Activation Energy Of Transition Research Articles

Generation, structures, relative energies, and isomerization reactions of C5H5+ cations.

The B3LYP, MP2, and CBS-QB3 quantum chemical methods are used to study the relative energy and isomerization reactions of C5H5+ cations. Ease of generation of 14 C5H5+ isomers by ionic dissociation of halide precursors does not correlate well with carbocation stability. The reaction profiles of concerted isomerization of various C5H5+ cations to six select cations are established along with the respective transition states. The rate coefficients of these processes are estimated by using transition state theory and activation energies computed. The transition states for these six reactions are characterized with regard to position along the isomerization pathway as per Hammond's postulate. The 6 isomerization reactions are combined to yield multi-step conversions of various C5H5+ species to the lowest energy vinylcyclopropenyl cation 1. Finally, three different routes for obtaining the select cations from C5H5Br precursors are profiled and the most favored pathways predicted.

One-dimensional dynamics of gaseous detonations revisited

Stability of one-dimensional gaseous detonations is revisited using both asymptotic analysis and high-order numerical simulations. The double limit of small heat release and a ratio of specific heats close to unity is considered, and attention is focused on weakly unstable detonations in the Chapman-Jouguet regime. It is shown that the time-dependent velocity of the lead shock can be obtained as the eigenfunction of a hyperbolic problem reducing to a single hyperbolic equation for the flow. The solution is then expressed in the form of an integral equation for the shock velocity, from which the threshold activation energy for transition to instability and the oscillation frequency can be obtained. These theoretical findings are validated against a set of direct numerical simulations of one-dimensional detonations in the same limit, performed using a high-order spectral difference scheme in which particular care is taken to ensure a high resolution of the flow with minimal numerical dissipation, while also suppressing post-shock numerical aberrations. Values of detonation parameters at the instability threshold obtained from numerical simulations are systematically compared against their theoretical counterparts, confirming the validity of the proposed asymptotic theory.

Enhancement of the glass forming ability of superelastic Ni-Ti-Cu-Zr-Si alloy

In this study, the use of (Ni0.35Ti0.30Cu0.15Zr0.20)100−xSix (x = 0, 0.5, 1.0, 2.0 at%) alloy as a metallic glass precursor for a superelastic alloy, following thermoplastic forming, is investigated. The addition of Si improved the glass forming ability such that a fully amorphous sample with a thickness of ~450 µm was obtained with the x = 2.0 at% alloy. The addition of Si effectively stabilises the supercooled liquid by significantly increasing the activation energy of glass transition. The incubation time, τ, increased from 89 s for the x = 0 alloy to 346 s for the x = 2.0 at% alloy. The parameters relevant to superelastic effects, such as the maximum indentation depth (Dmax) and remnant indentation depth (Drem), remained almost constant. However, the remnant depth ratio increased slightly with the addition of Si. The fabrication of millimetre-scale Ni-Ti-Cu-Zr-Si metallic glass was achieved via the hot pressing of overlapped as-cast plates.

3D-to-2D Transition of Anion Vacancy Mobility in CsPbBr3 under Hydrostatic Pressure.

Anion vacancy migration in the orthorhombic Pnma phase of the lead-halide perovskite CsPbBr3 under hydrostatic pressure is studied computationally. Density functional theory calculations are used to determine transition states, activation enthalpies, and attempt frequencies for vacancies to hop between nearby lattice sites, under pressure in the range 0.0-2.0 GPa. The resulting data are used to parametrize a kinetic model of vacancy migration under the influence of an electric field, which is solved in the steady state to determine the anion vacancy mobility tensor as a function of pressure. It is found that the mobility tensor becomes increasingly anisotropic with increasing pressure, such that at 2.0 GPa, the mobility within the (010) lattice plane is 3 orders of magnitude greater than the mobility normal to it. The results demonstrate the potentially significant influence of pressure, and by extension, other forms of stress, on defect migration in lead-halide perovskites.

