Site:           Fujikura, Ltd.
                Superconductivity Research Department 
                Materials Research Laboratory
                1-5-1, Kiba, Koto-ku
                Tokyo 135, Japan
                http://www.fujikura.co.jp/fujikuev.htm/
Date Visited:   7 June 1996
WTEC Attendees: J. Willis (report author), 
                D. Gubser, 
                D. Larbalestier, 
                M. Suenaga
Hosts:          Nobuyuki Sadakata, Manager, Superconductivity Research Dept., 
                   Materials Research Laboratory

BACKGROUND

Fujikura, Ltd., was established in 1885 in Tokyo to manufacture rubber insulated electrical wire and was incorporated as Fujikura Cable Works, Ltd., in 1910. The headquarters and plant were moved to their present site in Koto-ku, Tokyo, in 1923. This is also the location of the Tokyo R&D Center. Fujikura has three manufacturing plants in the Tokyo area and one near Nagoya. Fujikura has sales and manufacturing facilities in the Americas, including the United States, in Europe, and in Southeast Asia. These are about 50% owned by Fujikura and together contribute about 20% to total sales. Fujikura Cable Works, Ltd., was renamed Fujikura, Ltd., in 1992 to reflect the corporate goal to pursue non-cable business areas.

BUSINESS

Fujikura's original and still largest business area (approximately 70% of sales in 1995) is electric wire and cable, which includes products such as telecommunication cable, magnet wire, rubber- and plastic-insulated wire, and power transmission systems, including a new 500 kV underground cable. The second area is fiber optics and related products (19% of total sales). The third and a rapidly growing area is electronic materials and components (11% of sales), including such items as sensors, interface cables, flexible printed circuit boards, and membrane switches. Fujikura has been hard hit by the recession in Japan since 1991 and further by the appreciation of the yen in 1995. It restructured in October 1994 to respond to the recession. Net sales and net income have both been decreasing since 1991. Because of weak domestic demand, decreases in the wire and cable area have only been partially offset by increases in the other two product areas. For the year ending 31 March 1995, net sales and net income were $2.428 billion and $15 million, respectively. R&D expenditures were $106 million for the same period. The company's workforce grew to an all time peak of 4,365 in 1992, decreased by 100 in 1993, and then by another 100 in 1995 to 4,101.

SUPERCONDUCTOR RESEARCH AND DEVELOPMENT

Fujikura's R&D functions take place in five laboratories: Materials Lab, Advanced Technology Lab, Optoelectronics Lab, Energy Systems Lab, and Fujikura Technology America Corp. (FTAC). The Materials Research Lab has three divisions: Metallic Materials, Polymers and Chemicals, and Superconducting Materials. High temperature superconductor (HTS) R&D takes place at the Tokyo R&D Center. Metallic (low temperature superconductor, LTS) R&D and HTS wire manufacturing is done at the Numazu plant in Shizuoka Prefecture, about a one-hour train ride outside Tokyo. There are 20 researchers and technicians working on superconductivity. Of these, approximately 1/3 are working on LTS and 2/3 on HTS materials. Partial support of R&D activities comes from the New Energy and Industrial Technology Development Organization (NEDO) Super-GM project and through power companies, primarily Chubu Electric Power Company. These funding sources generally contribute less than half of the research funds for a particular project. Recent R&D at Fujikura focuses on research entrusted and consigned by NEDO (similar to contract work in the United States) and on collaborative research, always with shared funding, with electric power companies, universities, or national laboratories.

Fujikura management sees its most important R&D efforts to be on power transmission lines, generators, magnets, and current leads. Fujikura had no LTS or HTS products for sale at the time of the WTEC team's visit. Estimates of the future market for HTS products are $10 million, $100 million, and $5 billion in five, ten, and twenty years, respectively.

LTS

Fujikura has been active in superconductivity since 1970 when it began work on the development of force-cooled hollow conductors for fusion magnets using both Nb-Ti and Nb₃Sn in collaboration with MITI's Electrotechnical Laboratory (ETL). Fujikura then developed an internal tin plating method for Nb₃Sn wire production based on commercial 6% Sn bronze matrix material. It also developed a large current (10 kA at 10 T) Nb₃Sn hollow conductor in 1983. Starting in 1988, Fujikura began doing R&D for the Super-GM national project. Fujikura developed an in situ processed Nb₃Sn wire for the field coils of the 70 MW-class superconducting generator. The 1 kA ac wires have high mechanical strength and fine filaments (0.5 µm) for low ac losses. In a collaboration with Tohoku University begun in 1990, Fujikura has been developing a reinforced Nb₃Sn wire using a CuNb stabilizer for the conductor in the outer magnet (60-100 cm ID) of a hybrid magnet located at the university; the inner coil is a water-cooled copper magnet. The wire performed up to the very high stress levels of 224 MPa at 9 T during testing. Since 1991, Fujikura has been working in collaboration with Tohoku Electric Power Co. to produce a magnetically controlled 1 kA-class, fast response (20 ms) persistent current switch (PCS) for a small, quick response SMES for electric power conditioning. Finally, in 1993, Fujikura began development of a 600 A Nb-Ti ac conductor for a coreless autotransformer in a collaboration with ETL. This requires cabling of wires to achieve the current required and fine filaments to achieve a low ac loss conductor. Fujikura sells few LTS products; it mainly produces R&D materials.

