Influence Of Thermal Activation Research Articles

Kinetic of the development of a quantum vortex tangle in superfluids under the influence of thermal activation

The study explores the development of a thermally equilibrated quantum vortex tangle in superfluid liquids under the influence of thermal activation. This problem is of interest to both applied and fundamental research and has been investigated by many authors in various aspects. Despite the important and impressive results obtained, a significant part of the process, namely, the kinetics of processes leading to equilibrium state, remained unexplored. In this article, we conduct a study of kinetic phenomena and focus our attention on the evolution of the vortex line density (VLD) L(t), the total length of the filament per unit volume. The initial development of VLD is due to random thermal fluctuations. The increase in the vortex line length L(t) can be obtained based on the famous Novikov–Furutsu theorem, which shows that the growth rate of L(t) is proportional to a random force correlator. As the length of the vortex filaments increases, the interaction between the vortices becomes significant and affects the dynamics process. At this point, we turn to the phenomenological Feynman–Vinen theory, which offers various models for the evolution of the quantity L(t). Next, we examine the evolution of a vortex tangle as a combination of growth due to random thermal excitations and decay in the Feynman–Vinen theory. Several applications leading to significant and remarkable results are considered.

Reusing thermoactivated waste paste/concrete powder for sustainable alkali-activated materials: Effects of thermoactivated temperature

The construction waste powder encompasses waste paste powder (WPP) and waste concrete powder (WCP), exhibiting an irregular microstructural morphology and containing mineral constituents like portlandite, C-S-H gel, calcite and quartz. Under the influence of thermal activation, certain hydrated products within construction waste powder undergo decomposition, concurrently generating new substances like CaO and C2S, which contribute to enhanced reactivity. Minerals within construction waste powder participate in polymerization reactions under alkali activation. Furthermore, alkali-activated mortar produced from thermally treated construction waste powder generate an increased quantity of C-A-S-H/N-A-S-H gel, resulting in a denser microstructure. When construction waste powder is thermally treated at temperatures ranging from 600°C to 800°C, the resulting alkali-activated construction waste powder mortar (AAWM) exhibits higher compressive strength. For example, the 28d compressive strength of AAWM prepared with WCP subjected to heat treatment at 800°C increased by 195.69 % compared to AAWM prepared with untreated WCP. With the increase in thermal treatment temperature of construction waste powder, the drying shrinkage of the resultant AAWM progressively diminishes, along with a gradual reduction in porosity and water absorption. For instance, the porosity and water absorption of AAWM prepared with WCP treated at 800°C decreased by 15.58 % and 18.67 % respectively compared to AAWM prepared with untreated WCP. At a thermal treatment temperature of 800°C, AAWM exhibits strong resistance to chloride penetration. Particularly, AAWM containing WPP outperforms that containing WCP in terms of chloride resistance. Consequently, this study reveals that alkali-activated materials prepared using thermally treated waste powder exhibit commendable mechanical and durability properties.

Electrical conductivity of monolithic and powdered carbon aerogels and their composites

This study presents the correlation between the morphological, structural and electrical properties of four different carbon aerogels, as well as the influence of thermal activation on their properties. The role of conductive additives is discussed.

Influence of Thermal Activation and Silica Modulus on the Properties of Clayey-Lateritic Based Geopolymer Binders Cured at Room Temperature

