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: 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.

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: Anodization is known to be an effective way to slow down the initial corrosion rate of magnesium (Mg) and its alloys. Here, we investigated the specific use of oxy-salts to improve the corrosion resistance of anodizing coatings. Oxy-salts of silicate, phosphate, and carbonate were added separately to a sodium hydroxide alkaline electrolyte used to anodize Mg alloy AZ91D. The process was investigated in terms of anodizing behavior, the surface properties, and the corrosion behavior of AZ91D. Anodizing AZ91D using the silicate- containing electrolyte generated sparks, and produced a thicker and more corrosion-resistant layer than the other oxy-salts. In the process, MgO and SiO₂ formed Mg₂SiO₄ at high temperatures. Coatings from the phosphate- and carbonate- containing electrolyte anodizations did not contain phosphorus or carbon. We also studied the effects of silicate concentration on the corrosion resistance and properties of the surface.