Peculiar hierarchical microstructures in creatures inspire modern material design with distinct functionalities.Creatures can effortlessly construct sophisticated yet long-range ordered microstructure across bio-membr...Peculiar hierarchical microstructures in creatures inspire modern material design with distinct functionalities.Creatures can effortlessly construct sophisticated yet long-range ordered microstructure across bio-membrane through ion secretion and precipitation.However,microstructure biomimicry in current technology generally requires elaborate,point-by-point fabrication.Herein,a spontaneous yet controllable strategy is developed to achieve surface microstructure engineering through a natural surface phenomenon similar to ion secretion-precipitation,that is,coupled dissolution-precipitation.A series of hierarchical microstructures on mineral surfaces in fluids with tunable morphology,orientation,dimension,and spatial distribution are achieved by simply controlling initial dissolution and fluid chemistry.In seawater,long-range ordered film of vertically aligned brucite flakes forms through interfacial dissolution,nucleation,and confinement-induced orientation of flakes with vertically grown{110}plane,on the edge of which,fusiform aragonite epitaxially precipitates.With negligible initial surface dissolution,prismatic aragonite epitaxially grows on a calcite polyhedron-packed surface.By tuning fluid chemistry,closely packed calcite polyhedron and loosely packed calcite micro-pillars are engineered through rapid and retarded precipitation,respectively.Surprisingly,the spontaneously grown microstructures resemble those deliberately created by human or found in nature,and tremendously modulate surface functionality.These findings open new possibilities for facile and customizable engineering of microstructural surfaces,hierarchical heterostructures,and biomimetic materials.展开更多
The quality of semi-products of platinum metals and alloys, produced by way of plastic working, essentially depends on or, in many cases, is completely determined by the quality of ingots. Plastic working does not mak...The quality of semi-products of platinum metals and alloys, produced by way of plastic working, essentially depends on or, in many cases, is completely determined by the quality of ingots. Plastic working does not make it possible to eliminate or localize metallurgical defects. In many cases it promotes the occurence thereof. Low-rate casting with directional crystallization can ensure the production of dense ingots free of non-metallic inclusions, shrinkage and gas weakness, with observance of certain temperature/rate modes. After comparative tests of vertical and horizontal molds, preference has been given to horizontal water-cooled molds, allowing to cast all alloys in the conditions of directional crystallization.展开更多
Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomp...Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomposes. The decomposition result is fixed in the solid phase as inhomogeneous component distribution. Our experimental results enable to argue that the eutectic pattern forms due to interface instability and spinodal decomposition of non-equilibrium solution forming in front of the interface.展开更多
A transient numerical model was applied to simulating the axial-directional crystallization purification(ADCP) process of gallium(Ga) raw material at different coolant temperatures(Tc), and the evolutions of melt/crys...A transient numerical model was applied to simulating the axial-directional crystallization purification(ADCP) process of gallium(Ga) raw material at different coolant temperatures(Tc), and the evolutions of melt/crystal(m/c) interface shape, temperature distribution and thermal stresses were simulated and analyzed. The results showed that the m/c interface shape, temperature distribution, and thermal stress in the Ga material were determined by the Tc in the crystallizer during the ADCP process. The temperature gradient and thermal stress in the grown Ga crystal increased with decreasing Tc. At Tc=15 ℃, the m/c interface shape was flat, and the temperature gradient was ideal. Therefore, the Ga materials with lower thermal stresses and suitable m/c interface shape, and an ideal efficiency of impurity removal were obtained. The purity of Ga reached 6 N standard by using ADCP process repeated 6 times at Tc of 15 ℃. The results of the simulation showed good agreement with the experimental results.展开更多
