Papers by Author: Jae Ho Jeon

Abstract: A Mo-Si-C-N multi-layer anti-oxidation coating was in situ fabricated on C/C composites by fused slurry and reaction-sintering method in nitrogen atmosphere using Mo and Si element powders, and characterized by X-ray diffractometry, optical microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy. It is shown that the coating contains three distinctive layers, namely, SiC inner-layer, MoSi2/Si middle-layer and Si3N4/SiC/Si thin surface-layer. The MoSi2/Si middle-layer, whose thickness could be controlled by dipping process, is the main portion of coating. Oxidation test reveals that the Mo-Si-C-N multi-layer coating significantly improves the oxidation resistance of the C/C composites. Compared with the Mo-Si-C coating, the oxidation temperature is extended up to 1450°C. After oxidation pre-treating at 1400°C, the anti-oxidizing temperature of the Mo-Si-C-N multi-layer coated C/C composites can be raised to 1500°C and the weight loss is less than 1wt% after 12-hour oxidizing test.

Abstract: The concept of functionally graded materials (FGMs) was originated in the research field of thermal barrier coatings. Continuous changes in the composition, grain size, porosity, etc., of these materials result in gradients in such properties as mechanical strength and thermal conductivity. In recent years, functionally graded structural composite materials have received increased attention as promising candidate materials to exhibit better mechanical and functional properties than homogeneous materials or simple composite materials. Therefore the research area of FGMs has been expending in the development of various structural and functional materials, such as cutting tools, photonic crystals, dielectric and piezoelectric ceramics, thermoelectric semiconductors, and biomaterials. We have developed functionally graded structural ceramic/metal composite materials for relaxation of thermal stress, functionally graded anti-oxidation coatings for carbon/carbon composites, and functionally graded dielectric ceramic composites to develop advanced dielectric ceramics with flat characteristics of dielectric constant in a wide temperature range. This paper introduces functionally graded coatings for C/C composites with superior oxidation resistance at high temperatures.

Abstract: Four kinds of raw C/C composites with a density between 1.25~1.66g/㎤ were used in order to investigate the effect of the initial porosity of C/C composites on mechanical properties of liquid silicon infiltrated C/SiC composites. The microstructure observation, image analysis and flexural strength test of the composites were performed. The density and microstructural changes with the variation of the initial porosity was discussed in the terms of the infiltration behavior of liquid silicon and the reaction between liquid silicon and matrix carbon.