锆莫来石材料反应烧结过程的研究

本文利用XRD、SEM和EDAX等方法系统研究了含ZrO_2约33%的ZrO_2-Al_2O_3-SiO_2系耐火材料,从生坯煅烧至1600℃所发生的结晶相变化,显微结构变化及烧结过程中ZrSiO_4的分解温度.结果表胆:ZrSiO_4的分解比莫来石的形成要快,莫来石是由ZrSiO_4分解的非晶SiO_2与Al_2O_3反应形成的.1450～1550℃是锆莫来石耐火材料煅烧过程中物相变化最激烈的温度范围,该反应对致密化产生不利影响.要使结构致密,烧成温度必须大干1600℃.     

莫来石结合的浇注料

在耐火浇注料中用４种不同的骨料即电熔氧化铝、电熔莫来石、ＳｉＣ和石英对莫来石结合系进行了试验。这４种混合浇注料具有良好的流动性并且经一夜之后就可脱模。测定了高温强度和常温强度。含有电熔氧化铝或电熔莫来石的浇注料在１３００℃以上由于形成了莫来石改进了高温强度。而ＳｉＣ质浇注料在１３００℃以上虽形成莫来石，但没有提高其高温强度。在１２００℃￣１３００℃下，ＳｉＣ质浇注料的高温强度比其它浇注料的高温强度     

利用铝型材厂工业废渣制备莫来石质耐火材料

以铝厂污泥和苏州土合成的不同粒径级配的莫来石作为原料,添加少量堇青石作为结合剂,甲基纤维素、水作为添加剂研制优质莫来石耐火材料。通过测定耐火材料的抗折强度、热稳定性、气孔率等性能指标确定出最佳配方。结果表明：No.1配方的0次抗折强度为126.76 kgf/cm^2,1次热震抗折强度为81.07 kgf/cm^2,10次热震抗折强度为45.07 kgf/cm^2。1次热震强度保持率为49.24%,10次热震强度保持率为36.52%,10次热震后气孔率为40.37%,0次热震吸水率为24.76%,0次热震体积密度为1.61g/cm3。     

电熔锆莫来石研制

电熔锆莫来石研制施毓斐（上海日用玻璃制品公司耐火材料部２０００２０）ＡｎＩｎｖｅｓｔｉｇａｔｉｏｎｏｆＥｌｅｃｔｒｏ－ＭｅｌｔｅｄＺｉｒｃｏｎｉａＭｕｌｌｉｔｅ￥ＳｈｉＹｕｆｅｉ（ＳｈａｎｇｈａｉＤｏｍｅｓｔｉｃＧｌａｓｓｗａｒｅＣｏ．，Ｒｅｆｒａｃ...     

由纯合成材料制成的莫来石

通过使用合成配制的原料和在产品热处理过程中增加大颗粒的粒度,可提高高铝莫来石的耐火度。     

Porous Mullite Preforms via Fused Deposition

Nonrandom porous mullite ceramic preforms were fabricated by the indirect fused deposition process. MgO was added to commercial mullite powders as a sintering aid. The influence of porosity and the amount of MgO on the densification and mechanical properties was studied. The shrinkage and compressive strength of the porous samples were found to increase with increasing MgO content. At constant MgO concentration, shrinkage was found to decrease linearly as the volume fraction of porosity increased. The compressive strength of porous samples decreased with an increase in the volume fraction of porosity at constant MgO content.     

部分莫来石化陶瓷催化剂载体的研究

高温燃烧催化荆需要在高于1000℃的氧化气氛中,具有良好的耐热性、抗热冲击性和较大的比表面积。国内使用的催化荆仅能烧至600℃,高于600℃活性就会下降,甚至失活。本文探讨的部分莫来石化陶瓷催化荆载体,不但耐热性好,而且催化活性高,具有良好的使用前景。     

莫来石蜂窝陶瓷的阻力特性

本文以实验为基础,通过搭建的蜂窝陶瓷蓄热体阻力特性实验台,对莫来石蜂窝陶瓷的阻力特性进行了实验研究。研究表明:蜂窝陶瓷的阻力损失随蓄热体长度增加而增大,随孔隙率增加而减小;在蜂窝陶瓷的长度一定时,其阻力损失随雷诺数增加而增大,随气体流速增加而增大。根据实验数据得到了蜂窝陶瓷蓄热体摩擦阻力系数实验关联式,为煤矿乏风氧化装置的设计提供了数据支持。     

Mullite/Alumina Mixtures for Use as Porous Matrices in Oxide Fiber Composites

Weakly bonded particle mixtures of mullite and alumina are assessed as candidate matrixes for use in porous matrix ceramic composites. Conditions for the deflection of a matrix crack at a fiber-matrix interface are used to identify the combinations of modulus and toughness of the fibers and the matrix for which damage-tolerant behavior is expected to occur in the composite. Accordingly, the present study focuses on the modulus and toughness of the particle mixtures, as well as the changes in these properties following aging at elevated temperature comparable to the targeted upper-use temperature for oxide composites. Models based on bonded particle aggregates are presented, assessed, and calibrated. The experimental and modeling results are combined to predict the critical aging times at which damage tolerance is lost because of sintering at the particle junctions and the associated changes in mechanical properties. For an aging temperature of 1200°C, the critical time exceeds 10 000 h for the mullite-rich mixtures.     

