In order to well understand the elementary mechanisms that govern the hot working process of a V？5Cr？5Ti alloy （mass fraction, %）, thermal activation parameters under compression were measured in a temperature ran...In order to well understand the elementary mechanisms that govern the hot working process of a V？5Cr？5Ti alloy （mass fraction, %）, thermal activation parameters under compression were measured in a temperature range of 1373？1673 K by a Gleeble？3800 system. The results show that the stress exponentn is 4.87 and the activation energyQis 375.89 kJ/mol for the power law equation. The activation energy is determined as 288.34 kJ/mol, which is close to the self-diffusion energy of alloy （270？300 kJ/mol） by introducing a threshold stress（σ0） variable. The typical values of physical activation volume （Vp） and strain rate sensitivity （m） are measured as （120？700）b3 and 0.075？0.122, respectively, by the repeated stress relaxation tests. These activation parameters indicate that the rate controlling mechanism for V？5Cr？5Ti alloy compressed in ranges of 1373？1673 K and 0.001？1.0 s？1 is the dislocation climb by overcoming of forest dislocations.展开更多
In the background of little reuse and large stockpile for iron ore tailings, iron ore tailing from Chinese Tonghua were used as raw material to prepare cementitious materials. Cementitious properties of the iron ore t...In the background of little reuse and large stockpile for iron ore tailings, iron ore tailing from Chinese Tonghua were used as raw material to prepare cementitious materials. Cementitious properties of the iron ore tailings activated by compound thermal activation were studied. Testing methods, such as XRD, TG-DTA, and IR were used for researching the phase and structure variety of the iron ore railings in the process of compound thermal activation. The results reveal that a new cementitious material that contains 30wt% of the iron ore tailings can be obtained by compounded thermal activation, whose mortar strength can come up to the standard of 42.5 cement of China.展开更多
The effect of activation properties of the precursors of zeolite directly prepared from kaolin influenced by microwave field and conventional heating was investigated.XRD,TG-DSC,FT-IR,SEM,particle size analysis,specif...The effect of activation properties of the precursors of zeolite directly prepared from kaolin influenced by microwave field and conventional heating was investigated.XRD,TG-DSC,FT-IR,SEM,particle size analysis,specific surface area(BET),pore size distribution(BJH)and N2 adsorption-desorption were discussed to determine the optimal activation temperature.It is concluded that the conversion of kaolin to metakaolin in the microwave field is at 500°C holding for 30 min,which is 100°C lower than that in conventional calcination and 90 min shorter,and the phase transition process of kaolin under the effect of microwave field is the same as that of conventional heating method.SEM analysis indicates that the particle size is more uniform and agglomeration appears slightly in the microwave field.The N2 adsorption-desorption isotherm,BET and BJH of kaolin indicate that the pore properties are almost invariable regardless of calcination route during the process of calcining kaolin into metakaolin.It indicates that microwave calcination is superior to conventional calcination in the activation pathway of kaolin.It is attributed to microwave heating relying on objects to absorb microwave energy and convert it into thermal energy,which can simultaneously and uniformly heat the entire substance.展开更多
The aim of this investigation was to prepare geopolymeric precursor from vanadium tailing(VT)by thermal activation and modification.For activation,a homogeneous blend of VT and sodium hydroxide was calcinated at an el...The aim of this investigation was to prepare geopolymeric precursor from vanadium tailing(VT)by thermal activation and modification.For activation,a homogeneous blend of VT and sodium hydroxide was calcinated at an elevated temperature and then modified with metakaolin to produce a geopolymeric precursor.During the thermal activation,the VT was corroded by sodium hydroxide and then sodium silicate formed on the particle surfaces.After water was added,the sodium silicate coating dissolved to release silicon species,which created an alkaline solution environment.The metakaolin then dissolved in the alkaline environment to generate aluminum species,which was followed by geopolymerization.The VT particles were connected by a gel produced during geopolymerization,which yielded a geopolymer with excellent mechanical performance.This investigation not only improves the feasibility of using geopolymer technology for large-scale and in-situ applications,but also promotes the utilization of VT and other silica-rich solid wastes.展开更多
Papain (Papainase, EC 3.4.22.2) was immobilized on porous silica beads by cross linking with glutaraldehyde. The thermal activation of this immobilized papain in aqueous system was found at, a temperature range from 5...Papain (Papainase, EC 3.4.22.2) was immobilized on porous silica beads by cross linking with glutaraldehyde. The thermal activation of this immobilized papain in aqueous system was found at, a temperature range from 50 to 90 degrees C. The higher the temperature, the more active the immobilized papain will possess. At the same time, the durability of the immobilized papain on heating was greatly improved. The effect of additives and salts on the activity of the immobilized papain were also studied. The results showed that the additives and some of the salts studied could markedly enhance the activity of the immobilized papain at elevated temperature.展开更多
Variable temperature in situ FTIR spectroscopy has been used as the primary tool to investigate the effects of temperature(10 to 50 ℃) on formaldehyde dissociative adsorption and electro oxidation on the Ru(00...Variable temperature in situ FTIR spectroscopy has been used as the primary tool to investigate the effects of temperature(10 to 50 ℃) on formaldehyde dissociative adsorption and electro oxidation on the Ru(0001) electrode in perchloric acid solution, and the results were interpreted in terms of the surface chemistry of the Ru(0001) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that formaldehyde did undergo dissociative adsorption, even at -200 mV vs . Ag/AgCl, to form linear(CO L) and 3 fold hollow(CO H) binding CO adsorbates. In contrast to the adsorption of CO, it was found that increasing the temperature to 50 ℃ markedly increased the amount of CO adsorbates formed on the Ru(0001) surface from the adsorption of formaldehyde. On increasing the potential, the electro oxidation of the CO adsorbates to CO 2 took place via reaction with the active (1×1) O oxide. A significant increase in the surface reactivity was observed on the RuO 2(100) phase formed at higher potentials. Formic acid was detected as a partial oxidation product during formaldehyde electro oxidation. The data obtained at 50 ℃ are markedly different from those collected at 10 and 25 ℃ in terms of the amount of both CO 2 and formic acid formed and the adsorbed CO L and CO H species observed. These results were rationalized by the thermal effects on both the loosening of the CO adlayer and the activation of surface oxide on increasing the temperature.展开更多
