In situ electron microscopy studies of the inhibition of graphite oxidation by phosphorus

Abstract

A combination of in situ transmission electron microscopy and thermogravimetric techniques has been used to follow the manner by which phosphorus addition to graphite influences its interaction with oxygen. Direct observation of the process shows that the additive completely inhibits the reaction at temperatures below 830 °C. At higher temperatures phosphorus species are found to bond preferentially to the graphite “armchair”{1120} faces leaving the “zigzag” {100} faces vulnerable to attack by oxygen. In situ electron diffraction analysis indicates the formation of a chemical bond between the phosphorus and graphite edge atoms at high temperatures, which involves the formation of a complex believed to become an integral part of the structure. This unique type of chemical bonding is believed to be responsible for the observed thermal stability of P–O species on the graphite atoms at temperatures up to 1050 °C. In a further series of experiments, phosphorus was found to poison the catalytic activity of cobalt, which in its unadulterated state is a very effective promoter of the graphite-oxygen reaction.