Arrhenius Temperature Dependence Research Articles

Diffusion multiple study of the Co-Fe-Ni system at 800 °C

The Co-Fe-Ni system is a key system in a wide range of industrial applications. Knowledge of the thermodynamic and kinetic properties of the system is crucial for the alloy and process design. Although the system has been studied extensively, there remain several unexplained discrepancies between different literature data and, for mediate low temperatures, the information is scarce. In this work, a high throughput diffusion multiple approach was applied. The isothermal phase diagram section at 800 °C was determined using the Co-Fe-Ni multiple. The interdiffusion coefficients of the binary Co-Fe, Co-Ni, Fe-Ni systems and their composition dependence were calculated using the Sauer-Freise method based on the compositional profiles obtained from the diffusion multiple. Different from previous experimental results for mediate low temperature, our results coincide with the extrapolated Arrhenius temperature dependence from diffusion coefficient data at high temperature range. These observations are important for a better understanding and modelling of the interdiffusion behavior in this key alloy system.

Moisture absorption and hydrothermal aging of phenylethynyl-terminated pyromellitic dianhydride-type asymmetric polyimide and composites

The effects of moisture on a polymerized monomeric reactant (PMR)-type polyimide (TriA X) and associated composites were investigated. Water uptake tests were performed on the polyimide at various temperatures and relative humidity levels to investigate moisture absorption behavior. Two-stage moisture absorption was observed, in which the first stage was diffusion controlled, whereas the second stage was moisture plasticization controlled. As exposure temperature increased, the equilibrium moisture content of the polyimide decreased, indicating an exothermic absorption process. The Arrhenius temperature dependence and moisture saturation as functions of temperature and humidity in the neat polymer were determined using curve fitting based on the published mathematical models. Long-term hydrothermal aging at 95°C was conducted on the neat polyimide and associated carbon fiber composites. Reversible hydrolytic reactions and a trace of irreversible hydrolysis were observed in the long-term exposure. The tensile ductility of the neat polyimide and the short-beam shear strength of the composites decreased with increasing aging time, while the tensile strength and modulus and thermal properties of the polyimide exhibited little change after 2000-h aging, demonstrating hydrothermal stability. The decrease in the ductility of the neat polymer after long-term moisture exposure was attributed to the network structure change, driven by hydrolysis and moisture plasticization.

A model for charge transport in semicrystalline polymer thin films

ABSTRACTA model for simulating the charge transport properties of semicrystalline polymer (SCrP) using Monte Carlo simulation is reinvented. The model is validated by reproducing the experimentally observed field and temperature dependence of mobility in Poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) thin films. This study also provides a new physical insight to the origin of much debated negative field dependence of mobility (NFDM) observed at low electric field strengths in P3HT thin films. The observed NFDM, which is not explainable with the mechanisms proposed earlier, is attributed to the weak dependence of transit time on the applied electric field strengths. In the semicrystalline films, the charge transport takes place mostly through the crystalline regions, in which the charge transport is weakly dependent on the strength of the applied electric field. In addition, a possible explanation for the origin of Arrhenius temperature dependence of mobility (lnμ ∝ 1/T) commonly observed in SCrP thin films is also proposed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 137–141

Temperature Dependences of the Threshold Current and Output Power of a Quantum-Cascade Laser Emitting at 3.3 THz

The active region of a THz (terahertz) quantum-cascade laser based on three tunnel-coupled GaAs/Al0.15Ga0.85As quantum wells with a resonance-phonon depopulation scheme is designed. Energy levels, matrix elements of dipole transitions, and gain spectra are calculated as functions of the applied electric-field strength F and temperature. It is shown that the maximum gain is implemented at a frequency of 3.37 THz and F = 12.3 kV/cm. Based on the proposed design, a quantum-cascade laser emitting at ~3.3 THz with a double metal waveguide and Tmax ~ 84 K is fabricated. The activation energy Ea = 23 meV for longitudinal-optical (LO) phonon emission upon the stimulated recombination of hot electrons from the upper laser level to the lower one is determined from the Arrhenius temperature dependence of the output power.

