Kinetics Of Solid-state Reactions Research Articles

Reaction Atmosphere-Controlled Thermal Conversion of Ferrocene to Hematite and Cementite Nanomaterials-Structural and Spectroscopic Investigations.

Recently, we have reported the influence of various reaction atmospheres on the solid-state reaction kinetics of ferrocene, where oxalic acid dihydrate was used as a coprecursor. In this light, present study discusses on the nature of decomposed materials of the solid-state reactions of ferrocene in O2, air, and N2 atmospheres. The ambient and oxidative atmospheres caused the decomposition to yield pure hematite nanomaterials, whereas cementite nanomaterials along with α-Fe were obtained in N2 atmosphere. The obtained materials were mostly agglomerated. Elemental composition of each material was estimated. Using the absorbance data, the energy band gap values were estimated and the related electronic transitions from the observed absorption spectra were explored. Urbach energy was calculated for hematite, which described the role of defects in the decomposed materials. The nanostructures exhibited photoluminescence due to self-trapped states linked to their optical characteristics. Raman spectroscopy of hematite detected seven Raman modes, confirming the rhombohedral structure, whereas the D and G bands were visible in the Raman spectra for cementite. Thus, the reaction atmosphere significantly influenced the thermal decomposition of ferrocene and controls the type of nanomaterials obtained. Plausible reactions of the undergoing solid-state decomposition have been proposed.

COMSOL Simulation of the Storage Life of Zinc-silver Reserve Battery

We deduced the reaction kinetic equation of negative electrode zinc and oxygen at room temperature, and the solid-state reaction kinetics of AgO and silver, established the corresponding COMSOL model, verified and simulated the storage and discharge model, and predicted that the storage life of zinc-silver reserve battery is about 18-20 years.

A study on nitrile rubber/polyvinyl chloride blend vulcanization kinetics with different fillers by using single isothermal rheograph

An attempt has been made to establish a reasonably accurate microkinetics model for accelerated sulfur vulcanization of commonly used acrylonitrile rubber/polyvinyl chloride (NBR/PVC 70/30) blend (NVC73) from a single, isothermal rheograph data of torque versus time. The effect of three different types of fillers, such as pre-exfoliated organically modified montmorillonite (OMMT) clay, graphite (GRT) powder, and high abrasion furnace (HAF) carbon black (CB), were studied. The kinetics study was done with six solid-state reaction kinetics models. Among these, Sestak-Berggren (SB) equation was found to be the best model for the present compositions. The SB kinetic rate expressions were evolved after several iterations using empirical values of autocatalytic and non-autocatalytic orders of ‘ m’ and ‘ n’, respectively. The gum vulcanizate and OMMT clay-loaded compositions were found to have comparable conversion function f (α) and almost identical reaction rate constants at 150°C, under isothermal conditions. In comparison, HAF CB and GRT rate expressions differed from clay-loaded compositions. The validity of the reaction rate equations obtained was confirmed by comparison of plots for experimental and derived conversions with time.

Exploring nucleation modeling of the voltammetry of solid-to-solid-state redox processes with phase changes

An operational description of the linear potential scan voltammetry of solids experiencing a solid-state redox transformation with phase changes is described. The modeling is based on the application of nucleation equations of solid-state reaction kinetics to express the transferred charge/applied potential relationships. The flexible use of Prout-Tompkins and Avrami-Erofe’ev kinetics permits a satisfactory description of the voltammetry of solid-to-solid redox transformations with phase segregation. The model satisfactorily applies to reproduce linear potential scan curves recorded for graphite electrodes modified with several lead compounds in contact with aqueous electrolyte solutions.

Revealing the kinetics of non-metallic inclusion reactions in steel using in-situ high temperature environmental scanning electron microscopy

The kinetics of solid-state reactions involving non-metallic inclusions (NMIs) in steel is a topic of growing interest due to the need to understand the effects of heat treatments on NMI composition and stability. In this study, a High Temperature Environmental Scanning Electron Microscope (HT-ESEM) is utilized to conduct in-situ observations of various types of NMIs, including calcium aluminate complex, CaS, MgAl2O4-CaS, MnS, and TiN, in steels at temperatures of 800 °C and 900 °C for different holding times. The observed morphological variations in the NMIs indicate a decrease in the fractions of CaS and MnS, promoting void formation and ferrite–austenite phase transformation. To estimate the NMI reactions with the residual atmosphere in the sample chamber during experiments, HT-ESEM-driven thermodynamic calculations have been performed using FactSage 8.2 software. These calculations provide valuable insights into the interpretation of the experimental data, facilitating a better understanding of the complex NMI reactions in steel.

