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Content archived on 2024-05-29

Coated conductor by economic processsing route (COCON)

Final Report Summary - COCON (Coated Conductor by economic processsing route)

The COCON project targeted the creation of a new and more economic production technology for coated conductors. The project was characterised by scientific and technical improvements and breakthroughs as well as by administrative and economic problems.

First the metallic substrate was defined and intensively studied. The material is a nickel-tungsten-alloy that alloy offers good mechanical properties and allows a high deformation induced biaxial texture. This texture is essential because it acts as a template for the orientated growth of the following layers on the substrate necessary for high electrical performance. The consortium succeed in the production of high-quality long-lengths tapes up to 100 meters either in a batch process and as the first in the world in a continuous crystallisation process. Studies on the surface and the ageing of the tapes allowed a deeper understanding of corrosion processes. Continuous X-ray analysis enabled an in situ quality control.

After testing of different buffer materials lanthanum-zirkonate (LZO) was identified to be the most promising main buffer material. The buffer layer was successfully applied on the substrate by the chemical solution deposition (CSD) process. A special precursor chemistry of the coating solution was developed in the project based on propionic acid. The layer deposited from this new chemistry showed highest texture sufficient for the deposition of the following superconducting layer. A patent was filed by the consortium claiming this special precursor chemistry.

The superconducting material used in coated conductors is yttrium-barium-copper-oxide (YBCO). The precursor solution for this layer was based on TFA. On small samples the consortium succeeded in depositing a superconducting layer on a buffer layer both prepared by a CSD method. This result was really in the forefront of international research, because the main competitors still deposited at least parts of the layer architecture by cost intensive physical vacuum deposition techniques.

After the successful development of the architecture of the coated conductor processed via an all solution chemical coating in the first reporting period the scientific effort in the second reporting period concentrated on the adaption and upscaling of the basic research results. An important milestone was the delivery and successful installation of the continuous coating device for lengths up to 50 meters. Five meters of a fully textured metal substrate tape with a multilayer buffer architecture were processed. The architecture consisted of two LZO and one cerium oxide (CeO) layer. The deposition of the superconducting layer was demonstrated on short samples, but due to the lack of an appropriate annealing furnace so far only one metre samples could be processed. Nevertheless first steps towards an up-scaling o the coating solution by an industrial partner were made with encouraging results.

Another remarkable result was the worldwide first successful optimisation of the inks and the heat treatment for complete textured buffer layers by ink-jet-coating. Additional research efforts dedicated to a long term development like the electrochemical Ni-coating of substrates and the ink-jet-printing for reduced alternating current (AC)-losses were performed, but due to the lower priority compared to the up-scaling some minor deliverables, especially for AC losses, were not fulfilled. Nevertheless basic studies for structuring and patterning of coated conductors led to another patent application on two-dimensional negative printing.

The good scientific and technical results were reached in an extremely difficult environment. The near financial breakdown of the partner KRAFT electronics and the insolvency of the coordinator Trithor in summer 2006 caused massive delays and uncertainties within the project. Over more than half a year the legal status of the project was unclear and due to this some key persons left the research and technological development (RTD) partners, because contracts could not be renewed. Nevertheless all partners agreed in keep on working on this promising topic in the overall successful project even in the unclear situation and with the financial risks for the partners.

One of the major problems in commercialisation was described by Joseph Mulholland in his study 'Analysis of future prices and markets for high temperature superconductors' for the United States (US) Department of Energy from September 2001 as the 'chicken and egg' problem. The problem was that all market penetration problems were only valid, if the produced amount of tape and the number of devices was high enough. Therefore it was important for the exploitation of the results that HTS applications were realised with the available first-generation tape in order to allow a broad market introduction of the second generation tape when the up-scaling or the process was finalised. The strategy was to introduce coated conductors as fast as possible into applications to demonstrate the general feasibility. This fast access to applications would allow an accelerated market introduction compared to the first generation HTS tapes.

The main markets were considered generators, motors and cables. Special applications like linear motors, induction heaters, magnets or fault current limiters were addressed in industrial cooperative projects.