The microstructures and crystal growth directions of permanent mould casting(PMC) and directionally solidified(DS) Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouri...The microstructures and crystal growth directions of permanent mould casting(PMC) and directionally solidified(DS) Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouring temperature on the microstructure and crystal growth direction of permanent mould casting pure Al were also discussed. The results indicate that the α(Al) crystals in the pure Al do not always keep common columnar grains, but change from the columnar grains to columnar dendrites with developed arms as the pouring temperature rises. The growth direction also varies with the change of pouring temperature. Cu element has similar effects on the microstructures of the PMC and DS casting Al-Cu alloys and the α(Al) crystals gradually change from columnar crystals in turn to columnar dendrites and developed equiaxed dendrites as the Cu content increases. The crystal growth direction in the PMC alloys gradually approaches (110) orientation with increasing Cu content. But the resulting crystals with growth direction of (110) do not belong to feathery grains. There are also no feathery grains to form in all of the DS Al-Cu alloys.展开更多
The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg al oys with different Mg contents have been investigated. The results indicate that the effect of Mg cont...The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg al oys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basical y same for the al oys prepared by these two methods. The primary grains change from cel ular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cel ular or columnar grain region and the primary trunk spacing decrease. Al of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more paral el than those of the permanent mould casting al oys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.展开更多
Highly substituted n-atkyl celluloses with sidechains 3 to 10 carbon atoms long have been prepared from cellulose acetate, sodium hydroxide and n-alkyl bromides with dimethyl sulfoxide as solvent. Synthetic conditions...Highly substituted n-atkyl celluloses with sidechains 3 to 10 carbon atoms long have been prepared from cellulose acetate, sodium hydroxide and n-alkyl bromides with dimethyl sulfoxide as solvent. Synthetic conditions of n-alkyl celluloses were studied with respect to reaction temperature, time and yield. The molecular structure of the n-alkyl celluloses, which were obtained as white powders or as sticky, soft and birefringent solids at room temperature, was investigated by IR and NMR spectra and elemental analysis. The highly substituted n-alkyl celluloses all exhibited both therotropic and lyotropic liquid crystalline cholesteric phases in some non-polar solvents. The metting behavior and solubility of the n-alkyl celluloses were examined.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
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
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 modes of grain selection in spiral selector were investigated by both a ProCAST simulation and experimental confirmation.The results show that the efficiency of grain selection in starter block is associated with ...The modes of grain selection in spiral selector were investigated by both a ProCAST simulation and experimental confirmation.The results show that the efficiency of grain selection in starter block is associated with the geometry shape.At the early stage of grain selection,the optimization of grain orientation is dominated by competitive grain growth,but the optimization of grain orientation in starter block is gradually dominated by geometry shape at the later stage of grain selection.Besides,the spiral part could also optimize the orientation of the selected single crystal when the initial angle is large enough,and the single crystal selection in spiral parts with different pitch lengths and initial angles is dominated by different modes.The simulation results agree well with experimental ones.展开更多
Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a...Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions were investigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.展开更多
A theory of ultrasonic generation via direct interaction of transverse optic (TO) phonons with photons in anharmonic lattice of ionic crystals is presented. There are two methods of supplying light energy for the exci...A theory of ultrasonic generation via direct interaction of transverse optic (TO) phonons with photons in anharmonic lattice of ionic crystals is presented. There are two methods of supplying light energy for the excitation of TO lattice wave as a high frequency ultrasound: (A) incident light comes from the source outside the cavity? fulfilled with ionic crystal medium, (B) photon mode of the cavity possesses the gain of amplification by stimulated radiation of active atoms doping in the medium. More attention is drawn to the case (B). The working system of case (B), as a mixture of lasing action and ultrasonic generation, has the threshold phenomena like usual laser. And the linear stability analysis shows that the nonlineax phonon-photon coupling and the interaction among phonons themselves, both of which reflect the anharmonicity of lattice vibration, are necessary to the stable ultrasonic output. So this laser-ultrasonic generation mixture would be also a measure to investigate the lattice-dynamic nonlinearity and correlated electromagnetic properties of ionic crystals.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
基金Project(51061010)supported by the National Natural Science Foundation of ChinaProject(NCET-10-0023)supported by the Program for New Century Excellent Talents in University of ChinaProject(J201103)supported by the Program for Hongliu Outstanding Talents of Lanzhou University of Technology,China
文摘The microstructures and crystal growth directions of permanent mould casting(PMC) and directionally solidified(DS) Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouring temperature on the microstructure and crystal growth direction of permanent mould casting pure Al were also discussed. The results indicate that the α(Al) crystals in the pure Al do not always keep common columnar grains, but change from the columnar grains to columnar dendrites with developed arms as the pouring temperature rises. The growth direction also varies with the change of pouring temperature. Cu element has similar effects on the microstructures of the PMC and DS casting Al-Cu alloys and the α(Al) crystals gradually change from columnar crystals in turn to columnar dendrites and developed equiaxed dendrites as the Cu content increases. The crystal growth direction in the PMC alloys gradually approaches (110) orientation with increasing Cu content. But the resulting crystals with growth direction of (110) do not belong to feathery grains. There are also no feathery grains to form in all of the DS Al-Cu alloys.
