Traditional selection of combustion catalysis is time-consuming and labor-intensive.Theoretical calculation is expected to resolve this problem.The adsorption energy of HMX and O atoms on 13 metal oxides was calculate...Traditional selection of combustion catalysis is time-consuming and labor-intensive.Theoretical calculation is expected to resolve this problem.The adsorption energy of HMX and O atoms on 13 metal oxides was calculated using DMol3,since HMX and O are key substances in decomposition process.And the relationship between the adsorption energy of HMX,O on metal oxides(TiO_(2),Al_(2)O_(3),PbO,CuO,Fe_(2)O_(3),Co_(3)O_(4),Bi_(2)O_(3),NiO)and experimental T30 values(time required for the decomposition depth of HMX to reach 30%)was depicted as volcano plot.Thus,the T30 values of other metal oxides was predicted based on their adsorption energy on volcano plot and validated by previous experimental data.Further,the adsorption energy of HMX on ZrO_(2)and MnO_(2)was predicted based on the linear relationship between surface energy and adsorption energy,and T30 values were estimated based on volcano plot.The apparent activation energy data of HMX/MgO,HMX/SnO_(2),HMX/ZrO_(2),and HMX/MnO_(2)obtained from DSC experiments are basically consistent with our predicted T30 values,indicating that it is feasible to predict the catalytic activity based on the adsorption calculation,and it is expected that these simple structural properties can predict adsorption energy to reduce the large quantities of computation and experiment cost.展开更多
This work is a simulation modelling with the LAMMPS calculation code of an electrode based on alkali metals (lithium, sodium and potassium) using the MEAM potential. For different multiplicities, two models were studi...This work is a simulation modelling with the LAMMPS calculation code of an electrode based on alkali metals (lithium, sodium and potassium) using the MEAM potential. For different multiplicities, two models were studied;with and without gap. In this work, we present the structural, physical and chemical properties of the lithium, sodium and potassium electrodes. For the structural properties, the cohesive energy and the mesh parameters were calculated, revealing that, whatever the chemical element selected, the compact hexagonal hcp structure is the most stable, followed by the face-centred cubic CFC structure, and finally the BCC structure. The most stable structure is lithium, with a cohesion energy of -6570 eV, and the lowest bcc-hcp transition energy of -0.553 eV/atom, followed by sodium. For physical properties, kinetic and potential energies were calculated for each of the sectioned chemical elements, with lithium achieving the highest value. Finally, for the chemical properties, we studied the diffusion coefficient and the activation energy. Only potassium followed an opposite order to the other two, with the quantities with lacunae being greater than those without lacunae, whatever the multiplicity. The order of magnitude of the diffusion coefficients is given by the relationship D<sub>Li</sub> > D<sub>Na</sub> > D<sub>k</sub> for the multiplicity 6*6*6, while for the activation energy the order is reversed.展开更多
This study is an extension of the previous work done with ARS-680 Environmental Chamber. Drying is a complex operation that demands much energy and time. Drying is essentially important for preservation of ginger rhiz...This study is an extension of the previous work done with ARS-680 Environmental Chamber. Drying is a complex operation that demands much energy and time. Drying is essentially important for preservation of ginger rhizome. Drying of ginger was modeled, and then the effective diffusion coefficient and activation energy were determined. For this purpose, the experiments were done at six levels of varied temperatures: 10°C, 20°C, 30°C, 40°C, 50°C and 60°C. The values of effective diffusion coefficients obtained in this work for the variously treated ginger rhizomes closely agreed with the average effective diffusion coefficients of other notable authors who determined the drying kinetics and convective heat transfer coefficients of ginger slices.展开更多
The apparent activation energy,Eapp,is a common measure in thermal catalysis to discuss the activity and limiting steps of catalytic processes on solid-state materials.Recently,the electrocatalysis community adopted t...The apparent activation energy,Eapp,is a common measure in thermal catalysis to discuss the activity and limiting steps of catalytic processes on solid-state materials.Recently,the electrocatalysis community adopted the concept of Eappand combined it with the Butler-Volmer theory.Certain observations though,such as potential-dependent fluctuations of Eapp,are yet surprising because they conflict with the proposed linear decrease in Eappwith increasing overpotential.The most common explanation for this finding refers to coverage changes upon alterations in the temperature or the applied electrode potential.In the present contribution,it is demonstrated that the modulation of surface coverages cannot entirely explain potential-dependent oscillations of Eapp,and rather the impact of entropic contributions of the transition states has been overlooked so far.In the case of a nearly constant surface coverage,these entropic contributions can be extracted by a dedicated combination of Tafel plots and temperature-dependent experiments.展开更多
