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This study aimed to investigate the contribution of carbothermal reduction to the overall thermal decomposition process of different Ag 2 CO 3 samples in Ag 2 CO 3 –graphite mixtures and the possible formation of Ag 2 O–Ag and Ag 2 CO 3 –Ag core–shell structures as intermediate compounds. Distinguishable contribution of the carbothermal reduction process was observed during the second mass loss process of the thermal decomposition. The second mass loss process was characterized by two partially overlapping reaction steps: (i) the carbothermal reduction of surface Ag 2 O; and (ii) subsequent thermal decomposition of bulk Ag 2 O or Ag 2 CO 3 . The overlapping features of the carbothermal reduction and thermal decomposition processes were analyzed via the kinetic deconvolution analysis. The present results provide us with fundamental information for preparing possible functional Ag compound materials with Ag 2 O–Ag and Ag 2 CO 3 –Ag core–shell structures in a controlled manner during the thermal decomposition of Ag 2 CO 3 .

International audience; The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations offer guidance for obtaining kinetic data that are adequate to the actual kinetics of various processes, including thermal decomposition of inorganic solids; thermal and thermo-oxidative degradation of polymers and organics; reactions of solids with gases; polymerization and crosslinking; crystallization of polymers and inorganics; hazardous processes. The recommendations focus on kinetic measurements performed by means of thermal analysis methods such as thermogravimetry (TG) or thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). The objective of these recommendations is to assist a non-expert with collecting adequate kinetic data by properly selecting the samples and measurement conditions.

For the precipitation of calcium carbonate polymorphs in ethanol/water solutions of calcium chloride by the diffusion of the gases produced by sublimation–decomposition of solid ammonium carbonate, polymorph selection and morphology control of the precipitates were demonstrated by the effect of ethanol/water ratio in the mother liquor. The precipitated phases change systematically from gel-like aggregates of hydrated amorphous calcium carbonate in the absolute ethanol solution to well-shaped rhombohedral particles of calcite in the absolute aqueous solution via almost pure phase of vaterite with dendrite structure in 75%-ethanol/25%-aqueous and 50%-ethanol/50%-aqueous solutions. On heating the precipitated sample in flowing dry nitrogen, all the samples transformed to calcite before the thermal decomposition, where the thermal decomposition temperature shifts to higher temperatures with increasing the water content in the mother liquor due to the systematic increase in the particle size of calcite. Accordingly, the present method of controlled precipitation of calcium carbonate polymorphs is also useful to control the particle size and reactivity of calcite produced by heating the precipitates. Selecting vaterite with dendrite structure from the present series of precipitated samples, the structural phase transition to calcite was characterized as the three-dimensional growth of rhombohedral particles of calcite with the enthalpy change ΔH = − 2.8 ± 0.1 kJ mol−1 and the apparent activation energy Ea = 289.9 ± 5.8 kJ mol−1.

Copper(II) hydroxide sulfate was synthesized by a microwave-assisted hydrothermal method from a mixed solution of CuSO 4 and urea. Needle-like crystals of ca. 20–30 μm in length precipitated by irradiating microwave for 1 min were characterized as Cu 3 (OH) 4 SO 4 corresponding to mineral antlerite. The reaction pathway and kinetics of the thermal decomposition of the synthetic antlerite Cu 3 (OH) 4 SO 4 were investigated by means of thermoanalytical techniques complemented by powder X-ray diffractometry and microscopic observations. The thermal decomposition of Cu 3 (OH) 4 SO 4 proceeded via two separated reaction steps of dehydroxylation and desulfation to produce CuO, where crystalline phases of Cu 2 OSO 4 and CuO appeared as the intermediate products. The kinetic characteristics of the respective steps were discussed in comparison with those of the synthetic brochantite Cu 4 (OH) 6 SO 4 reported previously.

Reaction steps and mechanisms of the thermal dehydration of lithium metaborate dihydrate were investigated by means of thermoanalytical measurements, high temperature powder X-ray diffractometry, FT-IR spectroscopy, and microscopic observations. The first half of thermal dehydration was characterized by the melting of the sample producing viscous surface layer, the formation of bubbles on the particle surfaces, and the sudden mass-loss taking place by an opportunity of cracking and/or bursting of the bubble surface layer. The second half of the dehydration with a long-tailed mass-loss process in a wide temperature region was divided further into three distinguished reaction steps by the measurements of controlled rate thermal analysis. During the course of the thermal dehydration, four different poorly crystalline phases of intermediate hydrates were observed, in addition to an amorphous phase produced by an isothermal annealing. Just after completing the thermal dehydration, an exothermic DTA peak of the crystallization of β-LiBO 2 was appeared at around 750 K. The phase transition from β-LiBO 2 to α-LiBO 2 was observed in the temperature range of 800–900 K, which subsequently melted by indicating a sharp endothermic DTA peak with the onset temperature at 1101.4 ± 0.6 K.

