Synthesis of porous metals Keiji Nagai ILE Osaka

Contents  Sphere temple method Established synthetic method to prepare porous material.  Design of porous tungsten for the wall material.  We will discuss about the merits and demerits of porous tungsten. 1) Controllability of the synthesis. 2) high surface area (>100m 2 /g). 3) conductivity.  Future plan as a summary

Sphere temple method is powerful tool to prepare porous material. K. Nagai et al., Trans. Mater. Res. Soc. Jpn., 29 (3) 943 (2004) Pore size and density were well controlled by the template spheres. I um I0 um Liquid metal source Removal of template

Surfactant-free emulsion polymerization to prepare mono-dispersed sized nanoparticles Styrene/water~1/9 80 o C, 24 hours Water suspension 100  m Nanoparticle film

Porous metal tin (Sn) was prepared electrochemically. 1 mm Porous Sn film 2  m Thickness: 10 µm, Density: 20% of  -Sn Nagai et al., Fusion Sci. Technol SnSO 4 electrochemical plating -> Sn metal Removal of PS using toluene Electrode PS template

Lithium can be filled into the voids of porous Sn. Electrode deposition of Li 1  m Sn Li Nagai et al., Laser Partcl. Beams 2008

Thickness: 2 µm, Density: 4.3g/cm 3 (23% of Au) Porous metal gold (Au) was also prepared electrochemically. Nagai et al., Fusion Sci. Technol., 49 (4), , (2006). [Au(CN) 2 ] - electrochemical plating -> Au metal Electrode 1 mm

Helium implantation & thermal conduction (100 MW m -2 s 0.5 )* are the erosion mechanisms. * After TJ Renk pulse duration / s Heat Flux Parameter P x sqrt (t) / MW m -2 s 0.5 RHEPP-1 B R - roughening C - cracking M - melting B - boiling M R M M M C C Performance of Tungsten under short transient thermal loads Thermal conduction is a dominant mechanism J. Linke et al, JNM (2007)

Polycrystalline Tungsten He exposure behavior pulses Pulsed Power Sciences, Sandia National Laboratories TJR 9/27/2008 Ave 0.8 J/cm 2 / pulse Ave 1.4 J/cm 2 /pulse All samples initially Room Temperature (RT) ~1000°C Average MaxTemp (50 µm) 350 GW/m 2 /pulse  Average maximum surface temperature < 1500°C  No effect 1st 400 pulses: below threshold  Using √t scaling: 0.8 J/cm 2 equivalent of 0.4 MJ/m 2. Consistent with QSPA plasma exposure of tungsten PFCs (ref: A. Zhitukhin et al, JNM (2007)  Final J/cm2: probable cumulative mass loss 400 pulses 800 pulses 1200 pulses 1600 pulses All images 1000X magnification ~1500°C Average MaxTemp ~600°C Average MaxTemp Ave 0.6 J/cm 2 /pulse Ave 0.85 J/cm 2 /pulse ~1050°C Average MaxTemp (Est) total He implantation ~ 1.8e16 /cm 2 Ra ~ 1.5 µm After TJ Renk

Design of porous tungsten  Porous tungsten has merits of 1) small and controllable distance of nanowall. 2) high surface area (~100m 2 /g) for high radiation cooling.  Porous tungsten has demerits of 3) poorer conductivity than the metal bulk. 4) mechanical fragility.

1) The template technique gives small and controllable distance of nanowall. n=2 n=4 n=6 n=10 Q.C.Gu et al., Chem. Mater., 17 (5), , (2005). More EtOH (n), lower contact angle (higher affinity for PS) n=2 n = EtOH mol / SnCl 4 mol Volume template -> Closed cell n=10 Surface template -> Open cell Volume template vs. Surface template SEM images before removal of template

2) The template technique gives high surface area (~100m 2 /g) which would effective for radiation cooling.  An example of surface area of 60 m 2 /g Q.C.Gu et al., Chem. Mater., 17 (5), , (2005). The porous SnO 2 shows a hierarchical pore system at three different scale length, 1) mesopore, the interparticle space (<10 nm), 2) small macropore-window ( ∼ 10 2 nm), and 3) large macropore-cell ( ∼ 10 3 nm). 1  m BET isotherm

3) Estimation of conductivity of the porous metal.  Current during the electroplating is an indicator of the conductivity of the porous metal. V A Working electrode Reference electrode gives relative potential (V) from Ag + /Ag 0 Counter electrode pf platinum supplies the current (A).

Estimation of conductivity of the porous metal V vs Ag/AgCl V vs Ag/AgCl V vs Ag/AgCl V vs Ag/AgCl Although the over potentials for porous metal plating mean the larger resistance than the bulk, the time independent currents indicate that that is due to the interfaces.

coulomb efficiency of the electrochemical plating ________________________________________________________ materialthicknessweightdensityelectric coulomb charge efficiency [  m/cm 2 ][g/cm 2 ][g/cm 3 ][C/cm 2 ] ________________________________________________________ bulk Sn porous Sn bulk Au porous Au ________________________________________________________ coulomb efficiency = Faraday const. x (mole of metal)/charge We did not find a large difference of conductivity between the bulk and porous metals.

Two arrayed needle geometries investigated  Left: ‘ Array ’ - Sewing needles and dressmaker pins on Al-6061 substrate, mylar strip in center. Hole diameter 0.029in, 175 drilled into 1/8 in substrate 0.060in apart.  Needle Composition; high carbon steel with Nickel plating  Bottom Left: ‘ Bundle ’ - sewing needles tied together by wires  Below: Arrays mounted before 400 shot He series Pulsed Power Sciences, Sandia National Laboratories TJR 9/25/2008 Cost ~ $5 HAPL After TJ Renk Needle like millimeter-sized structure is effective to decrease the threshold per cross section area.

Control of pore in micro~milli-meter  Millimeter sized pore tungsten would be a candidate material as seen in the tungsten needle. Liquid metal source Removal of template We can prepare millimeter pore by changing millimeter templates

Millimeter sized templates can be prepared using droplet generator and emulsion technique. W1W1 OW2W2 Compound emulsion W2W2 W1W1 O W 1 : inner water W 2 : outer water O: oil

Future plans  Ion beam irradiation using RHEPP-1 at SNL.  Estimation of the resistivity depending on the thickness (~50 nm)  Re-design of the porous tungsten.  PISCES irradiation