The aftereffect field of thermal activation, which corresponds to the fluctuation field of a domain wall, is investigated via specific measurements of the magnetization behavior in PraFel4B nanocrystalline magnets. Th...The aftereffect field of thermal activation, which corresponds to the fluctuation field of a domain wall, is investigated via specific measurements of the magnetization behavior in PraFel4B nanocrystalline magnets. The thermal activation is a magnetization reversal arising from thermal fluctuation over an energy barrier to an equilibrate state. According to the magnetic viscosity and the field sweep rate dependence of the coercivity, the calculated values of the fluctuation field are lower than the aftereffect field and in a range between those of domain walls and individual grains. Based on these results, we propose that the magnetization reversal occurs in multiple ways involving grain activation and domain wall activation in thermal activation, and the thermal activation decreases the coercivity by-0.2 kOe in the PrzFe14B ribbons.展开更多
This paper investigates the thermal activation behaviour of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height by numerical simulation. The analytical Gaussian distribution model...This paper investigates the thermal activation behaviour of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height by numerical simulation. The analytical Gaussian distribution model predicted that the I-VT curves may intersect with the possibility of the negative thermal activation of current, but may be contradictory to the thermionic emission mechanism in a Schottky diode. It shows that the cause of the unphysical phenomenon is related to the incorrect calculation of current across very low barriers. It proposes that junction voltage Vj, excluding the voltage drop across series resistance from the external bias, is a crucial parameter for correct calculation of the current across very low barriers. For correctly employing the thermionic emission model, Vj needs to be smaller than the barrier height Ф. With proper scheme of series resistance connection where the condition of Vj 〉 Ф is guaranteed, I-V T curves of an inhomogeneous Schottky diode with a Gaussian distribution of barrier height have been simulated, which demonstrate normal thermal activation. Although the calculated results exclude the intersecting possibility of I-V T curves with an assumption of temperature-independent series resistance, it shows that the intersecting is possible when the series resistance has a positive temperature coefficient. Finally, the comparison of our numerical and analytical results indicates that the analytical Gaussian distribution model is valid and accurate in analysing I-V-T curves only for small barrier height inhomogeneity.展开更多
A formula is derived for determining the influence of temperature and loading rate on dynamic fracture toughness of a high strength low alloy steel (HQ785C) from thermal activation analysis of the experimental results...A formula is derived for determining the influence of temperature and loading rate on dynamic fracture toughness of a high strength low alloy steel (HQ785C) from thermal activation analysis of the experimental results of three-point bend specimens as well as introducing an Arrhenius formula. It is shown that the results obtained by the given formula are in good agreement with the experimental ones in the thermal activation region. The present method is also valuable to describe the relationship between dynamic fracture toughness and temperature and loading rate of other high strength low alloy steels.展开更多
Aluminum alloy 5083(AA5083)processed by large-scale Equal-channel angular pressing(ECAP)is an excellent engineering material with great prospects for industrial applications.An accurate assessment of the underlying co...Aluminum alloy 5083(AA5083)processed by large-scale Equal-channel angular pressing(ECAP)is an excellent engineering material with great prospects for industrial applications.An accurate assessment of the underlying constitutive relationships with easily determined material constants is critical for the predictive design and informed processing of such structural materials.To develop such a design framework,uniaxial dynamic compressive tests over a wide range of temperatures(293-573 K)were carried out for an ECAP-processed AA5083 alloy.Additionally,the microstructure before and after dynamic loading was characterized by SEM and TEM.Based on the experimental results,a new dynamic constitutive model,based on thermal activation theory,was established to describe the plastic flow behavior of the AA5083 alloy that incorporates the effects of plastic strain,temperature,and strain rate.The input parameters of the new model were determined using a particle swarm optimization(PSO)method.The model predictions show excellent agreement with experimental results,which suggests that the current predictive constitutive model is highly effective in reproducing the dynamic deformation behavior of the large-scale ECAP-processed AA5083.展开更多