Atomistic study on reaction kinetics and reactivity of Ni/Al clad particles composites under shock loading.

In prior research on shock-induced reaction, the interfacial crystallization of intermetallics, which plays an important role in solid-state reaction kinetics, has not been explored in detail. This work comprehensively investigates the reaction kinetics and reactivity of Ni/Al clad particle composites under shock loading with molecular dynamics simulations. It is found that the reaction acceleration in a small particle system or the reaction propagation in a large particle system breaks down the heterogeneous nucleation and continuous growth of B2 phase at the Ni/Al interface. This makes the generation and dissolution of B2-NiAl show a staged pattern consistent with chemical evolution. Importantly, the crystallization processes are appropriately described by the well-established Johnson-Mehl-Avrami kinetics model. With the increase in Al particle size, the maximum crystallinity and growth rate of B2 phase decrease and the value of the fitted Avrami exponent decreases from 0.55 to 0.39, showing a good agreement with the solid-state reaction experiment. In addition, the calculations of reactivity reveal that the reaction initiation and propagation will be retarded, but the adiabatic reaction temperature can be elevated when Al particle size increases. An exponential decay relationship is found between the propagation velocity of the chemical front and the particle size. As expected, the shock simulations at non-ambient conditions indicate that elevating the initial temperature significantly enhances the reactivity of large particle systems and results in a power-law decrease in the ignition delay time and a linear-law increase in the propagation velocity.

Relative Kinetics of Solid-State Reactions: The Role of Architecture in Controlling Reactivity.

Countless inorganic materials are prepared via high temperature solid-state reaction of mixtures of reagents powders. Understanding and controlling the phenomena that limit these solid-state reactions is crucial to designing reactions for new materials synthesis. Here, focusing on topotactic ion-exchange between NaFeO2 and LiBr as a model reaction, we manipulate the mesoscale reaction architecture and transport pathways by changing the packing and interfacial contact between reagent particles. Through analysis of in situ synchrotron X-ray diffraction data, we identify multiple kinetic regimes that reflect transport limitations on different length scales: a fast kinetic regime in the first minutes of the reaction and a slow kinetic regime that follows. The fast kinetic regime dominates the observed reaction progress and depends on the reagent packing; this challenges the view that solid-state reactions are necessarily slow. Using a phase-field model, we simulated the reaction process and showed that particles without direct contact to the other reactant phases experience large reduction in the reaction rate, even when transport hindrance at particle-particle contacts is not considered.

Reaction kinetics in the system Y2O3/Al2O3 – Use of an external electric field to control the product phase formation in a system forming multiple product phases

This study investigates the influence of an external electric field on the kinetics of a heterogeneous solid state reaction between Al2O3 and Y2O3. The reaction couples were prepared by means of pulsed laser deposition (PLD) by growing Y2O3 films on single crystalline alumina substrates with an (0001) orientation. The solid state reaction was performed at a temperature of 1400° (1673 K). Utilising attached platinum electrodes, an electric field of 350 V/mm was applied. The superposed field led to an ionic current through the reacting sample and modifies the individual growth kinetics of the three product phases/layers, Y3Al5O12 (YAG), YAlO3 (YAP) and Y4Al2O9 (YAM) The cross-sections of the reacted samples were characterised by means of SEM and XRD. Depending on the direction of the ionic current, the kinetics of the YAP phase formation in particular was strongly influenced. The general kinetics of a solid state reaction forming multiple product phases was analysed using linear transport theory. The effect of an electric field for controlling the product phase formation to prefer or to kinetically suppress the formation of a distinct phase is demonstrated.

