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A novel method of crystal growth by introducing jet flow to the pyramidal‐restriction long‐seed growth system of potassium dihydrogen phosphate (KH2PO4, KDP) in rotating crystal method, namely, the jet‐rotating crystal method, is proposed. To evaluate the prospect of this new method, three‐dimensional (3D) time‐dependent numerical simulations of flow and mass transfer involved in the jet‐rotating crystal method are conducted. Compared with the rotating crystal method, the jet‐rotating crystal method can improve the magnitude and distribution homogeneity of the prismatic face supersaturation and obtain high‐quality KDP crystals. The supersaturation on the prismatic face as a function of rotation rate, jet velocity, and crystal size is investigated. The effects of solution flow on mass transfer are analyzed in detail. A further improvement in the magnitude and distribution homogeneity of the prismatic face supersaturation can be observed through designing the jet flow pipes to swing periodically in vertical plane. Besides, the role of natural and forced convection in mass transport is discussed, which indicates that the effects of natural convection can be neglected when the jet velocity is equal to or greater than 0.6 m s–1. [ABSTRACT FROM AUTHOR]

Transparent potassium dihydrogen phosphate (KDP) crystals that are grown from different translational velocities and orientation configurations were obtained during growth through a novel motion mode called 2D translation method. The grown crystals were investigated by microhardness, dielectric, chemical etching, thermal analysis and laser damage threshold studies. A higher mechanical hardness is observed in crystals grown by the 2D translation method than that grown by the rotating-crystal method. Low dielectric loss and less dislocation density show that the 2D translation method grown crystals contain minimum defects. The thermal stability and damage threshold of the 2D translation method grown crystals are higher than those of the crystal grown using the rotating-crystal method. Moreover, the properties of various crystals grown by the 2D translation method under different conditions are compared, and results show that the grown crystals' quality is best when the translation velocity is 0.04 m/s. [ABSTRACT FROM AUTHOR]

A novel technique of growing large crystals of potassium dihydrogen phosphate (KDP) named solution-jet method is proposed. The aim is to increase supersaturation on the pyramidal face, especially for crystal surface regions close to the rotation axis. The fluid flow and surface supersaturation distribution of crystals grown under different conditions were computed using the finite-volume method. Results indicate that the time-averaged supersaturation of the pyramidal face in the proposed method significantly increases and the supersaturation difference from the crystal center to edge clearly decreases compared with the rotating-crystal method. With increased jet velocity, supersaturation on the pyramidal face steadily increases. Rotation rate considerably affects the magnitude and distribution of the prismatic surface supersaturation. With increased crystal size, the mean value of surface supersaturation averaged over the pyramid gradually decreases; conversely, standard deviation increases, which is detrimental to crystal growth. Moreover, the significant roles played by natural and forced convection in the process of mass transport are discussed. Results show that further increased jet velocity to 0.6 m/s renders negligible the effects of natural convection around the pyramid. The simulation for step propagation indicates that solution-jet method can promote a steady step migration and enhance surface morphology stability, which can improve the crystal quality. [ABSTRACT FROM AUTHOR]

A numerical study of the unsteady turbulent flow and mass transfer involved in the potassium dihydrogen phosphate crystal growth from an aqueous solution with a three-dimensional spiral motion configuration was performed using the standard k – ε model with an enhanced wall treatment. The three-dimensional spiral motion is composed of a uniform circular motion on the horizontal plane and a reciprocating motion in the vertical direction. The simulation indicates that the crystal spiral motion will drive the mainstream solution rotating around the axis of the growth vessel and form an oscillatory flow near the crystal, which results in a periodical reversal of the supersaturation distribution on the crystal faces and effectively suppresses the morphological instability of the crystal surfaces. With the increase of the orbital radius R or the characteristic rotation rate ω , the line speed V 0 of crystal in the horizontal plane will increase, leading to a decline of the thickness of the diffusional boundary layer and an increase of the time-averaged supersaturation on the crystal faces. At the same time, the homogeneity of the surface supersaturation will be improved too, which would benefit the morphological stability of the crystal surfaces. However, when the crystal size increases, the time-averaged supersaturation on the crystal faces will decrease and its homogeneity will deteriorate. Therefore, with crystal growth, increasing the orbital radius, R , and reducing the period, T 1 , of the crystal circular motion are necessary. [ABSTRACT FROM AUTHOR]

