Ruddlesden-Popper iridate Sr_(3)Ir_(2)O_(7)is a spin-orbit coupled Mott insulator.Hole doped Sr_(3)Ir_(2)O_(7)provides an ideal platform to study the exotic quantum phenomena that occur near the metal-insulator transi...Ruddlesden-Popper iridate Sr_(3)Ir_(2)O_(7)is a spin-orbit coupled Mott insulator.Hole doped Sr_(3)Ir_(2)O_(7)provides an ideal platform to study the exotic quantum phenomena that occur near the metal-insulator transition(MIT)region.Rh substitution of Ir is an effective method to induce hole doping into Sr_(3)Ir_(2)O_(7).However,the highest doping level reported in Sr_(3)(Ir_(1-x)Rh_(x))_(2)O_(7)single crystals was only around 3%,which is far from the MIT region.In this paper,we report the successful growth of single crystals of Sr3(Ir_(1-x)Rh_(x))_(2)O_(7)with a doping level of~9%.The samples have been fully characterized,demonstrating the high quality of the single crystals.Transport measurements have been carried out,confirming the tendency of MIT in these samples.The electronic structure has also been examined by angle-resolved photoemission spectroscopy(ARPES)measurements.Our results establish a platform to investigate the heavily hole doped Sr_(3)Ir_(2)O_(7) compound,which also provide new insights into the MIT with hole doping in this material system.展开更多
The polymorphism of D-Mannitol(mannitol) is reviewed in this paper. It was found that the structure of the stable form is consistent in most literatures, but different authors have given different information about th...The polymorphism of D-Mannitol(mannitol) is reviewed in this paper. It was found that the structure of the stable form is consistent in most literatures, but different authors have given different information about the two metastable forms. Therefore the commonly used nomenclature of mannitol was summarized based on the crystal unit cell parameters with the help of X-ray powder diffraction. Moreover, the crystal growth mechanism of mannitol polymorphs was summarized. Considering the lack of kinetic data for the metastable form especially, a reported method was attempted to apply to δ mannitol in an aqueous cooling crystallization process based on the induction time previously measured, and it was identified that the growth of the δ form follows the two-dimensional(2D) nucleationmediated mechanism. The results also indicate that the method based on induction time and supersaturation should have the potential to be expanded to the metastable polymorphs for the growth property study in a bulk system.展开更多
Numerical results show that an external magnetic field may influence significantly the flow pattern inthe molten semiconductor of Czochralski crystal growth. The melt flow could be pronouncedly damped by a magnet.ic f...Numerical results show that an external magnetic field may influence significantly the flow pattern inthe molten semiconductor of Czochralski crystal growth. The melt flow could be pronouncedly damped by a magnet.ic field with the intensity of several thousands Gauss, while the temperature field is affected only in a less extent by themagnetic field.展开更多
The crystal growth and nucleation in glasses in the lithium silicate system have been investigated. Phase separation in ultimately homogenized glasses of the lithium silicate system xLi<sub>2</sub>O·(...The crystal growth and nucleation in glasses in the lithium silicate system have been investigated. Phase separation in ultimately homogenized glasses of the lithium silicate system xLi<sub>2</sub>O·(100 ﹣ x)SiO<sub>2</sub> (where x = 23.4, 26.0, 29.1, and 33.5 mol% Li<sub>2</sub>O) has been studied. The glasses of these compositions have been homogenized using the previously established special temperature-time conditions, which make it possible to provide a maximum dehydration and removal of bubbles from the glass melt. The parameters of nucleation and growth of phase separated in homogeneities and homogeneous crystal nucleation have been determined. The absolute values of the stationary nucleation rates I<sub>st</sub> of lithium disilicate crystals in the 23.4Li<sub>2</sub>O·76.6SiO<sub>2</sub>, 26Li<sub>2</sub>O·74SiO<sub>2</sub> and 29.1Li<sub>2</sub>O·70.9SiO<sub>2</sub> glasses with the compositions lying in the metastable phase separation region have been compared with the corresponding rates I<sub>st</sub> for the glass of the stoichiometric lithium disilicate composition 33.51Li<sub>2</sub>O·66.5SiO<sub>2</sub>. It has been found that the crystal growth rate has a tendency toward a monotonic increase with an increase in the temperature, whereas the dependences of the crystal growth rate on the time of low temperature heat treatment exhibit an oscillatory behavior with a monotonic decrease in the absolute value of oscillations. The character of crystallization in glasses with the compositions lying in the phase separation region of the Li<sub>2</sub>O-SiO<sub>2</sub> system is compared with that in the glass of the stoichiometric lithium disilicate composition. The conclusion has been made that the phase separation weakly affects the nucleation parameters of the lithium disilicate and has a strong effect on the crystal growth.展开更多
The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys 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 alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All 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 parallel than those of the permanent mould casting alloys. 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
