The kinetic model for diffusion-controlled intermolecular reaction of homogenous polymer under steady shear was theoretically studied. The classic formalism and the concept of conformation ellipsoids were integrated t...The kinetic model for diffusion-controlled intermolecular reaction of homogenous polymer under steady shear was theoretically studied. The classic formalism and the concept of conformation ellipsoids were integrated to get a new equation, which directly correlates the rate constant with shear rate. It was found that the rate constant is not monotonic with shear rate. The scale of rate constant is N^-1.5 （N is the length of chains）, which is in consistent with de Gennes＇s result.展开更多
In studying the diffusion-controlled adsorption kinetics of aqueous surfactant solutions at the air/solution surface by means of the maximal bubble pressure method, Fick's diffusion equation for a sphere should be...In studying the diffusion-controlled adsorption kinetics of aqueous surfactant solutions at the air/solution surface by means of the maximal bubble pressure method, Fick's diffusion equation for a sphere should be used. In this paper the equation was solved by means of Laplace transformation under different initial and boundary conditions. The dynamic surface adsorption F(t) for a surfactant solution, which was used to describe the diffusion-controlled adsorption kinetics at the solution surface, was derived. Different from the planar surface adsorption, the dynamic surface adsorption F(t) for the short time consists of two terms: one is the same as Ward-Tordai equation and the other reflects the geometric effect caused by the spherical bubble surface. This effect should not be neglected for the very small radius of the capillary. The equilibrium surface tension γeq and the dynamic surface tension γ(t) of aqueous C10E6 [CH3(CH2)9(OCH2CH2)6OH] solution at temperature 25℃ were measuredby means of Wilhelmy plate method and maximal bubble pressure method respectively. As t→ 0, the theoreticalanalysis is in good agreement with experimental results and the dependence of γ(t) on is linear.展开更多
In this paper, the equilibrium surface tension and the dynamic surface tension of aqueous Triton X-100 solution at temperature 25 ℃ were measured by means of Wilhelmy plate method and maximal bubble pressure method r...In this paper, the equilibrium surface tension and the dynamic surface tension of aqueous Triton X-100 solution at temperature 25 ℃ were measured by means of Wilhelmy plate method and maximal bubble pressure method respectively. The determined critical micellar concentration（cmc） of Triton X-100 at 25 ℃ is (2.2×10-4) mol/dm3. The adsorption mechanics of Triton X-100 at air/solution was determined. For the submicellar concentrations it is diffusion-controlled. The diffusion coefficient was calculated from the experimental data in the range of short limit. In the range of long time adsorption, the subsurface concentration is fitted from the measured dynamic surface tensions.展开更多
A refined double integral method has been applied to the problem encountered in the diffu-sion release of a drug from a polymeric matrix.The finite external mass transfer resistance has alsobeen incorporated into the ...A refined double integral method has been applied to the problem encountered in the diffu-sion release of a drug from a polymeric matrix.The finite external mass transfer resistance has alsobeen incorporated into the present analysis.Experimental release rates of 5-fluorouracil fromethylene-vinyl alcohol copolymer into distilled water were measured in order to test the applicabilityof these models.All system parameters were measured by experiments and models were built up.Themodels presented here are much more accurate than Higuchi model and much easier than the exactsolutions.In view of accuracy,the models are almost the same as the exact solutions.The experi-mental release data agree Well with the computed展开更多
In order to clarify and control the silver defect on surface of cold-rolled sheet of the Ti-stabilized ultra-pure ferrite stainless steel, the distribution of TiN inclusions on the cross section of hot-rolled plate wa...In order to clarify and control the silver defect on surface of cold-rolled sheet of the Ti-stabilized ultra-pure ferrite stainless steel, the distribution of TiN inclusions on the cross section of hot-rolled plate was studied using automated scanning electron microscopy/energy-dispersive X-ray spectroscopy inclusion analysis (ASPEX 1020 system). It was found that the number density decreases sharply from the surface to the center of the hot-rolled plate, whereas the average size increases. Then, the distribution of TiN inclusions on the cross section of continuously cast slab was investigated. Similarly, numerous