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The multistep thermal dehydration of DCPD to form γ-CPP via DCPA is significantly controlled by the physico-geometrical constraints of the reaction.

The effect of atmospheric water vapor on the thermal dehydration of sodium carbonate monohydrate (SC-MH), which was characterized as cubic grains of a compacted composite comprising columnar SC-MH crystals and a matrix, was systematically assessed using a humidity-controlled thermogravimetry system at various atmospheric water vapor pressures (

Different reaction pathways of thermal dehydration controlled by the bivariant of temperature and p(H2O) exhibit different kinetic features characterized by different temperature and p(H2O) dependences.

In this study, we investigated the mechanistic features and kinetics of the thermal decomposition of solids accompanied by liquefaction as exemplified by the thermal dehydration reactions of monosodium L-glutamate monohydrate (MSG-MH). The thermal dehydration of MSG-MH occurs

Physico-geometrical reaction pathway and kinetics of the thermal dehydration of D-glucose monohydrate (DG-MH) dramatically alter by the melting of the reactant midway through the reaction. By controlling the reaction conditions,...

The influence of atmospheric water vapor on the kinetics of the thermal decomposition of perlite concrete, which is used in the construction of sodium-cooled fast reactor (SFR) plants, was investigated. Changes in the overall thermal behavior were systematically tracked using humidity-controlled thermogravimetry (TG) at various heating rates (β) and atmospheric water vapor pressures (p(H2O)). The multistep process, mainly composed of the thermally-induced removal of various types of water molecules in the cement matrix and the thermal decompositions of Ca(OH)2 and CaCO3, was successfully separated into component reaction steps using kinetic deconvolution analysis (KDA) based on a cumulative kinetic equation. During the thermal dehydration steps, three derivative TG peaks became more clearly distinguishable and shifted to higher temperatures with increasing p(H2O). A significant retardation effect of p(H2O) was observed for the thermal decomposition of Ca(OH)2. Conversely, a slight but detectable catalytic effect of p(H2O) was observed for the thermal decomposition of CaCO3. Through isoconversional analysis of the kinetic curves extracted using KDA, universal kinetic descriptions for the thermal decompositions of Ca(OH)2 and CaCO3 over different β and p(H2O) values were achieved by introducing accommodation functions considering the effect of p(H2O) into the fundamental kinetic equation. The achieved universal kinetic descriptions for the thermal decompositions of Ca(OH)2 and CaCO3 can be introduced into the cumulative kinetic equation for the overall thermal decomposition of perlite concrete as a means to improve the kinetic information used in SFR plant simulation systems for safety assessment.

The thermal behavior of perlite concrete, which is used in sodium-cooled fast reactor plants, was subjected to kinetic modeling to gather the fundamental data for establishing a reliable safety assessment system. In this study, the influence of atmospheric CO2 on the multistep kinetic behavior of perlite concrete was investigated in detail by separating the component reaction steps using kinetic deconvolution analysis (KDA) based on a cumulative kinetic equation. The carbonation of Ca(OH)2 during its thermal decomposition was identified as a specific process observed in the presence of atmospheric CO2. The process was characterized by KDA as the successive thermal decomposition of Ca(OH)2 to form CaO and the subsequent carbonation of CaO. A shift in the temperature range of the overall carbonation process to higher temperatures with increase in partial pressure of CO2 (p(CO2)) was also identified as a specific phenomenon. The thermal decomposition of CaCO3 was separated from the multistep thermal decomposition of the perlite concrete using KDA and analyzed kinetically considering the influence of p(CO2). A universal kinetic description over different temperatures and p(CO2) values was achieved by introducing an accommodation function composed of p(CO2) and the equilibrium CO2 pressure for the reaction. Introduction of the modified kinetic equation with the accommodation function into the corresponding reaction step of the cumulative kinetic equation enables a universal kinetic description of the overall thermal decomposition of perlite concrete over different temperature and p(CO2) conditions.

