In situ mullite foam fabrication using microwave energy

In situ mullite ceramic foams were fabricated using polymeric sponge replication method from ceramic slurry containing alpha alumina and kaolin mixtures. Ceramic preforms were processed using microwave energy and conventional heating. The sintered foam samples were characterized by SEM and XRD observations, density measurements and compression tests in order to observe the effect of two different sintering techniques on the structure and properties. It was found that the microwave processing was completed in a shorter burning out and sintering cycle and produced structures having higher mullite transformation ratio and fine grains.     

Using increased fabrication pressures for making articles from certain electrofused highly refractory materials

Conclusions The porosity of refractories made from fused materials can be greatly reduced (to 10–13%) by using increased fabrication pressures and coarse grained bodies with low quantities of finely milled bond (10–15%).The densification mechanism in the coarse-grained bodies consists in breaking up the large grains and redistributing them. The requirement for maximum density of packing in selecting the grain-size composition of the bodies is of first rate importance.The maximum fabrication pressure should not exceed the values at which the critical density is reached.Translated from Ogneupory No.6, pp.49–53, June, 1972.     

On fabrication of refractory articles by injection

A principally novel technology for molding and compacting articles from low-moisture powder materials by continuous zonal injection directly into open molds is suggested. The method excludes air inclusions, the elastic aftereffect, the inaccuracy of the sizes of the articles, and other defects typical for cyclic semidry pressing. The use of the new technology in the production of refractories makes it possible to increase their density, decrease the forces acting on the material by 1 – 2 orders of magnitude (i.e., to the ultimate strength of the greenware), increase the accuracy of the sizes, decrease the expenses per unit product, and increase the output of the molding equipment. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 47–49, March, 2000.     

Porous mullite templated from hard mullite beads

Porous mullite bodies were developed by spark plasma sintering (SPS) amorphous mullite beads of about ∼30 μm in diameter at two temperatures, 950 and 1300 °C. Materials showed a close random stacking of solid spheres that retained their original packing but slightly flattened at the contacts in some cases. Depending on the thermal history, the beads were partially or fully crystallized. The thermal conductivity of the different porous mullite materials was analyzed as a function of the microstructure. Owing to the particular porous network, high gas permeability and very low thermal conductivities (1-2 W m⁻¹ K⁻¹) were achieved, among the lowest reported for sintered mullite materials.     

Recycling of waste red mud for fabrication of SiC/mullite composite porous ceramics

SiC/mullite composite porous ceramics were fabricated from recycled solid red mud (RM) waste. The porous ceramics were formed using a graphite pore forming agent, RM, Al(OH)₃ and SiC in the presence of catalysts. The influence of firing temperature and the pore-forming agent content on the mechanical performance, porosity and the microstructure of the porous SiC ceramics were investigated. Optimal preparation condition were determined by some testing. The results indicated that the flexural strength of specimens increased as a function of firing temperature and a reduction in graphite content, which concomitantly decreased porosity. The ceramic prepared under optimal conditions having 15?wt% graphite and sintered at 1350?°C, demonstrated excellent performance. Under optimal preparation conditions the flexural strength and porosity of the ceramic were 49.4?MPa and 31.4%, respectively. Scanning electron microscopy observation result showed that rod-shape mullite grains endowed the samples with high flexural strength and porosity. X-ray diffraction analysis indicated that the main crystallization phases of the porous ceramics were 6H-SiC, mullite, cristobalite and alumina. This work demonstrates that RM can be sucessfully reused as a new raw material for SiC/mullite composite porous ceramics.     

Experimental technology for manufacturing ceramic articles

The production of ceramic articles includes five principal operations, namely, preparation of the powder, pressing of the preform, its treatment, sintering, and grinding. If it is necessary to increase the adaptability to manufacture and improve the physicomechanical properties of the sintered material, the operations of hydrostatic treatment of the powder, preliminary sintering of the preforms, repeated mechanical treatment, etc. can be added. The technology is used for manufacturing the working part of cutting tools, dies, tools for shaping alloys of nonferrous metals, bearings, hinges, valves, ball locks, nozzles of hydromonitors, parts of pressing molds, lining parts, milling bodies, etc.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 25 – 27, June, 1996.     

Electrospun mullite nanofibers derived from diphasic mullite sol

Fine‐grained mullite nanofibers derived from the diphasic mullite sol were successfully fabricated by electrospinning and subsequent pyrolysis at 1500°C. Polymethylsiloxane and aluminum tri‐sec‐butoxide were selected as the silicon and aluminum source to synthesize the diphasic sol. Results show that the weight loss of mullite precursor fibers in our work was about 60 wt.%, which is similar with that of fibers fabricated using the monophasic sol. This low weight loss was mainly attributed to the high ceramic yield of polymethylsiloxane and low introduced polyvinylpyrrolidone content, which ensures the integrity of fiber morphology during the sintering process. Mullite fibers with 216 nm average diameter were fabricated after sintered at 1500°C and the corresponding grain size was only ~100 nm, much smaller than that in mullite fibers derived from monophasic sols. Therefore, it can be predicated that mullite fibers in this work should possess a higher mechanical strength than those derived from monophasic sols when the sintering temperature was higher than 1400°C and therefore was an ideal starting materials for the fabrication of mullite nanofibrous ceramics used as the high‐temperature thermal insulation materials.     

