Effect of heat treatment and zircon addition on the properties of low-cement castables based on recycled alumina grog

In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content.     

用注凝成型技术制备莫来石陶瓷坯体

用注凝成型技术，通过控制合成莫来石粉料的细度，调节好pH值在单体和交联剂的比例，制备出稳定性好的料浆和强度高的生坯。     

钒钛渣对刚玉莫来石耐火材料的侵蚀研究

通过不同温度下钒钛渣对刚玉莫来石耐火材料的侵蚀实验，分析了炉渣、温度对材料的影响，认为致密结构、低气孔率是提高炉衬寿命的关键，板条状莫来石的存在利于减缓渣的侵蚀过程。     

Crystallization of glass in fireclay refractories; part III: Detailed study on the mullite crystal size in the ‘synthetic’ glass

Poor-grade fireclay products contain substantial amount of glass. A glass of similar composition was synthesized, nucleated and heat-treated for crystallization of mullite. The size and size-distribution of mullite crystals, the rate of change of size and the aspect ratio of the crystals were investigated in relation to the nucleating agents and temperature.     

Technique for Producing Mullite and Other Mixed-Oxide Systems

Mixed-oxide systems are of interest in a variety of technical ceramic applications. The key in many systems is to achieve a high degree of homogeneity, approaching the molecular level. A technique for producing mixed oxides via direct oxidation of mixtures of organometallic compounds is discussed as a potential route. Preliminary work performed on producing mullite is discussed.     

稀土锆莫来石耐火材料的显微结构研究

本文运用ＸＲＤ、ＳＥＭ等方法对稀土锆莫来石耐火材料的显微结构，物相变化，以及稀土的作用机制进行了研究。     

Effect of sillimanite beach sand composition on mullitization and properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

Mullite was developed by reaction sintering of sillimanite beach sand and calcined alumina. Two varieties of sillimanite beach sand viz. S and Z having different compositions were selected. Synthesis and properties of mullite were very much dependent on the sillimanite beach sand composition. Presence of higher amount of impurities in the Z-variety of sillimanite sand favours the densification by liquid phase formation. Presence of zircon in Z-variety increases the hardness and fracture toughness. Alumina addition improves the mechanical/thermomechanical properties of the samples. Mullite retains the usual orthorhombic habit of sillimanite. Rounded to sub rounded zirconia dispersed within the mullite matrix of the sample ZA is noticed.     

Effects of micro-sized mullite on cristobalite crystallization and properties of silica-based ceramic cores

Silica-based ceramic cores are extensively used in investment casting process, during which they must exhibit sufficient flexural strength and deformation resistance. In this study, micro-sized mullite was used as an additive to silica-based ceramic cores to optimize their high temperature properties. To investigate the effects of micro-sized mullite on cristobalite crystallization, mechanical and thermal properties of silica-based ceramic cores, ceramic cores with different amounts of micro-sized mullite were fabricated. The XRD results showed that additional micro-sized mullite diminished the crystallization of cristobalite at high temperatures, primarily caused by the mullite related compressive stresses on the surface regions of fused silica particles. Three-point bending tests and SEM results showed that micro-sized mullite had a more significant effect on the flexural strength of ceramic cores compared with conventional additives. Particularly, the fracture mechanism of silica-based ceramic cores had been changed from intergranular fracture into a mixed fracture consisting of both intergranular and transgranular fracture. The mechanical and thermal properties of ceramic cores were all reduced slightly as the mullite content exceed 4.6 wt%. Hence, to optimize the properties of silica-based ceramic cores, the micro-sized mullite content should not exceed 4.6 wt%.     

Influences of mullite fibers on mechanical and thermal properties of silica-based ceramic cores

Mullite fibers composite silica-based ceramic cores were successfully prepared by injection molding. The effects of mullite fibers on the mechanical and thermal properties of ceramic cores were investigated. The results indicated that the linear shrinkage was significantly decreased and the porosity was gradually increased with the increase of mullite fibers. In addition, the flexural strength for the room temperature and the simulated casting temperature of 1500°C was increased to a maximum value when the content of mullite fibers was about 1 wt.%, and then decreased with the increase of mullite fibers. The mullite fibers of 1 wt.% presented excellent mechanical properties with a linear shrinkage of .65%, a porosity of 6.96%, and a flexural strength of 17 MPa at room temperature and 34.83 MPa at the simulated casting temperature of 1500°C. Besides, the change in microstructure and properties in various contents of mullite fibers were analyzed.     

延缓与加速A1-Cu合金时效析出反应的研究

研究了溶质原子浓度、Si晶体第二相、残余形变、外加莫来石(Mullite)短纤维及其交互作用，对二元Al—Cu合金时效析出行为的影响。试验材料采用挤压铸造方法制备，复合材料中纤维体积分数为18％。实验结果表明：随溶质原子浓度的升高，A1-Cu二元合金中GP，θ″和θ′相的析出都得到了相应加快；Si含量超过一定值后，随Si含量增加，A1-Cu-Si合金中GP区形成受到抑制，而θ″和θ′相的析出得到加快；形变对GP区的抑制和对θ″，θ′和θ相的加速析出具有十分明显的作用；纤维本身除对GP区抑制和对θ″，θ′相的析出加速外，还会与溶质原子、合金元素或第二相以及残余形变交互作用，使GP区被抑制，而θ″，θ′甚至θ相被加速析出等现象进一步加强。用位错理论能较好地解释析出反应延缓与加速的微观机理。