Change In Activation Energy Research Articles

On the Dependence of Ionic Transport on Crystal Orientation in Nasicon-Type Solid Electrolytes

The dependence of ionic transport on crystal orientations in NaSICON-type solid electroytes is studied on flux-grown M3Sc2(PO4)3 (M = Na, Ag) single crystals with well-defined facets. Herein, we provide the first impedance spectroscopy study to characterize ion conduction along different crystallographic orientations in this important class of materials for electrochemical energy storage systems. Moreover, we used single crystal X-ray diffraction, differential scanning calorimetry, 23Na NMR spin-lattice relaxation measurements, and ab initio molecular dynamics simulations to study the interplay of structure and ion transport taking place at different length scales. We conclude that the phase behavior in NaSICON-type materials is strongly linked to ion diffusion. At room temperature, ionic conductivity is slightly anisotropic along the crystallographic orientations [001] and [100]. The slightly different activation energies are related to diffusion bottlenecks solely changing along [001]. This change is caused by anisotropic thermal lattice expansion. With increasing temperature, ion transport increasingly becomes isotropic finally resulting in an order-disorder phase transition from C2/c to R−3c. This phase transition is associated with a clear change in activation energy solely along [001]; it can be traced back to the increasing jump distance along this crystal orientation with temperature. Astonishingly, changing the ionic charge carrier, i.e., when going from Na+ to Ag+, shifts the phase transition temperature by 140 K toward lower temperature. The Arrhenius behaviour remains, however, similar. This finding is related to the higher mobility of Ag+ in the NaSICON framework leading to isotropic ion diffusion at much lower temperatures. Overall, flux-grown M3Sc2(PO4)3 allowed us to show that ionic transport parameters and phase stability sensitively depend on crystal chemistry.

Detailed Study on the Mechanical Properties and Activation Energy of Natural Rubber/Chloroprene Rubber Blends during Aging Processes

Selection of a suitable thermal aging process could render desirable mechanical properties of the rubbers or blended rubbers. In this work, the effect of the aging processes on the mechanical properties and activation energies of natural rubbers (NR) and NR/chloroprene rubbers (CR) blends with low CR contents (5–10%) was investigated. Three aging processes including heat aging (at 110°C for 22 hours), mechanical aging (under dynamic loading to 140% strain for 16000 cycles), and complex aging (heat and mechanical aging) were studied. The results revealed that the compatibility of CR in natural rubber matrix had a significant effect on the dynamic properties of the blended rubber and negligible effect on the static properties. The changes in activation energies of the blended rubber during aging processes were calculated using Arrhenius relation. The calculated changes (ΔUc, ΔUd, and ΔUT) in activation energies were consistent with the results of mechanical properties of the blended rubber. Interestingly, the change in activation energies using complex aging conditions (ΔUc) was mostly equal to the total changes in activation energies calculated separately from heat aging (ΔUT) and mechanical aging (ΔUd) conditions. This indicates that, in complex aging conditions, the heat and dynamic loading factors act independently on the properties of the blended rubber.

Rheological studies of energetic binder-plasticizer blends

ABSTRACT Two azido ester plasticizers, bis(1,3-diazido prop-2-yl) malonate and bis(1,3-diazido prop-2-yl) glutarate, were mixed with three different binders, Glycidyl azido polymer (GAP), 3,3-bis-(azidomethyl)oxetane-tetrahydrofuran (BAMO-THF or BT) and 3- nitratomethyl-3-methyl oxetane or Poly NIMMO (PLN) in the ratio of 20:80 (w/w) to study their rheological properties. The addition of plasticizer has reduced the viscosity of three polymer blends, which improved the flow behaviour to an acceptable range. The change in activation energies of polymer blends is also calculated. For all the combination of blends, the rate of change in shear stress and linear range of strain with stress decreases after addition of plasticizers. Variation of viscosity with applied stress is unaffected initially and then increases significantly which limits the linear viscoelastic region (LVR) due to the dilution effect.

