Crystal growth apparatus and method based on thermal convection mass transfer and applications

Abstract

This invention relates to a crystal growth apparatus, method, and application based on thermal convection mass transfer, belonging to the field of crystal material preparation technology. The invention aims to solve the problems of spontaneous nucleation, secondary nucleation, and the intrusion of impurities into the growth zone leading to decreased crystal quality, as well as poor interfacial stability caused by mechanical stirring, in existing single crystal preparation processes. The method involves: 1. Establishing a temperature field and gradient; 2. Adding crystal raw materials and growth media to the dissolution zone reactor, ensuring the crystal raw materials form a saturated solution in the dissolution zone reactor with some solid raw material remaining, suspending the seed crystal; 3. Not adding crystal raw materials to the high-temperature zone reactor; 4. Cooling after growth to obtain a single crystal. This invention reduces the probability of microcrystals / clusters entering the growth zone, and reduces interfacial disturbance and further suppresses the intrusion of impurities into the growth zone without introducing mechanical stirring, resulting in higher crystal quality.

Description

Technical Field

[0001] This invention relates to a crystal growth apparatus, method, and application, belonging to the field of crystal material preparation technology. Background Technology

[0002] Single-crystal material growth often employs solution methods or melt methods. Solution methods can grow crystals at relatively low temperatures, but solution stability, supersaturation control, and spontaneous nucleation / impure crystal problems are common engineering challenges. Patents on large-size KDP-type crystal growth methods point out that while traditional cooling methods have simple equipment, their long growth cycles and the tendency for spontaneous nucleation during cooling can disrupt normal crystal growth. Furthermore, the presence of impure crystals in the growth tank can compete with the target crystal for raw materials, preventing normal crystal growth. Additionally, related device patents address secondary nucleation and impure crystal problems in solution crystal growth by aiming to suppress secondary nucleation, reduce local supersaturation, and prevent rapid impure crystal growth. In solution crystallization routes such as cooling crystallization and evaporation crystallization, spontaneous nucleation, secondary nucleation, and the entry of impure crystals into the growth region lead to decreased crystal quality, increased failure risk, and poorer process repeatability.

[0003] From the perspective of mass transfer mechanisms, a solute boundary layer typically exists near the solution growth interface, and mass transport within this boundary layer can exhibit a coupling effect of convection and diffusion. Therefore, in engineering, stable and repeatable concentration fields are required through controllable flow and temperature fields. Simultaneously, thermal convection is closely related to the crystal growth process and crystal quality; the morphology and intensity of thermal convection affect the stability of heat and mass transfer processes. Existing zoned temperature control and circulating flow strategies can improve the temperature and concentration fields, but in some systems, they may still be accompanied by risks such as impurity migration, local concentration disturbances, and flow field shear disturbances introduced by mechanical stirring / pump circulation (poor interface stability, introducing undesirable defects). Furthermore, many structures still lack specific elimination sections designed to prevent "microcrystals / clusters from entering the growth region along the transport path."

[0004] Melt growth is widely used in obtaining bulk single crystals. However, in some halide systems, large-size melt growth can lead to defects such as surface cracks, subgrain boundaries, or twins due to structural phase transformations and thermal stress. Related Chinese reviews have summarized these issues. Therefore, for single-crystal systems that are prone to cracking, sensitive to impurities / inclusions, and require high uniformity of concentration gradients, a new crystal growth scheme is still needed that balances controllable temperature field, stable mass transfer, suppression of microcrystal / secondary nucleation migration, and reduced external agitation. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of spontaneous nucleation, secondary nucleation and impurity crystals entering the growth zone leading to a decrease in crystal quality during the existing single crystal preparation process, and poor interface stability caused by mechanical stirring. This invention provides a crystal growth device, method and application based on thermal convection mass transfer.

[0006] The crystal growth apparatus based on thermal convection mass transfer is a vertical reactor, which, from bottom to top, includes a dissolution zone reactor, a high-temperature zone reactor, and a growth zone reactor.

[0007] The reaction vessel in the dissolution zone and the reaction vessel in the high-temperature zone are equipped with a water bath heating device, and the reaction vessel in the growth zone is equipped with a water bath cooling device.

[0008] The upper end of the growth zone reactor is provided with a thermometer socket and a seed crystal suspension port. A thermometer is inserted into the thermometer socket, and a seed crystal suspension device is provided in the seed crystal suspension port. The seed crystal is suspended at the lower end of the seed crystal suspension device. The upper side of the growth zone reactor is provided with the water outlet of the growth zone reactor water bath heating device, and the lower side of the growth zone reactor is provided with the water inlet of the growth zone reactor water bath heating device.