莫来石材料制备工艺研究的现状

高温性能稳定、抗热震性能好的莫来石是一种重要的陶瓷材料。对莫来石材料的制备工艺进行了系统的总结，重点介绍了溶胶-凝胶法和水解沉淀法，以及部分制备方法的制备过程。     

Improving the slip-casting technology for ceramic articles

Ways of optimizing the technology for ceramic articles based on the method of slip casting under the effect of capillary forces in porous molds under pressure are considered. The technology for preparing fired molds with channels for slip casting under pressure is presented.Translated from Steklo i Keramika, No. 12, pp. 15–17, December, 1995.     

Developing technology for production of combined fibres for protective articles

The possibility of fabricating inhomogeneous conducting fibres for preparation of special clothing on the winding machine bench was demonstrated. The structure of a combined conducting fibre in which the necessary contact between the current-conducting intermediate product and contact conductor is attained was developed; it ensured electrical resistance of gloves of less than 30 Ω and a high breaking load. __________ Translated from Khimicheskie Volokna, No. 3, pp. 30–32, May–June, 2007.     

The fabrication of porous mullite ceramics based on the different sizes of aluminum hydroxide

In this research, for studying the influence of size and heat treatment temperature of initial Al(OH)₃ on the physical properties of porous mullite ceramics, porous mullite ceramics were prepared by in situ reaction sintering of amorphous silica and treated Al(OH)₃. The transition phases χ-Al₂O₃, к-Al₂O₃, and stable phase α-Al₂O₃ can be obtained in turn when the treatment temperature of raw Al(OH)₃ is 500, 1000, and 1500°C, respectively. The coarser the raw Al(OH)₃, the higher the strength of porous mullite ceramics. When the sintering temperature is 1500°C, the bending strengths of PS500-C, PS1000-C, and PS1500-C (PSx-C represents that the specimen was prepared by the coarse grade Al(OH)_3, which was previously treated at x°C) are 40.3 ± 2.1, 54.9 ± 5.2, and 64.8 ± 4.8 MPa, respectively. In addition, although the activated Al₂O₃ can decrease the formation temperature (∼100°C) of porous mullite ceramics, the strength and density of porous mullite ceramics prepared by activated Al₂O₃ will decrease at the same sintering temperature. It is believed that the increase of defects and pores during the phase transformation should be responsible for this phenomenon.     

Improving the design and technology of molds for ceramic articles

Ways of improving the design and the manufacturing technology of porous and poreless molds for shaping ceramic articles by the methods of slip casting and plastic molding are considered. New techniques for the production of porous molds are suggested, which make it possible to decrease the cost of the molds and optimize the processes of slip casting and plastic molding of ceramic articles.     

合成莫来石烧结工艺对其抗弯强度的影响

系统研究了合成莫来石烧结工艺对其抗弯强度的影响。结果表明经1300℃,3h+1500℃,4h处理的试样的常温抗弯强度最高;在800℃以前,其高温抗弯强度基本不变,在接近于1000℃时突然上升,而后又快速下降。借助于SEM照片,对实验条件下的断裂机理进行了深入分析,指出了断裂方式,并从微观上解释了抗弯强度的测定结果。     

Boron-doped mullite derived from single-phase gels

Mullite with low dielectric constant and high transparency in infrared and microwave range has potential applications in communication industry. To improve the above properties of mullite, boron-doped mullite single-phase gels with a constant molar ratio of Al/Si = 3/1 and various B/Al ratios (B/Al = 0–0.4/3) were prepared in this study by slow hydrolysis of aluminum nitrate, boric acid and tetraethoxysilane. It was found that boron reduces the mullite formation temperature and suppresses spinel formation. The cell unit lattice parameters and cell volume in boron-doped mullite generally decrease with the increase of boron amount. The SEM observation shows that a small amount of boron reduces the grain sizes of mullite sintered bodies while a large amount of boron facilitates the formation of elongated grains and the amorphous glass phase. Boron decreases the transmittance of mullite ceramic and produces additional intensive absorption bond at 3.9 μm and also reduces the dielectric constants in the frequent range of 1 M–1 GHz.     

Development of technology and equipment for isothermal shaping of glass articles

Technology and equipment for isothermal shaping of glass articles effectively used in the industry is described. The results of the investigation can become the basis for complex research aimed at the development of a new generation of glass-shaping equipment.Translated from Steklo i Keramika, No. 10, pp. 8–12, October, 1996.     

Slip technology for fabrication of highly porous cellular glass material

The possibility of using slip technology in production of highly porous cellular materials from alumino-borosilicate glass was demonstrated. The factors that affect the rheology and stability of the slip system and the structural and strength characteristics of the finished material were identified. The materials obtained can be used as substrates in chromatography, for treatment of liquids and gases in filtration, etc.