To facilitate a realistic prediction of the chemical reactivity of materials such as plasma sprayed Be, irradiated Be with porosity, and tokamak dust, we have measured BET (Brunauer, Emmett, and Teller) surface areas for various materials. These data are important in ITER fusion safety studies that evaluate the accidents in which plasma-facing components are exposed to air or steam. Correlation of measured surface areas for test materials with chemical reaction rates establishes a baseline for predicting chemical reactivity for fusion-relevant materials.

In this paper we present the results of surface area measurements for steel powder, porous and full-dense beryllium, graphite powders and larger graphite pieces. The results are based on gas-adsorption measurements in which N2 was used as the adsorptive for high surface area samples and Kr was used for samples with low specific surface area and small sample size. To evaluate our approach for measuring surface areas for low specific surface area samples, we conducted Kr gas-adsorption measurements for centrifugally-atomized type 304 stainless steel powder. These measurements provided a BET surface area of 0.018 m²/g, a value about 40% higher than the geometric surface area for the nominal 56 micro-m diameter, spherical steel powder. The higher BET surface area is attributed to surface roughness associated with dendritic and cellular microstructure formed during solidification of the powder. To obtain background information for plasma-sprayed and irradiated beryllium samples, we measured surface areas of cylindrical beryllium samples that were hot-pressed and sintered, with densities ranging from 80 to 100 % theoretical density. Kr gas-adsorption measurements for samples of 80 and 85 % theoretical density yielded a nominal BET surface area of 0.2 m²/g. Assuming that the adsorbing gas has fully penetrated the porous Be specimens, a measured BET surface area of 0.2 m²/g would correspond to specimens fabricated from spherical powders of about 15-micro-m diameter, in good agreement with the 18-micro-m mean particle diameter of the sieved powder that was actually used in the fabrication. Kr gas-adsorption measurements for samples of 97 and 100 % theoretical density provided BET surface area estimates that were about two orders of magnitude below that for the porous Be, but still several times greater than the calculated geometric surface areas. In support of our efforts to characterize dust from a carbon-based tokamak such as DIII-D, we measured BET surface areas for bulk pieces and various size powders of POCO, AXF-5Q graphite. BET surface areas for the graphite powder particles increased from 3 to 33 m²/g as particle diameter decreased from 63 to 15 micro-m. These values are in reasonable agreement with values in the literature for comparable graphite powders.

*This work is supported by the U. S. Department of Energy, Director of Energy Research, Office of Fusion Energy Sciences, Idaho Operations Office, under Contract DE-AC07-94ID13223.