[0009] A nanofiltration membrane structure is provided between the high-temperature zone reactor and the growth zone reactor. The nanofiltration membrane structure includes a membrane support frame, a replaceable nanofiltration membrane, a membrane frame, and a sealing ring.

[0010] The liquid phase exchange between the dissolution zone reactor and the growth zone reactor is achieved through a nanofiltration membrane.

[0011] The high-temperature zone reactor is provided with an outlet of the high-temperature zone reactor water bath heating device on the upper side and an inlet of the high-temperature zone reactor water bath heating device on the lower side (8).

[0012] The upper side of the dissolution zone reactor is provided with the outlet of the water bath cooling device for the dissolution zone reactor, the lower side of the dissolution zone reactor is provided with the inlet of the water bath cooling device for the dissolution zone reactor, and the bottom of the dissolution zone reactor is provided with a discharge port, and a switch is provided on the discharge port.

[0013] The crystal growth device based on thermal convection mass transfer is a closed container or a controllable container. The closed and controllable containers are used to reduce volatilization loss and the introduction of external pollution.

[0014] The total length L of the crystal growth apparatus based on thermal convection mass transfer is 300~3000 mm, the inner diameter D is 50~500 mm, the liquid column height H is 0.5~0.9 L, and the axial length L of the reactor in the high-temperature zone is... H The value is 0.2 ~ 0.7 L.

[0015] The nanofiltration membrane is installed on the nanofiltration membrane structure in the form of a flat sheet, tubular or hollow fiber membrane module, and the nanofiltration membrane structure is sealed to the inner wall of the container by a sealing ring or the inner wall of the vessel.

[0016] The nanofiltration membrane is provided with at least one of the following: necking channels, slit channels, capillary channels, honeycomb channels, and septum channels, in order to increase the residence time of fluid in the high-temperature zone to promote the elimination of microcrystals / clusters;

[0017] The nanofiltration membrane has a pore size of 0.6~10 nm and a molecular weight cutoff of 200~2000 Da. It has selective permeation characteristics for solutes larger than the pore size range. As a membrane separation method between ultrafiltration and reverse osmosis, the pore size and molecular weight range that nanofiltration membrane can intercept are typically defined in literature and patents. Furthermore, the pore size of the nanofiltration membrane remains stable under heated conditions.

[0018] The nanofiltration membrane material is selected from at least one of aromatic polyamide composite membrane, cellulose acetate, polysulfone, polyvinyl alcohol, sulfonated polysulfone, and sulfonated polyethersulfone.

[0019] The materials of the dissolution zone reactor, the high-temperature zone reactor, and the growth zone reactor are selected from at least one of quartz, glass, alumina, boron nitride, glassy carbon, or coated composite materials.

[0020] The crystal growth method based on thermal convection mass transfer is as follows:

[0021] 1. Turn on the water bath heating devices outside the melting zone reactor, the high-temperature zone reactor, and the water bath cooling devices outside the growth zone reactor. The temperature inside the high-temperature zone reactor is T. H The temperature inside the reaction vessel in the dissolution zone is T. D The temperature inside the reactor in the growth zone is T. G Establish the temperature field and gradient under the following conditions:

[0022] T H >T D >T G T D = T G + ΔT DG And ΔT DG The temperature range is 0.3 ~ 3.0 ℃; and T H = T D + ΔT HD And ΔT HD The temperature ranges from 1.0 to 3.0 ℃; the temperature inside the reaction vessel in the dissolution zone is T. D Temperature T inside the reactor in the growth zone G The axial temperature gradient between them is 0.5~5 ℃ / m, the temperature field stabilization time is 12 h~72 h and then maintained at that temperature;

[0023] 2. Add crystal raw materials and growth medium to the dissolution zone reactor to form a saturated solution of crystal raw materials in the dissolution zone reactor and leave solid raw materials in the dissolution zone reactor. Suspend the seed crystal at the lower end of the seed crystal suspension device in the growth zone reactor. Do not add crystal raw materials to the high temperature zone reactor. Grow for 28 to 35 days without mechanical stirring. After growth, the temperature in the growth zone reactor is controlled to decrease by 0.01 to 5 ℃ / h to obtain single crystals.

[0024] The growth medium described in step one is water, heavy water, aqueous haloacid solution, ionic liquid or organic solvent. The selection principle is to have moderate solubility within the target temperature window and allow the establishment of a steady-state temperature gradient and natural convection.

[0025] The orientation of the seed crystal in step one is the specified crystal plane orientation of the material to be grown.

[0026] The crystal raw materials include halides, oxides, sulfides, selenides, or their doping systems.