Hydrate crystals growth on the surface of methane bubble(hydrate film)in pure water was studied by using a high-pressure visible microscope under the conditions of subcoolingΔT=5.44-13.72 K and methane concentration ...Hydrate crystals growth on the surface of methane bubble(hydrate film)in pure water was studied by using a high-pressure visible microscope under the conditions of subcoolingΔT=5.44-13.72 K and methane concentration differenceΔC=2.92-8.19 mol·L^(-1).It was found the hydrate film is porous and the hydrate crystals grow towards the liquid phase on the film substrate.The crystal morphology and growth rate are affected byΔT andΔC.WhenΔT<8.82 K andΔC<4.12 mol·L^(-1),the hydrate grows into scattered columnar crystals,and the axial growth rate of the crystal gradually decreases.WhenΔT>8.82 K orΔC>4.12 mol·L^(-1),the hydrate crystals grow in dendritic shape,and the axial growth rate increases first and then decreases.The perimeter and area of the growing hydrate crystals were measured,and the fractal dimension of hydrate crystal under differentΔC andΔT was calculated.The results show that the fractal dimension of columnar hydrate crystal is greater than 3.When3.87 mol·L^(-1)<ΔC<4.20 mol·L^(-1) and 7.4 K<ΔT<8.8 K,the fractal dimension of columnar hydrate crystal is greater than 4;The fractal dimension of dendritic hydrate crystal is less than 3.WhenΔC>4.77 mol·L^(-1),ΔT<8.52 K,the fractal dimension of dendritic hydrate crystal is less than 2.展开更多
The 0.6 at.%Pr^(3+)-doped CaF_(2)-YF_(3)crystal was successfully grown by the temperature gradient technique(TGT).X-ray diffraction analysis showed that the grown crystal still had cubic structure.The absorption spect...The 0.6 at.%Pr^(3+)-doped CaF_(2)-YF_(3)crystal was successfully grown by the temperature gradient technique(TGT).X-ray diffraction analysis showed that the grown crystal still had cubic structure.The absorption spectrum,emission spectrum,Judd-Ofelt analysis and fluorescence decay curve at room temperature were discussed.The fluorescence lifetime of Pr:CaF_(2)-YF_(3)crystal was 45.46µs,and theσem·τof ^(3)P0→^(3)H_(6) and ^(3)P0→^(3)F_(2) transitions were calculated to be 80.92×10^(−20) cm^(2)·µs and 388.7×10^(−20) cm^(2)·µs,respectively.The FWHMs are 20.1 nm and 6.8 nm,which are higher than those of Pr:LiYF_(4),Pr:LiLuF_(4),Pr:LiGdF_(4) and Pr:BaY_(2)F_(8) crystals.The results show that the Pr:CaF_(2)-YF_(3)crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.展开更多
Melt flow has an important influence on the microstructure formation of alloys. In this paper the growth behaviour of constrained crystals is systematically studied. It is discovered that the constrained crystals have...Melt flow has an important influence on the microstructure formation of alloys. In this paper the growth behaviour of constrained crystals is systematically studied. It is discovered that the constrained crystals have a quite complicated response to melt flow. It may grow upstream or downstream or keep its growth direction unchanged with the influence of melt flow. Also low growth velocity and high flow velocity favour the formation of spike-like crystal. A new model is suggested to explain these experimental展开更多
The growth kinetics of spherical NiAl and CuZr crystals are studied by using molecular dynamics simulations.The growth rates of crystals are found to increase with the grain radius. The simulations show that the inter...The growth kinetics of spherical NiAl and CuZr crystals are studied by using molecular dynamics simulations.The growth rates of crystals are found to increase with the grain radius. The simulations show that the interface thickness and the Jackson α-factor increase as the growth proceeds, indicating that the interface becomes increasingly rough during growth. Due to the increasing interface roughening, the fraction of repeatable growth sites at interface f is proposed to actually increase in growth. An attachment rate, which is defined as the fraction of atoms that join the crystal interface without leaving, is used to approximate f, displaying a linear increase. With this approximation, we predict the growth rates as a function of the crystal radius, and the results qualitatively agree with those from the direct simulations.展开更多
The paper reports the recent achievement of the research on CZT for the application of X-ray andγ-ray detectors in Northwestern Polytechnical University.The crystals of both un-doped and In doped were grown with a se...The paper reports the recent achievement of the research on CZT for the application of X-ray andγ-ray detectors in Northwestern Polytechnical University.The crystals of both un-doped and In doped were grown with a self-designed Bridgman furnace.The microstructure analyses show that the crystals possess high crystallinity.Through In doping,the electronic properties were greatly improved and as high as 5×10^(10)Ωcm resistivity was obtained.The detectors produced with our crystal exhibits high resolutions o...展开更多
We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and ...We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and high temperature (HPHT). We employ both the finite element method (FEM) and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.展开更多
