Please use this identifier to cite or link to this item: http://buratest.brunel.ac.uk/handle/2438/5483
Title: Adsorptive properties of chromium oxides and silica
Authors: Baker, Frederick Stanley
Advisors: Sing, KSW
Issue Date: 1974
Publisher: Brunel University Institute for the Environment PhD Theses
Abstract: The adsorption of nitrogen, argon and water vapour was studied on various well-characterised chromium oxides and silicas outgassed at selected temperatures between 25° and 1000°C. Standard data derived on non-porous oxides provided a basis for the analysis of the isotherms by the as-method, which has been found especially useful for the identification of the various physisorption processes, e. g. micropore filling and capillary condensation. The Frenkel-Halsey-Hill (FHH) method has also been used to analyse the multilayer region of the isotherms. Chromia gels precipitated at about pH 6 were found to be microporous. These gels, when outgassed at 25°C, exhibited molecular sieve properties; the sorption capacity for water was high, whereas the pore volume available to nitrogen and argon was small. It is suggested that cavities were formed in the gel in the vicinity of the Cr3+ ions through the removal of water ligands under conditions where the hydroxide structure was slow to develop. The molecular sieve character was considerably reduced in the case of gels precipitated at high pH (about 10.5), presumably because of the more efficient replacement of water ligands by hydroxyl ions. Chromia gels outgassed at high temperature retained a strong affinity for water vapour, and gave argon and water vapour isotherms which exhibited some slight stepwise character. On the other hand, silicas outgassed at 1000 °C were found to be strongly hydrophobic. Mercury vapour adsorption was found to take place very readily on some outgassed chromium oxides. This presents a problem in both volumetric and gravimetric adsorption measurements unless special precautions are taken to exclude mercury vapour from the system. Pressure-sensitive transducers have been used to overcome this problem in the case of the water vapour adsorption studies.
Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.
URI: http://bura.brunel.ac.uk/handle/2438/5483
Appears in Collections:Chemistry
Institute for the Environment

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