Thermally-induced reaction between liquid sodium (Na(l)) and calcium hydroxide (Ca(OH)2(s)) was investigated as one of the possible component reactions when Na(l) was reacted with concrete materials under a postulated severe accidental condition in a sodium-cooled fast reactor. The Na(l)–Ca(OH)2(s) reaction was traced using a differential scanning calorimetry (DSC), placed in an argon substituted glove box. An exothermic DSC peak appeared in the temperature range of 550–700 K was attributed to the Na(l)–Ca(OH)2(s) reaction to form a mixed phase comprised of calcium oxide (CaO(s)), sodium hydroxide (NaOH(s,l)) and sodium oxide (Na2O(s)). Based on morphological analyses of reacting system, a physico-geometrical reaction model was proposed: the reaction initiates at the initial contact area of Na(l) and Ca(OH)2(s) and proceeds by the movement of the reaction interface toward Ca(OH)2(s), where the product layer is composed of CaO(s), NaOH(s,l), and Na2O(s). Therefore, the Na(l) diffusion through the product layer is the necessary process to promote the reaction between Na(l) and Ca(OH)2(s), for which a significant influence of the melting of NaOH(s) that has on the overall kinetic behavior is expected. This melting occurs midway through the Na(l)–Ca(OH)2(s) reaction at 594 K. The overall Na(l)–Ca(OH)2(s) reaction was analyzed kinetically using the DSC curves recorded at different heating rates. A partially overlapping two-step reaction feature was evidenced, in which the primary and secondary reaction steps were characterized by the apparent activation energy values of 128 and 138 kJ mol−1, respectively. The multistep feature of the Na(l)–Ca(OH)2(s) reaction could result from the melting of NaOH(s) in the product layer.

This study focuses on the relationship between the aragonite-calcite (A-C) transformation and the thermal dehydration of included water in the biomineralized aragonite construction using freshwater pearl. These thermally induced processes occur in the same temperature region. The thermal dehydration of included water was characterized through thermoanalytical investigations as an overlapping of three dehydration steps. Each dehydration step was separated through kinetic deconvolution analysis, and the kinetic parameters were determined. A single-step behavior of the A-C transformation was evidenced using high-temperature X-ray diffractometry and Fourier transform infrared spectrometry for the heat-treated samples. The kinetics of the A-C transformation was analyzed using the conversion curves under isothermal and linear nonisothermal conditions. The A-C transformation occurred in the corresponding temperature region of the thermal dehydration, ranging from the second half of the second dehydration step to the first half of the third dehydration step. Because the thermal dehydration process is constrained by the contracting geometry kinetics, the movement of the thermal dehydration reaction interface can be a trigger for the A-C transformation. In this scheme, the overall kinetics of the A-C transformation in the biomineralized aragonite construction is regulated by a contracting geometry.

To evaluate the websites of Brazilian fertility clinics included in the 11th Report of the National Embryo Production System (SisEmbrio, 2017) for compliance with the 2004 American Society for Reproductive Medicine (ASRM) and the Brazilian Medical Council (Conselho Federal de Medicina, CFM) guidelines for advertising.We performed an online evaluation of the websites of clinics listed in the 11th SisEmbrio report based on criteria from the 2004 ASRM guidelines (publication of success rates, live birth rates (LBR), method of LBR calculation, success rates by age range and diagnosis, experimental/investigational nature of procedures and the practice of comparison marketing) and CFM guidelines (clinic director name and register visible on the website; no prices displayed, no photos of patients nor success stories with patient identification).A total of 161 SiSEmbrio-registered clinics were evaluated: 153 (95.0%) had functional websites, and only seven were public clinics. Social media presence was as follows: 87 (54.03%) were on WhatsApp; 128 (79.5%) were on Facebook; and 122 (75.8%) were on Instagram. Seventy-five (46.6%) were on other social media platforms (YouTube, LinkedIn, and Twitter). Regarding CFM recommendations, 49 (30.4%) showed information of a registered director, 85 (52.8%) showed patient photos on their websites and/or social media accounts. Fifty-four clinics published success rates (33.5%) and 19 (11.8%) used their own data, whereas seven (4.3%) showed pregnancy rates by age. None reported LBR or advertised prices.The information published online by Brazilian fertility clinics is heterogeneous in nature. A significant portion of the websites does not follow some of the ASRM and CFM guidelines for advertising.

Thermal dehydration of a compacted composite of an inorganic hydrate occurs via a multistep process comprising successive contracting geometry reactions.

