Surface Product Layer Research Articles

The physico-geometrical reaction pathway and kinetics of multistep thermal dehydration of calcium chloride dihydrate in a dry nitrogen stream.

Several inorganic hydrates exhibit reversible reactions of thermal dehydration and rehydration, which is potentially applicable to thermochemical energy storage. Detailed kinetic information on both forward and reverse reactions is essential for refining energy storage systems. In this study, factors determining the reaction pathway and kinetics of the multistep thermal dehydration of inorganic hydrates to form anhydride via intermediate hydrates were investigated as exemplified by the thermal dehydration of CaCl2·2H2O (CC-DH) in a stream of dry N2. The formation of CaCl2·H2O (CC-MH) as the intermediate hydrate is known during the thermal dehydration of CC-DH to form its anhydride (CC-AH). However, the two-step kinetic modeling based on the chemical reaction pathway considering the formation of the CC-MH intermediate failed in terms of the reaction stoichiometry and kinetic behavior of the component reaction steps. The kinetic modeling was refined by considering the physico-geometrical reaction mechanism and the self-generated reaction conditions to be a three-step reaction. The multistep reaction was explained as comprising the surface reaction of the thermal dehydration of CC-DH to CC-AH and subsequent contracting geometry-type reactions from CC-DH to CC-MH and from CC-MH to CC-AH occurring consecutively in the core of the reacting particles surrounded by the surface product layer of CC-AH. The acceleration of the linear advancement rate of the reaction interface during both contracting geometry-type reactions was revealed through multistep kinetic analysis and was described by a decrease in the water vapor pressure at the reaction interface as the previous reaction step proceeded and terminated.

New perspective on the depassivation mechanism of chalcopyrite by ethylene thiourea

The catalytic effect of ethylene thiourea (ETU) during the acidic ferric sulfate leaching of chalcopyrite was studied through various approaches. Bioleaching experiments showed that the addition of ETU rapidly dissolved the Cu-rich passivation layer on chalcopyrite, bringing the dissolved Cu/Fe mole ratio back to 1. Continuation of the leaching experiment shows that ETU also enhances copper extraction from depassivated chalcopyrite. Bioleaching tests carried out on pure covellite showed a similar catalytic effect from ETU. Chemical leaching tests conducted on chalcopyrite in acidic ferric/ferrous sulfate solution confirmed that the catalytic effect of ETU does not originate from changes in solution potential. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the leached chalcopyrite surfaces showed that ETU can supress the formation of a copper polysulfide phase during leaching. Ex-situ I-V analysis proved that the product layer is a p-type semiconductor and forms a diode with the n-type bulk mineral. ETU helped dissolve the p-type surface product layer and therefore transitioned the passivated chalcopyrite from a diode back to its native resistor form. Electrochemical impedance spectroscopy (EIS) analysis further demonstrated that the catalytic effect of ETU is more pronounced for passivated chalcopyrite than for a fresh surface. Combined, the results prove that ETU is an excellent remedy for passivated chalcopyrite as it readily catalyzes the dissolution of the passive layer and then continues to catalyze the leaching of native chalcopyrite.

A review of hydrogen chloride removal from calcium- and sodium-based sorbents.

With the steady progress of ultra-low emissions in various industries, the management of unconventional pollutants is gradually attracting attention. A such unconventional pollutant that negatively affects many different processes and pieces of equipment is hydrogen chloride (HCl). Although it has strong advantages and potential in the treatment of industrial waste gas and synthesis gas, the process technology of removing HCl by calcium- and sodium-based alkaline powder has not yet been thoroughly studied. The impact of reaction factors on the dechlorination of calcium- and sodium-based sorbents is reviewed, including temperature, particle size, and water form. The most recent developments in sodium- and calcium-based sorbents for capturing hydrogen chloride were presented, and the dechlorination capabilities of various sorbents were contrasted. In the low-temperature range, sodium-based sorbents had a stronger dechlorination impact than calcium-based sorbents. Surface chemical reactions and product layer diffusion between solid sorbents and gases are crucial mechanisms. Meanwhile, the effect of the competitive behavior of SO2 and CO2 with HCl on the dechlorination performance has been taken into account. The mechanism and necessity of selective hydrogen chloride removal are also provided and discussed, and future research directions are pointed out to provide the theoretical basis and technical reference for future industrial practical applications.

