Solution crystal growth quality prediction and motion control method

Abstract

The invention discloses a solution crystal growth quality prediction and motion control method, and mainly solves the problems that the existing crystal growth quality is difficult to predict and the motion mode design is not based on. Comprising the following steps: S1, creating a three-dimensional physical model of the crystal growth system, performing grid discretization on the three-dimensional physical model, and setting the distance between adjacent discrete points as L; s2, obtaining a crystal face solute concentration field; s3, obtaining a series of step columns of the crystal face; s4, analyzing the morphology stability of the crystal face step column according to the distance between adjacent steps of the crystal face step column and the bending degree; judging whether the crystal face morphology is stable or not; s5, if a conclusion that the morphology of the crystal face is stable is obtained, the given motion mode meets the requirement, and the growth of the high-quality crystal can be ensured; and if a crystal face morphology instability conclusion is obtained, a motion mode is given again, and evaluation is carried out again according to the steps S1-S4. According to the method, the morphology stability of the crystal face can be directly analyzed in a given growth environment and a given motion mode, and whether the morphology instability phenomenon occurs or not is predicted.

Description

Technical Field

[0001] The invention belongs to the technical field of crystal preparation, and in particular relates to a solution crystal growth quality prediction and motion control method. Background Art

[0002] Solution crystal growth is an important method for preparing crystal materials and is currently the only method for growing large-diameter nonlinear optical crystals. In the process of solution crystal growth, convective material transport is an important part of crystal growth, which directly affects the growth rate and quality of the crystal. On the one hand, convection can significantly improve the material transport at the crystal / liquid interface, which can increase the crystal growth rate by an order of magnitude [1]. On the other hand, convection can induce inclusion defects [2], which can reduce the performance or service life of the crystal [3]. In the actual crystal growth process, relative movement of the crystal to generate forced convection and enhance the mass transfer process at the growth interface is one of the necessary measures to achieve rapid crystal growth. However, studies have shown that under different movement modes, the hydrodynamic conditions of the crystal surface are different, and there are obvious differences in the growth quality of the crystal. Designing a crystal growth method that can fully utilize the enhanced mass transfer effect of convection while avoiding the adverse effects of convection is the key to rapidly growing high-quality crystals.

[0003] The growth of solution crystals is accompanied by the spreading of adjacent steps on the crystal surface, forming layers of crystal surfaces. A large number of studies have shown that the effect of convection on the quality of crystal growth is actually the effect of convective material transport on the morphological stability of the crystal surface. The instability of the crystal surface morphology will induce the formation of liquid inclusions, which will eventually lead to a decrease in crystal quality [4]. It can be seen that the stability of crystal surface morphology plays a qualitative role in the quality of crystals.

[0004] The step height of crystal growth is about a few nanometers to tens of microns, and conventional morphological observation and analysis requires the use of optical or atomic force microscopes. Due to the high-speed movement of the crystal, real-time observation of the crystal surface morphology is difficult to achieve based on existing technical means. As a result, the relationship between the crystal motion characteristics and the stability of the crystal surface morphology has not yet been established. In actual crystal growth, the design and adjustment of the crystal movement mode still mainly rely on experience at this stage. Therefore, in order to grow high-quality crystals, especially large-sized high-quality nonlinear optical crystals used in inertial confinement nuclear fusion, it is urgent to establish a set of crystal quality prediction methods that can guide the design of crystal movement modes.

[0005] The existing technology uses optical technology to quickly measure the supersaturation of crystal solutions, which can be combined with a solution crystal growth device and applied to crystal growth. This technology can be used as a supplementary means of crystal growth, but it is difficult to predict the quality of crystals.

[0006] Another method is to use a laser phase-shift interferometer system to measure the surface microstructure of a growing crystal. This method uses a designed system to observe the surface microstructure of a stationary crystal surface. For actual crystal growth, the crystal must be stationary before observation; however, this process will change the hydrodynamic conditions of the crystal surface and will also affect the crystal surface morphology. The observed morphology may be different from the crystal surface morphology under actual hydrodynamic conditions. At the same time, the application text also points out that accurate observation has specific requirements for the quality of the container material, which limits its further application.

[0007] [1].Wilcox W R.Influence of convection on the growth of crystals fromsolution[J].Journal of Crystal Growth,1983,65(1-3):133-142.

[0008] [2].Vekilov PG, Alexander J ID, Rosenberger F.Nonlinear response oflayer growth dynamics in the mixed kinetics-bulk-transport regime[J].PhysicalReview E,1996,54(6):6650.

