This paper analyzes the oxidation law of metal particles and proposes a new oxidation reaction rate model,based on measurements of thermogravimetric-mass spectrometer(TG-MS),X-ray diffractometer(XRD)and scanning elect...This paper analyzes the oxidation law of metal particles and proposes a new oxidation reaction rate model,based on measurements of thermogravimetric-mass spectrometer(TG-MS),X-ray diffractometer(XRD)and scanning electron microscope(SEM).The model is named EBM(egg broken model)with a formula of exponential law.According to the model,the aluminum particles do not react in a spherical shape,but crack and the melted metal inside flows out to form a new nonspherical surface and the reaction rate is still determined by the surface area.The model is verified with heating rates of 5℃/min,10℃/min and 25℃/min,and with particle size of 1–2μm,8–9μm and 20–22μm.Many models are based on spherical hypothesis and the new model gives a different physical illustration to explain oxidation progress of metal particles.The new model gives an exponential law,which fits the experimental data well,and it may be useful to understand oxidation mechanism of metal particles.展开更多
Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model,...Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model, based upon which a two-dimensional cylindrical kinetics model is developed for the oxidation of silicon nanowires and is extended for tungsten. In the model, diffusivity is affected by the expansive oxidation reaction induced stress. The dependency of the oxidation upon curvature and temperature is modeled. Good agreement between the model predictions and available experimental data is obtained. The de- veloped model serves to quantify the oxidation in two-dimensional nanostructures and is expected to facilitate their fabrication via thermal oxidation techniques.展开更多
To confirm sub-regular solution model valid for predicting the activity of component in binary oxide systems, seven systems in the whole concentration and twelve systems presenting saturation concentration have been s...To confirm sub-regular solution model valid for predicting the activity of component in binary oxide systems, seven systems in the whole concentration and twelve systems presenting saturation concentration have been studied. The total average relative errors of component 1 and 2 are 3.2 % and 4.1% respectively by application of the sub-regular solution model into the systems within the whole concentration. However, the total average relative errors are 16 % and 1088 % in the systems presenting saturation concentration. The results show that sub-regular solu- tion model is not good for predicting the systems presenting saturation concentration, especially for the systems con- taining acidic or neutral oxide. The reason may be that the influence of the two types of oxide on the configuration is greater in binary oxide systems. These oxides can be present in the form of complex anion partly, Si-O, Al-O, Ti-O and so on, for example （SiO4）4-. That is contrary to sub-regular solution model which is supposed that the oxide systems consist of cation and O2-. But compared with regular solution model and quasi-regular solution model, sub- regular solution model is closer to the characteristics of actual solution and the calculated results are superior.展开更多
Based on conduction,convection and radiation heat transfer among the flue gas,kiln wall,and the pellet bed material,and on the basis of the coal combustion and analysis of reaction heat of pellet induration in the rot...Based on conduction,convection and radiation heat transfer among the flue gas,kiln wall,and the pellet bed material,and on the basis of the coal combustion and analysis of reaction heat of pellet induration in the rotary kiln,the temperature field model of rotary kiln was established.Using visual studio net,matlab and open source computer vision library as development tools,combining with the ActiveX data objects database technology,the temperature field simulation system for rotary kiln of iron ore oxidized pellet production was developed.Temperature distribution of pellet and flue gas in rotary kiln was dynamically displayed.展开更多
Transport behaviors of graphene oxide nanoparticles（GONPs） in saturated porous media were examined as a function of the presence and concentration of anionic surfactant（SDBS）and non-ionic surfactant（Triton X-100...Transport behaviors of graphene oxide nanoparticles（GONPs） in saturated porous media were examined as a function of the presence and concentration of anionic surfactant（SDBS）and non-ionic surfactant（Triton X-100） under different ionic strength（IS）. The results showed that the GONPs were retained obviously in the sand columns at both IS of 50 and200 mmol/L, and they were more mobile at lower IS. The presence and concentration of surfactants could enhance the GONP transport, particularly as observed at higher IS. It was interesting to see that the GONP transport was surfactant type dependent, and SDBS was more effective to facilitate GONP transport than Triton X-100 in our experimental conditions. The advection–dispersion–retention numerical modeling followed this trend and depicted the difference quantitatively. Derjaguin–Landau–Verwey–Overbeek（DLVO）interaction calculations also were performed to interpret these effects, indicating that secondary minimum deposition was critical in this study.展开更多
