A method for predicting the quality of solution crystal growth and motion control

Abstract

The present invention discloses a method for predicting the quality of solution crystal growth and motion control, which mainly solves the problems that it is difficult to predict the quality of existing crystal growth and there is no basis for the design of motion modes. The method includes the following steps: S1, 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 set as L; S2, obtaining the solute concentration field on the crystal surface; S3, obtaining a series of step columns on the crystal surface; S4, analyzing the morphological stability of the crystal surface step column according to the adjacent step spacing and bending degree of the crystal surface step column; judging whether the crystal surface morphology is stable; S5, if it is concluded that the crystal surface morphology is stable, it means that the given motion mode meets the requirements and can ensure the growth of high-quality crystals; if it is concluded that the crystal surface morphology is unstable, a new motion mode is given, and the evaluation is carried out again according to steps S1-S4. The present invention can directly analyze the morphological stability of the crystal surface under a given growth environment and motion mode, and predict whether the phenomenon of morphological instability will occur.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystal preparation, and specifically relates to a method for predicting the quality of solution crystal growth and motion control. Background Art

[0002] Solution crystal growth is an important method for preparing crystal materials and is currently the only method for growing large-aperture nonlinear optical crystals. During the solution crystal growth process, convective mass transport is an important link in crystal growth, directly affecting the growth rate and quality of the crystal. On the one hand, convection can significantly improve the mass transport at the crystal / liquid interface, resulting in an order-of-magnitude increase in the crystal growth rate [1]; on the other hand, convection can induce the generation of inclusion defects [2], leading to a decline in the performance or service life of the crystal [3]. In the actual crystal growth process, relative motion of the crystal is used to generate forced convection and strengthen the mass transfer process at the growth interface, which is one of the necessary measures to achieve rapid crystal growth. However, research shows that under different motion modes, the hydrodynamic conditions on the crystal surface are different, and there are obvious differences in the growth quality of the crystal. Designing a crystal growth mode that can make full use of the enhanced mass transfer effect of convection while avoiding the adverse effects of convection is the key to rapidly growing high-quality crystals.

[0003] Solution crystal growth proceeds with the spreading of adjacent steps on the crystal surface to form layer upon layer of crystal surfaces. A large number of studies have shown that the essence of the influence of convection on crystal growth quality is that convective mass transport affects the morphological stability of the crystal surface. The instability of the crystal surface morphology will induce the formation of liquid inclusions, ultimately leading to a decline in crystal quality [4]. It can be seen that the morphological stability of the crystal surface plays a decisive role in crystal quality.

[0004] The step height of crystal growth is about a few nanometers to dozens of micrometers. Conventional morphological observation and analysis require the aid of optical or atomic force microscopes. Due to the high-speed movement of the crystal, it is difficult to achieve real-time observation of the crystal surface morphology based on existing technical means. Thus, the relationship between crystal motion characteristics and crystal surface morphological stability has not been established yet. In actual crystal growth, the design and adjustment of crystal motion modes mainly rely on experience at present. Therefore, in order to grow high-quality crystals, especially large-size high-quality nonlinear optical crystals applied to inertial confinement fusion, there is an urgent need to establish a crystal quality prediction method that can guide the design of crystal motion modes.

[0005] The prior art uses optical technology to quickly measure the supersaturation of the crystal solution. This technology can be combined with the solution crystal growth device and applied to crystal growth. This technology can be used as a supplementary means for crystal growth and is difficult to achieve the prediction of crystal quality.

[0006] Another method is to measure the microscopic structure of the crystal growth surface using a laser phase-shifting interference system. The designed system can be used to observe the microscopic structure of a stationary crystal surface. For actual crystal growth, the crystal needs to be stationary before observation; however, this process will change the hydrodynamic conditions of the crystal surface and also affect the surface morphology, and the observed morphology may be different from that under actual hydrodynamic conditions. At the same time, the application text also points out that there are specific requirements for the container material quality for accurate observation, which limits its further application.

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

[0008] [2].Vekilov P G, Alexander J ID, Rosenberger F. Nonlinear response of layer growth dynamics in the mixed kinetics - bulk - transport regime[J]. Physical Review E, 1996, 54(6): 6650.

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

[0010] [4].Van Enckevort W J P, Janssen - van Rosmalen R, Klapper H, et al. Growth phenomena 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 object of the present invention is to provide a method for predicting the quality of solution crystal growth and controlling the movement, mainly solving the problems that it is difficult to predict the quality of existing crystal growth and there is no basis for designing the movement mode.