small-sized TiN inclusions were generated at the subsurface of the slab. The average size rapidly increased and the number density dramatically decreased from the subsurface to 1/4 thickness, while from 1/4 thickness to 1/2 thickness, the increase in average size and the decrease in number density were slight. Thermodynamics results showed that TiN inclusion was formed below the liquidus temperature, which indicated that TiN inclusions could not be formed during secondary refining. Considering the microsegregation of solute elements and the equilibrium of TiN formation during solidification, TiN precipitated in the mushy zone when the solid fraction was close to 0.2. The growth of TiN was analyzed based on the diffusion-controlled growth model. With the increase in cooling rate, the time for TiN growth decreased and the size of TiN inclusions was diminished, which revealed the size distribution of TiN inclusions in the cast slab qualitatively.展开更多
The leaching kinetics of silver and lead simultaneously from zinc residue by chloride was investigated.The effects of stirring speed,temperature,sodium chloride concentration,particle size and liquid/solid ratio on Ag...The leaching kinetics of silver and lead simultaneously from zinc residue by chloride was investigated.The effects of stirring speed,temperature,sodium chloride concentration,particle size and liquid/solid ratio on Ag and Pb dissolution in sodium chloride were studied.It was determined that the dissolution rates increased with increasing sodium chloride concentration,temperature and decreasing particle size.The dissolution kinetics followed a shrinking core model,with inter-diffusion through gangue layer as the rate determining step.This finding is in accordance with the apparent activation energy(E_a) of 26.8 kJ·mol^(-1)(Ag) and 26.5 kJ·mol^(-1)(Pb),and a linear relationship between the rate constant and the reciprocal of squared particle size.The orders of reaction with respect to sodium chloride concentration,temperature and particle size were also achieved.The rate of reaction based on diffusion-controlled process can be expressed by semi-empirical equations.展开更多
A hydrogen evolution-assisted one-pot aqueous approach was developed for facile synthesis of trimetallic Pd Ni Ru alloy nanochain-like networks（Pd Ni Ru NCNs） by only using KBHas the reductant, without any specific ...A hydrogen evolution-assisted one-pot aqueous approach was developed for facile synthesis of trimetallic Pd Ni Ru alloy nanochain-like networks（Pd Ni Ru NCNs） by only using KBHas the reductant, without any specific additive（e.g. surfactant, polymer, template or seed）. The products were mainly investigated by transmission electron microscopy（TEM）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The hierarchical architectures were formed by the oriented assembly growth and the diffusioncontrolled deposition in the presence of many in-situ generated hydrogen bubbles. The architectures had the largest electrochemically active surface area（ECSA） of 84.32 mgPdthan Pd Ni nanoparticles(NPs,65.23 mgPd), Pd Ru NPs(23.12 mgPd), Ni Ru NPs（nearly zero）, and commercial Pd black(6.01 mgPd), outperforming the referenced catalysts regarding the catalytic characters for hydrazine oxygen reaction（HOR）. The synthetic route provides new insight into the preparation of other trimetallic nanocatalysts in fuel cells.展开更多
Polysulfide absorption in a micropore-rich structure has been reported to be capable of efficiently confining the shuttle effect for high-performance lithium-sulfur(Li–S)batteries.Here,a labyrinth maze-like spherical...Polysulfide absorption in a micropore-rich structure has been reported to be capable of efficiently confining the shuttle effect for high-performance lithium-sulfur(Li–S)batteries.Here,a labyrinth maze-like spherical honeycomb-like carbon with micropore-rich structure was synthesized,which is employed as a template host material of sulfur to study the shuttle effects.The results strongly confirm that a diffusion controlled process rather than an absorption resulted surface-controlled process occurs in an even micropore-rich cathode but still greatly inhibits the shuttle effect.Thus,the battery achieves a high initial discharge specific capacity of 1120 mAh g1 at 0.25 C and super cycling stability for 1635 cycles with only 0.035%capacity decay per cycle with 100%Coulombic efficiency.We would like to propose a new mechanism for shuttle effect inhibition in micropores.In terms of the diffusion control process in microporous paths of a labyrinth maze structure,polysulfides experience a long travel to realize continuous reductions of sulfur and polysulfides until formation of the final solid product.This efficiently prevents the polysulfides escaping to electrolyte.The labyrinth maze-like honeycomb structure also offers fast electron transfer and enhanced mass transport as well as robust mechanical strength retaining intact structure for long cycle life.This work sheds lights on new fundamental insights behind the shuttle effects with universal significance while demonstrating prominent merits of a robust labyrinth maze-like structure in high performance cathode for high-performance Li–S batteries.展开更多