[0027] The crystal based on thermal convection mass transfer is used for nonlinear optics or scintillation detection.

[0028] To solve the above-mentioned technical problems, the present invention provides a crystal growth apparatus, method, and application based on thermal convection mass transfer, the key of which is:

[0029] (1) A high-temperature zone (also known as a thermal filtration zone / microcrystal elimination zone) is set between the dissolution zone and the growth zone to redissolve the microcrystals / clusters transported by convection by increasing the solubility;

[0030] (2) By establishing a stable temperature field through independent temperature control in three zones, the temperature of the high-temperature zone is higher than that of the dissolution zone and the growth zone. By utilizing the natural convection mass transfer driven by the temperature gradient, a stable and controllable solute transport and concentration gradient can be obtained without mechanical or magnetic stirring. This reduces the disturbance to the interface caused by microcrystals / clusters entering the growth zone, thus realizing solute circulation transport.

[0031] (3) Introducing a nanofiltration membrane between the high-temperature zone and the growth zone ensures that the liquid phase exchange between the dissolution zone and the growth zone must pass through the nanofiltration membrane; this allows microcrystals, clusters, or secondary nucleation nuclei carried in the migration path to be intercepted and re-dissolved by the nanofiltration membrane in the high-temperature zone, thereby reducing the probability of impurities entering the growth zone and improving the stability of the growth interface.

[0032] Terminology and Section Definitions:

[0033] (1) Dissolution zone: The temperature zone used to dissolve the crystal raw material and form a solute-rich saturated solution, preferably maintaining solid-liquid coexistence to maintain saturation.

[0034] (2) "High temperature zone": The temperature zone located between the dissolution zone and the growth zone is higher than that of the dissolution zone and the growth zone, thereby preventing this zone from becoming a new nucleation source. At the same time, the high temperature is used to increase the solubility in order to achieve the redissolution of microcrystals / clusters.

[0035] (3) “Growth zone”: refers to the temperature zone where seed crystals are set and controlled supersaturation is maintained to achieve directional growth.

[0036] (4) "Natural convection mass transfer": refers to the convective transport process formed under the action of temperature gradient and density difference without external pumping or mechanical stirring.

[0037] (5) Nanofiltration membrane: a membrane separation element between ultrafiltration and reverse osmosis. Its pore size can be 0.6~10 nm and it can intercept substances with a molecular weight of 200~1000 Da. Common materials include inorganic ceramics and polymer composite systems.

[0038] The method of this invention is performed according to the following basic process:

[0039] A. Raw material preparation and loading: Add the crystal component raw materials and growth medium to the dissolution zone; fix the seed crystal in the growth zone; do not place solid raw materials in the high-temperature zone or place only a small amount of raw materials that are significantly lower than those in the dissolution zone.

[0040] B. Establish the temperature field: Set T H >T D >T G And establish an axial temperature gradient.

[0041] C. Natural convection mass transfer and redissolution: The solute-rich solution is transported upward from the dissolution zone, and must pass through the high-temperature zone, where microcrystals / clusters are redissolved.

[0042] D. Growth control: Maintain moderate supersaturation and achieve stable growth in the growth zone through constant temperature supersaturation or programmed cooling.

[0043] E. Termination and Cooling: After growth, the crystal is cooled in a controlled manner, removed, processed, and characterized.

[0044] This invention relates to the field of crystal growth and crystal material preparation technology, specifically to a method and apparatus for achieving high-quality single crystal growth by driving natural convection mass transfer through temperature gradient and combining high-temperature "thermal filtration" with nanofiltration membrane isolation. It is applicable to single crystal material systems such as nonlinear optical crystals and scintillation crystals that are sensitive to crystal integrity, defects and impurity content.

[0045] This invention utilizes natural convection driven by a temperature gradient to transport a saturated solution from the dissolution zone through a high-temperature zone to the downstream of the nanofiltration membrane and into the growth zone without the need for mechanical or magnetic stirring. Within the high-temperature zone, microcrystals, clusters, or secondary nucleation nuclei transported by convection are re-dissolved. Simultaneously, the nanofiltration membrane traps microcrystals / clusters with a particle size larger than the effective pore size and dampens the flow through the membrane, thereby reducing the probability of impurities entering the growth zone and minimizing interfacial disturbance. This results in a more uniform fluid phase entering the growth zone and directional growth at the seed crystal, ultimately yielding a single crystal.

