The non-isothermal oxidation behavior and oxide scale microstructure of Ti-Cr alloy （0≤w（Cr）≤25%） were studied from room temperature to 1723 K by thermogravimetric analysis （TGA）, X-ray diffraction （XRD） and...The non-isothermal oxidation behavior and oxide scale microstructure of Ti-Cr alloy （0≤w（Cr）≤25%） were studied from room temperature to 1723 K by thermogravimetric analysis （TGA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The influencing mechanism of chromium on the oxidation resistance of Ti-Cr alloys was discussed. The results show that the oxidation resistance of the alloys decreases with Cr below a critical chromium content wC and increases above wC; above 1000 K, the oxidation kinetics obeys parabolic rule and titanium dominates the oxidation process; after oxidation, the oxygen-diffusing layer is present in the alloy matrix, the oxide scale is mainly composed of rutile whose internal layer is rich in chromium, and chromium oxides separated out from TiO2 near the alloy-oxide interface improve the oxidation resistance. Ignition of metals and alloys is a fast non-isothermal oxidation process and the oxidation mechanism of Ti-Cr alloys during ignition is predicted.展开更多
The pyrolysis kinetics of three different kinds of fresh biomass (grass: triple A, wheat straw, corn straw) in nitrogen flow were studied by thermogravimetric analysis at five different heating rates. The kinetic para...The pyrolysis kinetics of three different kinds of fresh biomass (grass: triple A, wheat straw, corn straw) in nitrogen flow were studied by thermogravimetric analysis at five different heating rates. The kinetic parameters of the pyrolysis process were calculated using the method of Ozawa-Flynn-Wall and the mechanism of reactions were investi- gated using the method of Popescu. It was found that the values of activation energy varied in different temperature ranges. The pyrolysis processes are well described by the models of Zhuravlev (Zh) and valid for diffusion-controlled between 200 ℃ and 280 ℃, by Ginstling-Brounshtein (G-B), valid for diffusion-control between 280 ℃ and 310 ℃, for first-order chemical reaction between 310℃ and 350 ℃, by Zhuravlev (Zh) valid for diffusion-control between 350 ℃ and 430 ℃ and by the one-way transport model when temperatures are over 430 ℃.展开更多
Non-isothermal combustion kinetics of two kinds of low volatile pulverized coals （HL coal and RU coal） were investigated by thermogravimetrie analysis. The results show that the combustibility of HL coal was better ...Non-isothermal combustion kinetics of two kinds of low volatile pulverized coals （HL coal and RU coal） were investigated by thermogravimetrie analysis. The results show that the combustibility of HL coal was better than that of RU coal, and with increasing heating rate, ignition and burnout characteristics of pulverized coal were improved. The volume model （VM）, the random pore model （RPM）, and the new model （NEWM） in which the whole combustion process is considered to be the overlapping process of volatile combustion and coal char combustion, were used to fit with the experimental data. The comparison of these three fitted results indicated that the combustion process of coal could be simulated by the NEWM with highest precision. When calculated by the NEWM, the activation energies of volatile combustion and coal char combustion are 130.5 and 95.7 kJ · mol^-1 for HL coal, respectively, while they are 114.5 and 147.6 kJ ·mol^-1 for RU coal, respectively.展开更多
Polymer based on (polyethyl-methacrylate) (PEMA) were exposed to different doses of gamma radiation up to 100 kGy and the physical properties have been studied. The effects of gamma irradiation on the optical spectrum...Polymer based on (polyethyl-methacrylate) (PEMA) were exposed to different doses of gamma radiation up to 100 kGy and the physical properties have been studied. The effects of gamma irradiation on the optical spectrum of PEMA films have been investigated using spectrophotometric measurements of reflectance and transmittance in the wavelength range 200-1100 nm. The structure of the sample is analyzed by X-ray diffraction technique and is found to be amorphous and partially crystalline. TGA studies revealed that the thermal stability of polyethyl methacrylate, improved after irradiation doses up to 100 kGy. On other hand driving absorption coefficient α(ω), consequently the band tail width Ee and optical band gap estimated. This behavior is believed to be associated with the generation of excess of electronic localized states. Also, Optical constants such as refractive index (n), extinction coefficient (K) have been determined using Swanepole method. Optical dispersion parameters and the dispersion parameters, such as Eo (single–oscillator energy), Ed (dispersive energy) are discussed in terms of the single-oscillator Wemple-DiDomenico model.展开更多
