INFLUENCE OF NITRILOTRISMETYLPHOSPHONIC ACID ON ZINC ELECTRODEPOSITION
The work is devoted to the study of the effect of complexing substances on the electrolytic reduction of zinc from alkaline solutions. This issue has been studied in the literature on the example of carboxylic and aminocarboxylic acids. In this work, we investigated the features of the reduction of zinc from zincate solutions with the addition of nitrilotrimethylphosphonic acid (NTMPA). Electrolytes were used with a concentration of zinc oxide 0.2 mol / L and sodium hydroxide 2.0 mol / L. NTMPA was added to the electrolyte at concentrations of 0.2 and 0.4 mol / L. During the electrolytic deposition of coatings, uniform coatings of a dull gray color were obtained from electrolytes with and without the NTMPA additives. It is noticed that in the presence of NTMPA, the thickness of zinc coatings and the current efficiency decrease. Using scanning electron microscopy, it was shown that zinc deposits in the presence of NTMPA become coarser, and, in addition, the morphology changes (the coatings become inhomogeneous). The electrolytic reduction of zinc in electrolytes with and without additives was investigated by constructing voltammetric dependences. The addition of the additive decreases the cathodic current and shifts the potential of zinc reduction to the negative region. The decrease in the cathodic current in the presence of NTMPA is also confirmed by the results of potentiostatic measurements. This may be due to the fact that the addition of the additive reduces the diffusion of zinc to the electrode. The maximum of the cathodic current linearly depends on the square root of the potential sweep, which indicates the diffusion mode of the process. The introduction of the NTMPA additive into the zincate electrolyte reduces the reduction current, the thickness of the coating, and increases the size of the zinc crystallites.