Superconducting YBa 2 Cu 3 O 7−x (YBCO) bulks have demonstrated promising applications in quasi-permanent magnets, levitation, etc. Recently, the applications of bulk superconductors have been proposed, such as in portable, ultralight superconducting devices. These applications require bulk superconductors with lightweight, complex morphology, and good processability. However, the traditional fabrication method of YBCO bulks requires prolonged supplemental oxygenation and produces limited geometries with many randomly distributed cracks. This, combined with the inherent brittleness of the ceramic material, seriously impedes its wide application. In this study, a YBCO bulk with a multiscale hierarchical geometric configuration is constructed by a direct-inkwriting-based 3D-printing process. The 3D-printed YBCO green bodies exhibit a robust structure after directional freezing, which promotes intimate contact between the precursor particles in the deposited layers. This technology offers the advantage of a low shrinkage of 13.6 vol% after sintering at 920 °C. The 3D-printed bulks show lightweight, highly crystalline, and good electromagnetic properties compared with those produced by traditional cold-pressed sintering. Importantly, the multilevel void structure with a large specific surface area significantly reduces the oxygenation time and retains superconductivity. The proposed 3D-printing process can be adopted for the industrial production of superconducting bulk with complex geometries for novel applications.
Recently, YBa2Cu3O7−x coated conductor (YBCO CC) has been developed intensively for different applications including power cables and high-filed magnets. Of all its physical properties, the thermal conductivity of the YBCO CC is considered as one of the most important parameters in guiding the temperature distribution, heat flux, and prediction of quench propagation. To accurately predict this property, a thermometry technique of high-speed fluorescent thermal imaging is introduced to monitor heat diffusion of commercial YBCO CCs in real time based on the Europium tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorate] (EuTFC) in this study. We propose a new imaging process to eliminate the influences of background intensity and non-uniform illumination on the calibration results accompanying with good accuracy of measurement. And the fluorescence performances are evaluated by static and dynamic calibration experiments. The experimental results show that the photoluminescence of EuTFC has excellent photostability and temperature dependence, and there is no hysteresis in the temperature response when comparing with the PT100 measurements. Subsequently, four kinds of commonly used theoretical models of thermal conductivity and the corresponding calculation curves of the YBCO CC are presented. Finally, the numerical simulation based on the theoretical models has been conducted to reproduce the transient heat conduction process. The simulation results show that the transient heat conduction predicted by the Maxwell’s equivalent model show the best agreement compared with experimental results.
Superconducting flywheels have potential application value in aerospace field, and its suspension time is a key factor. Alternating Current (AC) loss associated with rotation is an important parameter that affects the suspension time, so it is very important to study how to reduce the AC loss. Recently, a method of preparing YBa2Cu3O7−x (YBCO) high-temperature superconducting flywheels by Direct-Ink-Writing (DIW) 3D printing was developed. In this paper, the circular hole superconducting flywheel prepared by this method is optimized by the idea of structural optimization. Based on the finite element method, the AC loss before and after optimization is calculated and analyzed. It is found that the elliptical holes make the superconducting flywheel have lower AC loss than circular holes, with a reduction of 58.49%. Then, the YBCO superconducting flywheel with an optimized elliptical structure was prepared by the DIW 3D printing method. The magnetic levitation experiment found that the levitation time of the optimized superconducting flywheel was increased to 162 s compared with the previous 120 s under the same conditions, and the optimized structure had a higher levitation mass ratio. It provides theoretical and experimental support for reducing the AC loss of superconductors by applying the idea of structural optimization design in engineering practice.
Superconducting YBa2Cu3O7-x (YBCO) bulks have promising applications in quasi-permanent magnets, levitation, etc. Recently, a new way of fabricating porous YBCO bulks named Direct-Ink-Writing (DIW) based 3D-printing process has been reported. In this method, customized precursor paste and programmable shape are the two main advantages. Here, we have put forward a new way to customize the YBCO 3D-printing precursor paste which is doped with Al2O3 nano particles to obtain YBCO with higher thermal conductivity. The great rheological properties of precursor paste after doped with Al2O3 nano particles helped the macroscopic YBCO samples with high thermal conductivity being fabricated stably with high crystalline and lightweight properties. Test results shows that the peak thermal conductivity of Al2O3 doped YBCO with larger thermal conductivity can reach twice as much as pure YBCO, which made great effort to reduce the quench propagation speed significantly. Based on analysis of this YBCO with larger thermal conductivity’s microstructure, one can find that the thermal conductivity of doped YBCO would be determined not only by its components but also by the microstructure. We have proposed a macroscopic theoretical model to assess the thermal conductivity of different microstructures. One can find that the calculated results take good agreement with the experimental results. Meanwhile, a microstructure with high thermal conductivity is found. At last, we have designed a macroscopic YBCO structure, which is made up with the presented high thermal conductivity microstructure, fabricated by the DIW 3D-printing process. Compared with the traditional 3D-printed YBCO, the structural designed samples make a great effort to further enhance thermal conductivity of YBCO. Our customized design of 3D-printing precursor pastes and novel concept of structural design for enhancing thermal conductivity of YBCO superconducting material can be widely used in other materials which are suitable for the DIW 3D-printing process.
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