Design of operational temperature for immobilized glucose isomerise using an accelerated inactivation method

Abstract Thermal inactivation of immobilized glucose isomerase in a concentrated glucose solution was investigated in the batch mode and temperature range of 83–95 °C, which is substantially higher than the temperature used in the industrial production of high-fructose corn syrup. Simultaneous evaluation of all inactivation data showed that first-order kinetics with the Arrhenius temperature dependence of the rate constant provided a good approximation of the biocatalyst stability under the investigated conditions. The model parameters were then used to predict the operational temperature for this biocatalyst in the production of high-fructose corn syrup based on the set operational life-time of the biocatalyst. The simulation predicted a window of operational temperature of 60–65 °C, which corresponds very well with the industrial applications of this biocatalyst. This observation demonstrates that the multi-temperature method of enzyme inactivation can provide a good estimate of biocatalyst process stability and is thus a useful tool in the development of biocatalytic processes.

Temperature dependence of daily respiration and reaeration rates during baseflow conditions in a northeastern U.S. stream

Study regionFinger Lakes Region, New York, USA. Study focusThe relationship between stream temperature and daily respiration and reaeration rates was investigated from May 2015 – May 2016 for two sites, one in the headwaters and the other near the mouth of a net heterotrophic stream. Daily respiration and reaeration rates were calculated by applying the night time slope method to open-channel diel oxygen concentrations during baseflow conditions. New hydrological insights for the regionReference values for activation energy (Ea) are presented that could be applicable to lower order streams in temperate climates receiving significant inputs from surface and subsurface flows. There was a sizeable difference in temperature sensitivity between upstream and downstream sites. Ecosystem respiration (ER) exhibited a strong Arrhenius temperature dependence with daily respiration rates of 0.5–9.5 g O2 m−2 d−1 (Ea = 0.61 eV) in the headwaters and 1.8–30.3 g O2 m−2 d−1 (Ea = 0.67 eV) at the downstream location where ER in the headwaters was less sensitive to temperature. Ea for both sites fell within the expected theoretical range for heterotrophic respiration in aquatic ecosystems. Temperature reaeration rate coefficients ranged from 1.011 to 1.020 at the headwaters and from 1.005 to 1.009 downstream suggesting that daily reaeration rates at the headwaters were more sensitive to temperature than the downstream location where reaeration was likely controlled by stream discharge and driven by turbulence.

Structure and dynamics of polypyrrole/chitosan nanocomposites

AbstractPolypyrrole/chitosan (PPy/Cs) nanocomposites with various amounts of polypyrrole nanoparticles (PPy‐NPs) have been synthesized and afterwards exposed to UV irradiation for 240 min. Structure, dynamics and antibacterial activity of pure compounds and the corresponding nanocomposites were investigated by means of wide‐angle X‐ray scattering, Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, broadband dielectric spectroscopy and antibacterial activity assay. The occurrence of a pronounced interaction between PPy‐NPs and Cs has been verified. Broadband dielectric spectroscopy measurements revealed two relaxation processes at low and high frequencies. The low‐frequencyα‐relaxation associated with the glass–rubber transition is attributed to the presence of hydrogen‐bonded water (plasticizing effect) appearing at low temperature (<373 K). The high‐frequencyσ‐relaxation is related to water molecules which become desorbed upon heating atT > 373 K and demonstrates Arrhenius temperature dependence with activation energy in the range 70–90 kJ mol−1in good agreement with previous reports. On the contrary, PPy‐NPs do not show any structural relaxation process and the charge transport mechanism follows the correlated barrier hopping model. All PPy/Cs nanocomposites exhibit an improved antibacterial activity against bothStaphylococcus aureusandEscherichia colibacteria as compared with pure Cs and PPy‐NPs. © 2018 Society of Chemical Industry

NMR studies on the coupling of ion and water dynamics on various time and length scales in glass-forming LiCl aqueous solutions.

