THE OXIDATION AND CORROSION OF ZIRCONIUM AND ITS ALLOYS XI. THE OXIDATION KINETICS OF ZIRCONIUM-NIOBIUM BINARY ALLOYS IN STEAM AT 300-500°C

摘要

Kinetic data on the oxidation of zirconium-niobium binary alloys in steam at 300 - 500°C and 1 atmosphere pressure are presented. Alloys contained 2, 5, 10, 15, 20, 30, 40, 50, 60, 70 and 80 per cent by weight of niobium in sponge zirconium. Additions of niobium to zirconium of between 20 and 50 wt.% result in retardation of the characteristic "breakaway" oxidation to times longer than those found for zircaloy-2;spalling of the oxide from alloys of this type masks rate transitions occurring at long times. Oxidation tests in which spalled oxide was retained showed that a rate transition occurs for alloys containing more than 50 wt.% niobium before the normal zircaloy-2 curve is crossed. Data are compared with that for zircaloy-2 rather than zirconium since any alloy having commercial value must compete with zircaloy-2, the currently accepted material for reactor use. It is considered that in view of the low hydrogen absorption found with alloys containing 20-40% niobium, they have sufficiently superior corrosion resistance over zircaloy-2 to merit further study. Further study is needed of the processes involved in the sharp rate transitions observed with some alloys, and the reasons for the apparent recovery which occurs subsequently.