Cel
This project would promote a concerted European research effort in one of the main potential applications of high temperature superconductors, namely power cables, with the aim of developing superconducting power cables that will operate at above 77K, and ideally at ambient temperature or higher.
The newly discovered superconducting ceramic materials are of immediate technological interest because they can maintain their superconductivity up to temperatures where applications based on this property become technically and economically attractive. This fact is widely appreciated in Japan and the United States of America, where substantial funds are being committed to research and development of these novel materials. This project promotes a concerted European research effort in one of the main potential applications of high temperature superconductors, namely power cables, with the aim of developing superconducting power cables that will operate at above 77K, and ideally at ambient temperature or higher. The project will focus on the basic research that needs to be done towards reaching this goal. Emphasis is being placed on identifying and characterising new materials with improved superconducting properties and on developing technologies for fabricating experimental cable conductors that incorporate these advantageous materials. Efforts will be made to optimise these in terms of current carrying capability and minimise alternating current (AC) power loss. If successful, this precompetitive research will represent a major step towards the realisation of superconducting power lines that could save a large proportion of the 2.5 billion European currency units (Ecu) or more, that is lost annually in electricity transmission throughout the European Community (EC).
The use of high critical temperature (Tc) superconductors in power cables requires conductors to be available in long lengths with critical current density (Jc) values at liquid nitrogen temperature exceeding 1E5A cm{-2} throughout the conductor in moderate self fields of the order of 0.1T.
The search for new superconducting phases involved the synthesis of thousands of different sample compositions. A robot system was used to mix solutions containing the individual metal elements in the required ratio, and then to dispense these solution onto silver substrates. Liquid precursors which used ethylene diamine tetraacetic acid (EDTA) as a complexing agent for the metal ions were prepared and suitable conditions established for mixing, dispensing, drying and firing the samples so that they yielded fully reacted phases. Plumbate, bismuthate and palladate systems were investigated but most effort was concentrated on the synthesis of new cuprates.
Several new nonsuperconducting phases were discovered and the resulting information on phase diagrams proved extremely valuable in determining the composition of the impurity phases normally present in high Tc materials. It provided an improved understanding of the yttrium barium cuprate and the bismuth strontium calcium cuprate systems. By using liquid precursors and carefully controlling the heat treatment, the Tc of the (bismuth, lead) 2223 phase was raised to 116 K and the preparation of the yttrium 248 phase was optimised.
An attempt was made to generate more effective pinning centres by particle irradiation of bismuth 2212 melt textured samples. It was concluded that thermally activated depinning is an intrinsic limitation for Jc in the bismuth 2212 phase and that it cannot be used for the development of conductors operated at 77 K.
Magnetization measurements on a wide range of cuprate materials supported these observations and showed that the flux pinning ability of 1212 and 1223 phase materials is superior to that of 2212 and 2223 phase materials. Unfortunately, all of the 1212 and 1223 phase materials known to be superconducting at 77 K contain thallium. A search for a less toxic and more chemically stable substitute for thallium was undertaken. This led to the synthesis of a novel series of superconducting lead cuprates. These materials readily form as the 1212 phase in air and they exhibit superconducting without the need for annealing or quenching treatment. The highest transition temperature recorded in these materials is 92 K as measured by the onset of diamagnetism.
Superconducting power scale conductors consist of a superconducting ceramic film in contact with a metallic substrate. The substrate serves as a mechanical reinforcement and provides electrical stabilization for the superconductor. Silver is the best candidate for the material in contact with the superconductor since it does not react with at the high temperatures (800 C to 900 C) employed during the processing. If the chosen substrates are more chemically reactive buffer layer is also necessary to prevent the harmful interaction between the superconductor and substrate. Various candidate substrate and buffer layer combinations were studied in this project.
In order to obtain a high critical current in the superconducting ceramic film, the individual grains must have a high intrinsic critical current density (Jc). There must also be strong coupling between the grains (clean grain boundaries) and a high degree of crystal alignment (texture). One method of achieving this is to impose a large temperature gradient during the processing of the material and melt textured yttrium 123 rods (1 mm diameter) were produced which has a transport Jc of 35000 A cm{-2} and a critical current of 200 A. However the textured length was less than 35 mm and it was not possible to reproducibly control the direction of the texture. A new melt processing furnace which permitted more accurate control of the thermal gradients was constructed.
