Key Engineering Materials Vols. 336-338

Abstract: A novel process with low cost to fabricate SiCN MEMS based on UV lithographic technique is present in this paper. The prepared MEMS are very promising to be used in high-temperature environments. By adding a photo initiator to the polysilazane precursor, the precursor becomes UV-sensitive and can be solidified upon exposure to UV light, which leads to the formation of UV photo lithographical patterns. Key issues of the fabrication process are investigated and various SiCN MEMS structures are fabricated by this technique.

Abstract: The silica-alumina sol bonding agent, prepared by the sol gel route from ethyl silicate and aluminium isopropanol, was characterized by X ray diffraction, infrared spectroscopy, thermogravimetric analysis, particle size distribution. It was utilized in the corundum based refractory castables. The properties and characters such as cold crushing strength, apparent porosity, hot modulus of rupture, pore size distribution, scanning electron microscopy, energy dispersive spectral analysis, thermal shock and slag corrosion resistance tests of the selected samples from both the sol-gel bonding castables and the cement bonding castables were determined to identify the role of sol-gel additive in castables. The results show that the sol-gel bonding castables have a lot of advantages compared with traditional cement bonding castables and are more suitable for application in the ladles.

Abstract: The Al2O3-mullite system porous refractories were fabricated, and then pretreated by sol-gel. The samples were sintered at 1200°C for 3 hours. The microstructures and phases of the samples were analyzed by SEM and XRD respectively. The physical properties of the samples were measured according to National Standard of Refractory. Mullite-whiskers were formed in the pores of the samples. The pretreated samples were more permeable, and were greatly strengthened.

Abstract: To prevent the shrinkages by the densification during the application of unfired Al2O3-C refractories or Al2O3 castables in steel making conditions, MgO was added as aggregate or matrix powder and the expansion caused by spinel formation was studied. Because the spinel was formed at the contacting areas between Al2O3 and MgO particles and the volume of in-situ formed spinel increased more abnormally at the side of Al2O3 particles than MgO, the addition of MgO aggregates was not recommendable due to the formation of large voids around the MgO aggregates. Nevertheless, corrosion resistance was increased with the amount of fine MgO added, and the finer MgO powder added, the better residual expansion and minute structure formation was observed. In the contrary, in case of castables volume expansion due to spinel formation was not obvious because the degree of densification was less than high-pressure formed refractories. But CA6 phase would not form around alumina aggregates during corrosion so the corrosion resistance was much more enhanced.

Abstract: β-Sialon bonded corundum multiphase ceramic refractory was prepared by the method of carbothermal reduction and nitridation reactions of clay mineral doped with corundum particle phase. The high-temperature oxidation resistance and the thermal-shock resistance behaviors of the material were tested and investigated. The results show that the oxidation reaction history at 1573K can be divided into two reaction kinetic phases. The circle times of the thermal-shock resistance ($
=1473K) reached to more than 200 times and the thermal shock failure is not a brittle rupture but a desquamate damage.

Abstract: Fe-Al intermetallic/TiC-Al2O3 ceramic composites were fabricated by in-situ carbothermic and aluminothermic reduction from natural ilmenite. Synthesis and sintering of the composites were accomplished unanimously in the vacuum hot pressure furnace. The thermodynamic process, the composition, the microstructure as well as the properties of the FeTiO3-Al-C system were studied in detail through theoretical analysis and experimental research. It was shown that the synthesis process started from the melting aluminium, followed by the deoxidation of ilmenite step by step via a series of different valent titanium oxides to form TiC, Al2O3 and Fe-Al as the ultimate productions. The particle sizes are mostly 3-5μm, and their distributions are uniform. Meanwhile, the addition of additives can improve the wettability of alloy to ceramic phases and the combination of the interfaces, giving rise to the properties of the composites as a whole.

Abstract: Ultra-light calcium silicate material constructed with fibrous xonotlite crystals has an advantage of low-thermal conduction coefficient. But the microporous structure can hardly make a better performance in terms of super thermal insulation. Although nanoporous structure of SiO2-aerogel satisfies the requirement, its tenacity is not strong enough to produce by itself blocky super thermal insulation material. This research, thus proposes to apply SiO2-aerogel as nanoporous carrier in the process of preparation, with Ultra-light calcium silicate material constructed with fibrous xonotlite crystals as the matrix so as to prepare nanoporous super thermal insulation material compounded with Xonotlite-SiO2-aerogel via so-gel method and ethanol supercritical drying. SEM and pore size distribution techniques were here applied to characterize the morphology and pore structure of the composite material. The results show that the SiO2-aerogels were better distributed in pore of calcium silicate matrix, with the pore size distribution of composite ranging from 10 nanometers to 50 nanometers, and average pore size less then 20 nm.