Manufacturing of high quality hydrotalcite by computational fluid dynamics simulation of an impinging jet crystallizer

Hydrotalcite was produced by solid-state reaction with magnesium hydroxide particles as the precursor using the impinging stream method. Traditional impinging stream reactors are complex or prone to blockage during the reaction process. To solve this problem, computational fluid dynamics (CFD) simulation was used to optimize the operating conditions in 1 L and 10 L impinging jet crystallizers to produce hydrotalcite. The produced hydrotalcite had a uniform morphology, large particle size, narrow particle size distribution and high purity (>99%), which enabled the controlled reactive crystallization of high-quality hydrotalcite and provided theoretical support for industrial scale-up. Moreover, the solid-state reaction kinetics were analyzed and showed that the reactive crystallization of hydrotalcite could be explained by nucleation and nuclei growth mechanism.

Impact of Solvent-Drug Interactions on the Desolvation of a Pharmaceutical Solvate.

In drug manufacturing, solvent-based methods are used for the crystallization of active pharmaceutical ingredients (APIs). Often, the solvent interacts with the API resulting in the formation of a new solid compound, the solvate. When desolvation occurs upon heating, it might result in the formation of new solid forms with significantly different physicochemical properties. Therefore, in this work, we study the desolvation kinetics by combining in situ powder X-ray diffraction (PXRD), all-atom molecular dynamics (MD) simulations, and macroscopic solid-state reaction kinetics modeling. The fluorobenzene (FB) solvate of Bruton's tyrosine kinase inhibitor Ibrutinib (IBR) was used as a model system. While the macroscopic solid-state modeling provides information about the desolvation kinetics, the MD simulations were used to trace individual FB molecules inside the crystal lattice. The activation energy of confined solvent diffusion, obtained by MD simulations, agrees well with results of the macroscopic solid-state reaction kinetics modeling. In addition, MD simulations provided detailed information about the IBR-FB interactions at the nanoscale. The mechanism revealed is that the solvent molecules diffusion, controlled by distinct open-close gating conformational changes of the drug, triggers the desolvation throughout the crystal lattice.

Al11Mn4 formation on Al8Mn5 during the solidification and heat treatment of AZ-series magnesium alloys

The crystallography and kinetics of Al11Mn4 formation on Al8Mn5 have been studied in magnesium alloys AZ80 / AZ91 and AZ31. During solidification, Al11Mn4 formation was promoted by low cooling rates where triclinic Al11Mn4 nucleated on rhombohedral Al8Mn5 particles with one of multiple related orientation relationships (ORs) and their variants. Al11Mn4 grew as (010) plates that were commonly twinned and the interrelationships amongst Al11Mn4 twins, Al8Mn5 twins and Al8Mn5-Al11Mn4 ORs are discussed. During solid state heat treatment at 410 °C, Al8Mn5 particles transformed into Al11Mn4 by a core-shell reaction with cracking in the Al11Mn4 shell. The solid-state reaction kinetics were consistent with interface reaction controlled growth. The results show that heat treatment can be used to tailor the Al-Mn compound in contact with the matrix (Mg) phase which may enable some control of corrosion performance.

Reaction kinetics in the system Y2O3/Al2O3 – A solid state reaction forming multiple product phases investigated by using thin film techniques

The kinetics of the heterogeneous solid state reaction between Al2O3 and Y2O3 is investigated by using thin film techniques. Y2O3 films are grown by means of pulsed laser deposition (PLD) on single crystalline alumina substrates with a (0001) orientation. The solid state reactions are performed at a temperature of 1400 °C (1673 K). The cross sections of the reacted samples were investigated by means of SEM and XRD and exhibit a sequence of three product layers, Y3Al5O12 (YAG), YAlO3 (YAP) and Y4Al2O9 (YAM). The simultaneous growth of the product layers is controlled by a diffusional kinetics and the thickness increases are coupled to each other. According to Wagner and Schmalzried, one has to distinguish between rate constants of the first kind (“practical” Tammann constant), in the case of simultanous and coupled growth of multiple product phases, and rate constants of the second kind (“true” Tammann constant), in the case of the uncoupled and only growth of one product phase in equilibrium with the adjacent phases. The growth kinetics for a solid reaction forming three product phases (layer) is analysed in detail using linear transport theory. For the formation of YAG, YAP and YAM the rate constants of the second kind are determined from the experimental data and those of the first kind are calculated and compared to the available literature data. Based on these considerations, a detailed overview about the phase formation kinetics in the temperature range of 1200–1400 °C can be given for the first time. The (Nernst-Planck coupled) cation conductivities are calculated.