We combine 1H, 2H, and 7Li NMR methods to investigate the dynamics of water molecules and lithium ions in LiCl aqueous solutions over wide ranges of time and length scales down to their glass transitions. Structural relaxation times τ and self-diffusion coefficients D reveal that water and lithium dynamics are faster for lower salt content at ambient temperatures, while the differences vanish upon cooling when fractional freezing leads to similar salt concentrations in the remaining liquid phases. Relaxation times and diffusion coefficients of water molecules agree with those of lithium ions in the weakly supercooled regime, indicating that the dynamics are strongly coupled. Furthermore, non-Arrhenius temperature dependence is found and the Stokes-Einstein relation is obeyed in this temperature range. However, we observe various decoupling phenomena for the motion of the constituents and for dynamics on different length scales in the deeply supercooled regime. Most notably, the rotational motion of the water molecules does not follow the glassy slowdown of the studied salt solutions below ∼145 K, but it rather resembles that in nanoscopic confinement, molecular solutions, and high-density amorphous ice at low temperatures. This common low-temperature water dynamics is characterized by large-angle reorientation and Arrhenius temperature dependence.

On the Apparent Non-Arrhenius Temperature Dependence of Charge Trapping in IIIV/High-<inline-formula> <tex-math notation="LaTeX">${k}$ </tex-math> </inline-formula> MOS Stack

Operating temperature has a significant imp-act on the reliability of metal–oxide–semiconductor field effect transistors (MOSFETs). In Si-channel MOSFETs, the effective density of charged oxide defects ( $\Delta {N}_{\text {eff}}$ ) at operating condition typically shows an Arrhenius temperature dependence with ${E}_{\text {A}}$ ~ 0.1 eV. In contrast, apparent non-Arrhenius temperature dependence is reported here for InGaAs devices subjected to BTI stress in a wide range of temperature (77–373 K). This apparent non-Arrhenius temperature dependence is explained here by the presence of three distinct populations of electron traps. Capture–emission-time maps are derived from the experimental data, and are modeled by three bivariate distributions of energy barriers for the capture and emission processes. The total $\Delta {V}_{\text {th}}$ measured in bias-temperature-instability experiments reflects different contributions from the three defect populations, depending on the chosen temperature range, and on the measurement timing. We show that a correct description of the three defect distributions is crucial to properly assess their impact on the device performance.

Evaluation of palladium diffusion in Ti-Rich TiNi alloys

In order to study the diffusion kinetics of Pd into Ti-rich TiNi alloys, diffusion annealing treatments of palladium-coated Ti53Ni47 and Ti50.2Ni49.8 alloys were carried out at temperatures ranging from 700 to 1000 °C. Linear Arrhenius temperature dependencies with the pre-exponential factors of 2 ± 1.1 × 10−10 and 1.05 ± 1.5 × 10−8 m2 s−1 and the activation energies of −128 ± 4 and −153 ± 10 kJ mol−1 were obtained for Pd diffusivity into Ti53Ni47 and Ti50.2Ni49.8 alloys, respectively. The suggested mechanism for Pd diffusion in Ti53Ni47 was anti-site bridge mechanism. While the rapid diffusion of Pd in Ti50.2Ni49.8 was attributed to the high volume fraction of vacancies in Ni sub-lattice of TiNi lattice and Next Nearest jumps of Pd atoms into abundant Ni vacancies. The lower diffusivity of Pd in Ti53Ni47 was related to the dominant diffusion mechanisms in two systems and low solubility of Pd in Ti2Ni precipitates which located in grain boundaries, as well.The other part of the study was denoted to inter-diffusion studies in Ti53Ni47/Pd and Ti50.2Ni49.8/Pd diffusion couples, which confirmed the higher diffusivity of Pd in Ti50.2Ni49.8.

