REDUCTION IN PISTON-CYLINDER EXPERIMENTS - THE DETECTION OF CARBON INFILTRATION INTO PLATINUM CAPSULES

Problems associated with intermittent and variable degrees of sample b lackening are often reported for studies involving the preparation of CO2-bearing silicate glasses in piston-cylinder apparatus. This phenom enon is generally attributed to H infiltration, which leads to the red uction of CO2 and the precipitation of graphite with the concomitant f ormation 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 spectros copy (FTIR) to identify the presence of CO without elevated H2O conten ts. The simulated infiltration of C-12 from a graphite furnace into a C-13-bearing sample is illustrated using secondary ion mass spectrosco py (SIMS) and micro-FTIR analysis. Careful FTIR monitoring of variable sample reduction has helped to identify the precautions required to r educe C (and H) infiltration in solid media assemblies and it appears that physical barriers can be more important than the chemical buffers traditionally employed.