Change of morphology of titanium surface by pickling in nitric-hydrofluoric acid solutions

Accompanying the expanding use of titanium, various qualities have been in demand for the product surfaces. Above all, from a viewpoint of landscapes and designs antiglare, quality is required for roofs and walls of buildings. Authors have noticed dissolving product surfaces by nitric-hydrofluoric acid solutions to obtain dull surfaces and examined the effects of the solution composition (concentrations and metal contaminants) on surface morphologies, glossiness and whiteness. In the case of constant hydrofluoric acid concentrations, the glossiness decreases and the whiteness increases as nitric acid concentration is lower because roughness increases due to unevenness formation that is the same size with grains. In opposition with increasing nitric acid concentration and iron contaminant from stainless steels the surfaces of titanium, products become smooth and therefore their glossiness increase. These effects are thought to be due to depressing the anisotropy of titanium solution velocity by both nitric acid and contaminants from stainless steels.