Key Engineering Materials Vol. 403

Abstract: Zirconium diboride based composites containing silicon carbide with relative densities in excess of 99 % were produced by hot-pressing. Oxidation test was conducted in air at 1500 °C. ZrB2-SiC composite showed relatively low oxidation resistance due to the non-uniform surface silica-rich layer. But in case of mixed boride-SiC composites further improvement of the oxidation performance were observed due to the phase separation in the surface silica-rich layer.

Abstract: The fabrication conditions of dense silicon carbide (SiC) composites containing chopped Tyranno Si-Al-C (SA) fiber were examined in this work; SiC compacts containing SA fiber (mean lengths: 214, 394 and 706 m) were hot-pressed at 1800°C for 30 min under a pressure of 31 MPa in Ar atmosphere. The fracture toughness of SiC composites with 40 mass% of SA fiber addition (sintering aid: 5 mol% Al4C3) increased from 2.8 up to 4.7 MPa•m1/2 as the fiber length increased from 214 to 706 m. The enhanced fracture toughness of the SiC composites was attributed to the lowering of fiber orientation angle (i.e., the angle between the fiber length and direction perpendicular to the hot-pressing direction) to 5° with increasing fiber length. The fracture toughness of SiC composites could be further enhanced through the incorporation of SA fibers with a carbon interface (thickness: 100 nm) into the SiC matrix. The fracture toughness of SiC composite containing 40 mass% of these fibers attained 6.0 MPa•m1/2. The thermal conductivity of SiC composites increased with fiber length from 30.5 W•m-1•K-1 to 45.5 W•m-1•K-1; with no significant influence being noted for the case of fibers with a carbon interface.

Abstract: Exergy is a measure which can commonly deal with the quantification of the variety of resources, products and energy coming in and going out the manufacturing systems. In this study, exergy analysis was conducted on ceramics and steel heater protection tube used in aluminum casting, and the amount of exergies consumed through their life cycle were calculated. In the production stage, ceramic heater tube consumes much higher exergy than the steel one does, however, analysis throughout the life cycle including production, operation and waste in seven years shows that exergy consumption for the ceramic tube is less than that of the steel tube.

Abstract: This paper is focussed on the development of microstructure during liquid phase sintering and post-densification crystallisation heat treatment of ceramic materials based on the α- and β-Si3N4 structures. Grain shape and size distributions, assessed by quantitative microscopy in combination with stereological methods, and fine scale microstructures, investigated by electron diffraction and high resolution imaging and microanalysis in the transmission electron microscope, are discussed in relation to the fabrication process and the overall composition of the ceramic material.

Abstract: Synthesis of titanium carbide ceramic powders and control of particle size were tried by carbothermic reduction of a precursor, comparing synthesis of silicon carbide from a precursor. Metal alkoxides were used as a metal source and phenolic resin was done as a carbon source. Homogeneous sol-like mixture was obtained by mixing ethylsilicate and phenolic resin with alcohol. Gel-like precursor was formed by drying the sol-like mixture. Precipitation was formed by mixing titanium(IV) tetraisopropoxide and phenolic resin. The precursor was amorphous and ceramization occurred by heat treatment in argon flow. Growth of particles and phase formation were investigated.