硅溶胶结合刚玉-莫来石浇注料的研制及应用

摘要 以电熔板状刚玉及莫来石为骨料;以白刚玉粉、α-Al2O3微粉及莫来石粉为细粉;研制了以硅溶胶为结合剂的刚玉-莫来石浇注料。该浇注料已成功应用于武钢铁厂风口处和烧结厂点火炉的炉顶及侧墙;有效地简化了干燥和烘烤工艺;缩短了炉衬的烘烤时间。关键词 硅溶胶;刚玉-莫来石浇注料;加热炉     

莫来石结合的浇注料

在耐火浇注料中用４种不同的骨料即电熔氧化铝、电熔莫来石、ＳｉＣ和石英对莫来石结合系进行了试验。这４种混合浇注料具有良好的流动性并且经一夜之后就可脱模。测定了高温强度和常温强度。含有电熔氧化铝或电熔莫来石的浇注料在１３００℃以上由于形成了莫来石改进了高温强度。而ＳｉＣ质浇注料在１３００℃以上虽形成莫来石，但没有提高其高温强度。在１２００℃￣１３００℃下，ＳｉＣ质浇注料的高温强度比其它浇注料的高温强度     

硅溶胶结合刚玉和刚玉-莫来石浇注料的性能研究

以电熔白刚玉、电熔莫来石、氧化铝微粉、二氧化硅微粉和硅溶胶为主要原料,制备了硅溶胶、二氧化硅微粉结合刚玉浇注料以及硅溶胶结合刚玉-莫来石浇注料,研究了不同温度处理后浇注料的常温性能、冷态和热态抗折强度以及弹性模量等性能,并进行了差热、X射线衍射和显微结构分析。研究结果表明:1)与二氧化硅微粉相比,硅溶胶能够显著提高浇注料800℃以下的抗折强度;硅溶胶结合和二氧化硅微粉结合的机制以及随温度变化的规律基本一致。2)高温下刚玉骨料中β-Al2O3分解产生的Na2O大部分进入液相,使液相中Na2O含量增加,不利于浇注料中原位生成莫来石,并降低材料的高温强度。3)莫来石加入到硅溶胶结合刚玉浇注料中,能显著降低浇注料的弹性模量,借助于高温下液相的传质作用,莫来石彼此连接形成网络,从而增加了浇注料的强度。     

点火炉用硅溶胶结合刚玉-莫来石浇注料的性能及应用

以致密刚玉、莫来石为骨料,以白刚玉粉、α-Al2O3微粉及莫来石粉为细粉,研制了点火炉用硅溶胶结合刚玉-莫来石浇注料,并在武汉钢铁集团烧结厂点火炉改造中与水泥结合刚玉-莫来石浇注料进行了实际应用对比。结果表明:1)硅溶胶结合刚玉-莫来石浇注料中温处理后的强度、体积稳定性、抗热震性、抗CO侵蚀均优于水泥结合浇注料的。2)硅溶胶结合刚玉-莫来石浇注料的一次性施工厚度大,可快速烘烤,能有效缩短点火炉改造时间;而且能有效降低因衬体开裂,使煤气、热风窜漏而导致的炉顶温度升高,同时使炉衬挂渣、剥落的现象减轻,从而有望提高炉衬的使用寿命。     

莫来石结合碳化硅浇注料的研制

对碳化硅含量在 70 %以上的莫来石结合碳化硅质浇注料进行了试验研究。结果表明 :该浇注料从常温到 150 0℃均有较高的强度 ,并且 150 0℃烧后表面不氧化 ,可在 150 0℃及 150 0℃以下的高温环境中应用     

铝酸钙水泥结合莫来石-碳化硅浇注料的组成及性能

采用烧结莫来石、Secar71水泥及SiC为原料,制备了不同水泥和SiC含量的莫来石质浇注料,研究了浇注料的常温物理性能、热导率及热震稳定性,并借助XRD和EDS研究了材料的物相组成和显微结构.结果表明:随着水泥的加入,浇注料110℃ 24h显气孔率降低、抗折强度逐渐提高;1100℃ 3h和1400℃ 3h抗折强度呈现出先增大后逐渐减小的趋势,当水泥量为25%(质量分数,下同)时,浇注料的显气孔率最高,同时抗折强度达到最大值.随着水泥加入量的增多,浇注料的热震稳定性稍有降低,当水泥量超过25%后,浇注料的热震稳定性逐渐恢复;通过加入5%～10%的SiC,浇注料的热震稳定性明显改善.浇注料的性能同其物相组成及显微结构相关.     

