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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]