RU2262214C2 - High-temperature electric device for heating resistance - Google Patents

Abstract

FIELD: high-temperature heating devices.

SUBSTANCE: device is made of assembled lamellas made of rods of refractory metals and alloys, forming a heating chamber with opening in the bottom, and ends of lamellas, connected to current guides to be cooled down. Lamellas are made U-shaped, have same length and curved shape, current guides are made in form of two closed rings, ends of each lamella are held along perimeter circle of current guides along generatrix of cylindrical surface with forming of vertical and horizontal portions of heating chamber, and an opening in the bottom of chamber is formed by centering ring, around perimeter of which vertexes of closed portions of lamellas, converging to center, positioned in horizontal plane and forming the bottom of chamber, are held, while distance between lamellas equals distance between branches of lamellas. Construction of high-temperature electric heater is the reason for homogeneousness of heating field along vertical line and horizontal line and exclusion of negative effect of sign-alternating axial gradients of temperatures and magnetic field; decreases loss of costly materials due to growing of profiled mono-crystals and increases their quality, allows to replace broken down lamellas and increase durability of heating device as a whole.

EFFECT: higher efficiency, lower costs, higher durability, higher quality.

5 cl, 5 dwg

Description

The invention relates to the field of high-temperature heating equipment and can be used in installations for growing single crystals from melts with a convex shape of the crystallization front.

The technical problem solved by this invention is the creation of a high-temperature resistance electric heater for growing profiled single crystals and the creation of a thermal field with radial symmetry along the entire length of the heater, which leads to the growth of single crystals of a given shape that are defect-free and uniform in structure and purity.

Known high-temperature resistance heater used in vacuum and gas-filled electric furnaces, including heating elements - lamellas made of U-shaped rods of refractory metals and alloys. The vertical sections of the lamellas are mechanically bonded and located along the generatrix of the cylindrical surface with an equal gap from each other. They form the vertical walls of the heating chamber. The bottom of the chamber is formed by horizontal sections. The ends of the rods are connected by current leads (see US Pat. No. 3,155,758, class H 05 V 3/42).

This design of a high-temperature resistance heater cannot be effectively used in installations for growing single crystals from a melt, because the uniform arrangement of horizontal sections of lamellas along the entire bottom of the heating chamber gives a flat shape of the crystallization front, and when the crystal grows, the front changes to concave due to the released heat of crystallization. This reduces the yield of single crystals.

Known high-temperature resistance electric heater mainly for installations for growing single crystals from a melt (see AS USSR No. 674254 dated 05/05/77, class N 05 V 3/42, C 30 V 15/18), adopted as a prototype. The heater is made of prefabricated lamellas from U-shaped rods of refractory metals and alloys. The vertical sections of the lamellas are mechanically bonded and located along the generatrix of the cylindrical surface with an equal gap from each other. The vertical sections of the lamellas form a heating chamber with a bottom of horizontal sections. The vertical sections are connected to the current lead in the form of two half rings, one end of the lamellas is connected to the positively charged half ring of the current lead, the other end to the negatively charged half ring of the current lead.

To obtain an island-convex crystallization front, horizontal sections of U-shaped heating elements are located on the periphery of the bottom of the chamber, forming a hole in the center, the area of which is 10-50% of the bottom area.

To prevent deformation and displacement of the heating elements (lamellas) due to the heterogeneity of their heating and the presence of large magnetic fields during the operation of the heater, the lamellas are additionally fastened with a pair of external and internal half rings located on their vertical part at some distance from each other.

The disadvantages of this design are as follows.

1. Heating U-shaped elements have different lengths and configurations of horizontal parts of lamellas. Since the current goes along the shortest path, the temperature of the smallest along the horizontal part of the lamella will be higher. In addition, intersecting lamellas, shielding each other, locally increase the temperature in these places.

2. The horizontal parts of the lamellas, overlapping the bottom of the heating chamber, are uneven, i.e. there is no radial symmetry of the thermal field. The isotherm of the bottom of the chamber in this case is an oval. This negatively affects the stability of the shape of the crystallization front, and hence the structure of the grown crystal.

3. The fixing vertical parts of the half-ring lamellas, as an additional mass and an increased cross-section for the passage of current at the joints with the lamellas, reduce the temperature in these places, and the axial temperature gradient along the heater changes sign from (+) to (-) by the number of half rings. As a result, the diameter of the grown crystals varies in accordance with the passage of the crystallization front along the heater, which negatively affects the shape of the crystal and the homogeneity of the structural characteristics, and therefore the properties of products from these single crystals.

4. The fixing vertical parts of the lamellas of the half rings straighten themselves when heated and increase the gap between the extreme lamellas of the half rings. This leads to a distortion of radial isotherms along the entire length of the heater, which take the form of an oval rotated 90 ° relative to the oval in the lower part of the heater.

5. Studies have shown that in the presence of an island-convex crystallization front as a consequence of a large radial temperature gradient, the cooling of the grown crystal under these conditions leads to plastic deformation of the crystal (slip bands), and when completely cooled, to elastic stresses and cracks.

The technical result of the proposed invention is the creation of a heater that provides radial symmetry of the thermal field along the entire length of the heater with the ability to obtain controlled radial isotherms of round, square, rectangular, hexagonal shapes for growing shaped faceted single crystals.

The technical result is achieved by the fact that in a high-temperature resistance heater of a melt single crystal growth apparatus made in the form of prefabricated lamellas from rods of refractory metals and alloys forming a heating chamber with an opening in the bottom and ends of the lamellas connected to cooled current leads, according to the invention, the lamellas are made of U- shaped, have the same length and curved shape with the formation of vertical and horizontal sections of the heating chamber, the current leads are made in the form of of closed rings, the ends of each lamella are fixed around the circumference of the current leads with alternating signs of the current load, and the hole in the bottom of the chamber is formed by a centering ring, along the circumference of which the vertices of the closed, converging to the center parts of the lamellas located in the horizontal plane and forming the bottom of the chamber are fixed, and also that the distance between the lamellas is equal to the distance between the branches of the lamellas.