Change in Concentration-Dependent Diffusion Activation Energy and Frequency Factor with Time: Identified by Numerical Analyses of Experimental Data

A newly developed fully explicit numerical diffusion model coupled with a forward simulation technique, to avoid flaws in conventional methods such as the Boltzmann–Matano, Sauer–Freise and Hall procedures, is used to compute the concentration-dependent activation energy and frequency factor for diffusion in two different alloy systems. In contrast to what has been commonly reported in the literature, the results show that the concentration dependence of activation energy and frequency factor can significantly change with time. In this situation, the use of concentration-dependent activation energy and frequency factor that does not vary with time to predict diffusion effect can lead to considerable error. Furthermore, when there is a time variation in the dependence of activation energy and frequency factor on concentration, a common expectation that diffusion-controlled kinetics would increase with an increase in temperature may not always apply for all time durations.

Catalytic oxidation and reaction kinetics of low concentration benzene over CuxMnyOz/SiO2

Reducing reaction temperature of catalytic combustion is the fundamental way to improve adaptability of catalysts to complex volatile organic compounds (VOCs) and off-design conditions. Using benzene which is the most difficult to be oxidized in VOCs as the catalytic target and by means of multiple characterization methods, silicon dioxide supported copper-manganese catalysts were optimized through changing the load of active material, the ratio of bimetal and calcination condition, the conclusions as following: Cu3Mn9/SiO2 with calcination temperature of 300 °C, molar ratio for Cu/Mn of 3:9 and total load mass for active substance of 11% demonstrates the best catalytic performance. And the benzene which is lower than 2000 mg/m3 in air can be completely oxidized at 265 °C. The change of activation energy and mechanism of deactivation in the process of catalyst optimization were obtained by catalytic reaction kinetic analysis. After the optimization, reaction activation energy decreased from 65.08 kJ/mol to 56.82 kJ/mol, and complete conversion temperature of the C6H6 decreased by nearly 20 °C. Additionally, the fundamental reason for deactivation of the catalyst is the structure changes at high temperature, and surface oxides agglomerate, which greatly reduces the oxygen content of the catalyst. With the increase of reaction temperature, the mass transfer capacity of O2 on the surface of catalyst increase less than that of C6H6, leading to carbon deposition, and the joint action results in the decrease of catalyst activity.

Nanocluster formation and two-step aging behavior in Al–Mg–Si(-xCu: X = 0–4 mass%) alloys

The effects of Cu addition on the clustering and two-step aging behavior in Al–Mg–Si(-Cu) alloys were analyzed by differential scanning calorimetry (DSC), the Vickers hardness and tensile tests, the three dimension atom probe (3DAP) and the transmission electron microscope (TEM). A high amount of Cu up to 4 mass % was added to the Al–Mg–Si alloys. Several types of clusters, namely, Cu–Mg, Cu–Si, Cu–Cu and Mg–Si–Cu, after natural aging for 2419.2 ks were formed in the Al–Mg–Si–Cu alloys. The size distribution and chemical composition of the clusters were characterized using 3DAP based on the maximum separation method. The cluster formation was promoted by 1Cu addition, but it was suppressed by 2Cu and 4Cu additions based on the analyses of cluster formation temperature and activation energy. Thermally unstable clusters were confirmed at the early stage of two-step aging at 170 °C after natural aging for 2419.2 ks. The amount of thermally unstable clusters was increased based on the hardness results. The peak hardness during single aging at 170 °C increased with an increasing Cu content. The negative and positive effect of two-step aging at 170 °C after natural aging for 2419.2 ks was clarified in Al–Mg–Si and Al–Mg–Si–Cu alloys, respectively. The formation temperature, activation energy, cluster size, and hardness changes with the cluster formation during natural aging and dissolution of cluster and precipitate formation during two-step aging at 170 °C are quantitatively described and those behaviors are discussed based on the age-hardening phenomena.