Computational analysis of the three-dimensional flow and mass transfer involved in the growth of KDP crystal with a planetary motion (PM) was conducted, in which the crystal executes an orbital revolution with a constant revolution rate during its self-rotation together with periodically changing the direction of crystal rotation. Compared with the conventional KDP growth method which conducts centric rotation (CR), this new configuration can avoid the sharp fluctuation of surface supersaturation during the phases of crystal spin down, stalling and spin up, and brings about an oscillatory fluid field during the steady self-rotation phase, all of that being able to promote the morphological stability of the growing crystal. By increasing the self-rotation rate, the frequency of the oscillatory fluid field will increase, and the morphological stability will be enhanced. The time-averaged supersaturation fields of the crystal surfaces are obtained, which are greatly affected by the orbital revolution rate and the orbital radius. For a higher orbital revolution rate or larger orbital radius, higher time-averaged value and better homogeneity of the surface supersaturation could be obtained. [ABSTRACT FROM AUTHOR]

• The long seed KDP crystal grown by the 2D TM was proposed. • The low-supersaturation regions on the prismatic faces is eliminated basically. • The surface supersaturation distribution under different conditions was presented. • The effect of flow on surface supersaturation distribution was analyzed. • The crystal mounting method was modified to further improve the surface supersaturation. A novel motion method, namely, the two-dimensional translation method (2D TM) had been proposed by our team to effectively utilize convection to enhance morphological stability and mass transfer. To evaluate this new method and apply it to the long seed KDP crystals growth, numerical simulations on the hydrodynamics and mass transfer involved in the growth of the long seed KDP crystals through this new method have been performed. Comparisons with the rotating crystal method (RCM) indicates that 2D TM improves the value and distribution homogeneity of the surface supersaturation. As the translational velocity increases, the value of the surface supersaturation on the prismatic faces increases. However, as the translational distance becomes long, there is a decrease in the value of the prismatic surface supersaturation, but the homogeneity of the surface supersaturation is improved. Moreover, the increase of the crystal size not only reduces the value of the surface supersaturation on the prismatic faces, but also degrades the homogeneity of the surface supersaturation. A further improvement in the magnitude and distribution homogeneity of the prismatic face supersaturation can be observed through modifying the crystal mounting method. [ABSTRACT FROM AUTHOR]

In this study, a novel motion mode for crystals during growth, i.e., 2D translation, is proposed. Numerical simulations of flow and mass transfer are conducted for the growth of large-scale potassium dihydrogen phosphate (KDP) crystals subjected to the new motion mode. Surface supersaturation and shear stress are obtained as functions of the translational velocity, distance, size, orientation of crystals. The dependence of these two parameters on the flow fields around the crystals is also discussed. The thicknesses of the solute boundary layer varied with translational velocity are described. The characteristics of solution flow and surface supersaturation distribution are summarized, where it suggests that the morphological stability of a crystal surface can be enhanced if the proposed 2D translation is applied to crystal growth. [ABSTRACT FROM AUTHOR]

A novel solution-based crystal growth method, namely, the three-dimensional motion growth method (3D MGM) is proposed to effectively utilize convection for simultaneous enhancement of morphological stability and mass transfer. To evaluate this new growth method, numerical simulations of flow and mass transfer are carried out on growth of potassium dihydrogen phosphate (KDP) crystals subjected to 3D MGM. The supersaturation field of the crystal surface is presented as functions of translational velocity and distance since it is critically involved in the processes of morphological instability and inclusion formation; the dependences of surface supersaturation on the solution flow surrounding the crystal surface are analyzed in detail. The correlations between thickness of the solute boundary layer and translational velocity and distance are described. The roles of natural and forced convection in mass transfer under different conditions are discussed, with results showing that the effects of natural convection are significant only at low translational velocities. The Damkohler number is introduced to measure the significance of mass transport limitations in the solution system of 3D MGM crystal growth, where it implies that with the increase of translational velocity, the limitations in mass transport decrease. Comparisons with the traditional rotating-crystal method indicate that 3D MGM has advantages in terms of the distribution homogeneity of surface supersaturation. The model of steps moving on the prismatic face demonstrates that the step-train propagates more stably on the crystal surface when the 3D MGM is applied. [ABSTRACT FROM AUTHOR]

A novel system for rapid crystal growth, namely three-dimensional motion growth method ('3D MGM') was proposed. Using this system, a potassium dihydrogen phosphate (KDP) seed was grown to a single crystal with a final size of 50×55×85 mm3. The KDP crystal was characterized by Raman spectroscopy, UV-vis-NIR spectroscopy, extinction ratio, laser damage threshold, and etching studies. Raman spectrum shows KDP crystal grown by '3D MGM' maintains good crystallinity as that grown by rotating-crystal method ('RCM'). The '3D MGM' grown KDP crystal has much better transmittance, higher extinction ratio, higher damage threshold and less dislocation density, compared to 'RCM' grown crystal. [ABSTRACT FROM AUTHOR]

