This was a short-lived project that in some ways is related to our prior work on carbon nanotube growth, described elsewhere on this site. When metals, such as process tubing, are exposed to a gas atmosphere with a carbon activity greater than one, two things can happen. One is that carbon deposits can form, fouling the process equipment. The other is that the carbon can penetrate into the metal and cause it to disintegrate slowly forming a metal dust. The objective of this project is to develop quantitative models for the processes that lead to this metal dusting phenomenon. A few different qualitative mechanistic models have been presented in the literature. They all seem to concur that carbon diffusion into the metal is an underlying reason, but they tend to be somewhat vague in fully specifying the path along which diffusion occurs and what establishes the carbon activity gradient along that path. In some cases the pathway is not clearly identified, and in others carbon appears to enter the metal and later leave it, with both processes occurring through the same face and both attributed to diffusion. That is, they seem to require carbon gradients in both directions through the same face of the metal.

We have encountered an additional complication in our early experimental work, that has also been seen in recent literature reports. Specifically, most models assume that the diffusion into the metal is the rate limiting process, and consequently they assume that the gas phase establishes an equilibrium surface carbon activity that drives this diffusion. If this were true, then one could use either a CO/CO₂ mixture or a CH₄/H₂ mixture, and as long as they had the same carbon activity, the diffusion rate would be the same. We have performed experiments where this expectation is not met, and there are similar observations elsewhere in the literature.