TEM study of nanopores and the embrittlement of CVD nickel foam

AbstractNi foam, manufactured by depositing Ni onto polyurethane foam using the carbonyl CVD process, exhibits brittleness which has been correlated with the presence of a high number-density of 'nanopores'. These nanopores, which were typically less than ~25 nm in diameter, tended to be associated with sulphur, which is present in the form of H2S as a catalyst during the deposition process. The as deposited foam also shows significant hardening, ascribed to the high density of nanopores. This hardening may also help to reduce the ductility compared to well annealed nickel foam. High temperature annealing restores the foam to the high ductility typical of high purity nickel by coarsening the nanopores and removing the sulphur. The failure of the pores to sinter during high temperature annealing indicates the presence of stable gas molecules, the pressure from which balances the surface tension forces that drive sintering.