A new type of magnetic device was used to replace the conventional electro-magnetic field for CZSi (doped with Ge) growth. The device was composed of three permanent magnetic rings and called PMCZ device. The lines of...A new type of magnetic device was used to replace the conventional electro-magnetic field for CZSi (doped with Ge) growth. The device was composed of three permanent magnetic rings and called PMCZ device. The lines of magnetic force are horizontally distributed at radial 360°. Using the ring permanent magnetic field, thermal convection in melt and centrifugal pumping flows due to crystal rotation could be strongly suppressed so that the fluctuations of temperature and micro-growth rate at solid/liquid interface could be restrained effectively. In the PMCZ condition, the growing environment of SiGe bulk single crystal was similar to the crystal growth in space under the condition of micro-gravity. The motion of impurities (Ge, oxygen, etc.) had been controlled by diffusion near the solid/liquid interface. Oxygen concentraion became lower and the distribution of composition became more homogeneous along longitudinal direction and across a radial section in the grown SiGe crystal. The mechanism of PMCZ superior to MCZ was also discussed.展开更多
In this paper, the spectral and luminescence properties of a series of KGd(WO4)2 powder samples codoped with different concentrations of Er3+ and Yb3+ were reported,and the best doping concentrations were found to be ...In this paper, the spectral and luminescence properties of a series of KGd(WO4)2 powder samples codoped with different concentrations of Er3+ and Yb3+ were reported,and the best doping concentrations were found to be l at% Er3+ and 10at% Yb3+ for attaining the strongest intensity.The Er3+/Yb3+ codoped KGd(WO4)2 crystal with good optical quality was grown by the TSSG method and the growth conditions were presented.The unpolarized absorption and emission spectra of the crystal have been measured.The strong absorption peak is at 980 nm with a FWHM of 65 nm, and the emission peak is at 1536 nm when pumped by 976 nm.The fluorescence lifetime of manifold 4I13/2 is estimated to be 4.5 ms at room temperature.Investigations of Er, Yb:KGW crystal have shown it to have necessary combination of properties to get an effective generation of ～ 1.54 μm eye-safe radiation with laser diode pumping.展开更多
Crystal growth of tungsten during hydrogen reduction of tungsten oxide (WO3) to prepare coarse grain tungsten powder at high temperature (950 ℃) was studied. The phase composition and morphologies of products were in...Crystal growth of tungsten during hydrogen reduction of tungsten oxide (WO3) to prepare coarse grain tungsten powder at high temperature (950 ℃) was studied. The phase composition and morphologies of products were investigated by means of XRD and SEM. The results show that the reduction sequence of hydrogen reduction of WO3 is WO3→WO2.9→W18O49→WO2→W. The step of WO2→W is the critical step which determines the grain size of tungsten powder. The partial pressure (pH2O/pH2) of H2O within powder layer shows strong effect on the nucleation and grain growth of tungsten. By increasing the pH2O/pH2 within powder layer, well-developed coarse grain tungsten powder with particle size above 15 μm is obtained. After carburizing, the powder can be used to produce ultra-coarse grain cemented carbide with grain size above 5 μm.展开更多
The effects of aspartic acid on the crystal growth, morphology of hydroxyapatite(HAP) crystal were investigated, and the inhibition mechanism of aspartic acid on the crystal growth of hydroxyapatite was studied. The r...The effects of aspartic acid on the crystal growth, morphology of hydroxyapatite(HAP) crystal were investigated, and the inhibition mechanism of aspartic acid on the crystal growth of hydroxyapatite was studied. The results show that the crystal growth rate of HAP decreases with the increase of the aspartic acid concentration, and the HAP crystal is thinner significantly compared with that without amino acid, which is mainly due to the (1 010) surface of HAP crystal being inhibited by the aspartic acids. The calculation analysis indicates that the crystal growth mechanism of HAP, following surface diffusion controlled mechanism, is not changed due to the presence of aspartic acid. AFM result shows that the front of terrace on vicinal growth hillocks is pinned, which suggests that the aspartic acid is adsorbed onto the (1 010) surface of HAP and interacts with the Ca2+ ions of HAP surface, so as to block the growth active sites and result in retarding of the growth of HAP crystal.展开更多
The temporal and spatial growth behaviour of protein crystals, subject to different cooling strategies in protein crystallisation was investigated. Although the impact of temperature and cooling rate on crystal growth...The temporal and spatial growth behaviour of protein crystals, subject to different cooling strategies in protein crystallisation was investigated. Although the impact of temperature and cooling rate on crystal growth of small molecules was well documented, much less has been reported on their impact on the crystallisation of proteins. In this paper, an experimental set-up is configured to carry out such a study which involves an automatic temperature controlled hot-stage crystalliser fitted with a real-time imaging system. Linbro parallel crystallisation experiments(24-well plate) were also conducted to find the suitable initial conditions to be used in the hot-stage crystallisation experiments, including the initial concentration of HEW lysozyme solutions, precipitate concentration and pH value. It was observed that fast cooling rates at the early stage led to precipitates while slow cooling rates produced crystal nuclei, and very slow cooling rates, much smaller than for small molecules are critical to the growth of the nuclei and the crystals to a desired shape. The interesting results provide valuable insight as well as experimental proof of the feasibility and effectiveness of cooling as a means for achieving controlled protein crystallisation, compared with the evaporation approach which was widely used to grow single large crystals for X-ray diffraction study. Since cooling rate control can be easily achieved and has good repeatability, it suggests that large-scale production of protein crystals can be effectively achieved by manipulating cooling rates.展开更多
