Kinetics Of Solid-state Reactions Research Articles

Characterization of In-Situ TiB/TiC Particle-Reinforced Ti-5Al-5Mo-5V-3Cr Matrix Composites Synthesized by Solid-State Reaction with B4C and Graphite through SPS

In-situ TiB/TiC particle-reinforced titanium matrix composites (TMCs) based on a near-β Ti-5Al-5Mo-5V-3Cr alloy (Ti-5553) were synthesized by solid-state reaction with B4C and graphite particles during spark plasma sintering (SPS). In this study, investigations were focused on the influence of the molar TiB:TiC ratio on the mechanical properties of the composites. With respect to the adjustment of the molar TiB:TiC ratio, the formation of stoichiometric TiC or nonstoichiometric TiCy was considered as the literature provides conflicting information in this respect. Furthermore, the solid-state reaction behavior influenced by the matrix alloying elements is discussed in comparison to a pure titanium matrix. The hardness, compressive strength and bending strength of the TMCs were improved successfully due to the TiB and TiC particles maintaining acceptable levels of ductility. However, X-ray diffraction experiments revealed that for the adjustment of the molar TiB:TiC ratio, the stoichiometry of the TiCy particles formed must be considered as nonstoichiometric TiC0.5 resulted from the solid-state reaction of carbon and titanium. Compared to TMCs with pure titanium matrices, more sluggish solid-state reaction kinetics were observed. This was attributed to the matrix alloying elements molybdenum, vanadium and chromium, which formed solid solutions within the reinforcing particles.

Mechanochemical synthesis of zinc and palladium complexes of dialkyl 2,2′-bipyridine-4,4′-dicarboxylate and analysis of solid-state reaction kinetics

Abstract Mechanochemical synthesis of a series of Zn and Pd dialkyl 2,2′-bipyridine-4,4′-dicarboxylate complexes (Ln, where n specifies the number of carbons in the α- or β-substituted alkyl chains) including ZnLβ12Cl2, ZnLβ14Cl2, ZnLα14Cl2, ZnLα14I2, and PdLα14Cl2 is explored through a variety of linear and sigmoidial reaction models. The Johnson-Mehl-Avrami-Yerofeev-Kolmogrov (JMAYK) and Finke-Watzky (FW) models are largely equivalent as demonstrated through analysis of Akaike weights. This analysis was extended to the previously reported syntheses of PdLβ10I2, PdLα16I2, and PdLβ16I2 with similar results, except that the JMAYK model is significantly superior to the FW model for PdLβ16I2. The physical properties of the reaction mixture, most prominently whether the product phase is easily mixed, is a major factor in determining the rate of reaction.

Kinetic analysis of isothermal solid state process for synthesized potassium sodium niobate piezoelectric ceramics

Solid state kinetic models were developed for predicting conversion fraction (α), reaction rate (dα/dt), kinetic triplet (model f(α), frequency factor (A) and activation energy (Ea)) of (K0.5Na0.5)NbO3ceramics using thermos-gravimetric analysis data obtained at constant temperature of 900°C .The integral reaction model g(α), were evaluated for experimental data and theoretical reaction models. Kinetics of solid state reaction of KNN ceramics was a homogenous nucleation process with one dimensional nuclei growth per particle at constant rate, 2D diffusion controlled reaction mechanism, particles with spherical/cubical shape based on Mapel, JMAEK nucleation, Jander Model and contracting volume model respectively.

Mechanosynthesis of nanostructured composites copper-fullerite, copper-graphite

Comparative studies of the influence of carbon allotropic form on the formation of the structural-phase composition of copper-based composites have been performed by means of Scanning Electron Microscopy, X-ray and Thermal analysis and Raman spectroscopy. It has been stated that the kinetics of solid state reactions in the systems Cu-C60/70 and Cu-Cg obtained in process of mechanosynthesis depend on deformational stability and oxidation-reduction properties of fullerite and graphite. It has been shown that partial destruction of fullerene molecules in the Cu-C60/70 sample results in the formation of an amorphous fullerite-like phase, copper oxide Cu2O, and supersaturated solid solution Cu(C, O). Total destruction of fullerene molecules in the system Cu-C60/70 results in the formation of supersaturated solid solution Cu(C), just like in the case of the composite Cu-Cg.

