Corrosion activity of mineral fertilizers and protective properties of a copper chelate complex for agricultural machinery

Corrosion of agricultural machinery exposed to mineral fertilizers represents a critical issue, leading to substantial economic losses and deterioration of operational performance. The study aimed to test the hypothesis that a copper chelate complex exhibits anticorrosion properties and is capable of forming protective films on metal surfaces. The corrosion behavior of structural steel St3, widely used in agricultural machinery components, was investigated in aqueous solutions of various mineral fertilizers, including urea, ammonium nitrate, two types of nitrogen-phosphorus-potassium sulfur-containing fertilizers, and a micronutrient fertilizer containing a copper chelate complex. The solution concentration range (0.5-3 wt%) was selected to simulate realistic operating conditions for agricultural machinery. Distilled water served as the reference medium. Corrosion resistance was evaluated in accordance with GOST 9.908-85 using the gravimetric method. The results demonstrated that ammonium nitrate exhibits the highest corrosion activity, with a corrosion rate ranging from 1.2172 to 1.8937 g/m²·h, exceeding that of the control by a factor of 8.5. In contrast, the copper chelate complex showed pronounced inhibiting properties, reducing the corrosion rate to that between 0.0008 and 0.0019 g/m²·h, which corresponds to a reduction of approximately 99% relative to the control. Electrochemical studies were performed under potentiodynamic conditions using an Autolab PGSTAT 302N potentiostat. Measurements conducted in accordance with GOST 9.509-89 revealed that the copper chelate acts as an anodic inhibitor, shifting the corrosion potential toward more positive values by 0.34-0.59 V. The hypothesis was thus confirmed, and the corrosion protection mechanism was attributed to the formation of an adsorption film on the steel surface. The use of copper chelate is proposed as a bifunctional agent – serving simultaneously as a micronutrient fertilizer and a corrosion inhibitor – to reduce the corrosion activity of working solutions in contact with agricultural machinery components.

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