1987 Volume 36 Issue 3 Pages 142-147
Sodium molybdate gives an excellent corrosion inhibition for carbon steel in the presence of lithium hydroxide in a solution of 12.45mol/l lithium bromide at 160°C which is the operating condition of a two stage absorption refrigerator. However, in a low concentration, 0.001mol/l, of sodium molybdate the effect decreases enormously. We have revealed that the low concentration of sodium molybdate mixed with benzotriazole gives an excellent corrosion inhibition for carbon steel in the same manner as the high concentration of sodium molybdate. In the presence of 0.15mol/l lithium hydroxide, the most effective solution is the 0.001mol/l sodium molybdate one added with 0.0015 to 0.0075mol/l benzotriazole. In addition, this mixed inhibitor is also effective for galvanic and crevice corrosion inhibition. It is suggested that this corrosion suppression effect by the above mixed inhibitor is resulted from the complemental effect of the compact inner layer film composed of molybdate oxides mainly such as MoO2 and Fe3O4, and the outer layer film composed of molybdate compounds, Fe-benzotriazole and α-Fe2O3 which are formed on the surface of carbon steel.