Browsing by Author "Mulokozi, A. M."

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    Activation Energy of Thermal Decomposition of LaC2O4Br
    (Kluwer Academic Publishers, 1991) Lugwisha, Esther H. J.; Mulokozi, A. M.; Masabo, M. K. J.
    The activation energy of the thermal decomposition of finely ground LaC2O4Br was determined according to the method of Ozawa asE a=203.83 kJ mol–1. As compared to the value for the parent oxalate La2(C2O4)3 E a=130 kJ/mol), this value is higher by about 70 kJ/mol, which is consistent with the increased interaction between the metal and oxalate ions. The substitution of Br by Cl does not affect the decomposition kinetics profoundly.Gem der Methode von Ozawa wurde die Aktivierungsenergie der thermischen Zersetzung von fein zermahlenem LaC2O4Br mitE a=208.83 kJ/mol bestimmt. Beim Vergleich mit dem entsprechenden Wert fr die Mutterverbindung La2(C2O4)3 (E a=130 kJ/mol) erweist sich dieser Wert um etwa 70 kJ/mol hher, was mit der verstrkten Wechselwirkung zwischen Metall- und Oxalationen bereinstimmt. Der Ersatz von Br durch Cl hat keinen tiefgreifenden Einflu auf die Kinetik der Zersetzung
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    Influence of Sample Particle Size and Heating Rate on the Thermal Decomposition of K2C2O4
    (Kluwer Academic Publishers, 1991) Mulokozi, A. M.; Lugwisha, Esther H. J.
    The thermal decomposition of K2C2O4 in a current of dry nitrogen according to the reaction (1) $$K_2 C_2 O_4 \to K_2 CO_3 + CO$$ is shown to be influenced profoundly by the sample particle size and the heating rate. For finely ground samples, a lower activation energy (E a =255.15±5 kJ mol−1) is obtained as compared with the 312.6±6 kJ mol−1 observed for crystal chips weighing 30–40 mg. The characteristic temperatures (the reaction start, peak and end temperatures) are markedly reduced by fine grinding. High heating rates tend to separate the thermal decomposition process into two kinetic phases, shown by splitting of the DTG peak. The significance of these observations is discussed, and the results are theoretically accounted for.
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    New Aspects of the Decomposition Kinetics of Calcite, Part-I. Isothermal Decomposition
    (Elsevier, 1992-01) Mulokozi, A. M.; Lugwisha, Esther H. J.
    Under experimental conditions which tend to minimise the effects of heat and mass transfer, the kinetics of the decomposition of calcite according to CaCO3(s) CaO(s) + CO2(g) is split by the restriction of CO2 transport at the degree of conversion αt when the channels in the CaO(s) surrounding the reactant provide the only diffusion path. Because of the resulting convective cooling beyond αt, the phase boundary reaction proceeds initially with the reaction-only activation energy Ea(1) = 192.89 kJ mol−1 up to αt, after which the reaction proceeds with an apparent activation energy of Ea(2) = 210.33kJ mol−1. The diffusion-controlled reaction proceeds with the mean value of the activation energy Ea(D1) = 0.5 (Ea(1) + Ea(2)) = 201.65 kJ mol−1. The activation energies differ by the same amount, i.e. Ea(D1) − Ea(1) = Ea(2) − Ea(D1) = 8.72 kJ mol−1, equivalent to the degenerate deformation vibration v4 = δ(O-C-O) of calcite observed at 706 cm−1 (infrared) and 714 cm−1 (Raman), which for a transition state sensitive to the instantaneous transport of CO2, complements the cage effect exercised by the lattice, thus giving strong evidence supporting our mechanistic interpretation of the decomposition kinetics.