The transition from a fiat solid-liquid interface to a skeletal shape during BaB2O4 （BBO） single crystal growth in Li2B4O7 flux is observed in real time by an optical high-temperature in-situ observation system. The...The transition from a fiat solid-liquid interface to a skeletal shape during BaB2O4 （BBO） single crystal growth in Li2B4O7 flux is observed in real time by an optical high-temperature in-situ observation system. The movement of crystal step is also investigated. The observation results demonstrate that the steps propagate along and parallel to the fiat interface when the crystal size is small. Nevertheless, they will ‘bend＇ close to the face centre if the crystal size becomes greater. Atomic force microscopy reveals that more deposition places near the face centre give rise to the bending of advancing steps and thus the formation of a vicinal interface structure. Measurements of step velocity show that the velocity keeps nearly constant at different moments for one specific step, whereas the step on a newly formed layer advanced faster than that on a previously formed one when the crystal size is larger than 210μm or so. Thus interracial morphological instability occurs and a skeletal interface is obtained.展开更多
The cell-to-dendrite transition of succinonitrile melt suspended on a loop-shaped Pt heater is observed in real time by a differential interference microscope coupled with Schlieren technique. The transition is divide...The cell-to-dendrite transition of succinonitrile melt suspended on a loop-shaped Pt heater is observed in real time by a differential interference microscope coupled with Schlieren technique. The transition is divided into two parts： a dendrite coalition process and a subsequent dendrite elimination process. Firstly the dendrites from the same cell are united into a single dendrite. Secondly the competitive growth of dendrites from different cells leads to the elimination of dendrites. The two processes can be understood when involving crystallographic orientation. In addition, the tip velocity and primary spacing of a cell/dendrite are also measured. It turns out that the primary spacing has a significant jump, whereas the growth velocity has no abrupt change during the cell-to-dendrite transition.展开更多
The solid-liquid interface motion of NaBi（WO4）2 （NBWO） melt crystal growth is observed in an in situ system, in which the whole processes of interface transition from fiat interface and cellular to dendrite are vi...The solid-liquid interface motion of NaBi（WO4）2 （NBWO） melt crystal growth is observed in an in situ system, in which the whole processes of interface transition from fiat interface and cellular to dendrite are visualized. The spacing of the dendrite under smaller temperature gradient turns out to be larger than that under larger temperature gradient, which is found to be sensitive to the temperature distribution. The mechanism of dendrite growth of NBWO is studied based on the model of the growth units of anion coordination polyhedra. The { 001} face has two apex links, so it shows higher stability and has high growth rate and forms the arm of dendrite, whereas the {010} face has only one apex link, and thus shows relative slower growth rate and firstly forms the branches.展开更多
The formation of macrostep during high-temperature phase of barium meta-borate （^-BaB204） single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy （AFM）. T...The formation of macrostep during high-temperature phase of barium meta-borate （^-BaB204） single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy （AFM）. The in- si$u observation results demonstrate that the critical linear size of growing facet exceeding the size that the macrostep generates is significantly anisotropic. The critical linear sizes are around 280 ~m and 620 ~m for {1010} and （T010} planes, respectively. AFM study illustrates that macrostep train with a height of 150 nm^200 nm is one typical morphological feature of the as-grown crystal surface. The riser of each macrostep consists of several straight and parallel sub-steps, indicating the occurrence of step bunching. Additionally, triangular sub-steps with heights of several nanometers on the treads of the macrosteps are found to be another typical feature of surface morphology, which implies a microscopically competitive bunching of sub-steps between various crystallographic orientations.展开更多
This paper reports that the rapid solidification of mixed Li2B4O7 and KNbO3 melted in a Pt loop heater has been performed experimentally by the method of quenching, and various morphologies of KNbO3 crystals have been...This paper reports that the rapid solidification of mixed Li2B4O7 and KNbO3 melted in a Pt loop heater has been performed experimentally by the method of quenching, and various morphologies of KNbO3 crystals have been observed in different regions of the quenched melt-solution. Dendrites were formed in the central region where mass transfer is performed by diffusion, whereas polygonal crystals with smooth surface grew in the marginal region where convection dominates mass transport. Based on measurement of KNbO3 concentration along crystal interface by electronic probe analysis, it finds the variety of crystal morphologies, which is the result of different solute distributions： in the central region the inhomogeneity of solute concentration is much sharper and morphological instability is easier to take place; nevertheless in the marginal region the concentration homogeneity has been greatly enhanced by convection which prevents the occurrence of morphological instability. Additional solute distribution in the melt along the primary dendrite trunk axis as well as that in mushy zones has also been determined. Results show that the solute concentration in the liquid increases linearly with distance from the trunk tip and more solutes were found to be concentrated in mushy zones. The closer the mushy zone is to trunk tip, the lower the solute concentration will be there.展开更多