Thermal dehydration of D-glucose monohydrate in solid and liquid states.

The 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 thermal dehydration of DG-MH was systematically traced by thermoanalytical techniques in three different reaction modes: (1) solid-state reaction, (2) switching from a solid- to liquid-state reaction, and (3) liquid-state reaction. Solid-state thermal dehydration occurred under isothermal conditions and linear nonisothermal conditions at a small heating rate (β ≤ 1 K min-1) in a stream of dry N2. The kinetic behavior comprised the presence of an induction period and a sigmoidal mass loss process characterized by a derivative mass loss curve with a symmetrical shape under isothermal conditions, resembling the autocatalytic reaction in homogeneous kinetic processes. When DG-MH was heated at a larger β (≥2 K min-1), the melting of DG-MH occurred midway through the thermal dehydration process, by which a core-shell structure of molten DG-MH and surface product layer of crystalline anhydride was produced. Subsequently, thermal dehydration proceeded as a complex multistep process. Furthermore, the thermal dehydration initiated at approximately the melting point of DG-MH upon the application of a certain water vapor pressure to the reaction atmosphere, and proceeded in the liquid-state, exhibiting a smooth mass loss process to form crystalline anhydride. The reaction pathway and kinetics of the thermal dehydration of DG-MH and the corresponding changes with the sample and reaction conditions are discussed on the basis of the detailed kinetic analysis.

Effect of temperature, oxygen partial pressure and calcium lignosulphonate on chalcopyrite dissolution in sulfuric acid solution

The pressure leaching mechanism of chalcopyrite was studied by both leaching tests and in-situ electrochemical measurements. The effects of leaching temperature, oxygen partial pressure, and calcium lignosulphonate, on copper extraction and iron extraction of chalcopyrite pressure leaching were investigated. The leaching rate is accelerated by increasing the leaching temperature from 120 to 150 °C and increasing oxygen partial pressure to 0.7 MPa. The release of iron is faster than that of copper due to the formation of iron-depleted sulfides. Under the optimal leaching conditions without calcium lignosulphonate, the copper and iron extraction rates are 79% and 81%, respectively. The leaching process is mixedly controlled by surface reaction and product layer diffusion with an activation energy of 36.61 kJ/mol. Calcium lignosulphonate can effectively remove the sulfur passive layer, and the activation energy is 45.59 kJ/mol, suggesting that the leaching process with calcium lignosulphonate is controlled by surface chemical reactions. Elemental sulfur is the main leaching product, which is mixed with iron-depleted sulfides and leads to the passivation of chalcopyrite. Electrochemical studies suggest that increasing the oxygen partial pressure leads to increasing the cathodic reaction rate and weakening the passivation of chalcopyrite.

Kinetics of copper extraction from copper smelting slag by pressure oxidative leaching with sulfuric acid

The accumulation of copper smelting slag not only pollutes the environment but also wastes resources, using oxygen pressure acid leaching process to treat copper slag has incomparable advantages over other processes, but there are few researches reported at home and abroad. In this paper, copper slag was treated by this process. Under the premise of fully studying the influence of various factors on copper dissolution, the selective leaching behavior and kinetics of copper oxy-pressure acid system in copper slag were expounded. The experimental results showed that the dissolution kinetics analysis of the experimental data based on the shrinking core model for various conditions indicated that the reaction rate of leaching was mainly controlled by the chemical reaction during its early stages, then switched to be controlled by mixed chemical-reaction and product-layer diffusion which could be ignored because of its short lifetime, and finally was controlled solely by diffusion through a surface product layer in the later stage. The activation energy was calculated to be 47.03 kJ·mol/L in the early surface chemical reaction controlling stage and 11.35 kJ·mol/L in the later diffusion controlling stage, respectively. The leaching rate of copper is mainly determined by the chemical reaction control stage, in which the reaction orders of sulfuric acid concentration, oxygen partial pressure and particle size are 0.83, 0.92 and −1, respectively.

