Search

Two different samples of amorphous calcium carbonate (ACC) hydrates were prepared respectively by mixing aqueous solutions of CaCl2 and Na2CO3-NaOH and by allowing the diffusion of (NH4)2CO3 sublimate into ethanol solution of CaCl2. Thermal behaviors of the synthetic ACCs were investigated comparatively by means of thermoanalytical techniques complimented by powder X-ray diffraction, FTIR spectrometry and microscopic observations. The anhydrous ACCs produced by the thermal dehydration of the respective samples were crystallized to calcite in different ways. The sample prepared in aqueous medium was crystallized at around 600 K in a single step. Crystallization in two separated steps at around 600 and 825 K was observed for the sample prepared in ethanol medium. Characteristics of the crystallization processes were discussed from thermodynamic and kinetic points of view.

Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements. A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for the decarbonation process.

Some historical and recent attitudes aimed to bioactive inorganic materials are reviewed. The theory of bridging and non-bridging oxygen is reconsidered as well as the acid and alkali treatment of titanium surface necessary to achieve a good osteointegration. Some theoretical models to characterize mechanical properties are also reviewed.

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.

As a possible candidate for the left-handed metamaterial with negative permeability, a series of Ti, Co-substituted M-type barium hexaferrite BaFe12−x(Ti0.5Co0.5)xO19 (x=0, 1, 2, 3, 4 and 5) was prepared by citrate precursor method. The formation processes of the substituted barium hexaferrite compounds from the precursors were followed by the measurements of powder X-ray diffraction (XRD), Infrared absorption spectra (FT-IR), and thermogravimetry and differential thermal analysis (TG/DTA) coupled with mass spectroscopy (MS). In the case of the non-substituted sample, the formation of the barium hexaferrite is regulated by the thermal decomposition of BaCO3 and the solid-state reactions of BaO and Fe2O3 in the temperature range from 800 to 1100 K. The formation temperature of the substituted BaFe12−x(Ti0.5Co0.5)xO19 is higher than that for the non-substituted sample and increases with the value of x, due to the effects of carbonate ions incorporated by the partial substitution of Fe3+ by (Ti0.5Co0.5)3+. On heating up to ca. 1200 K, all the substituted samples transform into the magenetoplumbite phase as is the non-substituted sample. The compositional dependence of the magnetic properties of the substituted barium hexaferrite was investigated by the magnetization measurement. The decrease in the magnetic anisotropy was confirmed by the change in the magnetization curve and coercivity HC with the composition x. A negative permeability spectrum was observed in the BaFe9(Ti0.5Co0.5)3O19 in the frequency range from 2 to 4 GHz.

This study focused on the kinetic modeling of the thermal decomposition of sodium percarbonate (SPC, sodium carbonate-hydrogen peroxide (2/3)). The reaction is characterized by apparently different kinetic profiles of mass-loss and exothermic behavior as recorded by thermogravimetry and differential scanning calorimetry, respectively. This phenomenon results from a combination of different kinetic features of the reaction involving two overlapping mass-loss steps controlled by the physico-geometry of the reaction and successive endothermic and exothermic processes caused by the detachment and decomposition of H2O2(g). For kinetic modeling, the overall reaction was initially separated into endothermic and exothermic processes using kinetic deconvolution analysis. Then, both of the endothermic and exothermic processes were further separated into two reaction steps accounting for the physico-geometrically controlled reaction that occurs in two steps. Kinetic modeling through kinetic deconvolution analysis clearly illustrates the appearance of the net exothermic effect is the result of a slight delay of the exothermic process to the endothermic process in each physico-geometrically controlled reaction step. This demonstrates that kinetic modeling attempted in this study is useful for interpreting the exothermic behavior of solid-state reactions such as the oxidative decomposition of solids and thermal decomposition of oxidizing agent.