Cerium and cerium-based oxides are found to be an important element in three-way catalytic converter(TWC).The effective utilization of TWC is found to be reduced due to thermal loading which results in structural defo...Cerium and cerium-based oxides are found to be an important element in three-way catalytic converter(TWC).The effective utilization of TWC is found to be reduced due to thermal loading which results in structural deformation of ceria,Doping Zr^(4+)into the rare earth element can increase the oxygen storage capacity and thermal stability.Hence,an attempt was made to study the oxygen storage capacity and thermal stability of ceria by doping Zr^(4+)and Nd^(3+).Cerium-based nanocrystallite in the composition of Ce_(0.6)Zr_(0.4-x)Nd_(1.3)xO_(2)(0≤x≤0.4)was prepared by sol-gel synthesize technique with citric acid as a gel-forming agent.X-ray diffraction(XRD)result shows that doping Nd^(3+)into ceria lattice forms homogenous solid solution of cubic fluorite structure up to 25%of substitute only.Doping higher amount of Nd^(3+)into ceria lattice leads to the formation of Nd_(2)O_(3).Raman spectrum study confirms that oxygen storage capacity band is present in Ce_(0.6)Zr_(0.4)O2 and Ce_(0.6)Zr_(0.3)Nd_(0.13)O_(2).The oxygen storage capacity was calculated through weight loss of the sample during the second heating cycle with cyclic heating from30 to 800℃in thermogravimetric analysis(TGA).The TGA study reveals that the oxygen storage capacity of Ce_(0.6)Zr_(0.4)O2 decreases after the substitution of Nd^(3+),which is due to the larger ionic radius of Nd^(3+)compared with that of Zr4+and CeO2.展开更多
Titanium(IV) oxide (TiO2) nanoparticles have been incorporated into mixed matrix membranes (MMMs) to improve gas separation performance. However, TiO2 nanoparticles tend to agglomerate due to high surface energy and v...Titanium(IV) oxide (TiO2) nanoparticles have been incorporated into mixed matrix membranes (MMMs) to improve gas separation performance. However, TiO2 nanoparticles tend to agglomerate due to high surface energy and van der Waals forces. This leads to precipitation which causes the formation of non-homogeneous MMM morphology. In this study, the effect of octaisobutyl polyhedral oligomeric silsesquioxane (POSS) addition on TiO2/polysulfone MMM was investigated. The aims are to enhance gas separation performance whilst preventing agglomeration of TiO2 nanoparticles. The results demonstrated that inclusion of POSS as dispersant increases MMMs’ CO2/CH4 selectivity and permeance, possibly due to less void formation and more evenly distributed pore structure. For example, synergistic addition of 5 wt% TiO2 and 5 wt% POSS increased the CO2/CH4 selectivity up to 390% compared to MMM without POSS. This is supported by elemental mapping of titanium which revealed that POSS successfully dispersed TiO2 nanoparticles and prevented aggregation. TiO2-POSS/PSf MMMs also retained their favorable thermal stability.展开更多
文摘The non-isothermal oxidation behavior and oxide scale microstructure of Ti-Cr alloy （0≤w（Cr）≤25%） were studied from room temperature to 1723 K by thermogravimetric analysis （TGA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The influencing mechanism of chromium on the oxidation resistance of Ti-Cr alloys was discussed. The results show that the oxidation resistance of the alloys decreases with Cr below a critical chromium content wC and increases above wC; above 1000 K, the oxidation kinetics obeys parabolic rule and titanium dominates the oxidation process; after oxidation, the oxygen-diffusing layer is present in the alloy matrix, the oxide scale is mainly composed of rutile whose internal layer is rich in chromium, and chromium oxides separated out from TiO2 near the alloy-oxide interface improve the oxidation resistance. Ignition of metals and alloys is a fast non-isothermal oxidation process and the oxidation mechanism of Ti-Cr alloys during ignition is predicted.
基金Project 50474056 supported by the National Natural Science Foundation of China
文摘The pyrolysis kinetics of three different kinds of fresh biomass (grass: triple A, wheat straw, corn straw) in nitrogen flow were studied by thermogravimetric analysis at five different heating rates. The kinetic parameters of the pyrolysis process were calculated using the method of Ozawa-Flynn-Wall and the mechanism of reactions were investi- gated using the method of Popescu. It was found that the values of activation energy varied in different temperature ranges. The pyrolysis processes are well described by the models of Zhuravlev (Zh) and valid for diffusion-controlled between 200 ℃ and 280 ℃, by Ginstling-Brounshtein (G-B), valid for diffusion-control between 280 ℃ and 310 ℃, for first-order chemical reaction between 310℃ and 350 ℃, by Zhuravlev (Zh) valid for diffusion-control between 350 ℃ and 430 ℃ and by the one-way transport model when temperatures are over 430 ℃.