To create circular radial isotherms, the number of lamellas is a multiple of 12.

To create radial isotherms of rectangular or other polygonal shapes, lamellas are collected in sections whose length corresponds to the lengths of the sides specified by the shape of the polygon.

The area bounded by the centering ring is 6-90% of the bottom of the chamber.

Water-cooled ring current leads can be located coaxially or one below the other.

The design of a high temperature resistance heater is shown in FIG.

The heater includes U-shaped curved lamellas 1 with ends 2 fixed to ring water-cooled current leads 3-4 located coaxially, a centering ring 5, around the circumference of which the vertices 6 of the lamellas 1 are fixed, the current lead 3 has grooves 7 through which the lamellas 1 approach the ring water-cooled current lead 4. The arrows and signs (+), (-) indicate the direction of electric current pressure along the lamella and the heater as a whole.

Figure 2 (a, b, c) shows heaters in which the lamellas are assembled in a section for creating radial isotherms of polygonal shapes (square, rectangle and hexagon) for growing single crystals of the corresponding profile.

The essence of the invention lies in the fact that the curved U-shape of the lamellas and the fixation of the lamellas at only two points (the ends of the lamellas in the current leads, and the vertices on the ring) form a heating chamber with a uniformly distributed current density along the entire length of the lamellas, as along the vertical wall of the chamber, and along the horizontal (bottom) part.

This ensures the constancy of the shape of the radial isotherms along the entire length of the grown single crystal.

In addition, connecting the ends of the lamellas with alternating signs (+) and (-) around the circumference of water-cooled ring current leads eliminates the occurrence of a magnetic field in the melt and its negative effect on the temperature gradient in the melt.

To create profiled isotherms when growing single crystals with cubic and hexagonal lattices with natural faceting, the total number of lamellas in the heater is a multiple of the number of faces of a single crystal and a multiple of 12. When growing crystals of polygonal farms, lamellas are collected in sections whose length corresponds to the lengths of the sides of the grown polygon profile. To change the profile of the grown single crystal, the number of lamellas in the sections is changed.

A multiple of 12, the number of lamellas in the heater is determined by the composition of the number 12 - 2, 3, 4, 6. The numbers 2, 3, 4, 6 determine the shape of the oriented grown single crystals of cubic and hexagonal lattices.

So, for example, the number 2 corresponds to a ribbon grown in the [1120] direction with the orientation of the {1010} and {0001} faces of the hexagonal lattice.

The number 3 or 6 - corresponds to triangular or hexagonal single crystals grown in the [111] direction with the orientation of the {110} planes of the cubic lattice or in the [001] direction with the orientation of the {1010} faces of the hexagonal lattice.

The number 4 - corresponds to a quadrangular single crystal grown in the [100] direction with the {111} faces of the cubic lattice or in the [1120] direction with the {1010} and {0001} faces of the hexagonal lattice, etc.

The diameter of the bottom of the chamber is related to the magnitude of the axial temperature gradients. The diameter in the claimed range of values determines, as a rule, the method of growing single crystals.

So, for example, the minimum diameter is used when growing single crystals according to the Czochralski and Kyropoulos method, and the maximum - according to the Bridgman-Stockbarger method.

The principle of operation of the heater is as follows.

Electric current from the inner ring water-cooled current lead 3 enters directly to the ends 2 of the slats 1, passes through the U-shaped part and returns through the grooves 7 of the internal current lead 3 to the water-cooled ring current lead 4. The lamellas 1 form a circle with a zero magnetic field inside and a uniform alternating load the circumference of the heating chamber and its bottom.

The design allows to obtain the following positive effect.

1. A significant increase in the quality of single crystals by ensuring the uniformity of the thermal field vertically and horizontally and eliminating the negative effects of alternating axial temperature gradients and magnetic fields.

2. Reducing the consumption of expensive materials due to the cultivation of profiled single crystals, which also leads to an increase in the quality of products from them.

3. The possibility of replacing defective heater elements (lamellas), which generally significantly prolongs the period of use of the heater.

4. Ergonomic design, providing the ability to change technological tasks for the cultivation of multi-profiled single crystals.

Claims (5)

1. High-temperature resistance heater for the installation of growing single crystals from the melt, made in the form of prefabricated lamellas from rods of refractory metals and alloys forming a heating chamber with a hole in the bottom, and the ends of the lamellas connected to current leads, characterized in that the lamellas are made U-shaped, have the same length and curved shape with the formation of vertical and horizontal sections of the heating chamber, the current leads are made in the form of two closed rings, the ends of each lamella are fixed along the circumference of the current leads with alternating signs of the current load, and the hole in the bottom of the chamber is formed by a centering ring, around the circumference of which are fixed the vertices of the closed converging to the center parts of the lamellas located in the horizontal plane and forming the bottom of the heating chamber. 2. The high-temperature resistance heater according to claim 1, characterized in that the distance between the lamellas is equal to the distance between the branches of the lamellas. 3. High-temperature resistance heater according to any one of claims 1 and 2, characterized in that for creating circular isotherms the number of lamellas is a multiple of 12. 4. The high-temperature resistance heater according to any one of claims 1 to 3, characterized in that to create radial isotherms of rectangular or other polygonal shapes, the lamellas are assembled in sections whose length corresponds to the lengths of the sides specified by the shape of the polygon. 5. A high temperature resistance heater according to any one of claims 1 to 3, characterized in that the area bounded by the centering ring is 6-90% of the bottom area of the chamber.

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