Experimental Study on the Inhibition Effects of Nitrogen and Carbon Dioxide on Coal Spontaneous Combustion

Inert gases can effectively inhibit coal spontaneous combustion. In this paper, the inhibition effect of inert gases (N2 and CO2) on coal spontaneous combustion was studied. In the low-temperature oxidation stage, the constant-temperature heat release and apparent activation energy of coal sample were measured and calculated by the C80 micro-calorimeter. In the high-temperature combustion stage, the critical temperature, maximum peak temperature, ignition temperature, and burn-out temperature of coal samples were analyzed by the synchronous thermal analyzer. The results demonstrate that with the decrease of O2 concentration, the oxidation heat release of coal samples drops gradually while the apparent activation energy increases gradually. In the N2 and CO2 atmospheres, as the O2 concentration is reduced to 1.5% and 3%, respectively, the value of apparent activation energy changes from negative to positive, and the spontaneous reaction transits to a nonspontaneous reaction. The TG-DTG (thermogravimetric-derivative thermogravimetric) curve of coal sample in the high-temperature combustion stage indicates that the critical temperature exhibits a W-shaped trend with the decrease of O2 concentration, which also leads to gradual increases of maximum peak temperature, ignition temperature, and burn-out temperature. The above results signify that increasing the inert gas concentration can gradually reduce the oxidation and combustion rate and improve the inhibition effect on coal spontaneous combustion. In addition, when the O2 concentration is the same, the inhibition effect of CO2 on coal spontaneous combustion is superior to that of N2.

Variation of activation energy determined by a modified Arrhenius approach: Roles of dynamic recrystallization on the hot deformation of Ni-based superalloy

The hot deformation behaviors of Ni18Cr9Co9Fe5Nb3Mo superalloy were explored in the formation temperature range free of γ’ phase with various strain rates applied. The hot deformation behaviors are initially modeled with Arrhenius equation which gives an average activation energy of 581.1 kJ mol−1. A modified Arrhenius approach, including the updated Zener-Hollomon parameter is proposed to consider the change of activation energy under different deformation conditions which turns out a relatively accurate computation for activation energy of hot deformation, i.e., the standard variance for modified model calculated in the covered deformation condition is just 35.4 % of that for Arrhenius equation. The modified model also proposes a map for activation energy which ranges from 571.5-589.0 kJ mol−1 for various deformation conditions. Microstructural features of the representative superalloy specimens were characterized by electron backscattered diffraction (EBSD) techniques in order to clarify the influence of activation energy on the microstructural formation. It is found that the Ni-based superalloy samples with higher activation energy are promoted by the degree of dynamic recrystallization which suggests that the rise in activation energy gives either a better recrystallization rate or finer grains.

Oxygen Vacancy Density Dependence with a Hopping Conduction Mechanism in Multilevel Switching Behavior of HfO2-Based Resistive Random Access Memory Devices

We report a switching model that directly explains the change in activation energy (EAC) at different RESET stop voltages (Vstop) in HfO2-based resistive random access memory devices. The dependenc...

Kinetics and Thermodynamic Analysis of Recent and Ancient Buried Phoebe zhennan Wood.

Kinetics and thermogravimetric analysis of recent Phoebe zhennan wood (RZ) and ancient buried P. zhennan wood (ABZ) were investigated under a nitrogen atmosphere at different heating rates of 5, 10, 15, and 20 K/min. The activation energy values were estimated based on the Flynn–Wall–Ozawa model-free method, and then, the Coats–Redfern model-fitting method was used to predict the reaction mechanism. The best model of RZ for regions 1 and 2 was based on the diffusional and reaction order (second-order) mechanism, respectively, while a diffusional (Jander equation) mechanism is the best model for ABZ. The change in enthalpy and activation energy of the RZ was lower than that of the ABZ at different conversion rates. When the conversion rate was less than 0.4, the RZ may require lower thermal decomposition reaction energy, but the overall energy of thermal decomposition reactions and the degree of disorder was not much different.

