiO₂ failed to behave in the same manner. To determine whether the pink specks formed were color centers or F centers, the samples were subjected to UV, IR, and X-ray irradiation; however, the samples showed no tenebrescence properties. External addition of iron as an impurity in a nonlayered system also resulted in pink speck formation. This observation indicated that impurities present in the natural kaolin were the cause of this phenomenon. Moreover, the LiCl-based samples did not result in pink specks, even though the kaolinitic samples contained iron as an impurity. Therefore, although β-spodumene was formed in aluminosilicates in the presence of Li₂CO₃ and LiCl, the pink variety of β-spodumene (kunzite) formation occurred only in the presence of lithium-rich aluminosilicates and in the presence of iron as an impurity. The phase identification and microstructure were explained based on XRD, DTA, and SEM studies.     

Influence of Hydrostatic Pressure and Humidity on Superplastic Ductility of Two β-Spodumene Glass-Ceramics

The extent of superplastic deformation in two lithium aluminosilicate glass-ceramics was found to be limited either by intergranular cavitation or by the initiation and growth of surface cracks. Tensile tests were performed under a superimposed hydrostatic pressure to distinguish between the two failure mechanisms. Two materials, one with a high flow stress and the other with a low flow stress, were studied. Cavitation was substantially suppressed by hydrostatic pressure in both materials. The strain-to-fracture, however, was enhanced only in the material with the lower flow stress. (In at least one instance the tensile ductility became almost infinite.) In the material with the higher flow stress, failure was caused by the initiation and propagation of cracks from the surface. The crack-propagation mode of failure was found to be sensitive to humidity, raising the possibility of stress-corrosion cracking at high temperatures in glass-ceramic materials.     

Joining of Calcium Phosphate Invert Glass-Ceramics on a β-Type Titanium Alloy

A bioactive calcium phosphate invert glass-ceramic containing β-Ca₃(PO₄)₂ crystals could be joined strongly with a Ti–29Nb–13Ta–4.6Zr alloy consisting of a β-titanium phase by heating the metal on which the mother glass powders with a composition 60CaO·30P₂O₅·7Na₂O·3TiO₂ (mol%) were placed, at 800°C for 1 h in air; the tensile joining strength was estimated to be ∼26 MPa on average. A compositionally gradient layer was developed on the metallic substrate during the heating. When the metal with glass powders on it was heated at 850°C in air, the phosphate glassy phase flowed viscously, permeating the oxide layer formed around the surface of the metal, which was thicker than that formed by heating at 800°C; a compositionally gradient layer was not developed, and a strong joining was not realized. The joining between the glass-ceramic and the metal is suggested to be controlled by viscous flow of the glassy phase in the glass-ceramic and by reaction of the glassy phase with the oxide phase formed around the surface layer of the metal.     

用工业废渣赤泥研制微晶玻璃

本研究利用山东铝业公司固体废弃物赤泥、粉煤灰、煤矸石等为主要原料,制备了装饰材料用微晶玻璃。探讨了微晶玻璃的热处理工艺制度及晶核剂对核化、晶化的影响。采用TG-DTA、XRD、SEM等测试技术测试了样品的理化性能和微观结构。     

Thermal Expansion of Synthetic β-Spodumene and β-Spodumene—Silica Solid Solutions

Synthetic β-Spodumene and several β-Spodumene-silica solid solutions were prepared, and their thermal expansion behavior was studied using high-temperature X-ray diffraction techniques. Data indicate that all β-Spodumenes are characterized by a pronounced anisotropy of thermal expansion much the same as that of the silica polymorph keatite. Anisotropy increases slightly and the volume expansion decreases as the compositions become richer in SiO₂. Specimens with more than 80.8 wt% SiO₂ at 130O°C and 1 atm contain P-cristobalite along with β-Spodumene. The lattice parameters of β-Spodumene compositions throughout the solid solution range were determined. The structural aspects of the anisotropy of thermal expansion are discussed.     

以宝钢矿渣为主要原料制备微晶玻璃

阐述了我国炼钢矿渣尚未得到充分利用和处理的现状,并从原料配方、工艺过程和材料性能三方面介绍了利用矿渣制备微晶玻璃的方法.     

