Solid-state Reaction Mechanism Research Articles

A comprehensive kinetics study on non-isothermal pyrolysis of kerogen from Green River oil shale

Fundamentally understanding the pyrolysis kinetics of kerogen is of prime scientific and industrial importance. Herein, bitumen- and carbonates-free kerogen sample is prepared through Soxhlet extraction followed by decarbonation of Green River oil shale, and its pyrolysis is studied by non-isothermal thermogravimetric analysis. The systematic analyses show that both the Popescu and master plots methods are not applicable to describe the kerogen pyrolysis process due to the changed reaction model and the varied activation energy over certain conversion range, respectively, while the piecewise non-linear least squares analysis is identified as an effective method to discriminate the most probable kinetic model from commonly used 15 reaction models based on four solid-state pyrolysis mechanisms. Two-stage reaction model, i.e., F1 at the early stage and F2 at the later one, is proposed to well describe the kerogen pyrolysis process, which demonstrates a wide applicability owing to their insensitivities on the heating rate and estimation methods of the activation energies. The methodology revealed here could be applicable to determine other solid-state pyrolysis kinetics and reaction mechanism.

Lithium ion sieve synthesized via an improved solid state method and adsorption performance for West Taijinar Salt Lake brine

Monoclinic β-Li2TiO3 (LTO) is regarded as a lithium adsorbent precursor. In order to inhibit agglomeration during solid state reaction, C2H3LiO2·2H2O instead of Li2CO3 was firstly used as the lithium resource to synthesize LTO. Lithium ion sieve H2TiO3 (HTO) was then obtained by acid treatment of LTO. Physicochemical properties of obtained LTO and HTO were characterized via powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size distribution analysis (PSD). Lithium adsorption selectivity and stability of prepared HTO for West Taijinar Salt Lake were investigated. Solid state reaction mechanism of C2H3LiO2·2H2O and TiO2 was investigated by TG-DTA analysis. Results show that melting of C2H3LiO2·2H2O (at 64.5 °C) during the early calcination stage could form liquid–solid phase and remarkably improve mixing of C2H3LiO2·2H2O and TiO2. Compared to Li2CO3 used as the lithium resource, huge heat and gases released during the reaction of dehydrated C2H3LiO2·2H2O and TiO2 (between 380 °C and 515 °C) accelerate the nucleation process and effectively inhibits agglomeration, which leads to a smaller particle size (∼70 nm). It is shown that lithium uptake and adsorption rate were improved because of easier mass transfer during the ion-exchange process. Lithium adsorption behavior could be well described by the Langmuir isotherm and pseudo-second-order kinetic model. Seperation factor α (Li/Mg) of obtained HTO in West Taijinar Salt Lake brine reached 5441.17, meaning remarkable lithium adsorption selectivity in real lake brine. Besides, adsorption uptake remained 24.5 mg/g after 5 cycles in West Taijinar Salt Lake brine, which indicates obtained HTO has good stability.

Pyrolysis of Musa balbisiana flower petal using thermogravimetric studies

In the present study, thermogravimetric analysis of Musa balbisiana flower petal was carried out to study the degradation behaviour and the kinetics in the pyrolytic reaction. The pyrolysis was carried out in the temperature range of 35–900 °C at different heating rates of 5, 10 and 20 °C/min. The kinetics was investigated using different models like Kissinger–Akahira–Sunose (KAS), Flynn–Ozawa–Wall (FOW), Friedman and Broido’s plot. The average Ea values determined by KAS, FOW and Friedman methods were 137.94, 136.76 and 133.36 kJ/mol respectively. Coats–Redfern method was utilized to determine the pre-exponential factors and the reaction order of the pyrolysis. For the conversion rates 0.1 and 0.2, both Valensi and Ginstling diffusion models were found out to be appropriate for the solid state reaction mechanism. The HHV of Musa balbisiana flower petal was 16.35 MJ/kg, suggested as a potential bio-feedstock energy source from agro-waste.

Structure Evolution and Reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.0) System.