In this study, a laterite soil which is a locally available material in many parts of the world was used as the aluminosilicate precursor. The main objective of this study is to investigate the effect of calcination temperature on physicochemical properties of the resulting geopolymers synthesized from calcined laterite soils. In order to produce the geopolymer binders, the laterite soil was activated thermally through calcination (from 550 to 750 °C) and the resulting calcined laterite was activated with an alkali activator composed of 8 and 10 M of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) in mass of 0.5. Then, the calcined laterite soils and synthesized geopolymer products were analyzed using X-ray diffraction (XRD), Brunner-Emmet-Teller (BET), Fourier Transform Infra-Red (FTIR), X-Ray Fluorescence (XRF), thermogravimetry (TG), scanning electron microscopy (SEM/EDX), and differential scanning calorimetry (DSC). The results from this study indicate that increasing the calcination temperature from 550 to 750 °C resulted in the transformation of phases and an increase in the reactivity of the laterites, resulting in material with improved properties. The use of laterite calcined at 750 °C and activated with 8 M NaOH solution resulted to an increase in the 28 days compressive strength by 35.3 MPa when compared to laterite calcined at 550 °C. Increasing the concentration of the NaOH solution was also found to yield higher material performance. Microstructural investigations showed a heterogeneous compact and dense structure resulting from high polycondensation much pronounced with the rise of calcination temperature from 550 to 750 °C.

Visualization of electrolyte flow in vanadium redox flow batteries using synchrotron X-ray radiography and tomography – Impact of electrolyte species and electrode compression

The electrolyte distribution inside the porous electrodes of vanadium redox flow batteries is critical to the performance, as it determines the electrochemically active surface area. Herein, the influence of thermal activation, compression, and the injected electrolyte species on the pressure drop and the wetting is investigated by means of synchrotron X-ray radiation. The saturation versus the through-plane position is quantitatively displayed as a function of time to resolve the wetting process. The initial state after the imbibition is then quantitatively compared to the saturation after flow-through conditions. It was concluded that thermal activation plays a major role in the wetting, resulting in an up to six times higher saturation. Only a minor increase in saturation between the initial wetting state and after flow-through was observed. Additionally, there are only minor differences in the wetting behavior between the vanadium species in the electrolyte, the V(III) electrolyte shows the highest saturation. Increasing compression leads to a higher pressure drop and the saturation decreases only at compression ratios higher than 50%. Air pocket formation inside the liquid column was observed and the displacement and re-emergence of air pockets after flow-through is displayed.

Observation of hopping transitions for delocalized electrons by temperature-dependent conductance in silicon junctionless nanowire transistors**Project supported by the National Key R&D Program of China (Grant No. 2016YFA0200503) and the National Natural Science Foundation of China (Grant No. 61327813).

We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance characteristics. There are two obvious transition platforms within the critical temperature regimes for the experimental conductance data, which are extracted from the unified transfer characteristics for different temperatures at the gate voltage positions of the initial transconductance gm peak in Vg1 and valley in Vg2. The crossover temperatures of the electron hopping behaviors are analytically determined by the temperature-dependent conductance at the gate voltages Vg1 and Vg2. This finding provides essential evidence for the hopping electron behaviors under the influence of thermal activation and long-range Coulomb interaction.

Implementation of heterogeneous detonation in a pulsed combustor – PDE model

ABSTRACTThis work is devoted to the use of detonative combustion of a liquid fuel in technical devices to obtain a jet thrust. The experimental and theoretical aspects of the organization of detonation in heptane/air/oxygen mixtures are considered. The pulsed regime of detonation at a frequency of 50 Hz has been implemented for the first time in a small-size tube (25 mm in diameter and 740 mm in length). The physical and technical methods that could accelerate the deflagration-to-detonation transition have been studied. The influence of thermal activation of a combustible mixture prior to its ignition and of the special form of a porous obstacle on the magnitude of the predetonation distance is established. The degree of this influence depends on the component composition, equivalence ratio, and the degree of filling the tube with a mixture.

