Development of Mica Glass-Ceramic Glazes

The effect of iron content on crystallization of a mica glaze as coating for fast firing stoneware substrates has been investigated. Measurements by differential thermal analysis (DTA) combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM) have shown the development of preferential crystal orientation in the mica glass-ceramic glaze. By comparison with amorphous and partly crystalline glazes, an enhancement of the mechanical properties of coatings with aligned and interlocked crystals of mica has been observed.     

Microstructure of Mica-Based Nanocomposite Glass-Ceramics

A high-strength machinable glass-ceramic was prepared by controlling the crystallization of ZrO₂-containing Ca_0.43K_0.14Mg₃ (Si₃AlO₁₀)F₂ glass. A unique microstructure of the glass-ceramic was observed, using transmission electron microscopy (TEM): zirconia particles of nanometer size, 20–50 nm, were embedded in calcium mica crystal. After zirconia particles grew in nanometer size, the mica crystals were precipitated to embed the particles. The particles were identified as transformable tetragonal zirconia crystals. This texture leads to high strength (500 MPa in bending) and good machinability.     

The investigation of the crystalline phases development in Macor® glass-ceramic

The commercially available, machinable, fluormica glass-ceramic, Macor^®, was remelted to produce a glass. This glass was then characterized by differential scanning calorimetry (DSC), combined differential thermal analysis/thermal gravimetric analysis (DTA/TGA), X-ray powder diffraction (XRD) and ¹⁹F magic angle spinning ?nuclear magnetic resonance (MAS-NMR). The Macor^® glass was shown to crystallize to chondrodite (Mg₅F₂(SiO₄)₂), followed by the conversion of chondrodite to norbergite (Mg₃SiO₄F₂) and the conversion of norbegite to a potassium fluorphlogopite phase (KMg₃AlSi₃O₁₀F₂). The glass exhibited an optimum nucleation temperature just above its glass transition temperature, which is indicative of a nucleation route involving amorphous phase separation. The ¹⁹F MAS-NMR spectra showed the fluorine environments being present as F-Mg(3) in the original glass, the chondrodite, norbergite and fluorphlogopite phases, indicating that the fluorine structure is conserved throughout the crystallization process. The activation energies for crystallization were found to be 215, 431 and 251 kJ mol^?1 for chondrodite, norbergite and fluorphlogopite, respectively.     

Scratching and Grinding of a Machinable Glass-Ceramic with Weak Interfaces and Rising T-Curve

The scratching and grinding response of a machinable mica-containing glass-ceramic is examined relative to the base glass. The influence of weak interfaces and a rising toughness curve ( T -curve) on machinability and damage modes is investigated. A profound manifestation of these characteristics is a change in the nature of subsurface damage from macroscopic fracture in the base glass to distributed microfracture in the glass-ceramic. As a result, the mechanism of material removal changes from extension of macrocracks in the base glass to microfracture and dis-lodgement of the mica grains in the glass-ceramic. High removal rates in scratching compare with low forces in grinding of the glass-ceramic. The removal rates and the grinding forces are found to correlate with the short-crack toughness instead of the conventional long-crack toughness.
Abrasive machining of ceramics possessing weak grain boundaries and interfaces and associated rising T- curve behavior is discussed in light of these results.     

Sol–gel preparation and characterization of nano-crystalline lithium–mica glass–ceramic

The nano-crystalline lithium–mica glass–ceramic with separated crystallite size of 13 nm was prepared using sol–gel technique. In such a process, the structural evolutions and microstructural characteristics of the synthesized samples were investigated through X-ray diffraction, transmission electron microscopy, thermal analysis and Fourier transform infrared spectroscopy. It was found that the crystallite size of the mica obtained from sol–gel method is smaller than the one synthesized via conventional melted method. The XRD results also showed that the crystallization of mica occurred above 675 °C and it could originate from MgF₂ so that the next stage will also be the transformation from mica to norbergite and norbergite to chondrodite. The activation energy of the crystallization and Avrami factor were measured as 376.7 kJ mol^?1 and 2.3, respectively. It is found that the bulk crystallization could be considered as the predominant crystallization mechanism for the glass–ceramic.     

Ductile-Mode Material Removal of a Mica–Glass-Ceramic

The influence of crystal volume fraction on machining behavior was investigated for modified mica–glass-ceramic materials that contained B₂O₃, Na₂O, Li₂O, and ZnO and had low melting temperatures. The machining behavior was characterized by drilling rate under a constant drilling force and chip morphology in a cutting test. To achieve the greatest drilling rate, an optimization volume fraction of crystalline mica (40%) had to be used; a further increase in the fraction of crystalline mica resulted in a corresponding decrease in the drilling rate. For this type of mica–glass-ceramic, a continuous band of chips and a highly smooth cut surface could be formed during the cutting test at a high cutting velocity of 60 m/min and a depth of 1 mm. The results demonstrated that an outstanding machining behavior for glass-ceramics can be achieved and that it can be comparable with metallic materials.     