Kinetics of Dissolution and Crystallization in a β-Spodumene Glass-Ceramic

The kinetics of partial melting in a β-spodumene glass-ceramic was measured by holding fully crystallized material above the solidus but below the liquidus temperature. The kinetics was apparently limited by the rate of diffusion of silica in the crystalline phase. The measured lattice diffusivity of silica was 8×10⁻¹⁰ exp(-251 kJ mol⁻¹ /RT ) m² s⁻¹ with a possible error of ±60 kJ mol⁻¹ in the activation energy. The partially molten samples were heat-treated below the solidus to obtain the kinetics of crystallization, which was found to be interface-reaction-controlled.     

废玻璃粉反应析晶制备枪晶石玻璃陶瓷性能研究

将废玻璃粉与钙铝黄长石、氟化钙混合,使用反应析晶烧结法制备出主晶相为枪晶石的玻璃陶瓷.研究了钙铝黄长石和氟化钙含量、烧结温度对玻璃陶瓷晶相、相对密度、烧结率、吸水率及力学性能的影响.结果表明,加入15％(质量分数,下同)钙铝黄长石和6％氟化钙时,玻璃陶瓷中析出的主晶相为枪晶石.提高钙铝黄长石或氟化钙含量有硅灰石析出.在850℃和900℃烧结后,玻璃陶瓷的相对密度和烧结率都随钙铝黄长石或氟化钙含量的升高而降低,其中,提高氟化钙含量比提高钙铝黄长石含量对烧结阻碍作用更大;吸水率随钙铝黄长石或氟化钙含量的升高而升高;玻璃陶瓷的强度随钙铝黄长石或氟化钙含量提高而降低,随温度升高而变大.和850℃相比,900℃烧结后,枪晶石玻璃陶瓷的强度最大可提高51％.     

Crystallization and Chemical Strengthening of Stuffed β-Quartz Glass-Ceramics

Metastable solid solutions with the β-quartz structure can be crystallized from most glasses in the system SiO₂-Mg(AlO₂)₂-LiAlO₂ as well as from many containing the additional components Zn(AlO₂)₂ Al(AlO₂)₃, Li₂ZnO₂, and Li₂BeO₂. Internal nucleation is afforded by additions of ZrO₂ or TiO₂. Either transparent or opaque crystalline materials can be formed from glasses containing about 70% SiO₂. The transparency is due to a combination of low birefringence in the major stuffed β-quartz phase and minute crystal size. Thermal expansions vary from -20 to +50 × 10⁻⁷/°C. Thermal stability is highly variable. Breakdown products include spinel, cordierite, β-spodumene, willemite, mullite, and cristobalite. Magnesian compositions can be strengthened by a 2Li⁺⇌ Mg²⁺ ionexchange reaction. Abraded flexural strengths range from 30,000 to 160,000 psi.     

钙钛锆石玻璃陶瓷体的晶化和抗浸出性能

以SiO2、A12O3、B2O3、CaO、TiO2和ZrO2为原料,加入3％CeO2（质量分数,下同）作为模拟核素,利用熔融法制备钙钛锆石基玻璃陶瓷体,对含锕系元素的放射性废物进行固化处置。通过X射线衍射仪和场发射扫描电子显微镜等对热处理后玻璃陶瓷体进行表征。以电感耦合等离子体质谱测试玻璃陶瓷体抗浸出性能。结果表明：在晶化温度为1050℃,B203掺量为12．5％时,玻璃陶瓷体中低质量分数的TiO2和ZrO2更易参与生成钙钛锆石晶体,但固化体中仍有其他晶相存在;在同样晶化温度下,B203掺量为8．33％时对玻璃陶瓷体形成钙钛锆石单一晶相较为有利,且具有较好的抗浸出性能,其中Ce在产品一致性测试法下元素标准化浸出率7d后维持在10^-6数量级,固化效果明显。     

Sintering Behavior and Properties of Iron-Rich Glass-Ceramics

Iron-rich glass-ceramics were obtained by the sintering of two glass powders, labeled G1 and G2, at heating rates of 5° and 20°C/min followed by an isothermal step in the 850°–1050°C temperature interval. The sintering process was evaluated by the linear shrinkage; the closed porosity was estimated by density measurements; the structure and the morphology of the glass ceramics were observed by scanning electron microscopy. The bending strength, the Young modulus, and Vickers hardness of the glass-ceramics materials were evaluated. The results showed that the sintering process and morphology of the glass-ceramics depends on the amount of magnetite and pyroxene formed. With a low percentage of crystal phase formed (25%–30% typical of G1) the structure is characterized by closed porosity; at higher crystallization (45%–50% typical of G2) open porosity is mainly formed. The properties of the glass-ceramics were not influenced by the heating rate but improved with an increase in the degree of crystallization.     