[0009] [3].Woods BW,Runkel MJ,Yan M,et al.Investigations of laser damage in KDP using light-scattering techniques[C] / / Laser-Induced Damage in OpticalMaterials:1996.International Society for Optics and Photonics,1997,2966:20-31.

[0010] [4]. Van Enckevort WJP, Janssen-van Rosmalen R, Klapper H, et al. Growthphenomena of KDP crystals in relation to the internal structure [J]. Journal of Crystal Growth, 1982, 60 (1): 67-78. Summary of the invention

[0011] The purpose of the present invention is to provide a solution crystal growth quality prediction and motion control method, which mainly solves the problem that the existing crystal growth quality is difficult to predict and the motion mode design has no basis.

[0012] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0013] A method for predicting the growth quality of solution crystals and controlling their motion comprises the following steps:

[0014] S1, creating a three-dimensional physical model of the crystal growth system, and performing mesh discretization on the three-dimensional physical model, with the distance between adjacent discrete points being set to L;

[0015] S2, based on CFD simulation, solve the three-dimensional physical model to obtain the solute concentration field on the crystal surface;

[0016] S3, extracting the solute concentration field data of the crystal surface, simulating the pushing process of the step array on the crystal surface according to the step pushing kinetic model, and obtaining a series of step arrays on the crystal surface;

[0017] S4, analyzing the stability of the morphology of the crystal plane step array according to the adjacent step spacing and the bending degree of the crystal plane step array; judging whether the crystal plane morphology is stable;

[0018] S5, if the conclusion is that the crystal surface morphology is stable, it means that the given movement mode meets the requirements and can ensure the growth of high-quality crystals; if the conclusion is that the crystal surface morphology is unstable, the movement mode is re-given and re-evaluated according to steps S1-S4.

[0019] Furthermore, in the step S2, the fluid flow in the CFD method simulation is described by the NS equation; the mass transfer process involved in the growth is described by the component transport equation; wherein the solute consumption rate involved in the crystal surface is expressed by the formula:

[0020] m=(ρ s -ρ0C e )R

[0021] In the formula, ρ s is the crystal density, ρ0 is the solution density, C e is the solubility of the crystal material, R is the growth constant, which is determined by the growth rate of the crystal and ranges from 0 to 1.

[0022] Furthermore, in step S3, the specific steps of obtaining a series of step rows on the crystal plane are as follows:

[0023] S31, set the initial straight step sequence and time interval t and step moving speed V; wherein,

[0024] V=β s *σ s

[0025] In the formula, β s is the step dynamics coefficient, ranging from 0 to 1; σ s is the crystal plane supersaturation value at the step location;

[0026] S32, setting the distance between two points in the discretization of a straight step array consisting of a plurality of points to 1 / 5-1 / 3L;

[0027] S33, making the moving distance of each point on the step array equal to V*t, and the moving direction is the normal direction where the discrete point is located, that is, obtaining a series of step arrays on the crystal plane.

[0028] Furthermore, in step S4, the method for determining whether the crystal surface morphology is stable is:

[0029] If the spacing between step rows gradually decreases with the passage of time, it means that there is longitudinal step displacement on the crystal plane; if the step rows bend and there is a "concave" area with the passage of time, it means that there is lateral step displacement; if one of the above situations exists, it is concluded that there is morphological instability on the crystal plane; if neither of the above two situations exists, the crystal plane is judged to be stable.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention can directly analyze the stability of crystal surface morphology under a given growth environment and movement mode, and predict whether morphology instability will occur.

[0032] (2) The present invention can directly guide the design of the crystal growth movement mode based on the prediction results, thereby solving the current industry situation that the existing crystal movement design has no basis support and is based on experience or feeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the movement of the crystal using the three-dimensional motion method in an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the movement of the crystal using the traditional crystal rotation method in the embodiment of the present invention.

[0035] Figure 3 It is a three-dimensional physical model of the crystal growth system in the embodiment of the present invention.

[0036] Figure 4 Schematic diagram of the discrete grid on the crystal surface in the embodiment of the present invention.

[0037] Figure 5This is a schematic diagram of the solute concentration field on the crystal surface obtained by simulation of a crystal moving in a three-dimensional motion method in an embodiment of the present invention.

[0038] Figure 6 This is a schematic diagram of the solute concentration field on the crystal surface obtained through simulation of the crystal moving in the traditional crystal rotation method in the embodiment of the present invention.

