OXIDATION OF TITANIUM, ZIRCONIUM, MOLYBDENUM AND OF SOME OF THEIR ALLOYS

Although the corrosive behavior of Ti, Zr, and Mo has been studied exhaustively, only insufficient information is available at the lower temperature range. Therefore, the interaction of O/sub 2/ and air with these metals and with Ti alloys containing 10% Mo and 5% Cr +3% Al was investigated within the temperature range of 20 to 400 deg C. An optical polarization method involving the measurement of the thickness of the thin film formed on the surface of the metals by determining the change of the ellipticity of the reflected light was used for the measurements. From the kinetics of the film growth thus obtained it was established that in the temperature range above 200 deg C the Zr possesses the highest oxidation rate as a result of the increase of the monoclinic modification of ZrO/sub 2/. At temperature above 300 deg C Mo also presents a high oxidation rate but the Ti alloy containing 10% Mo had a lower rate at the same temperature than pure Ti; this might be due to differences in the structural defects in the oxide films. It was found to be lower in wet air than in dry air. At the lower temperaiures the growthmore » rate of the film follows the logarithmic law; at higher temperatures a parabolic correlation is noticed indicating that the growth is due to diffusion phenomena. (TTT)« less