Additive manufacturing and characterization of AgI and AgI–Al2O3 composite electrolytes for resistive switching devices

This work investigates the electrochemical dynamics and performance of additively manufactured composite electrolytes for resistive switching. Devices are comprised of a Ag/AgI–Al2O3/Pt stack, where the solid state electrolyte is additively manufactured using extrusion techniques. AgI–Al2O3 composite electrolytes are characterized by x-ray diffraction and electrochemical impedance spectroscopy. The ionic conductivities of the electrolytes were measured for different concentrations of Al2O3, observing a maximum conductivity of 4.5 times the conductivity of pure AgI for composites with 20 mol. % Al2O3. There was little change in activation energy with the addition of Al2O3. Setting the Ag layer as the positive electrode and the Pt layer as the negative electrode, a high conductivity state was achieved by applying a voltage to electrochemically establish an electrically conducting Ag filament within the solid state AgI–Al2O3 electrolyte. The low conductivity state was restored by reversing this applied voltage to electrochemically etch the newly grown Ag filament. Pure AgI devices switch between specific electrical resistivity states that are separated by five orders of magnitude in electrical conductivity. Endurance tests find that the AgI resistive switches can transition between a low and high electrical conductivity state over 8500 times. Composite AgI–Al2O3 resistive switches formed initial Ag filaments significantly faster and also demonstrated two orders of magnitude separation in resistivity when cycling for 1600 cycles.

Effect of Water-immersion and Air-drying Period on Spontaneous Combustion Characteristics for Long-flame Coal

ABSTRACT During the mining of coal seam groups, the physical and chemical properties of the residual coal in goaf will be changed after undergoing water leaching and air-drying, affecting the oxidation characteristics of the coal. To examine the effect of the water immersion and air-drying times on the oxidative combustion characteristics of long-flame coal, this paper uses thermal gravimetric (TG) analysis and infrared spectral analysis to analyze coal samples with different immersion and air-drying times. The change in activation energy (AE), which is associated with the change in the functional groups, was analyzed for the coal-oxygen chain reaction process under coal immersion and air-drying conditions. The results show that coal samples soaked in air-dried for 10 days after water for 20 days have a lower AE (39.14 kJ/mol) than coal samples that underwent other treatment times and have a higher oxygen absorption rate and a higher tendency to undergo spontaneous combustion. According to the TG-DSC test, a range of weight loss and exothermic strengths are observed during the longest immersion and air-drying times. Additionally, during the longest immersion and air-drying times, the variations in the different functional groups are more obvious, the aliphatic hydrocarbon chain breaks and the coal rank is lower. The period of immersion and air-drying can change the spontaneous combustion oxidation characteristics of coal. After being soaked in water for 20 days and air-dried for 10 days, the coal sample was looser and the chain reaction process was accelerated, which promoted the oxidation and spontaneous combustion of coal.

"Effect of Doping on Electrical Properties of Nickel Oxide (NPs) Prepared by Pulse Nd-Yag Laser Deposition Method "

"In this study, nickel oxide (NPs) films were produced by doping each element with 2% zinc, tin, iron, cobalt and magnesium. pulsed laser deposition was used to deposit them on glass substrates , and we used a pulsed Nd-YAG laser with a wavelength of 1064nm. All the films were annealed with one temperature (573k). The electrical properties of the prepared films were studied, such as the continuous electrical conductivity and activation energy, and we found that increasing the temperature increases the electrical conductivity values Also, the value of the electrical conductivity and the activation energy change according to the type of added doping. We also discovered many activation energy values in the temperature ranges of (308K-428K) , and observed the conduct of nanoparticle oxide doping with various metals at these temperatures.

