Some Effects of Heating Zirconium in Air, Oxygen, and Nitrogen

Abstract

Zirconium metal was heated in nitrogen, oxygen, and air at temperatures ranging from 425 to 1300 C. Observations were made on the gain in weight, micro-and macrohardness, and metallographic structures. Nitrogen diffuses into zirconium at a much slower rate than oxygen. A marked increase in penetration of both gases was found near 900 C, and this is evidently associated with the allotropic transformation from' hexagonal, to cubic form. Practical limits for the heating of zirconium in air, oxygen and nitrogen are given and the possibilities of producing hard surface coatings are discussed. INTRODUCTIONThe advent of Zirconium metal in quantities sufficient for thorough studies of the properties of the metal has been reported previously by the Bureau of Mines, U. S. Department of the Interior (1, 2, 3). This metal, which is produced by the magnesium reduction of zirconium chloride, continues to be the subject of considerable research. In the production of sheet, rod, and other shapes for various test purposes, it has been found (4) that the metal work hardens rather rapidly at room temperature and in general will take only 40 to 50 per cent reduction by cold working. The obvious answer of hot working is complicated by the fact that zirconium, when heated, reacts avidly with oxygen and nitrogen. It has been known for many years that small amounts of oxygen and nitrogen, when dissolved in the metal, cause it to lose its ductility, but no systematic approach seems to have been made to determine the effects of oxygen and nitrogen on ductile zirconium, that is, the limits to which it may be heated in either gas or air without impairing its desirable physical properties.The investigation described in this paper was undertaken with the object of determining the practical limits to which Bureau of Mines zirconium could be heated in oxygen, nitrogen, or air without deleterious effects. As a secondary feature, the general nature and hardness of the surface coatings produced were studied from the standpoint of hard-surfacing materials for zirconium. The hardness of some of the films proved so interesting that attempts were made to determine their stability when reheated in air.Fast (5) annealed zirconium made by the iodide process in vacuum, air, and a gas flame. His work was largely qualitative, in that it was restricted to a few minutes. He concluded that heating 3 to 5 minutes in air at 650 C was the maximum for thin (0.012 in.-0.305 mm) sheet.

Oxidation, Embrittlement, and Growth of TREAT Zircaloy-3 Cladding

“…Above the alpha-to-beta phase transformation the diffusion of oxygen into the metal was rapid." Alpha zirconium transforms to beta zirconium above 862°C as reported in Hayes, 1949. Both confirm that oxygen does not diffuse into zirconium below 862°C.…”

“…The above three correlations were extrapolated to 900°C and are shown in Figure 6 along with other data. Hayes [19] made measurements on zirconium in moist air up to and including 900°C. Hayes was only able to obtain oxidation data at 900°C for 1 hour whereas his 500 to 800°C data were gathered over a 24 hour period.…”

“…Hayes [19] concluded that the increase in the oxidation rate at 900°C is due to the change from alpha phase zirconium to beta phase zirconium at 862°C. He states "Microscopic examination of all specimens shows that there is no evidence of oxygen or nitrogen penetration into the body of the metal below 700°C.…”

GAS-SURFACE INTERACTIONS FOR SNAP FUEL PARTICLE REENTRY. Thermo-Physics Technical Note No. 59.

“…The absorption of NT, which occurs at a much slower rate than the absorption of oxygen, shows an increase in penetration into the body of the metal above the transformation temperature of 862°C as for oxygen (44) The rate of reaction of zirconium with nitrogen is much slower than reactions with oxygen. The (36) (27) rate law followed is parabolic.…”

SCALING OF ZIRCONIUM AND ZIRCONIUM ALLOYS. Technical Progress Report No. 1

“…The reaction rate· followed approximately the parabolic rate law for a time and then increased sharply. 2 Garibotti, Green, and Bald'Nin 6 performed research on zirconium scaled in air, nitrogen, oxygen, and mixt'ures of ni~rogen. and oxygen.…”