The oxidation behaviors of AZ80,AZ8O-0.32 Y and AZ8O-0.38 Nd(wt.%)alloys were researched at 413℃,420℃,427v and 433℃for up to 6 h in air environment via a high precision analytical balance,a laser confocal microscop...The oxidation behaviors of AZ80,AZ8O-0.32 Y and AZ8O-0.38 Nd(wt.%)alloys were researched at 413℃,420℃,427v and 433℃for up to 6 h in air environment via a high precision analytical balance,a laser confocal microscope,differential scanning calorimeter(DSC)analysis,X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and X-ray photoelectron spectroscopy(XPS)analysis.The results show that the weight gain and oxidation rate of AZ80 are reduced significantly,the initiation form and propagation of cracks in oxide layer are changed.Compact and protective oxide layer forms on alloy surface with Y or Nd addition.And the activation energies of AZ80,AZ80-0.32Y and AZ8O-0.38Nd alloys calculated via Arrhenius equation are 82.556 kJ/mol,177.148kJ/mol and 136.738 kJ/mol,respectively.展开更多
Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate conditi...Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate condition combinations of temperature and relative humidity were used. Results indicate that changes of concrete carbonation rate with environmental temperature agree the Arrhenius law well, which suggests concrete carbonation rate has obvious dependence on temperature. The higher the temperature is, the more quickly the concrete carbonates, and at the same time it is also affected by environmental relative humidity. Thereafter, the apparent activation energy Ea of concrete carbonation reaction was obtained, ranging from 16.8 to 20.6 kJ/mol corresponding 0.35-0.74 water cement ratio, and lower water cement ratio will cause the apparent activation energy increase. Concrete carbonation rates will increase 1.1-1.69 times as temperature increase every 10 ℃ at the temperature range of 10 to 60 ℃.展开更多
The apparent activation energy of concrete in early age was determined by adiabatic temperature rise test with different initial temperatures. The influence of mineral admixtures such as fly ash, slag and silica fume ...The apparent activation energy of concrete in early age was determined by adiabatic temperature rise test with different initial temperatures. The influence of mineral admixtures such as fly ash, slag and silica fume on the apparent activation energy of concrete was investigated. The equivalent age that expresses the maturity of concrete was calculated to evaluate the cracking risk of concrete in structures. The results reveal that a substitution of 20% fly ash for Portland cement obviously decreases the apparent activation energy of concrete, however, a substitution of 10% silica fume for Portland cement increases the apparent activation. Finite element method analysis of a simulating concrete wall shows that the concrete containing 20% fly ash has the lowest cracking risk.展开更多
The buoyancy driven flow of a second-grade nanofluid in the presence of a binary chemical reaction is analyzed in the context of a model based on the balance equations for mass,species concentration,momentum and energ...The buoyancy driven flow of a second-grade nanofluid in the presence of a binary chemical reaction is analyzed in the context of a model based on the balance equations for mass,species concentration,momentum and energy.The elastic properties of the considered fluid are taken into account.The two-dimensional slip flow of such non-Newtonian fluid over a porous flat material which is stretched vertically upwards is considered.The role played by the activation energy is accounted for through an exponent form modified Arrhenius function added to the Buongiorno model for the nanofluid concentration.The effects of thermal radiation are also examined.A similarity transformations is used to turn the problem based on partial differential equations into a system of ordinary differential equations.The resulting system is solved using a fourth order RK and shooting methods.The velocity profile,temperature profile,concentration profile,local skin friction,local Nusselt number and local Sherwood number are reported for several circumstances.The influence of the chemical reaction on the properties of the concentration and momentum boundary layers is critically discussed.展开更多
Bioconvection research is primarily focused on the augmentation of energy and mass species,which has implications in the processes intensification,mechanical,civil,electronics,and chemical engineering branches.Advance...Bioconvection research is primarily focused on the augmentation of energy and mass species,which has implications in the processes intensification,mechanical,civil,electronics,and chemical engineering branches.Advanced bioconvection technology sectors include cooling systems for electronic devices,building insulation,and geothermal nuclear waste disposal.Hence,the present investigation is mainly discoursing the impact of Marangoni convention Casson nanoliquid flow under gyrotactic microorganisms over the porous sheet.The partial differential equations(PDEs)are re-structured into ordinary differential equations(ODEs)via suitable similar variables.These ODEs are numerically solved with the help of the spectral relaxation method(SRM).The numerical outcomes are illustrated graphically for various parameters over velocity,temperature,concentration,and bioconvection profiles.Three-dimensional(3 D)views of important engineering parameters are illustrated for various parameters.The velocity of the Casson nanoliquid increases with increasing the Marangoni parameter but decreases against higher porosity parameter.The surface drag force enhances for enhancement in the Marangoni number.The rate of mass transmission is higher for reaction rate constraint but diminishes for activation energy parameter.The higher radiative values augment the rate of heat transmission.展开更多
