THE EFFECT OF NACL ADDITION ON THE CORROSION OF MILD-STEEL IN NANO3 MELT

Molten alkali metal nitrates are considered to be a promising heat tra nsfer and storage system and the addition of NaCl in these melts incre ases their specific heats which increases their energy storage capacit y. The effect of the addition of 7.5 wt% NaCl in NaNO3 melt on the hot corrosion of mild steel has been investigated in the temperature rang e from 350-degrees to 550-degrees-C by applying various techniques. Gr avimetric test results up to 10 h of immersion showed higher oxidation rates in the presence of NaCl. Scale and melt analysis results indica ted the diffusion of more iron from the scale into the NaNO3-NaCl melt . This suggests that the addition of NaCl increases the basicity of th e melt. The higher corrosion rate, a lower polarization resistance and a decrease of activation energy were found in the presence of NaCl by electrochemical studies. Metallography study revealed the existence o f localized attack at 350-degrees-C and the scale became non-adherent at 450-degrees-C in the NaNO3-NaCl melt.