4 main conductor fabrication routes were explored. These were chemical vapour deposition (CVD) of thin films (less than 10 um) of yttruim 123, laser melt texturing of plasma sprayed thick films (greater than 10 um) of yttruim 123, melt texturing of thick films of bismuth 2212 and (bismuth, lead) 2223 and the powder in tube technique for producing tapes of (bismuth, lead) 2223.
Reliable and comprehensive test methods were established for characterizing cable conductors.
The electromagnetic characterization of conductor samples was performed using facilities that were developed to permit the measurement of the critical temperature (Tc) and critical current density (Jc) values by means of a short duration pulsed current and the measurement of the alternating current (AC) critical current. In addition AC losses could be determined by both calorimetric and electrical methods. The results indicated that the measurement techniques are fully adequate to evaluate the direct current (DC) and AC performance of the conductor samples.
The thermal expansivity of composite conductor samples and of the various materials used in their fabrication have been measured in the range from 77 K to more than 800 C. The results show that some nickel based alloys are likely to be more compatible with the semiconductor than silver. Bending and tensile tests have been carried out on powder in tube bismuth 2212 and (bismuth, lead) 2223 tapes. These tests have enabled the stress strain characterization of representative samples to be made, and the effect of mechanical disturbance on their critical current to be evaluated under the application of controlled pulling strains during critical current measurements. The stress strain performance of the tape samples has been found to be reproducible but it is considered insufficient for cable conductors.
X-ray diffraction (XRD) and transmission electron microscope (TEM) examinations have been used to determine the phases present within the samples and to evaluate the degree of texturing that is achieved. The composition of the grains and the grain boundaries have been obtained by surface analysis and by scanning electron microscope (SEM) microprobe analysis. A correlation of the microstructure to the electrical performance has enabled the quality of the samples to be steadily improved.
A comparative ageing assessment was p erformed in controlled ambients ranging from room temperature to 70 C and up to 100% relative humidity. Test methods to evaluate the effect of thermal cycling between liquid nitrogen temperature and soldering temperature were applied to conductor samples. The tests indicated that the bismuth 2212 and (bismuth, lead) 2223 tapes are sufficiently stable for handling in a normal ambient atmosphere and are capable for withstanding repeated thermal cycling under realistic conditions of use.
The newly discovered superconducting ceramic materials are of immediate technological interest because they can maintain their superconductivity up to temperatures where applications based on this property become technically and economically attractive. This fact is widely appreciated in Japan and the USA, where substantial funds are being committed to research and development of these novel materials.
The project will focus on the basic research that needs to be done towards reaching this goal. Emphasis will be placed on identifying and characterizing new materials with improved superconducting properties and on developing technologies for fabricating experimental cable conductors that incorporate these advantageous materials. Efforts will be made to optimize these in terms of current carrying capability and minimise AC power loss. If the realization of superconducting power lines that could save a large proportion of the 2.5 billion Ecu, or more, that is lost annually in electricity transmission throughout the EC.
Dziedzina nauki (EuroSciVoc)
Klasyfikacja projektów w serwisie CORDIS opiera się na wielojęzycznej taksonomii EuroSciVoc, obejmującej wszystkie dziedziny nauki, w oparciu o półautomatyczny proces bazujący na technikach przetwarzania języka naturalnego.
Klasyfikacja projektów w serwisie CORDIS opiera się na wielojęzycznej taksonomii EuroSciVoc, obejmującej wszystkie dziedziny nauki, w oparciu o półautomatyczny proces bazujący na technikach przetwarzania języka naturalnego.
- nauki rolniczerolnictwo, leśnictwo i rybołówstworolnictwoziarna i nasiona oleiste
- nauki przyrodniczenauki chemicznechemia nieorganicznametale przejściowe
- nauki przyrodniczenauki chemicznechemia nieorganicznametale nieszlachetne
- inżynieria i technologiainżynieria materiałowapowłoki
- nauki przyrodniczenauki fizyczneelektromagnetyzm i elektronikanadprzewodnik
Aby użyć tej funkcji, musisz się zalogować lub zarejestrować
Temat(-y)
Data not availableZaproszenie do składania wniosków
Data not availableSystem finansowania
Data not availableKoordynator
HA9 7PP Wembley
Zjednoczone Królestwo