RU2643980C1 - Thermal node of installation for halogen crystals growing by horizontal unidirectional crystallization method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the field of technology, related to growing crystals from melts by horizontal unidirectional solidification (HUS), which are widely used as scintillators for ionizing radiation detectors, laser crystals and optical elements, working in a wide range of wavelengths from ultraviolet to infrared wavelengths. A thermal node of an installation for halogen crystals growing by horizontal unidirectional crystallization method is proposed, consisting of a housing inside which central and separate carbon-graphite heat-insulating modules are housed, a graphite container 9 with a set of thermal shields and a frame mounted movably horizontally within the heat insulating modules, a L-shaped upper heater 2 and a U-shaped lower heater 3 located inside the central heat-insulating module, a viewing window 8. The central heat-insulating module is made collapsible and consists of an external graphite heat-insulating casing 4, inside which diaphragms 7, upper 5 and lower 6 sections of internal graphite thermal shields are located, and individual carbon-graphite heat-insulating modules are made in the form of an internal graphite casing surrounded by external collapsible graphite heat insulating cassettes, each consisting of stacked thermal shields, with spacers laid in-between.

EFFECT: increased technological design of the thermal node, which allows to vary the magnitude of the temperature gradient in the crystal active growth zone, resulting in an optically homogeneous crystal.

5 cl, 8 dwg

Description

Technical field

The invention relates to the field of technology related to the growth of crystals from melts by the method of horizontal directional crystallization (SOC), which are widely used as scintillators for ionizing radiation detectors, laser crystals, and elements of optical devices operating in a wide spectral region from ultraviolet to mid-infrared range of lengths waves.

State of the art

Halide crystals are a group of minerals that are compounds of halogens with other chemical elements or radicals. These include fluoride, chloride and very rare bromide and iodide compounds. To grow mineral crystals, natural conditions are simulated artificially in special devices.

A known installation for growing crystals (RF patent for utility model No. 120658). In the installation comprising a housing, a heat-insulating casing, a heater and a device for vertical movement of the crucible, inside which melt crystallizes, the heat-insulating casing is made in the form of a series of sections. Each of the sections is formed by several telescopically located heat-insulating screens, between which there is a gap. Sections are vertically divided by horizontal partitions, the number of heat-insulating screens in sections and in each section may be different. The lower section is located under the heater and has vertically several rows of heat-insulating screens, and the number of screens in rows is different. In this case, the heat-insulating screens of all sections can be made in the form of telescopically mating cylinders, between which there are annular gaps filled with a gaseous medium. The number of heat-insulating screens in each of the sections can be in the range from 1 to 10, and the screens themselves can be made of graphite.

This installation works by the method of vertical directional crystallization (Bridgman method). Among the shortcomings, it is necessary to single out the impossibility (during high-temperature crystallization) to observe the position of the growth front and, accordingly, influence it. Another disadvantage is the problems associated with the mechanical effect of the walls of the crucible on a single crystal. There is also a purely technical problem associated with the extraction of a single crystal from a crucible.

The processes that occur during crystal growth during movement of the crucible with the working substance, a change in the thermophysical properties of the working substance during the transition from a liquid to a solid state, the release of latent heat of crystallization, etc. lead to changes in the temperature field in the working volume. Changes in the temperature field cause deviations of the axial crystal growth rate from the nominal crucible travel speed, which can negatively affect the perfection of the growing crystal. In addition, convective flows arising influence the crystal growth quality. The flows in the melt can both improve and worsen the uniformity of the distribution of impurities in the grown crystal.

Another of the disadvantages of the device is that the structural design of the installation is aimed at obtaining a low-gradient temperature region in the cooling zone of the crystals. But it is quite ineffective. In addition, the installation is very difficult.

