Browsing by Author "Lugwisha, Esther H. J."

Now showing 1 - 10 of 10
  • Thumbnail Image
    Item
    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
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Intermolecular Vibrational Coupling Associated With the 2 Nu 2 Features of the Raman Spectrum of Strontium Nitrate
    (1987) Kettle, S. F. A.; Lugwisha, Esther H. J.; Vorderwisch, P.; Eckert, Juergen
    The method of mixed isotopic crystal Raman spectroscopy shows no evidence for intermolecular vibrational coupling in dl-α alanine; the same method reveals coupling on the N-deutero analogue.
  • Thumbnail Image
    Item
    Intermolecular Vibrational Coupling in Glycine
    (Elsevier, 1989) Kettle, S. F. A.; Lugwisha, Esther H. J.; Eckert, Juergen; McGuire, Nancy K.
    A study of isotopomers of α-glycine by Raman, inelastic neutron scattering and i.r. methods reveals intermolecular vibrational coupling on modes which, superficially, appear vibrationally insulated.
  • Thumbnail Image
    Item
    Levels of Selected Heavy Metals in Soil, Tomatoes and Selected Vegetables from Lushoto District-Tanzania
    (Science Publishing Group, 2014-01) Lugwisha, Esther H. J.
    This study involved the determination of heavy metals of Cd, Cr, Cu, Pb and Zn in cauliflower (Brassica oleracea L. var botrytis L.), carrot root (Daucus carota L.), tomato fruit (Lycopersicum esculentum Mill.), onion bulb (Allium cepa L.) and leafy cabbage (Brassica oleracea L. var capitata L.) and the respective soils from Lushoto District, Tanzania. Samples were collected from eight growing sites. The accumulated heavy metals were quantified and the levels compared to the FAO/WHO CODEX-STAN 179:2003 and TZS 972:2007 contamination limits for such produce. The methodology involved random sampling, extraction of the metals from the vegetable and soil and determination of heavy metals by using ICP-OES and GFAAS. The levels of Cu in all vegetables were below the FAO/WHO limit while levels of Cr and Zn in all vegetables were found to be above this limit therefore advocating a health risk for consumers. Pb was only found in carrots at 2 sites (Montisory and Resource centre) and in onions at the market all at levels above the FAO/WHO limit while Cd was only found in onions and tomatoes at 2 sites (market and Montisory) at above the FAO/WHO limits. Vegetables especially onions from the Mlalo market advocate a health risk to consumers. Levels of heavy metals in the soils were below the limits of the Tanzanian standard (TZS 972: 2007) and were lower than levels found in vegetables. However, the bioconcentration factor for Cr, Pb, Cd and Zn in all vegetables and tomatoes where they were detected except for cabbages at the Garage site were found to be above 1, an indication of high uptake of heavy metals in the vegetables from the soil. Cu at 80% of the sites had a BCF lower than 1 indicating that Cu was more abundant in the soil compared to the vegetables. These results suggest that these vegetables from Lushoto district are not safe for consumption in their raw state.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    The Properties of Feldspathic Dental Porcelain from Tanzanian Aluminosilicate Materials
    (2014-11) Lugwisha, Esther H. J.; Siafu, Sempeho I.
    Kaolin and quartz from Pugu and feldspar from Morogoro were used to produce feldspathic dental porcelain bodies. Mineralogical results from XRD revealed the presence of kaolinite, illite, microcline and clinochlore in the kaolin samples; albite, microcline, sanidine in the feldspar samples and only silica in the quartz samples. The chemical results studies by XRF revealed the presence of BaO, SiO2, Al2O3, TiO2, Cr2O3, MnO, K2O, CaO, Cl, SO3, MgO, Na2O, and Fe2O3 in varying proportions. Particle size distribution of all the raw materials were determined and particles <63 μm were used for preparation of batches. The batches of different compositions with ranges: quartz (12-22%), feldspar (75-88%) and kaolin (3-5%) were fired at 1100, 1200 and 1250 oC, and the developed properties were tested. The physico-mechanical properties studied exhibited volumetric shrinkage between 2 and 55.17%, open porosity between 6.67 and 40.00%, water of absorption between 7.1 and 40%, bulk densty of 1.43 – 5.68 g/cm3, and compressive strength at 0.13 - 32.25 MPa. The optimal firing temperature for the best results was found to be 1250 oC. The results obtained indicate that kaolin and quartz from Pugu and feldspar from Morogoro are potential raw materials for the production of dental porcelain.