The efficient thickness of a composite electrode for solid oxide fuel cells was directly calculated by developing a physical model taking into account of the charge transfer process, the oxygen ion and electron transp...The efficient thickness of a composite electrode for solid oxide fuel cells was directly calculated by developing a physical model taking into account of the charge transfer process, the oxygen ion and electron transportation, and the microstructure characteristics of the electrode. The efficient thickness, which is defined as the electrode thickness corresponding to the minimum electrode polarization resistance, is formulated as a function of charge transfer resistivity, effective resistivity to ion and electron transport, and three-phase boundary length per unit volume. The model prediction is compared with the experimental reports to check the validity. Simulation is performed to show the effect of microstructure, intrinsic material properties, and electrode reaction mechanism on the efficient thickness. The results suggest that when an electrode is fabricated, its thickness should be controlled regarding its composition, particle size of its components, the intrinsic ionic and electronic conductivities,and its reaction mechanisms as well as the expected operation temperatures. The sensitivity of electrode polarization resistance to its thickness is also discussed.展开更多
A simple ultrasound-assisted co-precipitation method was developed to prepare ferroferric oxide/graphene oxide magnetic nanoparticles(Fe_3O_4/CO MNPs).The hysteresis loop of Fe_3O_4/GO MNPs demonstrated that the sampl...A simple ultrasound-assisted co-precipitation method was developed to prepare ferroferric oxide/graphene oxide magnetic nanoparticles(Fe_3O_4/CO MNPs).The hysteresis loop of Fe_3O_4/GO MNPs demonstrated that the sample was typical of superparamagnetic material.The samples were characterized by transmission electron microscope,and it is found that the particles are of small size.The Fe_3O_4/GO MNPs were further used as an adsorbent to remove Rhodamine B.The effects of initial pH of the solution,the dosage of adsorbent,temperature,contact time and the presence of interfering dyes on adsorption performance were investigated as well.The adsorption equilibrium and kinetics data were fitted well with the Freundlich isotherm and the pseudosecond-order kinetic model respectively.The adsorption process followed intra-particle diffusion model with more than one process affecting the adsorption of Rhodamine B.And the adsorption process was endothermic in nature.Furthermore,the magnetic composite with a high adsorption capacity of Rhodamine B could be effectively and simply separated using an external magnetic field.And the used particles could be regenerated and recycled easily.The magnetic composite could find potential applications for the removal of dye pollutants.展开更多
The optical parameters for three samples of intrinsic, doped Si and doped Mg (Al x Ga 1- x ) y In 1- y P prepared by the MOCVD on GaAs substrate were measured by using ellipsometry and were calc...The optical parameters for three samples of intrinsic, doped Si and doped Mg (Al x Ga 1- x ) y In 1- y P prepared by the MOCVD on GaAs substrate were measured by using ellipsometry and were calculated by the two-layer absorption film model. The results obtained were discussed. The grown rates and thickness of oxidic layer on the intrinsic (Al x Ga 1- x ) y In 1- y P surface exposed in the atmosphere were studied. A linear dependence of oxidic layer thickness on the time was obtained.展开更多
The doping dependence of dry thermal oxidation rates in n-type 6H-SiC was studied. The oxidation temperature ranged from 1050 to 1150℃ and the nitrogen doping concentration ranged from 9.53× 10^16, 1.44× 10...The doping dependence of dry thermal oxidation rates in n-type 6H-SiC was studied. The oxidation temperature ranged from 1050 to 1150℃ and the nitrogen doping concentration ranged from 9.53× 10^16, 1.44× 10^17, to 2.68×10^18 cm ^3. By combining the modified deal-grove model and Arrhenius equation, the linear and parabolic rate constants, and their corresponding activation energies were extracted. The results show that： higher temperature corresponded to thicker oxides; dry thermal oxidation rate in n-type 6H-SiC depended on the doping concentration; both linear-rate-constant and parabolic-rate-constant increased with the doping concentration; the parabolic activation energy increased from 0.082 to 0.104 e V, both linear and parabolic activation energies increasing with the doping concentration; and, the parabolic pre-exponential factor increased from 2.6 ×10^4 to 2.7 ×10^5nm^2/s, both linear and parabolic pre-exponential factor increasing with doping concentration. Moreover, the experiment also illustrated that it is unreasonable to use a variation of the Arrhenius activation energy to explain the doping dependence of thermal oxidation on SiC.展开更多