Kinetic modelling of thermal processes using a modified Sestak-Berggren equation

This study outlines the principles of modelling the kinetics of solid-state reactions through the simultaneous fitting of multiple peak curves using the modified Sestak-Berggren equation. This mathematical model gives an indication of the mechanism occurring and allows kinetic parameters, such as activation energy, to be estimated. This methodology is demonstrated using in silico thermo-conductivity detector (TCD) data showing the internal consistency of the Sestak-Berggren modelling approach, its applicability to noisy data and its ability to predict mechanisms occurring during a thermally induced solid state reaction. Using these in silico data it has been confirmed that this empirical model can separate overlapped peaks without a priori peak deconvolution. A rigorous statistical methodology based on the Akaike Information Criteria, is recommended to identify the optimum number of thermal events that should be applied to a system. This modified Sestak-Berggren model is then applied to an experimental dataset of temperature programmed reduction of a calcined cobalt on alumina catalyst precursor. This allows for the identification of a statistically adequate kinetic triplet for each thermal event. Recommendations on the treatment of datasets which contain “shoulders” and closely overlapped peaks are also given.

Mechanically Responsive Crystals: Analysis of Macroscopic Strain Reveals “Hidden” Processes

Mechanical response of single crystals to light, temperature, and/or force-an emerging platform for the development of new organic actuating materials for soft robotics-has recently been quantitatively described by a general and robust mathematical model ( Chem. Rev . 2015 , 115 , 12440 - 12490 ). The model can be used to extract accurate activation energies and kinetics of solid-state chemical reactions simply by tracking the time-dependent bending of the crystal. Here we illustrate that deviations of the macroscopic strain in the crystal from that predicted by the model reveal the existence of additional, "hidden" chemical or physical processes, such as sustained structural relaxation between the chemical transformation and the resulting macroscopic deformation of the crystal. This is illustrated with photobendable single crystals of 4-hydroxy-2-(2-pyridinylmethylene)hydrazide, a photochemical switch that undergoes E-to-Z isomerization. The irreversible isomerization in these crystals results in amorphization and plastic deformation that are observed as poor correlation between the transformation extent and the induced strains. The occurrence of these processes was independently confirmed by X-ray diffraction and differential scanning calorimetry. An extended mathematical model is proposed to account for this complex mechanical response.

Lab on a beam—Big data and artificial intelligence in scanning transmission electron microscopy

Abstract

Artificial neural network model for the evaluation of chemical kinetics in thermally induced solid-state reaction

The artificial intelligence technique is utilized to improve evaluation of thermally induced solid-state reaction kinetics. A general regression neural network (GRNN) model was applied to directly determine the kinetic triplets, i.e., activation energy, pre-exponential factor, and mechanism model. The effect of number of heating rate on prediction performance of the GRNN model was assessed based on the estimation indictors. The obtained kinetic triplets based on the triple heating rates were considered to be accepted. The prediction ability of the GRNN model was very robust at more than three heating rates. The relative errors for kinetic parameters derived from five heating rates were within ± 4%, and the cognition rates for mechanism models were up to 99.6%. The developed GRNN model was successfully applied in the high-temperature synthesis of Li4Ti5O12/C composites. It is expected that the model also could be extended to estimate the kinetics of other solid-state reactions.