Combustion kinetics of the hydrochar was investigated using a multi-Gaussian-distributed activation energy model(DAEM)to ex-pand the knowledge on the combustion mechanisms.The results demonstrated that the kinetic par...Combustion kinetics of the hydrochar was investigated using a multi-Gaussian-distributed activation energy model(DAEM)to ex-pand the knowledge on the combustion mechanisms.The results demonstrated that the kinetic parameters calculated by the multi-Gaussian-DAEM accurately represented the experimental conversion rate curves.Overall,the feedstock combustion could be divided into four stages:the decomposition of hemicellulose,cellulose,lignin,and char combustion.The hydrochar combustion could in turn be divided into three stages:the combustion of cellulose,lignin,and char.The mean activation energy ranges obtained for the cellulose,lignin,and char were 273.7-292.8,315.1-334.5,and 354.4-370 kJ/mol,respectively,with the standard deviations of 2.1-23.1,9.5-27.4,and 12.1-22.9 kJ/mol,re-spectively.The cellulose and lignin contents first increased and then decreased with increasing hydrothermal carbonization(HTC)temperature,while the mass fraction of char gradually increased.展开更多
Some commercial cold working die steels C.,Cr15 and CrWMn with ultra fine grain size were chosen as tested materials to research the activation energy for superplastic flow at different temperatures and strain rates a...Some commercial cold working die steels C.,Cr15 and CrWMn with ultra fine grain size were chosen as tested materials to research the activation energy for superplastic flow at different temperatures and strain rates above critical temperature. Based on the Arrhenius equation, the activation energy for superplastic flow is evaluated. The activation energy at constant strain rate is estimated by the logσ, vs 1/T relationship. The results show that the ac tivation energy is usually small under the conditions of optimal flow. The characteristics of superplastic deformation of steels above the critical temperature were also analyzed.展开更多
The thermal stability and the kinetics of glass transition and crystallization for Zr75-xNi25Alx (x = 8-15) metallic glasses were investigated using differential scanning calorimetry (DSC) under continuous heating...The thermal stability and the kinetics of glass transition and crystallization for Zr75-xNi25Alx (x = 8-15) metallic glasses were investigated using differential scanning calorimetry (DSC) under continuous heating conditions. The apparent activation energy of glass transition rises monotonously with the A1 content increasing; the activation energy of crystallization increases with A1 changing from 8at% to 15at%, and then decreases with A1 further up to 24at%, which exhibits a good correlation to the thermal stability and the glass-forming ability (GFA). The Zr60Ni25A115 metallic glass with the largest supercooled liquid region and GFA possesses the highest activation energy of crystallization. The relation between the thermal stability, GFA and activation energy of crystallization was discussed in terms of the primary precipitated phases.展开更多
The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimat...The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimated by introducing the equationproposed by Thompson, Spaepen and Turnbull. It can be seen that the Gibbs free energy differences decrease firstas the increases of Sn addition smaller than 3, then followed by a decrease due to the successive addition of Snlarger than 3, indicating that the thermal stabilities of these glass forming alloys increase first and then followed by adecrease owing to the excessive addition of Sn. Furthermore, the activation energy of Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9) and(Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9))_(0.97)Sn_3 was evaluated by Kissinger equation. It is noted that the Sn addition increases theactivation energies for glass transition and crystallization, implying that the higher thermal stability can be obtainedby appropriate addition of Sn.展开更多
The apparent activation energy of serrated yielding was measured by two different methods for a commercial brass H68.The results showed that the apparent activation energy of serrat- ed yielding measured by a method i...The apparent activation energy of serrated yielding was measured by two different methods for a commercial brass H68.The results showed that the apparent activation energy of serrat- ed yielding measured by a method involving(m+β)values increases with the grain size.In contrast,those measured by another method without involving(m+β)values are all the same for specimens with different grain sizes.Combining with the observation of the microstructures,the above phenomena have been explained.The method to measure the true activation energy of serrated yielding has also been proposed.展开更多
The in situ electrical resistance and transport activation energies of solid C60 fullerene have been measured under high pressure up to 25 GPa in the temperature range of 300-423 K by using a designed diamond anvil ce...The in situ electrical resistance and transport activation energies of solid C60 fullerene have been measured under high pressure up to 25 GPa in the temperature range of 300-423 K by using a designed diamond anvil cell. In the experiment, four parts of boron-doped diamond films fabricated on one anvil were used as electrical measurement probes and a W-Ta thin film thermocouple which was integrated on the other diamond anvil was used to measure the temperature. The current results indicate that the measured high-pressure resistances are bigger than those reported before at the same pressure and there is no pressure-independent resistance increase before 8 GPa. From the temperature dependence of the resistivity, the C60 behaviors as a semiconductor and the activation energies of the cubic C60 fullerene are 0,49, 0.43, and 0.36 eV at 13, 15, and 19 GPa, respectively.展开更多
