A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were ma...A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were made for reactions with different kinetic models,including chemical,diffusion(Janders)and mixed mechanism at different heating rates.The results show that,for reactions controlled kinetically by one mechanism,all solid state reaction models show linear trends by use of CR method and this method can not distinct the correct reaction model.For reactions with mixed mechanism,the CR method shows nonlinear trends and the reaction models and kinetic parameters can not be extracted from CR curves.The overall conclusion from this comparative appraisal of the characteristics of the CR approach to kinetic analysis of TGA data is that the CR approach is generally unsuitable for determination of kinetic parameters.展开更多
From the environmental consideration,it would be very interesting to use natural fibers such as banana,jute or coir as reinforcement materials instead of artificial fibers or any kind of synthetic materials.Natural fi...From the environmental consideration,it would be very interesting to use natural fibers such as banana,jute or coir as reinforcement materials instead of artificial fibers or any kind of synthetic materials.Natural fibers have many advantages over synthetic ones.Polypropylene banana fiber composites(PPBC)are prepared using untreated and alkali-treated banana fibers at 10-25%by weight of the fiber loading.The thermal properties of polypropylene natural fiber composites are very important for technological uses.Thermogravimetric measurements show that the incorporation of banana fiber into PP enhances the thermal stability of composites containing treated fibers,in comparison with untreated fibers.A composite of biodegradable polypropylene(PP)reinforced with short banana natural fibers was prepared by melt blending followed by a hot press molding system.The thermal properties of matrix materials were studied using thermogravimetric analyzers TGA units.It is observed that the introduction of short banana fibers slightly improved the thermo oxidative stability of PP-banana composites.Physical and chemical changes occurred through dehydration,phase transition,molecular orientation,crystallinity disruption,oxidation and decomposition,and incorporation of several functional groups.Systematic investigations of the thermal behavior of polymers in gas,vacuum or inert atmosphere give the knowledge of how change takes place in polymers.To understand such changes thermogravimetric analysis(TGA)and thermal analysis(TG)were performed.It is observed reinforcement of short banana fiber leads to little improvement in the thermooxidative stability of PPBC.Due to the enhancement of thermo-mechanical properties,such composites may be used as building materials namely roof materials,selling materials and many other engineering applications.展开更多
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
Super plasticizer was synthesized by using coal coking by product washing oil and industrial naphthalene. The results show that sulfonationt time （2.5 h）, sulfonation temperature （160 ℃） and condensation time （5...Super plasticizer was synthesized by using coal coking by product washing oil and industrial naphthalene. The results show that sulfonationt time （2.5 h）, sulfonation temperature （160 ℃） and condensation time （5.0 h） are key factors. Adding oxidizing agent MO in the course of synthesis can decrease the emission of SO2 in exhaust （20%）. Compared with NF, NF-30 have some advantages in lower cost, high water reducing rate （19.7%） and optimum early strengths. Moreover, TGA-DTA and SEM analysis were adopted to research the NF-30 modified concrete on hydyation mechanism. The analysis show that, compared with NF, there are a large number of hydration products such as Ca （OH）2, C-S-H, AFt etc of NF-30, the structure of NF-30 is dense and the performance is good.展开更多
The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the i...The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content,microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy,universal tensile testing machine and thermo-gravimetric analyzer.Additionally,the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing.The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant.The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80℃ demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing.Moreover,the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0°and 90°fiber directions,when the laminate was cooled to 60℃.展开更多
Biomass usually is noticed a composition of various types of waste materials that can be utilized as useful form of energy alternative to the conventional fossil fuels. However, this new kind of energy has not met its...Biomass usually is noticed a composition of various types of waste materials that can be utilized as useful form of energy alternative to the conventional fossil fuels. However, this new kind of energy has not met its full potential in production of energy, especially electricity generation due to its lower performance in terms of thermal efficiency. Algae （included Microalgae ＆ Macroalgae） are widely used for multi-application developments such as fishery aquaculture, food/nutrient supplement, cosmetics, and biomass energy. Microalgae have been treated as the source of bio-fuel. In this paper, we selected the two types of freshwater microalgae ＂Chlorella Vulgaris＂ ＆ ＂Spirulina＂ and macro algae （Laminariaceae） as the main materials and we analyzed TGA （thermal gravity analysis） and calorific values （heat of combustion）. We found the calorific values are 1,000-5,000 KC/KG and TGA results show that the microalgae decrease rapidly after reached 300 ℃. The results in this paper will be used as a reference material for microalgae multi-oriental energy application and biomass composition proximate and ultimate research development in the future.展开更多
文摘A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were made for reactions with different kinetic models,including chemical,diffusion(Janders)and mixed mechanism at different heating rates.The results show that,for reactions controlled kinetically by one mechanism,all solid state reaction models show linear trends by use of CR method and this method can not distinct the correct reaction model.For reactions with mixed mechanism,the CR method shows nonlinear trends and the reaction models and kinetic parameters can not be extracted from CR curves.The overall conclusion from this comparative appraisal of the characteristics of the CR approach to kinetic analysis of TGA data is that the CR approach is generally unsuitable for determination of kinetic parameters.