A new device was designed,which can effectively avoid the undesired nucleation and agglomeration of fine particles on the experimental results during the sead ed precipitation of sodium aluminate solution,and moreover...A new device was designed,which can effectively avoid the undesired nucleation and agglomeration of fine particles on the experimental results during the sead ed precipitation of sodium aluminate solution,and moreover,the experimental co nditions are nearly kept constant during the experiment. With the new device,it is proven that a good result can be obtained on the kinetics study of the cryst al growth in seeded precipitation of sodium aluminate solution.Experiments were carried out with the concentration of Na2O （Nk）170 g/L,the mole ratio of Na2O to Al2O3 （αk） all between 1.52 to 2.01,at 65,70,75 ℃,respectively. And the kinetics equation of crystal growth of gibbsite was deduc ed.展开更多
Based on the population balance equation in a batch crystallizer characteristic of seeded precipitation, a model to calculate the rate of apparent crystal growth of aluminum hydroxide from the size distribution was de...Based on the population balance equation in a batch crystallizer characteristic of seeded precipitation, a model to calculate the rate of apparent crystal growth of aluminum hydroxide from the size distribution was deve- loped. The simulation results indicate that the rate of apparent crystal growth during seeded precipitation exhibits a manifest dependence on the crystal size. In general, there is an obvious increase in the apparent crystal growth rate with the augment in crystal size. The apparent activation energy increases with the increase of characteristic crystal size, which indicates that the growth of small crystals is controlled by surface chemical reaction; it is gradually controlled by both the surface reaction and diffusion with the augment in crystal size.展开更多
Thermoelectric selenides have attracted more and more attentions recently.Herein,p-type Sn Se polycrystalline bulk materials with good thermoelectric properties are presented.By using the SnSe_2 nanostructures synthes...Thermoelectric selenides have attracted more and more attentions recently.Herein,p-type Sn Se polycrystalline bulk materials with good thermoelectric properties are presented.By using the SnSe_2 nanostructures synthesized via a wetchemistry route as the precursor,polycrystalline Sn Se bulk materials were successfully obtained by a combined heattreating process under reducing atmosphere and following spark plasma sintering procedure.As a reference,the Sn Se nanostructures synthesized via a wet-chemistry route were also fabricated into polycrystalline bulk materials through the same process.The thermoelectric properties of the Sn Se polycrystalline transformed from SnSe_2 nanostructures indicate that the increasing of heattreating temperature could effectively decrease the electrical resistivity,whereas the decrease in Seebeck coefficient is nearly invisible.As a result,the maximum power factor is enhanced from 5.06×10^(-4)W/m·K^2to 8.08×10^(-4)W/m·K^2at 612~?C.On the other hand,the reference sample,which was obtained by using Sn Se nanostructures as the precursor,displays very poor power factor of only 1.30×10^(-4)W/m·K^2at 537~?C.The x-ray diffraction(XRD),scanning electron microscope(SEM),x-ray fluorescence(XRF),and Hall effect characterizations suggest that the anisotropic crystal growth and existing Sn vacancy might be responsible for the enhanced electrical transport in the polycrystalline Sn Se prepared by using SnSe_2 precursor.On the other hand,the impact of heat-treating temperature on thermal conductivity is not obvious.Owing to the boosting of power factor,a high z T value of 1.07 at 612~?C is achieved.This study provides a new method to synthesize polycrystalline Sn Se and pave a way to improve the thermoelectric properties of polycrystalline bulk materials with similar layered structure.展开更多
Pattern selection during crystal growth is studied by using the anisotropic lattice Boltzmann-phase field model.In the model,the phase transition,melt flows,and heat transfer are coupled and mathematically described b...Pattern selection during crystal growth is studied by using the anisotropic lattice Boltzmann-phase field model.In the model,the phase transition,melt flows,and heat transfer are coupled and mathematically described by using the lattice Boltzmann(LB)scheme.The anisotropic streaming-relaxation operation fitting into the LB framework is implemented to model interface advancing with various preferred orientations.Crystal pattern evolutions are then numerically investigated in the conditions of with and without melt flows.It is found that melt flows can significantly influence heat transfer,crystal growth behavior,and phase distributions.The crystal morphological transition from dendrite,seaweed to cauliflower-like patterns occurs with the increase of undercoolings.The interface normal angles and curvature distributions are proposed to quantitatively characterize crystal patterns.The results demonstrate that the distributions are corresponding to crystal morphological features,and they can be therefore used to describe the evolution of crystal patterns in a quantitative way.展开更多
