Evaluation of Joint Resistance Between Bi-2223/Ag Superconducting Tapes
We fabricated Bi-2223/Ag jointed tape and evaluated its current carrying capacity and joint resistance at 77.3 K as a function of the contact length. The tapes were jointed by the conventional resistive joint method with 40Pb-60Sn solder as an insert material and their joint resistance was measured by two different techniques, i.e., the standard four-probe and field decay methods. It was observed that the current carrying capacity and joint resistance were significantly dependent on the contact length. As the contact length increased, the current carrying capacity improved and increased to the level of critical current in the unjoined tape at the contact length of 5 cm. On the other hand, the joint resistance linearly decreased as the contact length increased. In addition, the joint resistances measured by the two methods were similar to each other (7.3times10-9 Omega~8.0times10-9 Omega), indicating that the standard four-probe method maintained a moderate degree of accuracy at the level of resistance of 10-9 Omega
Measurement of joint properties of Bi(Pb)-Sr-Ca-Cu-O (2223) tapes by field decay technique
We joined 19-multifilamentary Bi-2223 superconductor tapes and fabricated double-pancake coils by using resistive- and superconducting-joint methods. The critical current ratio (CCR) of the jointed tape and the decay characteristics, joint resistance, and n-value of the pancake coils were evaluated. The joint resistance of the coils was characterized by the field decay technique. It was observed that the CCR was higher in the joined tape made by the resistive-joint method, compared to that by the superconducting-joint method. On the other hand, joint resistance was measured to be 4 orders of magnitude smaller in the superconducting-joint coil; approximately 40% of critical current was retained in the persistent current mode and the joint resistance was 0.18 n/spl Omega/. Better and longer retention of the magnetic field in the superconducting-joint coil is believed to be due to the direct connection between the superconducting cores.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.