The main problem of galvanic zinc plating and other galvanic processes is their high ecological danger due to the possibility of toxic substances entering the environment with sewage. For the purpose of coating using the electrolyte method, it was proposed to use an environmentally safe electrolyte zinc coating of 350 g/l ZnSO4, 30 g/l (NH4)2SO4. In order to improve the quality of the resulting precipitate, it is proposed to add citric acid, which is an environmentally safe substance, to the solution.
Figure 1 − Polarization curves taken in electrolyte of 175 g/l ZnSO4, 30 g/l (NH4)2SO4, 0...20 g/l citric acid
Figure 2 − Polarization curves taken in electrolyte of 350 g/l ZnSO4, 30 g/l (NH4)2SO4, 0...20 g/l citric acid
The study of the effect of zinc sulfate and citric acid concentration on the polarization of zinc extraction has shown the following. As can be seen from Fig. 1, the highest value of the polarization of zinc extraction occurs at the concentration of citric acid 2 g/l, with a further increase in its content, polarization decreases. In a more concentrated solution of electrolyte in Fig. 2, one can also see that the greatest polarization is achieved with the content of citric acid 5 g/l, with further increase in its content, the polarization decreases.
Figure 3 − Precipitated zinc coatings in electrolyte 175 g/l ZnSO4, 30 g/l (NH4)2SO4, 5-10 g/l citric acid, pH = 2 for current densities: a − 2 A/dm2; b − 3 A/dm2; c − 4 A/dm2
Figure 4 − Precipitated zinc coatings in the electrolyte 350 g/l ZnSO4, 30 g/l (NH4)2SO4, 5-10 g/l citric acid, pH = 2 for the current densities: a − 5 A/dm2; b − 10 A/dm2; c − 20 A/dm2
The study of the influence of the solution composition and the current density on the quality of copper cathode precipitate has indicated the following. In the region of low current density, non-continuous with gaps coatings are obtained (Fig. 3, 4-a). However, for solid densities corresponding to about 50% of the limit, solid, semi-glowing zinc deposits precipitate. (Fig. 3, 4-b). When approaching the limiting current density, there is a burn-on at the edges of the samples (Fig. 3,4-c). According to the data obtained, an increase in zinc content results in a disproportionate increase in the maximum working current density, which may be explained by the presence of migration mass transfer. On the other hand, the obtained data can indicate the possibility of significant intensification of the zinc plating process by the method of electro-wiping.