The kinetics and mechanism of the thermal decomposition of granular sodium percarbonate (SPC), which is used as a household oxygen bleach, were studied by thermoanalytical measurements under systematically changing conditions and morphological observation of the reactant solids at different reaction stages. A physico-geometrical kinetic behavior of the reaction that occurs in a core-shell structure composed of an outer surface layer and internal aggregates of SPC crystalline particles was illustrated through detailed kinetic analyses using the kinetic deconvolution method. Simultaneously, the hazardous nature of SPC as a combustion improver was evaluated on the basis of the kinetic behavior of the thermal decomposition. It was found that the outer surface layers of the SPC granules hinder the diffusional removal of product gases generated by the thermal decomposition of the internal SPC crystalline particles. The reaction rate decelerates because of an increase in the internal gaseous pressure as the reaction advances. However, the reaction rate accelerates once crack formation occurs in the outer surface layer at the midpoint of the reaction. Therefore, the overall reaction was empirically demonstrated to consist of two overlapping reaction steps owing to the changes in the self-generated reaction conditions in the interior of the SPC granules.

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.

For the quantitative analyses of evolved CO2and H2O during the thermal decomposition of solids, calibration curves, i.e. the amounts of evolved gases vs. the corresponding peak areas of mass chromatograms measured by TG-MS, were plotted as referenced by the reaction stoichiometry of the thermal decomposition of sodium hydrogencarbonate NaHCO3. The accuracy and reliability of the quantitative analyses of the evolved CO2and H2O based on the calibration curves were evaluated by applying the calibration curves to the mass chromatograms for the thermal decompositions of copper(II) and zinc carbonate hydroxides. It was indicated from the observed ratio of evolved CO2and H2O that the compositions of copper(II) and zinc carbonate hydroxides examined in this study correspond to mineral malachite, Cu2CO3(OH)2, and hydrozincate, Zn5(CO3)2(OH)6, respectively. Reliability of the present analytical procedure was confirmed by the fairly good agreement of the mass fraction of the evolved gases calculated from the analytical values with the total mass-loss during the thermal decompositions measured by TG.

Two different processes of the thermal decomposition of synthetic bayerite, i.e., the non-isothermal decomposition of mechanically ground sample in flowing N2 and the controlled rate thermal decomposition of crystalline bayerite under vacuum, were investigated comparatively. In comparison with the conventional non-isothermal decomposition of crystalline bayerite in flowing N2, the reaction temperature of the thermal decomposition was lowered by the individual effects of mechanical grinding of the sample and the reaction rate control. These decomposition processes indicated similar behavior characterized by the restricted changes of the specific surface area during the course of decomposition reaction and the formation of an amorphous alumina as the decomposition product. Different thermal behaviors were observed for those amorphous Al2O3 produced by the respective decomposition processes.

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.

As one of the typical examples of producing an amorphous dehydration product, the thermal dehydration process of K2B4O7·4H2O was subjected to thermoanalytical and morphological studies. An anhydrous glass was formed via three distinguished dehydration stages. The overall thermal dehydration process was characterized as a self-induced sol-gel process to form anhydrous glass. The as produced anhydrous glass exhibited glass transition at around 700 K and subsequently crystallized via two consecutive exothermic peaks at around 770 and 900 K. The final crystallization product, triclinic K2B4O7, melted at 1072 K.

Kinetic analyses for the solid-state reactions of reactant particles in an assemblage with a particle-size distribution (PSD) have been reexamined for the reactions that proceed by the advance of the reaction interfaces inward toward the center of the individual reactant particles. The experimental kinetic curves for a particle assemblage are influenced by the existing PSD. It has been demonstrated that, even if PSD exists, a reliable activation energy E can be obtained from such overall kinetic curves by the empirical isothermal analysis without accounting for the PSD. The isoconversion methods, which enable us to determine the E value from the data points at a given fractional reaction of a series of experimental kinetic curves, are methodologically independent of the PSD. It is neccessary to incorporate the PSD into the kinetic equation to select an appropriate kinetic model and to evaluate the preexponential factor A. The method of kinetic calculation accounting for the PSD can be generalized, for the kinetic data under any thermal profiles, by extrapolating all the analytical conditions to infinite temperature. For the reaction characterized by the well-defined PSD and kinetic model function, the meaningful A value is obtained by the kinetic analysis at infinite temperature. Although the ability to discriminate the contracting geometry of the reaction interface in a single particle from the overall kinetic curve decreases with increasing PSD, the rate-controlling steps for the advance of the reaction interface, i.e., chemical reaction controlled or diffusion controlled, can be distinguised from each other even for the reactions with a fairly large PSD.

