University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

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Chapter One serves as an introduction to, and background information, on the thermal decomposition of metal oxalates and homonucleus carbonyl clusters. Emphasis is placed on the compounds under investigation, namely the oxalates of iron(II), cobalt(lI) and nickel(ll) oxalate dihydrate and their corresponding binary and ternary compounds, as well as triiron dodecacarbonyl and tetracobalt dodecacarbonyl. Topics specifically addressed are their structures as well as the thermodynamics of the dehydration and decomposition of compounds of this type. Given this background, the overall aims of the work are presented. These include finding the reaction conditions to form metal powders from metal oxalates, and a preliminary study of carbonyl clusters to see if they too may be used in the production of metal powders. Chapter Two gives the results of the dehydration and decomposition of the metal oxalates, characterised by way of infrared, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. The compounds under investigation are those of the single oxalates of iron, cobalt and nickel; the binary systems of Fe-Co, Fe-Ni and Co-Ni, in the molar ratios of 3:1, 1:1 and 1:3 for each system; and the ternary oxalate system in the molar ratios of Fe1 :Co1 :Ni1, Fe8:Co1 :Ni1, Fe1 :Co8:Ni1 and Fe1 :Co1 :Ni8. It was found that under certain reaction conditions all these compounds, excluding the ferrous oxalate dihydrate, decompose to the metal. It was found through experiments to modify the morphology of the crystals under investigation that the decomposition product is controlled by the crystal lattice system the starting material is synthesised in. When in the cobalt/nickel oxalate a-crystal system, decomposition is to the metal, or in the case of the binary and ternary systems, to the alloy. If the oxalate is synthesised in the crystal system of the iron oxalate, the resultant decomposition product is the respective oxide. Experiments were carried out on the iron/cobalt binary system to prove this hypothesis. Depending on the conditions of synthesis, the iron/cobalt binary system can form in either the crystal system analogous to iron (1), or analogous to cobalt (2). The products of pyrolysis for each case differs, with (1) decomposing to the oxide and (2) decomposing to the alloy. iii Chapter Three is a brief, preliminary study describing the thermal decomposition of triiron dodecacarbonyl and tetracobalt dodecacarbonyl. Characterisation of the pyrolysis products is given by infrared, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. A tentative theory for their decomposition route under an atmosphere of nitrogen is given. It was found that neither compound decomposed fully to the central metal, but that a mixture of oxide and metal were left. The conclusion reached from this study was that neither carbonyl under investigation was particularly successful. Although in both instances metal was produced, both contained large amounts of the respective oxide. This makes them unsuitable for an industrial application to form metal powders. Chapter Four describes in detail the all the experimental, materials, methods, techniques and equipment used in this study. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

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This investigation was made in an attempt to compare the casting properties of various commercially used grid-metal alloys and to study other alloys that promise to be of value in the battery manufacturing industry. In previous publications (1) it has been shown that zinc has a very market effect in raising the surface tension of type metals when it is present even in small amounts. A more recent publication (2) has shown that zinc in small amounts (which increases (1) the surface tension of type metals) and sodium in small amounts (which decreases the surface tension of type metals) does not impair the ability of type metal to flow in molds all parts of which are above capillary in size. As neither zinc nor sodium have any appreciable effect on runnability it is concluded that surface tension is a negligible factor in determining the runnability of an alloy in molds which are in all parts of above capillary size. Since the molds used in casting grid plates are above capillary size in all parts, and from evidence cited, it is concluded that surface tension does not enter this problem, and the procedure as outlined in the following section was chosen as the most logical for this study. (1) The Surface Tension of Type-Metal Alloys, by H.V. White, Bulletin of Virginia Polytechnic Institute, January 1993, Engineering Experiment Station Serious No. 13. The Effect of Impurities on the Surface Tension o Type-Metal Alloys, Bulletin of Virginia Polytechnic Institute, by H.V. White, June, 1934, Engineering Station Series No. 17. 2) "The Effect of Zinc and Sodium on the Relative Runnability of Type-Metal Alloys," by H.V. White and F.O. Reese: Bulletin of Virginia Polytechnic Institute, September, 1935, Engineering Experiment Station Series No. 21. / M.S.