硅溶胶结合刚玉-莫来石快干浇注料的性能与应用

对比测试了常温浇注成型及在模拟热态修补条件下浇注成型的硅溶胶结合刚玉-莫来石快干浇注料分别在815、1 100 和1 400 ℃保温3 h热处理后的常温抗折强度、常温耐压强度、体积密度和加热永久线变化以及常温浇注成型的硅溶胶结合刚玉-莫来石浇注料和矾土水泥结合刚玉质浇注料的抗热震性;并在钢厂对硅溶胶结合刚玉-莫来石浇注料进行了现场应用试验。结果表明:硅溶胶结合刚玉-莫来石浇注料的烘干强度与普通低水泥刚玉质浇注料的相当;815和1 100 ℃热处理后强度比烘干强度高;硅溶胶结合刚玉-莫来石浇注料热震循坏（1 100 ℃;水冷）100次后基本上没有出现裂纹;其耐压强度损失率仅为18.7%;在模拟热态条件下成型的硅溶胶结合刚玉-莫来石浇注料的性能与常温浇注成型的相当。在现场应用试验中;硅溶胶结合刚玉-莫来石浇注料的脱模时间和烘炉时间大大缩短;并且可以热态浇注;具有良好的使用性能。 关键词:高炉;热态修补;硅溶胶;快干浇注料;刚玉;莫来石     

莫来石结合Al2O3-SiC浇注料的显微结构特征

借助SEM和EDAX研究了莫来石结合Al2O3 -SiC浇注料的显微结构特征。结果表明 :在莫来石结合Al2 O3 -SiC浇注料中 ,莫来石相与填充在其间隙的玻璃相形成连续基质 ;刚玉颗粒与基质中SiO2 反应生成的二次莫来石与基质中的原生莫来石交错存在 ,构成网状结构 ;SiC颗粒表面高温氧化生成的SiO2 膜 ,改善了SiC颗粒与基质的润湿性 ,是其与基质直接结合的媒介。     

Comparative study of conventional and microwave sintered mullite fibres: structural study

Mullite fibres were synthesised from a mixture of aluminium, aluminium chloride and acidic silica solutions as monophasic salts using a sol–gel technique. The viscosity and rheological behaviour of the mullite precursor sol were examined. Mullite fibres were synthesised using both conventional and microwave sintering techniques. The samples were characterised by X-ray diffraction and scanning electron microscopy. Pure mullite fibres were synthesised by microwave sintering at a relatively low temperature of 1200°C. The grain size of the fibre samples sintered using the microwave technique was finer than that produced by conventional sintering. These results show that microwave sintering is a promising technique for processing mullite fibres.     

中间包用莫来石质自流浇注料的研制与应用

介绍了中间包永久层用自流浇注料的研制和使用。结果表明 ,该自流浇注料具有施工方便、整体性好、机械强度高、保温效果好、使用寿命长等优点 ,是理想的中间包永久层用耐火材料。     

Temperature-induced changes in morphology and microstructure of electrospun mullite nanofibers fabricated from a hybrid mullite sol

Mullite nanofibers with small diameter and high surface area are an ideal candidate as the reinforcements in composite materials, and have promising applications in the fields of catalysis, filtration, thermal storage and so forth. In this work, electrospun mullite nanofibers were successfully synthesized using a hybrid mullite sol. The morphology and microstructure of fibers calcined at different temperatures were investigated. The morphology of fibers synthesized at 900 °C is porous with coarse surface, and after crystallization it becomes compact with smooth surface. The densities of fibers increase with the increasing temperatures. At 1200 °C the surface of fibers becomes coarse again, as a result of the grain growth of mullite. The crystallization path of fibers was revealed that the Al-rich mullite (4Al₂O₃·SiO₂) together with amorphous silica formed at 1000 °C, changed into mullite with higher silica contents as temperature further increased, and finally transformed into a stable 3Al₂O₃·2SiO₂ phase at 1200 °C. During this crystallization process, the flow of amorphous silica phase and the formation of mullite crystal structure benefit the densification of fibers, leading to the resultant fibers with fine and compact microstructure. The present findings can provide a guideline for the preparation of the promising high-mechanical mullite nanofibers and the synthesized nanofibers display great potential as reinforcements in structural ceramic composites.     

