红柱石原料高温结构演变及抗钾蒸气侵蚀行为研究

红柱石是铝硅系耐火材料重要的原料之一，因完全莫来石化后具有莫来石-高硅氧玻璃相相间的结构而表现出优异的抗碱侵蚀性能。然而，其莫来石化程度与抗碱侵蚀性能之间的关系尚未厘清。为此，本工作以粒度为3～5 mm的红柱石为研究对象，在1 450～1 600℃下热处理红柱石3 h,研究了红柱石的莫来石化过程与结构演变，并采用碱蒸气法研究了抗碱侵蚀行为。结果表明，随着热处理温度的提高，红柱石表面及裂纹附近先转变形成莫来石-高硅氧玻璃相结构，随后莫来石化转变不断向内部发展，直至完全莫来石化。红柱石莫来石化程度不同决定了其不同的抗碱侵蚀行为。1 450℃热处理后的红柱石表面及大裂纹附近形成的莫来石-高硅氧玻璃相复合层较薄，侵蚀以红柱石与钾蒸气直接反应为主，抗碱侵蚀性能较差；1 500℃及以上温度热处理的红柱石表面及大裂纹附近形成了一定厚度的莫来石-高硅氧玻璃相复合层，钾蒸气首先与高硅氧玻璃相反应形成含钾硅酸盐液相，随后该液相对莫来石相产生侵蚀溶解，阻止了碱蒸气对莫来石的直接反应侵蚀，从而使红柱石表现出优良的抗碱侵蚀性能。     

红柱石及其引入方式对铝硅质浇注料性能的影响

为充分发挥红柱石在铝硅质浇注料中的优异性能,分别以特级矾土、棕刚玉为主要原料配以红柱石制备铝硅质浇注料.检测试样在不同温度下的抗折强度及体积密度、显气孔率及线膨胀率,并对烧后试样的物相组成及显微结构进行表征,以研究红柱石及其引入方式对不同配置的铝硅质浇注料性能的影响.研究结果表明:红柱石以细粉形式引入的铝硅质浇注料,在高温下莫来石反应及二次莫来石化较为充分,试样体积密度、高温抗折强度相对较高,线膨胀率相对较低;相比棕刚玉配置的浇注料,红柱石对矾土配置浇注料性能的改善更为明显,红柱石分解及二次莫来石化相对较为容易,产生的莫来石将矾土熟料紧密连接,有效改善试样的物理性能.     

红柱石——生产优质耐火材料用最有前途的材料

概述了红柱石的莫来石化过程，指出这一相转变过程是根据确定颗粒形状的假象机理和固相过程的化学作用进行的。莫来石的取向与红柱石沿着轴Ｃ形成的结晶方向一致。     

莫来石加入量和烧成温度对红柱石耐火材料性能的影响

红柱石颗粒本身为基本无气孔的密实体 ,烧后气孔率不增加或增加很少 ,且体积效应较小 (约为 3 %～ 5 % ) ,因此红柱石不需要煅烧便可以直接用于生产烧成制品 ,是生产高级Al2 O3 -SiO2 系耐火材料的优质原料。国产红柱石大颗粒的杂质含量较高 ,用它生产的红柱石制品性能不理想。而南非红柱石大颗粒的杂质虽较低 ,但价格较高 ,且有时不能及时供货 ,组织生产较困难。由于人工合成莫来石原料具有纯度高 ,耐火度高 ,热膨胀系数小 ,热传导性低 ,化学稳定性及高温力学性能好等优点。因此 ,用莫来石大颗粒替代红柱石大颗粒生产红柱石耐火材料 ,不…     

红柱石基刚玉-莫来石复相陶瓷的显微结构及性能

以红柱石颗粒为主要骨料,辅以莫来石颗粒和刚玉颗粒,硅微粉、铝微粉为基质料,经混合、困料及成型后,经不同温度下烧成4h,制得莫来石基刚玉-莫来石复相陶瓷,分析了烧成温度对复相陶瓷的物相组成、显微结构、烧成性能、力学性能及热学性能。结果表明:红柱石在高温下转化成针状和柱状莫来石改善复相陶瓷的烧成性能和抗热震性能;在1480℃烧成时,红柱石刚玉-莫来石复相陶瓷具有优越性能,其抗折强度为15.4MPa,耐压强度为91.6MPa,热膨胀系数为5.5×10-6/K,1100℃下水冷的抗热震次数达到99次。     

