Effect of zirconia in the corrosion behavior of intermetallic Mo3Si alloy in molten salts mixture of NaNO3 and KNO3

The corrosion effect of zirconia addition, 1, 2, and 5 atomic percent (at.%), on the hot corrosion behavior of Mo3Si intermetallic alloy in 60 wt.% NaNO3 + 40 wt.% KNO3 at 600 degrees C, has been evaluated by using electrochemical methods. Electrochemical techniques included electrochemical noise analyses (ENA), polarization curves (PC), and linear polarization resistance (LPR). The average grain size decreased when the specimen was alloyed with Zr from 90 mu m for as-cast Mo3Si, down to 25 and 10 mu m for alloys containing 1, 2, and 5 at.% Zr, respectively. All specimens showed a passive behavior, with the corrosion current density values decreasing for adding either 1 or 2 at.% Zr but increasing for specimens containing 5 at.% Zr. The corrosion process was under charge transfer control for the as-cast alloy or when 1 or 2 at.% Zr was added, but it was diffusion controlled when 5 at.% Zr was added. The noise resistance value (R-n) increased for specimens containing 1 or 2 at.% Zr but decreased when 5 at.% Zr was added. X-ray diffraction showed the presence of SiO2, MoO4, Mo4O11, and ZrO2 in the passive layer.