The thermal dehydration of calcium sulfate dihydrate exhibits a complex reaction behavior, in which the reaction pathway and kinetics vary depending on water vapor pressure (p(H2O)) applied as the atmospheric condition and generated in the course of the reaction. Under high p(H2O) conditions, a crystalline hemihydrate is produced as an intermediate, which subsequently dehydrates to form anhydride. In this study, the thermal dehydration of calcium sulfate hemihydrate under different self-generated p(H2O) conditions was investigated to gain further insight into the reactions in the calcium sulfate–water vapor system. The thermal dehydration of the hemihydrate under two sets of sampling conditions, namely, in open and lidded (semi-closed) pans, was systematically investigated via thermogravimetry (TG) in different heating program modes. The experimentally resolved TG curves were analyzed using the formal kinetic calculation methods based on isoconversional and isothermal kinetic relationships. Under both the sampling conditions, the thermal dehydration reaction was significantly influenced by self-generated p(H2O), which regulated the reaction proceeding from the top surface of the sample bed to the bottom. Under higher self-generated p(H2O) conditions in a lidded pan, the thermal dehydration under different heating program modes exhibited an invariant kinetic behavior characterized by a single set of kinetic parameters, whereas in an open pan the kinetic behavior varied between the reactions under isothermal and other heating modes. Based on the results of the formal kinetic analysis, an advanced kinetic modeling based on a physico-geometrical consecutive reaction model was examined to describe in detail the specific kinetic features of the reaction under self-generated p(H2O) conditions.

Thermal decomposition of solids is often accompanied by autocatalysis, one of the possible causes of which is the formation of a liquid phase. The kinetic model considering the liquefaction of solid reactants under isothermal conditions was proposed by Bawn in the 1950s. The present study reports the application of the Bawn model to the thermolysis of 3,4,5-trinitropyrazole ammonium salt (ATNP) under nonisothermal conditions. The thermal decomposition of ATNP is comprised of low-temperature and high-temperature stages. The low-temperature stage exhibits two distinct exothermic peaks in differential scanning calorimetry (DSC), fitted by two consecutive autocatalytic reactions with a model-fitting kinetic analysis. The liquefaction of the solid reactant during the first reaction is directly observed, giving mechanistic evidence for the Bawn model. We have expressed the Bawn model by a combination of two extended Prout-Tompkins (ePT) equations with the activation energy for the leading liquid-state reaction of Ea = 140.6 ± 0.3 kJ mol-1. The release of ammonia is detected from the beginning, suggesting that the thermal dissociation of ATNP to 3,4,5-trinitropyrazole is an initiation reaction of the thermal decomposition. We proposed ATNP liquefication, leading to the apparent autocatalytic behavior of the first global decomposition reaction, is caused by the eutectic formation between ATNP and 3,4,5-trinitropyrazole, as it was confirmed by DSC analysis of the artificial mixture. The presented approach of the combination of ePT formalism with a Bawn model is generally applicable to a broader range of thermal processes accompanied by liquid phase formation and apparent acceleration.

A newly developed laboratory learning program for high school chemistry courses is discussed, in which students discover the chemical mechanism governing exothermic phenomena during the reaction between a heating agent, namely, calcium oxide (CaO)–aluminum (Al) mixture, and water. Based on prior knowledge of simple heating agents such as CaO, the students were able to accurately identify the component chemical reactions in the CaO–Al mixture and water system using three pairs of comparable thermometric measurements arranged in a stepwise manner. In each step, the students designed the comparative experiments for each student group through logical thinking and argumentation to obtain relevant and reliable results. Active interpretation of the results enabled each student to learn the chemical phenomena inherent in the observed reactions, and their understanding was deepened through evidence-based argumentation and debate. Finally, students in each group proposed an overall chemical mechanism governing the reaction between the CaO–Al mixture and water by consolidating the knowledge acquired during the previous inquiry steps. The proposed chemical mechanism was fine-tuned through group presentations, followed by question and answer sessions. The 6-h evidence-driven activity provided numerous opportunities for experiencing the multifaceted aspects of the scientific inquiry process.

This study examines the thermal dehydration of β-maltose monohydrate into the anhydride, in which a liquid phase formation during the reaction process has significant influence on the mechanistic a...

The physico-chemical and physico-geometrical characteristics of the thermal decomposition of solids should be considered when interpreting the effects of atmospheric conditions on the kinetics.