Water and Pathogenic Viruses Inactivation—Food Engineering Perspectives

Water is an essential component of food structures and biological materials. The importance of water as a parameter affecting virion stability and inactivation has been recognized across disciplinary areas. The large number of virus species, differences in spreading, likelihood of foodborne infections, unknown infective doses, and difficulties of infective virus quantification are often limiting experimental approaches to establish accurate data required for detailed understanding of virions’ stability and inactivation kinetics in various foods. Furthermore, non-foodborne viruses, as shown by the SARS-CoV-2 (Covid-19) pandemic, may spread within the food chain. Traditional food engineering benefits from kinetic data on effects of relative humidity (RH) and temperature on virion inactivation. The stability of enteric viruses, human norovirus (HuNoV), and hepatitis A (HAV) virions in food materials and their resistance against inactivation in traditional food processing and preservation is well recognized. It appears that temperature-dependence of virus inactivation is less affected by virus strains than differences in temperature and RH sensitivity of individual virus species. Pathogenic viruses are stable at low temperatures typical of food storage conditions. A significant change in activation energy above typical protein denaturation temperatures suggests a rapid inactivation of virions. Furthermore, virus inactivation mechanisms seem to vary according to temperature. Although little is known on the effects of water on virions’ resistance during food processing and storage, dehydration, low RH conditions, and freezing stabilize virions. Enveloped virions tend to have a high stability at low RH, but low temperature and high RH may also stabilize such virions on metal and other surfaces for several days. Food engineering has contributed to significant developments in stabilization of nutrients, flavors, and sensitive components in food materials which provides a knowledge base for development of technologies to inactivate virions in foods and environment. Novel food processing, particularly high pressure processing (HPP) and cold plasma technologies, seem to provide efficient means for virion inactivation and food quality retention prior to packaging or food preservation by traditional technologies.

On the dependence of ionic transport on crystal orientation in NaSICON-type solid electrolytes

The dependence of ionic transport on crystal orientations in NaSICON-type solid electrolytes is studied on flux-grown M3Sc2(PO4)3 (M = Na, Ag) single crystals with well-defined facets. Herein, we provide the first impedance spectroscopy study to characterize ion conduction along different crystallographic orientations in this important class of materials for electrochemical energy storage systems. Moreover, we used single crystal x-ray diffraction, differential scanning calorimetry, 23Na NMR spin-lattice relaxation measurements, and ab initio molecular dynamics simulations to study the interplay of structure and ion transport taking place at different length scales. We conclude that the phase behavior in NaSICON-type materials is strongly linked to ion diffusion. At room temperature, ionic conductivity is slightly anisotropic along the crystallographic orientations [001] and [100]. The slightly different activation energies are related to diffusion bottlenecks solely changing along [001]. This change is caused by anisotropic thermal lattice expansion. With increasing temperature, ion transport increasingly becomes isotropic finally resulting in an order-disorder phase transition from C2/c to R−3c. This phase transition is associated with a clear change in activation energy solely along [001]; it can be traced back to the increasing jump distance along this crystal orientation with temperature. Astonishingly, changing the ionic charge carrier, i.e. when going from Na+ to Ag+, shifts the phase transition temperature by 140 K towards lower temperature. The Arrhenius behavior remains, however, similar. This finding is related to the higher mobility of Ag+ in the NaSICON framework leading to isotropic ion diffusion at much lower temperatures. Overall, flux-grown M3Sc2(PO4)3 allowed us to show that ionic transport parameters and phase stability sensitively depend on crystal chemistry.

Complex Impedance Analyses of Li doped ZnO Electrolyte Materials

The recent studies indicate that internal point defects in solid electrolytes modify the electronic and ionic conductivity and relaxation mechanism of solid oxide fuel cells. We focused on synthesis of Lithium (Li) doped Zn1-xCoxO (x = 0.00, and 0.10) nanoparticles employing chemical synthesis technique with a reflux setup under constant Argon gas flow. The structural characterizations were performed by x-ray powder diffractometer (XRD) and x-ray photoelectron spectroscopy (XPS). Then, Rietveld refinements were performed to investigate the replacement of Li atom amount in ZnO lattice. Moreover, the variations in ionic conduction dependent on 5, 10 and 20 mol% Li doped ZnO were analysed via ac impedance spectroscopy. The complex measurements were performed in an intermediate temperature range from 100 °C to 400 °C. Ac conductivity responses of each sample were disappeared at a certain temperature due to becoming electronic conductive oxides. However, this specific temperature was tuned to high temperature by Li doping amount in ZnO lattice. Furthermore, the activation energy change by Li dopant amount implied the tuneable ionic conduction mechanism.

