Comparative analysis on corrosion behavior of lightweight and dense mullite–corundum refractories: Role of Si-rich phase

The corrosion resistance of lightweight and dense mullite–corundum refractories to cement materials was examined. The specimens following static crucible treatment were investigated using phase analysis, microstructure, and thermodynamic simulation. The results reveal that diffusion of the silica-rich phase enhances alumina saturation solubility in the slag, reducing the corrosion resistance of the mullite–corundum refractories. The large proportion of closed pores and the continuous net-like structure of anorthite created by the corrosion reaction in the matrix, on the other hand, prevent further slag penetration into the lightweight mullite–corundum refractories. As a result, the presence of the silica-rich phase assures better slag penetration resistance of lightweight mullite–corundum refractories.     

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.     

Andalusite: An amazing refractory raw material with excellent corrosion resistance to sodium vapours

The chemical attack of alumina refractories by sodium vapours is far from been completely understood. In order to contribute to a better knowledge of this attack, a laboratory test was developed to simulate the sodium gaseous corrosion of different raw materials and refractories.Corrosion of alumina raw materials by sodium vapours is due to a dissolution–precipitation process by a Na₂O rich liquid phase. The gaseous corrosion strongly depends on the microstructures and the assemblage of phases in alumina raw materials. Fire clay and andalusite raw materials exhibit very high corrosion by Na vapours. In spite of an initial high silica glass content, and as a result of trapping of the main part of the glass in the capillary network of the mullite composite crystal, mullitised andalusite leads to excellent corrosion resistance which is close to monocrystalline fused mullite.Consequently, The use of mullitised andalusite particles in the matrix of alumina refractories limits the liquid phase formation during corrosion by sodium gas. These experimental results are in agreement with thermodynamic calculations.     

Effect of aggregate particle content on sintering and corrosion resistance of hibonite-cordierite saggar

An effective method to improve the corrosion resistance of the saggar to the cathode material for Li-ion batteries is to reduce the reaction between Li₂O and the components of the saggar matrix material. Saggars are multi-component and multi-graded functional materials, in which aggregate particles are an important factor in resisting corrosive media. Consequently, in this study, hibonite with good alkali corrosion resistance was selected as the main raw material to prepare hibonite-cordierite composite saggars with different aggregate particle contents. The effect of the aggregate particle content on the sintering performance and corrosion resistance of CA₆-M₂A₂S₅ saggars was systematically studied. The results show that the optimal hibonite aggregate content for saggar performance is 40 wt%, its bulk density is 2.44 g/cm³, and the cold and hot moduli (1100 °C × 30 min) of rupture are 15.66 MPa and 14.67 MPa, respectively, the strength retention rate of the sample after five thermal cycles at 1100 °C × 30 min was 53.30%. Additionally, during the sintering process, a dense anorthite protective layer was formed along the edges of the CA₆ particles, which hindered the reaction between the positive electrode material and saggar sample body, thereby improving the corrosion resistance of the saggar.     

Synthesis of an innovative zirconia-mullite raw material sintered from andalusite and zircon precursors and an evaluation of its corrosion and thermal shock performance

This paper deals with the synthesis and the properties of an innovative zirconia-mullite raw material sintered from an andalusite/alumina/zircon mix. The microstructure of these composite grains consists of fine zirconia particles in a mullite matrix. This study highlights that the synthesis process (sintering from SiO₂.Al₂O₃, Al₂O₃ and ZrSiO₄ raw materials) plays an essential role in the improvement of both the corrosion resistance to alumina-lime slag and soda-lime glass and the thermal shock resistance of this refractory. The microstructural observations correlated with non-destructive characterizations, ultrasonic pulse echography and acoustic emission techniques, underline the repairing mechanism exhibited by this material after experiencing repeated thermal shock.     

Porous mullite ceramics with enhanced compressive strength from fly ash-based ceramic microspheres: Facile synthesis,structure, and performance

Porous mullite ceramics are widely used in heat insulation owing to their high temperature and corrosion resistant properties. Reducing the thermal conductivity by increasing porosity, while ensuring a high compressive strength, is vital for the synthesis of high-strength and lightweight porous mullite ceramics. In this study, ceramic microspheres are initially prepared from pre-treated high-alumina fly ash by spray drying, and then used to successfully prepare porous mullite ceramics with enhanced compressive strength via a simple direct stacking and sintering approach. The influence of sintering temperature and time on the microstructure and properties of porous mullite ceramics was evaluated, and the corresponding formation mechanism was elucidated. Results show that the porous mullite ceramics, calcined at 1550 °C for 3 h, possess a porosity of 47%, compressive strength of 31.4 MPa, and thermal conductivity of 0.775 W/(m?K) (at 25 °C), similar to mullite ceramics prepared from pure raw materials. The uniform pore size distribution and sintered neck between the microspheres contribute to the high compressive strength of mullite ceramics, while maintaining high porosity.     