Solid oxide fuel cells (SOFCs) are solid-state electrochemical devices that directly convert chemical energy of fuels into electricity with high efficiency. Because of their fuel flexibility, low emissions, high conversion efficiency, no moving parts, and quiet operation, they are considered as a promising energy conversion technology for low carbon future needs. Solid-state oxide and proton conducting electrolytes play a crucial role in improving the performance and market acceptability of SOFCs. Defect fluorite phases are some of the most promising fast oxide ion conductors for use as electrolytes in SOFCs. We report the synthesis, structure, phase diagram, and high-temperature reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.00) oxide defect model system. For all Sc(2- x)V xO3.0 phases with x ≤ 1.08 phase-pure bixbyite-type structures are found, whereas for x ≥ 1.68 phase-pure corundum structures are reported, with a miscibility gap found for 1.08 < x < 1.68. Structural details obtained from the simultaneous Rietveld refinements using powder neutron and X-ray diffraction data are reported for the bixbyite phases, demonstrating a slight V3+ preference toward the 8b site. In situ X-ray diffraction experiments were used to explore the oxidation of the Sc(2- x)V xO3.0 phases. In all cases ScVO4 was found as a final product, accompanied by Sc2O3 for x < 1.0 and V2O5 when x > 1.0; however, the oxidative pathway varied greatly throughout the series. Comments are made on different synthesis strategies, including the effect on crystallinity, reaction times, rate-limiting steps, and reaction pathways. This work provides insight into the mechanisms of solid-state reactions and strategic guidelines for targeted materials synthesis.

Enhanced thermoelectric property of oxygen deficient nickel doped SnO2 for high temperature application

Motivated by the detailed investigation on the thermoelectric performance of oxide materials our work concentrated on the influence of acceptor dopants and defect density in the lattice plane for the enhancement of thermoelectric power. The series of Sn1−x Nix O2 (0.01 ≤ x ≤ 0.05) compositions were prepared by solid state reaction mechanism and found that 3 atomic percentage Ni doped SnO2 can be considered as a good candidate due to its promising electrical and transport properties. Defect lattices were introduced in the sample and the deviation from oxygen stochiometry was ensured using photoluminescence measurement. High power factor was obtained for the 3 atomic percentage nickel doped SnO2 due to the effective number of charge carrier concentration and the depletion of oxygen rich layers. Defect centered and acceptor doped SnO2 lattice opens a new door for energy harvesting at higher temperatures.

Comparative Investigation of Na2FeP2O7 Sodium Insertion Material Synthesized by Using Different Sodium Sources

Na2FeP2O7 powders were synthesized by a solid-state method by using different sodium sources (Na2CO3, NaH2PO4, and NaOH), and their solid-state reaction mechanism and the electrochemical properties of the synthesized Na2FeP2O7 were studied in detail. The results indicate that NaH2PO4 is conducive to the growth of the crystal surface with a wider spacing, which contributes to sodium-ion intercalation and deintercalation. Na2FeP2O7 synthesized at 600 °C by using NaH2PO4 exhibits the best electrochemical performance among them, showing an initial discharge capacity of 82.8, 79.4, 77.9, 75.3, 68.8, and 47.8 mAh g–1 under the cycle rate of C/10, C/5, C/2, 1C, 2C, and 5C, respectively. Moreover, a reversible capacity of 81.0 mAh g–1 at C/10, about 83.5% of the theoretical capacity, can be achieved after different cycle rates. The capacity retention is about 93.3% after 140 cycles under C/2. The results indicate that it is very important to choose the right sodium sources to synthesize Na2FeP2O7 with a good perf...

Thermal analysis study of LiFeO2 formation from Li2CO3–Fe2O3 mechanically activated reagents