The Schlieren technique coupling with a differential interference microscope was applied to visualize the KNbO_(3) melt motion in a loop-shaped Pt wire heater.The natural convection in KNbO_(3) melt was traced by obse...The Schlieren technique coupling with a differential interference microscope was applied to visualize the KNbO_(3) melt motion in a loop-shaped Pt wire heater.The natural convection in KNbO_(3) melt was traced by observing the movement of the tiny KNbO_(3) crystals(~10μm)and the stream velocities of these tracer crystals were measured.In theoretical analysis,the Navier--Stokes equation was solved as a stable field.The general solution for this system of the differential equation was expressed by an approximate power series of azimuth and radius vector.The expression was substituted in the differential equation;a non-trivial solution was obtained exactly.The velocity distribution in the vertical section was obtained which is in qualitative agreement with the experimental result.展开更多
We have investigated experimentally and theoretically the thermocapillary convective flow phenomena in a loop-shaped Pt wire heater of KNbO_(3)(20wt.%)and Li_(2)B_(4)O_(7) solution.Optical evaluations in connection wi...We have investigated experimentally and theoretically the thermocapillary convective flow phenomena in a loop-shaped Pt wire heater of KNbO_(3)(20wt.%)and Li_(2)B_(4)O_(7) solution.Optical evaluations in connection with thermocouple measurements made it possible to get a new type of thermocapillary convective flow in the considered system.To study the kinematical behavior of thermocapillary convection,we have measured the stream velocities of flow.In a theoretical analysis,the flow velocity due to thermocapillary effect alone was estimated by balancing the surface tension forces by viscous forces.The velocity distribution in the solution near the margin of the heater was obtained,which is in agreement with the experimental result.展开更多
In situ observation method has been carried out to investigate the growth kinetics of salol from the melt.The temperature-dependence of growth rate of salol crystals in a supercooling range of 0 to 3°C for(102)an...In situ observation method has been carried out to investigate the growth kinetics of salol from the melt.The temperature-dependence of growth rate of salol crystals in a supercooling range of 0 to 3°C for(102)and(012)faces are studied.The lateral(two dimensional nucleation)–to-continuous growth transition has been obtained.The free energy of stepε,the radius of the critical nucleus r*,and the excess free energy of a critical nucleusΔG*are measured for(102)and(012)faces.展开更多
The micro-morphology of the interface transition from(0112)facet to freezing isotherm curve has been observed.In the centre of the interface(the high supercooling region), the morphology of(0112)facet shows characteri...The micro-morphology of the interface transition from(0112)facet to freezing isotherm curve has been observed.In the centre of the interface(the high supercooling region), the morphology of(0112)facet shows characteristics of terrace-step-kink structure.By reducing supercoolings the growth interface gradually turn to agreeing with the freezing isotherm curve.展开更多
The morphology of salol crystals in relation to supercooling has been studied by means of the in situ obseirvation method and the Kyropoulos technique;and Hartman-Perdok's PBC method was used to analyse the morpho...The morphology of salol crystals in relation to supercooling has been studied by means of the in situ obseirvation method and the Kyropoulos technique;and Hartman-Perdok's PBC method was used to analyse the morphology based on the relationship between crystal form and its structure.The experimental results of the morphology of salol crystals are compared with the theoretical calculations.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 50331040, and the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KJCXZ-SW-105-03.
文摘The transition from a fiat solid-liquid interface to a skeletal shape during BaB2O4 （BBO） single crystal growth in Li2B4O7 flux is observed in real time by an optical high-temperature in-situ observation system. The movement of crystal step is also investigated. The observation results demonstrate that the steps propagate along and parallel to the fiat interface when the crystal size is small. Nevertheless, they will ‘bend＇ close to the face centre if the crystal size becomes greater. Atomic force microscopy reveals that more deposition places near the face centre give rise to the bending of advancing steps and thus the formation of a vicinal interface structure. Measurements of step velocity show that the velocity keeps nearly constant at different moments for one specific step, whereas the step on a newly formed layer advanced faster than that on a previously formed one when the crystal size is larger than 210μm or so. Thus interracial morphological instability occurs and a skeletal interface is obtained.
基金Supported by the National Natural Science Foundation of China under Grant No 50331040, and the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KJCXZ-SW-105-03.
文摘The cell-to-dendrite transition of succinonitrile melt suspended on a loop-shaped Pt heater is observed in real time by a differential interference microscope coupled with Schlieren technique. The transition is divided into two parts： a dendrite coalition process and a subsequent dendrite elimination process. Firstly the dendrites from the same cell are united into a single dendrite. Secondly the competitive growth of dendrites from different cells leads to the elimination of dendrites. The two processes can be understood when involving crystallographic orientation. In addition, the tip velocity and primary spacing of a cell/dendrite are also measured. It turns out that the primary spacing has a significant jump, whereas the growth velocity has no abrupt change during the cell-to-dendrite transition.
基金Supported by the National Natural Science Foundation of China under Grant No 50331040, and the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KJCXZ-SW-105-03.