尾矿制备微晶玻璃的研究进展

尾矿制备微晶玻璃是尾矿的综合利用的一种新的途径.本文综述了微晶玻璃的特性及制备工艺,介绍了尾矿作为原料在微晶玻璃生产中的应用.分别讨论了不同尾矿制备微晶玻璃的工艺及其对微晶玻璃微观结构与物化性能的影响.从尾矿综合利用的角度,分类论述了金属尾矿及非金属尾矿制备微晶玻璃的最新研究进展,展望了尾矿微晶玻璃的发展方向及应用前景.     

Phase Distribution and Transparency in Glass-Ceramics Based on a Study of the Sodium Niobate–Silica System

High transparency in the NaNbO₃ crystal–silica glass system at low silica content is attributed to maintenance of the glass-to-glass phase separation pattern in microstructure throughout the process of crystallization. Optical properties are explained by a characteristic of the phase-separated glass, internal connectivity, applicable in this case to both crystal and glass phases. This type of microstructure allows light propagation in each phase independently, without interference between phases. Deviation from this ideal behavior and light-scattering mechanisms which may apply to different phase distribution patterns here and in other glass-ceramic systems are discussed.     

CaO/MgO对花岗岩尾矿微晶玻璃物相和性能的影响

以花岗岩尾矿为主要原料(掺入质量分数:56%),TiO₂为主晶核剂,适量Na₂SiF₆为助熔剂和晶核剂,添加部分辅助原料,采用整体析晶法,制备了R₂O-CaO-MgO-Al₂O₃-SiO₂系花岗岩尾矿建筑微晶玻璃。研究了CaO/MgO质量比对微晶玻璃析晶能力、物相、微观结构及性能的影响。结果表明:CaO/MgO质量比的增加有利于增强基础玻璃的析晶能力,当CaO/MgO质量比≤0.88时,微晶玻璃的主晶相为钙长石和角闪石,当CaO/MgO质量比＞0.88时,主晶相转变为钙长石,且钙长石衍射峰的强度随着CaO/MgO质量比的增加而增大;随CaO/MgO质量比的增加,晶体数量逐渐增多,晶粒尺寸增大;微晶玻璃的体积密度和显微硬度随CaO/MgO质量比的增加呈先增大后减小的趋势,当CaO/MgO质量比为0.57时,体积密度达到最大值2.752 5 g/cm³,当CaO/MgO质量比为0.71时,显微硬度达到最大值为8.6 GPa。     

添加剂对铜渣还原尾渣微晶玻璃析晶行为及性能的影响

铜渣还原尾渣与CaO-Al₂O₃-SiO₂系微晶玻璃的化学组成相似,采用熔融法以铜渣还原尾渣为主要原料制备微晶玻璃可为铜渣的高效利用提供一种有效途径。通过DSC、XRD和SEM-EDS等技术研究了不同添加剂(B₂O₃、CaF₂、TiO₂和Cr₂O₃)对微晶玻璃物相组成、抗折强度、体密度、吸水率和显气孔率等性能的影响。结果表明:无论添加哪种添加剂,微晶玻璃均能析出力学性能较好的钙长石和钙铝黄长石,且能使晶体析晶方式转化为整体析晶;添加B₂O₃可使微晶玻璃性能最优,其次是TiO₂与CaF₂。     

氟化钙对钠钙玻璃反应析晶制备玻璃陶瓷性能的影响

用X射线衍射、Fourier变换红外光谱、扫描电子显微镜研究了不同氟化钙加入量的钠钙玻璃粉末在烧结过程中的反应析晶。结果表明:未加入氟化钙时,以钙铝黄长石作为析晶促进剂,在850℃反应析晶生成硅灰石玻璃陶瓷;当析晶促进剂含量低于15%(质量分数,下同)时,添加6%氟化钙在850℃反应析晶生成枪晶石玻璃陶瓷。随氟化钙添加量增加,制备的枪晶石玻璃陶瓷气孔率逐渐增大,体积密度减小,抗弯强度降低。当氟化钙添加量为6%时,制得的枪晶石玻璃陶瓷抗弯强度达到68MPa。