The solid-phase synthesis of LiFeO2 lithium ferrite from mechanically activated Fe2O3–Li2CO3 initial reagent mixtures was investigated by X-ray powder diffraction and thermal analysis techniques. The mechanical milling of powder mixture was carried out by AGO-2S planetary ball mill with a rotation speed of 2220 rpm for 60 min. According to the XRD data, the crystallite sizes of milled reagents decrease as a result of ball milling. From thermal analysis, it was shown that the ferrite synthesis starts with the interaction between reagents and lithium carbonate decomposition and accompanied by mass loss process due to CO2 evaporation. For non-milled mixtures, the mass loss process occurs in the temperature range 400–740 °C and comprises two steps. As for milled samples, this process shifts toward lower temperatures, where a slight mass loss process is observed from 100 °C up to 400 °C, while the main mass loss occurs in the temperature range of 400–550 °C in one stage. The results indicate that the major mechanism of solid-state reaction can be attributed to the two-step model of the reaction proceed, whose rate is diffusion controlled over the entire temperature range for non-milled mixture, but corresponds to the diffusion and n-order equation depending on conversion degree for milled mixture. Generally, a preliminary mechanical activation of Fe2O3–Li2CO3 considerably enhances the reactivity of the solid-phase system, thereby reducing the temperature of lithium ferrite thermal synthesis. Thus, LiFeO2 ferrite can be obtained from reagents mixture mechanically activated for 60 min at temperature of 600 °C for 2 h, that is, at a significantly lower synthesis time and temperature than in the case of using conventional solid-state synthesis from non-milled reagents.

Study of crystal structure, dielectric, magnetic and magnetoelecrtic properties of xCoFe2O4-(1-x)Na0.5Bi0.5TiO3 composites

Multiferroic composites of spinel ferrite and ferroelectric xCoFe2O4 – (1-x)Na0.5Bi0.5TiO3 (with x = 0.10,0.30,0.50) were efficiently prepared by standard solid state reaction mechanism. X-ray diffractometer was used to analyze crystal structure of the prepared composites. The observed XRD patterns of the composites comprise peaks of both the phases i.e. ferrite and ferroelectric, with no sign of secondary peaks. Rietveld refinement of XRD data further confirms the coexistence of these two phases with cubic (Fd3m) and rhombohedral (R3c) symmetry corresponding to ferrite and ferroelectric phase respectively. The 3-dimensional overview of crystal structure of pure CoFe2O4 and Na0.5Bi0.5TiO3 and of composite 0.50CoFe2O4−0.50Na0.5Bi0.5TiO3 is generated by using refined parameters. The dielectric constant (ε´) and dielectric loss (tanδ) values were recorded as a function of frequency ranging from 100 Hz to 7 MHz and at different temperatures. Both ε´ and tanδ follow dispersion pattern at lower frequencies while show frequency independent behavior at higher frequencies. The magnetic evaluation carried by analyzing M-H hysteresis loop reveals the ferrimagnetic characteristics of these composites. The highest value of magnetic moment is 1.12μB observed for composite 0.50CoFe2O4 – 0.50Na0.5Bi0.5TiO3. Magnetoelectric (ME) voltage coefficient (α) was also demonstrated to observe the interaction between ferrite and ferroelectric phases. The highest value of α (72.72μV/Oe cm) is obtained for low ferrite composition 0.10CoFe2O4 – 0.90Na0.5Bi0.5TiO3, which suggests the dependence of magnetoelectric response on the resistivity of the composites.

Aromatic C-Nitroso Compounds and Their Dimers: A Model for Probing the Reaction Mechanisms in Crystalline Molecular Solids

This review is focused on the dimerization and dissociation of aromatic C-nitroso compounds and their dimers, the reactions that could be used as a convenient model for studying the thermal organic solid-state reaction mechanisms. This molecular model is simple because it includes formation or breaking of only one covalent bond between two nitrogen atoms. The crystalline molecular solids of nitroso dimers (azodioxides) dissociate by photolysis under the cryogenic conditions, and re-dimerize by slow warming. The thermal re-dimerization reaction is examined under the different topotactic conditions in crystals: disordering, surface defects, and phase transformations. Depending on the conditions, and on the molecular structure, aromatic C-nitroso compounds can associate to form one-dimensional polymeric structures and are able to self-assemble on gold surfaces.