CO2 Capture via Crystalline Hydrogen-Bonded Bicarbonate Dimers

Summary Limiting global temperature rises is increasingly dependent on the development of energy-efficient carbon-capture methods. Here, we report a simple CO2-separation cycle using an aqueous bis(iminoguanidine) (BIG) sorbent that reacts with CO2 and crystallizes into an insoluble bicarbonate salt. X-ray diffraction analysis of the bicarbonate crystals revealed “anti-electrostatic” hydrogen-bonded (HCO3−)2 dimers, stabilized by guanidinium cations and water. Mild heating of the crystals releases the CO2 and regenerates the BIG sorbent quantitatively, thereby closing the CO2-separation cycle. Experimental and computational investigations support a CO2-release mechanism consisting of surface-initiated low-barrier proton transfer from guanidinium groups to bicarbonate anions with the formation of carbonic acid dimers, followed by CO2 and H2O release in the rate-limiting step, with a measured activation energy of 102 ± 12 kJ/mol. The minimum energy required for sorbent regeneration is 151.5 kJ/mol CO2, which is 24% lower than the regeneration energy of monoethanolamine, a benchmark industrial sorbent.

Kinetics of the Topochemical Transformation of (PbSe) m(TiSe2) n(SnSe2) m(TiSe2) n to (Pb0.5Sn0.5Se) m(TiSe2) n.

Solid-state reaction kinetics on atomic length scales have not been heavily investigated due to the long times, high reaction temperatures, and small reaction volumes at interfaces in solid-state reactions. All of these conditions present significant analytical challenges in following reaction pathways. Herein we use in situ and ex situ X-ray diffraction, in situ X-ray reflectivity, high-angle annular dark field scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy to investigate the mechanistic pathways for the formation of a layered (Pb0.5Sn0.5Se)1+δ(TiSe2) m heterostructure, where m is the varying number of TiSe2 layers in the repeating structure. Thin film precursors were vapor deposited as elemental-modulated layers into an artificial superlattice with Pb and Sn in independent layers, creating a repeating unit with twice the size of the final structure. At low temperatures, the precursor undergoes only a crystallization event to form an intermediate (SnSe2)1+γ(TiSe2) m(PbSe)1+δ(TiSe2) m superstructure. At higher temperatures, this superstructure transforms into a (Pb0.5Sn0.5Se)1+δ(TiSe2) m alloyed structure. The rate of decay of superlattice reflections of the (SnSe2)1+γ(TiSe2) m(PbSe)1+δ(TiSe2) m superstructure was used as the indicator of the progress of the reaction. We show that increasing the number of TiSe2 layers does not decrease the rate at which the SnSe2 and PbSe layers alloy, suggesting that at these temperatures it is reduction of the SnSe2 to SnSe and Se that is rate limiting in the formation of the alloy and not the associated diffusion of Sn and Pb through the TiSe2 layers.

Simple Interpretation of Kinetics of Fast Solid-State Reactions

A simple model of fast solid-state reaction of two substances on the phase boundary is proposed. It is assumed that the reaction is controlled by the formation of new surface. The dependence of a change in the surface on the value of shear deformation is calculated. Thus, the relation between the product yield and shear deformation independently of time is explained.

Processing, dielectric and electrical characteristics of strontium-modified Ca1Cu3Ti4O12

In the present paper, the strontium (Sr)-modified Ca1Cu3Ti4O12 ceramic (further termed as CSCTO) has been fabricated by a conventional cost-effective ceramic route. The prepared sample is characterized to obtain the relationship between the structural and electrical properties in a wide frequency (103–106 Hz) and temperature (25–315 °C) ranges. X-ray diffraction spectra depict a single-phase formation of the compound, crystallized in the cubic system. The dielectric relaxation mechanism and electrical properties of CSCTO have been revealed by studying frequency and temperature dependence of dielectric parameters (er and tanδ) by dielectric and impedance spectroscopy. The temperature-dependant dielectric constant plots depict that at frequency 1 kHz, the compound has very high dielectric constant (order of 104) and relatively low tangent loss. The occurrence of ultra high dielectric constant of the compound may be due to the space charge polarization, interface and Maxwell–Wagner dielectric relaxation around low frequencies and high-temperature range. The contributions of grains in resistive and capacitive properties of the material can be obtained from the Nyquist plot. It is interesting to note that at room temperature, polarization loop (P ~ E hysteresis loop) of the sintered CSCTO showed lossy behavior. The use of TiO2 and CuO2 nano-sized powders in the starting stage of sample preparation with micron size of CaCO3 and SrCO3 powder promotes the kinetics of quick conventional solid state reaction at a microscopic level, that favors above possible mechanisms.