基金supported by the USTC start-up fundthe National Natural Science Foundation of China(Grant Nos.12074358 and 12004363)+2 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000008 and WK2030000035)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302802)supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences under Contract No.DEAC02-76SF00515。
文摘Ruddlesden-Popper iridate Sr_(3)Ir_(2)O_(7)is a spin-orbit coupled Mott insulator.Hole doped Sr_(3)Ir_(2)O_(7)provides an ideal platform to study the exotic quantum phenomena that occur near the metal-insulator transition(MIT)region.Rh substitution of Ir is an effective method to induce hole doping into Sr_(3)Ir_(2)O_(7).However,the highest doping level reported in Sr_(3)(Ir_(1-x)Rh_(x))_(2)O_(7)single crystals was only around 3%,which is far from the MIT region.In this paper,we report the successful growth of single crystals of Sr3(Ir_(1-x)Rh_(x))_(2)O_(7)with a doping level of~9%.The samples have been fully characterized,demonstrating the high quality of the single crystals.Transport measurements have been carried out,confirming the tendency of MIT in these samples.The electronic structure has also been examined by angle-resolved photoemission spectroscopy(ARPES)measurements.Our results establish a platform to investigate the heavily hole doped Sr_(3)Ir_(2)O_(7) compound,which also provide new insights into the MIT with hole doping in this material system.
基金Supported by the National Natural Science Foundation of China(No.21406049)the Natural Science Foundation of Hebei Province(B2015202090)the China Postdoctoral Science Foundation(2015M581283)
文摘The polymorphism of D-Mannitol(mannitol) is reviewed in this paper. It was found that the structure of the stable form is consistent in most literatures, but different authors have given different information about the two metastable forms. Therefore the commonly used nomenclature of mannitol was summarized based on the crystal unit cell parameters with the help of X-ray powder diffraction. Moreover, the crystal growth mechanism of mannitol polymorphs was summarized. Considering the lack of kinetic data for the metastable form especially, a reported method was attempted to apply to δ mannitol in an aqueous cooling crystallization process based on the induction time previously measured, and it was identified that the growth of the δ form follows the two-dimensional(2D) nucleationmediated mechanism. The results also indicate that the method based on induction time and supersaturation should have the potential to be expanded to the metastable polymorphs for the growth property study in a bulk system.
基金supported by the National Natural Foundation of China
文摘Numerical results show that an external magnetic field may influence significantly the flow pattern inthe molten semiconductor of Czochralski crystal growth. The melt flow could be pronouncedly damped by a magnet.ic field with the intensity of several thousands Gauss, while the temperature field is affected only in a less extent by themagnetic field.
文摘The crystal growth and nucleation in glasses in the lithium silicate system have been investigated. Phase separation in ultimately homogenized glasses of the lithium silicate system xLi<sub>2</sub>O·(100 ﹣ x)SiO<sub>2</sub> (where x = 23.4, 26.0, 29.1, and 33.5 mol% Li<sub>2</sub>O) has been studied. The glasses of these compositions have been homogenized using the previously established special temperature-time conditions, which make it possible to provide a maximum dehydration and removal of bubbles from the glass melt. The parameters of nucleation and growth of phase separated in homogeneities and homogeneous crystal nucleation have been determined. The absolute values of the stationary nucleation rates I<sub>st</sub> of lithium disilicate crystals in the 23.4Li<sub>2</sub>O·76.6SiO<sub>2</sub>, 26Li<sub>2</sub>O·74SiO<sub>2</sub> and 29.1Li<sub>2</sub>O·70.9SiO<sub>2</sub> glasses with the compositions lying in the metastable phase separation region have been compared with the corresponding rates I<sub>st</sub> for the glass of the stoichiometric lithium disilicate composition 33.51Li<sub>2</sub>O·66.5SiO<sub>2</sub>. It has been found that the crystal growth rate has a tendency toward a monotonic increase with an increase in the temperature, whereas the dependences of the crystal growth rate on the time of low temperature heat treatment exhibit an oscillatory behavior with a monotonic decrease in the absolute value of oscillations. The character of crystallization in glasses with the compositions lying in the phase separation region of the Li<sub>2</sub>O-SiO<sub>2</sub> system is compared with that in the glass of the stoichiometric lithium disilicate composition. The conclusion has been made that the phase separation weakly affects the nucleation parameters of the lithium disilicate and has a strong effect on the crystal growth.