Reducing the equivalent magnetic noise of Metglas/Mn-PMNT laminate composites via annealing treatment

The variation of dielectric loss in [1 1 0] -oriented Mn-doped 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (Mn-PMNT) single crystals after different annealing treatments, as well as their influence on equivalent magnetic noise (EMN) for magnetoelectric laminate composites, were investigated in this study. Dielectric loss can be reduced significantly in oxygen-sufficient atmosphere and high annealing temperature, and dielectric constant varies little in this annealing process, which is favorable to the decrease of the dielectric loss noise. The temperature dependence of dc conductivity was used to characterize the change of dc conductivity and activation energy, which indicated that oxygen vacancies in Mn-PMNT single crystals can be reduced by the annealing treatment, leading to the decrease of dielectric loss. For the influence of magnetoelectric laminate composites, the EMN is clearly reduced in low frequency range (10 < f < 100 Hz) after annealing treatment, which is in good agreement with the simulation results.

RESISTIVITY-TEMPERATURE DEPENDENCE, THERMAL AND ELECTRICAL PARAMETERS OF Se65-xAs35Sbx THIN FILMS: (1µm, 5 K.min-1 )

Sheet resistance, Rs , measurements for the (Se65-xAs35Sbx thin films with (0 ≤ x ≥ 10) at. %) with thickness film 1000 nm and heating rate, 5 K/min has been explained in this work. Measurements of the sheet resistance used to compute the thermal and electrical parameters in the temperature range from 300 to 665 K. In the sheet resistance curves, two main regions have been considered clearly evidence of one crystallization region for the studied films. The activation energy, Ec , of crystallization and Avrami index, n, were estimated. The change of activation energy with volume of crystalline fraction has been deduced. The electrical results of the studied films appear two types of conduction channels which contribute two conduction mechanisms in crystallized region. The activation energies ΔE, two pre-exponential factors 0  , *  0 and other parameters has been computed in both of the extended and hopping states regions. The crystalline phases for the as-deposited and annealed films were identified using by x-ray diffraction (XRD).

Relevance of the Entropy Factor in Stereoselectivity Control of Asymmetric Photoreactions

Entropy as well as enthalpy factors play substantial roles in various chemical phenomena such as equilibrium and reactions. However, the entropy factors are frequently underestimated in most instances, particularly in synthetic chemistry. In reality, the entropy factor can be in competition with the enthalpy factor or can even be decisive in determining the overall free or activation energy change upon molecular interaction and chemical transformation, particularly where weak interactions in ground and/or excited states are significant. In this account, we overview the importance of the entropy factor in various chemical phenomena in both thermodynamics and kinetics and in the ground and excited states. It is immediately apparent that many diastereo- and enantioselective photoreactions are entropy-controlled. Recent advances on the entropy-control concept in asymmetric photoreactions are further discussed. Understanding the entropy-control concept will pave the way to improve, fine-tune, and even invert the chemo- and stereoselectivity of relevant chemical phenomena.1 Introduction2 Role of Entropy in Supramolecular Interactions3 Selected Examples of Entropy-Driven Thermal Reactions4 Classical Examples of Entropy Control in Photoreactions5 Entropy-Driven Asymmetric Photoreactions6 Advances in Entropy Control7 Perspective

Structural and optical band gap modification of Zn2SnO4 thin films after irradiation with swift heavy ions for transparent electrode applications

The structural changes and their effect on optical properties have been studied in Zn2SnO4 thin films irradiated by Ag9+ ions. The irradiation of thin films transforms the mixed crystal structures in to a single diffraction plane. In the XRD, the single peak is the result of atomic jump within the material due to the change in activation energy after irradiation. The XRD and SEM confirmed the modifications of lattice parameters and grains in accordance with the basic requirement of material to be used as transparent conducting oxides. In optical studies, the absorption spectra and Tauc plot confirm the neutralization of free electrons in conduction band minimum which results in an increase in the optical band gap for better transmission in visible range. The results indicate that the swift heavy ions passed from polycrystalline material synergistically with inelastic electronic energy loss to promote the formation of Zn2SnO4 oriented in a single direction and lead to rapid phase transformation.