In stress-augmented thermal activation, the activation energy barrier that controls the rate of atomic and molecular processes is reduced by the application of stress, with the result that the rate of these processes ...In stress-augmented thermal activation, the activation energy barrier that controls the rate of atomic and molecular processes is reduced by the application of stress, with the result that the rate of these processes increases exponentially with applied stress. This concept has particular relevance to Tribology, and since its development in the early twentieth century, it has been applied to develop important models of plastic flow, sliding friction, rheology, wear, and tribochemistry. This paper reviews the development of stress-augmented thermal activation and its application to all of these areas of Tribology. The strengths and limitations of the approach are then discussed and future directions considered. From the scientific point of view, the concept of stress-augmented thermal activation is important since it enables the development of models that describe macroscale tribological performance, such as friction coefficient or tribofilm formation, in terms of the structure and behaviour of individual atoms and molecules. This both helps us understand these processes at a fundamental level and also provides tools for the informed design of lubricants and surfaces.展开更多
Aggregation-induced thermally activated delayed fluorescence(TADF)phenomena have attracted extensive attention recently.In this paper,several theoretical models including monomer,dimer,and complex are used for the exp...Aggregation-induced thermally activated delayed fluorescence(TADF)phenomena have attracted extensive attention recently.In this paper,several theoretical models including monomer,dimer,and complex are used for the explanation of the luminescent properties of(R)-5-(9H-carbazol-9-yl)-2-(1,2,3,4-tetrahydronaphthalen-1-yl)isoindoline-1,3-dione((R)-ImNCz),which was recently reported[Chemical Engineering Journal 418129167(2021)].The polarizable continuum model(PCM)and the combined quantum mechanics and molecular mechanics(QM/MM)method are adopted in simulation of the property of the molecule in the gas phase,solvated in acetonitrile and in aggregation states.It is found that large spin–orbit coupling(SOC)constants and a smaller energy gap between the first singlet excited state and the first triplet excited state(△E_(st))in prism-like single crystals(SC_(p)-form)are responsible for the TADF of(R)-lmNCz,while no TADF is found in block-like single crystals(SC_(b)-form)with a larger △E_(st).The multiple ultralong phosphorescence(UOP)peaks in the spectrum are of complex origins,and they are related not only to ImNCz but also to a minor amount of impurities(ImNBd)in the crystal prepared in the laboratory.The dimer has similar phosphorescence emission wavelengths to the(R)-lmNCz-SC_(p) monomers.The complex composed of(R)-lmNCz and(R)-lmNBd contributes to the phosphorescent emission peak at about 600 nm,and the phosphorescent emission peak at about 650 nm is generated by(R)-lmNBd.This indicates that the impurity could also contribute to emission in molecular crystals.The present calculations clarify the relationship between the molecular aggregation and the light-emitting properties of the TADF emitters and will therefore be helpful for the design of potentially more useful TADF emitters.展开更多
AlN ceramics were prepared by plasma activation sintering(PAS)with compound additives yttrium acetylacetonate(Y(acac)_(3))and melamine(C_(3)H_(6)N_(6)).The effects of compound additives on the microstructure,density,a...AlN ceramics were prepared by plasma activation sintering(PAS)with compound additives yttrium acetylacetonate(Y(acac)_(3))and melamine(C_(3)H_(6)N_(6)).The effects of compound additives on the microstructure,density,and thermal properties of Al N ceramic were studied.Y(acac)3and C_(3)H_(6)N_(6)can form Y_(2)O_(3),residual organic carbon and reducing gas during the heating process,which improves the Al N sintering performance at a temperature of 1700℃and the bulk thermal conductivity.When the content of Y(acac)_(3)is 10 wt%and C_(3)H_(6)N_(6)is 3 wt%,the thermal conductivity of Al N ceramics is 105.6 W/(m·K),which is much higher than that of Al N ceramics with Y_(2)O_(3)under the same sintering conditions.This work provides theoretical reference for the preparation of high-performance Al N ceramic.展开更多
Red mud(RM)is a low-activity industrial solid waste,and its utilization as a resource is currently a hot topic.In this study,the micro characteristics of red mud at different calcination temperatures were analyzed usi...Red mud(RM)is a low-activity industrial solid waste,and its utilization as a resource is currently a hot topic.In this study,the micro characteristics of red mud at different calcination temperatures were analyzed using X-ray diffraction and scanning electron microscopy.The performance of calcined red mud was determined through mortar strength tests.Results indicate that high-temperature calcination can change the mineral composition and microstructure of red mud,and increase the surface roughness and specific surface area.At the optimal temperature of 700°C,the addition of calcined red mud still leads to a decrease in mortar strength,but its activity index and flexural coefficient increase by 16.2%and 11.9%with respect to uncalcined red mud,reaching values of 0.826 and 0.974,respectively.Compared with the control group,the synergistic activation of calcined red mud with slag can increase the compressive and flexural strength of the mortar by 12.9%and 1.5%,reaching 8.7 and 62.4 MPa,respectively.Correspondingly,the activity index and flexural coefficient of the calcined RM and GGBS(Ground Granulated Blast furnace Slag)mixtures also increase to 1.015 and 1.130,respectively.展开更多
In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlOx/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization pro...In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlOx/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.展开更多
Three kinds of triazine based organic molecules designed for thermally activated delayed fluorescence （TADF） emitters are investigated by first-principles calculations. An optimal Hartree-Fork （HF） method is adopt...Three kinds of triazine based organic molecules designed for thermally activated delayed fluorescence （TADF） emitters are investigated by first-principles calculations. An optimal Hartree-Fork （HF） method is adopted for the calculation of energy gap between the first singlet state （S1） and the first triplet state （T1）. The natural transition orbital, the electron- hole （e-h） distribution and the e-h overlap diagram indicate that the S1 states for the three systems include both charge-transfer and some localized excitation component. Further quantitative analysis of the excitation property is performed by introducing the index Ar and the integral of e-h overlap S. It is found that symmetric geometry is a necessary condition for TADF emitters, which can provide more delocalized transition orbitals and consequently a small S1-T1 energy gap. Artful inserting aromatic groups between donors and acceptors can significantly enhance the oscillator strength. Finally, the energy state structures calculated with the optimal HF method is presented, which can provide basis for the study of the dynamics of excited states.展开更多
