A numerical simulation based on a regularized phase field model is developed to describe faceted dendrite growth morphology. The effects of mesh grid, anisotropy, supersaturation and fold symmetry on dendrite growth m...A numerical simulation based on a regularized phase field model is developed to describe faceted dendrite growth morphology. The effects of mesh grid, anisotropy, supersaturation and fold symmetry on dendrite growth morphology were investigated, respectively. These results indicate that the nucleus grows into a hexagonal symmetry faceted dendrite. When the mesh grid is above 640×640, the size has no much effect on the shape. With the increase in the anisotropy value, the tip velocities of faceted dendrite increase and reach a balance value, and then decrease gradually. With the increase in the supersaturation value, crystal evolves from circle to the developed faceted dendrite morphology. Based on the Wulff theory and faceted symmetry morphology diagram, the proposed model was proved to be effective, and it can be generalized to arbitrary crystal symmetries.展开更多
Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a cry...Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.展开更多
A novel method was developed to deposit a large crystal diamond with good facets up to 1000 μm on a tungsten substrate using a microwave plasma enhanced chemical vapor deposition （MPCVD）. This method consists of tw...A novel method was developed to deposit a large crystal diamond with good facets up to 1000 μm on a tungsten substrate using a microwave plasma enhanced chemical vapor deposition （MPCVD）. This method consists of two steps, namely single-crystal nucleation and growth. Prior to the fabrication of the well-faceted, large crystal diamond, an investigation was made into the nucleation and growth of the diamond which were affected by the O2 concentration and substrate temperature. Deposited diamond crystals were characterized by scanning electron microscopy and micro-Raman spectroscopy. The results showed that the conditions of single-crystal nucleation were appropriate when the ratio of H2/CH4/O2 was about 200/7.0/2.0, while the sub- strate temperature Ts of 1000℃ to 1050℃ was the appropriate range for single-crystal diamond growth. Under the optimum parameters, a well-faeeted large crystal diamond was obtained.展开更多
Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is ...Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is indicated that the entire facet dendrite shapes are obtained by using regularized phase field model. Steady state tip velocity of dendrite drives to a fixed value when γ≤0.13. With further increasing the anisotropy value, steady state tip velocity decreases and the size is smaller. With the increase in the undercooling and coupling parameter, crystal grows from facet to facet dendrite. In addition, with increasing coupling parameter, the facet part of facet dendrite decreases gradually, which is in good agreement with Wulff theory.展开更多
Noble metallic nanocrystals are used in a wide variety of applications,such as catalysis,batteries,and bio-and chemical sensors.Most of the previous studies focus on the preparation of thermodynamically stable nanocry...Noble metallic nanocrystals are used in a wide variety of applications,such as catalysis,batteries,and bio-and chemical sensors.Most of the previous studies focus on the preparation of thermodynamically stable nanocrystals enclosed by low-index facets and discuss their corresponding catalytic properties.Recently,researchers have found that the nanocrystals with high-index facets(HIFs)are of more interest for electrocatalysis.Herein,we review recent key progress in the synthesis of noble metallic nanoparticles enclosed with HIFs and their facetdependent electrocatalytic behaviors.First,we introduce the concept of HIFs,and establish the correlation between their surface structure and catalytic activity.Then,we discuss various synthetic approaches for controlling the shapes and composition of the nanocrystals enclosed by HIFs.Afterwards,we showcase the enhanced electrocatalytic performance realized by HIF-based nanostructures.Finally,we provide guidance on how to improve the electrocatalysis by engineering HIFs on noble metallic nanocrystals.展开更多
目的利用三维有限元法评估腰椎经皮内镜下不同的关节突成形部位对椎体活动度(range of motion, ROM)的影响。方法建立正常L3～5三维有限元模型,模拟腰椎经皮内镜技术分别在L5上关节突"尖部"或"基底部"做直径0.75 c...目的利用三维有限元法评估腰椎经皮内镜下不同的关节突成形部位对椎体活动度(range of motion, ROM)的影响。方法建立正常L3～5三维有限元模型,模拟腰椎经皮内镜技术分别在L5上关节突"尖部"或"基底部"做直径0.75 cm圆柱状骨切除以模拟椎间孔成形,从而获得正常L3～5模型、关节突尖部成形模型和关节突基底部成形模型。给予特定加载条件,比较3种模型在前屈、后伸、左右侧曲、左右旋转工况下L3～4、L4～5节段ROM变化情况。结果 L5上关节突尖部成形后,在后伸、左右侧屈、左右旋转状态下L4～5节段ROM均较正常明显增大,以左旋最为明显;L5上关节突基底部成形后,在左右旋转状态下L4～5节段ROM较正常稍微增大。L5上关节突尖部、基底部成形后在6种不同运动状态下临近节段L3/4的ROM均无明显变化。结论腰椎经皮内镜技术下,L5上关节突尖部成形较关节突基底部成形对L4～5节段ROM影响较大。L5上关节突成型对临近节段L3～4的ROM无明显影响。展开更多