Corrosion of Li-ion battery cathode materials on mullite insulation materials during calcination

A specially designed experimental device was used in laboratory to investigate the corrosion of mullite during the calcination of Li(Ni_xCo_yMn_z)O₂ (LNCM) materials. The anti-corrosion tests were carried out at 1000, 1100, 1200 and 1300 °C, and characterized with X-ray diffraction and scanning electron microscopy. The influence of temperature on the interactions between mullite insulation materials and LNCM materials was determined. In addition, the high-temperature creep properties of the mullite insulation materials before and after corrosion were tested. The laboratory scale tests, thermodynamic and kinetic calculations allowed a more comprehensive understanding of the evolution of the mullite insulation materials during serving for the roasting process of LNCM materials. Through this research, it is suggested that the upgrading of the kiln lining in the lithium battery industry should select materials with excellent resistance to alkali corrosion, especially excellent resistance to Li⁺ corrosion.     

Firing properties and corrosion resistance of mullite-Al2TiO5 saggar materials

Conventional refractory materials used for calcining ternary lithium-ion battery cathode materials, such as mullite, cordierite, and magnesia-alumina spinel, are vulnerable to attack by Li(Ni_xCo_yMn_1−x−y)O₂ (LNCM) materials and therefore have a short service life. In order to improve the corrosion resistance of refractory materials to LNCM materials, mullite-Al₂TiO₅ materials with different contents were synthesized in this paper by using calcined mullite powder, TiO₂ powder, and La₂O₃ powder as raw materials, which were calcined at 1500–1600°C temperature, respectively. In this study, the potential of the materials for the preparation of LNCM materials was investigated in terms of its physical properties, resistance to the corrosion of LNCM materials, and resistance to thermal shock. The results showed that mullite-Al₂TiO₅ composites can be successfully synthesized at 1500–1600°C, and the physical properties of the materials met the production requirements. The prepared mullite-Al₂TiO₅ composites also exhibited better physical properties, good corrosion resistance, and proper thermal shock resistance compared with mullite refractories.     

Thermodynamic properties of aluminum titanate-mullite composite ceramics containing heat stabilizer

Using Al₂O₃ and TiO₂ as raw materials, adding MgO as heat stabilizer and mullite as enhancer, aluminum titanate-mullite multiphase ceramics were successfully prepared by solid phase synthesis. The effects of MgO and mullite were systematically studied on the phase composition, microstructure, thermal stability, sintering properties, and mechanical properties of aluminum titanate ceramics. The results showed that the introduction of Mg²⁺ can partially replace Al³⁺ to form Mg_xAl_2(1-x)Ti_(1+x)O₅ solid solution, improved the thermal stability of aluminum titanate ceramics, and promoted the formation and growth of grains, which reduced the sintering temperature. The crack deflections caused by mullite particles improved the mechanical properties. The filling effect of mullite particles and the formation of silica in mullite raw materials were conducive to ceramic densification. The statistics of Mg4M10 sample were as follows: the porosity was only 2.9%, the flexural strength was as high as 64.15 MPa, and the thermal expansion coefficient was 1.35 × 10⁻⁶ K⁻¹ (RT-700°C), encouraging the application of ceramics with high thermal mechanical properties.     

锆英石加入量对莫来石-刚玉材料性能的影响

以板状刚玉、电熔莫来石、Al2O3粉、硅线石和粘土为原料,制备了莫来石-刚玉高温窑具,并研究了锆英石加入量对其力学性能和抗热震性能的影响.试验结果表明,随着锆英石细粉的增加,抗折强度有所下降,抗热震性能有较大改善,当锆英石细粉加入量为12%时,获得较好的热震性能.同时还发现随着烧成温度的升高,试样热震性能出现下降.     

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℃.     

球土含量对环保型轻质材料性能的影响

本文以陶瓷抛光废料为主要原料,辅以球土、长石、石英等,制备一种以闭口气孔为主的新型轻质建筑材料.在此基础上,采用XRD、体式显微镜、导热仪等研究了球土含量对试样的体积密度、抗压强度、物相组成、导热系数等性能的影响.实验结果表明:随着球土含量的增多,材料中莫来石相开始形成并逐渐增多,抗压强度也逐渐增强;另一方面,随着球土添加量的增加,试样中孔径明显变小,体积密度增大,相应的导热系数随体积密度的增大而直线增大.     

粉煤灰资源化合成莫来石材料及其性能研究

以天然铝矾土和工业废物粉煤灰为原料,运用反应烧结合成了低成本的莫来石陶瓷材料。结果证明,刚玉与方石英相在1200～1300℃间通过固态反应生成二次莫来石,在温度高于1300℃时,刚玉相熔于短暂玻璃相中。二次莫来石化及莫来石晶体生长所导致的样品体膨胀大于液相烧结所引起的收缩,导致样品出现膨胀现象。1600℃烧结样品的平均热膨胀系数为5.40×10-6℃-1,平均抗弯强度186.19 MPa。莫来石在强酸强碱热溶液中表现出两个阶段:快速阶段(0～5h)和低速阶段(5～20h),这分别对应于样品的表面腐蚀和体腐蚀过程。     

