Tese de Doutorado

O objetivo deste trabalho é estudar e comparar a eficiência dos inibidores de corrosão benzotriazol (BTAH), N-feniltioureia (N-FTU) e cloreto de hexadeciltrimetil amônio quaternário (chtaq) para o ferro puro, aço carbono e aço arbl, em meio de 'H IND.2's'O IND.4' 0,5m e 2,0m através do ajuste dos resultados de perda de massa as diferentes isotermas de adsorção: Langmuir, Frumkin, Temkin e Flory-Huggins e também caracterizar a ação desses inibidores sobre o comportamento eletroquímico dos materiais estudados. Os ensaios de imersão com medidas de perda de massa foram realizados para diferentes concentrações de inibidor, visando determinar o grau de proteção. Dentre as técnicas eletroquímicas foram feitas medidas de potencial de corrosão em circuito aberto e levantadas curvas potenciostáticas de polarização anódina e catódica, na ausência e presença dos inibidores estudados. Todos os ensaios foram realizados a temperatura de 35'GRAUS'c e o tempo de imersão para os ensaios de perda de massa foi de duas horas. Os valores médios de velocidade de corrosão, obtidos na ausência de inibidor, mostram que o aço arbl e mais resistente que aço carbono e ferro puro para todas as concentrações, tempos de imersão e temperaturas estudadas. O btah apresentou-se como melhor inibidor para aço carbono em meio 'H IND.2's'O IND.4' 0,5m, com obediência a isoterma de adsorção de Langmuir.

The aim of this work, is to study and compare the inhibition efficiency of benzotriazole (BTAH), N-phenvlthiourea (N-PTU) and hexadevltrimethyl quaternaryammonium chloride (HTMQAC) to Armco iron, mild steel and high strength low alloy steel (HSLA) in 0,5M and 2.)M H2SO4 media, by weight loss measurements fitting to Langmuir, Frumkin, Temkin and Flory-Huggins adsorption isotherms. Its Aldo intended to characterize the inhibitors action on these metals electrochemical behavior. The weight loss immersion tests were carried out for many different inhibitor concentrations in order to determine the proctection degree. The corrosion potential (ecorr) measures and potentiostatic polarization curves were performed in presence and in absence of inhibitors. All tests were performed at a controlled temperature of 35°C and a immersion time of two hours was employed in weight loss experiments. The mean corrosion rates showed that the HSLA steel is more corrosion resistetn than mild steel and Armco iron for all H2SO4, concentrations, immersion times and temperatures studied. The BTAH showed to be efficient to mild steel in 0,5M H2SO4 and the film formed obeys Langmuir isotherm; it slightly shifts the corrosion potencial to more positive values for increasing concentrations, concerning to polirization curves, it is a mixed inhibitor. The N-PTU, to both 0.5M and 2.0M H2SO4, media, presented greater efficiency to HSLA steel than to other metals studied here, with protection degree results well fitted to Langmuir, Frumkin and Temkin isotherms with repulsive lateral interaction between adsorved N-PTU molecules on HSLA steel surface, it shifts the Ecorr of mild and HSLA steels to more positive values and to more negative ones to Armco iron, regarding to polarization curves it is mixed inhibitor with a stronger inhibiting action on catholic reactions. The HTMQAC showed the greatest efficiency to mild steel in 0.5M H2SO4, obeyingFrumkin isotherm with a lateral atractive interaction of adsorbed species. It acts as a mixed inhibitor shifting the Ecorr to more positive values. The cathodic Tafel slopes were determined with a mathematical model to correct the applied potencial values with respect to ohmic drop and the obtained values indicate that none of the three inhibitors can cahnge the H+ reduction mechanism. Corrosion rates determined from weight loss mesurments are in close agreement to corrosion current densities, Icorr, obtained from electrochemical technique.