I.H. Mutlu

High temperature insulation coatings and their electrical properties for HTS/LTS conductors

Abstract The high temperature compatible insulation coatings were produced using solutions of Zr, Mg, Y, Ce, Er, Sm, In, Sn, Sr, Pb, Ba, Al, and La based organometallic precursors using a non-vacuum sol–gel technique. The growth mechanism and microstructure of these coatings was characterized using environmental scanning electron microscopy and X-ray diffraction. Dielectric constants and breakdown voltages of these coatings were also measured by using an insulation tester. The results of microstructure and electric properties of these coatings are presented. The oxide structures were formed between temperatures of 450 and 550 °C from amorphous coating. MgO–ZrO2 coatings on Ag and AgMg sheathed Bi-2212 tapes have been used as the insulation for the 1 T and 3 T HTS high field insert coil. These ceramic insulation coating can be built up to ∼10 μm by successive dipping. Crack-free, dense, very thin (submicron) coatings were also obtained using different solvent and acid with the same method with appropriate dilution of solutions.

Electrical properties of high temperature insulation coatings by the sol-gel method for magnet technology

The electrical properties of high temperature insulation coatings, which were applied by sol-gel process on Ag or AgMg sheathed Bi-2212 tapes, bronze processed Nb/sub 3/Sn wires and Ni tapes, have been studied by resistive, capacitance, and high voltage breakdown techniques. The electrical properties of the coatings with varying composition, coating type, number of dippings, and temperature and time of annealing process have been presented.

Ceramic insulation for Nb3Sn wires and magnets

Abstract The processing of In 2 O 3 –ZrO 2 and SnO 2 –ZrO 2 coatings were evaluated on Nb 3 Sn wires. Coatings were produced by using reel-to-reel, continuous sol–gel system from solutions of Zr, In, and Sn based organometallic compounds. Microstructure, phase composition and formation of the coatings were characterized by means of ESEM, SEM, EDS, XRD and DTA studies. Sol–gel zirconia based ceramic coatings, varying from submicron to several of microns in thickness, have been successfully applied to Nb 3 Sn wires at the National High Magnetic Field Laboratory. Insulated and uninsulated Nb 3 Sn conductors, that were heat treated together, showed about the same J c .

Electrical characterization of ceramic insulation coatings for magnet technology

In this study, electrical characterization of ceramic insulation coatings were evaluated by resistive, capacitance, and high voltage breakdown techniques. The insulation coatings were produced on Ag or AgMg sheathed Bi-2212 tapes and CuNb/sub 3/Sn wires by continuous, reel-to-reel sol-gel process. The coatings were then annealed at several temperatures and times. Dielectric constant and high voltage breakdown values for the insulation coatings were measured by using a capacitive technique and a high voltage breakdown-AC dielectric tester, respectively. The electrical properties of the coatings with dopant materials, number of dips, temperature and time of annealing process are presented.

Non-vacuum YBCO films on buffer layered Ni tapes: processing, growth and properties

YBCO thin films on buffer layered Ni tapes were investigated via a sol-gel technique. YBCO films were prepared using solutions of various Y, Ba, and Cu precursor compounds. SrTiO/sub 3/ was used on Ni tapes as a buffer layer, ESEM, EDS, and XRD analysis were used to characterize the YBCO films. Sol-gel YBCO coated conductors on buffer layered Ni tapes yielded a T/sub c/ of 90 K by a transport 4-wire resistance measurement. The films produced in this manner were homogeneous, and free of pinholes and cracks.

Textured buffer layers for YBCO coated conductors by continuous sol-gel processing

In order to develop alternative buffer layers for YBCO coated conductors, RE/sub 2/O/sub 3/ (RE=La, Pr, Sm, Eu, Gd, Tb, Ho, Yb, and Lu) thin films were studied as candidate materials. Buffer layers were grown on Ni tapes using organometallic compounds that are 2,4-pentanedionates, isopropoxides, and acetates by a continuous, non-vacuum sol-gel process. Films were annealed at 900/spl deg/C-1200/spl deg/C under 4%H/sub 2/-Ar gas mixture. The buffer layers were characterized by means of ESEM, SEM, EDS, XRD and pole figure analysis. Textured, pinhole free crack free, continuous buffer layers were obtained by using 2,4-pentanedionates.