To study active heat insulation roadway in high temperature mines,the typical high temperature roadway of−965 m in Zhujidong Coal Mine of Anhui,China,is selected as prototype.The ANSYS numerical simulation method is u...To study active heat insulation roadway in high temperature mines,the typical high temperature roadway of−965 m in Zhujidong Coal Mine of Anhui,China,is selected as prototype.The ANSYS numerical simulation method is used for sensitivity analysis of heat insulation layer with different thermal conductivity and thickness,as well as surrounding rock with different thermal conductivity and temperature on a heat-adjusting zone radius,surrounding rock temperature field and wall temperature.The results show that the heat-adjusting zone radius will entirely be in the right power index relationship to the ventilation time.Decrease in thermal conductivity and increase in thickness of insulation layer can effectively reduce the disturbance of airflow on the surrounding rock temperature,hence,beneficial for decreasing wall temperature.This favourable trend significantly decreases with ventilation time,increase in thermal conductivity and temperature of surrounding rock,heat-adjusting zone radius,surrounding rock temperature field,and wall temperature.Sensitivity analysis shows that the thermal physical properties of surrounding rock determine the temperature distribution of the roadway,hence,temperature of surrounding rock is considered as the most sensitive factor of all influencing factors.For the spray layer,thermal conductivity is more sensitive,compared to thickness.It is concluded that increase in the spray layer thickness is not as beneficial as using low thermal conductivity insulation material.Therefore,roadway preferential consideration should be given to the rocks with low temperature and thermal conductivity.The application of the insulation layer has positive significance for the thermal environment control in mine roadway,however,increase in the layer thickness without restriction has a limited effect on the thermal insulation.展开更多
Fluorescence/phosphorescence hybrid white organic light-emitting devices（WOLEDs） based on double emitting layers（EMLs） with high color stability are fabricated.The simplified EMLs consist of a non-doped blue therm...Fluorescence/phosphorescence hybrid white organic light-emitting devices（WOLEDs） based on double emitting layers（EMLs） with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence（TADF） layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone（DMAC-DPS） and an ultrathin non-doped yellow phosphorescence layer employing bis[2-（4-tertbutylphenyl）benzothiazolato-N,C2＇]iridium（acetylacetonate）（（tbt）_2Ir（acac））.Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline（Bphen） and 1,3,5-tris（2-Nphenylbenzimidazolyl） benzene（TPBi） are selected as the electron transporting layer（ETL）,and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l＇Eclairage（CIE） coordinates variation of（0.017,0.009） at a luminance ranging from 52 cd/m^2 to 6998 cd/m^2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency（EQE）,current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer（FRET）from DMAC-DPS to（tbt）_2Ir（acac） is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.展开更多
Using a walnut shellas a carbon source and ZnCl_2 as an activating agent,we resolved the temperature gradient problems of activated carbon in the microwave desorption process.An appropriate amount of silicon carbide w...Using a walnut shellas a carbon source and ZnCl_2 as an activating agent,we resolved the temperature gradient problems of activated carbon in the microwave desorption process.An appropriate amount of silicon carbide was added to prepare the composite activated carbon with high thermalconductivity while developing VOC adsorption-microwave regeneration technology.The experimentalresults show that the coefficient of thermalconductivity of SiC-AC is three times as much as those of AC and SY-6.When microwave power was 480 W in its microwave desorption,the temperature of the bed thermaldesorption was 10 ℃ to 30 ℃ below that of normalactivated carbon prepared in our laboratory.The toluene desorption activation energy was 16.05 k J·mol^（-1）,which was 15% less than the desorption activation energy of commercialactivated carbon.This study testified that the process could maintain its high adsorption and regeneration desorption performances.展开更多
Martensitic transformation behavior was studied for zirconia containing 4%～10% CeO2 (in mole fraction) by using a dilatometric method. The Ms (Martensite start temperature) decreased near linearly with increasing CeO...Martensitic transformation behavior was studied for zirconia containing 4%～10% CeO2 (in mole fraction) by using a dilatometric method. The Ms (Martensite start temperature) decreased near linearly with increasing CeO2. Different transformation modes were observed depending on the composition and cooling rate. ZrO2 containing 6% CeO2 showed isothermal transformation behavior, whereas ZrO2 containing 9% and 10% CeO2 showed athermal transformation behavior. However, ZrO2 containing 8% CeO2 showed either isothermal or athermal transformations behavior depending on the cooling rate. A TTT (Time-Temperature-Transformation) diagram was proposed for ZrO2 containing 8% CeO2.展开更多
基金Project(11105127)supported by the National Natural Science Foundation of China
文摘In order to well understand the elementary mechanisms that govern the hot working process of a V？5Cr？5Ti alloy （mass fraction, %）, thermal activation parameters under compression were measured in a temperature range of 1373？1673 K by a Gleeble？3800 system. The results show that the stress exponentn is 4.87 and the activation energyQis 375.89 kJ/mol for the power law equation. The activation energy is determined as 288.34 kJ/mol, which is close to the self-diffusion energy of alloy （270？300 kJ/mol） by introducing a threshold stress（σ0） variable. The typical values of physical activation volume （Vp） and strain rate sensitivity （m） are measured as （120？700）b3 and 0.075？0.122, respectively, by the repeated stress relaxation tests. These activation parameters indicate that the rate controlling mechanism for V？5Cr？5Ti alloy compressed in ranges of 1373？1673 K and 0.001？1.0 s？1 is the dislocation climb by overcoming of forest dislocations.