基金financially supported by the joint fund of National Natural Science Foundation and China Academy of Engineering Physics(NSAF)under grant No.U1530157。
文摘This paper analyzes the oxidation law of metal particles and proposes a new oxidation reaction rate model,based on measurements of thermogravimetric-mass spectrometer(TG-MS),X-ray diffractometer(XRD)and scanning electron microscope(SEM).The model is named EBM(egg broken model)with a formula of exponential law.According to the model,the aluminum particles do not react in a spherical shape,but crack and the melted metal inside flows out to form a new nonspherical surface and the reaction rate is still determined by the surface area.The model is verified with heating rates of 5℃/min,10℃/min and 25℃/min,and with particle size of 1–2μm,8–9μm and 20–22μm.Many models are based on spherical hypothesis and the new model gives a different physical illustration to explain oxidation progress of metal particles.The new model gives an exponential law,which fits the experimental data well,and it may be useful to understand oxidation mechanism of metal particles.
基金financial support of this work by the National Natural Science Foundation of China(11472149)the Tsinghua University Initiative Scientific Research Program(2014z22074)
文摘Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model, based upon which a two-dimensional cylindrical kinetics model is developed for the oxidation of silicon nanowires and is extended for tungsten. In the model, diffusivity is affected by the expansive oxidation reaction induced stress. The dependency of the oxidation upon curvature and temperature is modeled. Good agreement between the model predictions and available experimental data is obtained. The de- veloped model serves to quantify the oxidation in two-dimensional nanostructures and is expected to facilitate their fabrication via thermal oxidation techniques.
基金Item Sponsored by National Natural Science Foundation of China(50764006,50574045)Yunnan Basic Applied Research Foundation of China(2006E0021M)
文摘To confirm sub-regular solution model valid for predicting the activity of component in binary oxide systems, seven systems in the whole concentration and twelve systems presenting saturation concentration have been studied. The total average relative errors of component 1 and 2 are 3.2 % and 4.1% respectively by application of the sub-regular solution model into the systems within the whole concentration. However, the total average relative errors are 16 % and 1088 % in the systems presenting saturation concentration. The results show that sub-regular solu- tion model is not good for predicting the systems presenting saturation concentration, especially for the systems con- taining acidic or neutral oxide. The reason may be that the influence of the two types of oxide on the configuration is greater in binary oxide systems. These oxides can be present in the form of complex anion partly, Si-O, Al-O, Ti-O and so on, for example （SiO4）4-. That is contrary to sub-regular solution model which is supposed that the oxide systems consist of cation and O2-. But compared with regular solution model and quasi-regular solution model, sub- regular solution model is closer to the characteristics of actual solution and the calculated results are superior.
基金Sponsored by Program for New Century Excellent Talents in University of China(NCET-05-0630)
文摘Based on conduction,convection and radiation heat transfer among the flue gas,kiln wall,and the pellet bed material,and on the basis of the coal combustion and analysis of reaction heat of pellet induration in the rotary kiln,the temperature field model of rotary kiln was established.Using visual studio net,matlab and open source computer vision library as development tools,combining with the ActiveX data objects database technology,the temperature field simulation system for rotary kiln of iron ore oxidized pellet production was developed.Temperature distribution of pellet and flue gas in rotary kiln was dynamically displayed.
基金financially supported by National Natural Science Foundation of China (NSFC NO. 41302196 and 51238001)supported by the Fundamental Research Funds for the Central Universities (NO. 14QNJJ026)
文摘Transport behaviors of graphene oxide nanoparticles（GONPs） in saturated porous media were examined as a function of the presence and concentration of anionic surfactant（SDBS）and non-ionic surfactant（Triton X-100） under different ionic strength（IS）. The results showed that the GONPs were retained obviously in the sand columns at both IS of 50 and200 mmol/L, and they were more mobile at lower IS. The presence and concentration of surfactants could enhance the GONP transport, particularly as observed at higher IS. It was interesting to see that the GONP transport was surfactant type dependent, and SDBS was more effective to facilitate GONP transport than Triton X-100 in our experimental conditions. The advection–dispersion–retention numerical modeling followed this trend and depicted the difference quantitatively. Derjaguin–Landau–Verwey–Overbeek（DLVO）interaction calculations also were performed to interpret these effects, indicating that secondary minimum deposition was critical in this study.