The closest in technical essence to the claimed is a device for producing single crystals of refractory fluorides (RF patent No. 2608891), operating by the SOC method, containing a vacuum chamber with a thermal unit located in it, consisting of carbon-graphite heat-insulating modules, upper and lower heaters and heat shields, a graphite container with a mixture of crystallizable material installed with the possibility of moving in a vacuum chamber, inert gas supply fittings and a vacuum and / or gas pumping system of different products, a viewing window, while the upper flat ribbon heater of the L-shaped form and the lower ribbon heater of the U-shaped inverted shape are made in the form of monoblock graphite monoblocks that are single with the tires and are unilaterally fixed to the water-cooled current leads of the vacuum chamber using a detachable connection.

However, in the description of the device there is no detailed detailing of the elements forming the thermal unit, which, in turn, forms a thermal field in the growth and annealing zones of the grown crystals.

As a rule, it is the design of the elements of the thermal unit, their mutual arrangement that determine the symmetry of the thermal field at the front of the crystal growth and the optimal temperature in the annealing zone, which avoids the occurrence of crystalline deformations at the stage of post-growth cooling of the grown crystal. These factors play a fundamental role in obtaining crystals of high optical quality in terms of minimizing the occurrence of dislocations, blocks, and cracks in the growing crystal.

Disclosure of the invention

The technical result of the invention is to improve the manufacturability of the design of the thermal unit, allowing you to vary the temperature gradient in the zone of active crystal growth, leading to the production of an optically homogeneous crystal.

To achieve this result, a thermal unit of a plant for growing halide crystals by horizontal directional crystallization is proposed, consisting of a housing inside which a central and separate carbon-graphite heat-insulating modules are placed, a graphite container with a set of heat shields and a frame installed with the possibility of horizontal movement inside the heat-insulating modules, the upper L-shaped heater and lower inverted U-shaped heater located inside the c a central heat-insulating module, a viewing window, while the central heat-insulating module is collapsible and consists of an external graphite heat-insulating casing, inside of which there are diaphragms, the upper and lower sections of the internal graphite heat shields, and individual carbon-graphite heat-insulating modules are made in the form of an internal graphite casing, surrounded by external collapsible graphite heat-insulating cassettes, each of which consists of heat stacked on top of each other screens between which spacers are laid.

Besides:

- the number of individual carbon-graphite thermal insulation modules is 4 pcs .;

- external collapsible graphite heat-insulating cassettes of each individual carbon-graphite heat-insulating module include heat shields in an amount of 2 to 5 pieces and a thickness of 8 to 20 mm from graphite grade MPG-6, or MPG-7, or MPG-8, or GS- 1900 and graphite spacers of SIGRABOND Standard or UKKM-2 brand, forming gaps between thermal screens from 2 to 5 mm;

- the diaphragms are made of graphite of the GS-1900 or SIGRABOND Standard brand, and the heat shields of the upper and lower sections of the inner graphite heat shields of the central heat-insulating module are made of graphite of the grades: MPG-6 or MPG-7, MPG-8 or of solid felt grades: Sigratherm , or SGL, or TUV;

- the number of diaphragms and heat shields in the upper and lower sections of the inner graphite heat shields of the central heat-insulating module is 1-4 pcs.

Brief Description of the Drawings

The invention is illustrated by diagrams and images shown in figures 1-8.

In FIG. 1 shows a general view of a thermal unit made, for example, of four separate and one central carbon-graphite thermal insulation modules where:

I, II, III, IV - individual carbon-graphite heat-insulating modules;

V - central thermal insulation module;

1 - water-cooled steel casing.

In FIG. 2 and FIG. 3 shows a central thermal insulation module (V), where:

2 - upper heater of the L-shaped form;

3 - lower heater inverted U-shaped;

4 - external graphite heat-insulating casing;

5 - the upper section of the internal graphite thermal screens;

6 - the lower section of the internal graphite thermal screens;

7 - aperture;

8 - viewing window;

9 - graphite container with a set of thermal screens and a frame;

10 - horizontal movement mechanism.

In FIG. 4 shows a design diagram of carbon-graphite thermal insulation modules (I, II, III, IV), where:

11 - inner graphite casing;

12 - external collapsible graphite insulating cassettes;

13 - thermal screens;

14 - spacers.