基金supported by the National Nature Science Foundation of China (No.50674062)the National Key Technologies R&D Program of China (No.2006BAC21B03)the Post doctoral Science Foundation (No.20070420354)
文摘In the background of little reuse and large stockpile for iron ore tailings, iron ore tailing from Chinese Tonghua were used as raw material to prepare cementitious materials. Cementitious properties of the iron ore tailings activated by compound thermal activation were studied. Testing methods, such as XRD, TG-DTA, and IR were used for researching the phase and structure variety of the iron ore railings in the process of compound thermal activation. The results reveal that a new cementitious material that contains 30wt% of the iron ore tailings can be obtained by compounded thermal activation, whose mortar strength can come up to the standard of 42.5 cement of China.
基金Projects(51604135,51504116)supported by the National Natural Science Foundational of ChinaProject(YNWR-QNBJ-2018-323)supported by the Yunan Ten Thousand Talents Plan Young&Elite Talents Project,China。
文摘The effect of activation properties of the precursors of zeolite directly prepared from kaolin influenced by microwave field and conventional heating was investigated.XRD,TG-DSC,FT-IR,SEM,particle size analysis,specific surface area(BET),pore size distribution(BJH)and N2 adsorption-desorption were discussed to determine the optimal activation temperature.It is concluded that the conversion of kaolin to metakaolin in the microwave field is at 500°C holding for 30 min,which is 100°C lower than that in conventional calcination and 90 min shorter,and the phase transition process of kaolin under the effect of microwave field is the same as that of conventional heating method.SEM analysis indicates that the particle size is more uniform and agglomeration appears slightly in the microwave field.The N2 adsorption-desorption isotherm,BET and BJH of kaolin indicate that the pore properties are almost invariable regardless of calcination route during the process of calcining kaolin into metakaolin.It indicates that microwave calcination is superior to conventional calcination in the activation pathway of kaolin.It is attributed to microwave heating relying on objects to absorb microwave energy and convert it into thermal energy,which can simultaneously and uniformly heat the entire substance.
基金This work was financially supported by the Major Tech-nical Innovation Project of Hubei Province,China(No.2018ACA157)the National Natural Science Foundation of China(No.51874222)the Excellent Dissertation Cul-tivation Funds of Wuhan University of Technology(No.2018-YS-052).
文摘The aim of this investigation was to prepare geopolymeric precursor from vanadium tailing(VT)by thermal activation and modification.For activation,a homogeneous blend of VT and sodium hydroxide was calcinated at an elevated temperature and then modified with metakaolin to produce a geopolymeric precursor.During the thermal activation,the VT was corroded by sodium hydroxide and then sodium silicate formed on the particle surfaces.After water was added,the sodium silicate coating dissolved to release silicon species,which created an alkaline solution environment.The metakaolin then dissolved in the alkaline environment to generate aluminum species,which was followed by geopolymerization.The VT particles were connected by a gel produced during geopolymerization,which yielded a geopolymer with excellent mechanical performance.This investigation not only improves the feasibility of using geopolymer technology for large-scale and in-situ applications,but also promotes the utilization of VT and other silica-rich solid wastes.
基金This research was supported by the Foundation of State Education Committee of China.
文摘Papain (Papainase, EC 3.4.22.2) was immobilized on porous silica beads by cross linking with glutaraldehyde. The thermal activation of this immobilized papain in aqueous system was found at, a temperature range from 50 to 90 degrees C. The higher the temperature, the more active the immobilized papain will possess. At the same time, the durability of the immobilized papain on heating was greatly improved. The effect of additives and salts on the activity of the immobilized papain were also studied. The results showed that the additives and some of the salts studied could markedly enhance the activity of the immobilized papain at elevated temperature.