Structural and kinetic analysis of CO2 sorption on NaNO2-promoted MgO at moderate temperatures

Alkali metal nitrate-/nitrite-promoted MgO sorbents are promising candidates for intermediate-temperature (200–500 °C) CO2 capture. However, the structure-performance relationship and kinetic characteristics of NaNO2-promoted MgO remain unclear. Here the effects of physical-chemical properties on the CO2 sorption performance of NaNO2-promoted MgO and the sorption kinetics were comprehensively studied to elucidate the detailed role of NaNO2. Samples were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The sorption kinetics were obtained by isothermal thermogravimetry and elucidated using a double exponential model. Compared with pure MgO and NaNO3-promoted MgO, NaNO2-modified MgO had a lower initial sorption temperature and a unique bimodal sorption characteristic. Characterization results revealed that such bimodal sorption was due to the presence of double promoters (mixture of NaNO2 and NaNO3) which implies that some of the nitrite was oxidized to nitrate during the preparation process. Deposition of double promoters further reduced the amounts of hydroxide and carbonate species for pure MgO while still preserving more hydroxide and carbonate species on the surface as compared with NaNO3-promoted MgO. The kinetics analysis demonstrated that the double exponential model can describe the sorption process well for both NaNO3- and NaNO2-promoted MgO, suggesting that the entire sorption occurs as a double process (surface chemisorption and product layer diffusion). Significant differences were seen from NaNO3-promoted MgO, and the surface chemisorption process of NaNO2-promoted MgO was independent of temperature, which suggests that an increased presence of hydroxide and carbonate species provides more active sites for greatly facilitating surface chemisorption.

Hydrogen sorption and desorption behaviors of Mg-Ni-Cu doped carbon nanotubes at high temperature

Hydrogen sorption and storage in a solid matrix can greatly improve its safety and efficiency when compared to the compressed gas or liquid hydrogen storage system, and kinetics mechanisms are of interest towards the development of such materials. In this study, the composites of Mg-Ni-Cu doped with singe-walled carbon nanotubes (Mg-Ni-Cu/CNTs) were synthetized. The activation performance, isothermal hydrogen sorption and desorption were systematically tested, and the experimental data were analyzed using the shrinking core model. The results show that three cycles of hydrogen sorption and desorption may be enough to fully activate Mg-Ni-Cu/CNTs and the stability can be kept for 150 cycles. A 10.1 wt% of Cu and 50.3 wt% of Ni in Mg-Ni-Cu/CNTs facilitates the hydrogen sorption and a reversible hydrogen capacity of ∼3.35 wt% can be achieved at 310 °C and 3.0 atm, and hydrogen capacity and kinetics shows significant decline during contact with 1.0 vol% CO impurity. Considering desorption at 600 °C, the kinetic profiles are about linear and desorption is completed within minutes. The gas-solid reaction processes for hydrogen sorption undergo three different rate-limiting stages, and hydrogen desorption can only be divided into two stages of surface chemical reaction and product layer diffusion.

Two-Phase Fluidized Bed Model for Pressurized Carbonation Kinetics of Calcium Oxide

A two-phase reactor model has been developed using a system of ordinary differential equations in MATLAB to model the carbonation reaction and therefore determine the kinetics of calcium oxide in a pressurized fluidized bed reactor as part of the calcium looping cycle. The model assumes that the particulate and bubble phases are modeled as a CSTR and a PFR, respectively. The random pore model developed by Bhatia and Perlmutter1 is incorporated into the system of equations to predict the rate of carbonation for pressures up to 5 bara total, and CO2 partial pressures up to 150 kPa. The surface rate constant and product layer diffusivity in the random pore model expression were obtained by fitting the model to experimental data for a range of pressures, CO2 concentrations, and temperatures by minimization of the residual sum of squares. The surface rate constants were found to be between 3.05 and 12.9 × 10–10 m4 mol–1 s–1 for a temperature range of 550 to 750 °C. The product layer diffusivities were found to...