While heating a seawater spiral shell (Euplica scripta), thermally induced aragonite–calcite (A–C) transformation occurred within the temperature region of multistep thermal dehydration. Here, the kinetic interplay between the A–C transformation and thermal dehydration was studied as a possible cause of the reduction in the A–C transformation temperatures. The kinetics of the A–C transformation was systematically investigated under isothermal conditions by powder X-ray diffractometry and under linear nonisothermal conditions by Fourier transform infrared spectroscopy. The thermal dehydration was characterized as a partially overlapping, three-step process by thermogravimetry–differential thermal analysis coupled with mass spectroscopy for the evolved gases. The A–C transformation occurred in the temperature range of the final part of the second dehydration step and the initial part of the third dehydration step. The kinetics of A–C transformation and thermal dehydration were characterized by contracting geometry-type models, in which the respective transformations were regulated by a constant linear advancement rate and diffusional removal of water vapor, respectively. Based on the kinetic results, the mutual interaction of those thermally induced processes is discussed as a possible cause of the reduction in the A–C transformation temperature.

This study aimed to evaluate the practical usefulness of kinetic deconvolution analysis (kDa) as a means to obtain the kinetic information on specific reaction steps that characterize the thermal properties of materials for various purposes. The partially overlapping multistep thermal decomposition of Maya Blue (MB)-type pigments was used as an example reaction. Red and yellow MB-type pigment materials, composed of a fibrous clay mineral and an organic dye, were synthesized using palygorskite and sepiolite as the clay minerals and Methyl Red and Alizarin as red and yellow dyes, respectively. The multistep thermal decompositions of the MB-type pigments were investigated using thermogravimetry. The thermoanalytical data were deconvoluted into individual component reaction steps using an empirical kDa technique based on a cumulative kinetic equation that considers the contribution of each reaction step to the overall thermal decomposition. By comparing the kDa results for the thermal decomposition of the composites with those for the decomposition of pure palygorskite and sepiolite, the thermal decomposition steps for the incorporated organic dyes were extracted from the multistep thermal decompositions of the MB-type pigments. Finally, the thermal stabilities of MB-type pigments comprising different clay minerals and organic dyes were compared using the kinetic results extracted for the reaction step associated with the decomposition of the organic dyes.

The thermal decomposition of Mg(OH)2 was selected to realize an integrated kinetic understanding of the thermal decomposition of inorganic solids by correlating the physico-geometrical mechanisms and the effect of the product gas presented in the reaction atmosphere. Herein, the mechanistic features of the reaction, as revealed by a systematic kinetic study on a reaction in flowing dry N2 gas, were reported as the first part of the study. In spite of the smooth mass loss under various heating conditions, the formal kinetic analysis based on an assumption of single-step reaction indicated a possible multistep reaction comprising the surface reaction (SR) and subsequent internal phase boundary-controlled reaction (PBR). Two physico-geometrical models were applied to find the mechanistic features of the overall reaction. One is a single reactant-body model with an assumption of independent SR and PBR. The other is based on the physico-geometrical consecutive SR–PBR model in the assemblage of reactant particl...

Complex kinetic behaviors in the thermal dehydration of CaSO4·2H2O under varying water vapor pressure (p(H2O)) conditions impel researchers in the field of solid-state kinetics to gain a more comprehensive understanding. Both self-generated and atmospheric p(H2O) are responsible for determining the reaction pathways and the overall kinetic behaviors. This study focuses on the influence of the self-generated water vapor to obtain further insights into the complexity of the kinetic behaviors. The single-step mass-loss process under conditions generating a low p(H2O) was characterized kinetically by a physico-geometrical consecutive induction period, surface reaction, and phase boundary-controlled reaction, along with the evaluation of the kinetic parameters for the individual physico-geometrical reaction steps. Under the conditions in which more p(H2O) was generated, the overall reaction to form the anhydride was interpreted as a three-step process, comprising the initial reaction (direct dehydration to the anhydride) and a subsequent two-step reaction via the intermediate hemihydrate, which was caused by the variations in the self-generated p(H2O) conditions as the reaction advanced. The variations in the reaction pathways and kinetics behaviors under the self-generated p(H2O) conditions are discussed through a systematic kinetic analysis conducted using advanced kinetic approaches for the multistep process.

This study focuses on designing a laboratory learning program for a high school chemistry course in which students could discover the fundamental principles of Hess’s law via stepwise inquiry. By e...

