Yui Yamamoto

Bio: Yui Yamamoto is an academic researcher from Hiroshima University. The author has contributed to research in topics: Thermal decomposition & Reaction step. The author has an hindex of 2, co-authored 4 publications receiving 22 citations.

Thermal Dehydration of Lithium Sulfate Monohydrate Revisited with Universal Kinetic Description over Different Temperatures and Atmospheric Water Vapor Pressures

Abstract: 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 Decomposition of Maya Blue: Extraction of Indigo Thermal Decomposition Steps from a Multistep Heterogeneous Reaction Using a Kinetic Deconvolution Analysis.

Abstract: Examining the kinetics of solids’ thermal decomposition with multiple overlapping steps is of growing interest in many fields, including materials science and engineering. Despite the difficulty of describing the kinetics for complex reaction processes constrained by physico-geometrical features, the kinetic deconvolution analysis (KDA) based on a cumulative kinetic equation is one practical method of obtaining the fundamental information needed to interpret detailed kinetic features. This article reports the application of KDA to thermal decomposition of clay minerals and indigo–clay mineral hybrid compounds, known as Maya blue, from ancient Mayan civilization. Maya blue samples were prepared by heating solid mixtures of indigo and clay minerals (palygorskite and sepiolite), followed by purification. The multistep thermal decomposition processes of the clay minerals and Maya blue samples were analyzed kinetically in a stepwise manner through preliminary kinetic analyses based on a conventional isoconversional method and mathematical peak deconvolution to finally attain the KDA. By comparing the results of KDA for the thermal decomposition processes of the clay minerals and the Maya blue samples, information about the thermal decomposition steps of the indigo incorporated into the Maya blue samples was extracted. The thermal stability of Maya blue samples was interpreted through the kinetic characterization of the extracted indigo decomposition steps.

Kinetic analysis of the multistep thermal decomposition of Maya Blue-type pigments to evaluate thermal stability

Abstract: 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.

Thermal decomposition of spherically granulated malachite: physico-geometrical constraints and overall kinetics

Abstract: 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.

Kinetics of contracting geometry-type reactions in the solid state: implications from the thermally induced transformation processes of α-oxalic acid dihydrate

Abstract: 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.

Universal Kinetics of the Thermal Decomposition of Synthetic Smithsonite over Different Atmospheric Conditions

Abstract: 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...

Kinetics and Mechanism of the Dehydration of Calcium Sulfate Dihydrate: A Comprehensive Approach for Studying the Dehydration of Ionic Hydrates under Controlled Temperature and Water Vapor Pressure

Abstract: We studied the kinetics and mechanism of the dehydration reaction of calcium sulfate dihydrate to hemihydrate under controlled temperature and water vapor partial pressure. From kinetic and reactio...