Reaction kinetic studies of metal-doped magnesium silicides

Metal-doped magnesium silicides are promising thermoelectric materials for waste heat recovery application at 500–800 K because of their low density, large natural availability, non-toxicity, good thermal stability, and transport properties. Reaction kinetics of metal-doped magnesium silicides, Mg2SiXm (X = Ti, Nb, Mn, and Co; m = 0.02, 0.04, and 0.08 mol) were investigated in this study. A simple and rapid synthesis of Mg2SiXm samples was carried out using pelletizing, and sintering method at 773–823 K for 300 s. The effect of metal doping on the lattice constants of Mg2SiXm samples was examined using X-ray diffraction technique. Differential thermal analysis heat flow experiments were conducted on (2Mg + Si + mX) sample mixtures to study the solid-state reaction kinetics of Mg2SiXm alloys formation at different scan rates of 0.08, 0.16, 0.25, 0.33 Ks−1. Activation energies for the formation reaction of Mg2Si were determined using Ozawa, and Kissinger–Akahira–Sunrose equations. A 3-D diffusion-controlled reaction mechanism was proposed based on Coats–Redfern (CR) model. The effect of concentration of the metal-dopants on the formation activation energies of Mg2SiXm was investigated using the CR equation plots.

Polymerization of 1,4-dinitrosobenzene: Kinetics and Submicrocrystal Structure

In this study, the structure of the polycrystalline poly(l, 4-phenyleneazine N, N- dioxide) was investigated by Scanning Electron Microscopy and related with the previously calculated molecular structure. Kinetics of polymerization of 1, 4-dinitrosobenzene, prepared by both cryogenic UV photolysis and in vacuo deposition were measured by time-resolved FT-IR spectroscopy. Acquired data was analyzed by curve fitting with the standard Avrami- Erofeev and two-step consecutive reactions models. Activation parameters were calculated from Arrhenius and Eyring-Polanyi equations, for both models. The results obtained by using the two models, along with the goodness-of-fit parameters, were compared. It was shown that both bulk-based and reaction-based models can be used to adequately describe solid-state chemical reaction kinetics. Furthermore, a two- step consecutive reactions model is a suitable alternative to the most commonly used AvramiErofeev model.

Solid state reaction kinetics of iron oxide reduction using hydrogen as a reducing agent

The thermochemical reduction of metal oxides is important for fuel production using chemical looping processes as well as metal extraction from ore. In this study, reaction kinetics for the reduction of iron oxide using hydrogen as a reducing agent is studied. Experiments are conducted with the iron-silica Magnetically Stabilized Porous Structure (MSPS) for different reaction conditions, including reaction temperature, hydrogen inlet molar concentration, and hydrogen inlet flow rate. The reduction reaction is characterized by step-wise conversion of magnetite to elemental iron via wustite. Thus the reaction kinetics is governed by the coexistence of two reactions, magnetite to wustite and wustite to iron conversions. A one-dimensional plug flow isothermal kinetic model is proposed, and a numerical scheme is developed to solve the species transport and substrate conservation equations. The numerical scheme is used as a tool to calibrate the kinetic model, and the critical kinetic parameters, including activation energy, pre-exponent, and order of reaction, are determined for both reactions. The reaction mechanism for both reactions is identified, and a transition in the reaction mechanism is captured with different models. The kinetic model shows good agreement with the experimental data for different operating conditions. This study provides a basis for scaling bench scale hydrogen reduction reactors to an industrial scale.

Structural and thermal characterizations of the solid-state reaction between Ni, Al, and Ti powders during mechanical alloying

The mixtures of Ni, Al, and Ti elemental powders with nominal compositions Ni-30 at.% Al-10 at.% Ti were mechanically alloyed in a planetary ball mill under argon atmosphere. The structural and morphological changes during high-energy mechanical alloying were investigated by X-ray diffraction and scanning electron microscopy. We have found differences in the kinetics of solid-state reactions which depend on the differences in the individual properties. The final products of the mechanical alloying process were nanocrystalline nickel-rich solid solutions with a mean crystallite sizes in the range of a few nanometers. As a result, the prolonged milling time allows the disordered Ni3(Al,Ti) solid solution to dissociate to the L20-Ni(Al,Ti) phase and L12-Ni3(Al,Ti) phase. Further, it was found that the formation of L20-Ni(Al,Ti) phase was favored when considering the total reaction of the finite quantities of Al and Ti in the presence of an excess of Ni. Calorimetric studies demonstrate the coexistence of overlapping exothermic peaks characteristic of crystallization processes associated with the identified phases.

