Mass density evolution during manufacturing of Ag-sheathed BPSCCO tapes

Abstract

The mass density of superconducting (bismuth, lead)-strontium-calcium-copper-oxide (PBSCCO) cores of silver-sheathed tapes, subject to different states of cold working and thermal treatment, has been determined taking advantage of a modified hydrostatic weighing. It turned out that the densification was more effective the smaller the initial density of the parent material. A core density of about 5 g cm −3 was attained, but could not be exceeded, independent of the deformation method and core density prior to deformation. When starting with high initial densities, drawing even reduced the core density. The density drop increased with reduced diameter reduction per drawing step, whereas rolling improved the core density. Heat treatment (reacting from the 2212 to the 2223 phase) resulted in a small loss of relative density, which raised with increasing core thickness. Nevertheless there is a positive correlation between densities before and after heat treatment. It is therefore important to obtain optimum core densities during the final steps of cold working.

The mechanical deformation of superconducting BiSrCaCuO/Ag composites

“…As mentioned above, a direct consequence of the powderflow model is that the final powder packing density is a critical density and does not directly depend on the initial density. This prediction has been supported by several independent experiments [10,18,[32][33][34][35][36] and the results are summarized in table 3. Figure 14 shows the core density against reduction as found by Korzekwa et al [18].…”

“…A deformation process with a small freedom parameter could build up large stresses in the sample, resulting in a high core density. For example, the core density of a composite tape deformed by large rollers could be higher than that of a tape made by small rollers [33] and a thinner tape could have a denser core than a thicker one [5].…”

Early work on Laves phases in East Germany

“…The chemical composition of samples has been determined using wet-chemical analysis [54,61,66], atomic spectrometry [49], electron beam microanalysis [49,55,57,65], X-ray fluorescent analysis [49,61,62], measurements of lattice parameters by powder diffractometry [49,61,65] as well as measurements of pycnometric density [49,61,72,73]. For several compounds, Kossel lattice parameter measurements had been calibrated combining distinct methods to achieve better accuracy and local resolution [65].…”

Through-process study of factors controlling the critical current density of Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Oxtapes

“…If we compare the density of the final sample D to the calculated density of Bi-2223, 6.3 g cm −3 [32], we find a relative density of 73%. A pore density of about 25% imposes major barriers to current flow and suggests immediately the physical basis for earlier positive correlations between increased indentation hardness and increased J c [17,18,21,22]. In any case the value of decreasing the pore fraction is obvious.…”

“…An underlying issue is the tendency of composites to swell during heat treatment. It is generally believed that this retrograde densification occurs during the formation of the Bi-2223 phase [18,19,21]. However, the reasons for retrograde densification are not clear, nor are there many measurements of its magnitude.…”