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Abstract : Phase Structure, Wear Resistance and Antimicrobial Response of Austenitic Stainless Steels 316L by Sputtering Cu during Plasma Nitriding and PECVD of Silicon Nitride
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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. |
Abstract : Sliding Wear Study of Flame Sprayed Co-Base Powder Coatings
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Abstract: Commercially available Co-base powder was modified with the addition of 10 wt. percentage WC which was further modified with 5 and 10 wt. percentage CrC addition in order to obtain three coatings namely Co+10 wt. percentage WC, Co+10 wt. percentage WC+5 wt. percentage CrC and Co+10 wt. percentage WC+10 wt. percentage CrC. The coatings were deposited by flame spraying process. The microstructure of these coatings mainly showed eutectic containing Co with almost same amount in three coatings. Other phases such as W dominated and Cr dominated carbides were also observed. The 10 wt. percentage CrC coating showed the highest Vickers hardness and lowest wear rate. The coefficient of friction was also observed low in the 10 wt. percentage CrC coating as compared with other coatings. Keywords: Atomic force microscopy, time of flight secondary ion mass spectrometry, Auger electron spectroscopy, coil coating, Cr-free pretreatment, topography. |
Abstract : Synthesis, Comparative Characterization and Photocatalytic Application of SnO2/MWCNT Nanocomposite Materials
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Abstract: Two different preparation methods were developed to cover successfully multi-walled carbon nanotubes (MWCNT) with tin-dioxide (SnO2) nanoparticles using SnCl2·2H2O as precursor under different solvent conditions. The applied mass ratios of the components were 1:4, 1:8, 1:16, 1:32 and 1:64, respectively. As-prepared tin-dioxide coverages were characterized by TEM, SEM, SEM-EDX, Raman microscopy, BET and X-ray diffraction techniques. Photocatalytic efficiencies of selected composites were investigated in a self-made photoreactor, equipped with UV-A fluorescence lamps. Photocatalytic degradation of phenol solution was followed by using HPLC. Observations revealed that using hydrothermal method we can easily control the layer of SnO2nanoparticleson the surface of MWCNTs. Using various solvents SnO2nanoparticles with different morphologies formed. The nanocomposites have low photocatalytic efficiencies under conditions used generally (when λ>300 nm). Keywords: Carbon nanotubes, chemical synthesis, electron microscopy, IR spectroscopy, photocatalysis. |
Abstract : Effect of Sodium Hydroxide on the Fast Synthesis of Superhydro-phobic Powder from Polymethylhydrosiloxane
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Abstract: The paper reports the role of sodium hydroxide in the synthesis of a superhydrophobic powder from polymethylhydrosiloxane (PMHS) in the presence of ethanol and water. The effects of other basic and acidic solutions as well as the absence of water were also investigated. PMHS exhibited rapid gelation (from 8 h to 2 h) by increasing the concentration of sodium hydroxide in the presence of ethanol and water. In contrast, gelation did not occur in the absence of sodium hydroxide or water or in the presence of acidic solutions. Delayed gelation (96 h to 120 h) occurred as a result of the introduction of dipotassium hydrogen phosphate trihydrate. Superhydrophobic powder was obtained by the evaporation of solvents from the gelated sol at 150 °C. The surface properties of the superhydrophobic powder were examined by scanning electron microscopy, high resolution transmission electron microscopy, N2 sorption isotherm, and X-ray diffraction. The particle size, functional groups and thermal stability of the powder were analyzed by dynamic light scattering spectroscopy, Fourier transform infrared spectroscopy, 29Si cross polarization magic angle spinning nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. The surface properties of the powder were also assessed by contact angle measurements. The results showed that increasing the concentration of sodium hydroxide added to PMHS or increasing the drying temperature of the gelated sol resulted in the more rapid formation of superhydrophobic powder. Keywords: Superhydrophobic, polymethylhydrosiloxane, sodium hydroxide, synthesis, powder. |