Hydrogen production and reduction of Ni-based oxygen carriers during chemical looping steam reforming of ethanol in a fixed-bed reactor

Hydrogen production and reduction of Ni-based oxygen carriers (OCs) during chemical looping steam reforming (CLSR) of ethanol were studied in a fixed-bed reactor using four OCs with different supports including NiO/SBA-15, NiO/MCM-41, NiO/MMT and NiO/Al2O3. The OCs prepared were characterized by N2 adsorption-desorption, TPR, TPO, XRD, TEM, FTIR and TGA-DSC. The results demonstrated that NiO component in all the OCs was first reduced by ethanol and the reduced OCs were responsible of catalytic steam reforming and water gas shift for hydrogen production. Mesoporous NiO/SBA-15 presented increasing conversion of NiO reduction and the highest selectivity of hydrogen production. The conversion of ethanol increased with reactions proceeding until the highest value is reached after about ∼300s, and the negative steam conversion obtained was resulted from H2O formation from ethanol oxidation by OCs. Compared with MMT and Al2O3 supports, the oxidization of NiO with MCM-41 and SBA-15 supports was very fast and less carbon was formed and deposited. Enhancement in hydrogen production from CLSR process was achieved by in-situ CO2 removal. Shrinking Core model (SCM) based on the constant pattern model for fixed-bed reactor indicated the rates of OCs reduction with ethanol were mainly controlled by surface chemical reaction and product layer diffusion. The reduction process was found to undergo three different rate-limiting stages, and the critical times for changes in the rate-limiting steps were determined.

Effect of Ca(II) additive on the thermal dehydration kinetics of cerium oxalate rods

Kinetics of the thermal dehydration of solid-state reaction between cerium oxalate microrods and calcium oxalate has been studied using non-isothermal TG–DTA technique. With the introduction of calcium oxalate in varying compositions, the diffusional removal of the incorporated water molecules is impeded due to the blocking action of the surface product layer and the interaction of Ca(II). The procedure of kinetic deconvolution is used as a tool for identifying the partially overlapped kinetic processes of the thermal dehydration of pure and mixed oxalates. Mixed oxalates take more complex reaction pathways for the dehydration rather than pure oxalates of calcium and cerium. The thermal dehydration of pure cerium oxalate decahydrate and calcium oxalate dihydrate occurs in two stages, whereas that of mixed oxalates occurs in three stages. The amount of activation energy needed for the removal of 10 molecules of water from pure cerium oxalate rods and its mixture with calcium oxalate was determined by the isoconversional methods such as KAS, FWO and iterative isoconversional procedure. Significant effect in the thermal stability was observed for the compositions containing lower mass% of calcium oxalate. The average values of \(E_{{{\text{a}}_{\text{i}} }}\) for each independent process of the thermal dehydration of the mixed oxalates follow the order CC4 < CC3 < CC2.

Physico-Geometrical Mechanism and Overall Kinetics of Thermally Induced Oxidative Decomposition of Tin(II) Oxalate in Air: Formation Process of Microstructural Tin(IV) Oxide

This study focuses on the physico-geometrical mechanism and the overall kinetics of the microstructural tin(IV) oxide formation process by the thermally induced oxidative decomposition of tin(II) oxalate in flowing air. Two tin(II) oxalate samples with different morphologies were subjected to a kinetic study involving thermogravimetrical and morphological observations. The reactions exhibited different behaviors at different steps (multistep behaviors); therefore, the overall reactions were resolved into each reaction step using kinetic analyses based on the cumulative kinetic equation. Oxidative decomposition is characterized by a phase boundary controlled reaction initiated by the surface reaction. The formation of the surface product layer at an early stage of the reaction inhibits diffusion of the product and reactant gases. Gaseous diffusion channels are produced via reformulation of the surface product layer by the reaction itself, and the residual reaction advances in the manner of autocatalytic reaction. The kinetic behavior is regulated by the self-generated reaction conditions under specific, transiently formed structural characteristics of the reacting particles, which vary depending on the applied reaction conditions. Therefore, the process control of the oxidative decomposition is an important factor for controlling the microstructure and physicochemical properties of the resulting tin(IV) oxide.

Phenomenological Interpretation of the Multistep Thermal Decomposition of Silver Carbonate To Form Silver Metal

Thermal decomposition of Ag2CO3 to form Ag occurs via a multistep reaction, and the reaction pathway varies drastically with the sample and reaction conditions. Understanding this complex reaction behavior has significance today with respect to the formation of Ag nanoparticles via the thermal decomposition of Ag compounds. In this study, the thermal decomposition of three different Ag2CO3 samples that exhibited different reactivities and reaction pathways was investigated via thermal analyses under linearly increasing temperatures and by studying the morphology of the reacting particles. The thermal decomposition was kinetically deconvoluted into four or five partially overlapping reaction steps, in which the contributions of each reaction step to the overall thermal decomposition of Ag2CO3 to Ag varied as a function of the properties of the sample particles and the heating rate. This complex reaction behavior resulted from the competitive interaction of two physicochemical processes, i.e., sintering of the product particles in the surface product layer and the diffusional removal of the generated gases, during the thermal decomposition of Ag2CO3 and the intermediate compound Ag2O in the geometrical reaction scheme for a contracting volume induced by surface reactions. The high sintering ability of the Ag2O and Ag formed in the surface product layer causes the complex reaction behaviors during the thermal decomposition and disturbs the formation of Ag nanoparticles.