基金financially supported by the National Natural Science Foundation of China(Grant No.51061010)the Program for New Century Excellent Talents in University of China(Grant No.NCET-10-0023)the Program for Hongliu Outstanding Talents of Lanzhou University of Technology
文摘The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg al oys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basical y same for the al oys prepared by these two methods. The primary grains change from cel ular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cel ular or columnar grain region and the primary trunk spacing decrease. Al of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more paral el than those of the permanent mould casting al oys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.
文摘Highly substituted n-atkyl celluloses with sidechains 3 to 10 carbon atoms long have been prepared from cellulose acetate, sodium hydroxide and n-alkyl bromides with dimethyl sulfoxide as solvent. Synthetic conditions of n-alkyl celluloses were studied with respect to reaction temperature, time and yield. The molecular structure of the n-alkyl celluloses, which were obtained as white powders or as sticky, soft and birefringent solids at room temperature, was investigated by IR and NMR spectra and elemental analysis. The highly substituted n-alkyl celluloses all exhibited both therotropic and lyotropic liquid crystalline cholesteric phases in some non-polar solvents. The metting behavior and solubility of the n-alkyl celluloses were examined.
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.
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.
基金supported by the National Basic Research Program(973 Program) of China under Grant No.2010CB631200(2010CB631206)the National Natural Science Foundation of China(NSFC) under Grant No.50801061,No.50931004,No.51071165the fund of the State Key Laboratory of Solidification Processing in NWPU under Grant No.SKLSP201112
文摘The modes of grain selection in spiral selector were investigated by both a ProCAST simulation and experimental confirmation.The results show that the efficiency of grain selection in starter block is associated with the geometry shape.At the early stage of grain selection,the optimization of grain orientation is dominated by competitive grain growth,but the optimization of grain orientation in starter block is gradually dominated by geometry shape at the later stage of grain selection.Besides,the spiral part could also optimize the orientation of the selected single crystal when the initial angle is large enough,and the single crystal selection in spiral parts with different pitch lengths and initial angles is dominated by different modes.The simulation results agree well with experimental ones.
文摘Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions were investigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.
基金This work is supported by the National Nature Science Foundation of China!(No. 69678003)
文摘A theory of ultrasonic generation via direct interaction of transverse optic (TO) phonons with photons in anharmonic lattice of ionic crystals is presented. There are two methods of supplying light energy for the excitation of TO lattice wave as a high frequency ultrasound: (A) incident light comes from the source outside the cavity? fulfilled with ionic crystal medium, (B) photon mode of the cavity possesses the gain of amplification by stimulated radiation of active atoms doping in the medium. More attention is drawn to the case (B). The working system of case (B), as a mixture of lasing action and ultrasonic generation, has the threshold phenomena like usual laser. And the linear stability analysis shows that the nonlineax phonon-photon coupling and the interaction among phonons themselves, both of which reflect the anharmonicity of lattice vibration, are necessary to the stable ultrasonic output. So this laser-ultrasonic generation mixture would be also a measure to investigate the lattice-dynamic nonlinearity and correlated electromagnetic properties of ionic crystals.
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.