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  • Author or Editor: D. Dollimore x
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The use of thermal analytical procedures to obtain both thermodynamic and kinetic parameters is outlined. The advantage of DTA techniques in establishing thermodynamic data is demonstrated. Kinetic data calculated from TG data is demonstrated. Kinetic data calculated from TG data leads to plots of the logarithm of the specific reaction rate constant against 1/T (whereT is the temperature in degrees Kelvin) and from this point onwards the calculation is the same to establish the kinetic parameters no matter whether the data was obtained from TG or isothermal studies. Information on changes in the density and surface area of solid residues in the decomposition process leads to the conclusion that the number of particles present changes significantly during the decomposition and it is pointed out that this factor is largely ignored in setting up kinetic models for the decomposition of solid materials.

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The environment can influence the thermal decomposition of an oxysalt by;(a)causing a change in the course of chemical decomposition or(b)causing an alteration in the physical nature of the solid product or solid intermediates.

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Abstract  

The techniques of thermal analysis are used to determine the mode of decomposition of nickel carbonates doped by the method of coprecipitation. Nickel carbonate prepared by this method is basic in nature with the stoichiometryxNiCO3·yNi(OH)2·zH2O. Isothermal Thermogravimetry was applied to determine the mechanism of decomposition. Rising temperature Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were used to study the effects of doping on the kinetics of the decomposition. Doping was found to strongly influence the kinetics of the decomposition. The kinetics of thermal decomposition of the doped carbonates were compared with conductivity studies. A compensation effect has been observed and is discussed, in the thermal decomposition of the doped nickel carbonates.

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Abstract  

By using a simultaneous thermogravimetry (TG) and differential thermal analyzer (DTA), the hydration processes of the pure C3S and with the addition of Ca(NO3)2 was followed. The peak temperature was determined and kinetic analysis on one of the hydration products, calcium hydroxide, was performed. Results show that the use of Ca(NO3)2 increased the activation energy value of calcium hydroxide formed which is one aspect of the accelerating properties of Ca(NO3)2 while there is no sign of hydration for the addition of sucrose which proved its retarding property. It was also shown that the activation energy increased when the hydrated pastes aged.

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Abstract  

TG, DTA, and TMA data on the pyrolysis of α-cellulase powder in air is reported together with the modified pyrolysis behavior of the cellulose impregnated with between 2–3% (w/w) of calcium, potassium, sodium and zinc chlorides. The lower temperature of onset of the pyrolysis (as shown by TG and TMA), the increased peak areas of the DTA exotherms, and the elimination of an initial endotherm present in the pure cellulose, all suggest an increased flammability for the impregnated samples. Other properties of the impregnated celluloses however favor a fire retardancy effect; these are an increase in the temperature of the first exothermic peak on the DTA, a reduction in the maximum rate of mass loss, a reduction in the% mass loss occurring in the first mass loss period, and an increase in the% ash remaining at 800°C. The relative effect of the various chlorides is examined and shown to correlate with other data already published.

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Abstract  

Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to 251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (Δvap H) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol−1. TheE act for the zero order reaction is in the range of 81.8–87.0 kJ mol−1 and is calculated by use of the derivative method. The value ofE act is about twice that for ΔH vap in Ibuprofen and differs from other compounds, whereE act ≈Δ H vap. It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the vapor state.

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Abstract  

Corn cobs obtained as waste from the corn industry, were analyzed by a TG-DTA unit in an atmosphere of flowing nitrogen. The carbonaceous products so formed were then produced on a preparative scale and activated chemically using potassium hydroxide. This resulted in the formation of a carbon with a very high surface area. The active carbon produced was then examined using thermal analysis in the temperature jump mode on a thermogravimetry unit. From this data the kinetics of degradation of the active carbon was determined using zero order rate kinetics. The pore structure of the active material was also examined using SEM. TheE a for activated corn cobs was found to be 106 kJ mol−1.

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