Arrhenius Plot Research Articles

Experimental constitutive relationships for high-temperature deformation of as-cast Al–Si binary alloys

ABSTRACT As-cast binary Al–Si alloys containing ∼2 to 30 wt.% Si were deformed by differential strain rate and differential temperature test techniques at 600–840 K and strain rates 10−4–10−2 s−1 to find the parameters of the constitutive relationships for high-temperature deformation. The maximum strain rate sensitivity index (m) of flow stress was found to be 0.28 in the eutectic Al-12Si alloy. The Arrhenius plot for activation energy for deformation (Q) exhibits bilinear behaviour, with Q being greater at higher test temperatures than at lower temperatures. The magnitude of Q varies as a function of Si content: 95.7 ± 9.8 kJ/mol for Al-2Si to 311.4 ± 98.1 kJ/mol for Al-12Si alloy. Also, the constant initial strain rate tests performed at selected strain rates and temperatures revealed flow hardening at small strains followed by flow softening. Deformation of Al–Si alloys is suggested to be controlled by the dislocation climb mechanism through the participation of both the grain interior and grain boundaries by consideration of effective stress instead of applied stress.

Impact of the electrospinning synthesis route on the structural and electrocatalytic features of the LSCF (La0.6Sr0.4Co0.2Fe0.8O3–δ) perovskite for application in solid oxide fuel cells

In-house electrospun La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) nanofibers have been tested through synchrotron x-ray diffraction and electrochemical impedance spectroscopy (EIS) in the 823–1173 K range, namely in the operating window of intermediate-temperature solid oxide fuel cells. Identical tests have been carried out on commercial LSCF powders, as a control sample. The results demonstrate that the electrospinning manufacturing procedure influences the crystalline properties of the perovskite. The rhombohedral structure (R), stable at room temperature, is retained by nanofibers throughout the whole temperature range, while a rhombohedral to cubic transition (R→C) is detected in powders at ⁓1023 K as a discontinuity in the rhombohedral angle α, accompanied by an abrupt change in oxygen occupation and microstrain. EIS data have a single trend in the nanofibers Arrhenius plot, and two different ones in powders, separated by a discontinuity at the structural transition temperature. Thus, a striking parallel is demonstrated between the variation with temperature of crystallographic features and electrochemical performance. Interestingly, this parallel is found for both nanofiber and granular electrodes. This opens up questions and new perspectives in attributing activation energies derived from EIS tests of LSCF materials to electrochemical processes and/or crystal structure variations.

Polaron-mediated transport and relaxation phenomena in the lead zinc niobate (PZN) modified bismuth ferrite solid solution

To investigate the dielectric and conductivity properties of PZN modified BF solid solution high temperature mixed oxide technique is employed. The material is subjected to analysis using XRD, SEM, and impedance spectroscopy. A polycrystalline PZN-BF sample with an average crystallite size of 63.3 nm has been formed. The scanning electron micrographs show that the grains and grain boundaries are distributed suitably. dielectric characteristics of the 0.1PZN-0.9BF compound are studied at frequencies ranging from 1 kHz to 1 MHz and temperatures ranging from ambient temperature to 400 °C. The confined mobility of charge carriers causes nearly continuous loss (NCL) behavior at low temperatures (<200 °C). High-temperature relaxation resulting from charge carrier hopping induces maximum loss and elevated conductivity. Rendering to the Overlapping Large Polaron Tunnelling (OLPT) model of conductivity, the transport mechanism in this modified BiFeO3 (BF) compound is facilitated by the short-range hopping of polarons. The NTCR behavior from Arrhenius plot of ac conductivity and temperature independent conductivity relaxation from loss modulus (M'') analysis are demonstrated. Sensors, actuators, and optoelectronic devices can benefit from the PZN-modified BF compound's electrical and dielectric characteristics, which have been studied in detail.

Reaction Kinetics of CH2OO and syn-CH3CHOO Criegee Intermediates with Acetaldehyde.

