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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 diffra...
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Context 1
... the annealing process, the coatings on one side of the conductors were removed using a SiC paper. The coated faces of samples were sandwiched together with and without epoxy to build a capacitor as seen in Fig. 3. After that, resistance and capacitance of the samples were measured using a Metrahit 16I Analog Digital Multimeter. The dielectric constant of the samples The continuous, reel-to-reel, sol-gel coating system; (1) three-zone furnace, (2) electric motor driven pay off and take up spools, (3) drive system and furnace controllers, (4) ...
Context 2
... tapes, Cu-Nb 3 Sn wires, stainless steel and Ni tapes by a continuous, reel-to-reel solgel technique were studied. Very thin (submicron) for ZrO 2 [14,[20][21][22][23]. Table 2 shows the capacitance and dielectric constant values of the sol-gel MgO-ZrO 2 insula- tion coatings measured using a capacitance sandwich with and without epoxy as seen in Fig. 3. Note that dielectric constant is decreasing as the thickness of the coating goes down. This is probably due to increased porosity and/or higher values of crack space (unfilled crack space with subsequent passes). Table 3 shows the dielectric constant and the high voltage breakdown values for the very thin, pinhole-free, crack-free ...
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A procedure of extracting the model parameters of a high-temperature superconductor (HTS) film from the experimental characteristics of resonators and filters is proposed. It is based on a correct phenomenological model of the HTS film surface impedance and an accurate simulation of the filter (resonator) structure by taking into account the temper...
Citations
... This insulation material also absorbs Ag from the sheath and Cu from the Bi-2212 core during the heat treatment, which reduces Jc by 15-20% compared to bare wire [10]. Considerable efforts have been made over the years to develop an effective insulation layer for Bi-2212 that is thin, chemically compatible, has good adhesive properties, and is viable for long length coating [11][12][13][14][15]. TiO2 insulation developed by nGimat LLC and by Kandel et al. appeared to be a successful solution for insulating Bi-2212 [16,17]. ...
In order to develop a high current density in coils, Bi-2212 wires must be electrically discrete in tight winding packs. It is vital to use an insulating layer that is thin, fulfils the dielectric requirements, and can survive the heat treatment whose maximum temperature reaches 890 °C in oxygen. A thin (20-30 µm) ceramic coating could be better as the insulating layer compared to alumino-silicate braided fiber insulation, which is about 150 μm thick and reacts with the Ag sheathed Bi-2212 wire during heat treatment. At present, TiO2 seems to be the most viable ceramic material for such a thin insulation because it is chemically compatible with Ag and Bi-2212 and its sintering temperature is lower than the maximum temperature used for the Bi-2212 heat treatment. However, recent tests of a large Bi-2212 coil insulated only with TiO2 showed severe electrical shorting between the wires after over pressure heat treatment (OPHT). The origin of the shorting was frequent silver protrusions into the porous TiO2 layer that electrically connected adjacent Bi-2212 wires. To understand the mechanism of this unexpected behaviour, we investigated the effect of sheath material and hydrostatic pressure on Ag protrusions. We found that Ag protrusions occur only when TiO2-insulated Ag-0.2%Mg sheathed wire (Ag(Mg) wire) undergoes OPHT at 50 bar. No Ag protrusions were observed when the TiO2-insulated Ag(Mg) wire was processed at 1 bar. The TiO2-insulated wires sheathed with pure Ag that underwent 50 bar OPHT were also free from Ag protrusions. A key finding is that the Ag protrusions from the Ag(Mg) sheath actually contain no MgO, suggesting that local depletion of MgO facilitates local, heterogeneous deformation of the sheath under hydrostatic overpressure. Our study also suggests that predensifying the Ag(Mg) wire before insulating it with TiO2 and doing the final OPHT can potentially limit Ag protrusions.
... Considerable efforts have been made in developing thin and effective electrical insulation in Bi-2212 magnets in last 15 years. Celik et al developed less than 15 μm thick ZrO 2 based thin ceramic coatings through a sol-gel technique [15][16][17][18][19][20]. This insulation coating was also applied on stainless steel tape for co-winding with the Bi-2212 tape conductor in a magnet coil which generated 25.05 T combined magnetic field in 19.94 T resistive magnet background [3]. ...
... The top coat contains the water base polyacrylic which improves the abrasion resistance of the green coating and provides winding durability. Compared to the metal organics based sol-gel coating process [15][16][17][18][19][20], our slurry formulation technique is simple and does not possess any major safety issues. Moreover, over 10 μm thick coating is achieved only in one coating cycle showing that the coating process is more cost effective and simple than the sol-gel dip coating or the CCVD process, where 10 or more coats are often required to achieve the same thickness. ...
