Influence of the heat exchange on the inhibition of copper corrosion in 3.5% NaCl by heterocyclic derivatives.

Copper and copper alloys are the most used metallic materials for the heat exchange and condensers in which their excellent characteristics of heat conductivity and corrosion resistance are exploited, When the environments are very corrosive, the use of inhibitors must be necessary to assure the safety of the operation. Usually the corrosion inhibition tests are conducted under isothermal conditions notwithstanding applications are under heat exchange conditions. To overcome this inconvenient a simple system, which permits to carry out tests under heat exchange conditions, was set up in our laboratory for some years. By usung this system the protective characteristics of films obtained by prefilming treatment of copper with benzotriazole (BTA) derivatives were examined. The inhibiting efficiency of 5,methyl-, 5,chloro-, 5,n-hexyl-BTA, 2,4dimercapto-pyrimidine and 2,amino-5,mercapto-thiadiadole on the copper corrosion in 0.1M NaCl was successively examined with deltaT=60°C. All tested inhibitors at 0.5M concentration showed high inhibiting characteristics. In all experimental conditions 5,n-hexyl-BTA provided the best inhibiting efficiency. In this paper the inhibiting effects of several heterocyclic derivatives on the copper corrosion in 3.5% NaCl solutions under different heat exchange conditions was investigated. The results were compared with those obtained in isothermal tests. The aim of the paper was to evidence if the corrosion rate was controlled by wall temperature or by heat flux.