INVESTIGADORES
VALCARCE Maria beatriz
congresos y reuniones científicas
Título:
Localized attack of copper and brass in tap water. The effect of pseudomonas
Autor/es:
M.B. VALCARCE; M. VÁZQUEZ; S.R. DE SÁNCHEZ
Lugar:
Sao Pedro, Brazil
Reunión:
Congreso; 54th Annual meeting of the international society of electrochemistry; 2003
Institución organizadora:
International society of electrochemistry
Resumen:
Copper and Copper alloys are frequently used in tubing systems that distribute tap water. In this application, microbiologically induced corrosion is a recurrent problem. In this context, the present paper deals with the susceptibility to pitting corrosion in copper and 70/30 brass under the influence of Pseudomonas fluorescens. In a first experiment weight-loss was evaluated in coupons after 90 days of immersion. Four containers were prepared with sterile tap water + 0.5% peptone, two for each material and one of them inoculated with the culture. The containers were kept under agitation at 32ºC, renewing the medium every 7 days. After 90 days of immersion, the coupons were cleaned and dried. Average weight loss is presented in Table 1. As can be seen, the presence of Zn as an alloying element decreases the mass loss, but the presence of bacteria enhances the attack in brass by a factor close to 7, as compared to a factor of about 2 for copper. The appearance of dezincification associated to the presence of bacteria was reveled by microscopic observation, as well as by the disappearance of the current peak attributed to Zn in potentiodynamic reduction curves. The susceptibility to pitting corrosion was also studied recording slow-rate voltamperometric curves in order to determine the critical pitting potential and the repassivation potential. The curves were registered at 0.1 mV s-1 in tap water simulating solution, with and without the presence of bacteria in the solution. The scan direction was reversed at 2.18 104 A cm-2 in the case of brass and at 6.40 104 A cm-2 in the case of copper. The results, an average of three independent measurements, show that in the presence of bacteria the pitting potential moves towards more positive (noble) values for both materials and the difference between the repassivation and the pitting potential also increases. When observed at the microscope, bigger and deeper pits can be seen in the presence of microorganisms. The interpretation of this fast response tests, where a biofilm does not have time to develop, can be misleading when compared to corrosion experiments over more extended periods of time, particularly when dealing with systems containing living microorganisms. Table 1   Cu + culture Cu (blank) Brass + culture Brass (blank) Weight loss/ mg cm-2 4.72 2.22 1.18 0.18 Type of attack Pitting None Pitting and dezincification Pitting