The peculiarities of electrochemical deposition and morphology of ZnMn alloy coatings obtained from pyrophosphate electrolyte

Abstract

The first successful attempt to electrodeposit ZnMn alloy coatings from alkaline bath was made only a few years ago. In this kind of solution, potassium pyrophosphate (K4P2O7) serves both as a complexing agent and as the basic electrolyte. The aim of this work was to study the electrodeposition process and properties of ZnMn alloy coatings deposited from pyrophosphate solution, with a new kind of alkaline pyrophosphate bath. Namely, chloride salts were used as the source of metal ions and ascorbic acid was used as reducing agent. The composition of the plating solution was as follows: 1 mol dm-3 K4P2O7 + 0.017 mol dm-3 ascorbic acid + 0.05 mol dm-3 ZnCl2 + 0.05 mol dm-3 MnCl2•4H2O. Cathodic processes during the alloy electrodeposition were investigated using linear voltammetry. The influence of addition of small amounts of ascorbic acid on the cathodic processes was established. It was shown that this substance inhibits hydrogen evolution and increases the current efficiency of alloy deposition. The current efficiency in the plating bath examined was in the range of 25 and 30%, which was quite higher as compared to the results reported in the literature for electrodeposition of ZnMn alloy from pyrophosphate bath. Electrodeposition of ZnMn alloys was performed galvanostatically on steel panels, at current densities of 20120 mA cm-2. The coatings with the best appearance were obtained at current densities between 30 and 80 mA cm-2. The surface morphology studies, based on atomic force microscopy measurements, showed that morphology of the deposits is highly influenced by deposition current density. ZnMn coating deposited at 30 mA cm-2 was more compact and possessed more homogeneous structure (more uniform agglomeration size) than the coating deposited at 80 mA cm-2. Such dependence of morphology on the current density could be explained by the high rate of hydrogen evolution reaction during the electrodeposition process

The influence of substituted aromatic aldehydes on Zn-Mn alloy electrodeposition

“…6 The deposition process in these cases has important drawbacks, particularly with regards to process control and current efficiency. 7 On the contrary, a simple bath without strong complexing agent shows several benefits, such as high current efficiency and good bath stability. 5 A simple electrolyte consisting of boric acid, potassium, and zinc and manganese chlorides was proposed for Zn-Mn electrodeposition in the past decade, 8 and this electrolyte was chosen for examination in the present study.…”

The study of Zn–Co alloy coatings electrochemically deposited by pulse current

“…Koroziona stabilnost Zn-Co legura određivana je praćenjem promene slobodnog korozionog potencijala [20] tokom dužeg vremena izlaganja dejstvu rastvora 3% NaCl, kao i određivanjem vrednosti gustine struje korozije u istom rastvoru [21,22]. Debljina prevlake je bila 11±0,5 µm, što je postignuto regulisanjem količine naelektrisanja koja protekne kroz ćeliju za vreme taloženja, na osnovu Faradejevog zakona.…”