Most Mediterranean regions face a high risk to forest fires, estimation and anticipation of this risk modeled as a stochastic propagation process reproduces well some fire properties. This model needs information on t...Most Mediterranean regions face a high risk to forest fires, estimation and anticipation of this risk modeled as a stochastic propagation process reproduces well some fire properties. This model needs information on the behavior of the bio-physical properties of vegetation associated to combustion. An experimental study to analyze the structure of a leaf of Laurel shrub at different biological stages is presented; it allows following the structural exchanges induced on the leaf by the effect of increasing temperature. For this purpose, both dielectric and TGA （Thermogravimetric Analysis）/DTA （Differentialthermal Analysis） was performed to a better understanding of the pyrolysis phenomenon. The results obtained provide information on the process of thermal degradation caused by fire. The evolution of the leaf impedance as a function of the applied frequency characterizes the moisture loss in plant species during pyrolysis. The dielectric response confirms the proposition to the equivalent circuit of the leaf as a composite of liquid and solid parts. The TGA/DTA results detected the behaviour of the solid parts in the fire under a constant heating rate, and were able to show all the transformation subjected by the Laurel leaf until ignition and all the gases released during it.展开更多
This work presents an integrated microsensor that combines the dual characterization capabilities of thermogravimetric analysis(TGA)and differential thermal analysis(DTA).We integrated two pairs of thermocouples,heati...This work presents an integrated microsensor that combines the dual characterization capabilities of thermogravimetric analysis(TGA)and differential thermal analysis(DTA).We integrated two pairs of thermocouples,heating resistors,and resonant drive/detection resistors into a single microcantilever,where the cantilever resonant frequency shifts respond to the mass change and the output voltage of the integrated thermocouples respond to the sample temperature.This integration enables programmable temperature control,temperature variation,and mass detection on a single chip.Our chip can achieve heating and cooling rates above 600°C/min,which is significantly faster than commercial instruments with satisfactory measurement accuracy.The integrated polysilicon thermocouples bring high power responsivity of 6 V/W,making them suitable for highly sensitive DTA measurements on a chip.Moreover,the cantilever offers picogram(10–12g)level mass resolution,reducing sample consumption from milligrams to nanogram levels.Additionally,the on-chip sample heating allows for easy observation of sample morphological evolution during heating under an optical microscope.We validated the dual functionality by conducting TGA measurements on a standard sample of calcium oxalate monohydrate(CaC2O4∙H2O)and DTA measurements on high-purity indium(In)and tin(Sn).The results indicate consistent measurements with the true values of the standard sample and high measurement efficiency.Our integrated cantilever chip is anticipated to have broad applications in high-performance and efficient TGA and DTA characterization.展开更多
The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain stru...The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis （DTA） experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al6（Mn,Fe） giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.展开更多
Solidification process of A357 alloy with Sr addition was investigated in this paper.In particular,the effects of strontium and cooling rate on α-Al dendrite and Al-Si eutectic characteristic temperature were charact...Solidification process of A357 alloy with Sr addition was investigated in this paper.In particular,the effects of strontium and cooling rate on α-Al dendrite and Al-Si eutectic characteristic temperature were characterized by differential thermal analysis(DTA).Sr addition not only modifies the Al-Si eutectic,but also affects the morphology and structure of primary α-Al dendrite.Sr decreases the growth temperature of α-Al dendrite and Al-Si eutectic,and it also affects the dendrite growth mechanism.It has been found that such effect becomes more significant with higher cooling rate.展开更多
Two kinds of activated ways are used to prepare activated coal gangue fine powder, one is calcining coal gangue at 800℃ （gangue A）, and the other is calcining coal gangue with a certain calcite at 800℃ （gangue B...Two kinds of activated ways are used to prepare activated coal gangue fine powder, one is calcining coal gangue at 800℃ （gangue A）, and the other is calcining coal gangue with a certain calcite at 800℃ （gangue B）. The experiment shows that strengths of blended cement mortar with coal gangue B are higher than that of blended cement with coal gangue A. Hydration of cements with the two kinds of activated coal gangue is investigated through a differential thermal analysis. The weight loss due to Ca（OH）2 decomposition of hydration products by differential thermal analysis/thermo gravimetric （DTA/TG） can be used to quantify the pozzolanic reaction. A new method based on the composition of hydration cement is proposed to determine the degree of pozzolanic reaction. The results obtained suggest that the degree of pozzolanic reaction of gangue B is faster than that of gangue A.展开更多
The phase diagram of the CsBr-CaBr2 system was re-determined by using differential thermal analysis and high ternperature and room ternperature X-ray diffraction analysis. It is concluded that there are three intermed...The phase diagram of the CsBr-CaBr2 system was re-determined by using differential thermal analysis and high ternperature and room ternperature X-ray diffraction analysis. It is concluded that there are three intermediate compounds in this system： a.congruently melting compound, CsCaBr3, with a melting point of 823℃ and two incongruently melting compounds, Cs2CaBr4 and Cs3Ca2Br7, whose peritectic points being 597℃ and 635℃, respectively. X-ray diffraction analysis indicated that compound CsCaBr3 is of slightly distorted perovskite structure.展开更多