[0046] This invention involves sequentially setting up a dissolution zone, a high-temperature zone, and a growth zone vertically from bottom to top within the same growth system. By establishing a stable temperature gradient field, natural convection driven by the temperature gradient is used to achieve continuous mass transfer of solute from the dissolution zone to the growth zone. The high-temperature zone, with a temperature higher than both the dissolution and growth zones, eliminates microcrystals, clusters, and secondary nucleation nuclei transported by convection. Furthermore, a nanofiltration membrane is added between the high-temperature and growth zones, ensuring that liquid-phase exchange between the dissolution and growth zones must pass through the nanofiltration membrane, thereby suppressing the convection of impurity crystals into the growth zone and reducing interfacial disturbances. This method creates a more uniform concentration gradient without mechanical stirring, eliminates flow field shear disturbances to avoid the risk of secondary nucleation, and achieves directional seed crystal growth. It is suitable for material systems sensitive to crystal integrity and purity, such as nonlinear optical crystals and scintillation crystals.

[0047] The present invention can achieve the following technical effects:

[0048] (1) The “thermal filtration and re-dissolution” in the high temperature zone can reduce the probability of microcrystals / clusters entering the growth zone, which is beneficial to reducing secondary nucleation-related defects.

[0049] (2) As an isolation / damping element between the high temperature zone and the growth zone, nanofiltration membrane can "low-disturbance" the cross-zone flow without introducing mechanical stirring, reduce interface disturbance and further suppress the entry of impurities into the growth zone.

[0050] (3) Compared with the partial melt method, which has the risk of defects such as cracks caused by structural phase transformation and thermal stress in halide systems, this method provides an alternative route with solubility-driven and temperature field / convection control as the core, which is suitable for systems that are sensitive to integrity.

[0051] (4) The Cs2HgI4 prepared by this method has a symmetrical single peak HRXRD rocking curve with FWHM=0.033° on the polished (020) surface, which reflects high crystal quality (the half width at half maximum of the rocking curve is used to characterize crystal quality). Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the crystal growth apparatus based on thermal convection mass transfer according to the present invention;

[0053] Figure 2 This is a schematic diagram of the temperature distribution along the axial direction of the crystal growth method based on thermal convection mass transfer of this invention (T). H T D T G (and gradient range).

[0054] Figure 3 This is a schematic diagram of the natural convection mass transfer flow lines in the crystal growth method based on thermal convection mass transfer of the present invention (rich solute rises; microcrystals / clusters redissolve in the high-temperature region);

[0055] Figure 4 This is an enlarged schematic diagram of the nanofiltration membrane structure (6) between the high-temperature zone reactor (14) and the growth zone reactor (13) in the crystal growth device based on thermal convection mass transfer of the present invention;

[0056] Figure 5 This is a flowchart of the Cs2HgI4 single crystal growth process in Example 1;

[0057] Figure 6 This is the HRXRD rocking curve of Cs2HgI4 single crystal obtained by the method of the present invention in Example 1;

[0058] Figure 7 This is the HRXRD rocking curve of the sample obtained in Comparative Example 1 (cooling crystallization method);

[0059] Figure 8 This is a schematic diagram of the appearance / defects of the sample obtained in Comparative Example 2 (evaporation crystallization method);

[0060] Figure 9 This is a hardness test diagram of the (020) crystal face of the crystal grown by the method of the present invention in Example 1. Detailed Implementation

[0061] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0062] Specific implementation method 1: The crystal growth device based on thermal convection mass transfer in this implementation method is a vertical reactor, which includes a dissolution zone reactor 15, a high temperature zone reactor 14 and a growth zone reactor 13 from bottom to top in the vertical direction;

[0063] A water bath heating device is installed outside the dissolution zone reactor 15 and the high temperature zone reactor 14, and a water bath cooling device is installed outside the growth zone reactor 13.

[0064] The upper end of the growth zone reactor 13 is provided with a thermometer socket 16 and a seed crystal suspension port 17. A thermometer 1 is inserted into the thermometer socket 16, and a seed crystal suspension device 2 is provided in the seed crystal suspension port 17. A seed crystal 3 is suspended at the lower end of the seed crystal suspension device 2. The upper side of the growth zone reactor 13 is provided with a water outlet 4 of the growth zone reactor water bath heating device, and the lower side of the growth zone reactor 13 is provided with a water inlet 5 of the growth zone reactor water bath heating device.

[0065] A nanofiltration membrane structure 6 is provided between the high-temperature zone reactor 14 and the growth zone reactor 13. The nanofiltration membrane structure 6 includes a membrane support frame 18, a replaceable nanofiltration membrane 19, a membrane frame 20, and a sealing ring 21.

