Oxygen exchange in Bi(2223) tapes with Ag and alloyed AgMg sheaths monitored by a thermogravimetrical relaxation method
Oxygen exchange in Bi(2223) tapes with Ag and alloyed AgMg sheaths monitored by a thermogravimetrical relaxation method
复制标题
通过热重松弛法监测具有 Ag 和合金 AgMg 护套的 Bi(2223) 带中的氧交换
DOI：
10.1088/0953-2048/11/6/006
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发表时间：
1998
影响因子：
3.6
通讯作者：
W. Goldacker
中科院分区：
文献类型：
--
作者：
M. Quilitz;W. Goldacker
在反应过程终止凹坑形成的条件下，我们研究了Ag和aGMG包套的Bi(2223)带材的氧交换动力学。为此，我们应用了一种化学松弛方法，在该方法中，随着氧分压从到的快速变化，随时间监测氧依赖重量变化的再平衡。从重量随时间重新平衡的斜率，可以得到描述BSCCO相和周围气相之间氧交换动力学的时间常数。在特殊假设下，可以得到氧交换的形式扩散系数。与小块磁带的情况相反，在超导体与周围气体直接接触的末端进行氧气交换的情况相反，在长度可达数百米的“真正”磁带中，我们遇到了不同的情况。模拟这种情况，我们研究了通过磁带侧面的交换，即通过鞘材料本身的交换。我们开发了一种实验技术，允许我们通过鞘分离扩散组分，从而能够获得通过银鞘的氧交换时间常数的值。我们成功地用样品长度d确定了扩散标度，这使得我们能够计算氧在银套带材内进入和向外扩散到Bi(2223)相的扩散系数。确定了超导体-气相界面的扩散激活能为0.39 eV。研究还表明，护套材料的改变对超导性能的影响也强烈地影响了带材中的氧交换动力学。
We investigated the kinetics of oxygen exchange in Ag- and AgMg-sheathed Bi(2223) tapes under the conditions of the reaction processes terminating PIT fabrication. For this purpose we applied a chemical relaxation method in which the reequilibration of the oxygen-dependent weight change was monitored with time following a rapid change of the oxygen partial pressure from to . From the slope of the re-equilibration of weight with time one obtains a time constant describing the exchange kinetics of oxygen between the BSCCO phase and the surrounding gas phase. Under special assumptions the formal diffusion coefficients for the oxygen exchange can be obtained. Contrary to the situation for small pieces of tapes where oxygen exchanges through the ends at which the superconductor is in direct contact with the surrounding gas phase, we encounter a different situation in `real' tapes with length up to several hundreds of metres. Simulating this case we investigated the exchange through the lateral faces of the tapes, i.e. through the sheath material itself. We developed an experimental technique which allows us to separate the diffusion component through the sheath and were thus able to obtain values for the time constant of oxygen exchange through the Ag sheath. We managed to determine the diffusion scaling with with d the sample length which allows us to calculate diffusion coefficients for the in- and outdiffusion of oxygen into the Bi(2223) phase inside the Ag-sheathed tapes. The activation energy of the diffusion at the superconductor-gas phase interface was determined to be 0.39 eV. It is also shown that modifications of the sheath material with consequences for the achievable superconducting properties also strongly affect the kinetics of oxygen exchange in the tapes.