Two kinds of experimental methods were tried in the present work:(i)the powder metallurgy method combined with differential thermal analysis(DTA)to determine the metastable liquidus miscibility gap for a Fe–Cu binary...Two kinds of experimental methods were tried in the present work:(i)the powder metallurgy method combined with differential thermal analysis(DTA)to determine the metastable liquidus miscibility gap for a Fe–Cu binary system and(ii)the high-temperature melting method combined with isothermal treatment to determine the stable liquidus miscibility gap for a Fe–Sn binary system.The experimental method was adopted according to the characteristics of the liquidus miscibility gap of the specific system.Using the powder metallurgy method,a uniform microstructure morphology and chemical composition was obtained in the DTA specimen,and the phase-separation temperature of the supercooled metastable liquid was measured.The isothermal treatment was applied for the samples inside the stable liquidus miscibility gap;here,equilibrated compositions were reached,and a layered morphology was formed after rapid cooling.The liquid miscibility gaps of the Fe–Cu and Fe–Sn binary systems were measured,and the peak temperatures of the corresponding miscibility gaps were determined to be about 1417°C at x(Cu)=0.465 at%and 1350°C at x(Sn)=0.487 at%,respectively.On the basis of the experimental results,both the Fe–Cu and the Fe–Sn binary systems were thermodynamically assessed.展开更多
The damping performance evaluation for electromechanical oscillations in power systems is crucial for the stable operation of modern power systems.In this paper,the connection between two commonly-used damping perform...The damping performance evaluation for electromechanical oscillations in power systems is crucial for the stable operation of modern power systems.In this paper,the connection between two commonly-used damping performance evaluation methods,i.e.,the damping torque analysis(DTA)and energy flow analysis(EFA),are systematically examined and revealed for the better understanding of the oscillatory damping mechanism.First,a concept of the aggregated damping torque coefficient is proposed and derived based on DTA of multi-machine power systems,which can characterize the integration effect of the damping contribution from the whole power system.Then,the pre-processing of measurements at the terminal of a local generator is conducted for EFA,and a concept of the frequency-decomposed energy attenuation coefficient is defined to screen the damping contribution with respect to the interested frequency.On this basis,the frequency spectrum analysis of the energy attenuation coefficient is employed to rigorously prove that the results of DTA and EFA are essentially equivalent,which is valid for arbitrary types of synchronous generator models in multi-machine power systems.Additionally,the consistency between the aggregated damping torque coefficient and frequency-decomposed energy attenuation coefficient is further verified by the numerical calculation in case studies.The relationship between the proposed coefficients and the eigenvalue(or damping ratio)is finally revealed,which consolidates the application of the proposed concepts in the damping performance evaluation.展开更多
Various bulk and transparent glasses were prepared by rapid melt quenching technique in the glass system 55[(Pb_(x)Bi_(1-x))TiO_(3)]-44[2Si_(O)2B_(2)O_(3)]-La2O3(x=0-0.7).The X-ray diffraction(XRD)studies of the glass...Various bulk and transparent glasses were prepared by rapid melt quenching technique in the glass system 55[(Pb_(x)Bi_(1-x))TiO_(3)]-44[2Si_(O)2B_(2)O_(3)]-La2O3(x=0-0.7).The X-ray diffraction(XRD)studies of the glass samples confirmed the amorphous nature.The differential thermal analyses(DTA)were carried out from room temperature to 900℃with a heating rate of 10℃/min.The DTA patterns of the samples showed one or more exothermic sharp peaks shifting towards lower temperature side with increasing concentration of bismuth oxide(BiO).On the basis of DTA results,the solid solution of bismuth titanum oxide(Bi_(2)Ti_(2)O_(7))/lead bismuth titanium oxide(Pb3Bi4Ti6O21)was precipitated in borosilicate glassy matrix as a major phase.The glasses were subjected to 4 h and 8 h heat treatment schedules to convert into glass ceramics.XRD analysis of these glass ceramic samples showed that the major crystalline phase of the entire glass ceramic samples with 0≤x≤0.5 is found to have cubic crystal structure,while it is tetragonal for glass ceramic sample with x=0.7.The scanning electron microscopy(SEM)micrographs indicated the uniform distribution of Bi_(2)Ti_(2)O_(7)and Pb3Bi4Ti6O21 crystallites in the glassy matrix.展开更多
文摘Most Mediterranean regions face a high risk to forest fires, estimation and anticipation of this risk modeled as a stochastic propagation process reproduces well some fire properties. This model needs information on the behavior of the bio-physical properties of vegetation associated to combustion. An experimental study to analyze the structure of a leaf of Laurel shrub at different biological stages is presented; it allows following the structural exchanges induced on the leaf by the effect of increasing temperature. For this purpose, both dielectric and TGA （Thermogravimetric Analysis）/DTA （Differentialthermal Analysis） was performed to a better understanding of the pyrolysis phenomenon. The results obtained provide information on the process of thermal degradation caused by fire. The evolution of the leaf impedance as a function of the applied frequency characterizes the moisture loss in plant species during pyrolysis. The dielectric response confirms the proposition to the equivalent circuit of the leaf as a composite of liquid and solid parts. The TGA/DTA results detected the behaviour of the solid parts in the fire under a constant heating rate, and were able to show all the transformation subjected by the Laurel leaf until ignition and all the gases released during it.