Influences of the product gases on the kinetics of the thermal decomposition of sodium hydrogencarbonate, NaHCO3, were investigated by means of controlled rate evolved gas analysis coupled with TG (CREGA-TG). From a series of CREGA-TG measurements carried out under controlled gaseous concentrations of CO2 and H2O by considering the self-generated CO2 and H2O during the course of reaction, anomalous effects of CO2 and H2O on the kinetic rate behavior of the thermal decomposition of NaHCO3 were revealed, that the reaction is decelerated and accelerated by the effects of atmospheric CO2 and H2O, respectively. The kinetic rate behavior under controlled atmospheric condition of CO2 = 0.1 g m−3 and H2O = 1.2 g m−3 was characterized by the apparent fitting to a kinetic equation of Avrami–Erofeev type with the apparent activation energy of Ea = 111.5 ± 4.8 kJ mol−1 and pre-exponential factor of A = (1.29 ± 0.01) × 1011 s−1. The effects of atmospheric CO2 and H2O on the apparent kinetic parameters were appeared as the decreases in both the values of Ea and A and the increase in the value of A, respectively.

By reviewing various microscopic studies on the mechanisms of the thermal dehydration and/or decomposition reactions of inorganic solids, the physico-geometric and chemical features of the solid-state reactions were investigated. A model of reaction interface and a classification of interfacial chemical behavior for the thermal dehydration of solids, which have extensively been studied by professors Galwey and Brown, were introduced in order to evaluate the significance of such mechanistic understandings on the solid-state reactions. The meanings of the kinetic models and kinetic equations, which have been employed conventionally for analyzing the overall kinetics of solid-state reactions, were discussed in relation to the complicated physico-geometric and chemical behaviors of the solid-state reactions revealed by the mechanistic investigations. Possible extensions of the conventional kinetic theory by incorporating various physico-geometric and chemical features were examined for an advanced kinetic understanding of the solid-state reactions. The kinetic data required for the advanced kinetic analysis of the solid-state reactions were discussed by emphasizing the usefulness of the controlled rate thermal analysis (CRTA). The present status and future subjects of the kinetic and mechanistic studies on the solid-state reactions were summarized briefly through the present review.

The influence of self-generated gaseous products on the kinetics and mechanism of the thermal decomposition of synthetic malachite, Cu 2 CO 3 (OH) 2 , was investigated by means of conventional TG–DTA under various atmospheric conditions, TG–MS and CRTA under a reduced atmospheric condition, and powder X-ray diffractometry of the partially decomposed sample. It was found that the sample decomposes at a lower temperature under a higher partial pressure of self-generated gases. This interesting behavior, in contrast to the general consideration of chemical equilibrium, results from catalytic action of evolved H 2 O on the crystallization of the product CuO, and from an interaction of evolved CO 2 with poorly crystallized CuO under reduced pressure.

The overall kinetics of the thermal dehydration of zinc acetate dihydrate was investigated by means of isothermal mass-change measurements, complemented by microscopic observations of the reaction geometry and morphological change during the reaction. Under isothermal conditions, the compound loses its water of crystallization in a well-defined single step; Zn(CH 3 COO) 2 · 2H 2 O → Zn(CH 3 COO) 2 + 2H 2 O. The microscopic observations for the single crystals confirm that the reaction initiates at the edge surfaces of the hexagonal thin plate by nucleation and growth processes, consequently forming the reaction interface which advances inward, toward the center of the hexagon. The kinetic results obtained from the thermoanalytical measurements indicated agreement to the first-order law, in spite of the two-dimensional shrinkage of the reaction interface. This discrepancy is discussed in connection with the interactions of the elementary nucleation and growth processes at the reaction interfaces with the self-generated water vapor. The overall kinetic behavior of the crushed crystals of different particle-size fractions, under various atmospheric conditions, was investigated. The apparent kinetic results varied systematically with the sample and atmospheric conditions, accompanied by changes of the roles of surface reaction, diffusion of evolved water vapor from the reaction interface and gross diffusion of water vapor through the assemblage of sample particles.

