The development of functional relationships between the observed deposition rate and the experimental conditions is an important step toward understanding and optimizing low-pressure chemical vapor deposition(LPCVD)or...The development of functional relationships between the observed deposition rate and the experimental conditions is an important step toward understanding and optimizing low-pressure chemical vapor deposition(LPCVD)or low-pressure chemical vapor infiltration(LPCVI).In the field of ceramic matrix composites(CMCs),methyltrichlorosilane(CH3 SiCl3,MTS)is the most widely used source gas system for SiC,because stoichiometric SiC deposit can be facilitated at 900°C–1300°C.However,the reliability and accuracy of existing numerical models for these processing conditions are rarely reported.In this study,a comprehensive transport model was coupled with gas-phase and surface kinetics.The resulting gas-phase kinetics was confirmed via the measured concentration of gaseous species.The relationship between deposition rate and 24 gaseous species has been effectively evaluated by combining the special superiority of the novel extreme machine learning method and the conventional sticking coefficient method.Surface kinetics were then proposed and shown to reproduce the experimental results.The proposed simulation strategy can be used for different material systems.展开更多
Carbon nanotubes(CNTs)as superior support materials for functional nanoparticles(NPs)have been widely demonstrated.Nevertheless,the homogeneous loading of these NPs is still frustrated due to the inert surface of CNTs...Carbon nanotubes(CNTs)as superior support materials for functional nanoparticles(NPs)have been widely demonstrated.Nevertheless,the homogeneous loading of these NPs is still frustrated due to the inert surface of CNTs.In this work,a facile gas-phase pyrolysis strategy that the mixture of ferrocene and CNTs are confined in an isolated reactor with rising temperature is developed to fabricate a carbon-coated Fe3O4 nanoparticle/carbon nanotube(Fe3O4@C/CNT)composite.It is found the ultra-small Fe3O4 NPs(<10 nm)enclosed in a thin carbon layer are uniformly anchored on the surface of CNTs.These structural benefits result in the excellent lithium-ion storage performances of the Fe3O4@C/CNT composite.It delivers a stable reversible capacity of 861 mA·h·g^-1 at the current density of 100 mA·g^-1 after 100 cycles.The capacity retention reaches as high as 54.5%even at 6000 mA·g^-1.The kinetic analysis indicates that the featured structural modification improves the surface condition of the CNT matrix,and contributes to greatly decreased interface impendence and faster charge transfer.In addition,the post-morphology observation of the tested sample further confirms the robustness of the Fe3O4@C/CNT configuration.展开更多
基金the National Key R&D Program of China(Grants No.2017YFB0703200)National Natural Science Foundation of China(Grants Nos.51702100,51972268)China Postdoctoral Science Foundation(Grants No.2018M643075)for financial support。
文摘The development of functional relationships between the observed deposition rate and the experimental conditions is an important step toward understanding and optimizing low-pressure chemical vapor deposition(LPCVD)or low-pressure chemical vapor infiltration(LPCVI).In the field of ceramic matrix composites(CMCs),methyltrichlorosilane(CH3 SiCl3,MTS)is the most widely used source gas system for SiC,because stoichiometric SiC deposit can be facilitated at 900°C–1300°C.However,the reliability and accuracy of existing numerical models for these processing conditions are rarely reported.In this study,a comprehensive transport model was coupled with gas-phase and surface kinetics.The resulting gas-phase kinetics was confirmed via the measured concentration of gaseous species.The relationship between deposition rate and 24 gaseous species has been effectively evaluated by combining the special superiority of the novel extreme machine learning method and the conventional sticking coefficient method.Surface kinetics were then proposed and shown to reproduce the experimental results.The proposed simulation strategy can be used for different material systems.
基金supported by the National Natural Science Foundation of China(Grant No.51702191)the Natural Science Foundation of Shanxi Province(Grant No.201701D221062)+1 种基金the Scientific and Technological Innovation Programs of High Education Institutions in Shanxi(Grant No.2017110)the Shanxi“1331 Project"Key Innovative Rescarch Team.
文摘Carbon nanotubes(CNTs)as superior support materials for functional nanoparticles(NPs)have been widely demonstrated.Nevertheless,the homogeneous loading of these NPs is still frustrated due to the inert surface of CNTs.In this work,a facile gas-phase pyrolysis strategy that the mixture of ferrocene and CNTs are confined in an isolated reactor with rising temperature is developed to fabricate a carbon-coated Fe3O4 nanoparticle/carbon nanotube(Fe3O4@C/CNT)composite.It is found the ultra-small Fe3O4 NPs(<10 nm)enclosed in a thin carbon layer are uniformly anchored on the surface of CNTs.These structural benefits result in the excellent lithium-ion storage performances of the Fe3O4@C/CNT composite.It delivers a stable reversible capacity of 861 mA·h·g^-1 at the current density of 100 mA·g^-1 after 100 cycles.The capacity retention reaches as high as 54.5%even at 6000 mA·g^-1.The kinetic analysis indicates that the featured structural modification improves the surface condition of the CNT matrix,and contributes to greatly decreased interface impendence and faster charge transfer.In addition,the post-morphology observation of the tested sample further confirms the robustness of the Fe3O4@C/CNT configuration.