In FIG. 5 shows a graph of thermal conductivity through the multilayer wall of one of the carbon-graphite heat-insulating modules (I, II, III, IV) in section AA, where:

15 - wall of the inner graphite casing 11;

16 - wall of the steel casing 1.

In FIG. Figure 6 shows the distribution of temperature fields (A-D) and gradients along the axial line from the melting zone of the crystal to the cooling zone, where:

A - temperature field in the center of the heaters (2, 3) for the implementation of the melting of the material, subsequent exposure of the melt for homogenization and fluorination;

B - a growth zone with the possibility of setting an axial temperature gradient over a wide range from 8 ° / cm to 80 ° / cm in the region of the crystallization front;

C is the average gradient thermal field (20-30 ° / m) at the stage of cooling onset;

D — low-gradient thermal field (3-5 ° / m) at the stage of annealing the grown crystal;

P is a melt of a halide crystal;

IFC - isotherm of the crystallization front.

In FIG. 7 shows thermal volumes, where:

VI - internal heat-insulating volume;

VII - external heat-insulating volume;

VIII - total heat-insulating volume.

In FIG. 8 shows a photograph of a plant for growing halide crystals by the method of horizontal directional crystallization with an attached thermal unit of the proposed design.

The implementation of the invention

The design of the heating unit consists of a central heat-insulating module V, four separate carbon-graphite heat-insulating modules I, II, III, IV, a graphite container with a set of heat shields and a frame 9, a horizontal movement mechanism 10 and a water-cooled steel case 1.

Each individual heat-insulating module I, II, III, IV (Fig. 4) includes a collapsible inner graphite casing 11 made of graphite plates, for example, 20 mm thick, which is surrounded by four plug-in collapsible graphite heat-insulating cassettes from below, from above and from the sides. 12. Collapsible graphite heat-insulating cassettes 12 consist of removable, one above the other heat shields 13, between which there are spacers 14, forming gaps up to 5 mm. The number of heat shields 13 in each collapsible cartridge 12 can vary and be in an amount of 2 to 5 pieces and a thickness of 8 to 20 mm.

The central heat-insulating module V (Fig. 2, 3) consists of an external graphite heat-insulating casing 4 made of graphite plates with a thickness in the range from 12 mm to 30 mm. Inside the casing 4, one above the other, the upper 5 and lower 6 sections of removable internal graphite thermal screens are located, between which there are gaps up to 5 mm. Screens can be made both from extruded grades of graphite MPG-6, or MPG-7, or MPG-8, and from solid felts of the Sigratherm, or SGL, or TUV type, depending on the need to create the necessary heat saving and symmetry of thermal fields in separate thermal insulation modules .

The lower section of the inner graphite heat-insulating shields 6 is located under the lower heater of an inverted U-shaped 3 and has a vertical to four horizontal heat shields. The upper section of the inner graphite heat-insulating shields 5 is located above the upper heater of the L-shaped form 2 and has a vertical to four horizontal heat shields. The number of thermal screens in the lower 6 and upper 5 sections of the module can vary depending on the brand of the resulting crystal. For example, to grow a Li (YLu) F4 crystal, it is necessary to install 4 MPG-6 graphite heat shields in each section.

The upper heater of the L-shaped form 2 and the lower heater of the inverted U-shaped form 3, made in the form of one-piece monoblock parts made of very clean (up to 5 ppm) isostatic graphite Ringsdorff R4550 from the German company SGL Carbon.

To observe the process of growing a halide crystal, a viewing window 8 is intended.

In the process of crystal growth, the material of both the central V and individual heat-insulating modules I, II, III, IV is exposed to high temperatures up to 1500-1700 ° C in some cases and more, as a result of which the material undergoes thermal expansion. For example, for graphite grade MPG-6, the coefficient of thermal expansion at T 1650 K = 8.04 × 10 ^-6 K ^-1 , as a result of which a plate with a length of 700 mm will have an expansion of about 9.2 mm (ΔL = αLΔT). Given this, the elements of the joints of the thermal insulation modules I, II, III, IV, V are made without the use of hard fasteners (bolts, screws, etc.). The module connections are made according to the tenon-groove principle, and the zones of thermal expansion compensation in them are sealed with soft carbon graphite felt (for example, МУВ-5 made of PAN fiber).

