Inhibition by CO of the corrosion of Fe, Ni, and their alloys in concentrated HCl solutions

Abstract

a b s t r a c tInhibition by CO of the corrosion of Fe, Ni, and three alloys, containing either Fe and large amounts of Ni (Incoloy 825) or large amounts of Fe (Uniloy-420 and N80 steels) in solutions containing between 7.5% and 28% HCl was studied using potentiodynamic polarization curves, gravimetric tests, and FTIRS. In all cases, but Uniloy-420 in 28% HCl, a clear inhibition of corrosion in the presence of CO in the solution was shown by the gravimetric tests and from cyclic voltammetry, the inhibition being higher in the case of Ni and Ni-containing alloys. CO chemisorbed on Fe and/or Ni atoms present on the alloy surface was identified as the species responsible for corrosion inhibition. The inhibition of corrosion is higher in the cases of Ni and Incoloy 825.

CO and trans-cinnamaldehyde as corrosion inhibitors of I825, L80-13Cr and N80 alloys in concentrated HCl solutions at high pressure and temperature

“…As we have shown recently [25], and as was actually to be anticipated, chemisorbed CO is the species responsible for the inhibition of corrosion of I825, U420 and N80 in CO-saturated concentrated HCl solutions. Increasing the pressure and the temperature must have opposing effects on the CO adlayer.…”

“…As can be seen in Figure 4, CO is an even better corrosion inhibitor at high pressure and temperature than at room temperature and normal pressure (compare with the results in reference [25]), suggesting that the increase in the solubility of CO at 6.9 MPa overwhelms the effect of increasing the temperature. This was actually to be expected, since the pressure has been multiplied by a factor of ca.…”

“…On I825 and N80, and at a constant pressure of 6.9 MPa, the inhibiting effect of CO is higher at Fe atoms at the surface of N80, as found at normal pressure and temperature [25]. On the contrary, in the case of U420, the inhibition of corrosion is higher at 175 o C than at 120 o C. This may be due to the high amount of Cr present in U420, onto which CO can adsorb dissociatively [28].…”

“…In all the cases but U420, E corr shifts to more positive values when the solutions are saturated with CO. In a previous work [25],…”

“…As a consequence of the strong bonding of CO to the surface of Fe, Co, and Ni, surface oxidation or dissolution of these metals is strongly impeded in CO-saturated solutions [13][14][15][16], and very recently, we have reported that CO can be used as an efficient inhibitor of the corrosion of Fe, Ni and their alloys in concentrated HCl solutions at room temperature and normal pressure [25]. In this paper, we describe the inhibiting effect of CO in 15% w/w HCl, under high pressure (6.9 MPa) and temperature (100-200°C) conditions, both when it is directly dosed and when it is generated from the formic acid dehydration reaction, and compare it with that of transcinnamaldehyde, a commonly used acid corrosion inhibitor.…”