The effect of thermal wave at the initial stage for non-conductive AlOpowders compact in field assisted sintering technique(FAST) was investigated. The Lord and Shulman type generalized thermoselastic theory was intro...The effect of thermal wave at the initial stage for non-conductive AlOpowders compact in field assisted sintering technique(FAST) was investigated. The Lord and Shulman type generalized thermoselastic theory was introduced to describe the influence of thermal-mechanical interaction, as well as the heat transport and thermal focusing caused by thermal wave propagation. The expression of vacancy concentration difference of the particles was deduced by considering transient thermal stress. Subsequently, the relationship between activation energy and vacancy concentration difference was obtained. The mechanism of surface diffusion, volume diffusion, simultaneous surface and volume diffusion was analyzed. The numerical simulations indicate that low sintering temperature can obtain high local temperature by the superposition effect of thermal wave. Vacancy concentration differences were improved during FAST compared with hot-pressure and pressureless sintering, thereby decreasing the sintering time. By contrast, the activation energy declined with the decrease of vacancy concentration difference in the neck growth process.展开更多
A complexes donor in neutron-transmutation-doped (NTD) silicon grown by floating-zone-refined in a hydrogen atmosphere [FZ(H)-Si] was studied by annealing, electrical and infrared absorption measurements. Resistivitie...A complexes donor in neutron-transmutation-doped (NTD) silicon grown by floating-zone-refined in a hydrogen atmosphere [FZ(H)-Si] was studied by annealing, electrical and infrared absorption measurements. Resistivities of the crystal subjected to annealing at 480°C are about an order of magnitude lower, as compared to the crystal in which the electrical property is restored completely. The values for the donor decomposition activation energy are 1.5±0.2 eV and 0.4±0.1 eV in the temperature ranges of 500-540°C and 580-640°C, respectively. According to the measurements of interstitial oxygen concentration in the crystal, oxygen is involved in the donor.展开更多
Physical implications of the activation energy derived from temperature dependent photoluminescence(PL) of In Ga Nbased materials are investigated, finding that the activation energy is determined by the thermal dec...Physical implications of the activation energy derived from temperature dependent photoluminescence(PL) of In Ga Nbased materials are investigated, finding that the activation energy is determined by the thermal decay processes involved.If the carrier escaping from localization states is responsible for the thermal quenching of PL intensity, as often occurs in In Ga N materials, the activation energy is related to the energy barrier height of localization states. An alternative possibility for the thermal decay of the PL intensity is the activation of nonradiative recombination processes, in which case thermal activation energy would be determined by the carrier capture process of the nonradiative recombination centers rather than by the ionization energy of the defects themselves.展开更多
In the present work, we find that both diffusion activation energy Ea(D) and Ea(S^ex) increase linearly with pressure and have the same slope (0.022±0.001 eV/GPa) for liquid Al. The temperature and pressure...In the present work, we find that both diffusion activation energy Ea(D) and Ea(S^ex) increase linearly with pressure and have the same slope (0.022±0.001 eV/GPa) for liquid Al. The temperature and pressure dependence of excess entropy is well fitted by the expression -S^ex (T, P)/kB = a(P)+ b(P)T + c(P) exp(Ef/kBT), which together with the small ratio of Ef/kB T leads to the relationship of excess entropy to temperature and pressure, i.e. Sex ~ -cEf/T, where c is about 12 and Ef (= △E - P△V) is the favourable energy. Therefore, there exists a simple relation between Ea(S^ex) and Ef, i.e. Ea(S^ex) ≈ cEf.展开更多
The available literature revealed a gap in reporting the rough rice drying kinetics parameters under isothermal conditions, particularly for Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112...The available literature revealed a gap in reporting the rough rice drying kinetics parameters under isothermal conditions, particularly for Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112 and Titan) and the long-grain (Diamond and Wells) rough rice varieties were dried under isothermal conditions. The drying process occurred under 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C in a system emulating the thermogravimetric analyzer. Drying kinetics models were studied for four well-known models: Page, Newton, Logarithmic, and Henderson & Pabis. The drying kinetics constants were determined for the four studied models. The initial moisture content of rough rice was 28.2% db. Profound moisture reduction was observed during the first three hours of drying, followed by less moisture content reduction. The results showed that at the drying temperature of 100°C and after 6 hours of the drying process, the lowest moisture content reached 13.9% (db) for Titan rough rice. The drying rate of rough rice ranged between 7.41 and 2.01%/h during the first hour of drying under the studied temperature range of 40°C to 100°C. The drying rate was higher with the higher temperature levels during the first three hours. Among all the studied models, the Page, Newton, and Logarithmic models best fit 25%, 25%, and 50% of the twenty-eight studied cases. The challenge that arose from these results led to evolving a mathematical solution by joining the three models in one equation. The combined model showed the best fit for all the studied cases, with R<sup>2</sup> ranging between 0.9999 and 0.9954 for the medium- and long-grain rice varieties. Increasing the drying temperature increased the effective moisture diffusivity values. The highest effective moisture diffusivity of 18.104 × 10<sup>-9</sup> m<sup>2</sup>/s was obtained at the drying temperature of 100°C for medium-grain rice, Titan. The activation energy values ranged between 17.77 and 24.48 kJ/mol for the four rough rice varieties.展开更多