International audience; The impact that product gas in the reaction atmosphere has on the kinetics of the thermal decomposition of inorganic solids is an outstanding issue that requires a solution to understand the reactions in a solid–gas system. Among a variety of kinetic phenomena induced by atmospheric gas, the restraining effect of the overall reaction rate with increasing partial pressure of the product gas in the reaction atmosphere is the most widely observed phenomenon. In this study, we describe the universal kinetics of the thermal decomposition of solids over different temperatures and partial pressures of the gas, as exemplified by the thermal decomposition of Cu(OH)2. Universal kinetic descriptions were enabled by introducing an accommodation function, with respect to atmospheric water vapor pressure, into the fundamental kinetic equation for solid-state reactions. The thermoanalytical curves as measured systematically under different temperatures and water vapor pressure conditions were kinetically analyzed in a step-by-step manner to attain kinetic modeling of the physico-geometrical consecutive process that comprises the induction period, surface reaction, and phase boundary-controlled reaction. The impact that atmospheric water vapor has on the kinetics of each physico-geometrical reaction step was separately evaluated using the universal kinetic approach.

In this study, the thermal behavior of the perlite concrete used in a sodium-cooled fast reactor was investigated for obtaining information on a plant simulation system for safety assessment. The thermal stability and kinetic behavior of multistep thermally induced processes of perlite concrete were examined using thermoanalytical techniques and other complementary methods. The partially overlapping thermal decomposition process comprising seven reaction steps was characterized by kinetic deconvolution analysis based on a cumulative kinetic equation by determining the contribution and all kinetic parameters for each component reaction step. The thermal decomposition product was a mixture of amorphous and crystalline phases located in a CaO-rich region in the SiO2–CaO phase diagram. The softening or melting of the decomposition product was initiated at approximately 1520 K. The significance and reliability of the results obtained were discussed on the premise of their practical uses for the safety assessment.

The thermal decomposition of spherically granulated malachite particles was investigated to unveil the specific kinetic features of the reaction in samples in granular form toward the improvement of the thermal processing of malachite as a precursor of functional CuO. Granular malachite underwent thermal decomposition via a partially overlapping two-step mass loss process upon heating the sample in a stream of dry N2 gas. Morphologically, the process was characterized by swelling of the granular particles and cleavage divisions of the surface layer. The kinetics of the thermal decomposition was investigated through step-by-step kinetic analyses of the systematically recorded thermoanalytical curves. Finally, the kinetics of the component reaction steps was separately characterized by performing a kinetic deconvolution analysis. The first reaction step, which contributed approximately 25% to the overall reaction and followed pseudo-first-order kinetics, was attributed to the thermal decomposition of the granular particle surface. The as-produced surface product layer impeded the diffusional removal of the gaseous products, i.e., CO2 and water vapor, from the interior of the granular particles, which caused swelling of the granular particles owing to an increase in the internal gaseous pressure and the cleavage division of the surface product layer by crack formation. The second mass loss step occurred inside the granular particles under significant variations in the self-generated reaction conditions and geometrical constraints and reached its maximum rate midway through the reaction. Possible causes of the observed specific rate behavior are discussed from the viewpoint of physico-geometrical kinetics in the solid–gas system.

International audience; The thermal decomposition of smithsonite (ZnCO3) was studied to obtain a universal kinetic description of the process applicable to a range of reaction conditions. A synthesized ZnCO3 was subjected to thermoanalytical measurements under various heating and atmospheric conditions in a flow of dry N2gas, N2–CO2, or N2–H2O mixed gases. Systematic shifts of the reaction temperature to higher and lower temperatures by the effects of CO2 and H2O, respectively, were identified as specific characteristics of the system. With reference to the physico-geometrical kinetic behavior of the reactionin a flow of dry N2 gas, the retardation effect of CO2 was demonstrated in the scheme of the physicogeometrical consecutive surface reaction (SR) and phase boundary-controlled reaction (PBR). The individual kinetics of the SR and PBR were universally described over different CO2 pressures using an accommodation function (AF) obtained by considering the consecutive elementary steps of SR and PBR. The catalytic effect of water vapor was assumed to result from contributions of the water molecules on the consecutive elementary steps of SR and on the crystal growth of the solid product of the reaction (ZnO). An alternative AF derived considering the adsorption of water molecules on solid surfaces allowed us to obtain the universal kinetic description of the thermal decomposition over different water vapor pressures.