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

[0013] A method for predicting the quality of solution crystal growth and controlling the movement includes the following steps:

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

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

[0016] S3, extracting the data of the solute concentration field on the crystal surface, and simulating the pushing process of the step rows on the crystal surface according to the step pushing kinetics model to obtain a series of step rows on the crystal surface;

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

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

[0019] Further, in the step S2, in the CFD method simulation, the fluid flow is described by the N - S equation; the mass transfer process involved in the growth is described by the component transport equation; among them, the solute consumption rate on the crystal surface is through 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, and R is the growth constant, which is determined by the growth rate of the crystal, and the value range is 0 - 1.

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

[0023] S31, setting the initial straight step row, the time interval t and the step pushing speed magnitude V; among them,

[0024] V = β s *σ s

[0025] where β s is the step kinetic coefficient, with a value range of 0 - 1; σ s is the supersaturation value of the crystal plane where the step is located;

[0026] S32: Set the distance between two points in the discretization of the straight step array composed of several points to 1 / 5 - 1 / 3L;

[0027] S33: Make 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, a series of step arrays on the crystal plane are obtained.

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

[0029] If the step array spacing gradually decreases over time, it means that there is a longitudinal step displacement on the crystal plane; if the step array bends and there is a "concave" region over time, it means that there is a transverse step displacement; if one of the above situations exists, it is concluded that there is a problem of 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 the crystal plane morphology under a given growth environment and movement mode, and predict whether there will be a phenomenon of morphological instability.

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

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

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

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

[0036] Figure 4 It is a schematic diagram of the discrete grid on the crystal surface in an embodiment of the present invention.

[0037] Figure 5Schematic diagram of the solute concentration field on the crystal plane obtained by simulation of the crystal with the three-dimensional motion method in an embodiment of the present invention.

[0038] Figure 6 Schematic diagram of the solute concentration field on the crystal plane obtained by simulation of the crystal with the traditional crystal rotation method in an embodiment of the present invention.

[0039] Figure 7 Schematic diagram of the morphology of the crystal plane step columns with the three-dimensional motion method in an embodiment of the present invention.

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

[0041] Figure 9 KDP crystal grown with the three-dimensional motion method in an embodiment of the present invention.

[0042] Figure 10 KDP crystal grown with the traditional crystal rotation method in an embodiment of the present invention.

[0043] Figure 11 Morphology diagram of the corrosion pits on the cylindrical surface of the crystal grown with the three-dimensional motion method in an embodiment of the present invention under different magnifications.

[0044] Figure 12 Morphology diagram of the corrosion pits on the cylindrical surface of the crystal grown with the traditional crystal rotation method in an embodiment of the present invention under different magnifications Detailed implementation manners

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments. The implementation manners of the present invention include but are not limited to the following embodiments.

[0046] Embodiment

[0047] A method for predicting the growth quality of solution crystals and motion control disclosed by the present invention includes the following steps: First, create a three-dimensional physical model of the crystal growth system, and perform grid discretization on the three-dimensional physical model, with the distance between adjacent discrete points set to L; based on CFD method simulation, solve the three-dimensional physical model to obtain the solute concentration field on the crystal plane; in the CFD method simulation, the fluid flow is described by the N-S equation; the mass transfer process involved in growth is described by the component transport equation; among them, the solute consumption rate on 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 Here, S is the solubility of the crystal material, and R is the growth constant, which is determined by the crystal growth rate and ranges from 0 to 1.

[0050] Subsequently, data on the solute concentration field of the crystal plane is extracted. According to the step propagation kinetics model, the process of step array propagation on the crystal plane is simulated to obtain a series of step arrays on the crystal plane. Set the initial straight step array, the time interval t, and the step propagation speed V. Among them,

[0051] V = β s *σ s

[0052] In the formula, β s is the step kinetics coefficient, ranging from 0 to 1; σ s is the supersaturation value of the crystal plane at the position of the step. Set the distance between two points in the discretization of the straight step array composed of several points to be 1 / 5 - 1 / 3L. Make the moving distance of each point on the step array equal to V*t, and the moving direction is the normal direction of the discrete point, that is, a series of step arrays on the crystal plane are obtained.

[0053] Analyze the morphology stability of the crystal plane step array based on the adjacent step spacing and bending degree of the crystal plane step array. Judge whether the crystal plane morphology is stable. If the step array spacing gradually decreases over time, it means that there is a longitudinal displacement of the steps on the crystal plane. If the step array bends and there is a "concave" region over time, it means that there is a transverse displacement of the steps. If one of the above situations exists, it is concluded that there is a problem of morphological instability of the crystal plane. If neither of the above two situations exists, the crystal plane is judged to be stable.

[0054] If it is concluded that the crystal plane morphology is stable, it means that the given motion mode meets the requirements and can ensure the growth of high-quality crystals. If it is concluded that the crystal plane morphology is unstable, a new motion mode is given and re-evaluated according to the above method.

