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.
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.
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.
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.
In this study gasification in air of activated carbons and carbon blacks is investigated using a simultaneous TG-DTA unit. It is found that a final acid or alkaline treatment can substantially alter their reactivity in the gasification reaction in air. To make a proper assessment of their solid state reactivity with respect to their gasification in air a simple method is advanced which has been used recently in assessing solid state reactivity of other materials. In this method a thermogravimetric (TG) plot is obtained on a reference carbon and then similar TG plots are obtained on the other samples of carbon using identical experimental conditions and the same TG unit. The solid state reactivity is assessed from plots of the αR (the value of αR, the extent of the gasification of the reference carbon) against the sample carbons values of the αS (labeled αS to denote the value of the various carbon samples). The values of appropriate couples of αR and αS at temperaturesT1,T2,T3,...Tn allow an αR-αS plot to be constructed. If the solid state reactivity of the carbon samples matches exactly that of the reference carbon the result will be a linear plot, showing coincidence of αS and αR at all values of αR. If the solid state reactivity of a carbon sample exceeds that of the reference carbon then the lines plotted will be on one side of the coincidence plot, while if they are less than the carbon reference they will lie on the other side. The results show that treatment of a carbon with alkaline or acid may have a significant effect on the reactivity of the carbon sample which is only partly explained by observable differences in surface area.
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.
Simultaneous TG-DTA units have a work station which allows plots to be made of temperature against time, as well as the conventional
TG and DTA plots. These time-temperature plots and their derivatives can be used to show details of both exothermic and endothermic
events. The melting behavior of zinc is used as illustrative of endothermic phase changes. Solid-solid transitions are exemplified
by noting the transitions in quartz. Examples of chemical reactions being treated to temperature-time plots are the decomposition's
of zinc oxalate in nitrogen (an endothermic event) and the oxidation of carbon black in air (a sustained exothermic event).
This wide selection of exothermic and endothermic events serves to illustrate the details which can be drawn from any thermogravimetric
plot irrespective of the other associated equipment present, which serves to reinforce the data presented in the present study.