This paper presents an investigation of the influence of nitrogen addition on the thermoelectric performance of diamond-like carbon (DLC) films on glass substrates using RF plasma chemical vapor diposition (CVD). The DLC films were prepared using methane (CH4) with 0—40% nitrogen (N2) concentrations as the source gas. The respective thermoelectric performances of the DLC films were evaluated and compared. The Seebeck coefficients of the DLC films decreased concomitantly with increasing nitrogen concentration at 0—20%. However, the Seebeck coefficients of 20% and the 40% were almost identical. The specific resistance of the DLC films decreased concomitantly with increasing nitrogen concentration at temperatures of room temperature to 150°C; above that temperature, the specific resistance of each DLC film was identical. The specific resistance decreases significantly with increasing nitrogen content, but the Seebeck coefficient decreases only slightly. The power factor (PF) of the DLC films increased concomitantly with increased nitrogen concentration below the temperature of 125°C. Results show that the PF quality of DLC films was affected strongly by the magnitude of the specific resistance. Hall effect measurements revealed a decreased specific resistance of the DLC films because of increased carrier concentration attributable to increased N2 contents. Raman spectroscopy measurements suggest that structural changes in the films influenced the DLC films' thermoelectric performance.
To produce a diamond-coated cutting tool with a smooth surface and high adhesive capability, a diamond film is deposited on a mirror-polished Co cemented tungsten carbide (WC-Co) substrate. Adhesion is usually better for substrates with high surface roughness, but a smooth substrate provides a sharp edge for cutting tools. For this study, the diamond film was deposited at 970 K on a mirror-polished WC-Co substrate (Ra=7 nm) treated using a nano-size diamond seeding process. The adhesive ability of the diamond film differs according to the nano-size diamond concentration in the seeding dispersion. A high adhesive diamond film that withstands a cavitation test for 240 min can be produced with 0.01 mass% nano-sized diamond dispersion. The diamond film surface roughness is Ra = 148 nm. To smooth the diamond films, deposition temperatures are examined. Using two-step deposition, which changes the substrate temperature from 970 K to 1070 K during deposition, the diamond film surface roughness decreased to Ra = 74 nm. When the deposition temperature becomes higher than 1070 K, Co segregation from WC-Co substrates occurs. Furthermore, the adhesive ability is reduced by the amorphous carbon layer formed at the interface as the diamond reacts with Co.
Magnesium is a light metal with high specific strength and electromagnetic shielding properties. however, magnesium is inferior to corrosion resistance. For that reason, it is important to improve its corrosion resistance through surface treatments. Typical surface treatments of magnesium include conversion coating, anodizing and coating. Chromate coating is well known as one method that is limited to use for surface treatments because of its carcinogenicity. Coating processing is an effective method of improving magnesium corrosion resistance. This paper describes the effects of silane coupling treatment on the corrosion resistance of magnesium alloys by aminoacrylate system coating. To improve magnesium's corrosion resistance, we evaluated corrosion resistance of Mg(OH)2 coating, silane coupling treatment, and inorganic-organic composite coating with graded structures from substrates by conducting salt-spray testing (SST), along with perspiration-resistance, cross-cut, and boilproof tests. Results show that the high-corrosion resistance treatment with silane coupling + inorganic-organic composite coating (aminoacrylate system coating) on magnesium alloy was about 1000 hr by SST. In addition, corrosion resistance of silane coupling + inorganic-organic composite coating affected the coating thickness.