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.

Investigations on the Diffusion of Oxygen in Nickel at 1000°C by SIMS Analysis

“…Oxygen is indeed suspected to be the species responsible for the pinning of the grain boundaries promoting ductility minima at high temperature ͑700-800°C͒. 3,4 Second, concerning the internal oxidation method used to determine the oxygen diffusion in nickel, [11][12][13][14][15][16][17] the presence of additions such as chromium, beryllium, or silicon may have a great influence on oxygen diffusivity in nickel as the results are quite different from those obtained in high-purity samples using the SIMS technique for the analysis. However, in the present study, the occurrence of NiO particles in metallic grain boundaries ͑several hundred micrometers under the metal/oxide scale interface͒ after oxidation treatments must be cleared up.…”

“…The primary current was fixed to 100 nA and all the profiles presented in this paper have been obtained by using an 80 ϫ 80 m 2 raster size with an 8 m field aperture. The detection of 12 C − , 14 N − , 16 O − , 32 S − , 28 Si − , and 58 Ni − secondary ions was realized. As the profiles obtained for 12 C − , 14 N − , 32 S − , and 28 Si − do not show any peculiar aspect, they are not presented in this study.…”

“…Again, thanks to the video camera, the user can easily focus the primary ion beam on a grain boundary. The chosen area is then sputtered and images of the chosen elements ͑ 16 O and 58 Ni in our experiments͒ can be obtained. The lateral resolution of the images is about 0.1 m.…”

“…To determine the diffusivity of oxygen in nickel, measurements of the permeability of oxygen in nickel, i.e., the product of the solubility and the diffusivity, were first made [11][12][13][14][15][16][17] using the internal oxidation method in Ni-Si, 11 Ni-Cr, 12 or Ni-Be alloys. 13,14 To calculate the diffusivity from the permeability, the solubility data of Seybolt 8 were used in the above works except for Smithells and Ransley, 16 who used a constant value of 600 at ppm for the solubility.…”

In situ X-ray tomographic microscopy of Kirkendall pore formation and evolution during homogenization of pack-aluminized Ni–Cr wires

“…Another hypothesis is that the pores are gas-filled. It has been demonstrated that oxygen can penetrate relatively large distances, e.g., 250 µm after 200 hours air exposure at 1000ºC, into polycrystalline Ni alloys via grain boundary diffusion and react with impurity levels of carbon to form carbon di-or monoxide gas bubbles [49,50]. However, it has been determined that high, ~ 22 wt.%, Cr levels can reduce the oxygen activity enough to prevent this mechanism [50].…”