Abstract
An investigation of the relation of surface H to that adsorbed in the metal was carried out. During the course of this investigation a number of subsidiary investigations were made. These include an investigation of the adsorption of thiourea and thiocyanate in solution on iron. The work carried out included the measurement of the coverage of iron electrodes with H as a function of potential in borate buffer solution, pH = 8.4, in the presence and absence of inhibitors, utilizing a new technique (FTIR); the determination of the hydrogen evolution reaction (HER) with H and D to obtain isotope effect; the determination of adsorption on iron as a function of potential and concentration of thiourea and thiocyanate ; the determination of diffusion and solubility of H in Fe at a variety of electrode potentials in ranges relevant to corrosion. Rationalization of the overpotential relation to θ[H] and C[H] was obtained. A plot of [H] vs θ[H] produces a straight line with slope K which was deduced from a Langmuirian approach. The presence of thiocyanate increased the K value due to a reduction in the rate of hydrogen discharge. It was also found that the majority of H is adsorbed on the surface, i.e., there is about one hydrogen inside the metal for 10^7 on the surface. The increase of hydrogen permeation in the presence of thiourea and thiocyanate is due to the adsorption of these additives on high energy sites leaving the low energy sites for the hydrogen discharge. A good inhibitor for permeation is that which adsorbs on the low energy sites and hence favors the discharge step. The adsorption of thiourea fits a Bockris-Swinkels isotherm which represents a water displacement model. Thiourea was found to displace 3 water molecules. The coverage overpotential relation at constant concentration fits the Bockris-Gileadi-Muller theory which explains a parabolic type of adsorption. Thiocyanate adsorption was found to fit a Bockris-Devanathan-Muller isotherm.
Carbajal Castaneda, Jose Luis (1986). Adsorption of hydrogen at the iron-solution interface : FTIR and RT approach. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -440166.