Criegee intermediates exert a crucial influence on atmospheric chemistry, functioning as powerful oxidants that facilitate the degradation of pollutants, and understanding their reaction kinetics is essential for accurate atmospheric modeling. In this study, the kinetics of CH2OO and syn-CH3CHOO reactions with acetaldehyde (CH3CHO) were investigated using a flash photolysis reaction tube coupled with the OH laser-induced fluorescence (LIF) method. The experimental results indicate that the reaction of syn-CH3CHOO with CH3CHO is independent of pressure in the range of 5-50 Torr when using Ar as the bath gas. However, the rate coefficient for the reaction between CH2OO and CH3CHO at 5.5 Torr was found to be lower compared to the near-constant values observed between 10 and 100 Torr. Furthermore, the reaction of syn-CH3CHOO with CH3CHO demonstrated positive temperature dependence from 283 to 330 K, with a rate coefficient of (2.11 ± 0.45) × 10-13 cm3 molecule-1 s-1 at 298 K. The activation energy and pre-exponential factor derived from the Arrhenius plot for this reaction were determined to be 2.32 ± 0.49 kcal mol-1 and (1.66 ± 0.61) × 10-11 cm3 molecule-1 s-1, respectively. In comparison, the reaction of CH2OO with CH3CHO exhibited negative temperature dependence, with a rate coefficient of (2.16 ± 0.39) × 10-12 cm3 molecule-1 s-1 at 100 Torr and 298 K and an activation energy and a pre-exponential factor of -1.73 ± 0.31 kcal mol-1 and (1.15 ± 0.21) × 10-13 cm3 molecule-1 s-1, respectively, over the temperature range of 280-333 K.

Structural Elucidation, IR spectroscopy and DC electrical conductivity of Ni0.6Zn0.4GdyFe2-yO4 nanoferrites synthesized via a low-temperature citrate gel combustion method

In the present work, we report the detailed Powder XRD Rietveld refinement and elucidation of structural factors of Ni0.6Zn0.4GdyFe2-yO4 nanoferrites. The Ni0.6Zn0.4GdyFe2-yO4 nanoferrites synthesized via low-temperature citrate gel combustion technique for the various levels of Gd3+ ion concentration (y = 0.0, 0.1, 0.15 and 0.20). The generated structural factors signify the dependence on the concentration of Gd3+ ions. The prepared samples were found to crystallize in the Fd-3m space group and also identified their occupancies; some of the Fe3+ ions of the octahedral site at the 16d position will be replaced by Gd3+ ions. The lattice constant and crystallite size dropped to a low value for y = 0.1, and then, later, noticed the small increment. The crystallite sizes of the sample are to fall in the range of 26.1 nm–37.6 nm. The cation distribution among the tetrahedral (AII) and octahedral sites (BII) has been estimated. The obtained values correlate with Gd3+ ion concentration, and the radius variation of AII and BII sites signifies the migration of Fe3+ ions from the BII site to the AII sites. The force constant of Metal-Oxygen bonds was determined from the infrared spectrographs; the force constant was found to be relatively low with the BII site. The DC electrical conductivity infers the semiconducting nature and distinct phase of conductivity, which is attributed to the magnetic phase change due to temperature. The magnetic curie temperatures of the sample are obtained by the Arrhenius plot, which signifies the dependence of Gd3+ion concentration.

Evaluation and Modeling of the Rate of Formation of Lath Martensite in Fe-C Alloys, Extracted from Ultra-Rapid Quenching Experiments

Isothermal information is rarely available for the formation of martensite in Fe or Fe alloys due to a very high rate of transformation compared to the rate of heat conduction. Such information has now been extracted for lath martensite in some sets of Fe alloys from available information on ultra-rapid quenching but only at a single temperature for each alloy, related to its two MS temperatures. The temperature dependence could, thus, be studied only on binary sets of alloys. Those results have been applied to mathematical models based on the Arrhenius equation and illustrated with Arrhenius plots. For three sets of binary Fe alloys, a large group of rates came close to the rate of an almost pure and carbon-free Fe-C alloy. It illustrated that Cr, Ni, and Ru in low contents have relatively small effects on the rate of formation of lath martensite in Fe. It also demonstrated that the present measurements have considerable reproducibility. In contrast, a set of Fe-C alloys did not give a straight line in the Arrhenius plot. Using a new mathematical model based on the concept of the Arrhenius equation to express the effect of carbon, it was possible to predict the rate of formation of lath martensite for Fe-C alloys with fixed C content and their temperature dependencies which are not available experimentally due to the very high rate of formation.

