High temperature neutron diffraction measurements were performed on Bi(2223)/Ag-sheathed monofilamentary tapes at the ILL high- flux reactor in Grenoble. Reactions leading to the conversion from Bi(2212) to Bi,Pb(2223), as well as other transformations involving secondary phases, were directly observed during the reaction heat treatment. The heating ramp and annealing conditions were exactly the same as those used for standard high-performance tapes processing. A quantitative analysis was carried out by means of a full-pattern profile refinement technique: up to 7 phases were simultaneously detected and successfully refined. An increase of the Bi(2212) phase during a slow cooling was found not to be related to a decomposition of Bi,Pb(2223), which remained stable during cooling. The role of secondary cuprates, in particular (Ca,Sr)(14)Cu24O41, was investigated. Since neutron diffraction allows for an absolute measurement of the weight of crystalline matter inside the sample, it was possible to measure the total crystalline matter amount as a function of temperature and time during processing. Evidence of partial melting at high temperature was found, strongly supporting the Bi,Pb(2223) formation via a nucleation-and-growth mechanism at the early stage of the process.
In-situ high temperature neutron diffraction study of Bi,Pb(2223) phase formation in Ag-sheathed monofilamentary tapes
Bellingeri E;
1999
Abstract
High temperature neutron diffraction measurements were performed on Bi(2223)/Ag-sheathed monofilamentary tapes at the ILL high- flux reactor in Grenoble. Reactions leading to the conversion from Bi(2212) to Bi,Pb(2223), as well as other transformations involving secondary phases, were directly observed during the reaction heat treatment. The heating ramp and annealing conditions were exactly the same as those used for standard high-performance tapes processing. A quantitative analysis was carried out by means of a full-pattern profile refinement technique: up to 7 phases were simultaneously detected and successfully refined. An increase of the Bi(2212) phase during a slow cooling was found not to be related to a decomposition of Bi,Pb(2223), which remained stable during cooling. The role of secondary cuprates, in particular (Ca,Sr)(14)Cu24O41, was investigated. Since neutron diffraction allows for an absolute measurement of the weight of crystalline matter inside the sample, it was possible to measure the total crystalline matter amount as a function of temperature and time during processing. Evidence of partial melting at high temperature was found, strongly supporting the Bi,Pb(2223) formation via a nucleation-and-growth mechanism at the early stage of the process.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
