Study of Ybco Superconductor Coating on Austenitic Stainless Steel By Electrophoretic Deposition Method
Authors: Sato Shuya , Koura Setsuko 
Published: December 2020

1. Introduction

Yttrium-based superconductors（YBCO）are expected to be applied to transmission lines. But, it haven’t been widely used, one of the reason is that the substrate and the film formation are too expensive. In order to solve these problems, using stainless steel and an Electrophoretic Deposition method (EPD) method were adopted as a new system. However, it has been reported that using stainless steel has low oxidation resistance in high-temperature. It may cause to decrease the conduction performance as a wire［1］. On the other hand it is generally known that a film produced by EPD has low adhesion［2］. Therefore, we aimed to improve the above two points and create the new superconducting wires.

2. Experimental

Producting the YBCO calcined powder is that mixture powder compounded by Y, Ba, and Cu in a 1:2:3 molar ratio was heated up to 880 ℃ during 10 h and then crushed. This process was performed three times in total. The powder was analyzed by X-ray diffraction (XRD).
EPD method was used to form a YBCO film or a CeO2 film. A bath containing 10 g/l of YBCO or CeO2 powder and 0.1~0.2 g/l of I2 in 100 ml of acetone was stirred with a magnetic stirrer at a rotation speed of 500 rpm. Stainless steel sheet was used as both the electrodes. 600 V was applied during 30 seconds to produce the YBCO coatings on the cathode.
Multilayer coatings were heated up to 950 ℃ during 6 h. After that it was analyzed by electron probe microanalysis (EPMA) to know the film thickness and diffusion behavior of elements for the interface between metal and oxide films.

3. Results and Discussion

3.1 Identification of YBCO calcine powder

Calcined powder was analyzed by XRD. Obtained patterns almost match with the standard YBCO. Therefore the powder was identified as YBCO.

3.2 Examination of optimal EPD conditions

At the first EPD, the YBCO film had peeled off and it was considered that hydrogen generated from the cathode is cause. This hydrogen is derived from hydrogen ions and it was generated by the catalytic action of enol type acetone and iodine present in the solution. Therefore, iodine concentration or enol type acetone concentration should be reduced than before in order to suppress the hydrogens. In this study, Iodine concentration was reduced from 0.2 g/l to 0.1 g/l. As a result of above conditions, the film didn’t peel off. From this, it was found that the cause of film peeling was generated hydrogen from the cathode, and 0.1 g/l iodine concentration is suitable for EPD when depositing the YBCO film. CeO2 film was also deposited in the same way.

Fig.1 shows the electron micrograph of the CeO2 and YBCO layers on stainless steel sheet. Comparing each layers, although the CeO2 layer is densely deposited, but YBCO layer is not densely and many voids can be confirmed. It is considered that the particle size of YBCO is too large. Therefore, the size will be reduced in next time.

3.3 Examination of optimal substrate for main calcination

Finally we analyzed interlayer mapping with EPMA between the stainless steel and the YBCO layers after heating up to 950 ℃. At this time, the existence of Fe was confirmed in the YBCO layer . YBCO is consisted of Y, Ba, Cu, and O. Including Fe is only stainless steel in the sample. From this, it is considered that Fe was diffused from the stainless steel layer to the YBCO layer by main calcination. While O was also detected in the stainless steel layer. However it isn’t included O. Therefore, it is considered that the diffusion of O occurred from the YBCO layer to the stainless steel layer, contrary to the diffusion of Fe. From this results, intermediate layer between the stainless steel and the YBCO layer is necessary to prevent the diffusion of Fe and O.

References

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Figure 1