Chemija / Chemistry
 ISSN 0235-7216 ISSN 2424-4538 (online) |
2016 m. Nr. 1 Characterization of as-deposited and annealed Cr–Zn–P coatings electrodeposited from a trivalent chromium bath
Black Cr–Zn–P coatings were electrodeposited on a steel substrate from a trivalent chromium bath using glycine as a complexing agent, ZnO as a second main component and sodium dihydro-phosphate as a source of phosphorus. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and spectral reflectance in the UV–visible–near IR and medium IR ranges were used to characterize the black coating before and after annealing. The relationship between the microstructure and optical properties of the black Cr–Zn–P coating deposited on the steel substrate has been studied using as-deposited and annealed samples. The deposits were found to have nodular crystals of various sizes with microcracks undergoing changes during heat treatment. XRD patterns suggest that the Cr–Zn–P alloy is a solid solution, which undergoes a series of transformations during annealing at 600 °C. The XPS results suggest that the near-surface layer is rich in Cr and Zn hydroxides, whereas oxides become dominant towards the substrate/coating interface. Besides, small amounts of phosphor and organic substances were also present in the coating. The phase constitution of black chromium varies by heating the sample up to 600 °C. The black Cr–Zn–P coating has good optical properties and these properties remain practically constant even when heat treated to a high temperature of 400 °C. It has been found that sample annealing at 600 °C initiated an increase in reflectance caused by the changes in the structure and chemical composition of the deposit and the diffusion of the substrate material (Fe) into black chromium.
: Keywords: black Cr–Zn–P coating, morphology, optical properties, annealing |
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