ADSORPTION SITES FOR WATER ON GRAPHITE .5. EFFECT OF HYDROGEN TREATMENT OF GRAPHITE

The effect of the H2 treatment of graphite on the adsorbability of H2O has been investigated by means of the measurement of the H2O adsorption isotherm, the calculation of the isosteric heat of adsorption q(st) thereform, and the analysis of the surface gas content. The H-2 treatment of graphite at 1000-degrees-C reduces remarkably the amount of surface oxides and produces C-H bonds instead. As a result, the amount of adsorbed H2O decreased drastically, and the q(st) curve of H2O revealed a deep minimum at a lower level than the heat of liquefaction of H2O. The effect of further heat treatment of the H2-treated graphite at 500 and 1000-degrees-C in vacuo on the adsorbability of H2O was also examined. The latter treatment reduced the amount of surface oxides to about one-fifth of that of the H2-treated graphite but did not change the shape of the q(st) curve as much; this treatment largely affected the shape of the first adsorption isotherm measured just after the treatment; i.e., steps appeared at moderate pressures. This result is interpreted in terms of the pore filling of silt-shaped pores by H2O, formed by the decomposition of surface compounds.