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 alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All 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 parallel than those of the permanent mould casting alloys. 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.
基金Financially supported by the National Natural Science Foundation of China(51991365 and 51876222)China National Petroleum Corporation(CNPC)Major Science and Technology Project(ZD2019-184-002)。
文摘Hydrate crystals growth on the surface of methane bubble(hydrate film)in pure water was studied by using a high-pressure visible microscope under the conditions of subcoolingΔT=5.44-13.72 K and methane concentration differenceΔC=2.92-8.19 mol·L^(-1).It was found the hydrate film is porous and the hydrate crystals grow towards the liquid phase on the film substrate.The crystal morphology and growth rate are affected byΔT andΔC.WhenΔT<8.82 K andΔC<4.12 mol·L^(-1),the hydrate grows into scattered columnar crystals,and the axial growth rate of the crystal gradually decreases.WhenΔT>8.82 K orΔC>4.12 mol·L^(-1),the hydrate crystals grow in dendritic shape,and the axial growth rate increases first and then decreases.The perimeter and area of the growing hydrate crystals were measured,and the fractal dimension of hydrate crystal under differentΔC andΔT was calculated.The results show that the fractal dimension of columnar hydrate crystal is greater than 3.When3.87 mol·L^(-1)<ΔC<4.20 mol·L^(-1) and 7.4 K<ΔT<8.8 K,the fractal dimension of columnar hydrate crystal is greater than 4;The fractal dimension of dendritic hydrate crystal is less than 3.WhenΔC>4.77 mol·L^(-1),ΔT<8.52 K,the fractal dimension of dendritic hydrate crystal is less than 2.
基金supported by the National Natural Science Foundation of China(Grant Nos.61805177,61861136007,and 61621001).
文摘The 0.6 at.%Pr^(3+)-doped CaF_(2)-YF_(3)crystal was successfully grown by the temperature gradient technique(TGT).X-ray diffraction analysis showed that the grown crystal still had cubic structure.The absorption spectrum,emission spectrum,Judd-Ofelt analysis and fluorescence decay curve at room temperature were discussed.The fluorescence lifetime of Pr:CaF_(2)-YF_(3)crystal was 45.46µs,and theσem·τof ^(3)P0→^(3)H_(6) and ^(3)P0→^(3)F_(2) transitions were calculated to be 80.92×10^(−20) cm^(2)·µs and 388.7×10^(−20) cm^(2)·µs,respectively.The FWHMs are 20.1 nm and 6.8 nm,which are higher than those of Pr:LiYF_(4),Pr:LiLuF_(4),Pr:LiGdF_(4) and Pr:BaY_(2)F_(8) crystals.The results show that the Pr:CaF_(2)-YF_(3)crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.
文摘Melt flow has an important influence on the microstructure formation of alloys. In this paper the growth behaviour of constrained crystals is systematically studied. It is discovered that the constrained crystals have a quite complicated response to melt flow. It may grow upstream or downstream or keep its growth direction unchanged with the influence of melt flow. Also low growth velocity and high flow velocity favour the formation of spike-like crystal. A new model is suggested to explain these experimental
基金Supported by the National Natural Science Foundation of China under Grant No 51171027
文摘The growth kinetics of spherical NiAl and CuZr crystals are studied by using molecular dynamics simulations.The growth rates of crystals are found to increase with the grain radius. The simulations show that the interface thickness and the Jackson α-factor increase as the growth proceeds, indicating that the interface becomes increasingly rough during growth. Due to the increasing interface roughening, the fraction of repeatable growth sites at interface f is proposed to actually increase in growth. An attachment rate, which is defined as the fraction of atoms that join the crystal interface without leaving, is used to approximate f, displaying a linear increase. With this approximation, we predict the growth rates as a function of the crystal radius, and the results qualitatively agree with those from the direct simulations.
文摘The paper reports the recent achievement of the research on CZT for the application of X-ray andγ-ray detectors in Northwestern Polytechnical University.The crystals of both un-doped and In doped were grown with a self-designed Bridgman furnace.The microstructure analyses show that the crystals possess high crystallinity.Through In doping,the electronic properties were greatly improved and as high as 5×10^(10)Ωcm resistivity was obtained.The detectors produced with our crystal exhibits high resolutions o...
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 51071074, 51172089, and 51171070)the Program for New Century Excellent Talents in University of Ministry of Education of China
文摘We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and high temperature (HPHT). We employ both the finite element method (FEM) and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.