文摘The efficient thickness of a composite electrode for solid oxide fuel cells was directly calculated by developing a physical model taking into account of the charge transfer process, the oxygen ion and electron transportation, and the microstructure characteristics of the electrode. The efficient thickness, which is defined as the electrode thickness corresponding to the minimum electrode polarization resistance, is formulated as a function of charge transfer resistivity, effective resistivity to ion and electron transport, and three-phase boundary length per unit volume. The model prediction is compared with the experimental reports to check the validity. Simulation is performed to show the effect of microstructure, intrinsic material properties, and electrode reaction mechanism on the efficient thickness. The results suggest that when an electrode is fabricated, its thickness should be controlled regarding its composition, particle size of its components, the intrinsic ionic and electronic conductivities,and its reaction mechanisms as well as the expected operation temperatures. The sensitivity of electrode polarization resistance to its thickness is also discussed.
基金Supported by the National Natural Science Foundation of China(21107143,21207033)the Fundamental Research Funds for the Central Universities,South-Central University for Nationalities(CZY15003)
文摘A simple ultrasound-assisted co-precipitation method was developed to prepare ferroferric oxide/graphene oxide magnetic nanoparticles(Fe_3O_4/CO MNPs).The hysteresis loop of Fe_3O_4/GO MNPs demonstrated that the sample was typical of superparamagnetic material.The samples were characterized by transmission electron microscope,and it is found that the particles are of small size.The Fe_3O_4/GO MNPs were further used as an adsorbent to remove Rhodamine B.The effects of initial pH of the solution,the dosage of adsorbent,temperature,contact time and the presence of interfering dyes on adsorption performance were investigated as well.The adsorption equilibrium and kinetics data were fitted well with the Freundlich isotherm and the pseudosecond-order kinetic model respectively.The adsorption process followed intra-particle diffusion model with more than one process affecting the adsorption of Rhodamine B.And the adsorption process was endothermic in nature.Furthermore,the magnetic composite with a high adsorption capacity of Rhodamine B could be effectively and simply separated using an external magnetic field.And the used particles could be regenerated and recycled easily.The magnetic composite could find potential applications for the removal of dye pollutants.
文摘The optical parameters for three samples of intrinsic, doped Si and doped Mg (Al x Ga 1- x ) y In 1- y P prepared by the MOCVD on GaAs substrate were measured by using ellipsometry and were calculated by the two-layer absorption film model. The results obtained were discussed. The grown rates and thickness of oxidic layer on the intrinsic (Al x Ga 1- x ) y In 1- y P surface exposed in the atmosphere were studied. A linear dependence of oxidic layer thickness on the time was obtained.
基金Project supported by the National Natural Science Foundation of China(No.F040405)
文摘The doping dependence of dry thermal oxidation rates in n-type 6H-SiC was studied. The oxidation temperature ranged from 1050 to 1150℃ and the nitrogen doping concentration ranged from 9.53× 10^16, 1.44× 10^17, to 2.68×10^18 cm ^3. By combining the modified deal-grove model and Arrhenius equation, the linear and parabolic rate constants, and their corresponding activation energies were extracted. The results show that： higher temperature corresponded to thicker oxides; dry thermal oxidation rate in n-type 6H-SiC depended on the doping concentration; both linear-rate-constant and parabolic-rate-constant increased with the doping concentration; the parabolic activation energy increased from 0.082 to 0.104 e V, both linear and parabolic activation energies increasing with the doping concentration; and, the parabolic pre-exponential factor increased from 2.6 ×10^4 to 2.7 ×10^5nm^2/s, both linear and parabolic pre-exponential factor increasing with doping concentration. Moreover, the experiment also illustrated that it is unreasonable to use a variation of the Arrhenius activation energy to explain the doping dependence of thermal oxidation on SiC.