Bulk dynamics of the thermoresponsive random copolymer of di(ethylene glycol) methyl ether methacrylate (MEO2MA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA)

A thermoresponsive, biocompatible and water soluble copolymer was synthetized via RAFT from 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo (ethylene glycol) methacrylate (OEGMA) in the molar ratio of 9:1.The thermal behavior of the bulk material was investigated through thermogravimetric analysis and differential scanning calorimetry, revealing a fully amorphous polymer whose glass transition's onset is located at -47 °C.The molecular mobility was investigated below and above the glass transition temperature by dielectric relaxation spectroscopy and thermally stimulated depolarization currents, covering the frequency range from 10−3–106 Hz. Multiple relaxation processes were detected. The main process (α) is associated with the dynamical glass transition, whose temperature dependence of relaxation times exhibits the curvature in the relaxation map typical of cooperative processes, with a fragility index characteristic of strong materials. Moreover, two secondary relaxations, β and γ, were observed with Arrhenius temperature dependence of their relaxation times. The β-process show features compatible with a Johari-Goldstein process.Additionally, conductivity of pure dc origin was detected in the low frequency side of the α-relaxation. Its temperature dependence (logσdcvs. 1/T) also shows a curvature indicative of a coupling between charge transport and the segmental relaxation.

Interfacial Diffusion of Silver Nanocrystals into Polymer Surfaces Monitored by Hybrid Plasmon Modes

Functional response of polymer–nanoparticle nanocomposites depend strongly on physical organization and interactions between constituting components. In this work, we study thermally induced embedding of silver nanocrystals (nanocubes, AgNC) into different polymer films to probe the interfacial nanoparticle diffusion dynamics and to determine temperature of embedding (Te) into the polymer substrates. The spatial sensitivity of the AgNCs hybrid plasmonic modes allowed the detection of a thin layer on top of the polymer film with increased polymer segmental motion and Te lower than the glass transition temperature Tg of the bulk polymer. Utilizing supported AgNCs as a nanoruler, diffusion constants of the nanocubes embedding into thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA), and polyvinyl chloride (PVC) were determined, and an Arrhenius temperature dependence on the diffusion constants was observed. The activation energies for the AgNCs embedding into the polymers were found to be 220 ± ...

Dipolar Relaxation in Functionalized Poly-p-phenylenes Bearing Ultrastrong Dipoles Perpendicular to the Backbone

Local polymer dynamics are studied in polymers bearing dipoles rigidly attached to the backbone. The compounds are based on cyano-substituted dihydrobenzimidazoles bearing ultrastrong dipole moments (∼12 D per repeat unit) incorporated in a poly-p-phenylene backbone, giving rise to polymers with rigid dipoles perpendicular to the chain. They belong to type B polymers according to the Stockmayer classification. They are ideal model systems for studying rotational isomers in the gas phase and the self-assembly and local dynamics in the solid state. Gas phase calculations (DFT) provided the dipole moments, the energetic barriers, and the backbone conformation as a function of the dipole strength and dipole separation. Calculated dipole moments show an odd–even effect as a function of dipole separation. Specific rotational isomers that maximize the dipole moment are obtained. In the solid state, dielectric spectroscopy and site-specific NMR techniques revealed that packing through intermolecular forces such as van der Waals, π–π, and dipole–dipole interactions dictates the dynamics. Dielectric spectroscopy further identified two modes, both with Arrhenius temperature dependence and activation energies of 20–23 kcal/mol. Combined results attribute the faster process to a libration motion of the highly polar group reorienting only the nonplanar five-membered ring and the slower process to larger amplitude and/or correlated motions of the polar groups. These dynamic results are in agreement with structural investigations (X-ray diffraction) demonstrating that type B polymers in the bulk have rigid backbones.

