The kinetics and mechanism of the oxidation of chromium (III) chloride
- Authors: Sole, Kathryn Clare
- Date: 1989 , 2013-08-28
- Subjects: Chromium chloride--Oxidation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4301 , http://hdl.handle.net/10962/d1004921 , Chromium chloride--Oxidation
- Description: The kinetic behaviour of anhydrous CrCl₃ in gaseous oxidising atmospheres has been examined in the temperature range 350 to 630°C in order to identify optimum reaction conditions and to establish the mechanism by which the reaction is controlled. The reaction under consideration is CrCl₃ (s) + ¾ O₂ (g) → ½ Cr₂O₃ (s) + ³/₂ Cl₂ (g). The main experimental techniques used were isothermal and programmed-temperature thermogravimetry, supplemented by scanning electron-microscopy, surface-area determinations and porosity measurements. The effects of sample pelletisation, gas flowrate, temperature, oxygen partial pressure, pellet porosity and the addition of other oxide species on the rate and extent of reaction have been studied. The reaction is shown to occur in a single step, starting at -350°C under non-isothermal conditions, and exhibiting a deceleratory rate over most of the reaction. Isothermal thermogravimetric curves were fitted to a number of kinetic rate expressions, and a series of statistical analyses used to identify the rate equation which best describes the experimental data. Supporting evidence was provided by scanning electron-microscopic examination of partially-reacted samples. It is concluded that the reaction is under chemical control, and that reaction occurs by means of a linearly-advancing reactant-product interface. The reaction kinetics can be described by a contracting-geometry rate expression. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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- Date Issued: 1989
The sedimentology and palaeoenvironmental significance of vlei sediments on the Winterberg range, South Africa
- Authors: Dewey, Felicity Joy
- Date: 1989
- Subjects: Geology, Stratigraphic -- Holocene Sedimentology Sediments (Geology) -- South Africa -- Eastern Cape -- Winterberg range Geology, Stratigraphic -- Pleistocene Paleoecology -- South Africa -- Eastern Cape -- Winterberg range
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4797 , http://hdl.handle.net/10962/d1001897
- Description: Palaeoenvironmental reconstruction of the late Pleistocene and Holocene geological periods for central and southern Africa has been hampered by the erratic distribution of suitable sites, incomplete and inaccurately dated sequences and the limited nature of published data. One geomorphological feature which has supplied valuable evidence for fluctuations in past environmental conditions, is the vlei or dambo. The type-site of these waterlogged features is in south central Africa, but similar features have been described on other continents. The clastic and organic sediments contained within these features are affected by, and therefore reflect to some degree, the environment under which they were formed. The characteristics of the sediments supply information as to their transport and mechanisms of deposition. From these processes, the environmental conditions at the time of vlei formation can be inferred. The environmental history of the Eastern Cape region has been considerably neglected, and is far less well understood than other countries such as Malawi, Zambia and Zimbabwe. A study site in the Winterberg Range (Eastern Cape) was selected which permitted the comparison of two vleis, the objective being to establish an accurate late Pleistocene sediment chronology for the entire plateau area. Radiocarbon dates from organic layers indicate that these sediments span the last 12 000 years BP, suggesting that organic accumulation at this site began at roughly the same time as at sites further afield. The vlei sediments are analysed in terms of their morphology, particle slze distribution, and other physical and chemical characteristics. These data facilitate the construction of detailed stratigraphic diagrams and a chronological summary of sediment accumulation, from which the period and governing processes of vlei development under changing environments may be described. It is found that the Winterberg vleis contain sediments which respond to changes in the prevailing environment. This makes these sediments useful indices from which to trace such changes during the late Pleistocene and Holocene times. These features are found to be similar in many respects to those described elsewhere in Southern Africa. The study attempts to provide greater understanding of contemporary vlei processes and emphasises the necessity of their preservation, as finite and valuable resources, by future generations
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- Date Issued: 1989