[0039] Figure 7 It is a schematic diagram of the crystal plane step array morphology of the three-dimensional motion method in the embodiment of the present invention.

[0040] Figure 8 Schematic diagram of the crystal plane step array morphology of the traditional crystal rotation method in the embodiment of the present invention.

[0041] Fig. 9 This is a KDP crystal grown by the three-dimensional motion method in the embodiment of the present invention.

[0042] Fig.10 This is a KDP crystal grown by the traditional crystal rotation method in the embodiment of the present invention.

[0043] Fig.11 The morphology of the corrosion pits of the crystal cylinder grown by the three-dimensional motion method in the embodiment of the present invention under different magnifications.

[0044] Fig.12 The morphology of the corrosion pits of the crystal cylinder grown by the traditional crystal rotation method in the embodiment of the present invention under different magnifications DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiments of the present invention include but are not limited to the following embodiments.

[0046] Example

[0047] The invention discloses a method for predicting the quality of solution crystal growth and controlling motion, comprising the following steps: firstly, creating a three-dimensional physical model of a crystal growth system, and performing grid discretization on the three-dimensional physical model, with the distance between adjacent discrete points being set to L; solving the three-dimensional physical model based on CFD simulation to obtain a crystal surface solute concentration field; using the NS equation to describe the fluid flow in the CFD simulation; and using the component transport equation to describe the mass transfer process involved in the growth; wherein the solute consumption rate involved in the crystal surface is expressed by the formula:

[0048] m=(ρ s -ρ0C e )R

[0049] In the formula, ρ s is the crystal density, ρ0 is the solution density, Ce is the solubility of the crystal material, R is the growth constant, which is determined by the growth rate of the crystal and ranges from 0 to 1.

[0050] Then, the solute concentration field data of the crystal surface is extracted, and the step-pushing process of the step array on the crystal surface is simulated according to the step-pushing kinetic model to obtain a series of step arrays on the crystal surface; the initial straight step array and the time interval t and the step-pushing speed V are set; wherein,

[0051] V=β s *σ s

[0052] In the formula, β s is the step dynamics coefficient, ranging from 0 to 1; σ s is the supersaturation value of the crystal plane where the step is located; the distance between two points in the discrete straight step column composed of several points is set to 1 / 5-1 / 3L; the moving distance of each point on the step column is equal to V*t, and the moving direction is the normal direction of the discrete point, that is, a series of step columns on the crystal plane are obtained.

[0053] The stability of the crystal plane step array morphology is analyzed based on the adjacent step spacing and the degree of curvature of the crystal plane step array; whether the crystal plane morphology is stable is judged; if the step array spacing gradually decreases with the passage of time, it means that there is longitudinal step displacement on the crystal plane; if the step array bends and there is a "concave" area with the passage of time, it means that there is lateral step displacement; if one of the above situations exists, it is concluded that the crystal plane has a morphological instability problem; if neither of the above two situations exists, the crystal plane is judged to be stable.

[0054] If the conclusion is that the crystal surface morphology is stable, it means that the given movement mode meets the requirements and can ensure the growth of high-quality crystals; if the conclusion is that the crystal surface morphology is unstable, the movement mode is re-given and re-evaluated according to the above method.

[0055] Taking a certain crystal growth as an example, in this crystal growth system, the crystal growth liquid pool is placed in a constant temperature water bath, and a certain amount of supersaturated solution with a supersaturation of 4%-8% is installed in the solution; the crystal and the crystal holding rod for fixing the crystal are placed in the solution, and the crystal holding rod is fixed on the driving device at the upper end and moves according to the set movement mode. Figure 1 Demonstrated the crystal motion of the three-dimensional motion method, Figure 2 The crystal movement of the traditional crystal rotation method is shown. During the entire growth process, the crystal moves along Figure 1 , Figure 2 The set motion mode is periodic motion.

[0056] For this crystal growth system, three-dimensional modeling of the crystal and solution parts was performed (such as Figure 3 ) and discrete meshing (as shown in Figure 4As shown in FIG. 1 ), the crystal is simulated by the method of the present invention, and the solute concentration field on the crystal surface is obtained. The relevant parameters involved in the KDP crystal are as follows: s =2338kg / m3; ρ0=1200kg / m3; C e =0.2984; R = 2.89*10 -6 The solute concentration field on the crystal surface is obtained as Figure 5 shown.