Reaction of FeSO4 · 7H2O with trans-1,2-bis(4-pyridyl)ethylene (tvp) and NaNCS in the mixed solvent of water and ethanol gave rise to the formation of different coordination polymers. One (Fe(tvp)2(NCS)2(H2O)2) is hydrogen bonded and π–π interacted structure, while the other ([Fe(tvp)2(NCS)2][0.5(tvp · 2EtOH)]) is 2D grid structure, which enclathrates tvp · 2EtOH. This enclathrated tvp · 2EtOH interacts with the two 2D grid sheets to form 3D structure. The same reaction was carried out with KNCSe instead of NaNCS (Fe(tvp)2(NCSe)2(H2O)2). 57Fe Mossbauer spectra revealed that all the present assembled complexes are in the FeII high-spin state. The dissociation behavior of enclathrated molecule and ligand was investigated by TG, and the resultant electronic state of iron atom was studied by 57Fe Mossbauer spectroscopy.

An instrument of controlled rate evolved gas analysis (CREGA) coupled with TG-DTA was constructed for analyzing the influences of product gases on the kinetics and mechanism of the thermal decomposition of solids that produce more than one gaseous products at the same stage of reaction. The thermal decomposition of synthetic malachite, Cu2(OH)2CO3, was subjected to the measurements of CREGA-TG under controlled concentrations of H2O and CO2 in the reaction atmosphere with taking account of self-generated H2O and CO2 during the course of reaction. By a series of CREGA-TG measurements carried out under various atmospheric conditions, it was reconfirmed that the reaction is accelerated and decelerated by the effects of atmospheric H2O and CO2, respectively. From the kinetic analysis of the CREGA-TG curves and results of high temperature X-ray diffraction measurements under various reaction atmospheres, it was revealed that the anomalous effects of atmospheric H2O on the reactivity and on the reaction rate of the thermal decomposition of synthetic malachite appear at the early stage of the reaction. Usefulness of the CREGA-TG technique for measuring the kinetic rate data for the thermal decomposition of solids was demonstrated in the present study, by emphasizing the importance of quantitative control of self-generated reaction atmosphere. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 346–354, 2005

The construction of a simple oxygen detector using a zinc–air battery as an oxygen sensor is described. It is a user-friendly device that can be employed in various laboratory activities in both junior and senior high schools. A short circuit can be introduced to reduce the O2 concentration in the air-diffuser layer of the battery that causes a decrease in the voltage. This phenomenon provides the basis to make an electrical device that can produce a voltage increase whenever oxygen gas is present. If the surroundings do not contain any available oxygen gas, the voltage in the zinc–air battery would remain static. In addition, time-to-operate of an electric component attached to the battery can also be used for semiquantitative determination of O2 concentration in a gas sample.