文摘Variable temperature in situ FTIR spectroscopy has been used as the primary tool to investigate the effects of temperature(10 to 50 ℃) on formaldehyde dissociative adsorption and electro oxidation on the Ru(0001) electrode in perchloric acid solution, and the results were interpreted in terms of the surface chemistry of the Ru(0001) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that formaldehyde did undergo dissociative adsorption, even at -200 mV vs . Ag/AgCl, to form linear(CO L) and 3 fold hollow(CO H) binding CO adsorbates. In contrast to the adsorption of CO, it was found that increasing the temperature to 50 ℃ markedly increased the amount of CO adsorbates formed on the Ru(0001) surface from the adsorption of formaldehyde. On increasing the potential, the electro oxidation of the CO adsorbates to CO 2 took place via reaction with the active (1×1) O oxide. A significant increase in the surface reactivity was observed on the RuO 2(100) phase formed at higher potentials. Formic acid was detected as a partial oxidation product during formaldehyde electro oxidation. The data obtained at 50 ℃ are markedly different from those collected at 10 and 25 ℃ in terms of the amount of both CO 2 and formic acid formed and the adsorbed CO L and CO H species observed. These results were rationalized by the thermal effects on both the loosening of the CO adlayer and the activation of surface oxide on increasing the temperature.
基金Project supported by the Knowledge Innovation Project of the Chinese Academy of Sciences and the National Basic Research Program of China
文摘The aftereffect field of thermal activation, which corresponds to the fluctuation field of a domain wall, is investigated via specific measurements of the magnetization behavior in PraFel4B nanocrystalline magnets. The thermal activation is a magnetization reversal arising from thermal fluctuation over an energy barrier to an equilibrate state. According to the magnetic viscosity and the field sweep rate dependence of the coercivity, the calculated values of the fluctuation field are lower than the aftereffect field and in a range between those of domain walls and individual grains. Based on these results, we propose that the magnetization reversal occurs in multiple ways involving grain activation and domain wall activation in thermal activation, and the thermal activation decreases the coercivity by-0.2 kOe in the PrzFe14B ribbons.
基金supported by Shanghai-Applied Materials Research and Development Fund (Grant Nos.07SA06 and 09700714200)Fok Ying Tong Education Foundation (Grant No.114006)
文摘This paper investigates the thermal activation behaviour of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height by numerical simulation. The analytical Gaussian distribution model predicted that the I-VT curves may intersect with the possibility of the negative thermal activation of current, but may be contradictory to the thermionic emission mechanism in a Schottky diode. It shows that the cause of the unphysical phenomenon is related to the incorrect calculation of current across very low barriers. It proposes that junction voltage Vj, excluding the voltage drop across series resistance from the external bias, is a crucial parameter for correct calculation of the current across very low barriers. For correctly employing the thermionic emission model, Vj needs to be smaller than the barrier height Ф. With proper scheme of series resistance connection where the condition of Vj 〉 Ф is guaranteed, I-V T curves of an inhomogeneous Schottky diode with a Gaussian distribution of barrier height have been simulated, which demonstrate normal thermal activation. Although the calculated results exclude the intersecting possibility of I-V T curves with an assumption of temperature-independent series resistance, it shows that the intersecting is possible when the series resistance has a positive temperature coefficient. Finally, the comparison of our numerical and analytical results indicates that the analytical Gaussian distribution model is valid and accurate in analysing I-V-T curves only for small barrier height inhomogeneity.
文摘A formula is derived for determining the influence of temperature and loading rate on dynamic fracture toughness of a high strength low alloy steel (HQ785C) from thermal activation analysis of the experimental results of three-point bend specimens as well as introducing an Arrhenius formula. It is shown that the results obtained by the given formula are in good agreement with the experimental ones in the thermal activation region. The present method is also valuable to describe the relationship between dynamic fracture toughness and temperature and loading rate of other high strength low alloy steels.
文摘Aluminum alloy 5083(AA5083)processed by large-scale Equal-channel angular pressing(ECAP)is an excellent engineering material with great prospects for industrial applications.An accurate assessment of the underlying constitutive relationships with easily determined material constants is critical for the predictive design and informed processing of such structural materials.To develop such a design framework,uniaxial dynamic compressive tests over a wide range of temperatures(293-573 K)were carried out for an ECAP-processed AA5083 alloy.Additionally,the microstructure before and after dynamic loading was characterized by SEM and TEM.Based on the experimental results,a new dynamic constitutive model,based on thermal activation theory,was established to describe the plastic flow behavior of the AA5083 alloy that incorporates the effects of plastic strain,temperature,and strain rate.The input parameters of the new model were determined using a particle swarm optimization(PSO)method.The model predictions show excellent agreement with experimental results,which suggests that the current predictive constitutive model is highly effective in reproducing the dynamic deformation behavior of the large-scale ECAP-processed AA5083.
