Effect of A Constant Electric Field on the Structure of the Oxide Layer Formed during Zinc Oxidation by Supercritical H2O and H2O/CO2 Fluids

It has been found that the interaction of a zinc anode with water under supercritical (temperature 673 K and pressure ≈23 MPa) and near-critical (673 K and ≈18 MPa) conditions at electric field strength of ≈300 kV/m produces an inhomogeneous ZnO layer containing regions with a capillary structure. The capillaries are oriented along the direction of the constant electric field and have an average diameter of ≈1 μm at 23 MPa and 50-100 nm at 18 MPa. During oxidation of zinc by supercritical H2O/CO2 fluid at 673 K and ≈35 MPa (molar fraction of CO2: 0.27-0.94) under the electric field conditions, a ZnO layer without capillary structure is formed. It has been found that the electric field promotes the growth of ZnO nanorods in the surface layer and the formation of zinc oxalate and carbonate, whose thermal decomposition produces the porous ZnO structure.