Morphology and structure effect of Ti additive on the solid-state reaction between Ni and Al powders during mechanical alloying

In this study, the mixtures of Ni, Al, and Ti elemental powders with nominal compositions Ni-40at.% Al and Ni-30at.% Al-10at.% Ti were fabricated by mechanically alloying technique. The structural and morphological changes during high-energy mechanical alloying were investigated by X-ray diffraction and scanning electron microscopy. Differences in the kinetics of solid-state reactions which depend on the differences in the individual properties were found. The final products of the mechanical alloying process were nanocrystalline fcc-Ni(Al) and fcc-Ni(Al, Ti) solid solutions with a mean crystallite sizes in the range of a few nanometers. As a result, although the Ti addition was found to accelerate the formation of the solid solution in Ni-Al alloy, it results in a coarser microstructure.

Analysis of reaction kinetics in the photomechanical molecular crystal 9-methylanthracene using an extended Finke–Watzky model

In order to develop an improved description of the photomechanical response of 9-methylanthracene (9MA) microcrystals, a detailed study of its solid-state photochemical reaction kinetics is performed. The reaction progress is monitored through the decrease in absorption of an optically microcrystalline thin film. The evolution of the time-dependent photoluminescence during the reaction is also measured. Both the photochemical reaction and nonradiative relaxation rates increase as more photoproduct is formed. In order to analyze the data, an extended version of the Finke-Watzky kinetic model for photochemical reactions is derived, denoted the FW-P model. This extended version enables a systematic analysis of photochemical reaction kinetics in solid-state molecular systems at varying levels of approximation. The FW-P model describes the non-exponential decrease in reactant and also correctly predicts the magnitude of the observed decrease in photoluminescence lifetime over the course of the reaction. The lifetime analysis is complicated by the fact that the microcrystalline 9MA sample contains multiple emitting species, and the extended FW-P model fails to capture the exact dependence of the photoluminescence on product formation. Analysis of the 9MA data indicates that both the photodimerization and the nonradiative relaxation rates can be accelerated by a factor of 10 over the course of the reaction. The results in this paper demonstrate that autocatalytic photodimerization kinetics are present in crystalline 9MA and may influence its photomechanical response.

Real-Time and In Situ Monitoring of Mechanochemical Reactions: A New Playground for All Chemists.

We provide a brief overview of the first techniques for direct, real-time observation of mechanochemical reactions by milling. Whereas mechanisms and kinetics of solid-state reactions induced by temperature or pressure have been extensively investigated, transformations of materials under continuous impact in a milling assembly remain largely unexplored and based on ex situ studies. The recent introduction and development of techniques for in situ monitoring of milling reactions by synchrotron X-ray powder diffraction and Raman spectroscopy has enabled the first direct insight into milling mechanochemistry, opening a new area for studies of chemical reactivity. So far, these techniques have revealed rapid, multistep reaction mechanisms and metastable intermediates that are impossible or difficult to observe or isolate in solution and have highlighted shortcomings of ex situ mechanistic studies. These pioneering advances also highlight the low level of mechanistic understanding and future challenges in developing a clear mechanistic picture of physicochemical transformations by milling.

Synthesis Of Magnesium-Aluminum Layered Double Hydroxides By Mechanochemical Method And Its Solid State Reaction Kinetics

Abstract A mechanochemical method is developed in preparing magnesium-aluminum-layered double hydroxides (MgAl-LDHs). This approach includes activation process and diffusion process. In order to verify the LDHs structure and study the reaction kinetics, X-ray diffraction (XRD) patterns, inductively coupled plasma(ICP) and physical adsorption instrument were characterized. The results show that activation time can change the surface of particles and affect the reaction grade. During the diffusion process, reaction time is the most important factor. The reaction energy (ΔQ) was calculated that is 6kJ/mol.

The kinetics of solid-state isotope-exchange reactions for clumped isotopes: A study of inorganic calcites and apatites from natural and experimental samples

