Electrodeposition-anodising for preparing corrosion-resistant copper coatings for Gd metal

Abstract

The magnetic refrigeration effect of gadolinium (Gd) metal allows for room temperature cooling, offering a wide range of potential applications. Gd is typically manufactured into thin sheets for the production of array-type magnetic refrigeration (MR) heat exchangers. However, due to its highly reactive chemical properties, Gd is prone to susceptible to corrosion when exposed to the heat transfer medium. Therefore, enhancing the corrosion resistance of Gd sheets is essential for protecting the metal and extending their operational lifespan. In this study, a corrosion resistant coating was developed through the electrodeposition of high purity copper onto Gd sheet followed by anodic oxidation. It was observed that utilising a current density of 2 A/dm², Cu²⁺ concentration of 0.16 mol/L, PH of 10, temperature of 50 °C, and HEDP of 30 g/L resulted in the formation of a uniform copper layer measuring 23.41 μm and significantly improved corrosion resistance by 98.65% compared to the substrate. The analysis of the results indicates that the oxide layer is primarily composed of CuO, Cu₂O, CuOH and Cu(OH) ₂. The corrosion resistance of the anodised surface has been enhanced by 31.17% compared to before anodising, while the wettability of the anodised surface has been reduced. As a result, in this study, a method for depositing a corrosion-resistant copper coating is developed, which can significantly prolong the service life of Gd in MR heat exchangers.