The diffusion of gases through metals III-The degassing of nickel and the diffusion of carbon monoxide through nickel.

Abstract

When a piece of metal prepared by a commercial process is heated for the first time in vacuo , a considerable amount of gas is usually evolved. With the more refractory metals like nickel or molybdenum, evacuation for a few minutes at 1000° C is sufficient to remove part only of gas present, and prolonged heating for many hours is necessary before the evolution ceases to be measurable. It may be assumed that some part at least of this gas is derived from the body of the metal and must presumably reach the surface by diffusion. The total gas is extracted much more rapidly if the metal is actually melted, and this method of estimating the gases in steel and other metals has been very generally adopted. The fact that the evolution of gases from metals on heating depends upon a process of diffusion from the interior to the surface of the metal, and subsequent evaporation, has been established for the simple gases. The desorption of nitrogen from molybdenum, and of hydrogen from hydrogen-charged nickel has been shown to follow theoretical equations derived from Fick's diffusion law. In practice, the gases obtained from commercial metals often contain a large proportion of compound gases, particularly the oxides of carbon, but very little information is available on the diffusion of such gases through metals.