In situ atomic force microscopy (AFM) has been utilized in studies of the growth mechanism on the (100) face of zinc tris (thiourea) sulphate (ZTS) crystals growing from solution. The growth on the (100) face of pure ZTS crystal is mainly controlled by two dimensional (2D) nucleation mechanisms, under which the hillock is formed through layer-by-layer growth. It is easier to form 2D nuclei at edge dislocation and the apex of steps. The growth of 2D nucleus is in accord with nucleation-spreading mode. The growth rate along the 〈010〉 direction is faster than that along 〈001〉 direction, both of which increase firstly and then decrease with the spread of nucleus. The kinetic coefficients of one nucleus have been roughly estimated to be 3.6 × 10−4 cm/s and 1.8 × 10−4 cm/s in two directions, while the activation energy E was calculated to be 53.7 kJ/mol and 55.4 kJ/mol, respectively. The 2D nuclei can be generated under lower supersaturation with the addition of EDTA. If there are several hillocks growing together, step bunches will form when the steps moving in the same direction meet each other, while the meeting of steps that move in the inverse direction will result in the separation of steps. The ability of nucleation of edge dislocation outcrops are different even they are close to each other on the same surface. When the nucleus was generated at the edge dislocation sites, it cannot spread speedily until finishes an 'incubation period'. Moreover, the detour of microsteps was observed due to the existence of pits. If the microcrystals attached on the surface block the step advancement, or leave the surface or are covered by the macrosteps, the pits are formed. If the macrosteps advanced across the pits, the pits will be covered and the liquid inclusions may form. However, if the microcrystal forming in the pit grow up and expose on the surface, the pit will not be covered by macrosteps. The formation of solid inclusions may be caused by the microcrystals being embedded into the single steps which move layer-by-layer. [ABSTRACT FROM AUTHOR]

Investigation of crystal growth under screw dislocation mechanisms on the (100) face of zinc tris (thiourea) sulphate (ZTS) crystals doped ethylene diamine tetraacetic acid (EDTA) has been carried out in a fluid cell by in situ atomic force microscopy (AFM). The generation of a dislocation spiral during the step advancing was observed. Through the measurement of the critical length of four sides of a rectangular spiral with a complete growth period, the advancement velocities, step edge free energies and kinetic coefficients of steps have been obtained. The changes in the step velocity with time have been studied. It was found that the relationship between the step velocity and step length is inconsistent with the previous report. The emergent points of dislocations do not disappear even though they are covered by either several elementary steps or macro-steps. It is also shown that the interchange of two spirals whose emergent points of dislocations are adjacent will lead to a distortion of two contiguous steps and affect the growth rates of spirals. The obviously asymmetric growth of spirals of opposite sign in real time was observed. The coexistence and competition of dislocation spirals under different conditions was emphasized considering the activity of dislocation. [ABSTRACT FROM AUTHOR]

Abstract: Interface morphology of the (100) face of zinc tris-thiourea sulphate (ZTS) crystals, grown under different supersaturations, at 30°C, was investigated using in situ atomic force microscopy (AFM). It comes out that the (100) face exhibits stepped surface characteristics. At lower supersaturations, nucleation easily occurred at the outcrops of edge dislocations which could act as persistent sources of monomolecular growth steps, and the edge dislocation sites appeared to exhibit a “memory function”. At higher supersaturations, however, poly-nucleation becomes the primary growth mechanism. The rates of step advancement in the [010] and [001] directions of the two-dimensional nuclei were different, as it ensues from the symmetry anisotropy. The activation energy of the two-dimensional nuclei along with the step kinetic coefficients in the [010] and [001] directions, were calculated. We also found that microcrystals on the surface of the crystal could be better integrated into the crystal surface, or otherwise lead to the generation of pits by migration of the microcrystals. Pits could be gradually filled by elementary steps and thus no defect would be formed, or they might also be covered directly by macrosteps, which would result in liquid inclusions. [Copyright &y& Elsevier]

Abstract: A new system for improving the growth of KDP crystal with rotary flow field and stationary crystal is proposed. The 3D numerical simulation for flow and mass transfer shows that the rotation rate is the key factor that has a significant effect on the surface supersaturation and surface homogeneity. Especially for the high rotation rate, higher surface supersaturation and better surface homogeneity can be gained. Bulk supersaturation and inlet velocity also affect surface supersaturation and surface homogeneity to a certain extent. The surface shear stress increases with enhancing the rotation rate or the inlet velocity. The optimization for the configuration has also been discussed, which is helpful for the surface homogeneity. [Copyright &y& Elsevier]

Abstract: Computational analysis of three-dimensional flow and mass transfer in a non-standard configuration for growth of a KDP crystal was conducted. The results show that the surface shear stress is mainly affected by the inlet velocity, and the distribution of the surface supersaturation is determined by the bulk supersaturation and the inlet velocity. By adjusting the inlet velocity, the homogeneity of surface supersaturation can be improved, which is helpful for reducing the occurrence of inclusions and enhancing the crystal quality. The thickness of solute boundary layer is closely related to the flow intensity, but it is almost free from the impact of the bulk supersaturation. [ABSTRACT FROM AUTHOR]