Characterization of Activated and Aged Carbon Felts for All-Vanadium Redox Flow Batteries

The electrodes are a crucial part of the Vanadium Redox Flow Batteries (VRFB), since its chemical, physical and structural properties affect cell performance, efficiency, durability as well as acquisition and operating costs1. The most common electrode materials are carbonized or graphitized polyacrylamide (PAN) or Rayon (cellulose) fibres, and commercially available as paper or felts. Due to its relatively low activity towards vanadium and poor wettability, several approaches have been made to improve this surface related properties2. The conventional treatment is a thermal activation procedure, where the electrode material is oxidized in an air atmosphere for up to 30 h at 400°C3. In this current study, the influence of thermal activation, chemical ageing and electrochemical ageing has been investigated on commercially available Rayon (GFA6 EA) and PAN based (GFD 4.6 EA, KFD 2.5 EA) carbon felts from SGL carbon (Meitingen, Germany). The activation process is conducted by heating all the samples for 25 h at 400°C4. The chemical ageing consists of soaking the previously activated samples in 4 M sulfuric acid at 40°C for 15 days. The electrochemical ageing is realized by applying 1.2 V vs. RHE to the felt for 5 days in a vanadium electrolyte (0.1 M V(V+) in 2 M sulfuric acid, prepared by electrolysis of adequate V(IV+) electrolyte). This electrolyte represents a nearly charged state of a VRFB and a typical potential exposure for the positive electrode during charging4. All samples were characterized by scanning electron microscopy (SEM), thermogravimetric analysis coupled with mass spectrometry (TGA-MS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and cyclic voltammetry (CV). We found significant differences in how the surface composition, thermal stability and electrochemical behaviour is affected by the means of the different treatment methods. Thermal treatment was found to reduce the overall surface oxygen content5 for all felt types but increases the content of single bonded oxygen for graphitized carbon felts, only. Furthermore, for the carbonized felt type, thermal activation leads to a decreased thermal stability and highly reduces the electrochemical activity, presumably due to increasing C=O and C=C contents. Soaking increases the surface oxygen content of all felts due to the oxidizing nature of sulfuric acid and even further increases the electrochemical reversibility of Rayon based carbon felts, as shown in Figure 1 (a). This correlates to the high content of single bonded oxygen species and combined with an increased sp²/sp³ ratio (Figure 1 (b)). Figure 1 (c) and (d) show SEM images of an untreated and electrochemically aged felt, respectively. The yellow circle in the latter highlights a flaked off part of the carbon fibre. In general, soaking and electrochemical ageing both lead to a much lower thermal stability for all felt types. It is also noteworthy that electrochemically aged samples are more prone to side reactions. This work contributes to a better understanding in how the precursor material and the processing affects the properties of electrode materials in a VRFB. Furthermore, it provides a comprehensive overview of commercially available carbon felts by SGL and general characterization techniques. References C. Minke, U. Kunz, and T. Turek, J. Power Sources, 342, 116–124 (2017) http://dx.doi.org/10.1016/j.jpowsour.2016.12.039.P. Leung et al., RSC Adv., 2, 10125 (2012) http://xlink.rsc.org/?DOI=c2ra21342g.B. Sun and M. Skyllas-Kazacos, Electrochim. Acta, 37, 1253–1260 (1992) http://linkinghub.elsevier.com/retrieve/pii/001346869285064R.I. Derr et al., J. Power Sources, 325, 351–359 (2016) http://www.sciencedirect.com/science/article/pii/S037877531630742X.O. Nibel et al., J. Electrochem. Soc., 164, A1608–A1615 (2017) http://jes.ecsdl.org/lookup/doi/10.1149/2.1081707jes. Figure 1

Adsorption of methanol and water vapor on modified forms of mordenite–clinoptilolite rock

The influence of thermal activation, decationation, and dealumination on adsorption properties of rock from Transcarpathian deposit (Lypcha village, Ukraine) containing mordenite and clinoptilolite at the ratio 1:1 was studied in this research. Taking into account the need of preliminary thermal activation of adsorbent, the research of thermal stability of zeolite component of rock was conducted. Parameters of microporous structure of decationated and dealuminated samples were calculated. Obtained results show that decationation of mordenite–clinoptilolite rock leads to insignificant increase and dealumination leads to significant decrease of adsorption capacity for water. Maximal adsorption ability for methanol is about 50% dealumination degree of the sample.