Solid-state reaction mechanism and microwave dielectric properties of 0.95MgTiO3–0.05CaTiO3 ceramics

In this work, a method (marked as MCT1) to simplify the production process of MgTiO3–CaTiO3 ceramics was investigated. For the MCT1, MgTiO3–CaTiO3 ceramics were prepared by using the MgO, CaCO3 and TiO2 powders without preparing MgTiO3 and CaTiO3. For the traditional method (marked as MCT2), the CaTiO3 and MgTiO3 powders were firstly synthesized and then mixed to prepare MgTiO3–CaTiO3 ceramics. The MCT1 inhibited the formation of MgTi2O5 phase and improved the sintering behavior of ceramics, which resulted in the improvement of microwave dielectric properties for MgTiO3–CaTiO3 ceramics. The good microwave dielectric properties of e r = 19.4, Q × f = 101,951 GHz, and τ f = −15 ppm/°C were obtained for MCT1 ceramics.

Solid-State Reaction Mechanism and Deliquescence Phenomenon of K0.5Na0.5Nb0.7Al0.3O3 Ceramic

Development of (K,Na)NbO3-based ceramics has attracted much attention in recent decades. In this work, K0.5Na0.5Nb0.7Al0.3O3 ceramic was prepared using conventional solid-state processing. A deliquescence phenomenon was observed when the specimen was exposed to moist atmosphere. The reaction mechanism and cause of deliquescence were investigated using x-ray diffraction analysis, scanning electron microscopy, energy-dispersive spectrometry, electron microprobe analysis, inductively coupled plasma mass spectrometry, and thermogravimetric/differential scanning calorimetric analysis. The results revealed interactions mainly amongst the raw materials K2CO3, Na2CO3, and Nb2O5 as well as K2CO3, Na2CO3, and Al2O3, which can influence the sintering behavior of the mixture. (K,Na)NbO3 and (K,Na)AlO2 were present in the sintered K0.5Na0.5Nb0.7Al0.3O3 ceramic, with the latter leading to deliquescence. During the sintering process, Al2O3 reacts with alkali oxides (Na2O and K2O), which are the decomposition products of carbonates, to form (K,Na)AlO2. In addition, Al2O3 is more likely to react with K2O compared with Na2O.

Electrochemical Lithiation-Delithiation of Sulfur in Single-Walled Carbon Nanotubes

Lithium-sulfur (Li-S) batteries are one of the most promising energy storage technologies because of the high theoretical capacity of sulfur as cathode. However, the high electrical resistivity of sulfur and the dissolution of lithium polysulfides into electrolytes are greatly limiting the performance of Li-S batteries. Interestingly, when the sulfur confinement size is smaller than 1 nm, different electrochemical behaviors and excellent cycle stabilities have been observed. However, the mechanism of sub-nano confinement of sulfur has not been investigated in details. Single-walled carbon nanotubes (SWCNTs) with their various pore size, uniform pore size distribution, and excellent electron conductivity are ideal hosts for studying the effect of different sulfur confinement sizes. In this study, we investigate the effect of sulfur confinement size by incorporating sulfur into both EA- (electric arc) and HiPco- (high-pressure carbon monoxide) SWCNTs with diameter of 1.55 ± 0.1 and 1.0 ± 0.2 nm, respectively. Interestingly, when sulfur is incorporated into HiPco-SWCNTs, the polymerized long chain sulfur molecules inside the tubes largely changes the Raman spectra. The giant Raman response from the sulfur provides an ideal opportunity to perform in situ studies on the lithiation-delithiation reactions of the confined sulfur. High-resolution TEM images confirm the chain structure of sulfur in EA- and HiPco-SWCNTs. Cyclic voltammetry and galvanostatic charge–discharge are performed by using different electrolytes, and sulfur in EA- and HiPco-SWCNTs show distinctively different electrochemical behaviors. In situ Raman spectra and ex situ XPS are measured during galvanostatic charge–discharge to investigate the lithiation-delithiation mechanism. A solid-state reaction mechanism was proposed when sulfur is in sub-nano confinement.

Nonthermal effects in photostimulated solid state reaction of Mn doped SrTiO3

The effect of a photostimulated solid state reaction was investigated in Mn doped SrTiO3 samples. Light irradiation was performed by either halogen or UV lamps in order to study the effect of the spectral composition, and the results were compared with samples prepared at the same temperatures in a conventional furnace. The obtained samples were studied by X-ray diffraction for structural characterization and by Electron Paramagnetic Resonance, which provides microscopic information about the local environment as well as the valence state of Mn ions. It was found that light irradiation significantly enhances the solid state reaction rate compared to synthesis in the conventional furnace. Moreover, it was observed that UV lamp irradiation is much more effective compared to halogen lamps. This indicates that the absorption of light with energy larger than the materials band gap plays an important role and points towards the nonthermal mechanism of the photostimulated solid state reaction.