Sulfonation mechanisms of aromatic polymers for PEMFC applications

AbstractThe sulfonated aromatic polymers are competitive proton conducting materials for proton exchange membrane fuel cells because of their relatively low costs and adequate performances compared with the perfluorinated sulfonic acid ionomers. These polymeric materials can be economically synthesized by the sulfonation of existing aromatic polymers; however, the inadequate sulfonation degree has prevented the further optimization of their overall performances. In order to improve the overall performances of sulfonated aromatic polymeric proton conducting materials, the sulfonation mechanisms of typical aromatic polymers, including bisphenol A type polysulfone (BPA‐PSF), 4,4’‐biphenol type polysulfone (44BP‐PSF), poly(ether ether ketone) (PEEK), and poly(ether sulfone) (PES), are studied in terms of transition states and activation energies using density functional theory calculations with satisfactory results. It is concluded that the sulfonations are favored at the ortho‐position of direct arylene‐arylene linkage and ether bond linkage, but retarded by the bulky sulfonyl linkage, dimethyl methylene linkage, and carbonyl linkage. It is also concluded that the solvation effect from polar solvent reduces the activation barrier more efficiently than that from nonpolar solvent.

Effects of Tl content and magnetic field on phase formation of TlmBa2Can-1CunO2n+2+δ (m=1 and 2, n=4) superconductors

The effect of Tl content in TlmBa2Can-1CunO2n+2+δ (TBCCO) superconductor was studied with m=1 and 2, n = 1-4. Samples were prepared using the standard solid-state reaction one-step technique in a sealed quartz tube under normal pressure.The superconductivity was examined using electrical resistance measurements ranging from 300 K to 10 K. The effect of an applied magnetic field (up to 12 T) on the transition behavior has been studied. The transition width, ∆T, was increased sharply with a slight increase in the magnetic field, and then increased smoothly when the magnetic field increased significantly. The vorticity activation energy U(B) was studied as a function of magnetic field B. The value of U(B) was determined from the slope of the relationship ln (RB/R0) = - U(B)/kB T.Transport measurements indicated that the values of superconducting transition temperature of the samples depend on the Tl content. The values of the transition temperature, Tc, and activation energy U(B) of the samples decreased with increasing Tl content. The possible causes of the observed behavior in the superconducting and magnetic properties of Tl-1234 & Tl-2234 due to the Tl content are discussed.

Influence of sub-Tg annealing on microstructure and crystallization behavior of TiZr-based bulk metallic glass

Herein, the effect of sub-Tg annealing on microstructure, glass transition kinetics and crystallization behavior of Ti33Zr30Cu9Ni5.5Be22.5 bulk metallic glass (BMG) is systematically studied by high-temperature differential scanning calorimetry. The results reveal that sub-Tg annealing can improve the compactness of Ti33Zr30Cu9Ni5.5Be22.5 BMG and expand the supercooled liquid region. Also, the non-isothermal crystallization behavior indicates that the glass transition activation energy (Eg) of Ti33Zr30Cu9Ni5.5Be22.5 BMG decreases and crystallization activation energy (EP1, EP2) increases after sub-Tg annealing. The changes in Eg, EP1 and EP2 exhibit sensitivity to sub-Tg annealing temperature. It is demonstrated that the isothermal crystallization time of Ti33Zr30Cu9Ni5.5Be22.5 BMG is extended by ≈1 min after 593 K annealing, indicating the inhibition of crystallization process. The Avrami indices of as-cast and sub-Tg-annealed Ti33Zr30Cu9Ni5.5Be22.5 BMGs, calculated by the Johnson-Mehl-Avrami equation, range from 2.08 to 2.30 and indicate that the three-dimensional growth process is mainly controlled by the diffusion, which is not influenced by sub-Tg annealing.

Study on the crystallization mechanism of TiNiNb amorphous alloy

In order to study the crystallization mechanism of Ti44Ni47Nb9 amorphous alloy. Firstly, the Ti44Ni47Nb9 amorphous alloy was prepared by mechanical alloying (High energy ball milling). Then, the effect of amorphous mechanism and annealing process on the alloy was analyzed. The results showed that the crystallization effect of amorphous powder was the best, when the annealing process was 575 °C and the temperature was kept for 30 min. The glass transition temperature Tg, the initial crystallization temperature Tx and the peak crystallization temperature Tp all increased with the increase of the heating rate, showing obvious kinetic effects. The apparent activation energies of the glass transition, initial crystallization and crystallization peak were respectively 150.76, 146.57 and 331.74 kJ/mol by using the Ozawa equation.