We have developed TiO2 coating on Ag-alloy sheathed Bi2Sr2CaCu2O8−x (Bi-2212) round-wire conductor for electrical insulation in Bi-2212 magnets. The green coating has a base layer comprised of TiO2, polyvinyl butyral (PVB) and a small amount of polysilicate and a top layer made of polyacrylic. The coating was applied on the conductor using a continuous reel-to-reel dip coating process and showed very good adherence and flexibility that is suitable for magnet coil winding. The thickness of the coating is a function of slurry viscosity, wire withdrawal speed and wire radius. Small test coils were built with the coated Bi-2212 round-wires and were heat treated at 100 atm pressure. During the heat treatment, the PVB and polyacrylic were removed from the green coating and the polysilicate decomposed to SiO2 that served as a sintering aid for TiO2. After the heat treatment, the coating remained strongly adhered to the conductor and did not have a detrimental effect on the critical current (I c) values. The breakdown voltage was about 150 V across a 7 μm thick heat treated coating on Bi-22112 round-wire conductor, corresponding to a dc dielectric strength of about 21 MV m−1.
... Third, insulation components can accelerate the diffusion of core constitutes to the surface of the matrix. It should be emphasized that only limited sources are available that address these issues [18], [19]. ZrO 2 , Al 2 O 3 , Y 2 O 3 and high purity SiO 2 are possible candidates, ...
NbTi accelerator dipoles are limited to magnetic fields (H) of about 10 T, due to an intrinsic upper critical field (H<sub>c2</sub>) limitation of 14 T. To surpass this restriction, prototype Nb<sub>3</sub>Sn magnets are being developed which have reached 16 T. We show that Nb<sub>3</sub>Sn dipole technology is practically limited to 17 to 18 T due to insufficient high field pinning, and intrinsically to 20 to 22 T due to H<sub>c2</sub> limitations. Therefore, to obtain magnetic fields approaching 20 T and higher, a material is required with a higher H<sub>c2</sub> and sufficient high field pinning capacity. A realistic candidate for this purpose is Bi-2212, which is available in round wires and sufficient lengths for the fabrication of coils based on Rutherford-type cables. We initiated a program to develop the required technology to construct accelerator magnets from 'wind-and-react' (W&R) Bi-2212 coils. We outline the complications that arise through the use of Bi-2212, describe the development paths to address these issues, and conclude with the design of W&R Bi-2212 sub-scale magnets.
... The sol-gel technique provides a suitable low-temperature route to homogeneous MgO-ZrO 2 coating from Zr and Mg organometallic compounds. The insulations are compatible with both the high temperature required for processing and the cryogenic temperatures for the operation [7,8]. In this study, synthesis, characterization and application of the MgO-ZrO 2 insulation coatings on AgMg sheathed Bi-2212 superconducting tapes were evaluated for magnet technology. ...
In the present paper, synthesis, characterization and application of MgO-ZrO2 insulation coatings on Ag and AgMg sheathed Bi-2212 superconducting tapes were studied by using a reel-to-reel sol-gel technique. The investigation of synthesis mechanisms was attempted from the solution based structure to annealing process using TGA, XRD and SEM. Superconducting properties of the coated AgMg/Bi-2212 tapes were also evaluated.
... For low and high temperature applications, several insulators (Teflon tape, Alumina paper, Epoxy resin, Rubber, Glass Fiber, Glass woven etc.) were commonly used for insulation of superconductor tape and wire [2][3][4]. One of the important parameter for electrical insulation is dielectric strength properties of insulation layer, which is depends on the sort of materials and film thickness [5]. Various materials (ZrO 2 , TiO 2 ) and additives (MgO, In 2 O 3 , and SnO 2 ) were intensively investigated and adopted for silver, stainless steel and superconductor tape and wire applications for magnet technology by sol-gel dip coating method at NHMFL [6]. ...
The utilities of the electrical insulation of silver tape for magnet applications have been investigated. Two types of ZrO2 - 8 wt% MgO solutions, which are sol-gel and sol-gel composite solution, were used to coat the silver tapes by continuous dip coating method. The ceramic coatings were characterized by SEM and XRD analysis. The thicker ceramic insulation layers were obtained with less dip number by the use of sol-gel composite method.
... A thin, thermally stable and well-adhered coatings must (a) insulate at the coil's operating temperatures; (b) retain continuity when shaping the coil; (c) be permeable to oxygen; (d) not induce damage to the HTS material or any sheathing material it might be encased within; (e) not significantly increase the overall size of the coil; and (f) be compatible with the thermal processing of the HTS material [8 Á/11]. In these coatings, the most important problem is the bonding of coatings to the substrate during the winding process [12]. ...