文摘The solid-liquid interface motion of NaBi（WO4）2 （NBWO） melt crystal growth is observed in an in situ system, in which the whole processes of interface transition from fiat interface and cellular to dendrite are visualized. The spacing of the dendrite under smaller temperature gradient turns out to be larger than that under larger temperature gradient, which is found to be sensitive to the temperature distribution. The mechanism of dendrite growth of NBWO is studied based on the model of the growth units of anion coordination polyhedra. The { 001} face has two apex links, so it shows higher stability and has high growth rate and forms the arm of dendrite, whereas the {010} face has only one apex link, and thus shows relative slower growth rate and firstly forms the branches.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 50802105)
文摘The formation of macrostep during high-temperature phase of barium meta-borate （^-BaB204） single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy （AFM）. The in- si$u observation results demonstrate that the critical linear size of growing facet exceeding the size that the macrostep generates is significantly anisotropic. The critical linear sizes are around 280 ~m and 620 ~m for {1010} and （T010} planes, respectively. AFM study illustrates that macrostep train with a height of 150 nm^200 nm is one typical morphological feature of the as-grown crystal surface. The riser of each macrostep consists of several straight and parallel sub-steps, indicating the occurrence of step bunching. Additionally, triangular sub-steps with heights of several nanometers on the treads of the macrosteps are found to be another typical feature of surface morphology, which implies a microscopically competitive bunching of sub-steps between various crystallographic orientations.
基金supported by the National Natural Science Foundation of China (Grant Nos 50331040 and 50802105)the Innovation Funds from Shanghai Institute of Ceramics, Chinese Academy of Sciences (Grant No SCX0623)
文摘This paper reports that the rapid solidification of mixed Li2B4O7 and KNbO3 melted in a Pt loop heater has been performed experimentally by the method of quenching, and various morphologies of KNbO3 crystals have been observed in different regions of the quenched melt-solution. Dendrites were formed in the central region where mass transfer is performed by diffusion, whereas polygonal crystals with smooth surface grew in the marginal region where convection dominates mass transport. Based on measurement of KNbO3 concentration along crystal interface by electronic probe analysis, it finds the variety of crystal morphologies, which is the result of different solute distributions： in the central region the inhomogeneity of solute concentration is much sharper and morphological instability is easier to take place; nevertheless in the marginal region the concentration homogeneity has been greatly enhanced by convection which prevents the occurrence of morphological instability. Additional solute distribution in the melt along the primary dendrite trunk axis as well as that in mushy zones has also been determined. Results show that the solute concentration in the liquid increases linearly with distance from the trunk tip and more solutes were found to be concentrated in mushy zones. The closer the mushy zone is to trunk tip, the lower the solute concentration will be there.
基金Supported by a grant for key research project of microgravity science from the State Science and Technology Commission of China(95-Yu-34)the National Natural Science Foundation of China under Grant No.59832080National Space Development Agency of Japan(NASDA).
文摘The Schlieren technique coupling with a differential interference microscope was applied to visualize the KNbO_(3) melt motion in a loop-shaped Pt wire heater.The natural convection in KNbO_(3) melt was traced by observing the movement of the tiny KNbO_(3) crystals(~10μm)and the stream velocities of these tracer crystals were measured.In theoretical analysis,the Navier--Stokes equation was solved as a stable field.The general solution for this system of the differential equation was expressed by an approximate power series of azimuth and radius vector.The expression was substituted in the differential equation;a non-trivial solution was obtained exactly.The velocity distribution in the vertical section was obtained which is in qualitative agreement with the experimental result.
基金Supported by the Foundation for Kay Research Project of Microgravity Science of the State Science and Technology Commission of China(95-Yu-34)the National Natural Science Foundation of China under Grant No.59832080National Space Development Agency of Japan(NASDA).
文摘We have investigated experimentally and theoretically the thermocapillary convective flow phenomena in a loop-shaped Pt wire heater of KNbO_(3)(20wt.%)and Li_(2)B_(4)O_(7) solution.Optical evaluations in connection with thermocouple measurements made it possible to get a new type of thermocapillary convective flow in the considered system.To study the kinematical behavior of thermocapillary convection,we have measured the stream velocities of flow.In a theoretical analysis,the flow velocity due to thermocapillary effect alone was estimated by balancing the surface tension forces by viscous forces.The velocity distribution in the solution near the margin of the heater was obtained,which is in agreement with the experimental result.
文摘In situ observation method has been carried out to investigate the growth kinetics of salol from the melt.The temperature-dependence of growth rate of salol crystals in a supercooling range of 0 to 3°C for(102)and(012)faces are studied.The lateral(two dimensional nucleation)–to-continuous growth transition has been obtained.The free energy of stepε,the radius of the critical nucleus r*,and the excess free energy of a critical nucleusΔG*are measured for(102)and(012)faces.
基金supported by the Science Fund of the Chinese Academy of Sciences。
文摘The micro-morphology of the interface transition from(0112)facet to freezing isotherm curve has been observed.In the centre of the interface(the high supercooling region), the morphology of(0112)facet shows characteristics of terrace-step-kink structure.By reducing supercoolings the growth interface gradually turn to agreeing with the freezing isotherm curve.
文摘The morphology of salol crystals in relation to supercooling has been studied by means of the in situ obseirvation method and the Kyropoulos technique;and Hartman-Perdok's PBC method was used to analyse the morphology based on the relationship between crystal form and its structure.The experimental results of the morphology of salol crystals are compared with the theoretical calculations.