Phase formation,microstructure and electrical properties of mica glass-ceramics containing Cr2O3 produced by heat treatment

The mica glass-ceramics containing Cr₂O₃ were produced via heat treatment process from the bulk parent glass specimens. The appropriate treatment temperatures were selected according to the information provided by the DTA measurement. XRD analysis demonstrated that co-existence of the mica and MgAl₂Si₃O₁₀ phases were found at the lower treatment temperature while pure mica phase could be formed at a higher temperature. The SEM investigations revealed the effect of Cr₂O₃ addition on mica crystals development. The electrical resistivity of the glass-ceramic samples showed some significant relation with the added ions. With small amount of addition, an increase of the electrical resistivity was observed. The present glass-ceramics could be a promising candidate as advanced insulating materials, as evidenced from the presence of crystalline phases with machinable properties and good mechanical strength coupled with its high resistivity.     

Crystallization of a Tetrasilicic Fluormica Glass

The crystallization of a tetrasilicic synthetic mica glass of nominal composition K₂Mg₅Si₈O₂₀F₄ was investigated at selected temperatures from 560° to 1150°C using DTA, density measurements, electron microscopy, and X-ray diffraction techniques. Crystallization is shown to occur in 2 stages. (1) Initial structural ordering occurs at ∼600°C, as indicated by a strongly exothermic reaction, an increase in density, and the appearance of X-ray diffraction lines. (This transformation temperature is related to fluorine content.) (2) The crystal morphology of the glass-ceramic changes at 900° to 1150°C. A mechanism is proposed for the transformation from amorphous to crystalline structure in this synthetic mica system.     

Mechanical Properties of Mica Glass-Ceramics

The mechanical properties of fluorophlogopite mica-based glass-ceramics, such as fracture toughness, flexural strength, and machinability, were investigated. It has been shown that toughening increments in the glass-ceramics occurred by crack deflection and branching by crystals with a high aspect ratio. All the glass-ceramics heat treated at 1000°–1150°C exhibited a higher fracture toughness of 1.2–2.2 MPa-m^1/2 as compared to 0.8 MPa-m^1/2 for the parent glass, and showed average flexural strengths of 140–160 MPa. It has been suggested that ( H/K_Ic )² of the mica glass-ceramic be used to estimate the machinability, because it decreases linearly with machinability.     

Thermodilatometric Characterization for Devitrification of a Micaceous Dental Glass-Ceramic

The devitrification of an uncerammed micaceous glass-ceramic used for dental applications was studied by thermodilatometry and compared with the kinetics of mica crystallization studied by differential thermal analysis. The thermodilatometry plots and their derivative plots revealed thermally impeded processes, namely, structural relaxation, glass softening and nucleation, and crystallization, and they were characterized by glass-transition temperature, glass-softening temperatures, and crystallization temperature. The heating-rate dependence for these characteristic temperatures was used to determine the activation energy for structural relaxation of 338 kJ·mol^-1, the activation energy for viscous flow of 276 kJ·mol^-1, and the apparent activation energy for crystallization of 286 kJ·mol^-1 by one model and 342 kJ·mol^-1 by another model. The similar magnitudes for these activation energies suggested the mechanisms for different thermal processes involved analogous molecular motions. Furthermore, the activation energy for crystallization of the micaceous phase of the glass-ceramic could be estimated from thermodilatometry plots, because it was comparable in magnitude to that obtained from the widely used nonisothermal differential thermal analysis method. Finally, the dilatometry and scanning electron microscopy studies strengthened the earlier opinion that the devitrification of the base glass is a single-step process, that is, without occurrence of an intermediate phase before the formation of the final crystalline phase.     

Strengthening of a lithium disilicate glass-ceramic by rapid cooling

In order to improve the mechanical properties, a traditional physical strengthening process was applied to a lithium disilicate (LD) glass-ceramic with a dual-phase microstructure consisting of a glassy matrix and LD crystals. The strengthening process was based on the transformation behavior of the glass-ceramic. The process was conducted by heating the glass-ceramic to a temperature below the dynamic softening point, and then rapid cooling in silicon oil (quenching). Residual stresses and mechanical properties of the glass-ceramic were investigated after the quenching. It was found that residual compressive macro-stresses could be induced in the surface layer of the LD glass-ceramic by the quenching. The residual stresses remarkably increased with increasing the quenching temperature to near the dynamic softening temperature. Compared with the corresponding annealing state, the LD glass-ceramic could be effectively strengthened and toughened by the quenching at a suitable temperature. The results displayed the strengthening possibility and potential of the LD glass-ceramic by the traditional physical process.     

富铁矿渣微晶玻璃的研究与开发

对富铁矿渣微晶玻璃的开发与研究现状进行了评述,重点介绍了富铁矿渣的特点、富铁矿渣微晶玻璃的工艺和性能研究现状以及其研究开发前景。     

建筑装饰微晶玻璃板中应力产生与形变关系分析

CaO-Al2O3-SiO2系统微晶玻璃作为微晶玻璃中的一个新品种,具有非常鲜明的特点,并得到广泛的应用.在微晶玻璃的生产中,微晶玻璃板在由玻璃颗粒烧结、晶化以后会出现板面变形的现象.大多数的板面变形与微晶玻璃装饰板内的结构应力有关.本文讨论了CaO-Al2O3-SiO2系统微晶玻璃中形变与内应力产生的原因,这将对微晶玻璃的生产提供一定的参考.     

