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Abstract: The paper studies the possibility of superhydrophobic coatings formations at exposure of powder mixture of polytetrafluorethylene and hydrocarbons having various molecular weights to low-energy electron beam in vacuum. It is shown that paraffin and PTFE based thin composite coatings may be characterized by superhydrophobic properties. The superhydrophobic properties are attained due to low surface energy of the fluorine-containing component and structured surface due to peculiarities of composite layer formation. The chemical processes observed in electron beam exposed area determine the molecular structure, morphology and the contact angle of thin organic coatings deposited. It is shown that high-molecular-weight hydrocarbon compounds should not be recommended for vacuum electron-beam deposition of superhydrophobic thin coatings because of deep changes in the molecular structure exposed to electron beam. These processes are responsible for high degree of unsaturation of the thin layer formed and for occurrence of oxygen-containing polar groups. The influence of substrate temperature on molecular structure, morphology and hydrophobic properties of thin coatings deposited is investigated. Potentially such coatings may be applied for deposition on the surface of metal capillaries used in biotechnological analyzers. Keywords: Electron-beam deposition, superhydrophobic coatings, paraffin, polytetrafluorethylene, molecular structure, nanocomposite coatings. |
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Abstract: The surface of stainless steel 316L was plasma nitrided and subsequently deposited with silicon nitride from tetraethylorthosilicate (TEOS):H2:N2 gas mixtures by plasma enhanced chemical vapor deposition (PECVD). A copper mesh was employed to sputter copper atoms onto the surface during the two processes to consider its effect on the microstructure, tribology and antibacterial response of hard surface layers. The surface layers were characterized using XRD, optical and SEM microscopy, EDX analysis, microhardness test, pin-on-disc wear tests and microbial viability test. α-Si3N4 was found on the top surfaces of two steps processed stainless steel 316 L. Fe2–3N, Fe4N and CrN were identified in the compound layers. The overall thickness of the surface layers were more than 60 µm. The two step treatments improved the hardness up to 1600 HV0.1. The combination of plasma nitriding (with Cu sputtering) and PECVD of silicon nitride compound (with Cu sputtering) of SS 316 L resulted in superior high hardness, 3 times lower friction and 10 times higher wear resistance of treated surfaces if compared to those of conventional plasma nitrided surfaces.
Cu addition to single plasma nitridingresulted in an effective reduction of 100% of Escherichia coli (E. coli) within 2 to 3 h. However the bacteria viability after the two step processes with Cu addition diminished to zero in 3.5 to 4 h. The antimicrobial response of the surfaces depends mainly on the Cu action and does not interfere with the wear resistance of the surfaces.
Keywords: α-Si3N4, E. coli, Friction, Hardness, PECVD. |
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Abstract: : Microwave plasma CVD growth can produce black and white varieties of polycrystalline diamond (PCD), depending on their as-grown purity. These two types of PCDs have been polished by mechanical and chemo-mechanical polishing respectively. It has been observed that initial roughness of 2.21μm for white PCD can be brought down to 175 nm after 70 hours of combined polishing, whereas, 85 hours of combined polishing could bring down the high initial roughness of 11.2μm for black PCD down to 546 nm at the end. Although, the material that was removed during polishing was higher for the black variety of PCD but it had lower polishing rate of 4nm/hr than white PCD (13nm/hr) during chemo-mechanical polishing. Such differential polishing rate was due to harder top polished surface of the black diamond than the white diamond. The nanoindentation study on the polished PCD surfaces revealed that the black PCD has a final nanohardness of 32.58±1 GPa whereas the white variety PCD had a polished surface nanohardness of 28.5±2 GPa. More conversion of diamond surface into harder amorphous sp3 than softer graphite during polishing action may have resulted such slow rate of anisotropic polishing for black diamond than white diamond. Keywords: Microwave plasma CVD, Polycrystalline diamond, Polishing, Diamond quality, Nanohardness. |
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Keywords: Fusion devices, plasma, wall cleaning, electrical resistance, carbon film thickness. |
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Abstract: The possibility of preparation of nanocomposite coatings consisting of a solid lubricant matrix (MoSex) and nanocrystalline metal particles (nc-Mo) was demonstrated using pulsed laser deposition from synthesized target MoSe2.The particles had spherical shapes and their sizes were about 5 – 50 nm. The content of the nc-Mo nanoparticles in the MoSex/nc-Mo coatings was varied by changing the laser irradiation regimes and the conditions of expansion of the laser plume from the target to substrate. It was established that the tribological properties of the nanocomposite coatings MoSex/nc-Mo are depended on the concentration of nanoparticles in the bulk of the coatings as well as on the structure of the coating matrix. The MoSex/nc-Mo coating with increased crystalline order of matrix obtained on a steel substrate reduced the friction coefficient to ~0.04 during steel ball sliding in air of laboratory humidity. Probable mechanisms of nanoparticle formation were proposed and a role of these particles in the wear of the nanocomposite MoSex/nc-Mo coatings was discussed.
Keywords: Low friction coatings, Nanostructure, Nanoparticles, Coefficient of friction, Molybdenum diselenide. |