  • Thumbnail Image
    Item
    Spatial Monitoring of Organohalogen Compounds in Surface Water and Sediments of a Rural-Urban River Basin in Tanzania
    (Elsevier, 2013-02) Hellar-Kihampa, Harieth; De Wael, Karolien; Lugwisha, Esther H. J.; Malarvannan, Govindan; Covaci, Adrian; Van Grieken, René
    The presence of persistent organic pollutants in Tanzanian environment is not well monitored despite the existing pollution potential from a number of sources. In this study, we investigated for the first time, the concentration profiles of different organohalogen compounds such as organochlorine pesticide residues (OCPs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in environmental samples (water and sediments) from the Pangani river basin (PRB). The PRB is one of the largest drainage basins in Tanzania, with its watershed exposed to multiple input sources of trace organic contaminants. Surface water and sediments were sampled from 12 representative stations of diverse characteristics and land-use practices, in three distinct seasons, and extracted by liquid-liquid and Soxhlet extraction methods, respectively. Water samples were analyzed by GC-ECD for OCPs only, while sediment samples were analyzed for OCPs, PCBs and PBDEs by GC/MS. Seven compounds, dominated by HCH isomers (510-4460pg/L) and DDT analogs (160-1460pg/L),were detected in the water samples. These concentrations are far below the WHO guidelines for drinking water quality. A total of 42 compounds (8 OCPs, 28 PCB congeners and 6 PBDE congeners) were detected in the sediment samples. Their respective total concentration ranges were 245-10,230; 357-11,000 and 38-2175pg/g dry weight. The spatial distribution patterns and Hierarchical Cluster Analysis reflected the impact of historical agricultural usage in sugarcane plantations (OCPs), and urbanization (PCBs and PBDEs). Risk assessment using sediment quality guidelines indicated no ecotoxicological risks. The results we have found provide preliminary data on levels of the organic contaminants in Pangani river basin as a new insight on the environmental quality of the area.
  • Thumbnail Image
    Item
    Water Quality Assessment in the Pangani River Basin, Tanzania: Natural and Anthropogenic Influences on the Concentrations of Nutrients and Inorganic Ions
    (Taylor and Francis, 2013) Hellar-Kihampa, Harieth; De Wael, Karolien; Lugwisha, Esther H. J.; Van Grieken, René
    The ongoing rapid expansions of human activities and population dynamics have a potential impact on the environmental quality of the Pangani River basin, one of the largest water resources in Tanzania, including possible loadings of different kinds of micro-contaminants. However, the specific extent of the impacts is not well investigated. In this work, we assessed the environmental quality of the basin, based on the seasonal characterization of physicochemical water and sediment parameters, dissolved inorganic ions and nutrient loads. The contributions of geochemical processes and land-use practices were evaluated by multivariate correlations and principal component analysis (PCA). Hierarchical cluster analysis was used to classify similar water quality stations and identify the most and least enriched ones. Surface waters were slightly alkaline, characterized by low total dissolved solids (48–652 mg/L). Extremely low oxygen concentration (2.0 mg/L) was also a cause of concern at one station. The Na+ and HCO− 3 ions provided the dominant cation and anion, respectively. The PCA identified the weathering of carbonate- and Na+-bearing rocks, gypsum dissolution and atmospheric deposition of sea salt as the major factors controlling the ionic composition, contributing more than 60% of the spatial variance. The concentration profiles of the chemical species showed a generally low level of anthropogenic inputs, except at a few locations where nitrate and nitrite were significantly enriched above the limits of safe exposure, with patterns indicating influences of farming and livestock-keeping. A seasonal difference was observed, with lower ion concentrations during the rainy season, likely due to the dilution effect of increased water discharge. This study provides new insights into the environmental quality of the basin and indicates the need for continuous monitoring and assessment of the chemical species in the area.