The kinetics of nucleation and crystal growth in a Li2B4O7 glass were investigated using differential thermal analysis (DTA) and differential scanning calorimetry (DSC). This melt forms a glass even when it is cooled at a very slow rate (2 K/min). The temperature range of nucleation was determined by comparing the heights of the exothermic DTA crystallization peaks for samples that were annealed at different temperatures for a fixed time (10 min). Nucleation for this glass occurred in the temperature region of glass transition, where the nucleation rate had a maximum value at ∼770 K. The real detectable enthalpy change that was due to crystallization occurred at temperatures well above the temperature range for nucleation; hence, the temperature regions for nucleation and crystal growth were assumed to be well separated. The glass sample with an almost-saturated number of nuclei, which was prepared by annealing at a temperature of 770 K for 10 min while the melt was cooled, was subjected to DSC measurements at various heating rates (φh). The kinetics of crystal growth were analyzed via the conventional isoconversion method. For the sample without any annealing treatment, the number of nuclei for growth varied, depending on the thermal histories within the temperature region for nucleation, which was characterized by the linear cooling rate (φc) of the melt and the linear heating rate φh of the glass. A kinetic approach that considered the dependence of the number of nuclei on φc and φh was applied to the crystal growth in the nonannealed glass. The three-dimensional growth of the preexisting nuclei with apparent activation energies (E) of 315.6 ± 4.6 kJ/mol for the annealed glasses and 300.6 ± 9.5 kJ/mol for the nonannealed glasses was determined. This agreement in the values of E indicates that the change in the number of nuclei, depending on φc and φh, can be treated successfully by the present kinetic approach for crystal growth.

Influences of the controlled decomposition rate and controlled residual pressure on the thermal decomposition process of synthetic bayerite were investigated by applying a method of controlled rate evolved gas detection (CREGD). Comparing with the conventional process under linearly increasing temperature, the thermal decomposition process of the synthetic bayerite at a controlled decomposition rate (∼10 −2 mg min −1 ) under controlled residual pressure (∼10 −3 Pa) was characterized by the lowered reaction temperature profile and small changes in the specific surface area of the sample during the course of reaction. Formation of an amorphous alumina as the decomposition product is another important result of the process control by the present CREGD. The amorphous alumina crystallizes to η-Al 2 O 3 at around 1100 K. It is worth noting that the characteristics of the reaction process under controlled rate conditions and the formation of amorphous alumina as the decomposition product are very similar to those of mechanochemically activated bayerite under conventional linear heating.

Magnetic transition temperatures, Tc, are measured by simultaneous TM/DTA for Alumel, cobalt, nickel, and three alloys of Ni and Co. The observed values of Tc are corrected using the values for the melting temperatures of pure metals used to define the International Temperature Scale. These corrections are based on the simultaneous melting of these pure metals alongside, but separate from, the magnetic sample. Nine investigators, using a wide variety of instrumentation, have made these measurements utilizing a standard protocol. The results are compared for several heating rates. It is planned to make these same magnetic materials ultimately available to the public for calibration of temperature of their TG instruments.

Correlations between the structural properties of Na2O-CaO-SiO2 glasses characterized by the activity of oxygen ions and the bioactivity were examined by comparing the compositional dependence of the structural parameters calculated on the basis of a thermodynamic consideration with that of the bioactivity. A simple model of characterizing the glass structure by considering the bridging and non-bridging oxygen ions was employed as the first step for this purpose. Further detailed thermodynamic analysis on the anionic constitution in the glass was performed and the compositional dependences of the relative proportions of bridging, non-bridging and free oxygen ions were calculated. The bioactive region corresponded to the compositional region characterized by the higher relative proportion of non-bridging oxygen ions with co-existing an appreciable concentration of bridging oxygen ions, suggesting a possible important role of the non-bridging oxygen ions on the surface chemical process of bone-like apatite layer formation.

The Ozawa concept of generalized time has been used for developing master plots for the different kinetic models describing solid state reactions. These plots can be indistinctly used for analysing isothermal or non-isothermal experimental data. It is demonstrated that it is not possible to discriminate the kinetic model from a single non-isothermal curve without a previous knowledge of the activation energy. However, it has been shown that the ln [(da/dt)/f(a)] data taken from a set of DTG curves obtained at different heating rates lie on a single straight line when represented as a function of 1/T only if the kinetic model really obeyed by the reaction is considered. Moreover, the true values of E and A are obtained from the slope and the intercept of this straight line.

