Reactive deposition of metal thin films within porous supports from supercritical fluids

Continuous palladium films were synthesized at controlled depths within por ous alumina disks by Ha reduction of organopalladium compounds dissolved in supercritical CO2 at 60 degreesC using an opposing reactants deposition ge ometry. Film position was controlled by adjusting the relative concentratio ns of Ha and the palladium precursor (pi -2-methylallyl(cyclopentadienyl)pa lladium (II) or palladium(II) hexafluoroacetylacetonate) on opposite sides of the alumina substrate. Because of a disparity in the diffusivity of the metal precursor and Hz in the support, a temporary barrier of poly-4-methyl -1-pentene on the H-2 Side of the alumina substrate was used to reduce Ha f lux in a controlled manner. Guided by a simple mass transport model, Pd fil ms between 2 and 80 mum thick were deposited at prescribed depths between 8 0 and 600 mum as measured from the precursor side. Electron probe microanal ysis indicated complete pore filling of the porous alumina at the reaction zone and X-ray diffraction revealed that the structure of the deposit is na nocrystalline. The flux of Na through the alumina disk was reduced by over 4 orders of magnitude after deposition and annealing at 500 degreesC.