Influence of thermal activation on dislocation inelasticity of LiF crystals with different impurity compositions

The method of double piezoelectric oscillator is used to investigate the influence of thermal activation (293–573 K) on the dislocation inelasticity and dislocation structure of the annealed LiF crystals having different impurity compositions. On curves illustrating the dependence of the internal friction on the strain amplitude δ(e0), a peak having a hysteresis nature is established; it is displaced toward smaller e0 values with increasing temperature. A subsequent increase in δ(e0) after passage of the peak is caused by the processes of dislocation multiplication upon exposure to ultrasound.

The influence of thermal activation and the intrinsic temperature dependence of the spin torque effect in current-induced domain wall motion

An experimental study of domain wall motion in Ni80Fe20 ring structures induced by current pulses as well as conventional magnetic fields is presented. Using constrictions we demonstrate that current-induced domain wall motion can be used to displace walls into parts of the structure where no pulsed currents are flowing. Measurements at variable temperatures between 2 and 300 K show that the fields necessary for wall motion decrease with increasing temperature, which can be explained by thermal activation. For the current-induced case we find, depending on the geometry and temperature range, that the current densities necessary for displacement can increase or decrease with rising temperature. This indicates that, in addition to thermal excitations, an intrinsic temperature dependence of the efficiency of the spin torque effect is present and leads to an increase in the critical current density with increasing temperature.

Thermally induced transitions of polarons to bipolarons in poly(3-dodecylthiophene)

The influence of thermal activation on polaron interactions of poly(3-dodecylthiophene) (PDDT) was studied. It was found that when an undoped PDDT sample was heated above 450 K and subsequently cooled to under the glass transition temperature, there were strong spin–spin interactions. When the polaron concentration was increased by FeCl 3 doping, all polarons including the immobile ones started to interact mutually. Changes in its internal microstructure, caused by thermal activation of the sample, followed by its freezing can generate an amplification of polaron interactions, giving rise to diamagnetic inter- and intra-chain bipolarons. As a result of strong spin–spin interactions the doped polymeric sample of PDDT displays diamagnetism even at room temperature. The diamagnetic properties depend on the consecutive structural relaxation of PDDT, caused either by immediate temperature changes, or by long-term standing at room temperature.

Thermally activated effects in nanofriction

The influence of thermal activation on the motion of a nanotip sliding on a flat surface isdiscussed. In a dry environment thermal vibrations may induce the tip to jumpfrom an equilibrium position to the next one along its path. This effect leads toa logarithmic increase of friction with the sliding velocity at very low speeds(v<10 µm s−1). At higher speeds thermal activation plays a minor role, and the friction versusvelocity curve ends with a plateau. A new analytical formula is discussed, whichexplains both the increase and the stabilization of friction with velocity. In a humidenvironment, the situation is complicated by water capillaries, which form betweentip and surface, if this is rough. These bridges act as an obstacle for thermallyactivated jumps. Depending on the wettability of the surface, different behaviours areobserved.

Lattice model of equilibrium polymerization. IV. Influence of activation, chemical initiation, chain scission and fusion, and chain stiffness on polymerization and phase separation

The influence of thermal activation, chemical initiation, chain fragmentation, and chain stiffness on basic thermodynamic properties of equilibrium polymerization solutions is systematically investigated using a Flory–Huggins type lattice model. The properties treated include the average chain length L, extent of polymerization Φ, Helmholtz free energy F, configurational entropy S, specific heat CV, polymerization transition temperature Tp, osmotic pressure Π, and the second and third virial coefficients, A2 and A3. The dependence of the critical temperature Tc and critical composition φc (volume fraction of associating species) on the enthalpy Δhp and entropy Δsp of polymerization and on the strength εFH of the FH effective monomer–solvent van der Waals interaction (χ=εFH/T) is also analyzed as an illustration of the strong coupling between phase separation and polymerization. For a given polymerization model, both Tc and φc, normalized by their values in the absence of polymerization, are functions of the dimensionless “sticking energy” hε≡(|Δhp|/R)/(2εFH) (where R is the gas constant) and Δsp.

