Transient liquid phase sintering of high-purity mullite for high-temperature structural ceramics

High-purity mullite ceramics, promising engineering ceramics for high-temperature applications, were fabricated using transient liquid phase sintering to improve their high-temperature mechanical properties. Small amounts of ultrafine alumina or silica powders were uniformly mixed with the mullite precursor depending on the silica-alumina ratio of the resulting ceramics to allow for the formation of a transient liquid phase during sintering, thus, enhancing densification at the early stage of sintering and mullite formation by the reaction between additional alumina and the residual glassy phase (mullitization) at the final stage of sintering. The addition of alumina powder to the silica-rich mullite precursor resulted in a reaction between the glassy silica and alumina phases during sintering, thereby forming a mullite phase without inhibiting densification. The addition of fine silica powder to the mullite single-phase precursor led to densification with an abnormal grain growth of mullite, whereas some of the added silica remained as a glassy phase after sintering. The resulting mullite ceramics prepared using different powder compositions showed different sintering behaviors, depending on the amount of alumina added. Upon selecting an optimum process and the amount of alumina to be added, the pure mullite ceramics obtained via transient liquid phase sintering exhibited high density (approximately 99%) and excellent high-temperature flexural strength (approximately 320 MPa) at 1500 °C in air. These results clearly demonstrate that pure mullite ceramics fabricated via transient liquid phase sintering with compositions close to those of stoichiometric mullite could be a promising process for the fabrication of high-temperature structural ceramics used in an ambient atmosphere. The transient liquid phase sintering process proposed in this study could be a powerful processing tool that allows for the preparation of superior high-temperature structural ceramics used in the ambient processing atmosphere.     

Interactions of Li2O volatilized from ternary lithium-ion battery cathode materials with mullite saggar materials during calcination

In recent years, the rapid development of Li(Ni_xCo_yMn_1-x-y)O₂ (LNCM) materials for application in ternary lithium-ion batteries has led to an increased demand for refractory kiln saggars in industries. However, saggars used for firing ternary Li-ion battery cathode materials are often subjected to severe corrosion and spalling. To investigate the damage mechanism of the saggar materials, non-contact corrosion experiments were designed to study the effects of the precursor additions, calcination temperature, and number of calcinations during the interaction between mullite saggar and LNCM materials. The phase composition and microstructure of the mullite saggar specimens before and after corrosion were characterized using X-ray diffraction and scanning electron microscopy, respectively, to obtain a comprehensive understanding of the causes of the deterioration of mullite saggar materials during corrosion.     

Preparation and characterization of mullite whisker reinforced ceramics made from coal fly ash

Ceramics with mullite whiskers were prepared from coal fly ash and Al₂O₃ raw materials, with AlF₃ used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF₃ addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF₃, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm³ and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources.     

Effect of in-situ formation of columnar mullite and pore structure refinement on high temperature properties of corundum casatbles

The effects of in-situ synthesis columnar mullite and pore structure on the hot modulus of rupture (HMOR), thermal shock resistance and corrosion resistance of corundum castables have been investigated in this paper. When 2% nano silica was added, the pore diameters of castables could be decreased to 15 nm (at 110 °C), 1 μm (1100 °C) and 6 μm (1500 °C), respectively. The corresponding reducing magnitude of pore size is 98.5%, 83.3% and 33.3%. The HMOR of castables fired at 1500 °C increased by 110% to 3.64 MPa. Furthermore, after three thermal shock cycles, the residual strength ratio of castables increased from 5.2% to 15.3%. A large amount of cross-distributed columnar mullite was formed between nano silica and α-Al₂O₃ by the two-dimensional nucleation mechanism, which remarkably enhanced the high temperature properties. The penetration index reduced from 30.86% to 19.88%, suggesting that smaller pore size and higher viscosity had a great influence to the penetration process.     

SiC（w）／TZP＋mullite陶瓷复合材料界面和组成设计与力学性能

本文从理论上分析了ＳｉＣ（ｗ）ＴＺＰ＋ｍｕｌｌｉｔｅ（ｐ）复合材料界面残余热应力及其在基质内的分布规律。提出在ＳｉＣ（ｗ）表面涂复Ａｌ２Ｏ３和在ＰＺＴ中加入ｍｕｌｌｉｔｅ（ｐ）联合作用来降低晶须／基质界面残余热应力的界面设计方案，导出ＳｉＣ（ｗ）和ｍｕｌｌｉｔｅ（ｐ）协同补强ＰＺＴ的匹配条件。制备了ＳｉＣ（ｗ）／ＴＺＰ＋ｍｕｌｌｉｔｅ（ｐ）复合材料并了ＳｉＣ（ｗ）表面涂层Ａｌ２Ｏ３厚度和ＳｉＣ（ｗ     

莫来石材料的研究现状及其应用

较详细地介绍了莫来石的性能、生产、研究现状和用途。尤其对多元复合莫来石韧性陶瓷及莫来石超细粉末的制备进行了评述,同时展望了莫来石作为高级陶瓷材料的发展前景。     

组合肋板式陶瓷换热器材质的研究

以耐火粘土、高矾土及滑石为原料研制了堇青石基陶瓷材料,并对其组织和性能尤其是抗热震性进行了研究。结果表明,堇青石基上分布着针状莫来石的材料具有更高的抗热震性。对评价换热器用陶瓷材料抗热震性参数进行了讨论,指出抗热震损伤参数R″″更适合于作为优选陶瓷换热器用材质的指标。     

凝胶法片状莫来石粉的制备及应用

采用拟薄水铝石和非晶态超细SiO_2微粉为原料。以溶胶-凝胶工艺制取莫来石凝胶,通过干燥、煅烧研制得片状结晶莫来石粉。初步研究了凝胶法莫来石粉在钛酸铝陶瓷和烧结刚玉砖中的应用。实验结果表明:凝胶粉起到了促进烧结、降低烧成温度的作用,并使钛酸铝——莫来石复相陶瓷和刚玉砖的强度得到了显著提高。     

利用铝厂污泥合成莫来石/刚玉复相材料

采用铝型材厂污泥和粘土为原料合成莫来石刚玉复相材料，主要探讨不同Al2O3／SiO2比值对形成的晶相结构影响。采用XRD和SEM表征各样品的晶相，结果表明各样品都形成2种晶相：莫来石固溶体和刚玉相，其中No．2配方中莫来石和刚玉的比例为：71．6：28．4，莫来石在扫描电镜下呈柱状交织，为较佳配方。     

Dehydration of water/1-1-dimethylhydrazine mixtures by zeolite membranes

In this research, dehydration of water/1-1-dimethylhydrazine (UDMH) mixtures by zeolite NaA and hydroxy sodalite membranes has been investigated. Support of these membranes has been tubular mullites that have been made by extruding a mixture of about 67–75% kaolin clay and 33–25% distilled water using an extruder. Zeolite NaA and hydroxy sodalite membranes have been coated on the external surface of the porous supports by the hydrothermal synthesis.

UDMH/water mixtures have been separated at ambient temperature and pressure by pervaporation (PV) using these zeolite membranes. These membranes showed very high selectivity of water for all UDMH mixtures. For the UDMH/water mixtures, separation factor as high as 10 000 has been obtained for UDMH feed concentration of 2%. Total mass fluxes of 1.05–0.2 kg/(m² h) have been also obtained.