Surface and Coatings Technology

AISI 316 austenitic stainless steels have been plasma nitrided using a dc glow discharge unit in order to investigate the influence of gas composition on microstructure and corrosion behavior of treated samples. Corrosion properties of untreated and plasma nitrided 316 steels ...

In this paper, we report structural and optical properties of nanocrystalline chromium (Cr) doped ZnS particle, which have been synthesized by co-precipitation method. The structural properties of ZnS:Cr nanoparticles have been characterized by X-ray diffraction (XRD) analysis. The XRD patterns show hexagonal structure in nanoparticles without any additional phase. The mean crystallite size calculated from the XRD patterns has been found in the range 2.45-1.50 nm with the increase in molar concentration of doping agent. Absorption spectra have been obtained using UV-Vis spectrophotometer to find the optical direct band gap. The obtained values have been founded to being range 3.82-4.42 eV. It was also found that optical band gap (Eg) increases with the increase in molar concentration of doping agent is attributed to size quantization effect due to the small size of the particles.

ABSTRACT Graphite is one of the candidate materials proposed for application in pyrochemical reprocessing plants involving aggressive molten chloride environment. Post treatments are promising techniques for the improvement of properties of thermal spray coatings for different industrial applications. In the present work, the effect of post treatments like vacuum annealing (VA) and laser melting (LM) on the microstructure and chemical modification of plasma sprayed Al2O3-40 wt.% TiO2 coatings over high density (HD) graphite substrates has been investigated. When compared with sprayed coatings (SC), VA coatings showed cluster morphology and LM coatings exhibited homogenous microstructure. On laser melted surfaces networks of cracks were observed. XRD studies showed that the metastable γ-Al2O3 phase present in the SC is transformed to stable α-Al2O3 after post treatments. In LM coatings Al2TiO5 phase was more predominant in contrast to SC and VA coatings. The microhardness enhancement was observed in case of LM coating compared to the VA and SC. Due to elimination of coating defects in LM samples, there is a considerable reduction in the surface roughness.

Siloxane–polyurethane paints were formulated and characterized for coating properties and performance as fouling-release (FR) marine coatings. Paints were formulated at 20 and 30 pigment volume concentrations with titanium dioxide, and aminopropyl-terminated poly(dimethylsiloxane) (APT-PDMS) loadings were varied from 0 to 30% based on binder mass. The coatings were characterized for water contact angle, surface energy (SE), gloss, and pseudobarnacle (PB) adhesion. The assessment of the FR performance compared with polyurethane (PU) and silicone standards through the use of laboratory biological assays was also performed. Biofilm retention and adhesion were conducted with the marine bacterium Cellulophaga lytica, and the microalgae diatom Navicula incerta. Live adult barnacle reattachment using Amphibalanus amphitrite was also performed. The pigmented coatings were found to have properties and FR performance similar to those prepared without pigment. However, a higher loading of PDMS was required, in some cases, to obtain the same properties as coatings prepared without pigment. These coatings rely on a self-stratification mechanism to bring the PDMS to the coating surface. The slight reduction in water contact angle (WCA) and increase in pseudobarnacle release force with pigmentation suggests that pigmentation slowed or interfered with the self-stratification mechanism. However, increasing the PDMS loading is an apparent method for overcoming this issue, allowing for coatings having similar properties as those of clear coatings and FR performance similar to those of silicone standard coatings.