The significance of the empirical kinetic model function for diffusion-controlled reactions is discussed in connection with the fractal nature of the reaction geometry and the macroscopic character of the thermoanalytical curves for solid-state reactions. The mathematical properties of such empirical kinetic model functions based on the geometrical fractal were investigated numerically in order to evaluate their practical usefulness as a possible diagnostic tool for distinguishing the most appropriate kinetic model function. The procedure of distinguishing the kinetic model function is extended, including such empirical kinetic model functions based on the geometrical fractal, and applied to the kinetic analysis of the thermal dehydroxylation of synthetic brochantite Cu 4 (OH) 6 SO 4 .

The shape control of crystalline particles of α-FeO(OH) was performed through growth treatment in an aqueous medium and subsequent hydrothermal treatment. The samples were subjected to a thermogravimetric (TG) study. The different TG curves obtained for the samples before and after the hydrothermal treatment were explained in connection with the existence of an irregular outer surface layer on the samples before the hydrothermal trreatment. The overall decomposition kinetics of the samples after hydrothermal treatment were determined by analyzing the TG curves at different heating rates. An apparent activation energy of approx. 140 kJ mol−1 was obtained in the restricted range of fractional reaction 0.4 ≤ α ≤ 0.95, irrespective of the samples. The appropriate kinetic model functions changed from nucleation growth to reaction interface shrinkage with increasing particle size. The correspondence of the overall kinetics obtained from the thermoanalytical method with the physico-geometry of the reaction is discussed briefly.

Hydrated and anhydrous γ-FeO(OM) with different sizes and shapes of crystalline powders were prepared through an oxidative hydrolysis of iron(II) chloride solution using urea decomposition. Systematic thermogravimetric measurements under isothermal and non-isothermal conditions were performed in order to characterize kinetically the thermal dehydration and dehydroxylation processes. The dehydration of the bound water on the surface of γ-FeO(OH) observed at around 150°C obeyed the first-order law with an apparent activation energy of about 100 kJ mol −1 , being recognized as controlled by diffusional removal of evolved water vapor through the stacking assemblage of plate-like crystalline powders. As for the hydrated γ-FeO(OH), the thermal dehydroxylation process at around 280°C, subsequent to thermal dehydration of the bound water, was well characterized by the two-dimensional phase boundary controlled reaction law R 2 with apparent activation energy of about 150 kJ mol −1 , implying shrinkage of the reaction interface from the edge of the rectangular plate. The Avrami-Erofeyev A m law was estimated for the dehydroxylation process of the anhydrous samples, in which the kinetic exponents m in the A m law increased with increasing specific surface area and the aspect ratio of the rectangular plate of the sample powders.

As the first part of a series on kinetic studies on the thermal decomposition of iron(III) hydroxide oxide, α-FeO(OH), involved in a crustal material, banded iron formations, is subjected to thermogravimetric measurements at various constant and linearly increasing temperatures. The validity of the kinetic procedures employed in a series of kinetic studies is tested by a comparative kinetic study of the thermal decomposition of α-FeO(OH) involved in two characteristic parts of banded iron formations, in which 54.9 ± 1.2 and 44.5 ± 2.3 wt% of α-FeO(OH) are involved. Under isothermal conditions, kinetic agreement with an Avrami-Erofe'ev equation Am (m ≈ 1.5) was observed for the thermal decomposition of both samples to α-Fe2O3. The Arrhenius parameters calculated for the two samples are identical within the statistical error. For linearly increasing temperatures, the apparent activation energies calculated for these samples by a different isoconversion method were different by about 35 kJ mol−1. Kinetic agreement with A1.5 for the sample containing 54.9 wt% of α-FeO(OH) was identical to that found under isothermic conditions. The kinetics of the other sample were characterized by the larger apparent Arrhenius parameters and the kinetic agreement with the A1 law. The different kinetic behavior under non-isothermal conditions of the samples was probably due to the difference in diffusional removal of evolved water vapor, depending on the compositional difference in the two characteristic parts of banded iron formations.