Sol-gel processing of buffer layers on Ni tape for YBCO surface coated conductors

Perovskite buffer layers of SrTiO/sub 3/, LaAlO/sub 3/, PbTiO/sub 3/, and BaZrO/sub 3/ were deposited using a sol-gel process from solutions derived from basic acetates and alkoxides. Homogenous, crack-free, and dense films of perovskite were deposited onto Ni tapes between temperatures of 600/spl deg/C and 750/spl deg/C by adjusting the concentration of precursors in the solutions used as material for YBCO surface coated conductors. These films were characterized by SEM, EDS and XRD. SrTiO/sub 3/ and PbTiO/sub 3/ buffer layers on Ni tapes were produced for the sol-gel YBCO surface coated conductor development.

BaZrO3 insulation coatings for HTS coils

Abstract Barium zirconium oxide (BaZrO 3 ) thick films were grown on Ag and AgMg sheathed Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212) superconducting tapes for electrical insulation purposes. A BaZrO 3 (BZO) precursor solution was prepared by sol–gel synthesis using Ba and Zr based alkoxide. Reel-to-reel continuous sol–gel dip coating method was used to grow BZO coatings on superconducting tapes. Processing, microstructure and electrical properties of high temperature BZO insulation coatings have been studied. The BZO coatings were grown in the temperature range of 450 and 600 °C in air. ESEM and X-ray diffraction were used to investigate microstructure and crystallinity of the coatings. Room temperature resistance, dielectric constant, and high voltage breakdown strength of the coatings were measured to be 13 M Ω , 22.5 and 1.0 kV at 1.5 mA, respectively.

Electrical properties of MgO-ZrO2 insulation coatings on Ag and AgMg/Bi-2212 tapes for magnet technology

Abstract High temperature MgO–ZrO 2 insulation coatings were successfully fabricated on long-length Ag and Ag/AgMg sheathed Bi 2 Sr 2 Ca 1 Cu 2 O x (Bi-2212) superconducting tapes and wires from solutions derived from alkoxide-based precursors using a reel-to-reel, continuous sol–gel technique for 3–5 T high field insert magnets. The insulation coatings were annealed at 850 °C for 20 h under O 2 flow. The surface morphology of coatings were characterized by scanning electron microscope (SEM). Dielectric constant and high voltage breakdown of insulation on tapes was measured by a multimeter and a standard high voltage breakdown power supply. SEM observations showed that MgO–ZrO 2 insulation coatings possess homogenous and crack structures on AgMg/Bi-2212 tapes. It was found that dielectric constant and high breakdown voltage values of MgO–ZrO 2 coatings increased with increasing MgO content in ZrO 2 and coating thickness. Also, it was measured that the dielectric constant values of coatings with and without epoxy were 33 and 47, respectively. The maximum high breakdown voltage value was determined to be 1100 V in sample with 24 mol% MgO–ZrO 2 coating.

Processing dependence of texture development in La2Zr2O7 buffer layer by sol-gel technique for YBCO coated conductors

Perovskite textured La2Zr2O7 (LZO) films were deposited on Ni tapes using sol-gel process for fabrication of second generation high-Tc superconductors. LZO solutions were derived from acetate and alkoxide precursors. The effects of precursors, solvents, chelating agents, and annealing conditions (temperature and time), on epitaxial growth of LZO were investigated by XRD, SEM, EDS, and X-ray pole figure analysis. It was found that texture of LZO depended on, solution preparation, and annealing conditions. Textured, homogenous, dense, crack free and pinhole free, LZO films were produced on textured Ni tapes by postannealing at 1150 °C for 10 min under 4%H2-Ar gas flow when lanthanum (III) 2-methoxyethoxide precursor and 2-methoxyethanol solvent were used. When lanthanum acetate precursor and trifluoroacetic acid were used, texture was obtained at 1160 °C for 40 min annealing conditions.