Carbonate clumped-isotope geothermometry is a tool used to reconstruct formation or (re)equilibration temperatures of carbonate bearing minerals, including carbonate groups substituted into apatite. It is based on the preference for isotopologues with multiple heavy isotopes (for example, ^13^C^16^O~2~^18^O^2−^ groups) to be more abundant at equilibrium than would be expected if all isotopes were randomly distributed amongst all carbonate groups. Because this preference is only a function of temperature, excesses of multiply substituted species can be used to calculate formation temperatures without knowledge of the isotopic composition of water from which the mineral precipitated or other phases with which it may have equilibrated. However, the measured temperature could be modified after mineral growth if exchange of isotopes amongst carbonate groups within the mineral has occurred through internal isotope-exchange reactions. Because these exchange reactions occur through thermally activated processes, their rates depend on temperature and increase at higher temperatures. Thus internal isotope-exchange reactions could lead to effective re-equilibration at high temperatures, overprinting the original temperatures recorded during mineral growth. We measured clumped-isotope temperatures in carbonate bearing minerals (including apatites) from several carbonatites to constrain the kinetics of these internal isotope-exchange reactions. We observe two key trends for clumped-isotope temperatures in carbonatites: (*i*) clumped-isotope temperatures of apatites and carbonate-bearing minerals decrease with increasing intrusion depth and (*ii*) apatites record lower clumped-isotope temperatures than carbonate minerals from the same intrusion. We additionally conducted heating experiments at different temperatures to derive the temperature dependence for the rate constants that describe the alteration of clumped-isotope temperatures with time in calcites and apatites. We find that calcites exhibit complex kinetics as has been seen in previous studies. To quantify these results, we constructed a model that incorporates both diffusion of isotopes through the crystal lattice and isotope-exchange reactions between adjacent carbonate groups. We tested this model through comparison to previous measurements of optical calcites and brachiopods and to samples with known cooling histories and find that the model is able to reasonably capture kinetic data from previous experiments and the observed clumped-isotope temperatures of calcites assuming geologically reasonable cooling rates. A similar model for apatite over-predicts the observed clumped-isotope temperatures found in natural samples; we hypothesize this discrepancy is the result of annealing of radiation damage in our experiments, which lowers the diffusivity and rate of isotope exchange of carbonate groups compared to damaged natural samples. Finally, we constructed models to explore how heating can alter recorded clumped-isotope temperatures. Our model predicts that samples change in clumped-isotope temperatures in two stages. The first stage changes the recorded clumped isotope temperatures by \<1 °C if held at 75 °C for 100 million years and by up to ∼40 °C if held at 120 °C, but the clumped-isotope temperatures does not reach ambient values through this low-temperature mechanism. A second, slower change becomes effective at temperatures above 150 °C and can take the measured clumped-isotope temperature up to the true ambient temperature. This result implies that old (hundreds of million years) samples that have only experienced mild (\<100-125 °C) thermal histories could exhibit small but measurable (order 10 °C) changes in their clumped-isotope temperatures. We compared this heating model to clumped-isotope measurements from paleosol samples from the Siwalik Basin in Nepal, which were buried up to 5 km and then rapidly exhumed to the surface; these samples often do not give reasonable surface temperatures. The modeled temperatures agree with measured temperatures of these samples, suggesting that partial re-equilibration during shallow crustal burial is responsible for their elevated clumped-isotope temperatures.

Kinetic Study and Thermal Decomposition Behavior of Lignite Coal

A thermogravimetric analyzer was employed to investigate the thermal behavior and extract the kinetic parameters of Canadian lignite coal. The pyrolysis experiments were conducted in temperatures ranging from 298 K to 1173 K under inert atmosphere utilizing six different heating rates of 1, 6, 9, 12, 15, and 18 K min−1, respectively. There are different techniques for analyzing the kinetics of solid-state reactions that can generally be classified into two categories: model-fitting and model-free methods. Historically, model-fitting methods are broadly used in solid-state kinetics and show an excellent fit to the experimental data but produce uncertain kinetic parameters especially for nonisothermal conditions. In this work, different model-free techniques such as the Kissinger method and the isoconversional methods of Ozawa, Kissinger-Akahira-Sunose, and Friedman are employed and compared in order to analyze nonisothermal kinetic data and investigate thermal behavior of a lignite coal. Experimental results showed that the activation energy values obtained by the isoconversional methods were in good agreement, but Friedman method was considered to be the best among the model-free methods to evaluate kinetic parameters for solid-state reactions. These results can provide useful information to predict kinetic model of coal pyrolysis and optimization of the process conditions.

New Insights on the Kinetic Analysis of Isothermal Data: The Independence of the Activation Energy from the Assumed Kinetic Model

Isothermal experiments are widely employed to study the kinetics of solid-state reactions or processes to extract essential kinetic information needed for modeling the processes at an industrial scale. The kinetic analysis of isothermal data requires finding or assuming a kinetic function that can properly fit the evolution of the reaction rate with time, so that the resulting parameters, i.e., the activation energy and pre-exponential factor, can be considered reliable. In the present work, we demonstrate using both simulated and experimental data that the kinetic analysis of a set of isothermal plots obtained at different temperatures, considering a single-step solid-state reaction, necessarily leads to the real activation energy, regardless the mathematical function selected for performing the kinetic analysis. This makes irrelevant the election of the kinetic function used to fit the experimental data and greatly facilitates the estimation of the activation energy for any single process.

