Structure micro- and nanomodification by cyclic oxidation-reduction treatment of porous nickel sintered using a space holder

By performing high-temperature cyclic oxidation-reduction (redox) post-treatment of biporous nickel fabricated in the sintering-dissolution process using micron nickel powder and sodium chloride as a space holder, permeable materials with multilevel hierarchical porosity were created. After an oxidation stage in an air atmosphere, a porous material with a core-shell Ni – NiO structure and a cellular underlayer of micron-sized Kirkendall pores was formed. Subsequent reduction in hydrogen led to the formation of a developed nanoporous bumpy surface at sintered nickel particles. The obtained metallic nickel and ceramic nickel-oxide materials contain a hierarchical system of pores of different origin of four types: (a) macropores formed after the removal of the space holder; (b) interparticle micropores remaining due to incomplete sintering of the nickel powder; (c) intraparticle Kirkendall pores created at the oxidation stage and (d) nanopores formed during reduction. Depending on the dispersion of the space holder, the porosity and hydraulic permeability of the nickel samples were 80 – 82 % and 35·10–12 – 101·10–12 m2, respectively.