• The effect of temperature on ADP crystal growth by SCM is considered. • The interactions of heat, species transport and fluid flow are studied by numerical simulation. • The surface supersaturation distribution under different conditions is presented. • The effect of the secondary vortex on mass transfer is analyzed. Three-dimensional unsteady numerical simulations are carried out to study the interactions of heat, species transport and fluid flow during the ADP crystal growth by solution circulating method (SCM). The supersaturation distribution on the crystal surface under different conditions is investigated and the effects of temperature and flow fields on the surface supersaturation are analyzed in detail. The results show that the magnitude and distribution of the surface supersaturation are improved when the rotation rate gets high. With an increase of the inlet velocity, there is a reduction in the magnitude of the surface supersaturation, while the uniformity of the supersaturation distribution is improved slightly. Besides, the increase of the inlet temperature decreases the magnitude of the surface supersaturation. As the crystal size gets large from 50 to 70 mm, the magnitude of the supersaturation on the crystal surfaces reduces obviously, but a little improvement can be seen in the uniformity of the supersaturation distribution on the prismatic faces. [ABSTRACT FROM AUTHOR]

• A modified seed mounting mode is proposed for the growth of ADP crystals. • The flow stagnation regions near the prismatic surface is suppressed. • The effect of flow on the surface supersaturation distribution was analyzed. • The relation between the shear stress and the surface supersaturation was discussed. • ADP crystals with higher quality was successfully grown under the modified mode. A modified seed mounting geometry is proposed, aiming to improve the distribution homogeneity of the supersaturation on the crystal face during the growth of ammonium dihydrogen phosphate (NH 4 H 2 PO 4 , ADP) crystals. To evaluate the modification, three dimension transient numerical simulation of flow and solute transfer involved in the growth of ADP crystals have been performed. The effects of flow on the surface supersaturation distribution is analyzed in detail. Compared with the ordinary seed mounting geometry, the modified geometry is able to suppress the formation of flow stagnation regions near the prismatic surface and improve the magnitude and the distribution homogeneity of the supersaturation. Particularly even at a lower rotation rate (ω = 30 rpm), the distribution of the surface supersaturation still possesses a better uniformity under the modified geometry. Meanwhile, with the increase of rotation rate, there is an improvement in the magnitude and the distribution of the supersaturation on the crystal surfaces. The effects of natural convection adjacent to prismatic faces can be ignored when rotation rate is equal to or greater than 50 rpm. Moreover, as the crystal size increases, the magnitude of the supersaturation on the prismatic surface declines a little, and its uniformity deteriorates gradually. Consequently, as the crystal growing, it should increase the rotation rate appropriately. Finally, etching studies reveal that the ADP crystals with higher quality can be obtained by modifying the seed mounting geometry simply. [ABSTRACT FROM AUTHOR]

• A stirrer is introduced during the ADP crystal growth. • The low-supersaturation regions on the crystal face are suppressed. • The surface supersaturation distribution under different conditions was presented. • The effect of flow on the surface supersaturation distribution was analyzed. • The roles of natural and forced convection in mass transfer were discussed. A stirrer is added to the traditional rotating crystal growth system of ammonium dihydrogen phosphate (NH 4 H 2 PO 4 , ADP), aiming at effectively utilizing the convection to improve the mass transfer and the distribution homogeneity of the supersaturation on the crystal face. 3D numerical simulation on flow and surface supersaturation distribution under different conditions is performed employing the finite-volume method, and the effect of flow on the surface supersaturation distribution is analyzed in detail. Compared with the traditional rotating-crystal system, the introduction of a stirrer can produce stronger axial flow and accordingly improve the magnitude and distribution homogeneity of the surface supersaturation, which is favorable to grow high quality crystals. As the stirrer rotation rate increases, the magnitude of the axial flow velocity increases, resulting in a reduction of the thickness of the solute boundary layer and an increase of the supersaturation on the crystal faces. Meanwhile, the homogeneity of the surface supersaturation is also improved. The crystal rotation rate strongly influences the magnitude and distribution of the prismatic surface supersaturation. As the crystal size increases from 25 cm to 35 cm, the distribution homogeneity of the prismatic surface supersaturation improves significantly, which is beneficial to crystal growth. Additionally, the importance of natural and forced convections in mass transport are discussed. Results show that the effects of natural convection adjacent to crystal faces can be ignored when stirrer rotation rate is greater than 400 rpm. [ABSTRACT FROM AUTHOR]