Using the phase field crystal approach, the crystallization process within the liquid-solid coexistence region is inves- tigated for a square lattice on an atomic scale. Two competing growth modes, i.e., the diffusion...Using the phase field crystal approach, the crystallization process within the liquid-solid coexistence region is inves- tigated for a square lattice on an atomic scale. Two competing growth modes, i.e., the diffusion-controlled growth through long-range atomic migration in liquid and the diffusionless growth through local atom rearrangement, which give rise to two completely different crystallization behaviors, are compared. In the diffusion-controlled regime, the interface migrates in a layerwise manner, leading to a gradual change of crystal morphology from truncated square to four-fold symmetric dendrite with the increase of driving force. For the diffusionless growth mode, a single crystal with no significant density change occupies the whole system at a faster rate while exhibiting a small growth anisotropy. The competition between these two modes is also discussed from the key input of the phase field crystal model： the correlation function.展开更多
Growth of Czochralski (CZ) silicon crystals under the magnetic field induced by a cusp-shaped permanent magnet of NdFeB has been investigated. It is found that the mass transport in silicon melt was controlled by its ...Growth of Czochralski (CZ) silicon crystals under the magnetic field induced by a cusp-shaped permanent magnet of NdFeB has been investigated. It is found that the mass transport in silicon melt was controlled by its diffusion while the magnetic intensity at the edge of a crucible was over 0.15 T. In comparison with the growth of conventional CZ silicon without magnetic field, the resistivity homogeneity of the CZ silicon under the magnetic field was improved. Furthermore, the Marangoni convection which has a significant influence on the control of oxygen concentration was observed on the surface of silicon melt. It is suggested that the crystal growth mechanism in magnetic field was similar to that in micro-gravity if a critical value was reached, named the growth of equivalent micro-gravity. The relationship of the equivalent micro-gravity and the magnetic intensity was derived as g=(v0/veff)g0. Finally, the orders of the equivalent micro-gravity corresponding to two crucibles with characteristic sizes were calculated.展开更多
基金This work was financially supported by the National Natural Science Foundation of China (No. 50390090).
文摘The kinetic model for diffusion-controlled intermolecular reaction of homogenous polymer under steady shear was theoretically studied. The classic formalism and the concept of conformation ellipsoids were integrated to get a new equation, which directly correlates the rate constant with shear rate. It was found that the rate constant is not monotonic with shear rate. The scale of rate constant is N^-1.5 （N is the length of chains）, which is in consistent with de Gennes＇s result.
基金Supported by the Scientific Research Foundation of the State Education Ministry for the Returned Overseas Chinese Scholars (D4200111).
文摘In studying the diffusion-controlled adsorption kinetics of aqueous surfactant solutions at the air/solution surface by means of the maximal bubble pressure method, Fick's diffusion equation for a sphere should be used. In this paper the equation was solved by means of Laplace transformation under different initial and boundary conditions. The dynamic surface adsorption F(t) for a surfactant solution, which was used to describe the diffusion-controlled adsorption kinetics at the solution surface, was derived. Different from the planar surface adsorption, the dynamic surface adsorption F(t) for the short time consists of two terms: one is the same as Ward-Tordai equation and the other reflects the geometric effect caused by the spherical bubble surface. This effect should not be neglected for the very small radius of the capillary. The equilibrium surface tension γeq and the dynamic surface tension γ(t) of aqueous C10E6 [CH3(CH2)9(OCH2CH2)6OH] solution at temperature 25℃ were measuredby means of Wilhelmy plate method and maximal bubble pressure method respectively. As t→ 0, the theoreticalanalysis is in good agreement with experimental results and the dependence of γ(t) on is linear.