文摘In stress-augmented thermal activation, the activation energy barrier that controls the rate of atomic and molecular processes is reduced by the application of stress, with the result that the rate of these processes increases exponentially with applied stress. This concept has particular relevance to Tribology, and since its development in the early twentieth century, it has been applied to develop important models of plastic flow, sliding friction, rheology, wear, and tribochemistry. This paper reviews the development of stress-augmented thermal activation and its application to all of these areas of Tribology. The strengths and limitations of the approach are then discussed and future directions considered. From the scientific point of view, the concept of stress-augmented thermal activation is important since it enables the development of models that describe macroscale tribological performance, such as friction coefficient or tribofilm formation, in terms of the structure and behaviour of individual atoms and molecules. This both helps us understand these processes at a fundamental level and also provides tools for the informed design of lubricants and surfaces.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974216,11874242,21933002 and 11904210)Shandong Provincial Natural Science Foundation,China(Grant No.ZR2019MA056)+1 种基金the support of the Taishan Scholar Project of Shandong Provincethe project funded by China Postdoctoral Science Foundation(Grant No.2018M642689)。
文摘Aggregation-induced thermally activated delayed fluorescence(TADF)phenomena have attracted extensive attention recently.In this paper,several theoretical models including monomer,dimer,and complex are used for the explanation of the luminescent properties of(R)-5-(9H-carbazol-9-yl)-2-(1,2,3,4-tetrahydronaphthalen-1-yl)isoindoline-1,3-dione((R)-ImNCz),which was recently reported[Chemical Engineering Journal 418129167(2021)].The polarizable continuum model(PCM)and the combined quantum mechanics and molecular mechanics(QM/MM)method are adopted in simulation of the property of the molecule in the gas phase,solvated in acetonitrile and in aggregation states.It is found that large spin–orbit coupling(SOC)constants and a smaller energy gap between the first singlet excited state and the first triplet excited state(△E_(st))in prism-like single crystals(SC_(p)-form)are responsible for the TADF of(R)-lmNCz,while no TADF is found in block-like single crystals(SC_(b)-form)with a larger △E_(st).The multiple ultralong phosphorescence(UOP)peaks in the spectrum are of complex origins,and they are related not only to ImNCz but also to a minor amount of impurities(ImNBd)in the crystal prepared in the laboratory.The dimer has similar phosphorescence emission wavelengths to the(R)-lmNCz-SC_(p) monomers.The complex composed of(R)-lmNCz and(R)-lmNBd contributes to the phosphorescent emission peak at about 600 nm,and the phosphorescent emission peak at about 650 nm is generated by(R)-lmNBd.This indicates that the impurity could also contribute to emission in molecular crystals.The present calculations clarify the relationship between the molecular aggregation and the light-emitting properties of the TADF emitters and will therefore be helpful for the design of potentially more useful TADF emitters.
基金National Natural Science Foundation of China(Nos.51872217,51972246)the Guangdong Major Project of Basic and Applied Basic Research(Nos.2021B0301030001)。
文摘AlN ceramics were prepared by plasma activation sintering(PAS)with compound additives yttrium acetylacetonate(Y(acac)_(3))and melamine(C_(3)H_(6)N_(6)).The effects of compound additives on the microstructure,density,and thermal properties of Al N ceramic were studied.Y(acac)3and C_(3)H_(6)N_(6)can form Y_(2)O_(3),residual organic carbon and reducing gas during the heating process,which improves the Al N sintering performance at a temperature of 1700℃and the bulk thermal conductivity.When the content of Y(acac)_(3)is 10 wt%and C_(3)H_(6)N_(6)is 3 wt%,the thermal conductivity of Al N ceramics is 105.6 W/(m·K),which is much higher than that of Al N ceramics with Y_(2)O_(3)under the same sintering conditions.This work provides theoretical reference for the preparation of high-performance Al N ceramic.
基金“Key Science and Technology Project of Guangxi Department of Communications-Technology Development and Application of Cement Red Clay Stabilized Sea Sand Semi-Rigid Subgrade”(Grant:Gui Jiaotong 2020-No.150)“Key Science and Technology Project of Guangxi Department of Transportation-Key Technologies and Application Demonstrations for the Multi-Solid Waste Co-Processing of Bayer Red Mud in Large-Scale Road Construction”(Grant:Gui Jiaotong 2021-No.148).
文摘Red mud(RM)is a low-activity industrial solid waste,and its utilization as a resource is currently a hot topic.In this study,the micro characteristics of red mud at different calcination temperatures were analyzed using X-ray diffraction and scanning electron microscopy.The performance of calcined red mud was determined through mortar strength tests.Results indicate that high-temperature calcination can change the mineral composition and microstructure of red mud,and increase the surface roughness and specific surface area.At the optimal temperature of 700°C,the addition of calcined red mud still leads to a decrease in mortar strength,but its activity index and flexural coefficient increase by 16.2%and 11.9%with respect to uncalcined red mud,reaching values of 0.826 and 0.974,respectively.Compared with the control group,the synergistic activation of calcined red mud with slag can increase the compressive and flexural strength of the mortar by 12.9%and 1.5%,reaching 8.7 and 62.4 MPa,respectively.Correspondingly,the activity index and flexural coefficient of the calcined RM and GGBS(Ground Granulated Blast furnace Slag)mixtures also increase to 1.015 and 1.130,respectively.
基金supported by the National Natural Science Foundation of China (Grant No 50671048)
文摘In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlOx/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.
