Type of Document Thesis Author Merritt, Gary Adam Author's Email Address email@example.com URN etd-07072006-112537 Title Proof of Principle for Bi2Sr2CaCu2O8+x React Wind Sinter Magnet Manufacturing Degree Master of Science Department Mechanical Engineering, Department of Advisory Committee
Advisor Name Title Justin Schwartz Committee Chair Cesar A. Luongo Committee Member Simone Peterson Hruda Committee Member Keywords
- React Wind Sinter
Date of Defense 2006-07-05 Availability unrestricted AbstractManufacturing of solenoids from Ag-clad Bi2Sr2CaCu2O8+x conductors is complicated by the difficult thermo-mechanical processing required. The two approaches typically used for winding coils are React-and-Wind (R&W) and Wind-and-React (W&R). The R&W approach is limited by the amount of stress the conductor can tolerate before being damaged, and is more suitable for tape conductors of small thickness. The W&R approach is limited by the build up of considerable thermal mass in the form of the thickness of the solenoid which results in thermal gradients as well as causing a slower response to temperature changes during heat-treatment. Here we present results on an alternative approach that avoids the pitfalls of R&W and W&R: React Wind Sinter (RWS).
Two RWS approaches are considered. In the first RWS approach, the conductor is taken through the partial melt stage of the heat treatment, cooled to room temperature, wound into its final coil form, and then taken through the growth and sinter steps to complete the heat treatment and to heal potential damage to the ceramic cores that may have resulted from winding. In the second RWS approach, the conductor is taken through the partial melt and growth stage of the heat treatment, cooled to room temperature, wound into its final coil form, and then taken through the sintered step to complete the heat treatment and to heal potential damage to the ceramic cores that may have resulted from winding. Both of these alternatives were examined in detail.
In this work, the RWS approach is studied on short pieces of round Bi2Sr2CaCu2O8+x wire of the most recent generation to demonstrate the concept and test its validity for use as an alternative technique. These wires have 595 filaments throughout their cross-section.
First a series of typical heat treatment processes were run to set a benchmark for further experiments and to optimize the furnace used. Second, the heat treatment was separated into two parts. This step was taken to see if the separation of the heat treatment had adverse effects on the performance of the wire. This second phase had two distinct parts to itself, as there were two locations of interest in the conventional heat treatment profile that could be the point for cool down before the winding step.
To test the first technique, the samples were taken to the reaction, or partial melt stage, and then the samples were furnace cooled to room temperature and then taken though the growth and sintering process. These tests were called react-cool-grow-sinter. No drop in performance was noted.
To test the second RWS heat treatment technique, the samples were taken through the partial melt stage and the growth stage, and then furnace cooled to room temperature. The samples were then taken through the sintering step. These experiments were called react-grow-cool-sinter. These samples also showed no loss in performance.
A series of samples were run to test the necessity of the growth and sinter steps (for the first RWS technique), or the sinter step (for the second RWS technique). For the first technique, the samples were taken through the reaction step, furnace cooled to room temperature and then characterized. This series of experiments was called react-only. These samples were found to be highly resistive, showing the need for the growth step. To test the second technique, the samples were taken through the reaction and growth steps, and then furnace cooled, and characterized. These experiments were called react-grow-only. An increase in the critical current was noted when this step was compared to the react-grow-cool-sinter, thus confirming the benefit of the sinter step.
To test how much damage is caused by the bending of the superconducting wire, the next set of experiments were performed. The samples were taken through the first part of their heat treatment and then bent to a series of diameters ranging from 40 mm to 100 mm in 10 mm increments using a specially made apparatus. The spring back diameter was then noted. To examine the first RWS heat treatment technique, the samples were taken through the reaction step only. These experiments were called react bend only. As with the react-only experiments, these samples were found to be highly resistive. To examine the second RWS heat treatment a series of samples were heat treated through the reaction step, taken through the growth step, and then furnace cooled. These samples were then bent to the same set of diameters afore mentioned, and then the samples were characterized. This step, referred to as react grow bend only, compared with the react grow bend and sinter step to determine if any lowering of performance was occurring because of the bending, and, if so, if the damage caused by the bending was being alleviated by the sinter step.
The next tests were run to test the ability of both heat treatments to heal damage caused by bending. This series of tests was run to simulate RWS, and to check for a critical bending radius. To test the first technique, the samples were taken through the reaction stage, furnace cooled, and then bent to a series of diameters ranging from 40 mm to 100 mm in 10 mm increments. The apparatus also held one control sample that was not bent. The samples in the apparatus were placed inside the furnace and taken through the sintering process. Finally, the samples were removed, and then characterized. These experiments were called react-bend-grow-sinter. No critical radius was found for react-bend-grow-sinter, as all samples performed about the same; Ic values of approximately 316.8 A at 5 T.
To test the second RWS heat treatment technique the samples were taken through the reaction and growth stages, furnace cooled, bent to the aforementioned diameters, and then placed back in the furnace for the sinter step. These experiments were called react-grow-bend-sinter. These samples were found to show approximately the same losses as those noted in react grow bend only, thus showing the sinter step alone is not sufficient to heal damage caused by bending.
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