There are some different opinions on the formation of striped migmatite. Many striped migmatites are distributed around the plutonic rocks in the core of hot dome in nature. This shows that the pressure of intrusive r...There are some different opinions on the formation of striped migmatite. Many striped migmatites are distributed around the plutonic rocks in the core of hot dome in nature. This shows that the pressure of intrusive rocks to wall rocks must play an important role in the formation of stripes. This paper, at first, discusses the effects of directional pressure (i. e. compressive stress from intrusive rock to wall rock) on particle migration and crystallization, and the physical mechanism of Ostwald maturation and its adjusting effect in crystalline growth. And then, on the basic principles of physics and chemistry, we lay down the stochastic evolutional rules of the formation of crystal nucleus, diffusion, crystallization and dissolution of leucosome (melt) particles; and,neglecting other restrictive conditions, we build an idealizedly simplified two-dimensional model of stochastic cellular automaton for the recrystallization of metamorphic rock under directional pressure, and realize it by writing a program of Windows on PC. Theoretical analyses and computer simulations show that, at the beginning, the free particles of leucosome are initially even distributed in the system and form many crystal nucleus ; then, the anisotropies of diffusion, crystallization and dissolution caused by the directional pressure together with the mechanisms of Ostwald maturation can make the nucleus successively grow to form lenses, unevenly disconnected stripes, and layer-stripe structure, which correspond to low, medium and high grades of metamorphism and migmatization, respectively; that is, the effect of the pressure of intrusive rock to wall rock alone can form streaked structure in migmatite. Moreover, cellular automaton, adopted in this paper, is a kind of discrete and local grid dynamic model, and is extremely suitable for simulating the evolution of spatiotemporal structure of real systems and analyzing micro-mechanism creating complex macro-phenomenon. We believe that cellular automata will have broad applications in the geos展开更多
The microscopic observation of directional crystallization of transparent organic melt of mixed dichlorobenzene (DCB) is made to study the interface morphology of growing crystal, the pattern of crystal growth and the...The microscopic observation of directional crystallization of transparent organic melt of mixed dichlorobenzene (DCB) is made to study the interface morphology of growing crystal, the pattern of crystal growth and the cause of impurity inclusion. The results of microscopic observation will provide great benefit to the theoretical and numerical studies of related directional crystallization process.展开更多
This research summarizes the analytical and experimental results of heat-transfer processes influence on defects formation during sapphire crystal growth by horizontal directed crystallization method(HDC).The shape of...This research summarizes the analytical and experimental results of heat-transfer processes influence on defects formation during sapphire crystal growth by horizontal directed crystallization method(HDC).The shape of solid-melt interface significantly influences the process of sapphire crystals growth by this method.We receive the Stefan problem solution for sapphire crystals growth.It allows investigating the crystal growth process and the related factors(thermal stresses on different stages of growth process),their influence on defects formation.We investigate the main reasons for the formation of defective structures of the solid phase of sapphire crystals and the influence of thermal unit construction,the crystal geometry on the quality of the resulting sapphire crystal.We study the structure formation process,impurity distribution,and the nature of the defects in the crystal during it growth.展开更多
A tunable high-Q surface acoustic wave(SAW)resonator in the form of several parallel-connected interdigital transducers loaded on a varying capacitance on lithium niobate substrates was developed and studied.The worki...A tunable high-Q surface acoustic wave(SAW)resonator in the form of several parallel-connected interdigital transducers loaded on a varying capacitance on lithium niobate substrates was developed and studied.The working frequency range was 90-2450 MHz.A method of calculating such resonators,considering losses in the metal film as well as losses due to the propagation of SAWs and transformations into bulk waves is proposed.Such a design allows one to obtain a quality factor over 5000 in the frequency range 2400-2483 MHz.The resonant frequency shifts by 600 kHz when the capacitance changes by±25%of the value of 21 pF(or 32 ppm/pF)and has an almost linear character.展开更多
Magnesium hydroxide with high purity and uniform particle size distribution was synthesized by the direct precipitation method using MgCl_(2) and NaOH as reactive materials and NaCl as additive to improve the crystall...Magnesium hydroxide with high purity and uniform particle size distribution was synthesized by the direct precipitation method using MgCl_(2) and NaOH as reactive materials and NaCl as additive to improve the crystallization behavior of the product.The particle size distribution,crystal phase,morphology,and surface area of magnesium hydroxide were characterized by Malvern laser particle size analyzer,X-ray diffraction(XRD),scanning electron microscope(SEM)and Branauer-Emmett-Teller(BET)method,respectively.The purity of products was analyzed by the chemical method.The effects of synthesis conditions on the particle size distribution and water content(filtration cake)of magnesium hydroxide were investigated.The results indicated that feeding mode and rate,and reaction temperature had important effects on water content and the particle size distribution of the product,and sodium chloride improved the crystallization behavior of magnesium hydroxide.The ball-like magne-sium hydroxides with the particle size distribution of 6.0–30.0μm and purity higher than 99.0%were obtained.This simple and mild synthesis method was promising to be scaled up for the industrial production of magnesium hydroxide.展开更多
Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-ba...Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.展开更多
基金National Key R&D Program of China,Grant/Award Number:2021YFB2600900National Science Fund for Distinguished Young Scholars of China,Grant/Award Number:51925903+3 种基金National Natural Science Foundation of China,Grant/Award Numbers:52108195,U21A20150Natural Science Foundation of Jiangsu Province,Grant/Award Number:BK20210264Natural Sciences and Engineering Research Council of CanadaCanada Research Chairs Program。
文摘Peculiar hierarchical microstructures in creatures inspire modern material design with distinct functionalities.Creatures can effortlessly construct sophisticated yet long-range ordered microstructure across bio-membrane through ion secretion and precipitation.However,microstructure biomimicry in current technology generally requires elaborate,point-by-point fabrication.Herein,a spontaneous yet controllable strategy is developed to achieve surface microstructure engineering through a natural surface phenomenon similar to ion secretion-precipitation,that is,coupled dissolution-precipitation.A series of hierarchical microstructures on mineral surfaces in fluids with tunable morphology,orientation,dimension,and spatial distribution are achieved by simply controlling initial dissolution and fluid chemistry.In seawater,long-range ordered film of vertically aligned brucite flakes forms through interfacial dissolution,nucleation,and confinement-induced orientation of flakes with vertically grown{110}plane,on the edge of which,fusiform aragonite epitaxially precipitates.With negligible initial surface dissolution,prismatic aragonite epitaxially grows on a calcite polyhedron-packed surface.By tuning fluid chemistry,closely packed calcite polyhedron and loosely packed calcite micro-pillars are engineered through rapid and retarded precipitation,respectively.Surprisingly,the spontaneously grown microstructures resemble those deliberately created by human or found in nature,and tremendously modulate surface functionality.These findings open new possibilities for facile and customizable engineering of microstructural surfaces,hierarchical heterostructures,and biomimetic materials.
文摘The quality of semi-products of platinum metals and alloys, produced by way of plastic working, essentially depends on or, in many cases, is completely determined by the quality of ingots. Plastic working does not make it possible to eliminate or localize metallurgical defects. In many cases it promotes the occurence thereof. Low-rate casting with directional crystallization can ensure the production of dense ingots free of non-metallic inclusions, shrinkage and gas weakness, with observance of certain temperature/rate modes. After comparative tests of vertical and horizontal molds, preference has been given to horizontal water-cooled molds, allowing to cast all alloys in the conditions of directional crystallization.
文摘Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomposes. The decomposition result is fixed in the solid phase as inhomogeneous component distribution. Our experimental results enable to argue that the eutectic pattern forms due to interface instability and spinodal decomposition of non-equilibrium solution forming in front of the interface.
基金Project(51465014)supported by the National Natural Science Foundation of ChinaProject(Guike AA17204021-7)supported by the Innovation Driven Development Special Foundation of Guangxi,China。
文摘A transient numerical model was applied to simulating the axial-directional crystallization purification(ADCP) process of gallium(Ga) raw material at different coolant temperatures(Tc), and the evolutions of melt/crystal(m/c) interface shape, temperature distribution and thermal stresses were simulated and analyzed. The results showed that the m/c interface shape, temperature distribution, and thermal stress in the Ga material were determined by the Tc in the crystallizer during the ADCP process. The temperature gradient and thermal stress in the grown Ga crystal increased with decreasing Tc. At Tc=15 ℃, the m/c interface shape was flat, and the temperature gradient was ideal. Therefore, the Ga materials with lower thermal stresses and suitable m/c interface shape, and an ideal efficiency of impurity removal were obtained. The purity of Ga reached 6 N standard by using ADCP process repeated 6 times at Tc of 15 ℃. The results of the simulation showed good agreement with the experimental results.