基金funded by the National Key R&D Program of China(2021YFB3200800)National Natural Science Foundation of China(62227815,61831021,62271473,62104241,U21A20500)Innovation Team and Talents Cultivation Program of National Administration of Traditional Chinese Medicine(ZYYCXTD-D-202002,ZYYCXTD-D-202003).
文摘This work presents an integrated microsensor that combines the dual characterization capabilities of thermogravimetric analysis(TGA)and differential thermal analysis(DTA).We integrated two pairs of thermocouples,heating resistors,and resonant drive/detection resistors into a single microcantilever,where the cantilever resonant frequency shifts respond to the mass change and the output voltage of the integrated thermocouples respond to the sample temperature.This integration enables programmable temperature control,temperature variation,and mass detection on a single chip.Our chip can achieve heating and cooling rates above 600°C/min,which is significantly faster than commercial instruments with satisfactory measurement accuracy.The integrated polysilicon thermocouples bring high power responsivity of 6 V/W,making them suitable for highly sensitive DTA measurements on a chip.Moreover,the cantilever offers picogram(10–12g)level mass resolution,reducing sample consumption from milligrams to nanogram levels.Additionally,the on-chip sample heating allows for easy observation of sample morphological evolution during heating under an optical microscope.We validated the dual functionality by conducting TGA measurements on a standard sample of calcium oxalate monohydrate(CaC2O4∙H2O)and DTA measurements on high-purity indium(In)and tin(Sn).The results indicate consistent measurements with the true values of the standard sample and high measurement efficiency.Our integrated cantilever chip is anticipated to have broad applications in high-performance and efficient TGA and DTA characterization.
基金The Swedish KK-foundation, and the European Regional Development Fund supported this research financially
文摘The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis （DTA） experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al6（Mn,Fe） giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.
基金supported by the Natural Science Fund of Shanxi Province (No. SJ08-ZT05) Open Research Fund of Shenzhen Key Laboratory of Special Functional Materials,Shenzhen University (No. 2T0804)
文摘Solidification process of A357 alloy with Sr addition was investigated in this paper.In particular,the effects of strontium and cooling rate on α-Al dendrite and Al-Si eutectic characteristic temperature were characterized by differential thermal analysis(DTA).Sr addition not only modifies the Al-Si eutectic,but also affects the morphology and structure of primary α-Al dendrite.Sr decreases the growth temperature of α-Al dendrite and Al-Si eutectic,and it also affects the dendrite growth mechanism.It has been found that such effect becomes more significant with higher cooling rate.
基金supported by the Opening Project of State Key Laboratory of Green Building Materials (Grant No.GBM-08-KF105)the Engineering Research Center of Railway Environmental Vibration and Noise, Ministry of Education (Grant No.01306020)
文摘Two kinds of activated ways are used to prepare activated coal gangue fine powder, one is calcining coal gangue at 800℃ （gangue A）, and the other is calcining coal gangue with a certain calcite at 800℃ （gangue B）. The experiment shows that strengths of blended cement mortar with coal gangue B are higher than that of blended cement with coal gangue A. Hydration of cements with the two kinds of activated coal gangue is investigated through a differential thermal analysis. The weight loss due to Ca（OH）2 decomposition of hydration products by differential thermal analysis/thermo gravimetric （DTA/TG） can be used to quantify the pozzolanic reaction. A new method based on the composition of hydration cement is proposed to determine the degree of pozzolanic reaction. The results obtained suggest that the degree of pozzolanic reaction of gangue B is faster than that of gangue A.
文摘The phase diagram of the CsBr-CaBr2 system was re-determined by using differential thermal analysis and high ternperature and room ternperature X-ray diffraction analysis. It is concluded that there are three intermediate compounds in this system： a.congruently melting compound, CsCaBr3, with a melting point of 823℃ and two incongruently melting compounds, Cs2CaBr4 and Cs3Ca2Br7, whose peritectic points being 597℃ and 635℃, respectively. X-ray diffraction analysis indicated that compound CsCaBr3 is of slightly distorted perovskite structure.
