THE EFFECT OF CHANGE OF PH ON THE INHIBITORY-ACTION OF 3-(TRIMETHOXYSILYL)PROPANETHIOL-1 ON CORROSION BEHAVIOR OF CARBON-STEEL IN NACL SOLUTIONS

The inhibitory action of 3-(trimethoxysilyl)propanethiol-1 (TMSPT) on carbon steel corrosion in NaCl 3.5% solutions of different pH (2, 6 an d 12) at 25-degrees-C and with an initial dissolved oxygen content of 6.5 ppm was examined. Different amounts of TMSPT (0.5 x 10(-3), 1.1 X 10(-3) and 2.7 X 10(-3) mol l-1) were added to NaCl solutions. Electro chemical and weight loss tests show that the inhibitory action of TMSP T increases with increasing TMSPT concentration, and decreases with in creasing exposure time, more strongly in solutions at pH 2 and 12 and weakly in solutions at pH 6. At pH 2 and 6 TMSPT acts as both an anodi c and cathodic inhibitor, reaching an inhibiting power of 60% at its h ighest values; at pH 12, TMSPT mainly acts as a cathodic inhibitor, re aching a comparable inhibiting power.