Study of conduction mechanisms of InSeSb nano-chalcogenide alloys

The electrical conduction mechanisms for bulk samples of In0.1Se0.9−x Sb x (x = 0, 0.04, 0.08 and 0.12) nano-chalcogenide system, synthesized by the melt-quenching technique are investigated through current–voltage (I–V) characteristics. For the detailed study of conduction mechanism pellets of bulk samples are prepared. A thorough examination of electrical conductivity is done in the temperature range of 295–318 K and 0–50 V voltage range. From I–V measurements it is observed that samples are showing ohmic nature at lower field and non-ohmic nature at relatively higher field values. The temperature dependence of DC conductivity is analyzed using the Arrhenius relationship which is found to increase with Sb content. The value of activation energy and pre-exponential factor are calculated, which revealed that the conduction is due to the hopping of charge carriers among the localized states. Different parameters of Mott’s variable range hopping such as degree of disorder T 0, density of localized states N(E F), hopping distance (R hop), and hopping energy (W) are calculated. For the high field conduction process Poole–Frenkel, and Schottky processes are studied.

Chemically condensed liquid crystalline optical materials dielectric relaxation and phase variance of novel switching applications

Dielectric relaxations are studied at three different frequencies of a hydrogen bond liquid crystals composed of chloro benzoic acid with nonyloxy benzoic acid. The process of synthesis is described and the synthesized mesogen is a monophase variant with nematic phase. Hence, FT-IR studies conform the formation of hydrogen bond. Moreover, DSC studies enabled to examine the transition temperatures and corresponding enthalpy values. Profiles of dielectric loss variation with frequency from 5 Hz to 13 MHz are constructed and three different dielectric relaxations labelled as soft mode I relaxation, type II relaxation and type III relaxation at 1 KHz, 6577 KHz and 7654 KHz respectively are observed and investigated. Cole-Cole plots are constructed for all the dielectric relaxations. Arrhenius plots enabled to envisage the activation energies. For the first time in the history of liquid crystal dielectric work, we observed that in the present sample at higher frequency the process mentioned above is reversed. All the dielectric data points obtained at various temperatures when plotted they are found to converge at the ε∞ values and diverge at ε0 values. This process is referred as frequency cross over. Nematic growth order derived from dielectric studies is also presented.

MOTT’S VARIABLE RANGE HOPPING MODEL FOR POLYPYRROLE-PAPAIN COMPOSITE POLYMER: INFLUENCE OF PAPAIN ENZYME ON COMPOSITE POLYMER

Pure polypyrrole (ppy) doped with different weight percent of papain was synthesized by in situ polymerization. These different compositions of pyrrole and papain composite polymers were analyzed for direct current (DC) conductivity. The size of the particle calculated by using the Scherrer equation and Williamson-Hall (W-H) plot was found to be in the range of 15 nm – 20 nm. Activation energies evaluated by using Arrhenius plots show an increase in activation energy from base ppy to papain-ppy composite polymer. The activation energy was found to vary from 22.4 meV to 34.4 meV for papain-ppy composite. The experiment revealed that Mott’s Variable Range Hopping model (VRH) for three dimensions (3D) applies to pure polypyrrole and papain-ppy composite. The density of states at the Fermi level N(EF) were found to be 2.7 × 1021 eV–1cm–1 for pure ppy and ranged from 0.3 ×1019 eV–1cm–1 to 0.8 ×1020 eV–1cm–1 for the composite polymer. The average hopping range and average hopping energy of pure ppy and composite polymers were also calculated.

Microwave antenna focusing for spatially resolved modulation of burn rate

This study explores the ability to dynamically modulate the burn rate of nanothermites through microwave generated heat zones. These heat zones were generated by embedding a microwave receiving antenna in 3D printed Al/CuO samples. These thermal hot spots in the nanothermites are generated by the induced high electric fields at the terminus of an embedded receiving antenna and are monitored by an IR camera. The burn rates were investigated for different MW induced hot spot temperatures, geometries and receiving antenna materials. The local burn rate increase closely tracks the hot spot spatial distribution, and for our experimental condition enabled an amplification of burn rate of ∼6×. An effective burn rate activation energy was calculated to be ∼18 kJ/mol from the Arrhenius plot of local burn rate and initial temperature. Three color pyrometry confirms that the main mechanism of the local burn rate increase is related to the initial temperature profile in the sample. This study demonstrates the sensitivity of the local burn rate of nanothermites to initial temperature and provides a new approach to modulate the burn rate by localizing MW energy.

