湖南富钾钠高岭土的选矿提纯试验研究

湖南富钾钠高岭土，主要矿物为长石、石英和高岭土。作为陶瓷原料，应对高岭土和长石、石英进行分离，以满足陶瓷配方要求。本试验研究通过除砂，分级、高梯度磁选及剥片等手段，实现了高岭石的富集，获得高岭土精矿Al2O3 29．33％，SiO2 52．50％，Na2O 1．43％，K2O 2．55％，-2μm 43．22％的指标。     

高岭土改性玻璃钢研究

本文研究了四种高岭土对玻璃钢的性能影响。研究结果表明，加入高岭土后，玻璃钢的强度或多或少都有降低；改性314－2高岭土加量28．8％时，能赋予树脂体系触变性，可用于代替气相SiO2；高岭土930－3能使玻璃钢的马丁耐热温度提高到230℃以上。改性314－2和改性930－3高岭土可以在FRP中推广应用。     

高岭土尾矿微晶玻璃的烧结与晶化

本研究对高岭土尾矿为主要原料制备的CaO－Al2O3－SiO2系统玻璃进行了烧结收缩试验,借助X射线衍射分析了影响烧结致密化过程的因素;探讨了玻璃组成对烧结和晶化的影响,采用合适的玻璃组成,用烧结工艺获得了主晶相为β-CaO·SiO2的高岭土尾矿微晶玻璃。     

瓷质外墙砖烧成过程变化及微观结构初探

本文介绍了以高岭土－石英－钠钾长石为主的配料中此入较多量的滑石，使瓷质砖配料组成属R2O（Na2O,K2O)-Al2O3-SiO2-MgO体系，简单介绍这种体系瓷质砖的生产工艺过程，定性描述了烧成过程中的变化及瓷相组成。结果表明，这种瓷质砖具有吸水率低（＜0．5％）、强度高（＞55Mpa)的特点，瓷相组成中晶相为石英，次相为富含Na2O,K2O和MgO的玻璃相，少量相为高岭石分解后产生的结晶程度差的莫来石。     

陶瓷原料砂子岭高岭土精选试验研究

砂子岭高岭土由于含铁量高，铁杂质矿物颗粒极细，是一种难选高岭土矿。经采用高频细筛，选择性分散－絮凝，剥片，高梯度磁选等工艺，使高岭土精矿在Ａｌ２Ｏ３，Ｆｅ２Ｏ３－２μｍ含量等指标均达到精选二级高岭土的质量指标。     

高岭土的化学组成对碳热还原-氮化法合成β′-sialon粉末的影响

研究了以不同化学组成的高岭土为主要原料并采用碳热还原－氮化法合成的sialon粉末的相组成。结果表明：合成粉末的物相组成及β′-sialon的Z值与高岭土的m(SiO2)/m(Al2O3)比值密切相关。     

改性粘土作为橡胶补强剂的研究

通过对粘土进行物理和化学改性，可制成橡胶补强剂，其补强效果接近或达到白炭黑水平。在对橡胶制品密度要求不高的情况下以它替代白炭黑，可明显降低成本。研究了偶联剂ＫＨ－８４５－４和ＫＲ－３８Ｓ对高岭土、绢云母的改性效果，结果表明，用偶联剂ＫＨ－８４５－４改性高岭土，其补强效果明显优于ＫＲ－３８Ｓ。而用ＫＲ－３８Ｓ改性绢云母，其补强效果优于ＫＨ－８４５－４。     

大洲高岭土矿物组成和深加工试验研究

系统介绍了大洲高岭土矿的地质概况，矿床特征，对大洲高岭土的理化性能进行了深入研究并对其进行了深加工试验研究试验结果表明：大洲高岭土是一种结晶较差的高岭石，工艺性能一般．Ｆｅ２Ｏ３含量在１．２％－２％，经深加工可降低Ｆｅ２Ｏ３含量．一般可以达到陶瓷工业用高岭土的一、二级标准，为陶瓷工业产品高档化创造了物质条件。     

湖南界牌高岭土精选试验研究

本项目对湖南界牌高岭土分别进行了物质组成、试样特性的测定研究和精选试验，表明该矿区高岭土系白云母、斜长石片麻岩、绿泥石绢云母片岩和石英－斜长石斑岩等岩石风化而成的残积高岭土矿区；界牌高岭土中铁钛元素均以氧化物形式存在；高梯度磁选对界牌高岭土除铁钛效果较好。     