Ion Conduction and Viscoelastic Response of Epoxy‐Based Solid Polymer Electrolytes Containing Solvating Plastic Crystal Plasticizer

AbstractTo develop a safe electrolyte for lithium‐ion batteries, solid polymer electrolytes (SPEs) are prepared using a commercially available cross‐linkable diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin, a methyl tetrahydrophthalic anhydride (MeTHPA) curing agent, and a plastic crystal‐based electrolyte containing a mixture of succinonitrile (SN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) by a simple thermal curing process. For the uncured mixture of DGEBA/MeTHPA/SN/LiTFSI, oscillatory and steady shear measurements are conducted to investigate microstructure and processability; the storage modulus (G′) exceeds the loss modulus (G″) at all frequencies studied (solid‐like behavior) and the viscosity decreases with an increase in the shear rate (shear‐thinning behavior), demonstrating that there is a network structure, and the connected structure changes at high shear rates. Fourier transform infrared spectroscopy confirms the physical interactions between Li+of LiTFSI and anhydride group of MeTHPA, which are responsible for the network structure, and helps to rationalize the observed moduli and viscosity. For the cured epoxy‐based SPEs, their ionic conductivities follow the Arrhenius temperature dependence, and increasing SN/LiTFSI electrolyte content leads to higher conductivity and lower activation energy for conduction, resulting in ionic conductivity σDC≈ 2 × 10−4S cm−1with a shear modulus approachingG′ ≈ 1 MPa at room temperature.

Температурная зависимость порогового тока и выходной мощности квантово-каскадного лазера с частотой генерации 3.3 ТГц

AbstractThe active region of a THz (terahertz) quantum-cascade laser based on three tunnel-coupled GaAs/Al_0.15Ga_0.85As quantum wells with a resonance-phonon depopulation scheme is designed. Energy levels, matrix elements of dipole transitions, and gain spectra are calculated as functions of the applied electric-field strength F and temperature. It is shown that the maximum gain is implemented at a frequency of 3.37 THz and F = 12.3 kV/cm. Based on the proposed design, a quantum-cascade laser emitting at ~3.3 THz with a double metal waveguide and T _max ~ 84 K is fabricated. The activation energy E _ a = 23 meV for longitudinal-optical (LO) phonon emission upon the stimulated recombination of hot electrons from the upper laser level to the lower one is determined from the Arrhenius temperature dependence of the output power.

Structural Origin of Enhanced Dynamics at the Surface of a Glassy Alloy.

The enhancement of mobility at the surface of an amorphous alloy is studied using a combination of molecular dynamic simulations and normal mode analysis of the nonuniform distribution of Debye-Waller factors. The increased mobility at the surface is found to be associated with the appearance of Arrhenius temperature dependence. We show that the transverse Debye-Waller factor exhibits a peak at the surface. Over the accessible temperature range, we find that the bulk and surface diffusion coefficients obey the same empirical relationship with the respective Debye-Waller factors. Extrapolating this relationship to lower T, we argue that the observed decrease in the constraint at the surface is sufficient to account for the experimentally observed surface enhancement of mobility.

Pinpointing wastewater and process parameters controlling the AOB to NOB activity ratio in sewage treatment plants

Even though nitrification/denitrification is a robust technology to remove nitrogen from sewage, economic incentives drive its future replacement by shortcut nitrogen removal processes. The latter necessitates high potential activity ratios of ammonia oxidizing to nitrite oxidizing bacteria (rAOB/rNOB). The goal of this study was to identify which wastewater and process parameters can govern this in reality. Two sewage treatment plants (STP) were chosen based on their inverse rAOB/rNOB values (at 20 °C): 0.6 for Blue Plains (BP, Washington DC, US) and 1.6 for Nieuwveer (NV, Breda, NL). Disproportional and dissimilar relationships between AOB or NOB relative abundances and respective activities pointed towards differences in community and growth/activity limiting parameters. The AOB communities showed to be particularly different. Temperature had no discriminatory effect on the nitrifiers' activities, with similar Arrhenius temperature dependences (ΘAOB = 1.10, ΘNOB = 1.06–1.07). To uncouple the temperature effect from potential limitations like inorganic carbon, phosphorus and nitrogen, an add-on mechanistic methodology based on kinetic modelling was developed. Results suggest that BP's AOB activity was limited by the concentration of inorganic carbon (not by residual N and P), while NOB experienced less limitation from this. For NV, the sludge-specific nitrogen loading rate seemed to be the most prevalent factor limiting AOB and NOB activities. Altogether, this study shows that bottom-up mechanistic modelling can identify parameters that influence the nitrification performance. Increasing inorganic carbon in BP could invert its rAOB/rNOB value, facilitating its transition to shortcut nitrogen removal.