Mullite for Structural, Electronic, and Optical Applications

Mullite (3Al₂O₃·2SiO₂) is becoming increasingly important in electronic, optical, and high-temperature structural applications. This paper reviews the current state of mullite-related research at a fundamental level, within the framework of phase equilibria, crystal structure, synthesis, processing, and properties. Phase equilibria are discussed in terms of the problems associated with the nucleation kinetics of mullite and the large variations observed in the solid-solution range. The incongruent melting behavior of mullite is now widely accepted. Large variations in the solid solubility from 58 to 76 mol% alumina are related to the ordering/disordering of oxygen vacancies and are strongly coupled with the method of synthesis used to form mullite. Similarly, reaction sequences which lead to the formation of mullite upon heating depend on the spatial scale at which the components are mixed. Mixing at the atomic level is useful for low-temperature (<1000°C) synthesis of mullite but not for low-temperature sintering. In contrast, precursors that are segregated are better suited for low-temperature (1250° to 1500°C) densification through viscous deformation. Flexural strength and creep resistance at elevated temperatures are significantly affected by the presence of glassy boundary inclusions; in the absence of glassy inclusions, polycrystalline mullite retains >90% of its room-temperature strength to 1500°C and displays very high creep resistance. Because of its low dielectric constant, mullite has now emerged as a substrate material in high-performance packaging applications. Interest in optical applications mainly centers on its applicability as a window material within the mid-infrared range.     

Synthesis of Mullite Whiskers

Mullite whiskers were synthesized by heating a mixture of SiO₂ and silicon in an alumina tube reactor under a flow of H₂ and CF₄. The length and diameter of the whiskers were several hundred micrometers and >15 μm, respectively. It was postulated that a vapor phase reaction between SiF₄ and AlF₃ made possible the synthesis of the large mullite whiskers.     

Fabrication and Property of Mullite Whiskers Frameworks with an Ultrahigh Porosity by Expandable Mesocarbon Microbeads

Mullite whiskers frameworks with an ultrahigh porosity were fabricated by the vapor‐phase reaction of AlF₃, Al₂O₃, and SiO₂ and adding expandable mesocarbon microbeads (MCMB) as a pore‐forming agent. A large volume expansion of 122% for MCMB due to its layered structure occurred during the formation of mullite whiskers, resulting in the expansion of samples and high porosities of 87.7%–98.2% at 50–90 wt% MCMB contents. Perfect whiskers and a lap‐joint structure formed due to the formation of mullites through the vapor‐phase reaction. A bimodal pore structure was achieved from the spaces of the whiskers framework and burning of the expanded MCMB. High compressive strengths of 1.7 to 5.4 MPa were obtained for the porous mullite at porosities of 94.2%–87.7%, which suggested a rigid structure; these strengths at the ultrahigh porosities are attributed to the merit of the framework with high strength whiskers and their strong bonding.     

High-Temperature Hydroxylation of Mullite

A plane-parallel, polished, 0.9 mm thick, single-crystal (001) plate of 2:1 mullite was treated for 6 h at 1600°C in an Ar/H₂O (90/10) gas mixture at 100 kPa. Optical microscopy studies and infrared (IR) reflection spectroscopy studies of the lattice vibrations yielded no evidence for change with respect to the untreated reference crystal. However, IR absorption spectroscopy showed that structurally bound OH groups were formed by the heat treatment in the Ar/H₂O gas mixture. IR absorption depth profile analysis showed a rather homogeneous OH distribution through the crystal. Five different hydroxyl groups were separated according to dipole orientations and peak positions: E ‖ a , ω _{a 1}= 3447 cm⁻¹, ω _{a 2}= 3579 cm⁻¹; E ‖ b , ω _{b 1}= 3456 cm⁻¹, ω _{b 2}= 3544 cm⁻¹; and E ‖ c , ω _{c 1}= 3498 cm⁻¹. All IR peaks were strongly broadened (between 90 and 150 cm⁻¹) because of a distribution in O-H binding distances caused by the real structure of mullite.     

Phase-Pure Mullite from Kaolinite

Sintering of kaolinite in the presence of certain carbonate mineralizers, viz., CaCO₃, Na₂CO₃, and K₂CO₃, has been conducted at 950°–1350°C. The influence of these mineralizers at the above temperatures is evaluated using XRD and SEM techniques. A comparative study of phase formation of the above compositions shows that the sodium- and calcium-fluxed samples give rise to multiphase systems, while K₂CO₃-incorporated samples give phase-pure mullite. The observation that kaolinite in the presence of K₂CO₃ can act as a precursor material for phase-pure mullite is of great industrial significance.     

人工合成莫来石骨料的研制初探

目前国内外多数厂家已经形成合成莫来石骨料的基本模式：高岭土＋工业Al2O3,湿法球磨,酸洗除铁,高温烧成。本文着重介绍采用山东优质焦宝石代替高岭土进行人工合成莫来石MS－5O、MS－70的试验方法,并进行了生产性研制,最终达到预期目标。