粘土坩埚的使用损毁机制及性能改进

对熔化器皿玻璃等的粘土质坩埚使用中的高温软化变形、玻璃液侵蚀、热震开裂等损毁机制进行了分析研究。对坩埚性能改进的试验研究表明:纯化原料、选用球粘土作为坩埚的结合粘土,有益于降低坩埚的高温软化变形及不均匀收缩,提高坩埚的抗玻璃液侵蚀能力。增加熟焦用量、减少蜡石用量、引入少量蓝晶石细粉、蜡石以小粒径颗粒引入、提高坩埚泥料的密实性与均匀性等,有益于提高坩埚的耐高温、抗玻璃液侵蚀及抗热震性能。寻求坩埚新料源,开发出特种性能坩埚及复合型坩埚,是粘土坩埚行业技术发展的两项主要任务。     

Lightweight design of bauxite-SiC composite refractories as the lining of rotary cement kiln using alternative fuels

To meet the demand of energy-saving and adapt to the change from coal to the alternative fuel in the rotary cement kiln, bauxite-SiC refractories were fabricated by the incorporation of silica sol coated lightweight mullite aggregates in order to achieve low thermal conductivity and superior alkali vapor attack resistance simultaneously. Furthermore, the mechanism of resistance to alkali vapor attach was investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that the thermal conductivity of bauxite-SiC specimens decreased gradually with increasing amounts of silica sol coated lightweight mullite aggregates while changes in the alkali vapor attach were not detectable. The shell-covered structure with a silica sol coating on the surface of lightweight aggregates hindered alkali vapor diffusion into the aggregates at high temperature. Bauxite-SiC refractories possessed lower thermal conductivity, superior alkali attack resistance and higher mechanical properties compared with the specimens which contained pristine lightweight aggregates.     

Sintering behavior and morphology control of porous Al2O3-SiO2 ceramics for radome applications

Ceramics from porous Si₃N₄ and its derivatives SiAlON and Si₂N₂O were once considered the most promising high-temperature wave-transmitting materials. However, their large-scale application in the field of radomes is greatly restricted due to their poor oxidation resistance, high preparation costs, and expensive raw materials. Therefore, the development of low-cost porous oxide ceramics remains of significant interest to the field of high-temperature wave transmission. Surprisingly, mullite ceramics, which are representative of the Al₂O₃-SiO₂-system of ceramics, are ultra-low-cost materials with the potential to replace ceramics from Si₃N₄ and its derivatives. In this paper, integrated porous Al₂O₃-SiO₂-system ceramics were successfully prepared for load-bearing/wave-transmitting applications, using inexpensive calcined kaolin and alumina powder as the main raw materials. Calcined kaolin can provide seeds for the growth and development of mullite crystals in the ceramic system. High-strength and high-porosity ceramics were obtained with the mullite morphology controlled through the molar ratio of Al₂O₃ to SiO₂ and the resulting content of mullite seeds. With increasing of mullite seed content, the length and radial width of mullite whiskers with “interlocking structure” gradually change from rod-shaped “long and thick” to needle-like “short and thin.” The prepared porous Al₂O₃-SiO₂ ceramics have high flexural strength, fracture toughness, and good dielectric properties.     

Effect of mullite phase formed in situ on pore structure and properties of high-purity mullite fibrous ceramics

Porous mullite ceramics are potential advanced thermal insulating materials. Pore structure and purity are the main factors that affect properties of these ceramics. In this study, high performance porous mullite ceramics were prepared via aqueous gel-casting using mullite fibers and kaolin as the raw materials and ρ-Al₂O₃ as the gelling agent. Effects of addition of mullite fibers on the pore structure and properties were examined. The results indicated that mullite phase in situ formed by kaolin, and ρ-Al₂O₃ ensured the purity of mullite samples and mullite fibers bonded together to form a nest-like structure, greatly improving the properties of ceramic samples. In particular, the apparent porosity of mullite samples reached 73.6%. In the presence of 75% of mullite fibers, the thermal conductivity was only 0.289 W/m K at room temperature. Moreover, the mullite samples possessed relatively high cold compressive strength in the range of 4.9–9.6 MPa. Therefore, porous mullite ceramics prepared via aqueous gel-casting could be used for wide applications in thermal insulation materials, attributing to the excellent properties such as high cold compressive strength and low thermal conductivity.     

不同的烧失物对微孔莫来石性能的影响

莫来石的导热系数低、高温下体积稳定性好,适合用来制备轻质耐火材料。以硅石粉和工业氧化铝为起始物料,加入一定量的烧失物,通过在1350℃下煅烧6h制得了微孔莫来石轻质骨料。研究了碳黑、焦炭和无烟煤这三种烧失物对合成的莫来石骨料体积密度、气孔孔径分布、莫来石生成量及组织结构的影响。认为,不同的烧失物对微孔莫来石的体积密度、...     

中国耐火原料的新近发展

介绍了过去几年中国几种主要耐火原料,如矾土基原料(包括电熔刚玉、尖晶石、莫来石)、镁质原料(包括大结晶98电熔镁砂、高铁高钙镁砂、电熔或烧结镁铬砂)和非氧化物材料(包括氮化硅铁、氮化硅)的最新发展,同时讨论了非氧化物结合的新型材料在未来几年的发展趋势.