Adsorption characteristics and surface structural changes of transition metal sulphates by heat treatment.

Bajpai, Mukut Behari (1974) Adsorption characteristics and surface structural changes of transition metal sulphates by heat treatment. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The adsorption and desorption of trichlorofluoromethane (CFCl₃) was studied by using a microbalance on the sulphates of calcium, manganese, cobalt, nickel, copper and zinc. The effect of annealing the samples at 200, 300, 400 and 500°C on their adsorption characteristics and the heat of t solution has been measured. The surface structure of the annealed adsorbents is considered from crystal field effects. Thermodynamic parameters such as the heat of adsorption and entropy of adsorption have been derived from the various isotherms at 20.0, 6.0 and -10.0°C. These quantities have been used to discuss the surface structures. The heat of solution data are analyzed and the work of previous workers is considered in terms of the present scheme. The construction of a vacuum microbalance and the twin calorimeters is also described. -- Surface cobalt (II) is found to be in a tetrahedral environment at an annealing temperature of (200°C). On adsorption, the surface structure possibly changes to a trigonal bipyramidal structure. However, on annealing at higher temperatures, the surface of the anhydrous cobalt sulphate provides an octahedral environment for the cation which goes to Hush's intermediate symmetry and finally to the most stable pentagonal bipyramidal structure. Nickel sulphate manifests pentagonal bipyramidal structure on adsorption on trigonal bipyramidal surface structure. Copper sulphate most probably pro vides trigonal environment to the metal ion at the surface which transforms to trigonal bipyramidal structure on adsorption. Physical adsorption measurements are found to be a useful tool in analyzing possible surface structures.

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