基金Item Sponsored by National Basic Research Program(973Program)of China(2012CB720401)National Key Technology Research and Development Program in the 12th Five-year Plan of China(2011BAC01B02)
文摘Non-isothermal combustion kinetics of two kinds of low volatile pulverized coals （HL coal and RU coal） were investigated by thermogravimetrie analysis. The results show that the combustibility of HL coal was better than that of RU coal, and with increasing heating rate, ignition and burnout characteristics of pulverized coal were improved. The volume model （VM）, the random pore model （RPM）, and the new model （NEWM） in which the whole combustion process is considered to be the overlapping process of volatile combustion and coal char combustion, were used to fit with the experimental data. The comparison of these three fitted results indicated that the combustion process of coal could be simulated by the NEWM with highest precision. When calculated by the NEWM, the activation energies of volatile combustion and coal char combustion are 130.5 and 95.7 kJ · mol^-1 for HL coal, respectively, while they are 114.5 and 147.6 kJ ·mol^-1 for RU coal, respectively.
文摘Polymer based on (polyethyl-methacrylate) (PEMA) were exposed to different doses of gamma radiation up to 100 kGy and the physical properties have been studied. The effects of gamma irradiation on the optical spectrum of PEMA films have been investigated using spectrophotometric measurements of reflectance and transmittance in the wavelength range 200-1100 nm. The structure of the sample is analyzed by X-ray diffraction technique and is found to be amorphous and partially crystalline. TGA studies revealed that the thermal stability of polyethyl methacrylate, improved after irradiation doses up to 100 kGy. On other hand driving absorption coefficient α(ω), consequently the band tail width Ee and optical band gap estimated. This behavior is believed to be associated with the generation of excess of electronic localized states. Also, Optical constants such as refractive index (n), extinction coefficient (K) have been determined using Swanepole method. Optical dispersion parameters and the dispersion parameters, such as Eo (single–oscillator energy), Ed (dispersive energy) are discussed in terms of the single-oscillator Wemple-DiDomenico model.
文摘Cerium and cerium-based oxides are found to be an important element in three-way catalytic converter(TWC).The effective utilization of TWC is found to be reduced due to thermal loading which results in structural deformation of ceria,Doping Zr^(4+)into the rare earth element can increase the oxygen storage capacity and thermal stability.Hence,an attempt was made to study the oxygen storage capacity and thermal stability of ceria by doping Zr^(4+)and Nd^(3+).Cerium-based nanocrystallite in the composition of Ce_(0.6)Zr_(0.4-x)Nd_(1.3)xO_(2)(0≤x≤0.4)was prepared by sol-gel synthesize technique with citric acid as a gel-forming agent.X-ray diffraction(XRD)result shows that doping Nd^(3+)into ceria lattice forms homogenous solid solution of cubic fluorite structure up to 25%of substitute only.Doping higher amount of Nd^(3+)into ceria lattice leads to the formation of Nd_(2)O_(3).Raman spectrum study confirms that oxygen storage capacity band is present in Ce_(0.6)Zr_(0.4)O2 and Ce_(0.6)Zr_(0.3)Nd_(0.13)O_(2).The oxygen storage capacity was calculated through weight loss of the sample during the second heating cycle with cyclic heating from30 to 800℃in thermogravimetric analysis(TGA).The TGA study reveals that the oxygen storage capacity of Ce_(0.6)Zr_(0.4)O2 decreases after the substitution of Nd^(3+),which is due to the larger ionic radius of Nd^(3+)compared with that of Zr4+and CeO2.
基金financial support received from YUTP-FRG (No. 015 3AA-E08)FRGS (Ref. No. FRGS/1/2018/TK02/UTP/02/3, Cost Center 015MA0003)
文摘Titanium(IV) oxide (TiO2) nanoparticles have been incorporated into mixed matrix membranes (MMMs) to improve gas separation performance. However, TiO2 nanoparticles tend to agglomerate due to high surface energy and van der Waals forces. This leads to precipitation which causes the formation of non-homogeneous MMM morphology. In this study, the effect of octaisobutyl polyhedral oligomeric silsesquioxane (POSS) addition on TiO2/polysulfone MMM was investigated. The aims are to enhance gas separation performance whilst preventing agglomeration of TiO2 nanoparticles. The results demonstrated that inclusion of POSS as dispersant increases MMMs’ CO2/CH4 selectivity and permeance, possibly due to less void formation and more evenly distributed pore structure. For example, synergistic addition of 5 wt% TiO2 and 5 wt% POSS increased the CO2/CH4 selectivity up to 390% compared to MMM without POSS. This is supported by elemental mapping of titanium which revealed that POSS successfully dispersed TiO2 nanoparticles and prevented aggregation. TiO2-POSS/PSf MMMs also retained their favorable thermal stability.