PP—高岭土复合材料的增韧

醉庆加工设备中采用化学与物理改性相结合的方法对PP－高岭土复合材料的增韧进行了研究。结果表明，该复合体系在PE－g－MAH的存在下，加10份EPDM，体系的制品冲击强度提高到增韧前的289．7％，无缺口提高到增韧前的342．4％。在MAH、PE、高岭土接枝母料的存在下，EPDM量相同，体系的缺口冲击强度提高增韧前的324．1％，无缺口提高到增韧前的485．4％。本文还研究了橡胶种类、胶量、高岭土品种及改性工艺对增韧效果的影响，得出胶种以EPDM最好，用最10％，高岭土以超细土的品种为好。     

莫来石晶粒柱状生长对莫来石基陶瓷力学性能的影响

将AlF3加入莫来石(莫来石/氧化锆)先质中,生坯试样经密闭处理及常压烧结,可获得莫来石柱状晶粒生长.实验结果表明:莫来石柱状生长使莫来石陶瓷在其强度不下降的前提下,韧性提高,且随柱状晶粒粒径增大而增加有类似架桥作用.ZTM(含AlF3)材料韧性的提高是由于莫来石柱状晶粒生长使t-ZrO2形态发生了变化,具有较大长径比或有尖角的不规则形态的t-ZrO2晶粒容易发生应力诱导相变,使材料力学性能得到明显提高.     

Development of Textured Mullite by Templated Grain Growth

Highly textured mullite was obtained by enhancing anisotropic grain growth by TiO₂ doping and by templating grain growth on oriented acicular mullite seed particles in a mullite precursor. Upon heating, the mullite precursor crystallized and densified to an equiaxed microstructure of 1-2 µm mullite grains at which time the mullite seed particles grew rapidly in the length direction ( c -axis) to produce a highly textured microstructure. By changing the seed (template) particle concentration, a range of oriented microstructures and anisotropic grains could be produced.     

Microstructural evolution and densification behavior of porous kaolin-based mullite ceramic added with MoO3

Microstructural evolution and densification behavior of porous kaolin-based mullite ceramic added with MoO₃ were investigated. The results indicated that MoO₃ addition not only lowered the secondary mullitization temperature to below 950?°C, but also facilitated effectively the anisotropic growth of mullite grains. Fine mullite whiskers grew and interlocked with one another in the pre-existing pore regions, in-situ forming a stiff 3D skeleton structure of mullite whiskers, which arrested further densification of the sample. On the other hand, due to the great capillary attraction of small pores, the liquid phase tended to spread over small grains, which favored the growth from small mullite grains into whiskers at the expense of the liquid phase. Consequently, competitive mechanisms of sintering and crystal growth of mullite functioned, which further limited the sample densification. As a result, the total linear shrinkage of the sample added with MoO₃ after firing at 1400?°C was only ??2.75%, and its porosity was retained at as high as 67%.     

Microstructure and properties of porous anorthite/mullite whiskers ceramics with high porosity

Porous anorthite/mullite whiskers ceramics with high porosity (>91%) and high strength (>0.45 MPa) have been successfully prepared by foam gel-casting method. Effects of extra mullite whiskers on properties including thermal conductivity and compressive strength at different temperatures were investigated and discussed in terms of microstructure observed through SEM and TEM. The results showed that the addition of extra mullite whiskers in certain content could effectively reduce thermal conductivity, improve the compressive strength both at room and high temperature at same time. When the mullite whiskers content was 20 mol%, the porosity was as high as 91.6 ± 0.19%, the thermal conductivity was low to 0.034 ± 0.003 W/(m·K), and the compressive strength at 1000°C was high to 0.64 ± 0.11 MPa three times to the pure one. Small pores, small grains, and more phase interface or grain boundary caused by the addition of extra mullite whiskers were the main factors for low thermal conductivity. Meanwhile, small pores, closely bonded small grains, and the stable three-dimension network formed by mullite whiskers helped to improve strength.     