[0057] based on Figure 5 , Figure 6 The data of the present invention are used to obtain the crystal plane step array displacement morphology, and the step morphology stability is analyzed. Figure 7 , Figure 8 The step-column morphology of the crystal face is shown in two different motion modes. It can be seen intuitively that with the traditional method, the step-columns of the crystal face are obviously curved and the spacing between adjacent step-columns is constantly decreasing, which means that the crystal face has morphological instability problems and is prone to growth defects. This motion mode is not conducive to crystal growth and needs to be redesigned. In contrast, in the three-dimensional motion mode, the spacing between step-columns remains unchanged overall, and there is no "concave" area, which means that the crystal face morphology can remain stable, which is conducive to the growth of high-quality crystals.

[0058] The conclusions drawn by the present invention have also been confirmed by conducting experiments. Fig. 9 , Fig.10 It can be seen that obvious white opaque substances can be observed in the crystals grown by the traditional crystal rotation method, which indicates that there are growth defects in the crystals, and the generation of defects will inevitably lead to a decrease in crystal quality. The crystals grown by the three-dimensional motion method are transparent, regular, and have no obvious defects. Dislocation corrosion analysis also further proves the above conclusion. It can be observed under both low-power microscope (4×) and high-power microscope (20×) (such as Fig.11 , Fig.12 As shown in Figure 2, within the same observation range, the number of dislocations in the 3D motion method is significantly less than that in the crystal rotation method. During the growth process, the appearance of inclusions will cause the arrangement of atoms near them to be disordered, which will lead to the generation of dislocations and an increase in the number of dislocations. The effectiveness of the proposed method is further demonstrated through experiments.

[0059] The above embodiment is only one of the preferred implementation modes of the present invention and should not be used to limit the protection scope of the present invention. Any changes or modifications that are made to the main design concept and spirit of the present invention and have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A method for predicting the growth quality of solution crystals and controlling their motion, characterized in that: The following steps are involved: S1, creating a three-dimensional physical model of the crystal growth system, and performing mesh discretization on the three-dimensional physical model, with the distance between adjacent discrete points being set to L; S2, based on CFD simulation, solve the three-dimensional physical model to obtain the solute concentration field on the crystal surface; S3, extracting the solute concentration field data of the crystal surface, simulating the pushing process of the step array on the crystal surface according to the step pushing kinetic model, and obtaining a series of step arrays on the crystal surface; S4, analyzing the stability of the morphology of the crystal plane step array according to the adjacent step spacing and the bending degree of the crystal plane step array; judging whether the crystal plane morphology is stable; S5, if the conclusion is that the crystal surface morphology is stable, it means that the given movement mode meets the requirements and can ensure the growth of high-quality crystals; if the conclusion is that the crystal surface morphology is unstable, the movement mode is re-given and re-evaluated according to steps S1-S4.

2. A solution crystal growth quality prediction and motion control method according to claim 1, characterized in that: In step S2, the fluid flow in the CFD simulation is described by the NS equation; the mass transfer process involved in the growth is described by the component transport equation; wherein the solute consumption rate involved in the crystal surface is expressed by the formula: m=(ρ s -p0C e )R In the formula, ρ s is the crystal density, ρ0 is the solution density, C e is the solubility of the crystal material, R is the growth constant, which is determined by the growth rate of the crystal and ranges from 0 to 1.

3. A solution crystal growth quality prediction and motion control method according to claim 2, characterized in that: In step S3, the specific steps of obtaining a series of step rows on the crystal plane are as follows: S31, set the initial straight step sequence and time interval t and step moving speed V; wherein, V=β s *s s In the formula, β s is the step dynamics coefficient, ranging from 0 to 1; σ s is the crystal plane supersaturation value at the step location; S32, setting the distance between two points in the discretization of a straight step array consisting of a plurality of points to 1 / 5-1 / 3L; S33, making the moving distance of each point on the step array equal to V*t, and the moving direction is the normal direction where the discrete point is located, that is, obtaining a series of step arrays on the crystal plane.

4. A solution crystal growth quality prediction and motion control method according to claim 3, characterized in that: In step S4, the method for judging whether the crystal surface morphology is stable is: If the spacing between step rows gradually decreases with the passage of time, it means that there is longitudinal step displacement on the crystal plane; if the step rows bend and there is a "concave" area with the passage of time, it means that there is lateral step displacement; if one of the above situations exists, it is concluded that there is morphological instability on the crystal plane; if neither of the above two situations exists, the crystal plane is judged to be stable.

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