Smears of Titanium Metal

Abstract

A Remarkable phenomenon is shown by metallic titanium when rubbed against many hard surfaces. If a piece of the metal with a rounded end, of radius of curvature about 1 mm., is pressed firmly on to a hard surface and drawn across it, the metal is left behind in the form of a silvery smear. Smears are obtained with greater difficulty on some substances than on others, but only one crystalline material has been found on which no smear is produced (see accompanying table). The titanium metal may be removed by treatment with hot concentrated hydrochloric or sulphuric acids for about half an hour, or by treatment with cold commercial hydrofluoric acid for a few seconds. Some surfaces which were originally smooth and shiny are seen to have lost their polish after the titanium has been dissolved away. In this way, for example, it is possible to remove the polished surface of glass by rubbing with titanium and then dissolving the metallic smear in hydrochloric acid. The table gives a summary of the results obtained on a number of crystalline materials and on glass.