Topography and microrelief electroless Ni-P coatings at different loading densities

The aim of this study was to investigate the growth processes of Ni-P coatings at different loading densities of the electroless nickel plating bath. The Ni-P coatings can be used to improve the thermal and corrosion resistance of optical fiber used to manufacture sensors of various physical quantities. When depositing coatings on optical fiber, the loading density is an important parameter. The study investigated the influence of loading density on the topography, microrelief, roughness, and growth mechanism of Ni-P coatings using non-contact high-resolution optical profilometry. An increase in loading density from 0.5 to 3.0 dm2/l did not lead to a significant change in the roughness parameters of the coatings. During the growth of coatings, “spheroids” strongly elongated in the plane of the substrate were formed on the surface. An analysis of growth processes was carried out within the framework of the layered growth mechanism. The growth rates of spheroids in normal and lateral directions were assessed.An increase in the loading density led to a decrease in the growth of spheroids in the normal direction, while the growth rate in the lateral direction was maximal at a loading density of 2 dm2/l. Statistical analysis of the sizes of the “spheroids” showed that their distribution deviated from the normal law, which may be due to the fact that not only individual spheroids, but also their aggregates were considered in calculations. Another reason for the deviation may be a decrease in the proportion of the active surface on which the coating is deposited as the loading density increases. Since increasing the loading density from 0.5 to 3.0 dm2/l did not lead to a significant change in the roughness parameters even with coating thickness of ~ 8 µm or higher; deposition of coatings with the thickness up to 3.5 µm thick on optical fibers can be carried out at the specified loading densities with acceptable surface roughness