Research On The Corrosion Resistance Of Magnetic Refrigerant Material Gd Sputtered Protective Coatings

Room temperature magnetic refrigeration technology has the advantages of less energy expenditure , environmental friendship and so on ,which attract more human's attention. However magnetic refrigeration material is the key technology of Room temperature magnetic refrigeration technology, so the material plays an important role of the development of this technology. At the present time, Gd and its alloy or rare earth compounds are often used as active magnetic regeneration refrigeration in room temperature magnetic refrigeration technology, because Gd and its alloy or other rare earth compounds of all materials researched have better adiabatic temperature change effects, but Gd is corroded seriously in the heat exchange medium and does effects adversely on its service life and the cooling efficiency of magnetic refrigerator. In order to improve Gd corrosion performance in the medium, we have made protective coatings (Ti, 1Crl8Ni9Ti, Al, Cu) on the surface of Gd by magnetron sputtering technology, and have done some research on the property of Gd corrosion rate in different medium, electro-chemical potential curves, adiabatic temperature change and so on. The result of corrosion experiment in different medium shows that the surface of Gd will be passivated and inhibit the further corrosion;the coatings of Ti and Al have superior corrosion resistant performance, but appears corrosive pittings on the surface after 50 days for thecoatings are too thin;for the bad bonding strength between Cu and Gd, the coating becomes wrinkled and abscises;because of the different sputtering rate of each element of lCrl8Ni9Ti, the constituent of the coating is different from the original constituent of lCrl8Ni9Ti, so the corrosion performance is degraded. The result of the polarization curves of Gd sputtered different protective coatings, which is gained by the method of changing electric potential with three electrode system on American produced Potentiostat (EG&G M283), shows that the corrosive potential is elevated and the current density is decreased with protective coatings, so sputtering protective coatings on Gd elevates the electro-chemical corrosion performance. The research of influences on Gd magneto-caloric effect with sputtering different protective coatings is done by self-made adiabatic temperature change testing device. The adiabatic temperature change test results show that the coatings don't affect the temperature at which the maximum adiabatic temperature is gained, but affect the maximum adiabatic temperature of Gd in different extent.By the analysis of over-all properties of testing results, Ti coating not only has good corrosion resistant performance in aqueous corrosion system, but also good electro-chemical corrosion performance, and the adiabatic temperature test result also shows that sputtering Ti coating does little influence on Gd magneto-caloric effect;Although the corrosion resistant performance of Al coating, which is the best heat conductive metal among the four materials, is not as good as Ti coating, but it has better electro-chemical corrosion performance and also does little influence on Gd Magneto-Caloric effect. The conclusion above shows that the corrosion resistant coatings (Tk Al) by magnetron sputtering technology is an promising method used to promote the corrosion resistance of Gd.