[0066] The liquid phase exchange between the dissolution zone reactor 15 and the growth zone reactor 13 is achieved through nanofiltration membrane 19;

[0067] The high-temperature zone reactor 14 is provided with a water outlet 7 for the high-temperature zone reactor water bath heating device on the upper side and a water inlet 8 for the high-temperature zone reactor water bath heating device on the lower side.

[0068] The upper side of the dissolution zone reactor 15 is provided with a water outlet 9 for the dissolution zone reactor water bath cooling device, the lower side of the dissolution zone reactor 15 is provided with a water inlet 10 for the dissolution zone reactor water bath cooling device, and the bottom of the dissolution zone reactor 15 is provided with a discharge port 11, and a switch 12 is provided on the discharge port 11.

[0069] The crystal growth device based on thermal convection mass transfer is a closed container or a controllable container. The closed and controllable containers are used to reduce volatilization loss and the introduction of external pollution.

[0070] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the total length L of the crystal growth device based on thermal convection mass transfer is 300~3000 mm, the inner diameter D is 50~500 mm, the liquid column height H is 0.5~0.9 L, and the axial length L of the high-temperature zone reactor 14 is... H The concentration is 0.2 ~ 0.7 L. Everything else is the same as in Specific Implementation Method 1.

[0071] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the nanofiltration membrane is installed on the nanofiltration membrane structure 6 in the form of a flat plate, tubular or hollow fiber membrane module, and the nanofiltration membrane structure 6 is sealed to the inner wall of the container by a sealing ring or the inner wall of the vessel.

[0072] The nanofiltration membrane is provided with at least one of the following: necking channels, slit channels, capillary channels, honeycomb channels, and septum channels, in order to increase the residence time of fluid in the high-temperature zone to promote the elimination of microcrystals / clusters;

[0073] The nanofiltration membrane has a pore size of 0.6~10 nm and a molecular weight cutoff of 200~2000 Da. It exhibits selective permeation characteristics for solutes larger than its pore size range. As a membrane separation method between ultrafiltration and reverse osmosis, the pore size and molecular weight cutoff range of nanofiltration membranes are typically defined in literature and patents. Furthermore, the nanofiltration membrane maintains pore size stability under heated conditions. Other aspects are the same as in specific embodiments one or two.

[0074] Specific Embodiment Four: This embodiment differs from Specific Embodiments One to Three in that the nanofiltration membrane material is selected from at least one of aromatic polyamide composite membranes, cellulose acetate, polysulfone, polyvinyl alcohol, sulfonated polysulfone, and sulfonated polyethersulfone. Everything else is the same as in Specific Embodiments One to Three.

[0075] Specific Embodiment Five: This embodiment differs from Specific Embodiments One to Four in that the materials of the dissolution zone reactor 15, the high-temperature zone reactor 14, and the growth zone reactor 13 are selected from at least one of quartz, glass, alumina, boron nitride, glassy carbon, or coated composite materials. Everything else is the same as in Specific Embodiments One to Four.

[0076] Specific implementation method six: Crystal growth method based on thermal convection mass transfer is as follows:

[0077] 1. Turn on the water bath heating devices outside the dissolution zone reactor 15, the high-temperature zone reactor 14, and the water bath cooling devices outside the growth zone reactor 13. The temperature inside the high-temperature zone reactor 14 is T. H The temperature inside the dissolution zone reactor 15 is T. D The temperature inside reactor 13 in the growth zone is T. G Establish the temperature field and gradient under the following conditions:

[0078] T H >T D >T G T D = T G + ΔT DG And ΔT DG The temperature range is 0.3 ~ 3.0 ℃; and T H = T D + ΔT HD And ΔT HD The temperature ranges from 1.0 to 3.0 ℃; the temperature T inside the reaction vessel in the dissolution zone is 15 ℃. D Temperature T inside reactor 13 in the growth zone G The axial temperature gradient between them is 0.5 ~ 5 ℃ / m, and the temperature field stabilization time is 12h ~ 72h with heat preservation.

[0079] 2. Add crystal raw materials and growth medium to the dissolution zone reactor 15, so that the crystal raw materials form a saturated solution in the dissolution zone reactor 15 and there is solid raw material remaining in the dissolution zone reactor 15. Suspend the seed crystal 3 at the lower end of the seed crystal suspension device 2 in the growth zone reactor 13. Do not add crystal raw materials to the high temperature zone reactor 14. Grow for 28 to 35 days without mechanical stirring. After the growth is completed, the temperature in the growth zone reactor 13 is controlled and the temperature reduction range is 0.01 to 5 ℃ / h to obtain single crystals.