Phenomenological Kinetics of the Carbonation Reaction of Lithium Hydroxide Monohydrate: Role of Surface Product Layer and Possible Existence of a Liquid Phase

This article describes the physico-geometrical mechanism and overall kinetics for the carbonation of lithium hydroxide monohydrate (LHMH). The constituent reactions of thermal dehydration of LHMH and carbonation of as-produced anhydrous lithium hydroxide (LH) were investigated using thermogravimetry and morphological observations. On the basis of the kinetic information of the constituent reactions, the overall reaction of carbonation of LHMH under conditions of different CO2 concentrations and heating rates was kinetically deconvoluted into separate processes of thermal dehydration and reaction of the as-produced LH with CO2. The kinetic results were interpreted, with reference to the morphological characteristics of the partially reacted sample particles at different reaction stages, as the consecutive processes of the thermal dehydration of LHMH and the carbonation of as-produced LH starting at room temperature, which is geometrically controlled by shrinkage of the reaction interface, LHMH–LH–lithium carbonate (Li2CO3). The possible existence of a liquid phase at the reaction interface is deduced from the kinetic behavior and microscopic evidence. Variations in overall carbonation behavior as a function of heating rate and CO2 concentration are explained by the changes in the gaseous diffusion behaviors for H2O evolution and CO2 uptake via the surface product layer of Li2CO3 and the evaporation rate of the liquid phase.

Kinetics and Mechanism of the Thermal Decomposition of Sodium Percarbonate: Role of the Surface Product Layer

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.

Thermal Decomposition of Silver Carbonate: Phenomenology and Physicogeometrical Kinetics

Thermal decomposition of Ag2CO3 to Ag2O was investigated to identify the physicochemical events that occur during the reaction and to reveal the interactions that cause the complex kinetic behavior of the reaction. Based on comparative investigation of thermal decomposition behavior of six different commercially available Ag2CO3, a physicogeometrical reaction model of two partially overlapping reaction stages is proposed. The reaction stages involve the formation of a surface product layer and an internal reaction in the as-produced core–shell structure of the reacting particles. Immediately after the formation of the surface product layer, the structural phase transitions of Ag2CO3 to two different high-temperature phases occur. Under these conditions, the thermal decomposition behavior is controlled by the diffusional removal of CO2 through the surface product layer and/or the increase in internal partial pressure of CO2. The growth of Ag2O particles in the surface product layer produces possible channe...

Phenomenological Kinetics of the Thermal Decomposition of Sodium Hydrogencarbonate

Aiming to find rigorous understanding and novel features for their potential applications, the physico-geometrical kinetics of the thermal decomposition of sodium hydrogencarbonate (SHC) was investigated by focusing on the phenomenological events taking place on a single crystalline particle during the course of the reaction. The overall kinetics evaluated by systematic measurements of the kinetic rate data by thermogravimetry under carefully controlled conditions were interpreted in association with the morphological studies on the precursory reaction, mechanism of surface reaction, structure of the surface product layer, diffusion path of evolved gases, crystal growth of the solid product, and so on. The precursory reaction was identified as the decomposition of impurity, taking place at the boundary between the surface of the SHC crystal and the adhesive small SHC particles deposited on the surface. In flowing dry N(2), the thermal decomposition of SHC proceeds by two-dimensional shrinkage of the reaction interface controlled by chemical reaction with the apparent activation energy of about 100 kJ mol(-1), after rapid completion of the surface reaction and formation of porous surface product layer. Atmospheric CO(2) and water vapor influence differently on the overall kinetics of the thermal decomposition of SHC. Added gas phase of CO(2) slightly inhibits the overall rate because of the increasing contribution of the surface reaction. Under higher water vapor pressure, the physico-geometrical mechanism of the surface reaction changes drastically, indicating the preliminary reformation of reactant surface and the formation of needle crystals of solid product on the surface. The mechanistic change and extended contribution of the surface reaction result in the deceleration of the surface reaction and acceleration of the established reaction.