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 reaction process of the thermal dehydration of dilithium tetraborate trihydrate, Li2B4O7⋅3H2O, was reinvestigated from a viewpoint of reaction kinetics. On the basis of the results of thermogravimetry, constant rate thermal analysis, powder X-ray diffractometry, infrared spectroscopy and scanning electron microscopy, it was confirmed that the reaction proceeds via three consecutive kinetic steps characterized by different activation energies. The first and second kinetic steps, accompanied by the destruction of the original crystal structure of the reactant, seem to be assigned to the surface and internal reactions, respectively. During the third kinetic step, the thermal dehydration of hydrated amorphous intermediate, produced at the second kinetic step, and crystallization of the final dehydration product, Li2B4O7, are likely to take place concurrently.

In this study, ferrous oxalate dihydrate polymorph particles, α- and β-phases, with square bipyramidal and quadratic prismatic shapes, respectively, were synthesized. Thermal dehydration of the samples was subjected to kinetic study as a typical reaction that indicates a significant induction period and a sigmoidal mass-loss behavior. On the basis of the formal kinetic analysis of the mass-loss traces recorded under isothermal, nonisothermal, and constant transformation rate conditions and the morphological observations of the surface textures of the partially reacted sample particles, a combined kinetic model for the induction period-surface reaction-phase boundary reaction was developed. The sigmoidal mass-loss behavior after the significant induction period under isothermal conditions was satisfactorily simulated by the combined kinetic model. The kinetic parameters for the component processes of induction period, surface reaction, and phase boundary reaction were separately determined from the kinetic simulation. The differences in the kinetic behaviors of the induction period and the phase boundary reaction between α- and β-phase samples were well described by the kinetic parameters. The applicability of the combined kinetic model to practical systems was demonstrated through characterizing the physicogeometrical kinetics of the thermal dehydration of ferrous oxalate dihydrate polymorphs.

The formation process of bayerite, from an aqueous solution of sodium aluminate through enforced decomposition of aluminate ions by introducing CO2 gas and aging with mechanical stirring, was investigated by pH measurements of the mother solution during preparation reaction and characterization of precipitates obtained at various stages of preparation. An amorphous precipitate, produced initially by the reaction of introduced CO2, transformed to bayerite via pseudoboehmite during aging. It was found that the crystalline particle size and morphology of the crystallized bayerite change depending systematically on the preparation conditions. The reaction pathway of the thermal decomposition of the synthesized bayerite was investigated by using thermoanalytical techniques.

Master plot methods based on the integral and/or the differential forms of the kinetic equation describing solid-state reactions have been redefined by using the concept of the generalized time, θ, introduced by Ozawa. This redefinition permits the application of these master plots to the kinetic analysis of solid-state reactions, whatever the type of temperature program used for recording the experimental data. In isothermal conditions, a single curve is enough to construct the experimental master plots. In nonisothermal conditions, the knowledge of both α as a function of temperature and activation energy is required for calculating the master plot curves from the experimental data. Practical usefulness of the present master plot methods is examined, and exemplified by being applied to the thermal decomposition of ZnCO3 under isothermal, linear nonisothermal, and nonlinear nonisothermal conditions.

The kinetic behavior of the thermal decomposition of synthetic malachite was investigated by means of CRTA under different conditions of reduced pressure, flowing gases and quasi-isobaric atmospheres. The thermal decomposition was found to proceed at lower temperatures under the influence of the self-generated gases, CO2 and H2O. From a viewpoint of chemical equilibrium, the normal and opposite effects on the overall kinetics were observed for the self-generated CO2 and H2O, respectively. The complexity of the present reaction is also reflected by the variations of the apparent kinetic parameters which depend on the applied and self-generated atmospheric conditions. The practical usefulness of CRTA when applied to a complicated thermal decomposition is discussed as exemplified by the kinetic approaches to the present reaction.