Mechanical characterization of additively manufactured fiber-reinforced composites

The advancement in composite additive manufacturing allows the design of fiber placement to tailor the performance (stiffness and strength) of the structure and reduce its weight. However, the design process requires an understanding of various mechanical properties of the materials as well as the effective properties of the laminate. The present work focuses on obtaining the mechanical characteristic of a thermoplastic matrix composite, Onyx, with two different continuous fiber infill patterns. The interlaminar shear and tensile tests are performed to study the interlaminar strength and failure of additively manufactured composites. The experimental failure characteristics of the printed composites are compared with finite element analysis (FEA) using classical composite failure criteria. In addition, the current research utilizes dynamic mechanical analysis (DMA) for temperature/frequency sweeps to probe the viscoelastic performance and thermophysical properties (glass transition, creep strain rate and activation energy) of additively manufactured fiber-reinforced composites. It is shown in both failure and dynamic mechanical analyses that the fiber layout affects the strength, glass transition temperature and activation energy of printed composites. The DMA results also revealed the high temperature-dependency and unexpectedly low frequency-dependency of the storage modulus and damping parameter indicating that the materials are predominantly elastic with moderate viscoelastic behavior.

Martensitic transformations and kinetics in Ti-Ni-Cu-Hf shape memory alloy

The purpose of the paper was to investigate the martensitic transformation and its kinetic of the Ti-Ni-Cu-Hf shape memory alloy. The Ti47Ni44Cu6Hf3 alloy would undergo a reversible B2 ↔ B19′ martensitic transformation during thermal cycling process. The apparent activation energy was calculated based on seven different DSC cooling curves. A strong cooling rate dependence of martensitic transformation kinetics was observed and the corresponding mechanism was discussed. Moreover, the variation of transition activation energy for a specific martensite fraction was studied to further characterize the martensitic transformation kinetics.

Theoretical and Experimental Parameters of the Structure and Crystallization Kinetics of Melt-Quenched As30Te64Ga6 Glassy Alloy

The present framework reports the structural, fundamental parameters, and crystallization kinetics of the melt-quenched As30Te64Ga6 chalcogenide glass. The energy dispersive X-ray analysis of the As30Te64Ga6 glassy system reveals that the constituent element ratio of the investigated bulk sample agrees with the nominal composition. Also, X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC) were used to characterize structural properties, and crystallization kinetics; respectively. Four characteristic temperatures related to various phenomena are observed in the investigated DSC traces. The first one is $$T_{g}$$ that corresponds to the glass transition temperature. The second one is ( $$T_{c1}$$ , and $$T_{c2}$$ ) that corresponds to the onset of the double crystallization temperatures. The third one ( $$T_{P1}$$ , and $$T_{P2}$$ ) identifies the double peak crystallization temperatures. The last characteristic temperature ( $$T_{m}$$ ) is the melting point. The XRD analysis indicates the amorphous structure of the as-prepared glassy alloy, while the annealed samples are polycrystalline. The crystallization kinetics of the As30Te64Ga6 bulk are studied under non-isothermal conditions. In addition, the values of various kinetic parameters such as the glass transition activation energy, weight stability standard, and Avrami exponent were determined. The activation energy of the crystallization process for As30Te64Ga6 glass alloy was calculated using classical methods. The results indicated that the rate of crystallization is related to thermal stability and the ability to form glass. Kinetic parameters have been estimated with some conventional methods and found to be dependent on heating rates (β).