[0080] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the growth medium described in step one is water, heavy water, aqueous haloacid solution, ionic liquid, or organic solvent. The selection principle is to have moderate solubility within the target temperature window and to allow the establishment of a steady-state temperature gradient and natural convection. Everything else is the same as Specific Implementation Method Six.

[0081] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Six or Seven in that the orientation of the seed crystal in step one is the specified crystal plane orientation of the material to be grown. Everything else is the same as in Specific Implementation Method Six or Seven.

[0082] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Six to Eight in that the crystal raw material includes halides, oxides, sulfides, selenides, or their doped systems. Everything else is the same as in Specific Implementation Methods Six to Eight.

[0083] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Six to Nine in that the crystal based on thermal convection mass transfer is used for nonlinear optics or scintillation detection. Everything else is the same as in Specific Implementation Methods Six to Nine.

[0084] The effects of the present invention were verified using the following embodiments:

[0085] Example 1:

[0086] The crystal growth method based on thermal convection mass transfer is as follows:

[0087] 1. Turn on the water bath heating devices outside the dissolution zone reactor 15, the high-temperature zone reactor 14, and the water bath cooling devices outside the growth zone reactor 13. The temperature inside the high-temperature zone reactor 14 is T. H The temperature inside the dissolution zone reactor 15 is T. D The temperature inside reactor 13 in the growth zone is T. G The conditions for establishing the temperature field and gradient are as follows:

[0088] Where T H >T D >T G T D = T G + ΔT DG And ΔT DGIt is 0.5 ℃; and T H = T D + ΔT HD And ΔT HD It is 1.0 ℃;

[0089] Temperature T inside the dissolution zone reactor 15 D Temperature T inside reactor 13 in the growth zone G The axial temperature gradient between them is 1℃ / m, and the temperature field stabilizes for 12h to 72h and is kept at that temperature to achieve steady-state cycling.

[0090] 2. Add crystal raw materials (containing CsI and HgI2 in an equivalent stoichiometric ratio to form a Cs2HgI4 phase, wherein CsI 50 mmol and HgI2 25 mmol, or CsI 12.9905 g and HgI2 11.3600 g) to the dissolution zone reactor 15 of the thermal convection mass transfer-based crystal growth apparatus. g) and the growth medium methanol (the loading and sealing can be carried out under dry chamber conditions to suppress external pollution), so that the crystal raw material forms a saturated solution in the dissolution zone reactor 15 and there is solid raw material remaining in the dissolution zone reactor 15. Cs2HgI4 seed crystal 3 is suspended at the lower end of the seed crystal suspension device 2 in the growth zone reactor 13, with the orientation of (020) crystal plane. No crystal raw material is added to the high temperature zone reactor 14. The crystal is grown for 30 days without mechanical stirring (mass supply is carried out by natural convection driven by temperature gradient: dissolution zone → high temperature zone (redissolution heat filtration) → nanofiltration membrane → growth zone). After the growth is completed, the temperature is controlled in the growth zone reactor 13, with a cooling range of 0.05 ℃ / h. The grown crystal is taken out to obtain (020) single crystal.

[0091] The crystal growth apparatus based on thermal convection mass transfer is a vertical reactor made of glass, with the following geometric parameters: total length L: 1500 mm, inner diameter D: 250 mm, liquid column height H: 0.8 L, and axial length L in the high-temperature zone. H 0.5 L

[0092] In this embodiment, the high-temperature zone is used as a "thermal filtration zone": the temperature of the high-temperature zone is higher than that of the dissolution zone and the growth zone, so that the microcrystals / clusters transported by convection are re-dissolved before entering the growth zone.

[0093] Nanofiltration membrane installation location: It is set between the high temperature zone and the growth zone, and is sealed to the inner wall of the vessel by the membrane frame 20 and the sealing ring 21 to ensure that the liquid phase in the cross zone must pass through the membrane.

[0094] Membrane type and range: Nanofiltration membrane with a pore size of 0.6 nm is available; the molecular weight cutoff (MWCO) of the filter bag is 200 ~ 1000 Da;

[0095] The nanofiltration membrane material is cellulose acetate, which further inhibits microcrystals / clusters from entering the growth zone by convection and dampens the flow across the zone to reduce interfacial disturbances.

[0096] The grown (020) crystal facets were progressively ground and polished before testing. To highlight the differences of this method in terms of crystal quality, impurity control, and defect suppression, a comparative experimental matrix was established using the same raw material batch and the same solvent system.

