| dc.description.abstract | The sorption of ammonia was studied at 273 and 298 K
on Californian and Quebec chrysotile heat-treated at 150,
300, 500 and 700 degrees C. Another ammonia sorption study involving
the two chrysotiles treated at 500 degrees C at isotherm temperatures
of 266, 273, 288, 298 and 308 K was carried out. The
variation of the calorimetric heats of adsorption with
surface coverage and adsorption/desorption isotherms were
determined. From these data experimental differential molar
entropies of adsorption were calculated.
The results indicated that the high heats of adsorption
observed initially may have been due to a weak chemisorption
reaction perhaps involving ammonium complex formation with
impurities on the chrysotile surface. Hydrogen bonding and
van der Waals forces could possibly have accounted for the
lower heats of adsorption observed at higher surface coverages
The present studies appeared to belong to an unusual
class of adsorption phenomena where the heat of adsorption
was less than the heat oT llquifactlon of the ammonia. This
was attributed to the two hypotheses of significant entropy
Involvement in the adsorption and capillary adsorption.
Minor studies of the adsorption/desorption of ammonia
on Californian chrysotile treated with sodium nitrate
and boiling water were also performed. Heats of adsorption
at all degrees of surface coverage were approximately three
times those in the other experiments. This was attributed
to the highly hydroxylated surface which may have facilitated
chemisorption.
A group of experiments were carried out to determine
the desorption efficiencies of the two chrysotiles. The
Quebec samples generally proved to desorb the ammonia more
efficiently.
All adsorbents were characterised by low-temperature
(77 K) nitrogen adsorption/desorption Isotherms from which
surface area and pore size distribution data were obtained.
Also, direct examination of the topographical and structural
features of the adsorbents was made by transmission
electron microscopy and selected area electron diffraction. | |
