Z. Aslanoglu

Textured growth of multi-layered buffer layers on Ni tape by sol-gel process

Textured Cerium Oxide (CeO/sub 2/)/Yttrium-Stabilized Zirconia (YSZ)/CeO/sub 2/ buffer layers structure were grown by sol-gel dip coating process on bi-axially textured Ni tapes for processing of YBCO coated conductors. CeO/sub 2//YSZ/CeO/sub 2/ buffer layer structure has been demonstrated by vacuum techniques, but first time textured CeO/sub 2//YSZ/CeO/sub 2/ structure were grown by sol-gel on biaxially textured Ni tape. The buffer layer structure promoted c-axis oriented sol-gel YBCO films and prevented oxidation of nickel during YBCO processing. After each layer was coated, the layer was annealed. CeO/sub 2/ layers were annealed at 950 /spl deg/C for 30 min. and YSZ layers were annealed at 1150 /spl deg/C for 10 min. under 4% H/sub 2/ - Ar gas flow. Texture analysis of Ni substrates and bottom CeO/sub 2/ were done by Philips diffractometer. Sol-gel YBCO layers were coated on CeO/sub 2//YSZ/CeO/sub 2/ structure and critical current density was about 0.5 /spl times/ 10/sup 5/ A/cm/sup 2/. Microstructure of the buffer layer was investigated by Environmental Scanning Electron Microscope (ESEM).

Development of 100% lattice match buffer layers on RABiTS Ni tapes by sol-gel

Gd/sub 2/O/sub 3/-Yb/sub 2/O/sub 3/ and Gd/sub 2/O/sub 3/-Ho/sub 2/O/sub 3/ mixed RE oxides were used to produce buffer layers with a perfect lattice match with superconducting layer. Since these RE oxides are 100% miscible in each other, pseudocubic lattice parameter of the buffer layers can be modified by changing the ratio of components to perfectly match with any superconducting RE-123. Texture and the microstructure of the buffer layers were studied by XRD, Pole Figure and ESEM.

Y-and Yb-123 coated conductor development by PLD and sol-gel on (Gd/sub 1-x/Er/sub x/)/sub 2/O/sub 3/ buffered Ni tapes

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and YbBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// layers were coated by sol-gel and PLD on Gd/sub 1.91/Er/sub 0.09/O/sub 3/ (100% lattice match with Y- and Yb-123) textured buffer layer on Ni substrates. Different thickness of buffer layers and superconducting layer were tried to see the thickness effect on superconducting properties. Buffer layers were prepared with different lattice parameters for Y-123 and Yb-123. Coated conductors were characterized by means of XRD, ESEM and T/sub c/ and J/sub c/ measurement. Since the perfect lattice match can be achieved between buffer layer and superconducting layer, texture of superconducting film was improved, and consequently critical current density of Y- and Yb-123 were improved.

Silver doped YBCO coated conductor development by sol-gel process

The nonfluorinated YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) coated conductors with 1-3 wt%Ag have been fabricated by sol-gel process. Ag doped YBCO films were fabricated on CeO/sub 2//YSZ/CeO/sub 2/ buffer layered Ni tapes by continuous sol-gel dip coating process. Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) analysis were used to characterize the YBCO coated conductor. The superconducting properties (T/sub c/ and J/sub c/) of Ag doped YBCO coated conductors were found to be higher than those of the un-doped conductors. The Ag doped YBCO has a T/sub c,zero/ of 88 K and J/sub c/ of 1.0/spl times/10/sup 5/ A/cm/sup 2/.

Fabrication and Testing of W&R MgB2 Coils Using CTFF Cu/MgB2 Wires and the Sol‐Gel Insulation Process

We have sol‐gel insulated and characterized short samples of the Cu CTFF in Cu tube MgB2 wire with a view to fabricate the first US MgB2 coil from this conductor. The optimum heat treatment condition for this conductor was found to be half an hour at 700 °C under 4%H2‐Ar gas flow. We have sol‐gel insulated 25 meters of Cu/MgB2 wire with SnO2‐ZrO2, layer wound the coil, impregnated with stycast and then tested it between 4.2 K and 30 K together with a sister sample which was heat treated with the coil. The coil had a Jc of 66190 A/cm2 at 4.2 K and 21428 A/cm2 at 20 K in its self field. This is almost identical to that of the sister sample when the self field effect is considered. This is very significant, as it demonstrate that with CTFF process which is readily scalable, one can produce any lengths of MgB2 conductor which would demonstrate the short sample Jc which is unheard of in the HTS conductors.

