Y.S. Hascicek

Development of 3 T class Bi-2212 insert coils for high field NMR

Based on a successful 1 T Class PIT insert coil, the authors are now pursuing a 3 T Class insert coil. This paper describes the design and the latest conductor and coil test results, as well as supporting experiments. The final product is envisioned to contain 3 concentric sections, requiring over one kilometer of conductor. This will be tested in a 20 T large bore resistive magnet at the NHMFL. Experimental work focuses on the use of conductor with a silver-alloy matrix in the outer sections, that are subject to the largest stresses when operated in a background field. Results from heat treatment optimization for wound coils, mechanical test of conductors and coil design studies are reported.

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.

X-ray structure and microstructure determination of the mixed sesquioxides (Eu1-xYbx)2O3 prepared by a sol-gel process

Polycrystalline samples of (Eu1−xYbx)2O3 (x = 0.0, 0.1, 0.2, 0.5, 0.8, 0.9 and 1.0) were synthesized by a sol–gel process. X-ray diffraction data were collected and the crystal structures were refined by the Rietveld method. All samples are found to have the same crystal system and formed solid solutions over the whole range of x. The lattice parameters are found to vary linearly with the composition x. The cationic distribution over the two non-equivalent sites 8b and 24d of the space group Ia{\bar 3} is found to be random in the range 0.0 < x ≤ 0.5 and preferential in the range 0.5 < x ≤ 1.0. Replacing Eu3+ and Yb3+ by each other introduces slight changes in the atomic coordinates. Crystallite size and microstrain analysis are performed on single and multiple orders for each sample using profile fitting and the Warren–Averbach method. The obtained values of microstrain are correlated with the distribution of the rare earth (RE) ions over the two cationic sites of the structure. The average crystallite size ranges from 35 to 96 nm and the mean-square strain from 0.052 to 0.225 × 10−2.

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).

Irreversibility field and flux pinning in MgB2 with and without SiC additions

The critical current density (Jc) was measured at 4.2?K for MgB2 strands with and without SiC additions. In some cases measurements were performed on long (1?m) samples wound on barrels, the transport results being compared to the results of magnetic measurements. Most measurements were performed on short samples in fields of up to 18?T. It was found that in?situ processed strands with 10% SiC additions heat treated at 700?800??C showed improved irreversibility fields (Hr) and bulk pinning strengths (Fp) as compared to control samples; an increase in Hr of 1.5?T was noted. Heat treatment to 900??C gave even larger improvements, with Hr reaching 18?T and Fp values maximizing at 20?GN?m?3.

X-ray structure determination of the rare earth oxides (Er1−uGdu)2O3 applying the Rietveld method

Nanosized polycrystalline samples of (Er1−uGdu)2O3 (0 ≤ u ≤ 1.0) were synthesized by a sol–gel technique. X-ray diffraction data were collected and the crystal structures were refined by the Rietveld method. All samples are found to have the same crystal system and formed solid solutions over the whole range of u. The Er3+ and Gd3+ ions were randomly distributed over two cationic sites, 8b and 24d, in the space group Ia\bar{3} (206) in all refined structures. The lattice parameter was found to vary non-linearly with the composition (u). The average microstrain and average crystallite size have been calculated from the Williamson–Hall plots for each sample. The average size ranges from 50 to 70 nm, and the microstrain from 0.4 to 1.7%.

High temperature sol–gel insulation coatings for HTS magnets and their adhesion properties

Abstract This paper describes the adhesion properties of sol–gel insulation coatings with silver tape substrates using a mini-tensile-testing for HTS magnets. The sol–gel coatings were produced using solutions of Zr, Mg, Y, Ce, In and Sn based organometallic compounds. The growth mechanism of these coatings on Ag and AgMg sheathed Bi-2212 superconducting tapes was characterized by scanning electron microscopy, energy dispersive spectroscopy, differential thermal analysis and X-ray diffraction. The lap joints were fabricated by laying fresh sol–gel coated silver tape samples over each other and then heat treated. These joints with varying heat treatment conditions were pulled to failure by using a mini-tensile-tester. The results of bonding strength and microstructure of the failure surface are presented. Oxides were formed between temperatures of 450°C and 550°C. The results also indicated that the failure was in the form of a mixed type as interfacial/cohesive defect. The average adhesive strength of ZrO 2 , MgO–ZrO 2 , Y 2 O 3 –ZrO 2 , CeO 2 –ZrO 2 , In 2 O 3 –ZrO 2 and SnO 2 –ZrO 2 were found to be 0.763, 1.300, 2.400, 2.087, 1.650 and 1.580 MPa, respectively. Y 2 O 3 and CeO 2 doped ZrO 2 showed the best adhesive properties.

Structure and microstructure characterization of the mixed sesquioxides (Gd1−xYbx)2O3 and (Gd1−xHox)2O3 prepared by sol–gel process

Polycrystalline samples of (Gd 1-x Yb x ) 2 O 3 and (Gd 1-x HO x ) 2 O 3 (0.0 ≤ x ≤ 1.0) were synthesized by a sol-gel process. X-ray diffraction data were collected and crystal structure and microstructure analyses were performed using the Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. For the system (Gd 1-x HO x ) 2 O 3 , the cationic distribution over the two non-equivalent sites 8b and 24d of the space group Ia3 were found to be random for all values of x. For (Gd 1-x Yb x ) 2 O 3 , the distribution is random in the range 0.0 < x ≤ 0.5 and preferential in the range 0.5 < x ≤ 1.0. The lattice parameters are found to vary linearly with the composition x. Replacing Gd 3+ and Yb 3+ , or Gd 3+ and Ho 3+ , by each other introduces slight changes in relative atomic coordinates. Crystallite size and microstrain analyses were performed along different crystallographic directions and both are found to vary anisotropically with the composition parameter (x). The obtained values of microstrain are correlated with the distribution of the rare earth ions over the two cationic sites of the structure. The average crystallite size ranges from 45 to 144 nm and the root mean square (r.m.s.) strain from 0.018 to 0.409 × 10 -2 .

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.

CeO/sub 2/ buffer layers for YBCO: growth and processing via sol-gel technique

In this study, the processing and growth mechanisms of CeO/sub 2/ buffer layers were evaluated on Ni substrates for YBCO superconductor. The sol-gel technique was utilized to produce buffer layers from six different Ce based precursor materials. The microstructure, phase composition and formation of buffer layers were characterized by means of ESEM, SEM, EDS, XRD, pole figure XRD and DTA techniques. The results indicated that the CeO/sub 2/ formation starts at temperature of 420/spl deg/C. It was found that the best crack free CeO/sub 2/ thin films were obtained by using Ce(NO/sub 3/)/sub 3//spl middot/6H/sub 2/O and colloidal CeO/sub 2/ based precursor materials. Different anions and their concentrations also influenced the structure of thin films.