Properties of nanostructured oxide formed during oxidation of a zirconium wire by supercritical water

Synthesis of ZrO$_2$ during oxidation of a zirconium wire by supercritical water at $P$ = 25 MPa and $T$ = 500 or 525$^\circ$C has been investigated. It is established that an inhomogeneous nanostructured ZrO$_2$ layer is formed as a result of oxidation. Rate of $\langle$Zr$\rangle$ oxidation, oxide porosity and morphology, and average size and structure of crystallites are determined. The thermal conductivity of the synthesized ZrO$_2$ layer in supercritical water and in nitrogen is determined by pulsed electric heating of a partially oxidized wire. The low values of thermal conductivity (about 0.2 W/(m K)) correspond to a layered structure of porous material, with layers orientated parallel to the oxidized-metal surface.