基金supported by Key Science and Technology Innovation Team of Shaanxi Province(No.2022TD-33)National Natural Science Foundation of China(Grant Nos.21373161,21504067)。
文摘Traditional selection of combustion catalysis is time-consuming and labor-intensive.Theoretical calculation is expected to resolve this problem.The adsorption energy of HMX and O atoms on 13 metal oxides was calculated using DMol3,since HMX and O are key substances in decomposition process.And the relationship between the adsorption energy of HMX,O on metal oxides(TiO_(2),Al_(2)O_(3),PbO,CuO,Fe_(2)O_(3),Co_(3)O_(4),Bi_(2)O_(3),NiO)and experimental T30 values(time required for the decomposition depth of HMX to reach 30%)was depicted as volcano plot.Thus,the T30 values of other metal oxides was predicted based on their adsorption energy on volcano plot and validated by previous experimental data.Further,the adsorption energy of HMX on ZrO_(2)and MnO_(2)was predicted based on the linear relationship between surface energy and adsorption energy,and T30 values were estimated based on volcano plot.The apparent activation energy data of HMX/MgO,HMX/SnO_(2),HMX/ZrO_(2),and HMX/MnO_(2)obtained from DSC experiments are basically consistent with our predicted T30 values,indicating that it is feasible to predict the catalytic activity based on the adsorption calculation,and it is expected that these simple structural properties can predict adsorption energy to reduce the large quantities of computation and experiment cost.
文摘This work is a simulation modelling with the LAMMPS calculation code of an electrode based on alkali metals (lithium, sodium and potassium) using the MEAM potential. For different multiplicities, two models were studied;with and without gap. In this work, we present the structural, physical and chemical properties of the lithium, sodium and potassium electrodes. For the structural properties, the cohesive energy and the mesh parameters were calculated, revealing that, whatever the chemical element selected, the compact hexagonal hcp structure is the most stable, followed by the face-centred cubic CFC structure, and finally the BCC structure. The most stable structure is lithium, with a cohesion energy of -6570 eV, and the lowest bcc-hcp transition energy of -0.553 eV/atom, followed by sodium. For physical properties, kinetic and potential energies were calculated for each of the sectioned chemical elements, with lithium achieving the highest value. Finally, for the chemical properties, we studied the diffusion coefficient and the activation energy. Only potassium followed an opposite order to the other two, with the quantities with lacunae being greater than those without lacunae, whatever the multiplicity. The order of magnitude of the diffusion coefficients is given by the relationship D<sub>Li</sub> > D<sub>Na</sub> > D<sub>k</sub> for the multiplicity 6*6*6, while for the activation energy the order is reversed.
文摘This study is an extension of the previous work done with ARS-680 Environmental Chamber. Drying is a complex operation that demands much energy and time. Drying is essentially important for preservation of ginger rhizome. Drying of ginger was modeled, and then the effective diffusion coefficient and activation energy were determined. For this purpose, the experiments were done at six levels of varied temperatures: 10°C, 20°C, 30°C, 40°C, 50°C and 60°C. The values of effective diffusion coefficients obtained in this work for the variously treated ginger rhizomes closely agreed with the average effective diffusion coefficients of other notable authors who determined the drying kinetics and convective heat transfer coefficients of ginger slices.
基金funding by the Ministry of Culture and Science of the Federal State of North Rhine-Westphalia (NRW Return Grant)CRC/TRR247:"Heterogeneous Oxidation Catalysis in the Liquid Phase"(388390466-TRR247),the RESOLV Cluster of Excellence,funded by the Deutsche Forschungsgemeinschaft under Germany’s Excellence StrategyEXC 2033-390677874-RESOLV+1 种基金the Center for Nanointegration (CENIDE)supported by COST (European Cooperation in Science and Technology)。
文摘The apparent activation energy,Eapp,is a common measure in thermal catalysis to discuss the activity and limiting steps of catalytic processes on solid-state materials.Recently,the electrocatalysis community adopted the concept of Eappand combined it with the Butler-Volmer theory.Certain observations though,such as potential-dependent fluctuations of Eapp,are yet surprising because they conflict with the proposed linear decrease in Eappwith increasing overpotential.The most common explanation for this finding refers to coverage changes upon alterations in the temperature or the applied electrode potential.In the present contribution,it is demonstrated that the modulation of surface coverages cannot entirely explain potential-dependent oscillations of Eapp,and rather the impact of entropic contributions of the transition states has been overlooked so far.In the case of a nearly constant surface coverage,these entropic contributions can be extracted by a dedicated combination of Tafel plots and temperature-dependent experiments.