基金Projects(11102164,11304243)supported by the National Natural Science Foundation of ChinaProject(2014JQ1039)supported by the Natural Science Foundation of Shannxi Province,China+1 种基金Project(3102016ZY027)supported by the Fundamental Research Funds for the Central Universities of ChinaProject(13GH014602)supported by the Program of New Staff and Research Area Project of NWPU,China
文摘A numerical simulation based on a regularized phase field model is developed to describe faceted dendrite growth morphology. The effects of mesh grid, anisotropy, supersaturation and fold symmetry on dendrite growth morphology were investigated, respectively. These results indicate that the nucleus grows into a hexagonal symmetry faceted dendrite. When the mesh grid is above 640×640, the size has no much effect on the shape. With the increase in the anisotropy value, the tip velocities of faceted dendrite increase and reach a balance value, and then decrease gradually. With the increase in the supersaturation value, crystal evolves from circle to the developed faceted dendrite morphology. Based on the Wulff theory and faceted symmetry morphology diagram, the proposed model was proved to be effective, and it can be generalized to arbitrary crystal symmetries.
基金Project(11102164)supported by the National Natural Science Foundation of ChinaProject(G9KY101502)supported by NPU Foundation for Fundamental Research,China
文摘Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.
基金supported by the Natural Science Foundation of Hubei Province of China(2008CDB255)the Educational Commission of Hubei Province of China(No.Q20081505)the Key Laboratory for Green Chemical Process of the Ministry of Education of China (No.RGCT200801)
文摘A novel method was developed to deposit a large crystal diamond with good facets up to 1000 μm on a tungsten substrate using a microwave plasma enhanced chemical vapor deposition （MPCVD）. This method consists of two steps, namely single-crystal nucleation and growth. Prior to the fabrication of the well-faceted, large crystal diamond, an investigation was made into the nucleation and growth of the diamond which were affected by the O2 concentration and substrate temperature. Deposited diamond crystals were characterized by scanning electron microscopy and micro-Raman spectroscopy. The results showed that the conditions of single-crystal nucleation were appropriate when the ratio of H2/CH4/O2 was about 200/7.0/2.0, while the sub- strate temperature Ts of 1000℃ to 1050℃ was the appropriate range for single-crystal diamond growth. Under the optimum parameters, a well-faeeted large crystal diamond was obtained.
基金Projects(50331040 60171034) supported by the National Natural Science Foundation of China
文摘Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is indicated that the entire facet dendrite shapes are obtained by using regularized phase field model. Steady state tip velocity of dendrite drives to a fixed value when γ≤0.13. With further increasing the anisotropy value, steady state tip velocity decreases and the size is smaller. With the increase in the undercooling and coupling parameter, crystal grows from facet to facet dendrite. In addition, with increasing coupling parameter, the facet part of facet dendrite decreases gradually, which is in good agreement with Wulff theory.
基金This work was financially supported by the Beijing Natural Science Foundation(JQ18005)the National Natural Science Foundation of China(NSFC)(No.51671003)+2 种基金National Basic Research Program of China(No.2016YFB0100201)the China Postdoctoral Science Foundation(No.2017M620518)Open Project Foundation of State Key Laboratory of Chemical Resource Engineering,the start-up supports from Peking University and Young Thousand Talented Program.
文摘Noble metallic nanocrystals are used in a wide variety of applications,such as catalysis,batteries,and bio-and chemical sensors.Most of the previous studies focus on the preparation of thermodynamically stable nanocrystals enclosed by low-index facets and discuss their corresponding catalytic properties.Recently,researchers have found that the nanocrystals with high-index facets(HIFs)are of more interest for electrocatalysis.Herein,we review recent key progress in the synthesis of noble metallic nanoparticles enclosed with HIFs and their facetdependent electrocatalytic behaviors.First,we introduce the concept of HIFs,and establish the correlation between their surface structure and catalytic activity.Then,we discuss various synthetic approaches for controlling the shapes and composition of the nanocrystals enclosed by HIFs.Afterwards,we showcase the enhanced electrocatalytic performance realized by HIF-based nanostructures.Finally,we provide guidance on how to improve the electrocatalysis by engineering HIFs on noble metallic nanocrystals.