Influence of mechanical activation on the kinetic features of SrZrO3 formation

Strontium zirconate SrZrO3 has been synthesized via heating of equimolar mixture of SrCO3 and ZrO2 at 900–1050°C with and without preliminary mechanical activation of the reactants. Data on the degree of SrZrO3 formation have been analyzed using the basic equations of the kinetics of solid-state reactions. The best agreement of the theoretical prediction with the experimental results has been obtained in the case of the Zhuravlev-Lesokhin-Tempelman equation. Mechanical activation of the SrCO3-ZrO2 mixture for 2–10-min causes marked acceleration of SrZrO3 formation in the course of subsequent sintering.

Solid state reaction kinetics, mechanisms and catalysis: a retrospective rational review

Kinetic studies are widely used to characterize the factors that control the reactivity and the mechanisms of chemical changes that occur on heating solid reactants. This survey appraises the origins, assumptions and scientific foundations that underlie the theoretical methods that are conventionally, and unquestioningly, used to analyze and to interpret thermal analysis (TA) rate measurements. The extensive TA literature is reviewed in the context of the unusual history of this branch of science, in which TA has effectively superseded the formerly thriving subject of Thermal Decomposition of Solids (TDoS) (also reviewed). Such complete replacement of one scientific discipline by another is unusual, so that reasons for, and consequences of, this eclipse merit detailed consideration. The rapid rise of TA, after about 1970, resulted from the unprecedented advances in instrumental and computational methods which massively accelerated the collection and analysis of accurate rate data for thermal reactions (including solids). Consequently, TA theory initially tended to focus on developing experimental equipment together with facilitation of data interpretation by computer programs. These achievements have enabled each TA study to be completed very rapidly and with relatively much less effort than was usual in the former TDoS methodology. However, much less effort was also invested in developing coherent and soundly-based theory for the interpretation of TA kinetic data, with consequences that are critically appraised here in their historical context.

Mechanism of Photoinduced Bending and Twisting in Crystalline Microneedles and Microribbons Composed of 9-Methylanthracene

The solid-state photodimerization of 9-methylanthracene is used as a model system to investigate how crystal morphology and reaction dynamics affect photomechanical deformations of single microcrystals. By varying the crystallization conditions, two different crystal shapes, microneedles and microribbons, are grown on a clean water surface. The microribbons twist under irradiation, while the microneedles bend. In both shapes, the maximum deformation occurs at roughly the midpoint of the reaction, while further dimerization causes the crystals return to their original shapes. Powder X-ray diffraction patterns establish that the needles and ribbons have the same crystal orientation and that the photoreaction proceeds in a crystal-to-crystal manner. NMR spin-lattice relaxation measurements are consistent with the rapid formation of large (>100 nm) dimer crystal domains. Simultaneous measurement of the needle bending and monomer fluorescence signal allows us to correlate the bending with the reaction progress. The behavior is qualitatively reproduced by a model in which the motion is driven by strain between spatially distinct reactant and product domains, also called heterometry. We consider several different mechanisms that could give rise to these spatially distinct domains. The ability to control the photoinduced crystal deformation by manipulating crystal shape and solid-state reaction kinetics suggests that photoreactive molecular crystals may be useful for generating well-defined motions on small length scales.

Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe2O3 is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH4, CO and H2 respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe2O3 (20wt.%)/ZrO2 was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH4, CO and H2, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH4, but the phenomenon was not remarkable for the reduction by CO and H2. The reduction rate achieved using CO and H2 was relatively faster than achieved using CH4. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe2O3 to FeO by CH4, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH4. The reduction of Fe2O3 to Fe by CO and H2 can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe3O4 by water and FeO to Fe2O3 by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.

Fabrication and characteristics of nano LiFePO4/C composites with high capacity and high rate using nano Fe2O3 as raw materials

Nano LiFePO4/C particles with high capacity and high rate were fabricated by one-step solid-state reaction using nano Fe2O3, LiH2PO4 and sucrose as raw materials. The effect of synthesis temperature on the morphology and the electrochemical performance was investigated. LiFePO4/C materials were characterized by differential scanning calorimetry (DSC) and thermogravimetry (TG), X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the elemental analyzer. The results show that nano Fe2O3 can reduce and make uniform the LiFePO4 grain size (<100nm) effectively as well as accelerate the solid-state reaction kinetics which is a convenient way for industrialization. The precursor sintered at 740°C for 5h exhibits the highest electrochemical capacity (166.9mAh/g at 0.1C) and the best rate performance.