IN-SITU ELECTRON-MICROSCOPY STUDIES OF THE INHIBITION OF GRAPHITE OXIDATION BY PHOSPHORUS

A combination of in situ transmission electron microscopy and thermogr avimetric techniques has been used to follow the manner by which phosp horus addition to graphite influences its interaction with oxygen. Dir ect observation of the process shows that the additive completely inhi bits the reaction at temperatures below 830-degrees-C. At higher tempe ratures phosphorus species are found to bond preferentially to the gra phite ''armchair'' {1120}BAR faces leaving the ''zigzag'' {1010}BAR fa ces vulnerable to attack by oxygen. In situ electron diffraction analy sis indicates the formation of a chemical bond between the phosphorus and graphite edge atoms at high temperatures, which involves the forma tion of a complex believed to become an integral part of the structure . This unique type of chemical bonding is believed to be responsible f or the observed thermal stability of P-O species on the graphite atoms at temperatures up to 1050-degrees-C. In a further series of experime nts, phosphorus was found to poison the catalytic activity of cobalt, which in its unadulterated state is a very effective promoter of the g raphite-oxygen reaction.