Thermal Dehydration of Monohydrocalcite: Overall Kinetics and Physico-geometrical Mechanisms

Monohydrocalcite (CaCO(3)·H(2)O: MHC) is similar in composition and synthetic conditions to hydrated amorphous calcium carbonate (ACC), which is focused recently as a key intermediate compound of biomineralization and biomimetic mineralization of calcium carbonate polymorphs. Detailed comparisons of the physicochemical property and reactivity of those hydrated calcium carbonates are required for obtaining fundamental information on the relevancy of those compounds in the mineralization processes. In the present study, kinetics of the thermal dehydration of spherical particles of crystalline MHC was investigated in view of physico-geometrical mechanism. The reaction process was traced systematically by means of thermogravimetry under three different modes of temperature program. A distinguished induction period for the thermal dehydration and cracking of the surface product layer on the way of the established reaction were identified as the characteristic events of the reaction. By interpreting the kinetic results in association with the morphological changes of the reactant particles during the course of reaction, it was revealed that nucleation and crystal growth of calcite regulate the overall kinetics of the thermal dehydration of MHC. In comparison with the thermal dehydration of hydrated ACC, which produces anhydrous ACC as the solid product, the kinetic characteristics of the thermal dehydration of MHC were discussed from the viewpoint of physico-geometry of the component processes.

Formation and Transformation Kinetics of Amorphous Iron(III) Oxide during the Thermally Induced Transformation of Ferrous Oxalate Dihydrate in Air

Focusing on the formation and transformation of amorphous Fe(2)O(3) in the course of the thermally induced transformations of ferrous oxalate dehydrate in air, the kinetics and physico-geometric mechanisms of the respective reaction steps were investigated systematically by means of thermoanalytical methods, complemented by other techniques. The final product of α-Fe(2)O(3) is produced by heating the sample to 700 K via intermediates of poorly crystalline anhydrous FeC(2)O(4) and amorphous Fe(2)O(3), where the external shape and size of the original sample particles are retained during the overall course of reactions. The initial parts of all the three distinguished reaction steps, that is, thermal dehydration of crystalline water, oxidative decomposition of anhydrous FeC(2)O(4) and crystallization of amorphous Fe(2)O(3), are controlled kinetically by the formation or reconstruction of the surface product layers. The surface product layers play important roles of regulating the physico-geometric kinetic behavior of the established parts of the reactions. The oxidative decomposition of intermediate anhydrous FeC(2)O(4), characterized as the formation process of amorphous Fe(2)O(3), arrests in the final stage of the reaction. The as-produced amorphous Fe(2)O(3), protected probably by the outer shell of the surface product layer and the residual anhydrous FeC(2)O(3), crystallizes to α-Fe(2)O(3) being induced by the surface crystallization. Aiming to contribute notably toward provision of the establishment of the novel fabrication routes of nanosized iron oxides by the controlled crystallization of amorphous Fe(2)O(3), the possible factors controlling and/or affecting the formation and transformation kinetics of amorphous Fe(2)O(3) were discussed.

Thermal Decomposition of Indium(III) Hydroxide Prepared by the Microwave‐Assisted Hydrothermal Method

Cubic‐shaped In(OH)3 particles with average size of 0.348 μm were precipitated from a mixed aqueous solution of InCl3 and urea by a microwave‐assisted hydrothermal method. The kinetics and mechanisms of the thermal decomposition of the sample were investigated by means of thermoanalytical measurements under three different modes of temperature program, complemented by several physicochemical techniques. No intermediate compound was found during the course of thermal decomposition from cubic‐In(OH)3 to cubic‐In2O3. Distinguished induction period for the thermal decomposition was identified as one of the most characteristic kinetic phenomena of the present reaction, together with the crack formation on the surface product layer during the second half of the reaction. The kinetic rate behavior of the reaction was characterized physicogeometrically as the surface nucleation and subsequent advancement of the established reaction interface inward toward the center of the reactant particle, where the apparent activation energies for the surface nucleation and advancement of the reaction interface were estimated as 257 and 140 kJ/mol, respectively.