基金the National Key Research and Development Program of China(No.2016YFB0301104)Nation Natural Science Foundation of China(No.51771043)Foundation of State Key Laboratory of Baiyunobo Rare Earth researches and Comprehensive Utilization,and Programme of Introducing Talents of Discipline Innovation to Universities 2.0(the 111 Project 2.0 of China,No.BP0719037).
文摘The oxidation behaviors of AZ80,AZ8O-0.32 Y and AZ8O-0.38 Nd(wt.%)alloys were researched at 413℃,420℃,427v and 433℃for up to 6 h in air environment via a high precision analytical balance,a laser confocal microscope,differential scanning calorimeter(DSC)analysis,X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and X-ray photoelectron spectroscopy(XPS)analysis.The results show that the weight gain and oxidation rate of AZ80 are reduced significantly,the initiation form and propagation of cracks in oxide layer are changed.Compact and protective oxide layer forms on alloy surface with Y or Nd addition.And the activation energies of AZ80,AZ80-0.32Y and AZ8O-0.38Nd alloys calculated via Arrhenius equation are 82.556 kJ/mol,177.148kJ/mol and 136.738 kJ/mol,respectively.
基金Funded by National Natural Science Fundation of China(No.51178455)
文摘Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate condition combinations of temperature and relative humidity were used. Results indicate that changes of concrete carbonation rate with environmental temperature agree the Arrhenius law well, which suggests concrete carbonation rate has obvious dependence on temperature. The higher the temperature is, the more quickly the concrete carbonates, and at the same time it is also affected by environmental relative humidity. Thereafter, the apparent activation energy Ea of concrete carbonation reaction was obtained, ranging from 16.8 to 20.6 kJ/mol corresponding 0.35-0.74 water cement ratio, and lower water cement ratio will cause the apparent activation energy increase. Concrete carbonation rates will increase 1.1-1.69 times as temperature increase every 10 ℃ at the temperature range of 10 to 60 ℃.
基金the National High Technology Research and Development Program of China(863)(No.2003AA33X100)the National Post Doctoral Fund(No.20060400284)+1 种基金the Jiangshu Province Natural Science Fund(No.BK2005216)the Jiangshu Province Post Doctoral Fund(2006)
文摘The apparent activation energy of concrete in early age was determined by adiabatic temperature rise test with different initial temperatures. The influence of mineral admixtures such as fly ash, slag and silica fume on the apparent activation energy of concrete was investigated. The equivalent age that expresses the maturity of concrete was calculated to evaluate the cracking risk of concrete in structures. The results reveal that a substitution of 20% fly ash for Portland cement obviously decreases the apparent activation energy of concrete, however, a substitution of 10% silica fume for Portland cement increases the apparent activation. Finite element method analysis of a simulating concrete wall shows that the concrete containing 20% fly ash has the lowest cracking risk.
基金United Arab Emirates University,Al Ain,UAE with Grant No.31S363-UPAR(4)2018.
文摘The buoyancy driven flow of a second-grade nanofluid in the presence of a binary chemical reaction is analyzed in the context of a model based on the balance equations for mass,species concentration,momentum and energy.The elastic properties of the considered fluid are taken into account.The two-dimensional slip flow of such non-Newtonian fluid over a porous flat material which is stretched vertically upwards is considered.The role played by the activation energy is accounted for through an exponent form modified Arrhenius function added to the Buongiorno model for the nanofluid concentration.The effects of thermal radiation are also examined.A similarity transformations is used to turn the problem based on partial differential equations into a system of ordinary differential equations.The resulting system is solved using a fourth order RK and shooting methods.The velocity profile,temperature profile,concentration profile,local skin friction,local Nusselt number and local Sherwood number are reported for several circumstances.The influence of the chemical reaction on the properties of the concentration and momentum boundary layers is critically discussed.
文摘Bioconvection research is primarily focused on the augmentation of energy and mass species,which has implications in the processes intensification,mechanical,civil,electronics,and chemical engineering branches.Advanced bioconvection technology sectors include cooling systems for electronic devices,building insulation,and geothermal nuclear waste disposal.Hence,the present investigation is mainly discoursing the impact of Marangoni convention Casson nanoliquid flow under gyrotactic microorganisms over the porous sheet.The partial differential equations(PDEs)are re-structured into ordinary differential equations(ODEs)via suitable similar variables.These ODEs are numerically solved with the help of the spectral relaxation method(SRM).The numerical outcomes are illustrated graphically for various parameters over velocity,temperature,concentration,and bioconvection profiles.Three-dimensional(3 D)views of important engineering parameters are illustrated for various parameters.The velocity of the Casson nanoliquid increases with increasing the Marangoni parameter but decreases against higher porosity parameter.The surface drag force enhances for enhancement in the Marangoni number.The rate of mass transmission is higher for reaction rate constraint but diminishes for activation energy parameter.The higher radiative values augment the rate of heat transmission.
基金the National Nat-ural Science Foundation of China(Nos.52074029,51804026)the USTB-NTUT Joint Research Program(No.06310063)Chuan Wang would like to acknowledge the funding support from Vinnova(dnr:2017-01327).