Phase transition dynamics in one-dimensional halide perovskite crystals

Triiodide perovskites $${\rm CsPbI}_{3}$$ , $${\rm CsSnI}_{3}$$ , and $${\rm FAPbI}_{3}$$ (where FA is formamidinium) are highly promising materials for a range of optoelectronic applications in energy conversion. However, they are thermodynamically unstable at room temperature, preferring to form low-temperature (low-T) non-perovskite phases with one-dimensional anisotropic crystal structures. While such thermodynamic behavior represents a major obstacle toward realizing high-performance devices based on their high-temperature (high-T) perovskite phases, the underlying phase transition dynamics are still not well understood. Here we use in situ optical micro-spectroscopy to quantitatively study the transition from the low-T to high-T phases in individual $${\rm CsSnI}_{3}$$ and $${\rm FAPbI}_{3}$$ nanowires. We reveal a large blueshift in the photoluminescence (PL) peak (~38 meV) at the low-T/high-T two-phase interface of partially transitioned $${\rm FAPbI}_{3}$$ wire, which may result from the lattice distortion at the phase boundary. Compared to the experimentally derived activation energy of CsSnI3 (~1.93 eV), the activation energy of $${\rm FAPbI}_{3}$$ is relatively small (~0.84 eV), indicating a lower kinetic energy barrier when transitioning from a face-sharing octahedral configuration to a corner-sharing one. Further, the phase propagation rate in CsSnI3 is observed to be relatively high, which may be attributed to a high concentration of Sn vacancies. Our results could not only facilitate a deeper understanding of phase transition dynamics in halide perovskites with anisotropic crystal structures, but also enable controllable manipulation of optoelectronic properties via local phase engineering. Metal halide perovskites are a new class of semiconductors with great promise for a variety of optoelectronic applications. Owing to their soft ionic lattice, halide perovskites often exhibit rich phase transitions between different crystal structures, frequently from the “active” perovskite phases to undesirable “inactive” non-perovskite phases. Understanding and controlling this transition is vital for developing stable, high-performance devices. However, there is limited understanding on how different symmetry, crystal structure, and defect would impact such a phase transition process. In this report, in situ optical micro-spectroscopy is used to systematically investigate the phase transitions from non-perovskite to perovskite phases in individual CsSnI3 and FAPbI3 wires. Compared to the transition from an edge-sharing octahedral non-perovskite structure to a corner-sharing perovskite structure in CsSnI3, the activation energy for the FAPbI3 phase transition is relatively small, indicating a lower energy barrier when starting from a face-sharing octahedral structure in FAPbI3. The high concentration of Sn vacancies is probably responsible for the much higher phase propagation rate in CsSnI3 when compared to a CsPbBrxI3-x system with the same crystal structure but different halide vacancies. Our experimental results expand the knowledge of phase transition in halide perovskites and offer important guidance toward rationally designing more stable and efficient perovskite devices.

Polyurethane cationomers containing fluorinated soft segments with hydrophobic properties

The synthesis of ecological waterborne polyurethane cationomers containing fluorinated polyol (0–20 wt.%) was successfully performed. FTIR and NMR analysis results confirmed the structure of the obtained polyurethane cationomers and incorporation of fluorinated component into the polyurethane chains. Average molar mass and phase structure of the obtained PU thin films were determined based on GPC, FTIR, WAXD and SEM-EDX results. The obtained cationomers have linear structures with clearly visible microphase separation of soft and hard segment domains; the presence of fluorinated polyol changes the strength of hydrogen bonds and in consequence degree of phase separation. The activation energy of glass transition was calculated based on multi-frequency DSC data. It has been shown that the presence of soft fluorinated segments in the cationomer structure strongly influences the hydrophobic, thermal and mechanical properties of the obtained films.

Model fitted and model free approaches for crystallization kinetics in Se85Te15-xBix glasses

In this research work, we have described the model-fitted and model free approaches for the study of crystallization kinetics in Se85Te15-xBix chalcogenide glasses. Se85Te15-xBix bulk alloys were synthesized by melt quenching technique. High Resolution X- Ray diffraction (HRXRD) was used to confirm the amorphous nature of prepared alloys. Non-isothermal Differential Scanning Calorimetry (DSC) measurements were done at heating rates of 5, 10, 15, 20 and 25 K/min for crystallization kinetics studies in Se85Te15-xBix glasses. The various characteristic temperatures, such as glass transition (Tg), on-set crystallization (Tc) temperature, peak crystallization temperature (Tp) and melting temperatures (Tm) have been obtained from various DSC thermograms. The activation energies of glass transition (ΔEt) were calculated by using Kissinger and Moynihan approaches and found to be minimum for Se85Te12Bi3 chalcogenide glass which indicates that this alloy has maximum probability to jump into a less configurational energy state and has larger stability. The model-free approaches; Kissinger–Akahira–Sunose (KAS), Flynn-Wall-Ozawa (FWO), Tang and Straink (TS) reveal that the activation energy of crystallization varies with crystallization degree and temperature both. This variation shows that amorphous to crystalline phase transformation in Se85Te15-xBix chalcogenide glasses is a complex process with various nucleation and growth mechanisms.