Electrical, ferroelectric and electro-caloric properties of lead-free Ba0.85Ca0.15Ti0.95(Nb0.5Yb0.5)0.05O3 multifunctional ceramic

In this study, lead-free Ba0.85Ca0.15Ti0.95(Nb0.5Yb0.5)0.05O3 (BC15TYN5) ceramic has been successfully obtained through the conventional solid-state reaction. It has been found the multifunctionality of the BC15TYN5 ceramic. It exhibits ferroelectric properties, with a significant remanent polarization value of about Pr = 9.36 μC/cm2, and a recoverable energy storage density value of about Wrec = 42.21 mJ/cm3. Additionally, it displays a dielectric permittivity of about ε′r = 7230 around TC = 80 °C, and an electro-caloric strength value of about ξ = 0.12 K mm/kV. It's worth noting that these values surpass those typically found in BaTiO3 ceramics elaborated with similar experimental conditions. Electrical study (impedance, modulus, and conductivity characteristics) is essential for characterizing the BC15TYN5 material, determining its suitability for various technological applications, and optimizing manufacturing processes. The Cole-Cole plots exhibited two relaxations associated with the contribution of the grains and grain boundaries. The relaxation times for both grains and grain boundaries showed temperature-dependent variation following Arrhenius relation. The measured AC conductivity was evaluated by applying the Jonsher power law. Based on the thermal evolution of the exponent S, it was confirmed that the conduction mechanism follows the Correlated Barrier Hopping (CBH) model. These properties make BC15TYN5 ceramic suitable for applications such as dielectric capacitors, ferroelectric random-access memories, electrical energy storage units, and electro-caloric refrigeration systems.

On the temperature dependence of enzymatic degradation of poly(ethylene terephthalate)

Enzymatic recycling of poly(ethylene terephthalate), PET, has attracted significant attention in recent years. Temperature is a governing factor in the enzymatic degradation of PET, influencing simultaneously the catalytic activity and thermal stability of enzymes, as well as the biodegradability of PET materials from many perspectives. Here we present a detailed examination of the complex and mutual effects of temperature on the degradation of low-crystallinity PET (LC-PET, 7.6%) and high-crystallinity PET (HC-PET, 30%) microparticles using the WCCG variant of the leaf-branch compost cutinase (LCC). The degradation velocity apparently increases exponentially with increasing temperature at temperatures below 65 °C. Arrhenius plots show a sudden reduction in activation energy at temperatures higher than 40 °C, suggesting the onset of the surface glass transition of PET particles. This is more than 20 °C lower than the bulk glass transition temperature, underscoring the interfacial catalytic nature of enzymatic PET degradation. WCCG undergoes substantial conformational changes upon thermal incubation at temperatures ranging from 50 to 70 °C and exhibits enhanced activity, owing to the increased intrinsic catalytic activity and improved adsorption on PET surface. Further increasing the temperature leads to the inactivation of enzymes alongside the rapid recrystallization of amorphous PET, impeding the enzymatic degradation. These findings offer a detailed mechanistic understanding of the temperature dependence of the enzymatic degradation of PET, and may have implications for the engineering of more powerful PET hydrolases and the selection of favorable conditions for industrially-related recycling processes.

Electrochemical measurement of the corrosion rates of structural materials in molten NaCl–MgCl2 at 580℃

