Concentration dependent diffusion of carbon in tungsten

This paper concerns with the concentration dependence of the C diffusion in W. An effective, concentration dependent diffusion coefficient D(C) was used to model the diffusion of C in W in the temperature range from 1000 to 1100 K. D(C) was thereby determined experimentally by a Boltzmann–Matano analysis of depth profiles taken from C–W diffusion couples. In cases where this analysis was not applicable, additional values for D(C) were also obtained by iteratively fitting measured depth profiles using the diffusion code DIFFUSEDC and adjusting D(C) accordingly. All depth profiles were measured using Rutherford backscattering. The effective diffusivities were found to be below the limits of the method used (<10−22 m2/s) for temperatures below 1000 K. Between 1000 and 1100 K they are in the order of 10−19 m2/s and strongly dependent on the C concentration. This concentration dependence exhibits a sharp drop of approximately one order of magnitude for C concentrations larger than 20–40%.