[0055] Taking the growth of a certain crystal 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. A crystal and a crystal holding rod for fixing the crystal are placed in the solution. The crystal holding rod is fixed on the driving device at the upper end and moves according to the set motion mode. Figure 1 Shows the crystal motion mode of the three-dimensional motion method, Figure 2 Shows the crystal motion mode of the traditional crystal rotation method. During the entire growth process of the crystal, along Figure 1 、 Figure 2 the set motion mode performs periodic motion.

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

[0057] Based on Figure 5 , Figure 6 data, the step column migration morphology on the crystal plane is obtained by the method of the present invention, and the stability of the step morphology is analyzed. Figure 7 , Figure 8 show the step column morphologies on the crystal plane under two different motion modes. It can be directly seen from this that with the traditional method, there are obvious bends in the step columns on the crystal plane and the distance between adjacent step columns continuously decreases, which represents the problem of morphological instability on the crystal plane and is prone to the generation of growth defects. This motion mode is not conducive to crystal growth and needs to be redesigned; in contrast, under the three-dimensional motion mode, the distance between step columns generally remains unchanged and there is no "concave" area, which indicates that the crystal plane morphology can be kept stable and is conducive to the growth of high-quality crystals.

[0058] The conclusion drawn by the present invention is also confirmed by conducting experiments. As can be seen from Figure 9 , Figure 10 , 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. The generation of defects will inevitably lead to a decrease in crystal quality. However, the crystals grown by the three-dimensional motion method are transparent, regular and have no obvious defects. Dislocation etching analysis further proves the above conclusion. Whether under a low-power microscope (4×) or a high-power microscope (20×), it can be observed (as shown in Figure 11 , Figure 12 ) that within the same observation range, the number of dislocations in the three-dimensional motion method is significantly less than that in the crystal rotation method. During the growth process, the appearance of inclusions will cause the atomic arrangement near them to be disordered, thereby leading to the generation of dislocations and an increase in the number of dislocations. The effectiveness of the proposed method is further proved by experiments.

[0059] The above embodiments are only one of the preferred embodiments of the present invention and should not be used to limit the protection scope of the present invention. Any modifications or polishing made without substantial significance in the main design concept and spirit of the present invention, as long as the technical problems solved are still the same as those of the present invention, should be included in the protection scope of the present invention.

Claims

1. A method for predicting the quality of solution crystal growth and controlling movement, characterized in that, It includes the following steps: S1. Create a three-dimensional physical model of the crystal growth system, and discretize the three-dimensional physical model into grids, with the distance between adjacent discrete points set as L; S2. Based on CFD method simulation, solve the three-dimensional physical model to obtain the solute concentration field on the crystal plane; S3. Extract the data of the solute concentration field on the crystal plane, and according to the step propagation kinetics model, simulate the propagation process of the step columns on the crystal plane to obtain a series of step columns on the crystal plane; S4. Analyze the morphological stability of the crystal plane step columns according to the adjacent step spacing and bending degree of the crystal plane step columns; judge whether the crystal plane morphology is stable; S5. If it is concluded that the crystal plane morphology is stable, it means that the given motion mode meets the requirements and can ensure the growth of high-quality crystals; if it is concluded that the crystal plane morphology is unstable, a new motion mode is given, and the evaluation is carried out again according to steps S1-S4.

2. The method for predicting the quality of solution crystal growth and motion control according to claim 1, characterized in that, In the step S2, in the CFD method simulation, the fluid flow is described by the N-S equation; the mass transfer process involved in the growth is described by the component transport equation; among them, the solute consumption rate on the crystal surface is through the formula: m = (ρ s - ρ0C e )R where 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 crystal growth rate and ranges from 0 to 1.

3. A method for predicting the quality of solution crystal growth and motion control according to claim 2, characterized in that In the step S3, the specific steps to obtain a series of step columns on the crystal plane are as follows: S31. Set the initial straight step column, time interval t and step propagation speed magnitude V; where, V = β s *σ s Where β s is the step kinetic coefficient, with a value range of 0 - 1; σ s is the supersaturation value of the crystal plane where the step is located; S32. Set the distance between two points in the discretization of the straight step column composed of several points to 1 / 5 - 1 / 3L; S33. Make the moving distance of each point on the step column equal to V*t, and the moving direction is the normal direction where the discrete point is located, that is, a series of step columns on the crystal plane are obtained.

4. A method for predicting the quality of solution crystal growth and motion control according to claim 3, characterized in that, In the step S4, the method to judge whether the crystal plane morphology is stable is: If the step column spacing gradually decreases over time, it means that there is a longitudinal displacement of the steps on the crystal plane; if the step column bends and there is a "concave" area over time, it means that there is a transverse displacement of the steps; if either of the above situations exists, it is concluded that there is a problem of morphological instability of the crystal plane; if neither of the above two situations exists, the crystal plane is judged to be stable.

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