Cobalt coated tungsten carbide-cobalt composite powder has been prepared through wet chemical reductionmethod. The cobalt sulfate solution was converted to the cobalt chloride then the cobalt hydroxide. The tungsten carbidepowders were added in to the cobalt hydroxide, the cobalt hydroxide was reduced and coated over tungsten carbidepowder using hypo-phosphorous acid. Both the cobalt and the tungsten carbide phase peaks were evident in the tungstencarbide-cobalt composite powder by X-ray diffraction. The average particle size measured via scanning electron micro-scope, particle size analysis was around 380 nm and the thickness of coated cobalt was determined to be 30~40 nm bytransmission electron microscopy.

High-quality β-silicon carbide (SiC) coatings are expected to prevent the oxidation degradation of carbon fibers in carbon fiber/silicon carbide (C/SiC) composites at high temperature. Uniform and dense β-SiC coatings were deposited on carbon fibers by low-pressure chemical vapor deposition (LP-CVD) using silane (SiH4) and acetylene (C2H2) as source gases which were carried by hydrogen gas. SiC coating layers with nanometer scale microstructures were obtained by optimization of the processing parameters considering deposition mechanisms. The thickness and morphology of β-SiC coatings can be controlled by adjustment of the amount of source gas flow, the mean velocity of the gas flow, and deposition time. XRD and FE-SEM analyses showed that dense and crack-free β-SiC coating layers are crystallized in β-SiC structure with a thickness of around 2 micrometers depending on the processing parameters. The fine and dense microstructures with micrometer level thickness of the SiC coating layers are anticipated to effectively protect carbon fibers against the oxidation at high-temperatures.

The application of Carbon and graphite based materials in unprotected environment is limited to a temperature of 450℃ or so because of their susceptibility to oxidation at this temperature and higher. To over come these obstacles a low cost chemical vapour reaction process (CVR) was developed to give crystalline and high purity SiC coating on graphite and isotropic C/C composite. CVR is most effective carbothermal reduction method for conversation of a few micron of carbon layer to SiC. In the CVR method, a sic conversation layer is formed by reaction between carbon and gaseous reagent silicon monoxide at high temperature. Characterization of SiC coating was carried out using SEM. The other properties studied were hardness density and conversion efficiency.

Si3N4가 추진기관 연소조건 하에서 흑연의 산화와 마모를 효과적으로 방지하는 다층 코팅재료로 쓰일 수 있도록 하기 위하여 저압화학기상증착법(LPCVD)으로 Si3N4를 코팅할 때의 증착특성에 대해 연구하였다. 흑연 위에 pack cementation방법으로 SiC를 코팅하고 그 위에 저압화학기상증착법으로 Si3N4를 코팅 하였으며, 증착온도와 반응기체입력비를 변화시키면서 이에 따른 증착속도와 표면형상의 변화를 관찰하였다. 증착속도는 증착온도가 높아짐에 따라 처음에는 증가하다가 최대값을 나타낸 후 감소하는 경향을 나타냈으며, 그레인의 크기는 증착온도가 높아짐에 따라 작아지는 경향을 보였다. 한편, 반응기체의 입력비가 20≤NH3/SiH4≤40인 조건에서는 증착속도의 변화나 표면형상의 변화를 관찰할 수 없었다. 증착온도 800~1300˚C 범위에서 증착된 Si3N4가 비정질상인 것을 XRD로 확인할 수 있었으며 1300˚C, 질소 분위기에서 2시간 동안 열처리하여 결정상인 Si3N4를 인을 수 있었다.

The purpose of this study is to investigate the effect of long - term deterioration factor of 12 months on 6 kinds of coating waterproofing materials (polyurethane 1, 2, acrylic rubber, polyurea, rubber asphalt, cement - As a part of the study to characterize the performance change in material aspect, the research was carried out on the tensile strength of the polyurea coating waterproofing material against the performance change in the long term exposure to the chemical erosion environment. As shown in the test results, it was mainly performed in an acidic environment, and it can be confirmed that polyurea is not resistant to acid. In the alkali and sodium chloride environment, the tensile strength after immersion for the last 12 months showed a decrease in strength within about 10% of the initial tensile strength, and it was confirmed that the resistance was excellent in an alkali environment.

The purpose of this study is to investigate the mechanical property of concretes using surface treated lightweight aggregate. Slump of concretes using surface treated lightweight aggregate measured 120~140mm, which are lower than slump of NWAC. Compared to compressive strength of NWAC, compressive strength of concretes using surface treated lightweight aggregate showed a level of 82.8~95.9%.