X-ray diffraction and Rietveld characterization of radiation-induced physicochemical changes in Ariá (Goeppertia allouia) C-type starch

Extracted from a tuberous root of the Amazon forest named Ariá (Goeppertia allouia), starch samples were submitted to four γ-radiation doses of 1, 5, 20 and 50 kGy and investigated by powder X-ray diffraction (XRD) and pasting properties. The XRD patterns were quantified by the Rietveld refinement method and the pasting properties by Palabiyik's, Hill's and Arrhenius models. Crystallinity values were obtained considering the semi-crystalline microstructures (mean crystallites sizes and microstrains) and the weight fraction of the semi-crystalline phases were calculated considering the diffuse X-ray scattering. The combination of the techniques revealed that the increase in the amorphous component is related to the continuous degradation of the semi-crystalline phases in lower molecular weight sugars that also increased pasting temperature and delaying the gelation process. The reduction in the activation energy of the phase transition is associated with the accumulated energy in the defects, induced by γ-radiation.

Functional Thermal Stable Samples: Non-isothermal Calorimetric Analysis of MoO3–V2O5–TeO2 Oxide Glasses

In this research, xMoO3–(60 − x)V2O5–40TeO2 oxide glasses with (0 ≤ x ≤ 60) have been prepared by common melt-quenching method. Differential scanning calorimetry (DSC) at different heating rates (φ) was used to study non-isothermal thermal analysis, and also to gain more insight in to the Hruby index thermal stability, crystal growth index (n), glass forming tendency and so calorimetric characteristics of the present glasses. Also, the effects of the heating rate and MoO3 content on the glass transition temperature (Tg) and crystallization temperature (TCr) were studied. Further structural investigations were done by FESEM, EDX and Map. The glass transition temperature, glass transition region, the temperature corresponding to the onset of crystallization (Tx) and also the crystallization temperature were obtained at different heating rates; heating rate dependence of these parameters was employed estimate the key kinetic parameters of glass transition and crystallization activation energy by using Moyinhan, Ozawa, Kissinger and Avrami methods. Calorimetric curves were used to plot the specific heat capacity curves versus temperature at the constant pressure. In addition, the compositional dependence of the heat capacity and fragility parameter were investigated. Generally, results of this work show that the glass with x = 20 mol% has the highest thermal stability and glass forming tendency and samples having 10 and 20% of MoO3 are the optimal samples (with the least fragility) for thermomechanical applications and also in optical fibers.

The significance of long-range correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C.

Density functional theory has been gaining popularity for studying the radical scavenging activity of antioxidants. However, only a few studies investigate the importance of calculation methods on the radical-scavenging reactions. In this study, we examined the significance of (i) the long-range correction on the coulombic interaction and (ii) the London dispersion correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C. We employed B3LYP, CAM-B3LYP, M06-2X exchange-correlation functionals and B3LYP with the D3 version of Grimme’s dispersion in the calculations. The results showed that long-range correction on the coulombic interaction had a significant effect on the increase of reaction and activation energies. The increase was in line with the change of hydroperoxyl radical’s orientation in the transition state structure. Meanwhile, the London dispersion correction only had a minor effect on the transition state structure, reaction energy and activation energy. Overall, long-range correction on the coulombic interaction had a significant impact on the radical-scavenging reaction.