Molten chlorides find varied applications in engineering disciplines, notably in the nuclear energy sector. However, the utilization of molten chlorides in molten salt reactors (MSRs) requires investigation of the corrosion behavior of the reactor's structural materials in such environments. In this study, we proposed a facile method for determining the corrosion rates of structural materials immersed in a high temperature NaCl–MgCl2 molten salt, based on electrochemical measurements by cyclic voltammetry. The method involves measuring the electrochemical signals of the soluble corrosion products as a function of time. EuCl3-induced corrosion of Inconel 625 and stainless steel 316 (SS 316) in molten NaCl–MgCl2 was monitored by electrochemical detection of Ni2+ and Fe2+. The corrosion rates were linearly dependent on the EuCl3 concentration, and first-order rate constants of 1.03 × 10-4 and 3.20 × 10-5 s−1 at 580 ℃ were obtained for Inconel 625 and for SS 316, respectively. Arrhenius plot analysis of the temperature dependence of the rate constant provided an activation energy of 43.3 kJ mol−1 for Inconel 625 corrosion in molten NaCl–MgCl2–EuCl3. The rate constant became temperature-invariant above 620 ℃ indicating the mass-transfer limitation of corrosion at higher melt temperatures. The proposed approach enables accurate and real-time evaluation of the corrosion rate in the molten salt, and accordingly, offers a straightforward solution for in-situ corrosion monitoring in MSR systems.

A population balance model for the kinetics of covalent organic framework synthesis.

This study presents a population balance model for the kinetics of nucleation and growth in covalent organic framework (COF) synthesis. The model incorporates second-order nucleation and first-order growth rates, consistent with proposals in the literature. Despite having non-linear terms, an implicit analytic solution is derived and then converted to explicit solutions for the monomer concentration and size distribution of COF flakes as a function of time. For experimental definitions of the induction time and the initial growth rate based on yield (y) vs time (t) curves, the model predicts power-law relationships: tind=0.409kN-1/3kG-2/3cA0-1 and dy/dtmax=0.965kN1/3kG2/3cA0, respectively. We discuss the implications for the interpretation of Arrhenius plots. We also discuss key discrepancies with experiments, including the predicted attainment of 100% yield instead of 30%-40% as observed and the value of the yield at the inflection point in the yield vs time curve. We suggest extensions to the model, including nucleation and growth kinetics with equilibrium solubility limitations and two-dimensional nucleation for the formation of multilayer COF particles.

Impact of Starch Concentration on Chlorella-k-Carrageenan Gel Formation Mechanism

Despite their industrial popularity, plastics; specifically in packaging, have been known for their harmful environmental impact. In this work, as an alternative to plastic packaging, microalgae, and starch-based materials were employed. Here, gel formation mechanisms were investigated by using photometric analyses, namely photon transmission and absorbing techniques. Heating (gel-sol) and cooling (sol-gel) experiments were performed, and absorbance (A), transmittance (T), and Arrhenius plots were generated to observe the behavior of the mentioned materials during phase transition processes. The heating and cooling experiments revealed that the addition of starch quickened the gel-sol transitions but slowed down the sol-gel transitions. Hence, the results suggested that the sample containing _Chlorella, k-Carrageenan_, and starch was the most promising potential alternative for plastic packaging.

Influence of Ni2+ ions on structural, spectral and dielectric properties of Sr–Co spinel ferrites synthesized by sol-gel auto-combustion route

Nickel substituted Sr–Co nano spinel ferrites with composition Sr0.5-xNixCo0.5Fe2O4 (0.0, 0.1, 0.2, and 0.3) were prepared with the help of a sol-gel auto combustion route. The prepared materials were sintered at 800 for four and a half hours. Analysis of XRD confirmed that the material is composed of a cubic spinel structure with a single phase, and its space group is Fd-3m. Rietveld refinement of X-ray diffraction data was done for all prepared compositions using FULLPROF software. As the composition under study contains more nickel than lattice constant, crystalline size, X-ray density, and bulk density decrease. The dielectric properties were observed about frequency. The dielectric properties revealed that dielectric loss, dielectric constant, and ac conductivity decrease with increasing the Ni2+ content. The activation energy (ΔE) was calculated from the slope of Arrhenius plots. The ΔE found in the range of 0.580–0.096 eV. The analysis of XPS was carried out to examine the elemental state of annealed samples. The prepared material is suitable for employment in applications involving high frequencies because the Ni-doped Sr–Co ferrites with the greatest Ni2+ concentration have the lowest dielectric loss, dielectric constant, and tangent loss value.