文摘Combustion kinetics of the hydrochar was investigated using a multi-Gaussian-distributed activation energy model(DAEM)to ex-pand the knowledge on the combustion mechanisms.The results demonstrated that the kinetic parameters calculated by the multi-Gaussian-DAEM accurately represented the experimental conversion rate curves.Overall,the feedstock combustion could be divided into four stages:the decomposition of hemicellulose,cellulose,lignin,and char combustion.The hydrochar combustion could in turn be divided into three stages:the combustion of cellulose,lignin,and char.The mean activation energy ranges obtained for the cellulose,lignin,and char were 273.7-292.8,315.1-334.5,and 354.4-370 kJ/mol,respectively,with the standard deviations of 2.1-23.1,9.5-27.4,and 12.1-22.9 kJ/mol,re-spectively.The cellulose and lignin contents first increased and then decreased with increasing hydrothermal carbonization(HTC)temperature,while the mass fraction of char gradually increased.
文摘Some commercial cold working die steels C.,Cr15 and CrWMn with ultra fine grain size were chosen as tested materials to research the activation energy for superplastic flow at different temperatures and strain rates above critical temperature. Based on the Arrhenius equation, the activation energy for superplastic flow is evaluated. The activation energy at constant strain rate is estimated by the logσ, vs 1/T relationship. The results show that the ac tivation energy is usually small under the conditions of optimal flow. The characteristics of superplastic deformation of steels above the critical temperature were also analyzed.
基金supported by the Fundamental Research Funds for the Central Universities(Nos.DUT11RC(3)70 and DUT11RC(3)29)the National Natural Science Foundation of China(No.51171034)the China Postdoctoral Science Foundation Funded Project(No.2012M510802)
文摘The thermal stability and the kinetics of glass transition and crystallization for Zr75-xNi25Alx (x = 8-15) metallic glasses were investigated using differential scanning calorimetry (DSC) under continuous heating conditions. The apparent activation energy of glass transition rises monotonously with the A1 content increasing; the activation energy of crystallization increases with A1 changing from 8at% to 15at%, and then decreases with A1 further up to 24at%, which exhibits a good correlation to the thermal stability and the glass-forming ability (GFA). The Zr60Ni25A115 metallic glass with the largest supercooled liquid region and GFA possesses the highest activation energy of crystallization. The relation between the thermal stability, GFA and activation energy of crystallization was discussed in terms of the primary precipitated phases.
文摘The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimated by introducing the equationproposed by Thompson, Spaepen and Turnbull. It can be seen that the Gibbs free energy differences decrease firstas the increases of Sn addition smaller than 3, then followed by a decrease due to the successive addition of Snlarger than 3, indicating that the thermal stabilities of these glass forming alloys increase first and then followed by adecrease owing to the excessive addition of Sn. Furthermore, the activation energy of Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9) and(Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9))_(0.97)Sn_3 was evaluated by Kissinger equation. It is noted that the Sn addition increases theactivation energies for glass transition and crystallization, implying that the higher thermal stability can be obtainedby appropriate addition of Sn.
文摘The apparent activation energy of serrated yielding was measured by two different methods for a commercial brass H68.The results showed that the apparent activation energy of serrat- ed yielding measured by a method involving(m+β)values increases with the grain size.In contrast,those measured by another method without involving(m+β)values are all the same for specimens with different grain sizes.Combining with the observation of the microstructures,the above phenomena have been explained.The method to measure the true activation energy of serrated yielding has also been proposed.
基金supported by the National Basic Research Program of China (Grant No. 2011CB808204)the National Natural Science Foundation of China (Grant Nos. 11074094 and 91014004)the Fundamental Research Funds for Jilin University, China (Grant No. 450060491500)
文摘The in situ electrical resistance and transport activation energies of solid C60 fullerene have been measured under high pressure up to 25 GPa in the temperature range of 300-423 K by using a designed diamond anvil cell. In the experiment, four parts of boron-doped diamond films fabricated on one anvil were used as electrical measurement probes and a W-Ta thin film thermocouple which was integrated on the other diamond anvil was used to measure the temperature. The current results indicate that the measured high-pressure resistances are bigger than those reported before at the same pressure and there is no pressure-independent resistance increase before 8 GPa. From the temperature dependence of the resistivity, the C60 behaviors as a semiconductor and the activation energies of the cubic C60 fullerene are 0,49, 0.43, and 0.36 eV at 13, 15, and 19 GPa, respectively.