Microstructure, Microchemistry, and Flexural Strength of Mullite Ceramics

The microstructure of mullite ceramics hot-pressed and sintered at different temperatures was studied using transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) with EDS, and electron probe microanalysis (EPMA). The specimens, consisting of stoichiometric mullite grains without glassy phase, are obtained by hot-pressing stoichiometric mullite powder at 1575°C for 1 h. Silica-rich glassy phases are observed using TEM at three-grain junctions of mullite grains in specimens heated at and above 1600°C. However, high-resolution transmission electron micrographs show no glassy phase at two-grain boundaries in all specimens. SEM with EDS analyses show that the average value of Al₂O₃ contents of mullite grains increases slightly with increasing temperature. These results are consistent with a published Al₂O₃–SiO₂ phase diagram. The flexural strength of mullite specimens at room temperature depends on their microstructure, such as the grain size and grain size distribution of mullite grains. The strength is high at room temperature and up to 1200°C, and it decreases at and above 1350°C, irrespective of the presence of the glassy phase.     

Effect of Sol-Gel Mixing on Mullite Microstructure and Phase Equilibria in the α-Al2O3-SiO2 System

Starting powders containing 72 wt% Al₂O³ and 28 wt% SiO₂, were prepared by sol-gel methods classified as colloidal and polymeric. Compacts fired at 1700°C showed significant differences in microstructure. The specimens formed with the colloidal powder had mullite grains of prismatic shape and a liquid phase; with polymeric powder, mullite grains were granular with no liquid phase present. It is shown that the mullite grains in the first case are higher in AI₂O₃ content, resulting in an excess of SiO₂ which is the base for the liquid phase. In the second case, the mullite grains have the same Al₂O₃ content as the starting powders. The presence of a liquid phase in the first case is considered to be metastable, resulting from the nature of the starting materials and processing conditions employed.     

Sintering and Mechanical Properties of Yttria-Doped Tetragonal ZrO2 Polycrystal/Mullite Composites

Yttria-doped tetragonal ZrO₂ polycrystal (Y-TZP)lmullite composites were sintered at 1450° to 1500°C in air to disperse rodlike mullite grains at the grain boundary of Y-TZP and the mechanical and thermal properties were investigated. The aspect ratios of mullite grain were >2. High fracture strength of 1000 MPa and fracture toughness of 12 MPa·m^1/2 were obtained by dispersing <20 vol% of mullite into Y-TZP. The thermal expansion coefficient of Y-TZP/mullite composites decreased with increasing mullite content. The thermal shock resistance of Y-TZP was greatly improved by dispersion of rodlike mullite grains.     

Preparation of mullite ceramics with equiaxial grains from powders synthesized by the sol-gel method

Four different alumina content of mullite ceramics were fabricated by powders synthesized using the sol-gel method. The synthesis process of powders, microstructure evolution, mechanical and optical properties of the mullite ceramics were studied. The XRD results showed that the precursors transformed into aluminosilicate spinel phase at 1000 °C and mullite phase at 1200 °C. Equiaxial grains were easy to form in the alumina-rich mullite ceramics while elongated grains were easy to form in the alumina-poor mullite ceramics. With the increase of alumina content, the grain size of the samples firstly increased and then decreased, the number of elongated grains decreased while equiaxed grains increased. The flexural strength, compression strength, fracture toughness, and Vickers hardness all decreased firstly and then increased. While the infrared transmittance increased firstly and then decreased. The transmittance at 4 μm (thickness of 0.75 mm) of the ceramics containing 66mol% Al₂O₃ reached the highest (72%) when sintered at 1780 °C because of the equiaxial grains.     

SiC/ZTM Nanocomposite with Needlelike Mullite Grains and Enhanced Mechanical Properties

Zirconia-toughened mullite (SiC/ZTM) nanocomposites were prepared by a chemical precipitation method. The samples showed good sinterability and could be densified to >98.7% of the theoretical density at 1350°–1550°C. Because of the addition of mullite seeds in the starting powder and the pinning effects of ZrO₂ and SiC particles on mullite grain growth, a fine-grained microstructure formed. Mullite grains were generally equiaxed for the sample sintered at 1400°C; whereas, for the sample sintered at 1550°C, most mullite grains took a needlelike morphology, and SiC particles were primarily located within mullite grains. The strength and toughness increased with the increasing sintering temperature, and reached their respective maximum of 780 MPa and 3.7 MPa·m^1/2 for the sample sintered at 1550°C.     

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.