Microstructure Of Oxide Coatings Research Articles

Effect of Negative Current on the Microstructure of Oxide Coatings Prepared by Hybrid Pulse Anodization

The oxide coatings were prepared on 6061 Al alloy at different negative current densities in oxalic acid using the hybrid pulse anodization (HPA) method at room temperature. The variation curves of positive and negative voltages with anodization time were recorded. The nanopore diameters and distribution regularities in HPA coatings were analyzed with the Image-Pro Plus software based on field-emission scanning electron microscope (FE-SEM) images. The results showed that the negative current could reduce the growth rate of HPA coatings, and thus led to a small thickness of the coatings within the same anodization time. Besides, appropriate negative current densities resulted in the better distribution uniformity of nanopores, but the excessive negative current densities tended to cause inferior nanopore arrangement. These were attributed to the existence of the negative current, causing H+ and O2− to move in opposite directions, so that a large number of H+ concentrated on the surface of the HPA coatings, resulting in the accelerated dissolution of the coatings.

Influence of the Size of Nanoparticles on the Microstructure of Oxide Coatings

The microstructures and structures of composite coatings prepared on aluminum substrates are studied. Amorphous oxide layers Al2O3 are obtained on EN AW 5251 aluminum alloy. In the Al2O3 coatings, two kinds of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles (NPs) are introduced by a dip coating method. In order to show the difference between the possibilities of introducing NPs in the microstructure of Al2O3, we carried out the scanning electron microscopy and transmission electron microscopy analyses. The image processing and analysis were performed in order to study the shapes and sizes of the IF-WS2 nanoparticles. Visual comparative analysis reveals the difference in the quality of nanopowders that greatly affects their ability to form agglomerates and, hence, strongly affects the possibility of introducing NPs into nanopores.