The kinetic compensation effect (KCE) has been observed in numerous kinetic studies of solid-state reactions using thermoanalytical methods. An attempt has been made to separate phenomenologically the KCE into the variation and the mutual dependence of the resultant Arrhenius parameters. The probability of the mutual dependence of the Arrhenius parameters caused by the properties of the general kinetic equation was discussed in relation to: (1) the reaction temperature interval, (2) the fractional reaction α, (3) the kinetic model function f(αf), and (4) the isokinetic hypothesis. The mutual dependence of the Arrhenius parameters due to the properties of the general kinetic equation was first checked before discussing the KCE in relation to a physico-chemical factor for a series of reactions under investigation. The necessity of establishing a check system for the kinetic calculation is discussed briefly on the basis of the prerequisities of the methods of kinetic calculation and the properties of the general kinetic equation.

The effect of sample mass on the kinetics of the non-isothermal mass-loss process of molten NH4NO3 was investigated by TG—DTG. The apparent Arrhenius parameters were shown to decrease with increasing sample mass. Using the conventional method of kinetic calculation, it was shown that the sample-mass-dependent variation in the apparent pre-exponential factor results from the use of fractional reaction in the kinetic expression. The value of the apparent activation energy varies consequently to compensate the sample-mass-dependent change in the apparent pre-exponential factor on the regime of the mutual dependence of the Arrhenius parameters; this is known as the kinetic compensation effect. The specific Arrhenius parameters that are independent of sample mass were obtained by using the specific pre-exponential factor that is independent of sample mass, instead of the apparent pre-exponential factor.

The rate behavior of the isothermal dehydration of crushed crystals of Li 2 SO 4 · H 2 O was studied under a self-generated temperature condition by recording the mass loss and temperature deviation from the pre-set isothermal temperature. The sample temperature during the reaction was influenced by the effect of self-cooling. The rate process under such a temperature condition could be divided into three distinct stages: acceleratory, nearly constant rate, and deceleratory periods. The constant rate period was processed kinetically using the Friedman method. The apparent values of Arrhenius parameters during the constant rate process remained constant irrespective of the sample mass examined.

Effects of sample mass on the kinetics of isothermal dehydration of crushed crystals of Li2SO4·H2O were investigated using conventional TG. The process was characterized by a combination of Avrami-Erofeyev and contracting geometry models. Distribution of the fractional reaction, α, in particles within the sample assembly as well as the change in the rate of gross diffusion of the evolved water vapour appear responsible for the sample-mass-dependent kinetic parameters obtained for the system.

The fundamental problems in the thermoanalytical kinetics of solid state reactions were investigated as exemplified by the thermal dehydration of Li 2 SO 4 · H 2 O. Distortion of the Arrhenius parameters and their consequent interdependence are described mathematically. A possible way to increase the reliability of the thermoanalytical kinetic study is discussed in connection with the possibility of the establishment of a kinetic standard.

The kinetics and mechanism of YBa2Cu3Ox formation is reconsidered on the basis of literature data and our own data which have shown that their detailed solution from TA measurements alone is not feasible. Curves indicating morphological and chemical reactivity aspects are presented, diffusion and possibly two-dimensional nucleation being largely responsible for HTSC formation. The oxygen intake is also controlled by diffusion, and can strongly affect the high-temperature superconducting properties of the grain surface layer. The formation of intermediate superstructures is particularily noteworthy.

DTA curves for the crystallization of the title glasses of various particle size fractions were analysed kinetically using the modified Kissinger method proposed by Matushita and Sakka. The kinetic results were compared with those obtained from microscopic measurements. For the Na2O · CaO · SiO2 glass, it was observed that the kinetic obedience changes from a surface reaction model to a bulk crystallization model with increasing particle size. The values of the apparent activation energy Eapp corresponded excellently to that obtained microscopically, i.e. 343 kJ mol−1. However, the crystallization of Na2O · CaO · SiO2 glass was regulated by the surface reaction mechanism irrespective of the particle size examined; the values of Eapp decreased with increasing particle size but no direct correspondence of these values to those determined by the microscopic measurements were found. The complicated behaviour of Eapp was explained with reference to the role and function of the nucleation at the reaction interface.

Kinetic data of the title dehydration obtained from simultaneous TG-DSC measurements were compared between the single crystals and crushed crystal material. The kinetics were interpreted in relation to the reaction geometry observed by polarizing microscopy. The kinetic compensation effect established for the Arrhenius parameters evaluated by the Ozawa method was discussed in terms of the temperature interval analyzed.

