Comparison of the chemical erosion yields of doped graphites

The chemical erosion resistance of a series of doped graphite specimens against hydrogen ion bombardment and air exposure was studied as a function of temperature. Dopants included B, Si, Ti, Ni and W. In general, specimens with dopant concentrations higher than a few atomic percent provide improved resistance - over pure graphite - to H+-induced hydrocarbon formation at and above the temperature corresponding to the maximum chemical erosion yield (similar to 800 K). Specimens doped with boron (greater than or similar to 8 at% B surface concentration) provide the best resistance to hydrocarbon formation - up to a factor of 5 reduction in CH4 yield. A somewhat less improvement in chemical erosion resistance to H+ is seen for specimens with about 4-5 at% Ti or Si surface concentrations - up to a factor of 2 reduction in CH4 yield. B- and Ti-doping also provides resistance to oxidation during air exposure at high temperature; specimens with greater than or similar to 8 at% B surface concentration were found to resist erosion for temperatures as high as 1130 K.