Electrochimica Acta, Vol.43, No.1-2, 41-51, 1998
Corrosion of metallic materials in hot salt brines
The corrosion kinetics of fine grained construction steel (W.Nr. 1.0566), titanium with 0.2% Pd (W.Nr. 3.7568) and tantalum in three oxygen-free chloride sail brines at temperatures between 90 degrees C and 200 degrees C were investigated. Different electrochemical methods were proposed all yielding the same steady state corrosion rates. A procedure was developed and applied to measure the pH of the brines at elevated temperatures. Corrosion of the three materials was uniform. On steel, an inner magnetite or amakinite layer and an outer porous oxide layer containing salt grew according to the paralinear rate law. At the free corrosion potential, depending on temperature and nature of the brine steady state corrosion rates between 10 mu A/cm(2) and 100 mu A/cm(2), or between about 0.11 mm/a and 1.2 mm/a, were attained within about a day. The apparent activation enthalpies were small. Hydrogen activities determined from permeation experiments were very low and decreased with temperature. Thus there is a negligible danger of hydrogen embrittlement. Steady state corrosion rates between 0.1 mu A/cm(2) and 10 mu A/cm(2), or between about 0.8 mu m/a and 90 mu m/a, were observed with TiPd0.2, and between 0.3 mu A/cm(2) and 100 mu A/cm(2), or 2 mu m/a and 720 mu m/a, for tantalum. Activation enthalpies were small or even negative depending on the brine. TiPd0.2 or Ta do not corrode that much slower than steel in order to justify, from the viewpoints of technical properties and economy to prefer them to steel as container material for final disposal of nuclear waste.