Influence of heat treatment on in situ powder-in-tube-processed MgB2 tapes with added ethyltoluene and SiC powder

Previously (Yamada et al 2007 Supercond. Sci. Technol. 20 L30) we reported that the addition of both ethyltoluene (C9H12) and SiC powder to the starting powder for in situ powder-in-tube (PIT) processed MgB2/Fe tapes is much more effective in enhancing Jc values than addition of C9H12 and SiC. In this paper we investigate the influence of the heat treatment temperature on the superconducting properties of tapes with the addition of both C9H12 and SiC. At 4.2 K the tape heat treated at 600 deg. C showed higher Jc than the tape heat treated at 800 deg. C. At 20 K, however, the tape heat treated at 800 deg. C showed higher Jc than the tape heat treated at 600 deg. C. This is due to the improvement of crystallinity, and hence higher Tc, by the higher temperature heat treatment. When we add C9H12 to the precursor powder, C9H12 decomposes into gases during the heat treatment of the tapes. In the case of long tapes these gases can easily be trapped within the sheath, potentially causing serious manufacturing problems. We tried a pre-heat treatment of the mixed powder at 540 deg. C before packing into metal tubes. With this pre-heat treatment C9H12 decomposed and gases were removed from the precursor powder, but the short tapes fabricated with this pre-heat treated powder showed almost the same Jc values as the short tapes fabricated without pre-heat treatment. This result indicates that the pre-heat treatment solves the problem of gas generation and can be applied to the fabrication of long tapes and wire.