文摘In this paper, the equilibrium surface tension and the dynamic surface tension of aqueous Triton X-100 solution at temperature 25 ℃ were measured by means of Wilhelmy plate method and maximal bubble pressure method respectively. The determined critical micellar concentration（cmc） of Triton X-100 at 25 ℃ is (2.2×10-4) mol/dm3. The adsorption mechanics of Triton X-100 at air/solution was determined. For the submicellar concentrations it is diffusion-controlled. The diffusion coefficient was calculated from the experimental data in the range of short limit. In the range of long time adsorption, the subsurface concentration is fitted from the measured dynamic surface tensions.
文摘A refined double integral method has been applied to the problem encountered in the diffu-sion release of a drug from a polymeric matrix.The finite external mass transfer resistance has alsobeen incorporated into the present analysis.Experimental release rates of 5-fluorouracil fromethylene-vinyl alcohol copolymer into distilled water were measured in order to test the applicabilityof these models.All system parameters were measured by experiments and models were built up.Themodels presented here are much more accurate than Higuchi model and much easier than the exactsolutions.In view of accuracy,the models are almost the same as the exact solutions.The experi-mental release data agree Well with the computed
文摘In order to clarify and control the silver defect on surface of cold-rolled sheet of the Ti-stabilized ultra-pure ferrite stainless steel, the distribution of TiN inclusions on the cross section of hot-rolled plate was studied using automated scanning electron microscopy/energy-dispersive X-ray spectroscopy inclusion analysis (ASPEX 1020 system). It was found that the number density decreases sharply from the surface to the center of the hot-rolled plate, whereas the average size increases. Then, the distribution of TiN inclusions on the cross section of continuously cast slab was investigated. Similarly, numerous small-sized TiN inclusions were generated at the subsurface of the slab. The average size rapidly increased and the number density dramatically decreased from the subsurface to 1/4 thickness, while from 1/4 thickness to 1/2 thickness, the increase in average size and the decrease in number density were slight. Thermodynamics results showed that TiN inclusion was formed below the liquidus temperature, which indicated that TiN inclusions could not be formed during secondary refining. Considering the microsegregation of solute elements and the equilibrium of TiN formation during solidification, TiN precipitated in the mushy zone when the solid fraction was close to 0.2. The growth of TiN was analyzed based on the diffusion-controlled growth model. With the increase in cooling rate, the time for TiN growth decreased and the size of TiN inclusions was diminished, which revealed the size distribution of TiN inclusions in the cast slab qualitatively.
基金supported by the Natural Science Foundation of Shandong Province,China (No.ZR2010EL006)High Education Science Technology Program of Shangdong Province (No. J12LA04)
文摘The leaching kinetics of silver and lead simultaneously from zinc residue by chloride was investigated.The effects of stirring speed,temperature,sodium chloride concentration,particle size and liquid/solid ratio on Ag and Pb dissolution in sodium chloride were studied.It was determined that the dissolution rates increased with increasing sodium chloride concentration,temperature and decreasing particle size.The dissolution kinetics followed a shrinking core model,with inter-diffusion through gangue layer as the rate determining step.This finding is in accordance with the apparent activation energy(E_a) of 26.8 kJ·mol^(-1)(Ag) and 26.5 kJ·mol^(-1)(Pb),and a linear relationship between the rate constant and the reciprocal of squared particle size.The orders of reaction with respect to sodium chloride concentration,temperature and particle size were also achieved.The rate of reaction based on diffusion-controlled process can be expressed by semi-empirical equations.