This study focuses on the physico-geometrical constraints of the kinetics of the thermal decomposition of solids as exemplified by the thermal dehydration of α-oxalic acid dihydrate and the subsequent thermally induced sublimation/decomposition of the as-produced anhydride using the samples of crystalline particles (CPs) and a single crystal (SC) form. The CP and SC samples possess approximately similar geometrical figures with different sizes. The shapes of the original dihydrate and the as-produced anhydride from thermal dehydration are practically congruent. Therefore, proper evaluations of the current kinetic understanding of contracting geometry-type reactions were expected by the comparisons of the kinetic behaviors among different sample forms and thermally induced processes. The kinetic analysis of the thermal dehydration process revealed that the consecutive physico-geometrical processes comprised of an induction period, a surface reaction, and a phase boundary-controlled reaction, where distinguishable differences in the rate behavior were observed between the CP and SC samples for the surface reaction. On the other hand, the thermally induced sublimation/decomposition of the anhydride was described as an ideal single-step geometry contraction process, for which the CP and SC samples exhibited the same rate variation behavior under isothermal conditions. However, the sublimation/decomposition processes of the CP and SC samples were characterized by the different Arrhenius parameters, in which the compensative changes in the apparent activation energy and preexponential factor were apparent. Implications for the kinetic modeling of the solid-state reactions and the interpretation of kinetic results were obtained from the results of the comparative kinetic study for different sample forms and thermally induced processes.

International audience; This study aims to universally describe the kinetic features of the thermal dehydration of lithium sulfate monohydrate across different temperatures (T) and atmospheric water vapor pressures (p(H2O)) as a model reaction of the thermal dehydration of crystalline hydrates. The features of the physicogeometrical consecutive process, comprising the induction period (IP)–surface reaction (SR)–phase boundary-controlled reaction (PBR), and the effect of p(H2O) on kinetic behavior were revealed experimentally under various heating conditions. Then, the accommodation function (AF), accounting for the effect of p(H2O) on the kinetic behavior, was derived by considering the consecutive/concurrent elementary steps of SR and PBR at the atomic and molecular levels. The universal kinetic descriptions for the IP and subsequent mass-loss process were realized by introducing the AF into formal kinetic equations and using the isoconversional kinetic relationship. Furthermore, by combining the physicogeometrical consecutive IP–SR–PBR(n) model and the formulated AF, the universal kinetic descriptions for each physicogeometrical reaction step across different T and p(H2O) conditions were obtained, which reveal novel kinetic features of each reaction step and these variations as the reaction step advances. The significance of the revealed kinetic features is discussed through demonstrating the development of the novel kinetic approach.

Thermal behaviors of two different siliceous concretes used in a sodium-cooled fast reactor were comparatively investigated in a temperature range from room temperature to 1900 K for obtaining fundamental information required for establishing a plant simulation system for safety assessment under a postulated accidental condition. Silica crystals and Portland cement were identified as the major component of the aggregate and cement portions of the concrete samples, respectively. The thermal decomposition of the cement portion exhibited partially overlapping multistep reaction comprising the thermal dehydration, thermal decomposition processes of Ca(OH)2 and carbonate compounds including CaCO3. TG–DTG curves recorded for the multistep thermal decomposition process of the cement portion were analyzed using the kinetic deconvolution analysis, and the contributions and kinetic parameters of each reaction step were determined. The kinetics of comparable reaction steps between two samples were practically identical, while the difference between the samples was found in the content ratio of Ca(OH)2/CaCO3. The melting behavior of the siliceous concretes was revealed by the complementary interpretation of TG–DTA curves and the morphological observation of the sample heated to different temperatures. The softening and melting behaviors of the siliceous concretes initially occurred in the thermal decomposition product of the cement portion at a temperature range of 1400–1600 K. The subsequent melting behavior of the aggregate portion that occurs at a higher temperature was different between the samples, owing to the different compositions of the aggregates and the possible interaction of the aggregate with the molten cement portion.

The thermal behaviors of carbon/carbon (C/C) composites in flowing air were investigated on the basis of mechanical pencil leads with different hardness values and diameters as a model system. Two separated mass-loss processes were observed during heating the mechanical pencil leads in air, which are attributed to the evaporation–decomposition of an impregnation agent and the subsequent thermal oxidation of the residual C/C composite. The thermal behaviors were invariant among the mechanical pencil leads with different diameters, but they systematically changed with hardness. Variations in the thermal behaviors can be quantified by the mass-loss value during the evaporation–decomposition of the impregnation agent, in addition to the kinetic deconvolution analysis that was applied to the multistep thermal oxidation process of carbon components with different reactivities. These results correlate the thermal behavior with the compositional and structural characteristics of C/C composites, which can be usefu...