文摘From the environmental consideration,it would be very interesting to use natural fibers such as banana,jute or coir as reinforcement materials instead of artificial fibers or any kind of synthetic materials.Natural fibers have many advantages over synthetic ones.Polypropylene banana fiber composites(PPBC)are prepared using untreated and alkali-treated banana fibers at 10-25%by weight of the fiber loading.The thermal properties of polypropylene natural fiber composites are very important for technological uses.Thermogravimetric measurements show that the incorporation of banana fiber into PP enhances the thermal stability of composites containing treated fibers,in comparison with untreated fibers.A composite of biodegradable polypropylene(PP)reinforced with short banana natural fibers was prepared by melt blending followed by a hot press molding system.The thermal properties of matrix materials were studied using thermogravimetric analyzers TGA units.It is observed that the introduction of short banana fibers slightly improved the thermo oxidative stability of PP-banana composites.Physical and chemical changes occurred through dehydration,phase transition,molecular orientation,crystallinity disruption,oxidation and decomposition,and incorporation of several functional groups.Systematic investigations of the thermal behavior of polymers in gas,vacuum or inert atmosphere give the knowledge of how change takes place in polymers.To understand such changes thermogravimetric analysis(TGA)and thermal analysis(TG)were performed.It is observed reinforcement of short banana fiber leads to little improvement in the thermooxidative stability of PPBC.Due to the enhancement of thermo-mechanical properties,such composites may be used as building materials namely roof materials,selling materials and many other engineering applications.
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 Natural Science Foundation of China(No.51175004)Educational Commission of Anhui Province of China(No.KJ2012A078)
文摘Super plasticizer was synthesized by using coal coking by product washing oil and industrial naphthalene. The results show that sulfonationt time （2.5 h）, sulfonation temperature （160 ℃） and condensation time （5.0 h） are key factors. Adding oxidizing agent MO in the course of synthesis can decrease the emission of SO2 in exhaust （20%）. Compared with NF, NF-30 have some advantages in lower cost, high water reducing rate （19.7%） and optimum early strengths. Moreover, TGA-DTA and SEM analysis were adopted to research the NF-30 modified concrete on hydyation mechanism. The analysis show that, compared with NF, there are a large number of hydration products such as Ca （OH）2, C-S-H, AFt etc of NF-30, the structure of NF-30 is dense and the performance is good.
基金Projects(52175373,52005516)supported by the National Natural Science Foundation of ChinaProject(2018YFA0702800)supported by the National Key Basic Research Program,ChinaProject(ZZYJKT2021-03)supported by the State Key Laboratory of High Performance Complex Manufacturing,Central South University,China。
文摘The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content,microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy,universal tensile testing machine and thermo-gravimetric analyzer.Additionally,the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing.The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant.The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80℃ demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing.Moreover,the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0°and 90°fiber directions,when the laminate was cooled to 60℃.
文摘Biomass usually is noticed a composition of various types of waste materials that can be utilized as useful form of energy alternative to the conventional fossil fuels. However, this new kind of energy has not met its full potential in production of energy, especially electricity generation due to its lower performance in terms of thermal efficiency. Algae （included Microalgae ＆ Macroalgae） are widely used for multi-application developments such as fishery aquaculture, food/nutrient supplement, cosmetics, and biomass energy. Microalgae have been treated as the source of bio-fuel. In this paper, we selected the two types of freshwater microalgae ＂Chlorella Vulgaris＂ ＆ ＂Spirulina＂ and macro algae （Laminariaceae） as the main materials and we analyzed TGA （thermal gravity analysis） and calorific values （heat of combustion）. We found the calorific values are 1,000-5,000 KC/KG and TGA results show that the microalgae decrease rapidly after reached 300 ℃. The results in this paper will be used as a reference material for microalgae multi-oriental energy application and biomass composition proximate and ultimate research development in the future.
