Type of Document	Thesis
Author	LoSchiavo, Michael Philip
Author's Email Address	michael.loschiavo@gmail.com
URN	etd-08062009-140259
Title	Processing Issues of Bi2Sr2CaCu2O8 Round Wire Involving Leakage and Alumino Silicate Insulation
Degree	Master of Science
Department	Mechanical Engineering, Department of
Advisory Committee	Advisor Name Title Eric Hellstrom Committee Chair David Larbalestier Committee Member Patrick Hollis Committee Member
Keywords	Bi-2212 2212 Leakage Ic Loss Insulation Alumino Silicate
Date of Defense	2009-07-28
Availability	unrestricted
Abstract A major issue seen in Bi2Sr2CaCu2O8¬ (Bi-2212) conductor was leakage from the liquid within the wire during the partial (peritectic) melt. The leakage in the wire was the main focus of this work initially. By examining leaked wire, cracks along the length of the wire were found in several leakage regions. Green wire, which has not been heat treated, was examined for the presence of the same longitudinal cracks found in leaked wire. These defects were covered in yttria, which is non-reactive with Bi-2212, to wick out liquid through surface defects that might occur. After the samples were heat treated, some of the cracks exhibited leakage. The longitudinal cracks, caused during the manufacturing processes, were the source of the leaks. The processing parameters were changed by the wire manufacturer to ameliorate the cause of leakage, in parallel with this study, and the new wire does not have the same leakage problem as the preceding wire. Due to the issue of leakage being solved by the wire manufacture, the study ended. Insulation is used to separate the wire to prevent bonding at high temperatures. The insulation reacts with the surface of the wire leaving behind large sections stuck on the conductor and forming a glassy phase after the reaction. The alumino silicate fiber composition consists of crystalline alumina and amorphous silica. The fiber reacts with the wire by sticking to the surface. Different compositions of these compounds were tested against Ag using a line of 3M NEXTEL fibers and pure SiO2. Any amount of amorphous silica causes a reaction with Ag; however, pure amorphous silica does not have a reaction, but due to the ease with which it is contaminated with salts, which causes it to react with Ag, its use is currently not recommended. The insulation also has an effect on performance by decreasing Ic by 20%. Ag wire was wrapped around insulation to provide surface contact between the insulation and conductor to show this decreased performance in short side-by-side samples and along a length of wire. Although flux pinning is the same between insulated and bare samples, the connectivity is affected by insufficient grain growth. Cu was lost from the Bi-2212 core into the insulation. The loss of Cu to the interface of Ag and the braid causes a change in phases by creating an excess of secondary phases and pores and decreases the total density of the filaments. Cu loss is the mechanism behind the loss in Ic.
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