莫来石纤维制备方法综述

莫来石纤维是一种重要的陶瓷材料,被广泛用作高温隔热材料、金属基或陶瓷基复合材料的增强体等.本文主要综述了莫来石纤维的多种制备方法,特别是重点介绍了溶胶-凝胶法制备多晶莫来石纤维的研究现状.在溶胶-凝胶法制备莫来石纤维的过程中,原材料的选择、单相和双相溶胶的制备以及各种因素都会影响水解和浓缩过程,并决定莫来石纤维的最终性能.最后对制备莫来石纤维的发展方向进行了展望.     

红柱石骨料粒度对莫来石-刚玉材料抗热震性的影响

分别用20%(w)不同粒度(5～3、3～1、≤1 mm)的红柱石骨料等量替代莫来石-刚玉材料中同粒度的莫来石骨料,经1 450℃保温3 h烧成制备莫来石-刚玉材料,并着重研究红柱石骨料粒度对其抗热震性的影响。结果表明:随着红柱石骨料粒度的增大,烧成试样的抗折强度和弹性模量逐渐降低,但抗热震性逐渐提高。这是由于在试样烧结降温过程中,红柱石骨料与基质热膨胀系数失配产生了微裂纹,且微裂纹的尺寸随着红柱石骨料粒度的增大而增大;而微裂纹在热震过程中能够阻止新裂纹的产生和裂纹扩张,提高试样的抗热震性。     

杂质和高温液相对莫来石化动力学和抗热震性的影响

研究了煅烧红柱石颗粒的莫来石化和生成莫来石的显微结构。众所周知,莫来石生成的机理为:加热过程中,红柱石单晶转变为组成为3∶2的莫来石单晶,毛细网络由富二氧化硅液相所填充。但是很少有人研究杂质对莫来石化动力学的影响。本研究表明,红柱石中杂质(主要是铁和碱金属)的存在增加了液相量,降低了液体黏度。莫来石化动力学由红柱石的粒度、化学组成、红柱石矿的产地、液相含量和特性所决定。因为特殊的显微结构和液相的存在,在空气中进行热震时,已莫来石化了的红柱石晶体表现出典型的复合材料的特点:微裂纹被莫来石/玻璃相界面偏移了,而且在玻璃相区域终止。继续加热后,热震产生的裂纹又得到愈合。     

莫来石-堇青石陶瓷窑具材料的性能及显微结构

研究了红柱石骨料的莫来石化作用及添加剂SiC的加入量、合成莫来石的引入和烧成温度对莫来石-堇青石窑具材料性能及显微结构的影响。结果表明 ,在 1380℃ 4h下烧成时 ,红柱石的莫来石化作用能大大改善材料的烧结性能 ;加入 4 %的SiC可提高材料的物理性能 ;部分合成莫来石的加入可克服红柱石在莫来石化过程中的不足 ,强化材料的组织结构 ,提高材料的物理性能     

新疆红柱石的莫来石化试验

红柱石是一种性能优良的硅铝酸盐矿物原料,在高温下不可逆地转变为莫来石(3Al2O3·2SiO2)和富SiO2液相,转化完全后,莫来石的质量分数约占80%,玻璃相的质量分数约占20%.红柱石的莫来石化除受煅烧温度及保温时间的影响外,还与原料的粒度及杂质的成分、含量和分布有关.我国新疆巴州地区有丰富的红柱石资源,已在国内外大量使用,但对该红柱石的研究工作报道不多.本工作研究了不同纯度和粒度的新疆巴州红柱石精矿在不同温度和保温时间下煅烧后的莫来石化量.     