Kinetic modeling of the crystal growth from pre-existing nuclei was reexamined to obtain a fundamental information about the controlled crystallization of glasses during formation of advanced inorganic glass-ceramics. Methods of kinetic analysis were reviewed by taking account of thermal history of the sample within the temperature range of nucleation. An accommodation function depending on the thermal history was introduced in the kinetic equation. The role of the accommodation function was reinvestigated when determining the activation energy from a series of kinetic curves. The kinetic description of the crystal growth in the samples with different thermal history was generalized by extrapolating the rate behavior to infinite temperature.

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 crystallization process of Li2B4O7 in the glass of stoichiometric composition, characterized by the crystal growth of pre-existing nuclei, was analyzed kinetically by means of DTA. Because the number of pre-existing nuclei for the subsequent growth varies depending on the cooling rate of the glass-forming melt and heating rate of the as-prepared glass, a modified Kissinger plot was applied for evaluating the apparent activation energy to the crystal growth in the glass samples with three different thermal histories, i.e., the pre-annealed, slowly quenched and quickly quenched glasses. The process was characterized by the three dimensional growth of pre-existing nuclei with the apparent activation energy of ca 340 kJ mol−1.

In an attempt to show the importance of preparing extensively teaching materials for comprehensive education in thermal analysis at an undergraduate level, the significance of the teaching materials concerning the thermal analysis and kinetics of the solid-state reactions is discussed by reviewing our teaching activities at Hiroshima University. Application of the thermoanalytical techniques to thermal decomposition of basic copper(II) salts is appropriate for an introductory experiment to thermal analysis. Microscopic observations of the textural change during the thermal dehydration of inorganic salt hydrates are suitable for introducing the kinetics of solid-state reactions. A computer practice of drawing the experimental master plot enables students to understand the kinetic theory.

The influence of the mass transfer phenomena on the thermal decomposition of calcium carbonate powders under vacuum was investigated through a detailed kinetic analysis by the constant transformation rate thermal analysis (CRTA). Reliable kinetic curves, free from the mass transfer problems, can be obtained by CRTA under vacuum, but within a restricted range of small sample sizes

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 kinetic curves at infinite temperature for the solid-state reactions of the interface shrinkage type were drawn theoretically by taking account the particle size distribution in the sample mixture. The CRTA curves for the reactions with the particle size distribution can be drawn by utilizing the universal kinetic curves at infinite temperature. The proper kinetic treatment for the CRTA curves with the particle size distribution is discussed in connection with the property of the kinetic equation with respect to the particle size distribution. The present kinetic consideration is taken as a simulation for the reactions with a certain distribution in α among the reactant particles, produced preferably by the mass and heat transfer phenomena during the thermoanalytical measurements. The merit of the rate jump method by a single cyclic CRTA curve is also discussed on the basis of the present results.

The reaction pathway of the thermal decomposition of synthetic brochantite, Cu4(OH)6SO4, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu4O(OH)4SO4. The dehydrated sample, Cu4O3SO4, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO4 at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO3, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom.

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.

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.

The bioH gene, which is obligatory for biotin biosynthesis in Escherichia coli, was isolated as an 11-kb EcoRI fragment from E. coli by complementation for the growth of the bioH mutant. Deletion analysis of this fragment showed that the bioH gene was located within the 3.3-kb EcoRI-EcoRV fragment. Sequencing this fragment revealed the presence of two open reading frames, and a further complementation test showed that one of them codes for this gene. The molecular weight of the bioH gene product was about 25-kDa by the maxicell method, which was in good accordance with the molecular weight from the predicted nucleotide sequence. The promoter region of the bioH gene had no significant homology with that of the biotin operon and no operator sequence for the binding of the repressor protein (birA). LacZ-fusion analysis showed that the activity of this bioH promoter was not repressed by biotin, suggesting that the gene expression of the bioH is not regulated by the birA gene product, which acts as a repressor of the biotin operon. We attempted to increase the biotin productivity by the introducing the bioH gene into a high-copy plasmid in the presence of the biotin operon, but the productivity of the biotin and biotin intermediates (total biotin) significantly decreased. This indicated that the overexpression of the bioH gene reduces the level of a biotin precursor, although it is required for biotin biosynthesis.

