فصلنامه علوم و مهندسی سطح ایران
پیاپی 52 (تابستان 1401)

In this study, nickel oxide oblique columnar nanostructures were deposited on glass and steel substrates by physical evaporation deposition with oblique angle. The surface morphology, structural and wettability properties are affected by the substrate. XRD studies showed that the nanostructure deposited on steel has a better orientation than the nanostructure deposited on glass. AFM and FESEM studies showed that surface roughness and grain size depend on the type of substrate. The surface roughness of the nanostructure deposited on steel is higher compared to the nanostructure deposited on glass, and big grains are formed by the growth of small grains and merging them together. The grains size of the nanostructure deposited on steel are higher than the nanostructure deposited on glass. Contact angle measurements showed that the nanostructures deposited on glass and steel are hydrophilic and hydrophobic in nature with contact angles of 78 and 120, respectively. The morphology of the nickel oxide oblique columnar nanostructure surface deposited on steel causes to increase the contact angle of the water drop with the surface.

Chromate conversion coatings with anti-corrosion properties are used as coatings for external elements of space systems. The three main properties of these coatings that are effective in aerospace application are: corrosion resistance, adhesion strength of the coating to the substrate and abrasion resistance. In this paper, the parameters affecting these properties were investigated and in order to optimize these parameters, the response surface methodology (RSM) method was used in MiniTab program. Variable parameters are temperature, amount of refiner and amount of accelerator. The amount of constituent material, reaction time and age time were considered constant for all samples. The corrosion resistance, adhesion strength of the coating to the substrate and abrasion resistance are determined by salt spray test in 0.5% saline medium for 336 hours, Pull Off test and pin on disk wear test, respectively. The maximum amount of corrosion resistance obtained for chromate coating which was 71.8% of the surface remind intact, with the combination of 4 g/lit refiner, 1.8 g/lit accelerator at 45 °C. The maximum amount of coating stress from the substrate surface was 1.2 MPa, which was obtained in the amount of 4 g/lit refiner, 1.8 g/lit accelerator and 35 °C temperature. The minimum weight loss due to abrasion was 0.2 mg, which was obtained for coating with the composition 4 g/lit refiner, 6 g/lit accelerator at 35 °C. Therefore, by increasing the amount of accelerator and temperature, the thickness of the coating increased, and this increase to the optimum level increases the abrasion resistance and adhesion strength of the coating, but when the thickness increases beyond the optimum, the abrasion resistance and adhesion strength decrease.

The purpose of this study is to use of an Eco-friendly accelerator in zinc-calcium phosphating process. For this, the conventional phosphating parameters (containing nitrate and nitrite) were optimized using literature; Then, the accelerators were substituted with H2O2. The morphology of the phosphate coatings was observed by a scanning electron microscope (SEM), and the chemical compositions were investigated by energy dispersive X-ray spectroscopy (EDS). The crystalline structures of the phosphate coatings were analyzed by X-Ray Diffraction (XRD). The corrosion resistance of samples was assessed through polarization tests in 3.5 wt.% NaCl solution. According to the results, about 0.6 mL/L was obtained as optimum concentration of H2O2. Also, the optimum temperature and pH of phosphating were about 47 °C and 3.2 respectively. The XRD results indicated that the coating structure include phosphophyllite, hopeite and some scholzite phases. SEM images showed that, in the presence of H2O2, the geometrical shape of coating crystals is cubic, which are grown uniformly on the entire area the substrate. Also, according to the electrochemical parameters, the coating obtained from the bath containing 0.6 mL/L of H2O2, has the highest corrosion resistance. Therefore, it can be deduced that, H2O2 could be used to replace the traditional accelerators like nitrate and nitrite, since it is less pollutant and provides better quality of the coating.

In this study, the effect of injection of argon and hydrogen shielding gases on the properties of ZrC coatings, applied by solid shield plasma spraying (SSPS) and comparison with APS method were investigated. The effect of type and rate of injected gases on the microstructure of the coating were investigated by studying the morphology of the particles in the Single-line scan-spray. Also, the microstructure and phases of the coatings along with their porosity and oxide content were evaluated. The results show that the coating applied by SSPS method and injection of internal hydrogen gas at a rate of 20 l/min leads to an increase in the amount of splats in the coating and a decrease of more than 50% in the amount of oxides and porosity in the microstructure compared to APS coating. The H2 gas is injected to solid shield burns with O2 that caused a reduction in the amount of oxides in SSPS coatings and increase the heat and temperature around the plasma jet and increase the amount of molten particles in the coatings.