Microstructural evolution under load and high temperature deformation mechanisms of a mullite/alumina fibre

A two-phase mullite alumina fibre, the 3M Nextel 720 fibre, has been studied in tension and creep. The fibre shows the highest creep resistance of all current commercial fine oxide fibres up to 1500 °C. The creep mechanisms involve progressive dissolution of mullite and simultaneous reprecipitation of alumina into elongated oriented grains and grain boundary sliding by a thin alumino-silicate liquid phase. The rate of grain growth in creep at a given temperature is dependant on the applied stress. The combination of sub-micron size mullite crystallites and alumina grains gives rise to a high sensitivity to alkaline contamination. Stress enhanced diffusion of the contaminants from the fibre surface results in crack nucleation, dissolution of mullite, formation of a liquid phase and slow crack growth. From 1200 °C, this process is coupled with a fast α-alumina grain growth at the fibre surface.     

Temperature-induced fibre/matrix interactions in porous alumino silicate ceramic matrix composites

The thermal stability of alumino-silicate fibre (Nextel 720)/porous mullite matrix composites was investigated in the temperature range between 1300 and 1600°C. In the as-prepared state the fibres consist of mullite plus α-Al₂O₃, while the porous mullite matrix includes minor amounts of a SiO₂-rich glass phase. Temperature-controlled reactions between the silica-rich glass phase of the matrix and α-Al₂O₃ at the rims of the fibres to form mullite have been observed. At the end of this process, virtually all glass phase of the matrix is consumed. Simultaneously, alumina-free layers about 1 μm thick are formed at the periphery of the fibres. The mullite forming process is initiated above about 1500°C under short time heat-treatment conditions (2 h) and at much lower temperature (1300°C) under long-term annealing (1000 h). Subsequent to annealing below the thermal threshold, the composite is damage tolerant and only minor strength degradation occurs. Higher annealing temperatures, however, drastically reduce damage tolerance of the composites, caused by reaction-induced gradually increasing fibre/matrix bonding. According to this study, the thermal stability of alumino silicate (Nextel 720) fibre/mullite matrix composites ranges between 1500°C in short-term and 1300°C in long-term heat-treatment conditions.     

Single crystalline mullite fibres obtained by the internal crystallisation method: Microstructure and creep resistance

Single crystalline mullite fibres, which are expected to be an excellent reinforcement for high temperature composite materials, can be produced by using the internal crystallisation method. The present paper sheds light to mechanisms of crystallisation of mullite fibres under conditions of the internal crystallisation method, which is actually crystallisation of a melt in the continuous channels of a molybdenum carcass. Mullite occurs to appear close to 2:1 composition independent of the composition of the melt. Inclusions of a silica-based glassy phase are also present on the periphery of a fibre. The glassy phase yields a decrease in the creep resistance of mullite fibres at temperatures above 1500 °C. Still, the fibres obtained from the raw material with the Al₂O₃/SiO₂ molar ratio of 2.05 have excellent creep resistance at a temperature of 1400 °C and fairly high creep resistance at 1500 °C.     

Damage assessment of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue at ambient and elevated temperatures

The damage evaluation behaviour of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue was investigated by means of acoustic emission (AE) monitoring and forced resonance techniques. AE technique provided sufficient information about the damage initiation and progression in real time whilst the forced resonance (FR) technique allowed the detection of changes in elastic modulus (E) and internal friction (Q⁻¹) that occurred with increasing number of cyclic fatigue at room temperature. From the two non-destructive detection techniques results combined with microstructural observations, it is concluded that the composite cyclic fatigue damage evolution begins with multiple crack formation within the matrix and is followed by delamination (interfacial failure). Final failure of the composite is caused by fibre fracture and extensive cyclic sliding along the fibre/matrix interface. The strong bonding between mullite matrix and alumina fibre caused by the glassy phase within the mullite matrix determined the fatigue performance of the composite at 1350°C. Regions with glassy phase failed catastrophically as a result of early fibre fracture.     

数字装饰瓷砖技术与设备新进展

2014年9月22日-26日,意大利博罗尼亚（Bologna）举办了一年一度的陶瓷砖CERSAIE,展示了许多用数字装饰技术与设备生产的各类瓷砖。与此同时,在意大利里米尼（Rimini）举办了两年一度的陶瓷机械设备展（Tecnargilla）,中国广东东莞琅菱企业的超细研磨设备、广东佛山康立泰（国瓷）的陶瓷墨水、广东佛山新景泰陶瓷的喷墨设备,代表中国在瓷砖数字装饰领域的一股新兴力量参加了本次展会。本文对瓷砖产品不进行讨论,对国内企业的情况也不作展开,仅从宏观角度上介绍国外一些企业在瓷砖数字装饰技术与设备领域的新进展,供国内瓷砖行业同行参考,不对之处,敬请批评指正。     