Development of mullite fibers and novel zirconia-toughened mullite fibers for high temperature applications

Polycrystalline mullite fibers and novel zirconia-toughened mullite (ZTM) fibers with average diameters between 9.7 and 10.3 μm containing 3, 7 and 15 wt.-% tetragonal ZrO₂ (ZTM3, ZTM7, ZTM15) in the final ceramic were prepared via dry spinning followed by continuous calcination and sintering in air. A shift in the formation of transient alumina phases and tetragonal ZrO₂ to higher temperatures with increasing amounts of ZrO₂ was observed. Concomitantly, the mullite formation temperature was lowered to 1229 °C for ZTM15 fibers. X-ray diffraction revealed formation of the desired tetragonal crystal structure of ZrO₂ directly from the amorphous precursor. Room temperature Weibull strengths of 1320, 1390 and 1740 MPa and Weibull moduli of 9.5, 7.1 and 9.0 were determined for mullite, ZTM3 and ZTM15 fibers, respectively. Average Young’s moduli ranged from 190 to 220 GPa. SEM images revealed crack-free fiber surfaces and compact microstructures independent of the amount of ZrO₂.     

Microwave-assisted synthesis and sintering of mullite

Mullitization behaviour of a mixture of clay and alumina as the starting materials was examined by microwave heating of (a) mixed powder and (b) compacted powder samples for different soaking times. X-ray diffraction results showed that in compacted samples mullitization process was completed after 20 min heating with a density of about 87%. Densification and microstructure of samples with different green densities heated in a microwave oven and conventional electric furnace were compared. Results showed that the grain growth of mullite was restricted by microwave heating.     

锆英石微粉对镁质浇注料性能的影响

研究了锆英石微粉对镁质浇注料结构及性能的影响。结果表明：微粉粒径一定时,控制锆英石微粉加入量可以明显改善镁质浇注料显微结构和性能。由于MgO同ZrSiO4反应形成的ZrO2,能吸收渣中的CaO形成CaZrO3,堵塞材料中的气孔,同时提高熔海粘度,抑制了渣的渗透。     

Effect of yttria on sintering and microstructural behavior of reaction sintered mullite based on bauxite,fly ash and precipitated silica

The present investigation on the effect of Y₂O₃ towards the sintering behavior of mullite compacts revealed that rapid mullitization occurred through nucleation and normal grain growth due to the formation of yttrious silicate glassy phase. The intergranular voids were progressively eliminated by yttrious silicate glass leading to significant decrease in porosity with the corresponding remarkable rise in mechanical strength of sintered compacts. The uniform dispersion of microfine corundum grains into the mullite matrix with 1.5% Y₂O₃ content was noticed during sintering at 1550?°C and above.     

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.     

Effects of added polyvinyl pyrrolidone on morphology and microstructure of multiple-phase mullite nanofibers

In this study, mullite nanofibers with smooth surface and dense structure were successfully fabricated with various amounts of polyvinyl pyrrolidone (PVP) as polymer template using electrospinning. To optimize properties of mullite nanofibers, effects of PVP content on the morphology and microstructure of the nanofibers were investigated. Results show that the nanofibers were composed of multiple phases (including nanocrystalline mullite, Al-Si spinel, and amorphous phase), and all had good flexibility. When PVP content increased, diameters of the fibers decreased. Meanwhile, mullite grain size and phase content increased, which led to changes in mechanical properties. Also, it was revealed that removal of PVP polymers (which helps atom diffusion and promotes nucleation-growth of mullite) was the acceleration mechanism of the additives. From analysis of crystallization activation energy and chemical structure, clear picture of the acceleration mechanism is gained, and this can provide a guideline for future optimization of electrospinning processes for high-temperature ceramics nanofibers.