Corrosion-Protective Properties of N-Phenacylmethylpyridinium Bromides

A study of the effect of metal corrosion inhibitors on the hydrogenation of steel and changes in its plasticity upon etching in sulfuric acid solutions

“…For inhibitors In-1 (R The fact that these correlation dependences are observed, as also do those obtained previously [4], confi rms that adsorption of the inhibitors under study and their effect on the corrosion and hydrogen charging of steel become more pronounced as the electronic interaction of the pyridine ring or acyl group of additives with the steel surface becomes stronger. The experimental data we obtained suggest that introduction of the inhibitors under study into a corrosive medium hinders the cathodic process of hydrogen evolution and, consequently, makes smaller the fraction of hydrogen penetrating into the metal and causing its brittleness.…”

“…Seemingly, such a pronounced protecting effect of the inhibitors could be attributed to their stronger protective action (γ c = 29.2-33.3) and, consequently, to a more perceptible hindrance to the reaction in which hydroxonium ions are discharged and to a decrease in the amount of atomic hydrogen capable of penetrating deep into the metal. However, voltammetric measurements have shown [4,5] that In-9 and In-10 inhibitors raise the hydrogen overvoltage to a lesser extent, compared with inhibitors In-2 and In-3 and suppress the decrease in the plasticity of steel to a greater extent than it would be expected on the basis of their anticorrosive properties (Fig. 2).…”

“…It was found that the effi ciency of steel plasticity loss suppression by the inhibitors under study depends, as also does the corrosion rate hindrance [4], on the electronic properties of the substituents incorporated in their pyridine ring or acyl group. For inhibitors In-1 (R The fact that these correlation dependences are observed, as also do those obtained previously [4], confi rms that adsorption of the inhibitors under study and their effect on the corrosion and hydrogen charging of steel become more pronounced as the electronic interaction of the pyridine ring or acyl group of additives with the steel surface becomes stronger.…”

“…The experimental data we obtained suggest that introduction of the inhibitors under study into a corrosive medium hinders the cathodic process of hydrogen evolution and, consequently, makes smaller the fraction of hydrogen penetrating into the metal and causing its brittleness. The latter is confi rmed by voltammetric measurements [4] according to which the overvoltage of hydrogen evolution on steel at a current density of 5 × 10 -3 A cm -2 grows on passing from inhibitor In-2 to In-3 and by direct measurement of the amount of hydrogen diffused deep into steel in its etching. For example, etching of steel for 1 h in a sulfuric acid solution results in that the amount of hydrogen extracted from steel is 56 cm 3 per 100 g of the metal, and that in the presence of inhibitors In-1 and In-2, 12.5 and 13.8 cm 3 /100 g, respectively, i.e., the content of hydrogen in the steel decreases by approximately a factor of 4 in the presence of the additives under study in the corrosion medium.…”

“…On the one hand, inhibitors of this kind belong, similarly to other quaternary pyridinium salts, to corrosion i, to corrosion inhibitors of the energetic τ, min Q type [1,4,5,7], which can raise the overvoltage of hydrogen and change the nature of the hindered stage of its evolution on steel from recombination to discharge or electrochemical desorption. On the other hand, presence in inhibitors of this kind of additional atoms of oxygen and sulfur, capable of transferring the electron density to the metal, may favor weakening of the bonding between atoms of hydrogen and metal and, consequently, can raise the activation energy of discharging of hydroxonium ions and more strongly diminish the fraction of hydrogen atoms diffusing deep into the metal.…”