Reduction in piston-cylinder experiments; the detection of carbon infiltration into platinum capsules

Problems associated with intermittent and variable degrees of sample blackening are often reported for studies involving the preparation of CO 2 -bearing silicate glasses in piston- cylinder apparatus. This phenomenon is generally attributed to H infiltration, which leads to the reduction of CO 2 and the precipitation of graphite with the concomitant formation of water. In this study we demonstrate that carbon diffusion into platinum capsules may be a common cause of blackened glasses and this process may be detected using fourier transform infrared spectroscopy (FTIR) to identify the presence of CO without elevated H 2 O contents. The simulated infiltration of 12 C from a graphite furnace into a 13 C -bearing sample is illustrated using secondary ion mass spectroscopy (SIMS) and micro- FTIR analysis. Careful FTIR monitoring of variable sample reduction has helped to identify the precautions required to reduce C (and H) infiltration in solid media assemblies and it appears that physical barriers can be more important than the chemical buffers traditionally employed.