A new method of reducing the degree of hydrogen absorption of metal during electrochemical treatment

Abstract

At present a method of reducing the hydrogen absorption of metal during the application of galvanic coat- ings and during etching by the addition to the electrolyte of certain additions, organic compounds inhibiting hydrogen absorption (1), is well known. However, in a number of cases such as in cathodic polarization, the use of inhibitors has a negative effect on polarization. This is a result of electrolytic reduction of organic inln~itors at high cathodic potentials. Another disadvantage of the method is the fact that in chemical and electrochemical etching of metal parts, the inhibiting substances together with the electrolyte penetrate into voids and other microdiscontinuities of the metal. With subsequent application of a galvanic coating to the part, this may reduce the adhesion strength of the coating to the base metal. In addition, during application of a galvanic coating the inh~itors become a part of the coating and frequently have a detrimental effect on its physical and mechanical properties. Therefore, the use of this method requires constant control of coating quality and the chemical composition of the electrolyte and correction of it. We have developed a new electrophysical method of protecting metals from hydrogen absorption (2) the nature of which is that the sample is connected to a normal cathodic polarization circuit and to a supplementary electrical circuit providing passage through the part of an electrical current with a frequency of 10s-105 Hz and a density in the surface layer of the metal of 0.5-2.5 A/cm 2. The effectiveness of the proposed method of protection of metals from hydrogen absorption was deter- mined in the following manner. The rate of diffusion of hydrogen through cathodicaUy polarized membranes of 10 steel in relation to the frequency of the current passed through and its strength and also the absorbability of hydrogen by the metal under the same conditions were studied. The diffusion of hydrogen was judged from the quantity of hydrogen which had diffused through the membrane, which was the bottom of an electrolytic cell (3). An 0.5 N sulfuric acid solution was used as the electrolyte. The range of frequencies of current passed through the steel membrane during cathodic polarization with a current density of i A/din 2 was from 50 to 105 Hz and the strength of the current was 30-50 mA. At fre- quencies from 50 to 103 Hz no effect of the alternating current passed throughthe membrane on the rate of diffusion of hydrogen in the metal was observed. It appears only at higher ac frequencies starting at 103 Hz and more. With this there is retarding of the penetration of hydrogen into the metal during cathodic polariza- tion. For example, while the rate of diffusion of hydrogen in steel in the normal method (without passage of a current through the membrane) is 1.07 ~ 103 ml/cm 2 �9 with the action on it of a high-frequency current dur- ing polarization this drops by 3 or 4 times.