OXIDATION BEHAVIOUR AND ELECTROCONDUCTIVE PROPERTIES OF Si_3N_4 DOPED ZrB_2

摘要

Zirconium diboride sintered with 2.5wt% Si_3N_4 was oxidized in pure oxygen in the temperature range 850-1100℃ in a thermal balance for up to 24 hrs. At temperatures up to 850℃, a forming scale effectively blocks oxygen penetration. At temperatures up to 1100℃, the oxidation is well described by parabolic gain and superimposed linear evaporation. The process produces a layer of monoclinic Zirconia plus a partially or wholly removed layer of boric oxide after oxidation. The change in resistivity of oxidized samples is much higher than predicted from a simple change in cross-section. Therefore there must be a zone influenced by the oxidation treatment, which extends far deeper into the sample than visible to local chemical analysis. The change in resistivity correlates well with advancing oxidation and has the capability to be used as a corrosion monitor.