After frozen storage for 7 d, the viability and CO2 productivity of a conventional baker's yeast strain D greatly decreased. The viability of a freeze-tolerant strain, DFT, used for the frozen dough method slightly decreased after the same storage period, while the CO2 productivity greatly decreased. The CO2 productivity and DNase I inhibitory activity of actin of the cell-free extracts prepared immediately after thawing from 7-d frozen-stored cells markedly decreased in both strains. In DFT, however, the productivity and the inhibitory activity of the cell-free extract increased when the extract was prepared after incubation of the frozen-thawed cells at 30 degrees C. The increase in the inhibitory activity first occurred and then the increase in the CO2 productivity. Gel filtration patterns of actin and glycolytic enzymes were compared between cell-free extracts of both strains. Peaks of actin and activity peaks of hexokinase and pyruvate kinase decreased in the strain D after frozen storage, but only slightly in the strain DFT. After frozen storage, phosphofructokinase activity peak shifted to a lower molecular weight in strain D.

The reaction mechanism and overall kinetics of the thermal decomposition of sodium percarbonate crystals were investigated by thermoanalytical measurements and morphological observations. The reaction proceeds via a surface reaction and subsequent advancement of the as-produced reaction interface toward the center of the crystals, where the seemingly smooth mass-loss behavior can be described by the apparent activation energy Ea of ca. 100 kJ mol(-1). However, considering the rate behavior, as the reaction advances, it is expected that the secondary reaction step characterized by an autocatalytic rate behavior takes part in the overall reaction. The hindrance of the diffusional removal of the evolved gases by the surface product layer, Na2CO3, is the most probable reason for the change in the reaction mechanism. In the deceleration part of the first reaction step, the second reaction step is accelerated due to an increase in the water vapor pressure at the reaction interface inside the reacting particles. We also expect the self-generated reaction condition of the high water vapor pressure and the existence of liquid phase due to the formation of Na2CO3 whiskers as the solid product and the insensitive rate behavior of the second reaction step to a higher atmospheric water vapor pressure. A relevant reaction model for the thermal decomposition of SPC crystals are discussed by focusing on the role of the surface product layer.

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 kinetics and mechanism of the thermal dehydration of magnesium acetate tetrahydrate were investigated as a typical example of the glass formation process via the thermal decomposition of solids. Formation of an intermediate fluid phase was identified as the characteristic phenomenon responsible for the formation of anhydrous glass. Thermal dehydration from the surface fluid layer regulates the zero-order-like rate behavior of the mass-loss process with an apparent activation energy E(a) ≈ 70-80 kJ mol(-1). Because of variations in the mechanism of release of the water vapor with changes in the reaction temperature range, the mass-loss behavior is largely dependent on the particle size of the sample and heating conditions. The formation of hollow anhydrous glass is the novel finding of the present study. The mechanism of formation is discussed in terms of complementary interpretations of the morphological changes and kinetic behavior of the thermal dehydration. On further heating, the as-produced anhydrous glass exhibits a glass transition phenomenon at approximately 470 K with an E(a) ≈ 550-560 kJ mol(-1), and subsequently crystallizes via the three-dimensional growth of nuclei controlled by diffusion. The crystallization process is characterized by an E(a) ≈ 280 kJ mol(-1) and an enthalpy change ΔH = -13.3 kJ mol(-1), resulting in the formation of smaller, rounded particles of crystalline anhydrate.

