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Bismuth strontium calcium copper oxide, or Bi2Sr2CaCu2O8+x (Bi-2212) is a high-temperature superconductor very promising in applications for high field (~30 T) superconducting magnets. For Bi-2212 wire to function in these magnets it must be coated by a thin layer of strongly-adhered insulation capable of both preventing the magnets from short-circuiting and withstanding the heat treatment of Bi-2212 at 890˚C in an oxygen environment. This is accomplished by coating the bare wires in a solution of a metal oxide power (in this case either titanium or aluminum), organic solvents (ethanol, m-xylene), and other organic binders and plasticizers.[1] The new insulation is then tested for its ability to adhere to the wire when scratched. I will present information gathered in the preparation of insulation for Bi-2212 superconducting wire.
Introduc4on
The temperature along the wire may be significantly different from the set point of the furnace. This needs to be calibrated before samples of wire can be insulated. Bi-2212 heat treatment takes nearly 4 days. For the testing of insulation properties the heat treatment may be shortened. These trials were run to establish a new schedule for heating wire. Heat treatments A, B, and C were performed on Bi-2212 wire with TiO2 based insulation • The samples produced using schedule C were very brittle and did not
adhere well to the wires. Schedule B is sufficient to heat treat samples for insulation property studies. This shortens the HT time by a factor of two.
Experimental Condi4ons
Alumina Slurry Composi0on
CONCLUSION
• A significant difference in temperature between furnace set point and the actual temperature experienced by the wire was discovered and calibrated.
• The heat treatment of wires meant to test insulation has been shortened to roughly half of the heat treatment time for Bi-2212.
• Alumina slurry recipe has been improved by using considerably more H-5 binders.
• Scratch test results show that our insulation meets or exceeds the durability of commercial nGimat samples.
REFERENCES [1]. Richard E. Mistler, Eric R. Twiname, Tape Casting: Theory and Practice, Wiley-American Ceramic Society, 2000. [2]. Hom Kandel, J. Lu, J. Jiang, M. Matras, P. Chen, N. Craig, Y. Viouchkov, B. Best, U.P. Trociewitz, E. E. Hellstrom, and D. C. Larbalestier, “Development of Thin Ceramic Coating in Bi2Sr2CaCu2O8-x (Bi-2212) Round Wire”, Presentation at MT-23 conference, Boston, July, 2013.
ACKNOWLEDGEMENT Much appreciation to Jun Lu, Hom Kandel, The Center for Integrating Research and Learning, and The National High Magnetic Field Laboratory for all of the support throughout the course of this program. This project was sponsored by NSF DMR1157490
• These tests show that the strength of the insulation of wires coated at NHMFL is at least comparable to that of commercially available samples (nGimat).
• Samples coated in TiO2 are significantly more scratch-resistant than commercially available options.
These tests are performed to quantify statements about the strength of adherence between insulation and wire. They involve attaching a bare section of wire to lead A, adjusting the weight, and sliding the wire back and forth under the scratching implement until coating failure occurs.
• Samples:
• Ceramic slurry:
• Slurry mixing: • Reel to reel insulation: • Heat treatment: • Scratch test: • Diameter: • Computer setup
• Cu, Ag and Bi-2212 wire (0.8-1.0 mm diameter)
• TiO2, Al2O3 based. See compositions in table 1
• Ball milling with .25” ZrO2 media. • See Fig. 1 • Small Mellen furnace in air. • Modified Taber tester (Fig. 7) • Digital micrometer • National Instruments
CompactDAQ-9174
Insulation with TiO2 powder is successful. The next step is determining whether another ceramic powder can also be used. This was done by experimenting using Al2O3 powder with increasing H-5 content.
Scratch Tes0ng
Heat Treatment Schedule
Furnace Calibra0on
1Department of Chemistry, Harvard University, Cambridge, Ma 02138 2Na/onal High Magne/c Field Laboratory, Tallahassee, Fl 32310
Breshawn Best1, Jun Lu2, Hom Kandel2 Insula4on of Bi-‐2212 Superconduc4ng Wire
Furnace Cover A
Insula/on machine
Fume Hood Furnace
Cover B
Furnace A
Furnace B
Control Panel
Pay-‐off Spool
Dip Tank A
Dip Tank B
Take-‐up Spool
Fig. 1
Fig. 3 Temperature measured on the wire along the furnace.
TC* aWached
NI TC* input
Furnace TC*
Fig. 2 Furnace calibra/on setup. The wire speed is 0.6 m/min *Type K Thermocouple
• There is a considerable difference between furnace set point and wire temperature (~100˚C).
• A cover is necessary to maintain temperature when heating green samples of wire.
Sample Applied load (grams)
Number of scratches before coa4ng failure
Al2O3 (15 wt.% H-‐5) 50 83 100 5
TiO2 50 232 100 40
nGimat 50 75 100 20
Fig. 4 Three different heat treatment schedules used.
TiO2 Wt (grams) wt. % TiO2 18 16.3 Polyvinyl Butryl (PVB) 6 5.4 Ethanol 42 38.1 xylene 42 38.1 H-‐5 1.2 1.1 Butyl benzoyl pthalate 0.5 0.5 polybutylene glycol 0.5 0.5
• Al2O3 insulation adhesion property improves with H-5 content. • At 15% H-5, the adhesion is satisfactory.
Fig. 7 Scratch test setup
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60 70
T (C)
Time (hours)
A
B
C Table II. Scratch test results
Table I. Recipes of coa/ng slurry
Mul/meter
Lead A Lead B
Weight
Sample
Site of wire aWachment
Scratching implement
0
50
100
150
200
250
0 50 100 150
Temp. (C
)
Distance (cm)
Set pt. 300˚C, Covered Set pt. 250˚C, Covered Set pt. 200˚C, Covered Set pt. 200˚C, Uncovered
boWom of furnace
top of furnace
Al2O3 C Wt (grams) wt. % Al2O3 18 14.2 Polyvinyl Butryl (PVB) 6 4.7 Ethanol 42 33.1 xylene 42 33.1 H-‐5 18 14.2 Butyl benzoyl pthalate 0.5 0.4 polybutylene glycol 0.5 0.4
Al2O3 B Wt (grams) wt. % Al2O3 18 14.9 Polyvinyl Butryl (PVB) 6 5.0 Ethanol 42 34.7 xylene 42 34.7 H-‐5 12 9.9 Butyl benzoyl pthalate 0.5 0.4 polybutylene glycol 0.5 0.4
Al2O3 A Wt (grams) wt. % Al2O3 18 15.7 Polyvinyl Butryl (PVB) 6 5.2 Ethanol 42 36.5 xylene 42 36.5 H-‐5 6 5.2 Butyl benzoyl pthalate 0.5 0.4 polybutylene glycol 0.5 0.4
7 μm
Fig. 5 Sample of 5 wt.% H-‐5 coa/ng
Fig. 6 Sample of 15 wt.% H-‐5 coa/ng
Fig. 9 Cross-‐sec/on of insulated 1.0mm Bi-‐2212 wire[2]
Fig. 8 Microscopic view of the Al2O3-‐coated wire before scratch tes/ng.[2]