A graphite container with a set of heat shields and a frame 9 is made of dense (up to 1.9 g / cm ³ ) isostatic graphite in the form of a boat. It moves between the upper and lower sections of the heaters 2 and 3 using the horizontal movement mechanism 10 on graphite rollers mounted in the upper panel of the lower section of each of the individual carbon-graphite heat-insulating modules I, II, III, IV.

The central V and individual carbon-graphite thermal insulation modules I, II, III, IV are made according to the principle of two isolated volumes. The internal heat-insulating volume VI is the casing 4, and the external heat-insulating volume VII is collapsible graphite heat-insulating cassettes 12, which are made on the principle of “sandwich panels” (see Fig. 7), while the material of the heat shields 13 and spacers 14 has a different coefficient of thermal conductivity . For example, heat shields 13 can be made of graphite grades MPG-6, or MPG-7, or MPG-8, or GS-1900, and spacers 14 can be made of graphite grades SIGRABOND Standard or UKKM-2. The heterogeneity and thermophysical properties of these materials will allow for minimal heat transfer from the heated carbon-graphite heat-insulating module I, II, III, IV to the wall of the water-cooled steel casing 1, the dependence of which on the example of the standard arrangement of heat shields 13 from MPG-6 graphite in cassette 12 (4 pcs.) is presented in FIG. 5.

All four separate carbon-graphite heat-insulating modules I, II, III, IV are structurally tightly interconnected, forming a single integral design of the heat unit, and the number of removable heat shields 13 in the cartridges 12 of each module can be different. The design of carbon-graphite heat-insulating modules I, II, III, IV provides for a minimum contact of their graphite parts and a steel cooling case 1, which allows to achieve a minimum heat transfer effect on the case 1.

Water-cooled steel casing 1 performs the function of isolating the central V and individual carbon-graphite heat-insulating modules I, II, III, IV from the external atmosphere. In FIG. 1 it is depicted as an external steel single-section shell, inside of which the refrigerant circulates.

The dimensions of the casing 4, the upper 5 and lower 6 sections of the heat shields 13 and the diaphragms 7, as well as the number of heat shields 13 in each of the sections of the collapsible cartridge 12 and the diaphragms 7 are a determining factor for creating a temperature gradient inside the thermal unit.

The sizes of all elements of the thermal unit and their quantity are determined by the requirements for creating an optimal installation in terms of dimensions and optimal parameters for the crystallization process of a particular crystal.

The influence of the design of individual carbon-graphite thermal insulation modules I, II, III, IV on the operation of the installation for growing halide crystals is illustrated in FIG. 6, which shows the creation of a temperature gradient with the standard number and location of the heat shields 13 (4 pcs.) And diaphragms 7 (4 pcs.) Of the experimental setup and the temperature distribution along the thermal zones of the axial line, creating:

A - temperature field in the center of the heaters (2,3) for the implementation of the melting of the material, subsequent exposure of the melt for homogenization and fluorination;

B — a growth zone with the possibility of setting an axial temperature gradient over a wide range from 8 ° / cm to 80 ° / cm in the region of the crystallization front;

C is the average gradient thermal field (20-30 ° / cm) at the stage of the onset of cooling;

D — low-gradient thermal field (3-5 ° / m) at the stage of annealing the grown crystal;

By changing the number (from 2 to 5 pcs.) Of thermal screens 13 and replacing the material from which they can be made (graphite grade MPG-6, or MPG-7, or MPG-8, or GS-1900), and also by varying the material (graphite grade GS-1900) and the number of diaphragms 7 (up to 4 pcs.) forming the isotherm of the crystallization front, it is possible to vary the values of temperature gradients in the growth and cooling zones in the desired ranges when growing specific halide crystals.

The design of the heating unit is energy-saving and allows to obtain temperatures up to 2400 ° C on heaters 5 and 6 at low energy consumption up to 15 kW each, with a direct current up to 600 A and voltage up to 25 V.

