Densification behavior of mullite-Al2TiO5 composites by reaction sintering of natural andalusite and TiO2

In this work, mullite-Al₂TiO₅ composites were fabricated by natural andalusite with TiO₂ as an additive. The densification characteristic, phase composition and mullitization process of andalusite with TiO₂ addition was investigated by the Archimedes’ principle, dilatometry, X-ray diffraction and scanning electron microscopy (SEM-EDS) techniques. The results showed that the incorporation of TiO₂ not only enhanced the thermal stability of in-situ Al₂TiO₅ in the silica liquid yielded from the mullitization of andalusite, but also accelerated andalusite decomposition and retarded mullite formation, which facilitated the sintering and densification of mullite-Al₂TiO₅ composites.     

陕西眉县红柱石选矿试验研究

针对眉县红柱石矿石的特点，采用重选-强磁选、重磁选精矿酸浸、反浮选-强磁选工艺进行选矿试验，推荐采用反浮选-强磁选工艺流程，在磨矿细度65％～70％-0．071mm条件下，获得精矿产率57％，精矿品位58％，Al2O3回收率62％的选矿技术指标，为该矿的开发利用提供了可行性技术方案。     

酒泉某难选红柱石矿选别工艺对比试验研究

针对酒泉某难选红柱石矿开展了球磨和棒磨的磨矿细度对比试验、脱泥粒度试验和碱性与酸性介质浮选工艺对比试验研究。试验结果表明,该红柱石矿适合棒磨磨矿,较优磨矿细度为-0.074mm占85.19%,较优脱泥粒度为20μm,碱性介质浮选工艺的精矿指标较优。在确定碱性介质浮选工艺基础上,试样经过磨矿-脱泥-磁选-1粗8精1扫的闭路流程试验,获得了Al_2O_3品位为52.94%、红柱石回收率为54.10%、红柱石含量为83.88%的精矿。     

Preparation and thermal shock resistance of corundum-mullite composite ceramics from andalusite

Corundum-mullite composite ceramics have high hardness, small plastic deformation and other excellent performances at high temperature. Corundum-mullite composite ceramics were fabricated from andalusite and α-Al₂O₃ by in-situ synthesis technology. Effects of mullite/corundum ratio and sintering temperatures on the water absorption, apparent porosity, bulk density, bending strength, thermal shock resistance, phase composition and microstructure of the sample were investigated. Results indicated that the in-situ synthesized mullite from andalusite combined with corundum satisfactorily, which significantly improved the thermal shock resistance as no crack formed after 30 cycles of thermal shock (1100 °C-room temperature, air cooling). Formula A4 (andalusite: 37.31 wt%, α-Al₂O₃: 62.69 wt%, TiO₂ in addition: 1 wt%, mullite: corundum=6:4 in wt%) achieved the optimum properties when sintering at 1650 °C, which were listed as follows: water absorption of 0.15%, apparent porosity of 0.42%, and bulk density of 3.21 g⋅cm⁻³, bending strength of 117.32 MPa. The phase composition of the sintered samples before and after thermal shock tests were mullite and corundum constantly. The fracture modes of the crystals were transgranular and intergranular fractures, which could endow the samples with high thermal shock resistance.     

热风炉长寿与低蠕变Al2O3-SiO2系耐火材料的探究

回顾了中国热风炉用低蠕变Al2O3-SiO2系耐火材料研发的历程。通过对比矾土基低蠕变Al2O3-SiO2系耐火材料与莫来石基低蠕变Al2O3-SiO2系耐火材料的实际使用结果认为,要实现热风炉长寿命,对于热风炉用耐火材料而言,除了要求其具有优异的抗蠕变性能外,还应具有优良的抗热震性、抗CO和碱蒸气侵蚀等综合性能。针对中国资源综合利用的现状和可持续发展战略要求,建议使用红柱石或莫来石基原料制备Al2O3-SiO2系低蠕变系列耐火材料;即通过对原料进行分级,实现天然Al2O3-SiO2系原料(主要是红柱石)和人工合成Al2O3-SiO2系原料资源的综合利用,优化材料的矿物组成,制备以莫来石为主晶相结构,Al2O3质量分数低于75%的莫来石基低蠕变系列制品,并结合性价比进行优化配置,真正实现热风炉的长寿化,应该是今后长寿型热风炉用Al2O3-SiO2系耐火材料研发的重点。     