Iron Shell Formation by Electrolyzing Self-Assembled Nano-Particles

Electrochemical reaction process of iron oxide reduction has been investigated for several decades, and both solid-state reaction mechanism and dissolution/re-deposition mechanism were proposed for the reduction process. The previous studies observed the reaction process from macro- and micro-scale, and how the intermediate participates in the dissolution/re-deposition route is unclear. In this study, a mixture of Fe2O3 nano-particles and carbon powder was electrolyzed in an alkaline solution, and the morphology of the product depended on the electrolysis temperature. The Fe2O3 nano-particle aggregates can be electrolyzed into micro-size hollow partciles at 60°C. To explain this phenomenon, ex-situ SEM technique combining with TEM was adopted to observe the morphology change of Fe2O3 particles on the surface of the glass carbon electrode at nano-scale at a series of electrode potentials. The surface of the particle was reduced to amorphous compounds firstly, and these compound was the intermediate participating in dissolution/re-deposition process to form new crystals. The solubility of these amorphous compound is relative low at 60°C, and the compouds stayed in their original position, connected and stabilized each other to form micro-size iron shell. They can dissolve into eletrolyte, migrate to somewhere, and re-deposit to construct new crystals at higher temperature. This study not only presents an innovative and efficient way to electrolyze micro-size hollow iron particles, but also provides some new discovery about Fe2O3 electrochemical reduction process.

Solid-State Reaction Between Fe-Al-Ca Alloy and Al2O3-CaO-FeO Oxide During Heat Treatment at 1473 K (1200 °C)

The aim of this study was to control the physicochemical characteristics of inclusions in steel through appropriate heat treatment. Using a confocal scanning laser microscope (CSLM) and pipe furnace, the solid-state reactions between Fe-Al-Ca alloy and Al2O3-CaO-FeO oxide during heat treatment at 1473 K (1200 °C) and the influence of these reactions on the compositions of and phases in the alloy and oxide were investigated by the diffusion couple method. Suitable pretreatment of the oxide using a CSLM and production of the diffusion couple of Fe-Al-Ca alloy and Al2O3-CaO-FeO oxide gave good contact between the alloy and oxide. The diffusion couple was then sealed in a quartz tube with a piece of Ti foil to lower oxygen partial pressure and a block of Fe-Al-Ca alloy was introduced to conduct heat treatment experiments. Solid-state reactions between the alloy and oxide during heat treatment at 1473 K (1200 °C) were analyzed and discussed. A dynamic model to calculate the width of the particle precipitation zone based on the Wagner model of internal oxidation of metal was proposed. This model was helpful to understand the solid-state reaction mechanism between Fe-Al-Ca alloy and Al2O3-CaO-FeO oxide.

Characteristic and kinetics of corn stalk pyrolysis in a high pressure reactor and steam gasification of its char

Pyrolysis characteristics of the corn stalk were investigated at different temperatures and pressures, with focus mainly on the releasing profiles and forming behaviors of gas. The results show that a higher pressure was conducive to the yield of H2 and CH4, and was not conducive to the generation of CO. Combustible gas components increase with the increase temperature. H2 concentration was affected significantly by temperature, was mainly released at higher temperatures (>500°C). At 700°C, the combustible gas components are up to 90% and H2 concentration is up to 51.78%. The gas components of corn stalk pyrolysis char steam gasification mainly consisted of CO and H2, 25.7% and 50.7% respectively. The calorific value of gasification gas is up to 9508.9kJ/M3. A kinetic study of the pyrolysis process of the corn stalk was investigated using a thermogravimetric analyzer. As the heating rate increased, the activity energy reduced. By using the Popescu method to determine that shrinking core model can reflect the pyrolysis process of corn stalk truly at low temperature pyrolysis, and chemical reaction model can reflect the pyrolysis process of corn stalk truly at high temperature pyrolysis. Experimental results showed that values of kinetic parameters can be successfully used to understand the degradation mechanism of solid-state reaction.