The thermal dehydration of sodium thiosulfate pentahydrate (STS-PH), which has been studied as a potential thermal energy storage material, was investigated from the points of view of the physicoge...

This study focused on the thermal decomposition of biomineralized CaCO3, using avian eggshell. Biomineralized CaCO3, which exhibits a specialized structure, is a possible source of CaO used across various applications, including CO2 capture. An understanding of the relation between the thermal decomposition kinetics in producing CaO and the original structure of biomineralized CaCO3 may contribute to the further effective use of biowastes. The thermal decomposition of avian eggshell occurs via two mass-loss processes: the primary thermal degradation of the outer shell membrane and the subsequent thermal decomposition of calcite in the shell matrix. Each mass-loss process is composed of multiple reaction steps. The partially overlapping reaction steps originate from the structural characteristics of the eggshell, in addition to the physicochemical properties of the reactant in each process. The overlapping features of the component reaction steps were revealed by a detailed kinetic analysis of mass-loss cu...

Calcium looping (CaL) reactions in a Ca(OH)2-CaCO3-CaO system for energy storage and CO2 absorption occur during the thermal decomposition of cement and concrete materials. Herein, we report the kinetic behavior of the reactions in a cement matrix as the necessary information for establishing a CaL cycle supported by cement/concrete materials. The thermal decomposition of Portland cement samples, characterized by different Ca(OH)2/CaCO3 ratios, under different atmospheric water vapor and CO2 conditions were investigated to reveal the kinetic behavior of the component reactions and the changes with atmospheric conditions. The multistep thermal decomposition, characteristic of each sample and atmospheric condition, were separated into individual reaction steps through a kinetic deconvolution analysis. Using the extracted kinetic curves for the reactions of Ca(OH)2 and CaCO3, retardation effects of atmospheric water vapor and CO2 on the thermal decompositions of Ca(OH)2 and CaCO3, respectively, were kinetically described by introducing different accommodation functions (AF) comprised of the partial pressures of the gases and their equilibrium pressure. In addition, the kinetic description of the catalytic effect of water vapor on the thermal decomposition of CaCO3 was achieved by introducing alternative AF of water vapor pressure. The thermally induced carbonation of Ca(OH)2, which occurred in the presence of atmospheric CO2, was characterized kinetically as physico-geometrically regulated consecutive reactions of thermal decomposition of Ca(OH)2 and subsequent carbonation of the as-produced CaO. Kinetic information concerning the reactions of Ca(OH)2 and CaCO3 in the cement materials is reported in details.

Thermally induced carbonation of Ca(OH)2 in a CO2 atmosphere is a reaction exhibiting particular features, including stoichiometric completeness to form CaCO3 and a kinetic advantage over the carbonation of CaO particles. This study aims to gain further insight into the reaction mechanisms of CO2 capture by Ca(OH)2 and CaO. It focuses on the kinetic modeling of the carbonation of Ca(OH)2 as a consecutive reaction in a solid–gas system. The kinetic behaviors of the thermal decomposition of Ca(OH)2 in an inert gas atmosphere and of the overall process of thermally induced carbonation of Ca(OH)2 in a CO2 atmosphere were investigated using thermal analyses and other complementary techniques. Based on kinetic results, the overall reaction of the thermally induced carbonation of Ca(OH)2 in a CO2 atmosphere was separated by a kinetic deconvolution analysis into two consecutive reaction steps: the thermal decomposition of Ca(OH)2 and the subsequent carbonation of the CaO intermediate. The relationship between the two component reaction processes was well illustrated by a consecutive shrinkage of the dual reaction interfaces of Ca(OH)2–CaO and CaO–CaCO3. The continuous supply of water vapor and CO2 to the CaO–CaCO3 interface from different directions was suggested to be the physico-geometrical advantageous feature of the carbonation of Ca(OH)2.