纤维增强莫来石隔热材料的研制

引入耐火纤维,在相对简单的工艺条件下研制了纤维增强莫来石隔热材料。研究表明,耐火纤维的加入可提高制品的强度,通过加入高温膨胀剂以及添加物,采用合适的工艺,可制得性能优良的莫来石隔热材料。     

Oxide CMCs: interphase synthesis and novel fibre development

Strategies which have been used in the synthesis of high temperature interphases with debond capability in oxide/oxide systems have been: (i) the formation of layered oxides (β-aluminas or magnetoplumbites) with preferred crystal orientation due to in-situ interface reactions between phases deposited from vapour or liquid precursors and (ii) the deposition on fibre surfaces of complex oxides (vanadates and phosphates, principally of the rare earths) from colloidal precursors or by magnetron sputtering. This paper is primarily concerned with the latter. The constitution and thermal stability of these interphases has been studied with reference to potential fibres and matrices (alumina, YAG and mullite). Included within the program are newly developed single phase mullite fibres and examples of these are also presented.     

Chemical,phase and structural change of mullite synthesized during sintering of kaolin

Mullite is of great technological relevance but rarely occurs in nature and as a result different approaches have been adopted in its synthesis from alumina bearing minerals. In this study, chemical, phase and structural change of mullite synthesized from sintering of natural kaolinite clay is investigated. Thoroughly beneficiated kaolinite clay powder was obtained from Nigeria and uniaxially pressed into cylindrical compact of 40 × 30 mm followed by sintering at temperatures of 1200°C and 1300°C, respectively. The chemical composition, microstructure change, phase transformation, and reaction bonding were carried out using EDXRF, SEM, XRD, and FT-IR, respectively, to assess the synthesized mullite. The results showed that a well-dispersed primary mullite phase was obtained which was fully developed at increased temperature of 1300°C. Better mullite phase was also obtained with increasing alumina content at more elevated temperature of 1300°C while Si-O-Al bonding of mullite crystals was also obtained from the FT-IR spectra. However, the needle-shaped mullite structure was not achieved which might be attributed to the sintering temperatures 1200°C-1300°C utilized.     

Mullite (Nextel™ 720) fibre-reinforced mullite matrix composites exhibiting favourable thermomechanical properties

A mullite matrix containing homogeneously distributed ultra-fine (70–350 nm) pores was reinforced with NdPO₄-coated woven mullite fibre mats (Nextel™ 720) leading to damage-tolerant composites with good high temperature (1300 °C) strength and thermal cycling resistance. Electrophoretically deposited fibre preforms were placed in a high-load pressure filtration assembly, leading to formation of consolidated compacts with high green densities. After sintering at 1200 °C for 3 h, the compacts had a density of 86.4% of theoretical density and showed damage-tolerant behaviour up to 1300 °C, with flexural strength values of 235 MPa and 224 MPa at room temperature and 1300 °C, respectively. No significant microstructural damage was detected after thermal cycling the samples between room temperature and 1150 °C for up to 300 cycles. The thermomechanical test results combined with detailed electron microscopy observations indicate that the overall composite behaviour in terms of damage-tolerance, thermal capability and thermal cycling resistance is mainly controlled by two microstructural features: (1) the presence of a dense NdPO₄ interphase but weak bonding with the matrix or fibre and (2) the presence of homogeneously distributed nano pores (<350 nm) within the mullite matrix.     

高岭土加入量对合成轻质微孔莫来石性能的影响

以高岭土、工业氧化铝、硅石粉为起始原料,采用湿法共磨,注浆成型,利用高岭石热分解过程中形成一次莫来石及高活性的无定形SiO2,合成高纯轻质微孔莫来石.研究了高岭土加入量及煅烧温度对轻质莫来石体积密度与莫来石生成量的影响.结果表明,随配比中高岭土加入量的增加,莫来石的体积密度有下降的趋势,且有利于莫来石相含量的提高.高的煅烧温度虽能增加莫来石相的生成量,但不利于莫来石合成料的轻质化,适宜的煅烧温度为1450℃.