HTS R&D

Fujikura started oxide superconductor work in 1986, focused in three main areas: Y-123 coated conductors, Bi-2223/Ag sheath tapes, and Y-123 bulk rods. There are 12-13 researchers working in this area, divided about 40%, 40%, and 20%, respectively, between these three categories.

Fujikura pioneered and had the earliest successes with the ion beam assisted deposition (IBAD) process for preparing a biaxially textured buffer layer of yttrium-stabilized zirconia (YSZ) on top of a polycrystalline nickel alloy (Hastelloy) substrate. One ion gun is directed at the YSZ source and causes deposition of YSZ on the Hastelloy substrate while a second assisting ion gun directs Ar ions at the substrate at an angle near 55°, which has the effect of causing the YSZ film to be biaxially oriented (<100>) with respect to the substrate. Figure 5.12 (p. 73) shows the IBAD apparatus. A YBCO superconductive film is then deposited on the YSZ buffer layer by conventional deposition techniques, such as pulsed laser deposition (PLD). This film grows epitaxially on the YSZ and shows good c-axis and a-b-plane orientation, and as a result, good critical current density (J_c) properties. Figure 5.3 (p. 65) shows the layers in the conductor. Transmission electron microscope (TEM) orientation analysis of Fujikura's YBCO films shows that more than 50% of the grain boundaries have misorientation angles of less than 5°, and ~80% have angles of less than 10°. In addition, fewer dislocations are observed near the low angle grain boundaries. Short sample (1 cm) J_c values for a 0.4 µm thick film are greater than 1 MA/cm². At the time of the WTEC visit, the most recent long length result for this process was 0.17 (+/- 10%) MA/cm² and 18.1 A at 77 K and 0 T for an 0.8 m long, 1 cm wide, 1 µm thick Y-123 film. Y-123 films can be deposited at a rate of 1 m/h. This work is being done as an entrusted research of Super-GM, supported under the New Sunshine Program of AIST, under MITI, and consigned by NEDO.

For the IBAD process films to be used as long length conductors, it is necessary for the production process to be rapid. To accomplish this, Fujikura is also using metallorganic chemical vapor deposition (MOCVD) to deposit the YBCO on Hastelloy substrates 0.2 mm thick by 5 to 10 mm wide with an intermediate length goal of 1 m. The goal is to develop a continuous process for depositing a 10 µm thick YBCO film 10 m or more in length. Present issues being investigated are the presence of a barium zirconate reaction layer 15-20 nm thick on the YSZ buffer layer. The depletion of Ba may be responsible for the formation of second-phase precipitates of CuO in the rest of the film; these precipitates are thought to be responsible for the variation in J_c along the tape length. Also being investigated is the control of oxygen partial pressure by feedback from a residual gas analyzer. The oxygen partial pressure tends to change during a deposition in the hot wall reactor, resulting in Y-123 film stoichiometry variation. The best MOCVD deposited Y-123 on an IBAD YSZ buffer layer on Hastelloy yielded 0.21 MA/cm² and 17 A at 77 K and 0 T over 16 cm; the highest J_c value over 1 cm is 0.6 MA/cm². Film deposition rate is about 0.5 m/h. As yet, the thickness uniformity, alignment, and phase purity of the Y-123 films are not as high as that produced by PLD. This work is being done in collaboration with Chubu Electric Power Company.

Bi-2223/Ag sheathed 37-filament tape is being produced for use in an electric utility power cable. Fujikura has investigated fundamental issues, such as the effect of particle size on Bi-2223 phase formation, and practical properties, such as ac losses for tapes singly and in conductor configurations. Fujikura has recently designed a model flexible cable 150 mm in diameter to operate at 77 kV with cooling stations every 5 km. A 5 m long prototype was constructed using 37-filament Bi-2223/Ag tapes arranged in 10 stacks spaced radially in a 20 mm ID, 45 mm OD conductor. This carried 1.2 kA both before and after insulating with a semisynthetic paper and after fully fabricating the thermal insulation and outer sheaths. This work is also being performed in collaboration with Chubu Electric Power Company.

Bulk Y-123 current leads have been produced for power applications. The Y-123 is doped with Y-211 and Pt and Ag additions, cold isostatically pressed into rods 2-3 mm in diameter and 2-10 cm long, presintered, then directionally melted and solidified with a toroidal heater. It was found here (other groups have reported similar results) that Y-211 forms small pinning centers and that adding Pt constrains the size of the Y-211 precipitates and adding Ag helps prevent cracking. Fujikura has explored doping levels and obtained I_c values of 1,500-1,800 A and J_c values of 33 kA/cm² at 77 K, 0 T for the best rods 2-3 mm in diameter over a 2 cm gauge length. The Ag and Pt additions greatly improved the surface roughness of the melt-processed rods. Optimum conditions were achieved for Y-211 additions of 10:3 or 10:5 (Y-123:Y-211), Ag content of 5 wt %, and Pt content of 0.5 or 1 wt %. Growth rates of 1 mm/h gave slightly better results than at 3 mm/h. This work is being done in collaboration with Chubu Electric Power Company.

SUMMARY

Fujikura is producing high quality conductors and making important contributions to LTS applications, which continue to be supported by the national government and power companies. In the HTS area, Fujikura is one of the leaders in Y-123 coated conductor work and is also producing prototype power transmission cables. Continuation of HTS R&D at Fujikura will require ongoing external support.