基金This work is financially supported by the National Natural Science Foundation of China (No. 59772037)the Natural Science Foundation of Hebei Province (No. 500016)
文摘A new type of magnetic device was used to replace the conventional electro-magnetic field for CZSi (doped with Ge) growth. The device was composed of three permanent magnetic rings and called PMCZ device. The lines of magnetic force are horizontally distributed at radial 360°. Using the ring permanent magnetic field, thermal convection in melt and centrifugal pumping flows due to crystal rotation could be strongly suppressed so that the fluctuations of temperature and micro-growth rate at solid/liquid interface could be restrained effectively. In the PMCZ condition, the growing environment of SiGe bulk single crystal was similar to the crystal growth in space under the condition of micro-gravity. The motion of impurities (Ge, oxygen, etc.) had been controlled by diffusion near the solid/liquid interface. Oxygen concentraion became lower and the distribution of composition became more homogeneous along longitudinal direction and across a radial section in the grown SiGe crystal. The mechanism of PMCZ superior to MCZ was also discussed.
基金This project was supported by the Natural Science Foundation of Fujian Province (No. E0310031) ② Corresponding author. E-mail: tcy@fjirsm.ac.cn
文摘In this paper, the spectral and luminescence properties of a series of KGd(WO4)2 powder samples codoped with different concentrations of Er3+ and Yb3+ were reported,and the best doping concentrations were found to be l at% Er3+ and 10at% Yb3+ for attaining the strongest intensity.The Er3+/Yb3+ codoped KGd(WO4)2 crystal with good optical quality was grown by the TSSG method and the growth conditions were presented.The unpolarized absorption and emission spectra of the crystal have been measured.The strong absorption peak is at 980 nm with a FWHM of 65 nm, and the emission peak is at 1536 nm when pumped by 976 nm.The fluorescence lifetime of manifold 4I13/2 is estimated to be 4.5 ms at room temperature.Investigations of Er, Yb:KGW crystal have shown it to have necessary combination of properties to get an effective generation of ～ 1.54 μm eye-safe radiation with laser diode pumping.
文摘Crystal growth of tungsten during hydrogen reduction of tungsten oxide (WO3) to prepare coarse grain tungsten powder at high temperature (950 ℃) was studied. The phase composition and morphologies of products were investigated by means of XRD and SEM. The results show that the reduction sequence of hydrogen reduction of WO3 is WO3→WO2.9→W18O49→WO2→W. The step of WO2→W is the critical step which determines the grain size of tungsten powder. The partial pressure (pH2O/pH2) of H2O within powder layer shows strong effect on the nucleation and grain growth of tungsten. By increasing the pH2O/pH2 within powder layer, well-developed coarse grain tungsten powder with particle size above 15 μm is obtained. After carburizing, the powder can be used to produce ultra-coarse grain cemented carbide with grain size above 5 μm.
基金Project(2003AA302210) support by the National High-Tech Research and Development Program of ChinaProject(05JJ20014) supported by the Natural Science Foundation of Hunan Province, China
文摘The effects of aspartic acid on the crystal growth, morphology of hydroxyapatite(HAP) crystal were investigated, and the inhibition mechanism of aspartic acid on the crystal growth of hydroxyapatite was studied. The results show that the crystal growth rate of HAP decreases with the increase of the aspartic acid concentration, and the HAP crystal is thinner significantly compared with that without amino acid, which is mainly due to the (1 010) surface of HAP crystal being inhibited by the aspartic acids. The calculation analysis indicates that the crystal growth mechanism of HAP, following surface diffusion controlled mechanism, is not changed due to the presence of aspartic acid. AFM result shows that the front of terrace on vicinal growth hillocks is pinned, which suggests that the aspartic acid is adsorbed onto the (1 010) surface of HAP and interacts with the Ca2+ ions of HAP surface, so as to block the growth active sites and result in retarding of the growth of HAP crystal.
基金Supported by the China One Thousand Talent Scheme,the National Natural Science Foundation of China under its Major Research Scheme of Meso-scale Mechanism and Control in Multi-phase Reaction Processes(91434126)the Natural Science Foundation of Guangdong Province(2014A030313228)+1 种基金benefited from early work funded by UK Engineering and Physical Science Research Council(EP/H008012/1EP/H008853/1)
文摘The temporal and spatial growth behaviour of protein crystals, subject to different cooling strategies in protein crystallisation was investigated. Although the impact of temperature and cooling rate on crystal growth of small molecules was well documented, much less has been reported on their impact on the crystallisation of proteins. In this paper, an experimental set-up is configured to carry out such a study which involves an automatic temperature controlled hot-stage crystalliser fitted with a real-time imaging system. Linbro parallel crystallisation experiments(24-well plate) were also conducted to find the suitable initial conditions to be used in the hot-stage crystallisation experiments, including the initial concentration of HEW lysozyme solutions, precipitate concentration and pH value. It was observed that fast cooling rates at the early stage led to precipitates while slow cooling rates produced crystal nuclei, and very slow cooling rates, much smaller than for small molecules are critical to the growth of the nuclei and the crystals to a desired shape. The interesting results provide valuable insight as well as experimental proof of the feasibility and effectiveness of cooling as a means for achieving controlled protein crystallisation, compared with the evaporation approach which was widely used to grow single large crystals for X-ray diffraction study. Since cooling rate control can be easily achieved and has good repeatability, it suggests that large-scale production of protein crystals can be effectively achieved by manipulating cooling rates.