用红柱石制备莫来石纤维增强材料的实验研究

以红柱石为原料，对高温下红柱石－莫来石相变过程的微观物相结构及莫来石纤维特征进行了实验研究。认为，利用红柱石的高温相交，在陶瓷烧结过程中直接制取莫来石纤维是可行的。     

氧化铝纤维/红柱石复合材料的制备与性能

笔者针对红柱石和氧化铝纤维广泛的应用前景，通过两者的复合来提高红柱石制品的使用性能，采用传统无压烧结工艺制备氧化铝纤维增强红柱石基复合材料。探讨了红柱石细粉的粒度、氧化铝纤维的加入量和烧成温度对氧化铝纤维增强红柱石基复合材料物理性能以及常温力学性能的影响。结果表明：随着红柱石细粉粒度的降低，氧化铝纤维团聚现象加剧，由于纤维与基质的界面结合力较强，原料粒度的变化对材料常温力学性能影响不大；当氧化铝纤维加入量为5％。10％时，材料的体积密度最大，常温耐压强度和抗折强度最好，超过10％后由于纤维的团聚，材，料的力学性能显著下降；当烧成温度超过1400℃后纤维与基体开始反应，随着烧成温度的进一步提高，纤维遭到破坏的程度加剧。     

烧成温度和保温时间对红柱石基材料烧结性能的影响

以高纯度南非红柱石(有4～1mm、<1mm和<0.088mm三种粒级,且4～1mm的颗粒料为1500℃3h煅烧过的熟料)和活性氧化铝细粉(粒度<0.044mm)为原料,经配料、混练、成型、干燥后,将一部分试样分别在1300℃、1400℃、1500℃和1600℃下保温3h煅烧;另一部分试样在1600℃下分别保温1h、3h、6h和9h煅烧,待试样随炉冷却至常温后,检测其体积密度、显气孔率、耐压强度和烧成线变化率等,并采用XRD、SEM等手段分析各试样的物相组成和显微结构,以研究烧成温度及保温时间对高纯度红柱石的莫来石化程度及对红柱石基材料烧结性能的影响。结果表明:提高烧成温度对促进高纯红柱石的莫来石化十分有效,延长保温时间对于促进制品的烧结作用很大;高纯红柱石基材料需在1600℃下保温3h烧成,才能使红柱石完全莫来石化;欲使材料烧结良好且玻璃相含量低,物相较纯,则保温时间要达到6h左右。     

陕西眉县红柱石矿开发前景展望

介绍了红柱石性质、用途和国内外市场预测；眉县富矿型红柱石矿开发利用现状，重点分析存在技术和经营问题，调整产品方案，经济效益测算．提出了工艺流程改进意见，展望了本矿区开发利用前景。     

Enhanced alkali vapor attack resistance of bauxite-SiC refractories for the working lining of cement rotary kilns via incorporation of andalusite

Bauxite-SiC refractories as the working lining of cement rotary kiln are subjected to severe alkali attack due to alternative fuel combustion. Herein, the present work aims to enhance their alkali attack resistance via incorporation of different types of andalusite (aggregates and powder). Results show that addition of andalusite reduces penetration of alkali vapor by decreasing their pore size. In particular, the presence of andalusite aggregate traps alkali vapor inside its pore network, retarding the corrosion of refractory matrix. By comparison, the presence of andalusite powder contributes to formation of liquid corrosion products to block the pores, which prevent alkali vapor from further penetration. Incorporation of andalusite into BSRs is straightforward and sought-after, providing an effective approach for high-performance refractory materials with excellent alkali attack resistance.