Corrosion behavior of gadolinium and La–Fe–Co–Si compounds in various heat conducting fluids

• Corrosion resistance of gadolinium and La–Fe–Co–Si compounds was tested.
• The samples were immerged in water based fluids with inhibitors.
• Results were evaluated regarding corrosion resistance and specific heat.
• Three additives give a low corrosion rate, with a specific heat near that of water.
• Surface passivation of gadolinium with oxalic acid solutions is also efficient.

For successful implementation in magnetic refrigeration systems, the corrosion resistance of gadolinium and La–Fe–Co–Si compounds in different heat conducting fluids has been studied. Two types of tests were used: immersion at room temperature (ASTM G31-72), and accelerated tests at 88 °C during 336 h (ASTM D1384-05). Results were evaluated regarding corrosion and specific heat: the main objective was to increase the heat transfer and to reduce the corrosion rate. We have also tested a protection of gadolinium by passivation with oxalic acid solutions of pH lower than 1.00. This treatment is efficient, and doesn't affect the magnetocaloric effect. Finally, the optimal solutions were selected and proposed for use by thermal engineers. Passivation can be a good solution to protect gadolinium from corrosion but the use of water based fluids with oxygen inhibitors is better. Some fluids (water + additives) gives satisfaction, providing a heat transfer close to that of water and protecting well materials from corrosion.