文摘A new device was designed,which can effectively avoid the undesired nucleation and agglomeration of fine particles on the experimental results during the sead ed precipitation of sodium aluminate solution,and moreover,the experimental co nditions are nearly kept constant during the experiment. With the new device,it is proven that a good result can be obtained on the kinetics study of the cryst al growth in seeded precipitation of sodium aluminate solution.Experiments were carried out with the concentration of Na2O （Nk）170 g/L,the mole ratio of Na2O to Al2O3 （αk） all between 1.52 to 2.01,at 65,70,75 ℃,respectively. And the kinetics equation of crystal growth of gibbsite was deduc ed.
文摘Based on the population balance equation in a batch crystallizer characteristic of seeded precipitation, a model to calculate the rate of apparent crystal growth of aluminum hydroxide from the size distribution was deve- loped. The simulation results indicate that the rate of apparent crystal growth during seeded precipitation exhibits a manifest dependence on the crystal size. In general, there is an obvious increase in the apparent crystal growth rate with the augment in crystal size. The apparent activation energy increases with the increase of characteristic crystal size, which indicates that the growth of small crystals is controlled by surface chemical reaction; it is gradually controlled by both the surface reaction and diffusion with the augment in crystal size.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51572049,51562005,and 51772056)the Natural Science Foundation of Guangxi Zhuang Automomous Region,China(Grant Nos.2015GXNSFFA139002 and 2016GXNSFBA380152)the Open Fund of Key Laboratory of Cryogenics,Technical Institute of Physics and Chemistry,Chinese Academy of Sciences(Grant No.CRYO201703)
文摘Thermoelectric selenides have attracted more and more attentions recently.Herein,p-type Sn Se polycrystalline bulk materials with good thermoelectric properties are presented.By using the SnSe_2 nanostructures synthesized via a wetchemistry route as the precursor,polycrystalline Sn Se bulk materials were successfully obtained by a combined heattreating process under reducing atmosphere and following spark plasma sintering procedure.As a reference,the Sn Se nanostructures synthesized via a wet-chemistry route were also fabricated into polycrystalline bulk materials through the same process.The thermoelectric properties of the Sn Se polycrystalline transformed from SnSe_2 nanostructures indicate that the increasing of heattreating temperature could effectively decrease the electrical resistivity,whereas the decrease in Seebeck coefficient is nearly invisible.As a result,the maximum power factor is enhanced from 5.06×10^(-4)W/m·K^2to 8.08×10^(-4)W/m·K^2at 612~?C.On the other hand,the reference sample,which was obtained by using Sn Se nanostructures as the precursor,displays very poor power factor of only 1.30×10^(-4)W/m·K^2at 537~?C.The x-ray diffraction(XRD),scanning electron microscope(SEM),x-ray fluorescence(XRF),and Hall effect characterizations suggest that the anisotropic crystal growth and existing Sn vacancy might be responsible for the enhanced electrical transport in the polycrystalline Sn Se prepared by using SnSe_2 precursor.On the other hand,the impact of heat-treating temperature on thermal conductivity is not obvious.Owing to the boosting of power factor,a high z T value of 1.07 at 612~?C is achieved.This study provides a new method to synthesize polycrystalline Sn Se and pave a way to improve the thermoelectric properties of polycrystalline bulk materials with similar layered structure.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51728601 and 51771118)the Fund of the State Key Laboratory of Solidification Processing in NPU(Grant No.SKLSP201901)the Fundamental Research Funds for the Central Universities,China(Grant No.2242019K1G003).
文摘Pattern selection during crystal growth is studied by using the anisotropic lattice Boltzmann-phase field model.In the model,the phase transition,melt flows,and heat transfer are coupled and mathematically described by using the lattice Boltzmann(LB)scheme.The anisotropic streaming-relaxation operation fitting into the LB framework is implemented to model interface advancing with various preferred orientations.Crystal pattern evolutions are then numerically investigated in the conditions of with and without melt flows.It is found that melt flows can significantly influence heat transfer,crystal growth behavior,and phase distributions.The crystal morphological transition from dendrite,seaweed to cauliflower-like patterns occurs with the increase of undercoolings.The interface normal angles and curvature distributions are proposed to quantitatively characterize crystal patterns.The results demonstrate that the distributions are corresponding to crystal morphological features,and they can be therefore used to describe the evolution of crystal patterns in a quantitative way.
