A. Iwamoto

H. Homma

K. "Nagai

M. Nakai

T." Norimatsu

Y. Iyoda

National Institute for Fusion Science (NIFS-Repository)

Precise mass production of fuel capsules is requiredfor inertial fusion energy system [1]. The use ofmicrofluid device is a promising technology in the targetfabrication [2]. In this year, we provide precisefabrication of monolithic low density metal oxide using amicrofluid device [3].The advantage of the electrospinning sol-gel method is thatthe microstructure of the metal oxide fiber sheet can bedesigned and fabricated repeatedly to meet the demand ofthe target in a very convenient way. In the case of theprevious study on SnO2, the diameter of the fiber is afunction of the concentration of SnCl4 in the precursor [4].By increasing the concentration from 2.5% to 7.5%, thediameter of the SnO2 fibers increase from 180 nm to 460nm with densities of 0.825 g/cm3 to 0.214 g/cm3,respectively. When the fabrication parameters were fixed,both the morphology and the density of the mat were fixed,and the mass of SnO2 mat per unit area only correlated withthe thickness of the film. In order to obtain lower densitythan those of the previous report of SnO2, we preparednanofiber containing smaller concentration than those forSnO2. But in such cases the shrinkage during thecalcination was too large to obtain the density lower than50 mg/cm3. In order mitigate the shrinkage, the metalsources increased in comparison with the case of tin, thenthe optimized conditions were different from the scalabilityfor the case of SnO2.Figure 1. Schematic illustration of the basic setup forelectrospinning.Although SnCl4 is soluble in ethanol, other metal chloridesare sometimes difficult. PVP can be dissolved in water,while aqueous PVP does not easily give electrospinningnanofiber due to the low vapor pressure. In this study forother metals, ethanol/water mixture is chosen as solvents inorder to satisfy the two necessary conditions, 1) highsolubility of metal chloride, and 2) complete evaporation ofsolvent during the flight from the injection nodule to thenanofiber collector of the counter electrode. When thesolvent remained on the counter electrode, severe shrinkagehappened and density increased. For the vanadium, thewater content reached to 12.5 wt%.Another requirement is viscosity of precursor solution. Inthe present study, Mw was chosen to 44,000.Figure 2 shows obtained laser targets of copper andvanadium oxides. The area are well controlled to be 1.5 x2.0 (mm)2 for both cases. This area is typical for lasertargets of Gekko XII experiments. The densities are 27+2and 40+5 mg/cm3 for copper and vanadium oxides,respectively, which agrees to the specifications of the targetdesign at the experiments. Furthermore, these low densityof copper and vanadium oxides are difficult using otherfabrication technique such as aerogel method.(a) (b)Figure 2. The optical images of the monolithic and low-density (<50 mg/cc) metal oxides. CuO of 1.0d x 1.5w x2.0h (mm)3 (left) and V2O5 of 0.6d x 1.5w x 2.0h (mm)3(right).In order to determine the chemical composition of them, theweight of the metal component was measured using ICP(induced coupled plasma) analysis. These values supportsthe compositions of CuO(H2O)0.75 and V2O5. The x-raydiffraction patterns also agreed to those in the previousreports of CuO and V2O5. The SEM images shown in Fig3 are quite crystalline shape and different from the cases ofSnO2. In the case of V2O5, it is anisotropic and its lengthwas ~5m (a). The CuO did not show such large size andwas ~100 nm crystals which continuously connects one-dimensionally (b). Both anisotropic morphologies implythe formation of the crystals based on the initial nanofibricstructures.To summarize, by the use of electrospinning technique,metal halide containing PVP nanofiber film was obtainedfor cupper and vanadium. The nanofiber mats can be cutto centimeter-sized monolithic films. The films wereconverted to monolithic low-density metal oxides bycalcination. The density was less than 50 mg/cm3. Themetal oxides had anisotropic structures.(a) (b)Figure 3. SEM images of calcinated low-density metaloxide: (a) V2O5 (b) CuO.1) Norimatsu, T. et al, Fusion Sci. Technol., 49 (3), 483-499, (2006).2) Nagai, K. et al., Nuclear Fusion, 49 (9), 095028 (9pages), (2009).3) Nagai, K., et al., Fusion Sci. Technol, 59 (1), 216-220,(2011).4) Pan, C., et al., J. Appl. Phys., 100 (1), 016104, (2006).518§40. Control of Microfluid Devices towards Mass Production of IFE TargetsNagai, K., Iyoda, Y. (Tokyo Institute of Technology),  Iwamoto, A.,  Homma, H., Nakai, M., Norimatsu, T. (ILE, Osaka Univ.)

Control of Microfluid Devices towards Mass Production of IFE Targets

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