Oxidation at Elevated Temperature of Fe-42Ni-6Cr Alloy Used for Sealing

Abstract

Oxidation films of Fe-42Ni-6Cr alloy used for sealing of soft glass have been investigated. Oxidation of the alloy was carried out in air and in wet hydrogen. The results obtained are as follows.
(1) In the case of oxidation of the alloy is carried out in air, the oxidation film consists chiefly of α-Fe₂O₃ and Fe₃O₄, and the activation energy of oxidation changes at about 1000°C.
(2) In wet hydrogen, the oxidation film consists chiefly of Cr₂O₃ and (Fe, Mn)O·Cr₂O₃. The activation energy for oxidation is 28 kcal/mol and is nearly indepent of the humidity of hydrogen. The oxidation rate constant changes in proportion to the exponent of 1/2.5 of a partial pressure of oxigen and is almost independent of oxidation temperature.
(3) In wet hydrogen, in the initial stage of oxidation, the grain boundary of the alloy hill up. As the oxidation proceeds, the boundary becomes undistinguishable from the bulk, and three different whiskers of oxide have grown on the bulk. Those are the hill type, the needle type and the needle type with spherical crystallines on the top.