MOO3 catalysed hydrogenation of nitrobenzene to aniline at near room temperature

MoO3 with orthorhombic structure (α-MoO3) was evaluated for its catalytic performance in the hydrazine-assisted transfer hydrogenation of nitrobenzene to aniline at near room temperature. The conversion of nitrobenzene, ca. 88.6 % was obtained after 4 h reaction with > 99 % of selectivity to aniline. The activation energy from the Arrhenius plot was ca. 120.6 kJ/mol. In this system, hydrazine (N2H4) did not only act as a hydrogen donor but also as a reducing agent to generate an active catalytic phase as supported by the existence of an induction period at the early stages of the reaction. XRD and XPS characterisations of the hydrazine–treated catalyst revealed the phase transformation from α-MoO3 to (NH4)0.23H0.08MoO3 containing Mo5+ species, a possible adsorption site for hydrazine decomposition to produce active hydrogen species for the transfer hydrogenation of nitrobenzene. Based on the Hammett plot, an anionic intermediate was indicated to be involved in the rate-determining step.

Influence of NaOH Concentration on Structural, Morphological, Optical, and Electrical Characterization of Perovskite Sodium Bismuth Titanate Prepared by Hydrothermal Method

The hydrothermal method successfully prepares a lead-free sodium bismuth titanate (NBT) perovskite film. The prepared films were studied structurally, and morphologically using X-ray diffraction, and field-emission scanning electron microscopy (FESEM), respectively. Varying the concentration of NaOH showed a noticeable effect on the properties studied. Good crystallization of NBT perovskite films without impurities was obtained at 18 and 20 M concentrations, where the crystalline size was 14 nm according to the Scherer equation. Also, when varying the concentration of NaOH, a similar film thickness was obtained through a cross-section of the FESEM images. It was observed that there was a difference in the intensity of the peaks of the photoluminescence spectra of the prepared films with a change in the concentration of NaOH, which confirms a change in the concentration of oxygen vacancies. The activation energy of the prepared films was deduced from the Arrhenius plot, as it showed small values in the films prepared with a low concentration of NaOH. The results showed that the maximum value of mobility of NBT films was at 20 M of NaOH concentration through the Hall Effect.

Structural and dielectric properties of CaSnO3-doped Sr2.1Na0.8Nb5O15 ceramics

The crystallographic, microstructural, and dielectric properties of Sr2.1Na0.8-xCaxNb5-xSnxO15 (x = 0.00, 0.01, 0.05, 0.10) polycrystalline ceramics have been studied by X-ray diffraction, scanning electron microscopy, dielectric spectroscopy (DS) and impedance spectroscopy (IS). For x = 0.00, 0.05, and 0.10, samples are single phase with P4bm symmetry at room temperature with x = 0.01 showing a small quantity of secondary phase(s). All compositions show typical ceramic microstructures and d50 grain sizes ranging from 5.1 to 26.6 μm. DS shows a clear trend in the high temperature ferroelectric-paraelectric transition with the Curie temperature, T0, decreasing from ∼ 160 to ∼ 110 °C, and an additional relaxation at approximately 120 °C with increasing CaSnO3. IS reveals all samples have a homogeneous electrical microstructure with predominantly electronic conduction. The activation energy of conduction calculated from Arrhenius plots of the conductivity increases with CaSnO3 content from 1.27 to 1.38 eV likely due to the expansion of the band gap.

Investigation of sulphate hydride anti-perovskite as solid electrolyte

Over the last decade, anti-perovskites have drawn significant attention as potential solid-electrolytes for solid-state batteries. Due to the increase in consumption of lithium, there has been a push towards next generation batteries, including sodium-ion batteries. The first representative of the material class of sulphate hydride anti-perovskites, Na3SO4H, was synthesized by solid-state methods as a possible electrolyte for sodium solid-state batteries. Structural characterization confirms the results reported in literature with P4/nmm space group Thermal measurements (DSC and TGA) reveal the stability of the material up to 633 K with H2 release beginning shortly after. Here were report the first electrochemical measurements of this new sulphate hydride anti-perovskite with room temperature conductivity of 4.0 × 10−7 S/cm. Similarly, the electronic conductivity was also measured by Direct Current (DC) experiments to understand a non-linear Arrhenius plot of the conductivity. From the EIS and DC measurements, it is suggested that the electronic and ionic conductivities of this material fall in the same range at room temperature. Upon heating, the material becomes a mainly ionic conductor, explaining the change in the activation energy values in the Arrhenius plot (0.83 eV at low T and 0.24 eV at high T). Solid-state NMR hints at defects in the structure that correspond to Na1 and Hb-c-d dynamics.