This article demonstrates a kinetic approach to partially overlapping multistep chemical reactions in solid-gas systems as exemplified by the thermal decomposition of granular sodium perborate tetrahydrate. This reaction proceeds via successive thermal dehydration and decomposition occurring at different temperatures to form sodium metaborate. Each reaction process comprises several kinetic steps originating from different physicochemical and physico-geometric phenomena. The partially overlapping multistep processes were characterized using available thermoanalytical techniques and microscopic observations. Conventional isoconversional kinetic analysis and empirical mathematical deconvolution were applied to each reaction process as preliminary kinetic approaches to extracting provable kinetic information. Then, each reaction process was analyzed kinetically based on a cumulative kinetic equation, i.e., kinetic deconvolution analysis. The results of the kinetic deconvolution analysis were further examined by comparison with other kinetic information for the specific kinetic steps obtained from different thermoanalytical measurements. From the results of this comprehensive kinetic approach, the kinetic features of the thermal dehydration and decomposition processes were revealed by identifying their contributing physicochemical and physico-geometric phenomena and evaluating their influences on the overall multistep processes.

Under postulated accidental condition of sodium-cooled fast reactor (SFR), liquid sodium spill into the floor may lead to fail the steel liner. Consequently, sodium–concrete reaction (SCR) comes to occur by direct contact of liquid sodium with structural concrete. Significant phenomena of SCR for safety assessment of SFR are hydrogen release, energy release by exothermic heat generation, and concrete ablation by chemical corrosion. SCR consists of two reaction stages: (1) dehydration of concrete and hydrogen release by the reaction of evolved water vapor with Na as initial stage and (2) ablation of concrete by reactions between concrete compositions and Na compounds as secondary stage. In this study, the sodium hydroxide (NaOH)–silica (SiO2) reaction as one of the possible secondary stage reactions was investigated for safety assessment of SFR. Thermal behavior of NaOH–SiO2 reaction such as reaction onset was determined using a differential scanning calorimetry (DSC). As a result of DSC measurement, it was revealed that NaOH–SiO2 reaction occurs as rapid reaction right after NaOH melting at 583 K. Therefore, it was expected that NaOH–SiO2 reaction is dominant in the time frame of secondary stage of SCR if significant amount of NaOH has been generated during the initial stage reaction. Meta sodium silicate (Na2SiO3) was detected as the major solid product of NaOH–SiO2 reaction from XRD analysis. Considering the phase diagram of NaOH–SiO2 reaction system, likely overall reaction pathway of NaOH–SiO2 reaction was discussed.

The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations provide guidance on kinetic analysis of multi-step processes as measured by thermal analysis methods such as thermogravimetry (TGA) and differential scanning calorimetry (DSC). Ways of detecting the multi-step kinetics are discussed first. Then, four different approaches to evaluation of kinetic parameters (the activation energy, the pre-exponential factor, and the reaction model) for individual steps are considered. The approaches considered include multi-step model-fitting as well as distributed reactivity, isoconversional, and deconvolution analyses. For each approach practical advice is offered on its effective usage. Due attention is also paid to the typical problems encountered and to the ways of resolving them. The objective of these recommendations is to help a non-expert with efficiently performing multi-step kinetic analysis and interpreting its results.

International audience; Thermal decomposition of Ca(OH)2 under atmospheric water vapor exhibits special features, including an induction period (IP) and a subsequent sigmoidal mass-loss behavior under isothermal conditions. Atmospheric water vapor reduces the reaction rate at a specific temperature and causes a systematic shift of the mass-loss curve, which was recorded at a specific heating rate, to higher temperatures as the water vapor pressure, p(H2O), increases. The challenge in this study was to universally describe the kinetics of thermal decomposition under various p(H2O) conditions by introducing an accommodation function in the fundamental kinetic equation. The accommodation function in the multiplied form of two p(H2O) components with a variable exponent in each component was derived on the basis of the classical nucleation and interface reaction theories. The universal kinetic approach was realized by applying the accommodation function to formal kinetic analyses of the Arrhenius plot for the IP and the Friedman plot for the mass-loss process. Furthermore, the overall reaction process under isothermal conditions was analyzed kinetically on the basis of the physico-geometrical consecutive reaction model, which was composed of an IP, a surface reaction (SR), and a phase boundary-controlled reaction (PBR). Subsequently, the kinetic parameters for each physico-geometrical reaction step were determined by the modified Arrhenius plot with the accommodation function. The impact of the atmospheric water vapor on the kinetics of thermal decomposition was characterized in connection with physico-geometrical reaction mechanisms through the interpretation of the kinetic parameters and these variation behavior patterns as the overall reaction advanced.