Alina Tinaeva, a fifth-year student of the specialist’s programme of the Faculty of Chemistry developed a coating for metals based on a zinc-nickel alloy. Such coatings are better than most monometallic coatings as they combine useful properties of two or more metals. Zinc-nickel alloys are also of great interest because they comply with the highest standards of anticorrosion protection of steel.
“The idea is to obtain zinc-nickel alloy coatings from ammonium chloride electrolytes with relatively low concentrations of the solution components which can be used for protection of products from corrosion. What makes zinc-nickel alloys unique is the special mechanism of the formation of the layer and the structure of the coating itself. Another special feature of zinc-nickel alloys is related to the kinetics of their electrodeposition. This process is called “anomalous” codeposition, and during this process the coatings obtained from an electrolyte with equimolar concentrations of nickel and zinc have considerably less zinc content in their composition. Most functional properties of galvanic coatings are determined by the structure, phase and chemical composition of the alloy, and the presence of foreign inclusions. Zinc-nickel alloy coatings with the optimal content of nickel (8–17%) are characterised by corrosion resistance that is 3–10 times higher as compared to zinc coatings. Zinc-nickel coatings consisting of a gamma phase (Ni5Zn21) with 10–15 % nickel have the greatest protective properties. This coating is elastic, has an anodic nature of product protection, and is more corrosion-resistant: corrosion products are formed after 14 days. The protective properties of zinc-nickel coatings are preserved at the temperatures of up to 160 °C,” said Alina Tinaeva.
Zinc-nickel coatings are used more and more often as the replacement of toxic and expensive cadmium and cadmium-titanium coatings. In the USA zinc-nickel coatings are used for electronic equipment and aerospace engineering parts. In Russia these coatings are widely used in pipe and tube production: they are applied on the sleeves of pump compressor pipes to increase the corrosion resistance and mechanical stability of their screwed joints as well as on the tubes used for the production of brake and fuel systems in cars.
Alina’s supervisor Oleg Kozaderov, Head of the Department of Physical Chemistry, said the obtained data are unique.
“The choice of the topic of the scientific research project can be explained by the need to develop new methods for the synthesis of nanomaterials with special properties. The nickel-zinc system studied in the project is of interest as it can be used, on the one hand, for protection of steel and other metal constructions from corrosion damage and, on the other hand, it can act as the basis for obtaining nanoporous nickel which, as most people know from school, can be a catalyst in a number of reactions. The study of the patterns of obtaining nickel-zinc coatings depending on various conditions (composition of the electrolyte solution, its acidity, the presence of complexation additives) is a relevant problem of electrochemical material studies. We managed to achieve a lot while conducting the study: to obtain data on the kinetics of the electrodeposition of the coatings with zinc-nickel alloys, their chemical and phase composition depending on various factors, and the role of glycine, an organic additive which, it appears, improves morphological and anticorrosive properties of the synthesised coatings. Now we are working on the identification of the patterns of deposition of individual components of the deposited alloy, zinc and nickel. It is not an easy task, and the fact that a secondary process of hydrogen evolution can take place in the studied conditions makes it even more difficult. The main result of our work is that we have obtained a set of experimental data which allow synthesising a nickel-zinc coating of a certain composition with the specified properties. We are planning to modify the obtained nickel-zinc coatings using the method of selective dissolution, that is when a more active component, in this case it’s zinc, is etched from the alloy either chemically (for example, by leaching) or electrochemically (using electric current). The obtained material possesses really interesting properties. It is highly catalytically active, in other words, it significantly accelerates a number of practically important reactions primarily involving hydrogen. And it is much cheaper than such traditional catalysts as platinum or palladium. Taking into account the ever-growing interest in hydrogen energetics, the synthesis of this material seems highly relevant. In addition, the method of selective dissolution allows obtaining micro and nanoporous materials with great surface area, which also improves its activity.”
As a result of this study, three articles were published, two of which were translated into English and published in the international journals “Protection of Metals and Physical Chemistry of Surfaces” (quartile Q2) and “Condensed Matter and Interphases”. Researchers from the Faculty of Chemistry of VSU continue their detailed studies in the field of corrosion and the kinetics of electrodeposition of zinc-nickel alloy from ammonium chloride electrolytes.