| Research Abstract |
Preparing conditions of multi-layer steel/Co/TiC/SiC/SiO_2 were investigated in order to obtain an anti-corrosive material against halogens or halides at high temperature. The lowest layer of Co was electroplated onto low-carbon steel, in which application of ultra-acoustic wave to plating solution was confirmed to be effective to obtain a smooth coating. The second and the third layers of TiC and SiC, respectively, were plated by pulse CVD process, which is consisted of evacuation of vessel, instantaneous introduction of source gas and holding for deposition, TiC was deposited from the system TiCl_4-C_3H_8-H_2. Below 900ﾟC, Co diffusion into TiC layer along the grain boundary was very fast, therefore, bonding between Co layer and TiC layer was weekened. Above 920ﾟC, homogeneity and crystallinity of the TiC film was improved. After all, best condition of TiC deposition was determined as follows ; temperature 920-1000ﾟC, C/Ti ratio in source gas 1.0-1.2, hold-time 1-2s, layer thickness 3-5mum. The third layer of SiC was deposited from the system CH_3SiCl_3-H_2. To suppress the Co diffusion into the upper layers, temperature lowering to the range of 860-900ﾟC was necessary, and to obtain a homogenious film, the concentration of CH_3SiCl_3 had to be increased to 6%. The suitable thickness of 3-5mum was also determined. Corrosion test was conducted in an atmosphere of 30%Cl_2-30%O_<>-Ar at 900ﾟC. Among the multilayered specimens, the TiC and SiC thicknesses of which were 3 and 4mum, respectively, showed best result, however, some pin-corrosions could be found after the test.
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