Conversion of Marine Structures to Calcium Phosphate Materials: Mechanisms of Conversion Using Two Different Phosphate Solutions

Marine structure, coralline materials were converted to calcium phosphate using two different phosphate solutions. The aim was to study the conversion mechanisms under acidic and basic environment at moderate conditions of temperature. Crystal growth and morphology of converted corals were characterized by XRD and SEM respectively. The results suggested that under acidic conditions (H3PO4), dissolution and precipitation control and direct the crystal formation and morphology in which transition from plate like to rod like hydroxyapatite structure was favoured. Metastable phase such as monetite formed and transformed to HAp during reaction. During the first hour of the dissolution a monetite and hydroxyapatite mixture precipitates and then the full conversion to hydroxyapatite is observed. On the other hand, under basic conditions (NH4)2HPO4, just diffusional surface conversion of the calcium carbonate structure of coralline materials to hydroxyapatite and a very small amount of tri-calcium phosphate is observed. The mechanism can be classified as the solid-state topotactic ion-exchange reaction mechanism.

Solid state synthesis of ultrafine-LiCoO2 by enhanced thermal decomposition of carbonate precursors followed by double-calcining

Ultrafine LiCoO2 powders with the layered rock-salt structure are successfully synthesized by enhanced thermal decomposition of carbonate precursors followed by double calcining. The mean size of the primary nanoparticles is about 500nm with a narrow size distribution and is close to roundness with smooth surface. The LiCoO2 powders are also characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The lattice parameters of the synthesized LiCoO2 powders are the same as those of the corresponding powders formed by conventional high temperature solid-state synthesis processing. The double-calcining heating method can improve the crystalline perfection and produce the high temperature phase. The mechanism of solid-state reaction is also discussed. The electrochemical properties of as-formed ultrafine-sized LiCoO2 is examined and the maximum discharge capacities are 166.7mAh/g, 160mAh/g and 140mAh/g at 0.2C, 0.5C and 1C, respectively. After 50cycle performance, it is with a capacity retention of 88.84%, 88.10% and 72.90%, respectively.

The Conversion from Magnesium Hydroxychloride to Anhydrous Magnesium Chloride by Solid-State Reaction

To reduce the content of MgOHCl in anhydrous MgCl2, MgOHCl was converted to anhydrous MgCl2 by solid-state reaction. Factors that affect the conversion effects were investigated, including the mol ratio of NH4Cl to MgOHCl, thickness of covering agent, reaction temperature, and reaction time. The conversion process was characterized by XRD analysis and chemical analysis. The solid-state reaction mechanism was studied and discussed. The MgO content in anhydrous MgCl2 achieved 0.05 pct under the optimal conditions: the mol ratio of NH4Cl to MgOHCl was 3:1, thickness of Al2O3 powder 2 cm, reaction temperature 623 K (350 A degrees C), and reaction time 1 hour.

Thermogravimetric Kinetic Analysis of the Pyrolysis of Rice Straw

A kinetic of the pyrolysis of rice straw is investigated with thermogravimetric analyzer with non-isothermal methods selected for analyzing solid-state kinetics data is presented. The weight loss was measured by TGA in nitrogen atmosphere. The samples were heated over a range of temperature from 298K to 973K with three different heating rates of 5, 10 and 15K min-1. The results obtained from thermal decomposition process indicate that there are two main stages such as active and passive pyrolysis. In the DTG thermograms the temperature peaks at maximum weight loss rate changed with increasing heating rate. The activation energy and pre-exponential factor obtained by Kissinger method are 172.62kJ mol-1, 1.456 × 1011 min-1, while, the same average parameters calculated from FWO and KAS methods are 192.66kJ mol-1, 1.287 × 1022 min-1 and 193.60kJ mol-1, 6.887 × 1015 min-1, respectively. Experimental results showed that values of kinetic parameters obtained from three different methods are in good agreement, but KAS and FWO methods are more efficient in the description of the degradation mechanism of solid-state reactions.