The growth of fluoride and other halide crystals is realized by the method of horizontally directed crystallization, which is as follows. In a graphite container with a set of heat shields and a frame 9, a charge or a crystalline battle is loaded (the charge in Fig. 1 is not shown), and then it is melted by moving the container 9 by the movement mechanism 10 through the heating zone formed by the upper 2 and lower 3 heaters. As a result, the material crystallizes.

In order to obtain a strictly oriented crystal, a seed is installed in the container 9 and visually observes both the moment of seeding and the shape of the crystallization front in the process of growing a single crystal through a viewing window 8.

The open surface of the melt allows an activating impurity to be introduced into the melt at any stage of crystal growth. This method also allows multiple recrystallization of the substance. In addition, it is possible to grow crystals of various geometric shapes and to carry out a continuous process of growing crystals by directionally moving a series of containers 9 through the crystallization zone. When implementing this method, a low-gradient temperature field is created, which ensures the growth of unstressed crystals of such large sizes that it is almost impossible to obtain using other methods.

In FIG. 8 shows a plant for growing halide crystals by the method of SOC with a thermal node of the proposed design. For example, the thermal assembly of an installation for growing halide crystals by the SOC method when using separate carbon-graphite thermal insulation modules I, II, III, IV with heat shields 13 made of Sigratherm graphite, UKKM-2 spacers, GS-1900 diaphragms in an amount of 4 pcs ., thermal screens of the MPG-6 brand in the lower 6 and upper 5 sections of the central heat-insulating module V in the amount of 4 pcs. in each section under conditions of an average gradient field (up to 100 / cm) at the growth front, it is possible to grow a Li (YLu) F4 crystal 50 × 80 × 20 mm in size.

The design embodiment of the thermal unit described in the description does not cover all variants of its execution and depends on the characteristics of the grown crystals.

Thus, the proposed design of the thermal unit of the installation for growing halide crystals not only provides the opportunity to avoid disadvantages in the process of crystal growth, but also increases the optical quality and size of the grown crystals, leads to a significant reduction in energy consumption, which is an important factor in the mass production of crystals.

Claims (5)

1. The thermal assembly of a plant for growing halide crystals by horizontal directional crystallization, consisting of a housing, inside which there is a central and separate carbon-graphite heat-insulating modules, a graphite container with a set of heat shields and a frame installed with the possibility of horizontal movement inside the heat-insulating modules, the upper heater Г- shaped and lower heater of an inverted U-shaped, located inside the central heat-insulating module, with a motor window, characterized in that the central heat-insulating module is collapsible and consists of an external graphite heat-insulating casing, inside of which there are diaphragms, upper and lower sections of the internal graphite heat shields, and individual carbon-graphite heat-insulating modules are made in the form of an internal graphite casing surrounded by external collapsible graphite heat-insulating cassettes, each of which consists of thermal screens stacked on top of each other, between which rolozheny spacers. 2. Thermal unit according to claim 1, characterized in that the number of individual carbon-graphite heat-insulating modules is 4 pcs. 3. The heat assembly according to claim 1, characterized in that the external collapsible graphite heat-insulating cassettes of each individual carbon-graphite heat-insulating module include heat shields in an amount of 2 to 5 pieces and a thickness of 8 to 20 mm made of MPG-6 graphite, or MPG-7, or MPG-8, or GS-1900 and graphite spacers of the SIGRABOND Standard or UKKM-2 brand, forming gaps between thermal screens from 2 to 5 mm. 4. The heat assembly according to claim 1, characterized in that the diaphragms are made of graphite of the GS-1900 or SIGRABOND Standard brand, and the heat shields of the upper and lower sections of the inner graphite heat shields of the central heat-insulating module are made of graphite of the grades: MPG-6 or MPG- 7, MPG-8 or from solid felt brands: Sigratherm, or SGL, or TUV. 5. The heat assembly according to claim 4, characterized in that the number of diaphragms and heat shields in the upper and lower sections of the inner graphite heat shields of the central heat insulation module is 1-4 pcs.

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