Phase diagrams and energy barriers of exchange-biased bilayers with additional anisotropies in the ferromagnet

A general discussion of magnetization in exchange-biased bilayers with higher-order anisotropy contributions in an applied magnetic field is given. Allowed magnetic configurations for a ferromagnet in an applied magnetic field are shown in magnetic phase diagrams that illustrate competing effects of unidirectional, uniaxial, and fourfold anisotropies. The role and asymmetry of energy barriers during magnetization reversal are discussed in detail. A direct comparison with recent experimental results in epitaxial NiFe/FeMn bilayers is provided, and the influence of thermal activation on the magnetization reversal process is discussed.

Monitoring of HF and F 2 using a field-effect sensor

A sensor for the determination of fluorine and hydrogen fluoride in gases has been developed. Lanthanum fluoride and platinum are used as the gate materials in a field-effect device with silicon in direct contact with the ionic conductor. The determination of both gases is possible at room temperature in the ppm concentration range. The response time of the sensor is of the order of some minutes. Oxygen, which can also be determined with a similar sensor system, does not interfere. The influence of thermal activation is proved to be different for the two analytes. Selectivity for HF and F 2 can be achieved because of a very high difference in the gate voltage in both gases and the influence of the on-chip activation process.

Effect of thermally activated mechanisms on the martensitic transformation of modified Cu-Al-Ni alloys

The influence of thermal activation on the martensitic transformation of Cu-Al-Ni alloys containing boron and manganese has been studied by measuring the effect of heating/cooling rate during thermal cycling on the fraction transformed at a given time. The activation energies measured for the reverse and direct transformation of 70 and 140 kJ mol −1 respectively have been interpreted in terms of the mechanisms regarding nucleation and growth of the martensitic phase. The different mechanisms proposed together with the driving forces involved, the type of interface and the change in the ordered state of the structure have been used to discuss the stability of the transformation in the alloys with different manganese content.

The influence of thermal activation on measured critical currents in HTC and conventional weak links

A simple model for thermally activated phase slippage has been used to determine the effect of thermal fluctuations on critical current measurements in HTC, conventional BCS, and HTC/BCS superconducting junctions. The most important manifestation of such effects is a decrease in the measured critical current, below the intrinsic critical current of the junction. This also leads to a depression of the measured critical temperature of the junction, below that of the superconducting materials forming the junction. It is shown that such effects are significant for HTC superconductors with junctions, whether fabricated or naturally occurring between grains, with intrinsic low temperature critical currents <3 mA. This is almost always the case for intergranular ceramic or thin film material. Measurements of the critical temperature as a function of junction strength for both Nb/Nb and YBCO/YBCO junctions are shown to be consistent with the predicted depression due to thermal fluctuations.

Effect of Oxygen Concentration on the Resistive Superconducting Transition of YBa2Cu3O7−x in High Magnetic Field

AbstractThe resistivity, Tc and Hc2 are studied in YBa2Cu3O7−x as a function of oxygen deficiency for 0 &lt; x &lt; 0.46. For small x the resistive transition is dominated by thermally activated flux creep. The temperature dependence of the activation energy is discussed. For x = 0.46, the influence of thermal activation could be neglected and a pronounced positive curvature of Hc2(T) and Hc2(0) &gt; 45 T is found.

Thermally activated grain boundary unpinning

The influence of thermal activation on the nature of the interactions between an array of particles and a migrating grain boundary is considered, adapting concepts from the theory of thermally activated deformation. Thermally activated unpinning of boundaries is found to become significant at small particle sizes and high temperatures. For a given particle array, this leads to a time dependent average grain size which is coarser than the predictions of the traditional “Zener-Gladman” static equilibrium model. For grain sizes and temperatures of interest in ferrous alloys, substantial reductions in particle size and volume fraction of grain refining dispersions can be achieved before thermal activation interferes with the effectiveness of boundary pinning.