Characterization of MgB2 Conductors for Coil Development

The effects of the heat treatment conditions on microstructure and the transport critical current density of MgB2 wires, which were fabricated by the Continuous Tube Forming and Filling (CTFF) process, have been investigated. Two types of MgB2 conductors, Fe/MgB2 and Cu/MgB2, were studied. It was found that the sheath materials affect the optimum annealing profile of MgB2 conductor. The annealing temperature for Cu/MgB2 conductors was lower than that for the Fe/MgB2 conductors. The critical current density, Jc was measured to be 1.1×105 A/cm2 at 20 K in‐self field for Cu/MgB2 conductor of 1.25 mm in diameter. The processing, microstructure and superconducting properties are presented.

YBCO coated conductor development by continuous sol-gel process

YBCO coated conductor development on Ni tapes with various sol-gel buffer layers were investigated by a continuous, reel-to-reel sol-gel technique. YBCO films were prepared using solutions of various Y, Ba, and Cu precursor organometallic compounds. The coated YBCO tapes were annealed under argon/oxygen flow. ESEM, EDS, and XRD analysis were used to characterize the YBCO films. Sol-gel YBCO coated conductor on sol-gel buffered Ni tapes yielded a Tc,onset of 90 K and Jc of about 105 A/cm2. The films produced in this manner were homogeneous, and free of cracks.

Electrical Properties of Sol‐Gel MgO ‐ ZrO2 Insulation Coatings under Compression for Magnet Technology

The high temperature compatible MgO ‐ ZrO2 insulation coatings were applied on Stainless‐Steel‐304 (SS) ribbons by sol‐gel process for magnet technologies. SS ribbons did not considerably oxidize, even though the coating process occurs in an oxidation atmosphere. Electrical properties of the samples such as high voltage breakdown (HVbd), electrical strength and dielectric constant under varying stress, at Room Temperature (RT) and 77 K were investigated. The measurements were carried out with and without epoxy impregnation. Surface morphologies of insulated samples were examined by using Environmental Scanning Electron Microscope (ESEM), after high voltage breakdown test.

Growth and Characterization of YbBCO Films on Textured Gd2O3 Buffer-Layered Ni Tapes: All Sol–Gel Process

YbBa2Cu3O7−x (YbBCO) thick films were grown on buffered, cube-textured Nickel tapes by sol–gel dip-coating method. Yb-123 films were prepared using solutions of Yb, Ba, and Cu organometallic compounds. A solution-based Gd2O3 buffer layer was deposited by dip-coating process with excellent texture and uniformity. The texture development and surface morphology of the buffer-layer films were examined by X-ray diffraction, pole figures, and ESEM analysis. Microstructure and characterization of Yb-123 films were done by ESEM, EDS, and XRD analysis. Tc and Jc were conducted by four-wire measurement method

A Sol‐Gel Approach to the Insulation of Rutherford Cables

Two wind‐and‐react compatible variants for the electrical insulation of Rutherford cables by a sol‐gel route have been investigated. The first variant involves the direct application of a sol‐gel coating of SnO2‐ZrO2 to the surface of the strands in the cable, whereas the second is an indirect approach consisting of coating stainless steel tapes with MgO‐ZrO2 that are to be wrapped around or co‐wound with the cable. Following the application of the insulation by one of the two methods, the insulation electrical resistance and breakdown voltage were determined for samples consisting of two 7 inches long cables pressed together and vacuum impregnated with epoxy (CTD‐101K). With a notable exception, the breakdown voltages on directly insulated cables were too low for practical purposes. Better results, with breakdown voltages ranging from 20 to almost 200 V, were obtained for insulator coatings applied to stainless steel tapes. An additional sintering at 700–800°C for 6–12h of the coatings deposited on stain...