Role of Internal Friction in Indentation Damage in a Mica-Containing Glass-Ceramic

The indentation response of a mica-containing glass-ceramic that exhibits shear-driven yield in an indentation test is interpreted in terms of events occurring on the microstructural scale. It is proposed that shear-driven damage within the specimen occurs via internal sliding along cleavage planes within the mica platelets. The sliding surfaces in this case are considered to be atomically smooth so the real and apparent areas of contact coincide. The frictional shear stress is thus independent of the normal forces arising from thermal mismatch stresses and only depends on the work of adhesion of the interface and the scale of the contacts. The scale of contacts for these materials lies within an intermediate zone in which the frictional shear stress arises from the stress required to nucleate dislocation-like discontinuities within the material. This leads to a size effect similar to that experienced by a crack in Mode II loading and is in accordance with previous work in which a connection between such a size effect and the macroscopic response of the material was identified. This work has particular relevance to the design and manufacturing of ceramics in machining, wear, bearings, and coatings applications.     

矿渣微晶玻璃专家系统类比设计模型

类比学习是利用过去的经验来求解新问题的一种思维过程,是专家系统中实现知识自动获取的重要方法。根据矿渣微晶玻璃设计的基本特征,详细介绍了矿渣微晶玻璃类比设计的基本原理、类比因素以及类比准则。选择属性类比作为专家系统类比设计的主要方式,以矿渣的成分作为类比因素,以经过修正的综合类似度作为类比准则,结合矿渣微晶玻璃实例库和人工神经网络模型建立了专家系统类比设计模块。实验结果证明,该类比设计模块具有很好的设计效果,是矿渣微晶玻璃设计的有效方法之一。     

泡沫微晶玻璃的研究进展

概述了泡沫微晶玻璃的性能及应用,综述了泡沫微晶玻璃的研究进展,并对泡沫微晶玻璃的发展方向进行了展望.     

以粉煤灰为基础的微晶玻璃复合墙地砖研制

将粉煤灰引入微晶玻璃来制备复合墙地砖材料是一引人注目的课题。笔者以Li2O-CaO-Al2O3—SiO2为系统来制备微晶玻璃，利用其微负膨胀性，良好的析晶效果，易于与坯体相结合，消除内应力等优点来制备复合墙地砖。试验表明：将基础玻璃粉平铺于普通瓷质砖上，经一次烧结可制成表层为微晶玻璃，底层为普通瓷砖的复合材料。这既充分利用了粉煤灰，又具备微晶玻璃的各种优良性能，而且产品的工艺及合格率完全符合实际生产要求。     

自洁净微晶玻璃的制备工艺研究

为了制备表面具有高疏水性的自洁净微晶玻璃,文中首先以高炉矿渣和钾长石为原料制成微晶玻璃坯体,然后利用溶胶-凝胶的工艺制备出硅溶胶/聚四氟乙烯(PTFE)有机/无机镀液,利用浸渍提拉法在微晶玻璃表面进行镀膜,最后通过热处理制成表面具有自洁净功能的微晶玻璃。分析了乙醇用量、加水量、pH值、陈化时间及温度对于溶胶形成的影响,以及硅溶胶/PTFE配比对于镀液性能和镀膜效果的影响。利用XRD、SEM、接触角测定仪等对样品进行性能检测。结果表明,制备的微晶玻璃的主晶相是镁黄长石,聚四氟乙烯对硅溶胶有良好的修饰作用,自洁净微晶玻璃的接触角已达到120°,具有较强的疏水性。     

Sol-Gel法制备LAS微晶玻璃的研究现状与应用进展

LAS系统微晶玻璃由于其膨胀系数低,耐高温及抗热冲击性等优异性能而受到广泛重视。主要介绍了溶胶-凝胶制备过程及在LAS系微晶玻璃上的应用,简述了LAS系微晶玻璃的应用现状。     

CaO-Al2O3-SiO2系统微晶玻璃的冲蚀磨损研究

CaO-Al2O3-SiO2系统微晶玻璃装饰板材是一种新型建筑装饰材料。本文利用冲蚀磨损实验研究了影响CaO-Al2O3-SiO2系统烧结法微晶玻璃装饰板材磨蚀行为。讨论了微晶玻璃组成、结构、磨粒粒径、冲蚀角、冲蚀时间对CaO-Al2O3-SiO2系统微晶玻璃的冲蚀性的影响。结果表明:随着微晶玻璃中晶相含量的增加,磨料对其表面的冲蚀磨损量明显下降。微晶玻璃的冲蚀量随冲蚀角的增大、冲蚀时间的增长、磨粒粒度的增大而增加。