Chemical kinetics provides mathematical models for explaining and predicting the transformation rate of a chemical system. The fundamental concept of chemical kinetics is based on the law of mass action established by Cato M. Guldberg (1836–1902) and Peter Waage (1833–1900) in the latter half of the nineteenth century (Waage P, Guldberg CM, Studies concerning affinity. Forhandlinger: Videnskabs – Selskabet i Christinia: 35, English trans. (1986) J Chem Edu 63(12):1044–1047, 1864; Guldberg CM, Waage P Concerning chemical affinity. J Prakt Chem [2]. 19:69, 1879), where equilibrium constants were derived in terms of kinetic data and rate equations. The two different aspects, that is, equilibrium and kinetics, were encountered by the recognition that chemical equilibrium is a dynamic process in which rates of reaction for the forward and backward reactions must be equal, so that the chemical driving force of the forward reaction is compensated by that of the reverse reaction. Because the respective reaction rates are proportional to the product of active masses of the reactant species, the equilibrium constant K can be represented by the ratio of the affinity constants (rate constants) of the forward and reverse reactions, k and k′: K = k/k′. The law of mass action was lately reintroduced by J.H. van’t Hoff (1852–1911) from the aspect of chemical kinetics (van’t Hoff JH, Etudes de dynamique chimique. Frederik Muller, Amsterdam, 1884).

The crystal nucleation and growth taking place in glassy and/or amorphous states of solids are of technological importance for characterizing the kinetically controlled stability of the non-crystalline state and for fabricating glass-ceramics with desired properties (Strnad Z, Glass-ceramic materials. Elsevier, Amsterdam, 1986; Sestak J, Thermophysical properties of solids. Elsevier, Amsterdam, 1984). The real kinetics of the crystallization processes is fairly complicated, controlled by various factors of physical properties of glass (Sestak J, Mares JJ, Hubik P (eds), Glassy, amorphous and nanocrystalline materials. Springer, Dordrecht, 2011) and of physicochemistry of elemental kinetic processes. Enormous effort has been paid to formalize the fundamental kinetic theory for the complicated consecutive and/or concurrent processes of nucleation and growth. As one of the results, the overall kinetics of nucleation and growth was formalized as the well-known Johnson–Mehl–Avrami–Erofeyev–Kolgomorov (JMAEK) equation (Jacobs PWM, Tompkins FC, Classification and theory of solid reactions. In: Garner WE (ed) Chemistry of the solid state. Butterworth, London, 1955). The kinetic equation is widely applied for varieties of the solid-state transformation processes (Weinberg MC (ed), Ceramic transactions. Nucleation and crystallization in liquids and glasses, vol 30. The American Ceramic Society, Westerville, 1993; Galwey AK, Brown ME, Thermal decomposition of ionic solids. Elsevier, Amsterdam, 1999; Koga N, Tanaka H, A physic-geometric approach to the kinetics of solid-state reactions as exemplified by the thermal dehydration and decomposition of inorganic solids. Thermochim Acta 388:41–61, 2002). At the same time, the theoretical and practical validities of the application of JMAEK transformation kinetics to the respective processes are always open to discussion (Finney EE, Finke RG, Is there a minimal chemical mechanism underlying classical Avrami–Erofe’ev treatments of phase-transformation kinetic data? Chem Mater 21:4692–4705, 2009).

Geopolymers, X-ray amorphous inorganic polysialates, are geopolymeric ‘cementitous’ composites that are commonly produced by idiosyncratic wet copolymerization (i.e., synthesis via solution) of the individual alumina and silica components. An important role is played by an alkaline activation process in which a powder material of an aluminosilicate nature, such as metakaolin or fly ash, is mixed with an alkaline activator to produce a paste that can set and harden in a short time. These materials, frequently termed alkaline inorganic polymers, geopolymers, hydroceramics, etc., constitute a new family of products that, among other interesting properties, are capable of producing qualities peculiar to cements with those of traditional ceramics and zeolites. Source raw material such as various minerals and industrial by-product materials may be defined as compounds or a mixture of more components that are able to enter in reaction process with water and especially with activator. The polysialates are compared with similar systems based on natural opals and polyphosphates. Hypocrystalline Materials and Their ‘Mers’ Framework is analyzed and Simple Calculation Concepts for Non-bridging Oxygen in Silica Glasses is discussed.

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.