文摘There are some different opinions on the formation of striped migmatite. Many striped migmatites are distributed around the plutonic rocks in the core of hot dome in nature. This shows that the pressure of intrusive rocks to wall rocks must play an important role in the formation of stripes. This paper, at first, discusses the effects of directional pressure (i. e. compressive stress from intrusive rock to wall rock) on particle migration and crystallization, and the physical mechanism of Ostwald maturation and its adjusting effect in crystalline growth. And then, on the basic principles of physics and chemistry, we lay down the stochastic evolutional rules of the formation of crystal nucleus, diffusion, crystallization and dissolution of leucosome (melt) particles; and,neglecting other restrictive conditions, we build an idealizedly simplified two-dimensional model of stochastic cellular automaton for the recrystallization of metamorphic rock under directional pressure, and realize it by writing a program of Windows on PC. Theoretical analyses and computer simulations show that, at the beginning, the free particles of leucosome are initially even distributed in the system and form many crystal nucleus ; then, the anisotropies of diffusion, crystallization and dissolution caused by the directional pressure together with the mechanisms of Ostwald maturation can make the nucleus successively grow to form lenses, unevenly disconnected stripes, and layer-stripe structure, which correspond to low, medium and high grades of metamorphism and migmatization, respectively; that is, the effect of the pressure of intrusive rock to wall rock alone can form streaked structure in migmatite. Moreover, cellular automaton, adopted in this paper, is a kind of discrete and local grid dynamic model, and is extremely suitable for simulating the evolution of spatiotemporal structure of real systems and analyzing micro-mechanism creating complex macro-phenomenon. We believe that cellular automata will have broad applications in the geos
文摘The microscopic observation of directional crystallization of transparent organic melt of mixed dichlorobenzene (DCB) is made to study the interface morphology of growing crystal, the pattern of crystal growth and the cause of impurity inclusion. The results of microscopic observation will provide great benefit to the theoretical and numerical studies of related directional crystallization process.
基金The authors thank the Slovak partners(CEIT a.s.)for cooperation.The study was carried out with the financial support of the Russian Foundation for Basic Research,Project No.19-52-53026.
文摘This research summarizes the analytical and experimental results of heat-transfer processes influence on defects formation during sapphire crystal growth by horizontal directed crystallization method(HDC).The shape of solid-melt interface significantly influences the process of sapphire crystals growth by this method.We receive the Stefan problem solution for sapphire crystals growth.It allows investigating the crystal growth process and the related factors(thermal stresses on different stages of growth process),their influence on defects formation.We investigate the main reasons for the formation of defective structures of the solid phase of sapphire crystals and the influence of thermal unit construction,the crystal geometry on the quality of the resulting sapphire crystal.We study the structure formation process,impurity distribution,and the nature of the defects in the crystal during it growth.
基金This research work is supported by the Russian Ministry of Science and Higher Education under the project No.16.5405.2017/8.9。
文摘A tunable high-Q surface acoustic wave(SAW)resonator in the form of several parallel-connected interdigital transducers loaded on a varying capacitance on lithium niobate substrates was developed and studied.The working frequency range was 90-2450 MHz.A method of calculating such resonators,considering losses in the metal film as well as losses due to the propagation of SAWs and transformations into bulk waves is proposed.Such a design allows one to obtain a quality factor over 5000 in the frequency range 2400-2483 MHz.The resonant frequency shifts by 600 kHz when the capacitance changes by±25%of the value of 21 pF(or 32 ppm/pF)and has an almost linear character.
基金supported by the Shanghai Natural Science Foundation(No.09ZR147900)the Program for New Century Excellent Talents in University(NCET-08-0776).
文摘Magnesium hydroxide with high purity and uniform particle size distribution was synthesized by the direct precipitation method using MgCl_(2) and NaOH as reactive materials and NaCl as additive to improve the crystallization behavior of the product.The particle size distribution,crystal phase,morphology,and surface area of magnesium hydroxide were characterized by Malvern laser particle size analyzer,X-ray diffraction(XRD),scanning electron microscope(SEM)and Branauer-Emmett-Teller(BET)method,respectively.The purity of products was analyzed by the chemical method.The effects of synthesis conditions on the particle size distribution and water content(filtration cake)of magnesium hydroxide were investigated.The results indicated that feeding mode and rate,and reaction temperature had important effects on water content and the particle size distribution of the product,and sodium chloride improved the crystallization behavior of magnesium hydroxide.The ball-like magne-sium hydroxides with the particle size distribution of 6.0–30.0μm and purity higher than 99.0%were obtained.This simple and mild synthesis method was promising to be scaled up for the industrial production of magnesium hydroxide.
文摘Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.