基金financially supported by the Nation Natural Science Foundation of China(No.21475118)
文摘A hydrogen evolution-assisted one-pot aqueous approach was developed for facile synthesis of trimetallic Pd Ni Ru alloy nanochain-like networks（Pd Ni Ru NCNs） by only using KBHas the reductant, without any specific additive（e.g. surfactant, polymer, template or seed）. The products were mainly investigated by transmission electron microscopy（TEM）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The hierarchical architectures were formed by the oriented assembly growth and the diffusioncontrolled deposition in the presence of many in-situ generated hydrogen bubbles. The architectures had the largest electrochemically active surface area（ECSA） of 84.32 mgPdthan Pd Ni nanoparticles(NPs,65.23 mgPd), Pd Ru NPs(23.12 mgPd), Ni Ru NPs（nearly zero）, and commercial Pd black(6.01 mgPd), outperforming the referenced catalysts regarding the catalytic characters for hydrazine oxygen reaction（HOR）. The synthetic route provides new insight into the preparation of other trimetallic nanocatalysts in fuel cells.
基金Supplementary data to this article can be found online at https://doi.org/10.1016/j.matre.2022.100159.
文摘Polysulfide absorption in a micropore-rich structure has been reported to be capable of efficiently confining the shuttle effect for high-performance lithium-sulfur(Li–S)batteries.Here,a labyrinth maze-like spherical honeycomb-like carbon with micropore-rich structure was synthesized,which is employed as a template host material of sulfur to study the shuttle effects.The results strongly confirm that a diffusion controlled process rather than an absorption resulted surface-controlled process occurs in an even micropore-rich cathode but still greatly inhibits the shuttle effect.Thus,the battery achieves a high initial discharge specific capacity of 1120 mAh g1 at 0.25 C and super cycling stability for 1635 cycles with only 0.035%capacity decay per cycle with 100%Coulombic efficiency.We would like to propose a new mechanism for shuttle effect inhibition in micropores.In terms of the diffusion control process in microporous paths of a labyrinth maze structure,polysulfides experience a long travel to realize continuous reductions of sulfur and polysulfides until formation of the final solid product.This efficiently prevents the polysulfides escaping to electrolyte.The labyrinth maze-like honeycomb structure also offers fast electron transfer and enhanced mass transport as well as robust mechanical strength retaining intact structure for long cycle life.This work sheds lights on new fundamental insights behind the shuttle effects with universal significance while demonstrating prominent merits of a robust labyrinth maze-like structure in high performance cathode for high-performance Li–S batteries.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51174168 and 51274167)the Foundation for Fundamental Research of Northwestern Polytechnical University,China(Grant No.JC20120222)
文摘Using the phase field crystal approach, the crystallization process within the liquid-solid coexistence region is inves- tigated for a square lattice on an atomic scale. Two competing growth modes, i.e., the diffusion-controlled growth through long-range atomic migration in liquid and the diffusionless growth through local atom rearrangement, which give rise to two completely different crystallization behaviors, are compared. In the diffusion-controlled regime, the interface migrates in a layerwise manner, leading to a gradual change of crystal morphology from truncated square to four-fold symmetric dendrite with the increase of driving force. For the diffusionless growth mode, a single crystal with no significant density change occupies the whole system at a faster rate while exhibiting a small growth anisotropy. The competition between these two modes is also discussed from the key input of the phase field crystal model： the correlation function.
基金the National Natural Science Foundation of China (Grant No. 59972007) the Ministry of National Science and Technology and the Natural Science Foundation of Hebei Province (No.599033).
文摘Growth of Czochralski (CZ) silicon crystals under the magnetic field induced by a cusp-shaped permanent magnet of NdFeB has been investigated. It is found that the mass transport in silicon melt was controlled by its diffusion while the magnetic intensity at the edge of a crucible was over 0.15 T. In comparison with the growth of conventional CZ silicon without magnetic field, the resistivity homogeneity of the CZ silicon under the magnetic field was improved. Furthermore, the Marangoni convection which has a significant influence on the control of oxygen concentration was observed on the surface of silicon melt. It is suggested that the crystal growth mechanism in magnetic field was similar to that in micro-gravity if a critical value was reached, named the growth of equivalent micro-gravity. The relationship of the equivalent micro-gravity and the magnetic intensity was derived as g=(v0/veff)g0. Finally, the orders of the equivalent micro-gravity corresponding to two crucibles with characteristic sizes were calculated.