Kinetic obedience and Arrhenius parameters for the isothermal and non-isothermal dehydration of crushed crystals of lithium sulphate monohydrate were determined by TG using eight methods including differential and integral methods. Different apparent Arrhenius parameters were obtained by the different methods, including the differential and integral methods as well as the isothermal and non-isothermal methods. The difference in the kinetic results determined by the different methods is explained on the basis of the nature of these methods. The causation of the so-called kinetic compensation effect observed for a given dehydration reaction is discussed in connection with the reliability of TG data and the applicability of the calculation method.

It is shown that the kinetic compensation effect mathematically results from the exponential form of the rate constant. A change of activation energy is thus compensated by the same change in temperature or in the logarithm of the pre-exponential factor.

The titration reaction of an NaOH solution with a copper(II) sulphate solution occurred in two steps. The first-stage precipitate, Cu(OH) 2 and/or CuO, formed above pH 7, reacted with free SO 4 2− ions and excess CuSO 4 in solution to give basic copper( II ) sulphates such as synthetic brochantite. The reaction with excess CuSO 4 was confirmed by titrating Cu(OH) 2 and CuO powders suspended in water with a copper(II) sulphate solution. These products were analysed by thermogravimetry as well as chemical methods and IR spectroscopy.

Kinetic analysis of the thermal dehydration of crushed crystals of Cu(CH3COO)2· H2O was made by use of TG and DSC curves recorded under comparable experimental conditions. Isothermal TG was also employed, and the result was compared with that obtained nonisothermally. The isothermal reaction was described by a phase-boundary controlled reaction (Rn) law, 1 −(1-α)1n = kt, with 1 < n < 2. As for the nonisothermal reaction, there was a tendency for the appropriate kinetic law determined from TG to change from an Avrami-Erofeyev (Am) law, [−ln(1-α)]1m = kt, to one of diffusion-controlled reaction (DL laws as the reaction advanced, particularly for a larger particle-size fraction of the sample. According to DSC, the nonisothermal kinetics were described exclusively by an Am law. The difference in kinetics determined from TG and DSC was explained by the nature of the two methods.

The internal surfaces of crushed crystals of K2CuCl4·2H2O, dehydrated nonisothermally to various reaction fractions, were observed using a polarizing microscope. The reaction proceeds inward, through the advancement of reaction fronts, and is accompanied by some random nucleation in the bulk. The results are compared with those for the nonisothermal dehydration of single crystal K2CuCl4·2H2O (J. Phys. Chem., 92(1988)7023]. A marked difference in kinetic behavior between the two samples is explained by assuming that diffusion of the gaseous product is impeded by the outerlayer of the crystalline product. Mathematical analyses of the simultaneous TG and DSC traces at various heating rates suggest that the reaction, as a whole, is regulated by a contracting geometry law. However, an Avrami-Erofeyev law plays an important role in the early stage of the dehydration. Comparison of kinetic results, assessed from TG and DSC, favors the above assumption that the gaseous diffusion is a rate determining step, particularly at the later stages of reaction.

The compositions and thermal behavior of basic copper(II) sulfates, which were prepared by adding sodium hydroxide to copper(II) sulfate in solutions, were examined extensively by means of chemical analysis, IR spectroscopy, X-ray diffractometry, and thermal analysis. Synthetic brochantite and posnjakite were obtained by the methods used in the present study. The thermal decomposition processes of the compounds prepared to Cu 2 O were characterized by TG and DSC or DTA, as well as other physicochemical techniques.

A very high correlation in the logA-E plot was obtained for the nonisothermal dehydration of CaC 2 O 4 ·H 2 O at various heating rates using the most appropriate function F(α), A 1.9 , estimated from isothermal analysis. Selection of the most appropriate kinetic model function and its stability under the experimental condition examined are crucial to investigate the quantitative kinetic compensation effect.

Either R 1.24 or A 2.60 law was estimated as appropriate for the isothermal dehydration of single crystalline CuSO 4 · 5H 2 O, by analyzing mass-change traces at various temperatures. Microscopic examination of thin sections of single crystalline CuSO 4 · 5H 2 O dehydrated partly, under polarized light, revealed that the dehydration proceeds, on the whole, according to one-dimensional phase boundary controlled reaction mechanism, R 1 . It was proposed that the microscopic observation technique can be used effectively to enable students to recognize the complex feature of solid-state reactions.