基金supported by National Key Research and Development Program of China (No. 2016YFB0701201)National Natural Science Foundation of China (No. 51271027)
文摘Two kinds of experimental methods were tried in the present work:(i)the powder metallurgy method combined with differential thermal analysis(DTA)to determine the metastable liquidus miscibility gap for a Fe–Cu binary system and(ii)the high-temperature melting method combined with isothermal treatment to determine the stable liquidus miscibility gap for a Fe–Sn binary system.The experimental method was adopted according to the characteristics of the liquidus miscibility gap of the specific system.Using the powder metallurgy method,a uniform microstructure morphology and chemical composition was obtained in the DTA specimen,and the phase-separation temperature of the supercooled metastable liquid was measured.The isothermal treatment was applied for the samples inside the stable liquidus miscibility gap;here,equilibrated compositions were reached,and a layered morphology was formed after rapid cooling.The liquid miscibility gaps of the Fe–Cu and Fe–Sn binary systems were measured,and the peak temperatures of the corresponding miscibility gaps were determined to be about 1417°C at x(Cu)=0.465 at%and 1350°C at x(Sn)=0.487 at%,respectively.On the basis of the experimental results,both the Fe–Cu and the Fe–Sn binary systems were thermodynamically assessed.
基金This work was supported in part by the National Natural Science Foundation of China(No.51807171)the Guangdong Science and Technology Department(No.2019A1515011226)+1 种基金the Hong Kong Research Grant Council(No.15200418)the Department of Electrical Engineering,The Hong Kong Polytechnic University for the Start-up Fund(No.1-ZE68).
文摘The damping performance evaluation for electromechanical oscillations in power systems is crucial for the stable operation of modern power systems.In this paper,the connection between two commonly-used damping performance evaluation methods,i.e.,the damping torque analysis(DTA)and energy flow analysis(EFA),are systematically examined and revealed for the better understanding of the oscillatory damping mechanism.First,a concept of the aggregated damping torque coefficient is proposed and derived based on DTA of multi-machine power systems,which can characterize the integration effect of the damping contribution from the whole power system.Then,the pre-processing of measurements at the terminal of a local generator is conducted for EFA,and a concept of the frequency-decomposed energy attenuation coefficient is defined to screen the damping contribution with respect to the interested frequency.On this basis,the frequency spectrum analysis of the energy attenuation coefficient is employed to rigorously prove that the results of DTA and EFA are essentially equivalent,which is valid for arbitrary types of synchronous generator models in multi-machine power systems.Additionally,the consistency between the aggregated damping torque coefficient and frequency-decomposed energy attenuation coefficient is further verified by the numerical calculation in case studies.The relationship between the proposed coefficients and the eigenvalue(or damping ratio)is finally revealed,which consolidates the application of the proposed concepts in the damping performance evaluation.
基金The authors are gratefully acknowledged to the Uttar Pradesh Council of Science and Technology,Lucknow(India)for financial support under the“Young Scientist Scheme”as major research project No.CSTT/YSS/D-3913.Authors are also thankful to Dr.Atul Khanna,associate professor,for his constant support and to extending the XRD measurement facility at Department of Physics,Guru Nanak Dev University,Amritsar 143005,India.
文摘Various bulk and transparent glasses were prepared by rapid melt quenching technique in the glass system 55[(Pb_(x)Bi_(1-x))TiO_(3)]-44[2Si_(O)2B_(2)O_(3)]-La2O3(x=0-0.7).The X-ray diffraction(XRD)studies of the glass samples confirmed the amorphous nature.The differential thermal analyses(DTA)were carried out from room temperature to 900℃with a heating rate of 10℃/min.The DTA patterns of the samples showed one or more exothermic sharp peaks shifting towards lower temperature side with increasing concentration of bismuth oxide(BiO).On the basis of DTA results,the solid solution of bismuth titanum oxide(Bi_(2)Ti_(2)O_(7))/lead bismuth titanium oxide(Pb3Bi4Ti6O21)was precipitated in borosilicate glassy matrix as a major phase.The glasses were subjected to 4 h and 8 h heat treatment schedules to convert into glass ceramics.XRD analysis of these glass ceramic samples showed that the major crystalline phase of the entire glass ceramic samples with 0≤x≤0.5 is found to have cubic crystal structure,while it is tetragonal for glass ceramic sample with x=0.7.The scanning electron microscopy(SEM)micrographs indicated the uniform distribution of Bi_(2)Ti_(2)O_(7)and Pb3Bi4Ti6O21 crystallites in the glassy matrix.