DC conductivity of polyethylene and crosslinked polyethylene measured with a dynamic temperature program

Electrical conductivity of HVDC cable insulation materials is important for its function. It is very practical to evaluate this parameter by DC conductivity measurements on press molded polymeric plates samples. While in real operation conditions, the insulation undergoes both static and dynamic thermal conditions, most of the published research in this area is still focused only on steady state thermal conditions. In this work, the focus is instead on the behavior of electrical conductivity under dynamic thermal conditions. Press molded XLPE and LDPE plate samples with different preparations are tested under 25 kV/mm DC field with a dynamic temperature profile ranging from room temperature to 90 °C.It was discovered that in many cases, the measured conductivity during dynamic measurements strongly deviates from the expected Arrhenius temperature dependence; instead the conductivity shows a nonmonotonictemperature dependence manifested as conductivity peaks during heating and cooling. The behavior is found to be strongly related to the type of protective film used during press molding of the sample; further degassing leads to a reduction of the nonmonotonic temperature dependence and with longdegassing the behavior tends to the expected Arrhenius temperature dependence.

Kinetics of NaCl induced gelation of soy protein aggregates: Effects of temperature, aggregate size, and protein concentration

Soy protein aggregates with different sizes were prepared by heating soy protein isolate (SPI) in solution and characterized with light scattering. NaCl induced gelation of aqueous solutions of these aggregates was investigated as a function of protein concentration (10–75 g L−1), NaCl concentration (0–0.5 M) and temperature (20–80 °C). The structure and the mechanical properties of the gels were investigated with confocal laser scanning microscopy and oscillatory shear measurements. The gel stiffness did not depend on the size of the preformed aggregates nor on the salt concentration, but increased with increasing protein concentration. Gelation of preformed aggregates was compared with that of native SPI, which showed that gelation of aggregates was faster and occurred at lower protein concentrations and temperatures. The stiffness of gels formed by native SPI and preformed aggregates was not significantly different, but the structure of gels formed by aggregates was more homogeneous. For all systems, the gel time had an Arrhenius temperature dependence characterized by an activation energy of 72 kJ mol−1. A more limited investigation of gelation induced by adding CaCl2 was done to study the effect of the valence of the cation.

Dielectric properties of films of Ag-ED20 epoxy nanocomposite synthesized in situ. Temperature dependence of direct current conductivity

The influence of silver myristate used as a precursor of silver nanoparticles on the direct current conductivity σ dc of epoxy polymer within the concentration range of ≤0.8 wt % was investigated. The value of direct current conductivity was determined on the basis of analysis of the frequency dependence of complex permittivity within the frequency range of 10−2–105 Hz. The temperature dependence of σ dc is composed of two regions. The dependence corresponds to the Vogel-Fulcher-Tammann empirical law σ dc = σ dc0exp{‒DT 0/(T-T 0)} (where T 0 is the Vogel temperature and D is the strength parameter) at temperatures higher than the glass transition temperature T g. At the same time, T 0 does not depend on the concentration of nanoparticles. The Arrhenius temperature dependence characterized by activation energy about 1.2 eV is observed at temperatures lower than T g. The observed shape of the temperature dependence is related to the change in the mechanism of conductivity after “freezing” of ionic mobility at temperatures lower than T g. The value of σ dc is increased as the concentration of nanoparticles is raised within the temperature range of T > T g. The obtained dependence of σ dc on silver myristate concentration is similar to the root one, indicating the absence of percolation within the studied range of concentrations.