文摘Three kinds of triazine based organic molecules designed for thermally activated delayed fluorescence （TADF） emitters are investigated by first-principles calculations. An optimal Hartree-Fork （HF） method is adopted for the calculation of energy gap between the first singlet state （S1） and the first triplet state （T1）. The natural transition orbital, the electron- hole （e-h） distribution and the e-h overlap diagram indicate that the S1 states for the three systems include both charge-transfer and some localized excitation component. Further quantitative analysis of the excitation property is performed by introducing the index Ar and the integral of e-h overlap S. It is found that symmetric geometry is a necessary condition for TADF emitters, which can provide more delocalized transition orbitals and consequently a small S1-T1 energy gap. Artful inserting aromatic groups between donors and acceptors can significantly enhance the oscillator strength. Finally, the energy state structures calculated with the optimal HF method is presented, which can provide basis for the study of the dynamics of excited states.
基金This work was supported by the National Natural Science Foundation of China(51774011)Funding Project of Anhui University of Science and Technology(QN2019115)Introduced Research Funding of Anhui University of Science and Technology(13190022).
文摘To study active heat insulation roadway in high temperature mines,the typical high temperature roadway of−965 m in Zhujidong Coal Mine of Anhui,China,is selected as prototype.The ANSYS numerical simulation method is used for sensitivity analysis of heat insulation layer with different thermal conductivity and thickness,as well as surrounding rock with different thermal conductivity and temperature on a heat-adjusting zone radius,surrounding rock temperature field and wall temperature.The results show that the heat-adjusting zone radius will entirely be in the right power index relationship to the ventilation time.Decrease in thermal conductivity and increase in thickness of insulation layer can effectively reduce the disturbance of airflow on the surrounding rock temperature,hence,beneficial for decreasing wall temperature.This favourable trend significantly decreases with ventilation time,increase in thermal conductivity and temperature of surrounding rock,heat-adjusting zone radius,surrounding rock temperature field,and wall temperature.Sensitivity analysis shows that the thermal physical properties of surrounding rock determine the temperature distribution of the roadway,hence,temperature of surrounding rock is considered as the most sensitive factor of all influencing factors.For the spray layer,thermal conductivity is more sensitive,compared to thickness.It is concluded that increase in the spray layer thickness is not as beneficial as using low thermal conductivity insulation material.Therefore,roadway preferential consideration should be given to the rocks with low temperature and thermal conductivity.The application of the insulation layer has positive significance for the thermal environment control in mine roadway,however,increase in the layer thickness without restriction has a limited effect on the thermal insulation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61675041 and 61605253)the Foundation for Innovation Research Groups of the National Natural Science Foundation of China(Grant No.61421002)the Science&Technology Department Program of Sichuan Province,China(Grant No.2016HH0027)
文摘Fluorescence/phosphorescence hybrid white organic light-emitting devices（WOLEDs） based on double emitting layers（EMLs） with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence（TADF） layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone（DMAC-DPS） and an ultrathin non-doped yellow phosphorescence layer employing bis[2-（4-tertbutylphenyl）benzothiazolato-N,C2＇]iridium（acetylacetonate）（（tbt）_2Ir（acac））.Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline（Bphen） and 1,3,5-tris（2-Nphenylbenzimidazolyl） benzene（TPBi） are selected as the electron transporting layer（ETL）,and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l＇Eclairage（CIE） coordinates variation of（0.017,0.009） at a luminance ranging from 52 cd/m^2 to 6998 cd/m^2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency（EQE）,current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer（FRET）from DMAC-DPS to（tbt）_2Ir（acac） is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.
基金Funded by the National High Technology Research and Development Program of China("863"Program)(No.2006AA06A310)
文摘Using a walnut shellas a carbon source and ZnCl_2 as an activating agent,we resolved the temperature gradient problems of activated carbon in the microwave desorption process.An appropriate amount of silicon carbide was added to prepare the composite activated carbon with high thermalconductivity while developing VOC adsorption-microwave regeneration technology.The experimentalresults show that the coefficient of thermalconductivity of SiC-AC is three times as much as those of AC and SY-6.When microwave power was 480 W in its microwave desorption,the temperature of the bed thermaldesorption was 10 ℃ to 30 ℃ below that of normalactivated carbon prepared in our laboratory.The toluene desorption activation energy was 16.05 k J·mol^（-1）,which was 15% less than the desorption activation energy of commercialactivated carbon.This study testified that the process could maintain its high adsorption and regeneration desorption performances.
文摘Martensitic transformation behavior was studied for zirconia containing 4%～10% CeO2 (in mole fraction) by using a dilatometric method. The Ms (Martensite start temperature) decreased near linearly with increasing CeO2. Different transformation modes were observed depending on the composition and cooling rate. ZrO2 containing 6% CeO2 showed isothermal transformation behavior, whereas ZrO2 containing 9% and 10% CeO2 showed athermal transformation behavior. However, ZrO2 containing 8% CeO2 showed either isothermal or athermal transformations behavior depending on the cooling rate. A TTT (Time-Temperature-Transformation) diagram was proposed for ZrO2 containing 8% CeO2.
