There are many reactions of interest in which one or more of the reactants belong to some solid phases. Modern thermoanalytical instruments can conveniently provide reaction kinetic data of high precision and accuracy, from which the underlying activation energyE may be derived in principle. Unfortunately, no ‘best' method yet exists for the derivation when the data have been collected with a programmed linear increase in sample temperature, unlike the case of isothermal measurements, which however suffer from experimental limitations . Here we propose a method for extractingE from non-isothermal data, that promises general validity.
The Avrami model of solid-state reactions or transformations has frequently been presented and compared with other stochastic models. The equation often applied is shown to be merely a simplification of the full Avrami model equation (FAME). A convenient procedure for application of the FAME to the kinetics of solid-state reactions is proposed.
TG-DTG-DTA has been used to characterize various isomers of CoCl2·2(CH3C6H4NH2). Thermal analysis is further used to analyse the binary mixtures of these isomers. DTA recorded after different elapsed times follows the progress of reaction between cobalt chloride and benzocaine where progressively small endotherms are associated with starting materials. The application of thermal analysis to following the solid-solid reactions between metal acetates and 8-hydroxyquinoline was highlighted. The stoichiometry of such reactions was confirmed from the decrease in intensity of an endotherm as one increases the stoichiometry.
be avoided, the presence of cobalt in alumina supports may result in higher yield of C 5+ hydrocarbons in the FTS as suggested by Mikhailova et al. [ 32 ]. The Co x Al y O 4 compounds have been suggested to occur via the solid-statereaction of
The physico-geometric kinetics for the solid-state reactions by thermoanalytical (TA) measurements were reexamined by focusing
some fundamental aspects: (1) the fundamental kinetic equation, (2) the kinetic model function, (3) the fractional reaction
α, and (4) the apparent kinetic parameters. It was pointed out that some pitfalls in the practical kinetic study are originated
by the disagreement between the kinetic information from the TA measurements and the theory of the physico-geometric kinetics.
In order to increase the degree of coordination between the theory and practice, several attempts were made from both the
theoretical and experimental points of views. The significance of the apparent kinetic parameters was discussed with a possible
orientation for obtaining the reliable kinetic parameters.
Summary Previous study of the hydration and ageing products of two cement pastes created the basis for the postulate of the course of solid-state reactions between the portlandite Ca(OH)2 and the CO2 from air in the hydrated and air dry cement. XRD basal spacing d(001) of portlandite exceeded the nominal value and increased with ageing, with the wetting and drying procedure and with carbonate content of the paste, indicating that a part of OH- ions was gradually substituted by CO32- ions, which are about twice bigger. IR spectroscopy showed a considerable content of portlandite, of CO32- of water and silicates. Also HCO3- H2O and CO2 in cavities between hexagonal rings and hexagonal hydrates were indicated. By MS (mass spectrometry) in vacuum the evaporation of sorbed water was detected at 100-120°C, of gel water at 350°C of portlandite water at 400°C and of high temperature water between 500 and 700°C, simultaneously with CO2 escape. Slightly higher peak temperatures were found by the TG test either in air or in argon. From these results and from geometric considerations it is postulated that the solid-state reactions take place on ageing of the cement paste and on its heating: hexagonal portlandite?calcium carbonate hydroxy hydrate?calcium carbonate hydrate?hexagonal vaterite and/or orthorhombic aragonite?rhombohedral calcite The analysis of the standard files of the calcium carbonate hydroxy hydrates supports this postulate and indicates a gradual transformation.
Authors:Petr Bělina, Veronika Myšková, and Petra Šulcová
Two easy laboratory methods for preparation of rare-earth orthophosphates (crystallisation from phosphoric acid solution and
solid-state reaction with (NH4)2HPO4) were compared on the basis of the products’ properties with a focus on their application as new inorganic pigments. The
preparation method has a significant influence on optical properties. The samples prepared by crystallisation have lighter
and less rich colour and also change colour more under sunlight irradiation. The surface properties analysed by SEM and presence
of a greater amount of phosphoric acid in the crystallisation procedure influence the pH and resistivity of aqueous extract
of products and thus their corrosion-inhibition properties. The optical properties of rare-earth orthophosphates and their
preliminary corrosion tests show their potential application as highly efficient corrosion-inhibition pigments.