[0097] Comparative Example 1: Cooling Crystallization Method

[0098] Apparatus: Single-zone constant temperature bath;

[0099] Process: Prepare saturated solution → Cool down to produce supersaturation → Seed crystal growth;

[0100] Specific operation: Add crystal raw material (Cs2HgI4) and growth medium methanol to the growth reactor (13) (the loading and sealing can be carried out under dry conditions to suppress external pollution), and adjust the temperature of the reactor to T. G According to the solubility data, the crystal raw material or growth medium methanol is added to form a saturated solution of the crystal raw material in the growth reactor (13). A Cs2HgI4 seed crystal (3) is suspended at the lower end of the seed crystal suspension device (2) in the growth reactor (13), with the orientation of (020) crystal plane; the crystal is grown for 30 days without mechanical stirring at a cooling rate of 0.01 ℃ / h. After the growth is completed, the temperature is controlled and the cooling range is 0.05 ℃ / h to obtain (020) single crystal.

[0101] Key control parameters: cooling rate 0.01 ~ 0.05 ℃ / h; subcooling 0.1 ~ 0.3 ℃.

[0102] Comparative Example 2: Evaporation Crystallization Method:

[0103] Apparatus: Constant temperature autoclave evaporation;

[0104] Process: Supersaturation is achieved by controlling the solvent evaporation rate under constant temperature or slowly varying temperature conditions;

[0105] Specific procedures: Add the crystal raw material (Cs2HgI4) and the growth medium methanol to a standard open reactor (loading and sealing can be carried out under dry conditions to suppress external contamination), and place it in a reactor with a set temperature of T. G In the oven, methanol, the crystal raw material or growth medium, is added according to the solubility data to form a saturated solution in the crystal raw material reactor; Cs2HgI4 seed crystal (3) is suspended at the lower end of the seed crystal suspension device (2) in the reactor, with the orientation of (020) crystal plane; the temperature is kept constant at T. G (020) single crystals were obtained by volatilization and crystallization for 30 days without mechanical stirring.

[0106] Key control parameters: Evaporation rate is 3 ~ 5 mL / day.

[0107] Results and Discussion

[0108] The HRXRD rocking curve of the polished (020) surface of the single crystal grown using this patented method exhibits a symmetrical single peak, with FWHM = 0.033°. Figure 6 Characterization criteria: The half-width at half-maximum (FWHM) of the rocking curve can be used to determine crystal quality. A smaller FWHM usually corresponds to a lower defect density, as described in the HRXRD characterization literature.

[0109] The rocking curve of the crystal grown by cooling crystallization is FWHM=0.103° ( Figure 7 The half-width of the crystal (FWHM) is higher than that of the crystal grown by convective mass transfer using the method of this invention. The crystal has a smaller half-width and a lower defect density, indicating that the grown crystal is of good quality and has good crystallinity.

[0110] Crystals obtained through evaporation crystallization are prone to twinning, indicating that secondary nucleation was not well controlled and the growth rate was too fast. Figure 8 The average nanohardness of the (020) crystal facet of Cs₂HgI₄ is 6.205 GPa, and the average Vickers microhardness is 578.68 kg·mm². -2 The corresponding average Mohs hardness value is 5.62. Therefore, Cs2HgI4 crystal has a relatively moderate hardness, making it suitable for later crystal optics applications. Figure 9 ).

Claims

1. A crystal growth apparatus based on thermal convection mass transfer, characterized in that... The crystal growth apparatus based on thermal convection mass transfer is a vertical reactor, which includes a dissolution zone reactor (15), a high temperature zone reactor (14), and a growth zone reactor (13) from bottom to top in the vertical direction. The reaction vessel in the dissolution zone (15) and the reaction vessel in the high temperature zone (14) are equipped with water bath heating devices, and the reaction vessel in the growth zone (13) is equipped with a water bath cooling device. The upper end of the growth zone reactor (13) is provided with a thermometer socket (16) and a seed crystal suspension port (17). A thermometer (1) is inserted into the thermometer socket (16). A seed crystal suspension device (2) is provided in the seed crystal suspension port (17). A seed crystal (3) is suspended at the lower end of the seed crystal suspension device (2). The upper side of the growth zone reactor (13) is provided with a water outlet (4) of the growth zone reactor water bath heating device. The lower side of the growth zone reactor (13) is provided with a water inlet (5) of the growth zone reactor water bath heating device. A nanofiltration membrane structure (6) is provided between the high-temperature zone reactor (14) and the growth zone reactor (13). The nanofiltration membrane structure (6) includes a membrane support frame (18), a replaceable nanofiltration membrane (19), a membrane frame (20), and a sealing ring (21). The liquid phase exchange between the dissolution zone reactor (15) and the growth zone reactor (13) is carried out through a nanofiltration membrane (19). The high-temperature zone reactor (14) is provided with a water outlet (7) of the high-temperature zone reactor water bath heating device on the upper side and a water inlet (8) of the high-temperature zone reactor water bath heating device on the lower side. The upper side of the dissolution zone reactor (15) is provided with a water outlet (9) of the dissolution zone reactor water bath cooling device, the lower side of the dissolution zone reactor (15) is provided with a water inlet (10) of the dissolution zone reactor water bath cooling device, and the bottom of the dissolution zone reactor (15) is provided with a discharge port (11), and a switch (12) is provided on the discharge port (11). The crystal growth apparatus based on thermal convection mass transfer is a closed container or a controllable container.