基金Funded by the National Natural Science Foundation of China(No.11602042)the Chongqing Research Program of Basic Research and Frontier Technology(No.cstc2016jcyjA0259)the Scientific and Technological Research Program of Chongqing Municipal Education Commission(No.KJ1601304)
文摘The effect of thermal wave at the initial stage for non-conductive AlOpowders compact in field assisted sintering technique(FAST) was investigated. The Lord and Shulman type generalized thermoselastic theory was introduced to describe the influence of thermal-mechanical interaction, as well as the heat transport and thermal focusing caused by thermal wave propagation. The expression of vacancy concentration difference of the particles was deduced by considering transient thermal stress. Subsequently, the relationship between activation energy and vacancy concentration difference was obtained. The mechanism of surface diffusion, volume diffusion, simultaneous surface and volume diffusion was analyzed. The numerical simulations indicate that low sintering temperature can obtain high local temperature by the superposition effect of thermal wave. Vacancy concentration differences were improved during FAST compared with hot-pressure and pressureless sintering, thereby decreasing the sintering time. By contrast, the activation energy declined with the decrease of vacancy concentration difference in the neck growth process.
文摘A complexes donor in neutron-transmutation-doped (NTD) silicon grown by floating-zone-refined in a hydrogen atmosphere [FZ(H)-Si] was studied by annealing, electrical and infrared absorption measurements. Resistivities of the crystal subjected to annealing at 480°C are about an order of magnitude lower, as compared to the crystal in which the electrical property is restored completely. The values for the donor decomposition activation energy are 1.5±0.2 eV and 0.4±0.1 eV in the temperature ranges of 500-540°C and 580-640°C, respectively. According to the measurements of interstitial oxygen concentration in the crystal, oxygen is involved in the donor.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFB0401801 and 2016YFB0400803)the National Natural Science Foundation of China(Grant Nos.61674138,61674139,61604145,61574135,61574134,61474142,61474110,61377020,and 61376089)+1 种基金Science Challenge Project,China(Grant No.JCKY2016212A503)Beijing Municipal Science and Technology Project,China(Grant No.Z161100002116037)
文摘Physical implications of the activation energy derived from temperature dependent photoluminescence(PL) of In Ga Nbased materials are investigated, finding that the activation energy is determined by the thermal decay processes involved.If the carrier escaping from localization states is responsible for the thermal quenching of PL intensity, as often occurs in In Ga N materials, the activation energy is related to the energy barrier height of localization states. An alternative possibility for the thermal decay of the PL intensity is the activation of nonradiative recombination processes, in which case thermal activation energy would be determined by the carrier capture process of the nonradiative recombination centers rather than by the ionization energy of the defects themselves.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10674135,10874182 and 50803066)the Foundation of the Education Committee of Anhui Province,China(Grant Nos.KJ2010A031 and KJ2010A012)the Funds from the Centre of Computational Science,Hefei Institutes of Physical Sciences
文摘In the present work, we find that both diffusion activation energy Ea(D) and Ea(S^ex) increase linearly with pressure and have the same slope (0.022±0.001 eV/GPa) for liquid Al. The temperature and pressure dependence of excess entropy is well fitted by the expression -S^ex (T, P)/kB = a(P)+ b(P)T + c(P) exp(Ef/kBT), which together with the small ratio of Ef/kB T leads to the relationship of excess entropy to temperature and pressure, i.e. Sex ~ -cEf/T, where c is about 12 and Ef (= △E - P△V) is the favourable energy. Therefore, there exists a simple relation between Ea(S^ex) and Ef, i.e. Ea(S^ex) ≈ cEf.
文摘The available literature revealed a gap in reporting the rough rice drying kinetics parameters under isothermal conditions, particularly for Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112 and Titan) and the long-grain (Diamond and Wells) rough rice varieties were dried under isothermal conditions. The drying process occurred under 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C in a system emulating the thermogravimetric analyzer. Drying kinetics models were studied for four well-known models: Page, Newton, Logarithmic, and Henderson & Pabis. The drying kinetics constants were determined for the four studied models. The initial moisture content of rough rice was 28.2% db. Profound moisture reduction was observed during the first three hours of drying, followed by less moisture content reduction. The results showed that at the drying temperature of 100°C and after 6 hours of the drying process, the lowest moisture content reached 13.9% (db) for Titan rough rice. The drying rate of rough rice ranged between 7.41 and 2.01%/h during the first hour of drying under the studied temperature range of 40°C to 100°C. The drying rate was higher with the higher temperature levels during the first three hours. Among all the studied models, the Page, Newton, and Logarithmic models best fit 25%, 25%, and 50% of the twenty-eight studied cases. The challenge that arose from these results led to evolving a mathematical solution by joining the three models in one equation. The combined model showed the best fit for all the studied cases, with R<sup>2</sup> ranging between 0.9999 and 0.9954 for the medium- and long-grain rice varieties. Increasing the drying temperature increased the effective moisture diffusivity values. The highest effective moisture diffusivity of 18.104 × 10<sup>-9</sup> m<sup>2</sup>/s was obtained at the drying temperature of 100°C for medium-grain rice, Titan. The activation energy values ranged between 17.77 and 24.48 kJ/mol for the four rough rice varieties.