The use of complementary data in the application of thermal analysis techniques

Abstract

Tha 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 lIT (where Tis 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.Differential thermal analysis (DTA) and Thermogravimetry (TG) can be used to produce thermodynamic or kinetic data when dealing with the decomposition of solid oxysalts [1 ]. To obtain unambiguous interpretations however it is necessary to obtain data on the systems under investigations by as many different techniques as possible [2]. The complementary data that can be best utilised are those associated with surface texture and structure [3]. This is especially true when dealing with kinetic aspects of a reaction [4]. In the case of surface properties oftheresidues left in the decomposition the character of the surface is usually assessed from its adsorption properties. The adsorption usually studied is nitrogen adsorption at the temperature of liquid boiling nitrogen and the interpretation is in terms of the surface area [5] and the pore size distribution [6]. The other important property which changes in a solid state decomposition is the density. This can be combined with the surface area changes to indicate the change in particle size during decomposition [7], The manner by which the density is determined is important as also is the pretreatment received, such as effective outgassing before commencing measurements [8 ]. The investigation of solid's receiving heat treatment is made more important in that many industrial processes the solids involved are subjected to a rising temperature programme which can be simulated on DTA or TG equipment. The ancillary information is of two kinds, first information producing kinetic parameters by an alternative route or which restrict the number of possible kinetic processes and secondly data which adds to the general information regarding the Jr. Thermal Anal. 13, 1978

The kinetic compensation effect in the decomposition of calcium carbonate

“…If there is a change in the size distribution of the particles, and therefore, the average size during the course of heating, then this condition will no longer hold. Recently, Dollimore [11] has pointed out that many decomposition reactions can be accompanied by splitting of particles and consequently a decrease in the particle size and an increase in the particle number. This, of course, will introduce some scatter of the data in the compensation plot.…”