Experimental and theoretical studies of glass and crystallization kinetics of semiconducting As40Se40Ag20 chalcogenide glass

We report on the thermal analysis of As40Se40Ag20 glass using experimental and theoretical methods. The XRD analysis revealed the amorphous-crystalline transition in the annealed As40Se40Ag20 glass. Two overlapped crystallization peaks were observed, which are analyzed using different models. The activation energy of glass transition exhibited a change with conversion fraction χg. The fragility index showed that As40Se40Ag20 material belongs to strong glass-forming liquids. The kinetic transformation parameters were obtained by the theoretical developed (TDM) and Johnson–Mehl–Avrami (JMA) model. The crystallization activation energy varied with the conversion fraction. According to the average values of kinetic exponent parameters (n and m obtained by TMD and JMA models) two and three crystal growth process with heterogeneous nucleation of the studied composition are observed. The experimental results were compared with calculated ones by different models.

In English

Powders where the γ≈α-Al2O3-nano phases are the priority precursors for catalysts for heterogeneous catalysis with the maximum content of surface 5-coordinated Al centers for Pt attachment. Hydrogenated nano powders (~8 nm) of γ-, γ '-, θ-, κ-Al2O3 soluble in hydrochloric acid were obtained from the processing of aluminum boride powders with an icosahedral structure. Samples, which underwent a step-by-step and single heating of 50-100K heat treatment for 2 hours at temperatures of 570-1470K, were received in quantity of 34. The specific surface area of SВET, m2g-1 was measured by the thermal nitrogen desorption express method of gas chromatography through the GC-1 device. X-ray (phase and coherent), fluorescence and phase chemical-analytical evaluation of the samples were performed. The thermokinetic characteristics of the processes are calculated using the exponential Arrhenius law. Dimensional characteristics of crystallites (10.4-48 nm); specific surface area of powders (213-8.6 m2g-1, SВET); thermokinetic parameters of α-Al2O3 crystallite growth process (V α-Al2O3 - 1.44 10-3 - 6.67 10-3 nm s-1; E α-Al2O3 = 38.7±2.1kJ mol-1; A0 = 0.16±0.0 s-1 along the temperature line 1220-1470K were determined and calculated. The process of dehydration of two OH-groups occurs in the region 570-720K Ea H2O ↑ = 30.5 ± 0.5 kJ mol-1 A0 = 1.33±0.3 s-1. The last group of OH at temperatures of 820 -1070К and a rate of 2.13 10-4 - 4.93 10-4 mol s-1 Ea H2O ↑ = 13.2 ± 0.8 kJ mol-1 A0 = 16.9 ± 0.9 s-1. The activation energy of the phase transition is Ea., γ → α-Al2O3 = 23.9 ± 1.0 kJ mol-1 A0 = 2.01 ± 0.72 s-1 (770-970K) and Ea., γ → α-Al2O3 = 83.5 ± 0.8 kJ mol-1 A0 =(2,05±0,95) 103 s-1 (1070-1170K). It agrees well with the known heat of conversion Eа, γ→α-Al2O3 = 85 kJ mol-1. The TK of γ≈α-Al2O3-nano phases is at 1170K.

On the crystallization kinetics of multicomponent nano-chalcogenide Se79-x Te15In6Pbx (x = 0, 1, 2, 4, 6, 8 and 10) alloys

Nanotechnology continuously rises due to its potential applications. To control nano-materials design and microstructure, it is very essential to understand nucleation and crystalline growth in these materials. In this research contribution, crystallization kinetics and thermal behaviour of nano-crystalline Se79-x Te15In6Pb x (x = 0, 1, 2, 4, 6, 8 and 10 at. wt%) chalcogenide alloys is analyzed through differential scanning calorimetry (DSC) process under non-isothermal conditions at four different heating rates; 5, 10, 15 and 20 °C min−1. The examined Se-Te-In-Pb nano-chalcogenide system is prepared through melt-quenching process. Characteristic temperatures namely glass transition temperature (T g), onset crystallization temperature (To), peak temperature of crystallization (T p) and melting temperature (T m) show dependence on heating rate and composition. The various kinetic parameters such as activation energy of glass transition (E g), activation energy of crystallization (E c), reduced glass transition temperature (T rg), Hruby number (K gl), thermal stability parameters (S and H’) and fragility index (F i) are analyzed for investigated Se-Te-In-Pb nano-crystalline system. Different empirical approaches are applied to determine the apparent glass transition activation energy (E g) and crystallization activation energy (E c).