Self insulating substrate tapes (SIST) is the most promising insulation technique for high temperature MgO–ZrO2 coatings on Ag and AgMg sheathed Bi2Sr2Ca1Cu2Ox (Bi-2212) superconducting tapes and wires in applications of HTS/LTS coils and magnets. We have already reported successful results as to the synthesis, characterizations and applications of the insulation coatings using the SIST. In order to provide no electrical short circuit in Jc measurements of HTS/LTS coils, the bonding of the coatings onto the substrate is a very important issue. In this present research, the adhesion properties of high temperature MgO–ZrO2 coatings were scrutinized for different processing parameters. Lap joints were fabricated by laying fresh sol–gel coated silver tape samples over each other and then by heat-treating at temperature range of 500–800°C for several times in air. These joint samples were pulled to failure by using a mini tensile tester. MgO–ZrO2 was coated on Ag tapes by sol–gel process using Mg and Zr based precursors. The obtained results obviously pointed out that the best Mg precursor is Mg(C5H7O2)·2H2O to prepare solution and there is a strong relationship between film growth and adhesion properties. Also, MgO content in ZrO2 increased its bonding strength. The optimum heat treatment conditions are 600°C and 15 min for best bonding for these high temperature insulation coatings on HTS tape conductor. The failure mode of all samples was in the form of a mixed type interfacial/cohesive defects in MgO–ZrO2 coating.
... Also, effectiveness of insulation materials is a very important parameter in minimizing the leaks and resistance to reactions during the partial melt texturing process. To facilitate these, ZrO 2 , [10][11][12][13]. In 2 O 3 -ZrO 2 , and SnO 2 -ZrO 2 insulation coatings were used for insulation of low temperature Cu-Nb 3 Sn superconductors because of high adhesive strength on the round conductors with Cu or Cu-Sn matrix [14]. ...
Barium zirconium oxide (BaZrO3) thick films were grown on Ag and AgMg sheathed Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting tapes for electrical insulation purposes. A BaZrO3 (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, 22.5 and 1.0 kV at 1.5 mA, respectively.
... The processing advantages are: (a) excellent bonding, no flake off; (b) once applied, these coatings need no additional handling requirement during coil fabrication; (c) they can be as thin as submicron thus providing excellent packing density; (d) thickness can be controlled via solution chemistry, withdrawal rate or number of dipping; and (e) several conductors can be run in parallel and/or number of furnaces can be increased to scale up. The applications of sol-gel process for magnet technology are: (a) W&R HTS coil technology; (b) react&wind (R&W) HTS coil technology (Bi-2223 coils built, because of ease of handling and packing density improvement); (c) W&R and R&W LTS coil technology; (d) AC loss reduction applications on LTS and HTS cables through inter-strand resistance control; (e) Eddy current loss reduction in the laminated reinforcement in the pulse coils; and (f) reduction in the cool down time via reduction in joule heating [5,6]. ...
... The most important factors influencing the reliability and compactness of the superconducting apparatus are the dielectric performances and high breakdown voltage capabilities of electrical insulations [1][2][3][4][5][6][7]. The electrical insulation in super-conducting apparatus is subjected to uncommon synergetic conditions in addition to all stresses in conventional apparatus: high electrical stress, high magnetic stress, high mechanical stress by electromagnetic force, thermo-mechanical stresses caused by the cryogenic environments, phase transitions of coolant and high energy radiation etc. ...
High temperature MgO–ZrO2 insulation coatings were successfully fabricated on long-length Ag and Ag/AgMg sheathed Bi2Sr2Ca1Cu2Ox (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 O2 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–ZrO2 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–ZrO2 coatings increased with increasing MgO content in ZrO2 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–ZrO2 coating.
... Coils 2, 5 and 6 are candidate units for the A and B sections respectively of the 5 T insert [46], featuring a single co-wound stainless steel strip as reinforcement. The reinforcement strip is MgO-ZrO 2 coated [121] and provides the turn-to-turn insulation. All six doublepancake coils feature a Kapton sheet for pancake-pancake insulation and are vacuum epoxy-impregnated with STYCAST™ 1266. ...
... Another insulation coating method used in HTS transformer coils has been developed at National High Magnetic Laboratory (NHMFL), Tallahassee FL. [24][25][26][27]. The ceramic insulation coatings were made utilizing sol-gel for the high magnetic field coils. ...
A 3.5MVA High Temperature Superconductor (HTS) transformer has been in design at FAMU-FSU College of Engineering since 2002. The coils of the HTS transformer use stainless steel sheathed Bi2223 HTS wire. In order to make insulation around the HTS transformer coils, research has been conducted. The results of this research are the main contents of this thesis.
Since Siemens constructed the first HTS transformer in 1997, several HTS transformer projects have been developed around the world. In these HTS transformers, coils generally were wrapped by insulation materials. This insulation method is not ideal since wrapped insulation has disadvantages: displacement of insulation materials, low efficiency and variable insulation effect. In order to find a better approach, we wanted to investigate polymer coatings around HTS transformer coils.
Polyamide 6 coatings were made on aluminum substrate utilizing dipping, brush and spray methods. After which, their properties were studied, including density, breakdown strength, dielectric constant and dissipation factor. Through comparison of properties, spray coatings show the best insulating effect. Our research also included influence of heat treatment and vacuum treatment on spray coatings. Heat and vacuum treatments effect on breakdown strength is insignificant. Vacuum treatment can greatly increase the density of the coating. Heat treatment influences the dielectric constant and dissipation factor. But the breakdown strength of spray coatings is only one fifth of that of commercial polyamide film. And the density of spray coatings is about 60% of that of commercial polyamide film. All studies about polymer coating were conducted at room temperature.