2. The crystal growth apparatus based on thermal convection mass transfer according to claim 1, characterized in that... The total length L of the crystal growth device based on thermal convection mass transfer is 300 ~ 3000 mm, the inner diameter D is 50 ~ 500 mm, the liquid column height H is 0.5 ~ 0.9 L, and the axial length L of the high-temperature zone reactor (14) is... H The value is 0.2 ~ 0.7 L.

3. The crystal growth apparatus based on thermal convection mass transfer according to claim 1, characterized in that... The nanofiltration membrane is installed on the nanofiltration membrane structure (6) in the form of a flat plate, tubular or hollow fiber membrane module, and the nanofiltration membrane structure (6) is sealed to the inner wall of the container by a sealing ring or the inner wall of the vessel. The nanofiltration membrane is provided with at least one of the following: necking channels, slit channels, capillary channels, honeycomb channels, and septum channels; The nanofiltration membrane has a pore size of 0.6 to 10 nm and a molecular weight cutoff of 200 to 2000 Da.

4. The crystal growth apparatus based on thermal convection mass transfer according to claim 3, characterized in that... The nanofiltration membrane material is selected from at least one of aromatic polyamide composite membrane, cellulose acetate, polysulfone, polyvinyl alcohol, sulfonated polysulfone, and sulfonated polyethersulfone.

5. The crystal growth apparatus based on thermal convection mass transfer according to claim 1, characterized in that... The materials of the dissolution zone reactor (15), the high temperature zone reactor (14), and the growth zone reactor (13) are selected from at least one of quartz, glass, alumina, boron nitride, glassy carbon, or coated composite materials.

6. A crystal growth method based on thermal convection mass transfer, characterized in that... The crystal growth method based on thermal convection mass transfer is as follows: I. Turn on the water bath heating device outside the dissolution zone reactor (15), the high temperature zone reactor (14), and the water bath cooling device outside the growth zone reactor (13), and establish the temperature field and gradient under the conditions that the temperature in the high temperature zone reactor (14) is T H , the temperature in the dissolution zone reactor (15) is T D , and the temperature in the growth zone reactor (13) is T G . T H >T D >T G T D = T G + ΔT DG And ΔT DG The temperature range is 0.3~3.0 ℃; and T H = T D + ΔT HD And ΔT HD The temperature is 1.0 ~ 3.0 ℃; the temperature T inside the reaction vessel (15) in the dissolution zone is 1.0 ~ 3.0 ℃. D The temperature T inside the reactor (13) in the growth zone G The axial temperature gradient between them is 0.5 ~ 5 ℃ / m, the temperature field stabilization time is 12 h ~ 72 h and then maintained at that temperature; 2. Add crystal raw materials and growth medium to the dissolution zone reactor (15) so that the crystal raw materials form a saturated solution in the dissolution zone reactor (15) and there is solid raw material remaining in the dissolution zone reactor (15). Suspend the seed crystal (3) at the lower end of the seed crystal suspension device (2) in the growth zone reactor (13). Do not add crystal raw materials to the high temperature zone reactor (14). Grow for 28 to 35 days without mechanical stirring. After the growth is completed, the temperature in the growth zone reactor (13) is controlled and the temperature drop range is 0.01 to 5 ℃ / h to obtain a single crystal.

7. The crystal growth method based on thermal convection mass transfer according to claim 6, characterized in that... The growth medium described in step one is water, heavy water, aqueous solution of haloacid, ionic liquid, or organic solvent.

8. The crystal growth method based on thermal convection mass transfer according to claim 6, characterized in that... The orientation of the seed crystal in step one is the specified crystal plane orientation of the material to be grown.

9. The crystal growth method based on thermal convection mass transfer according to claim 6, characterized in that... The crystal raw materials include halides, oxides, sulfides, selenides, or their doping systems.

10. The application of the crystal based on thermal convection mass transfer as described in claim 6, characterized in that... The crystal based on thermal convection mass transfer is used for nonlinear optics or scintillation detection.

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