RU1820925C - Method for growing crystals by verneuil method and plant for its realization - Google Patents

Abstract

The invention relates to the growth of single crystals of refractory compounds used in laser technology, microelectronics, optics, medicine, precision instrumentation. A method of growing crystals includes feeding a charge into a chamber. The invention relates to the growth of single crystals of refractory compounds according to the Verneil method. for example, such as ruby, corundum with titanium, leucosapphire, rutile, strontium titanate, ferrites, and a number of others used in laser technology, microelectronics, optics, medicine, and precision instrument engineering. The purpose of the invention is to increase the size of the grown crystals with high optical uniformity. crystallization through a multi-channel burner with the simultaneous supply of oxygen and hydrogen flows through its channels, melting the charge and crystal growth. While the outer wall of the crystallization chamber is heated by additional flows of oxygen and hydrogen, which are fed from above through the channels of the additional burner. The mode parameters of the method are given. An apparatus for carrying out the method comprises a crystallization chamber in the form of two insulated coaxial muffles. A crystal holder is located in the inner muffle. Above it, the main and additional burners are coaxially placed. Moreover, an additional burner is connected to the outer muffle. The device is equipped with an automatic system for maintaining the crystallization front and crystal diameter. For feeding the charge, the device comprises a hopper and a dispenser associated with an automatic system. Relations are given for sizing muffles. 2 si.i. 4 cg f-ly, 3 ill. In FIG. 1 shows a diagram of a device; figure 2 - crystallization chamber; Fig. 3 is a graph of the temperature distribution on the inner wall of the inner muffle. A device for growing crystals contains a crystallization chamber made in the form of two isolated coaxial muffles 1 and 2. In the cavity of the crystallization chamber, a crystal holder 3 is mounted with the possibility of rotation and vertical movement. Above it, there is a main multi-channel Ј 00 ю 00 N SL OJ

Description

burner 4 and an additional burner 5 installed coaxially with it. In this case, the additional burner 5 is connected to the external muffle 2. The muffles 1 and 2 are surrounded by a plain lining b and metal sheathing 7, in which the window 8 is made. The charge to the grown crystal is fed from the hopper 9 through a dispenser 10 which ensures uniform and automatic or manual feed of the charge with an accuracy of at least 2%. The inner muffle consists of three sections: the upper - the flame section, the middle - the crystallization section and the lower - the cooling section. The outer muffle consists of two sections: the upper - the torch section and the lower - cooling section. The system for automatically maintaining the crystallization front and the diameter of the crystal includes a radiation source 11, a diametrical X-ray converter 12, a transmitting camera 13, an operator panel 14, consisting of a television monitor 15 and a block for highlighting and indicating a line, setting a line number 16, a measurement subsystem the diameter of the crystal 17, consisting of a comparator TV signal 18, a generator of counting pulses 19, a counter 20, a device 21 for comparing the current value of the diameter of the crystal with a given value, the programmer 22 d ametra crystal, crystallization timer 23, flow control subsystem of subsystem control charge and the gas flow rates.

The device operates as follows.

After the heating system is turned on, a crystal holder 3 with a seed crystal is introduced into the crystallization chamber. The latter in the area of the crystallization front is melted by increasing the oxygen consumption. From the hopper 9, crystallized material in the form of a fine powder-mixture is fed into the dispenser 10, and then the mixture is transported by a continuous stream in a quantity regulated by the technology using gas, for example oxygen, through the central channel of the main burner 4 and sent to the flame of the main burner 4. In the upper of the torch section of the inner muffle 1, the charge is melted and directed by a gas stream to the top of the previously fused seed crystal.

. As a result of matching the charge flow rate, the heat density of the burner flame and the speed of lowering the crystal holder 3 with the seed and grown 24 crystals from the crystallization section to the lower temperature cooling section, the crystal is grown.

The expansion of the crystal 24 to the desired diameter is carried out by increasing

the flow of gases and the mixture, in some cases, additionally, by changing the lowering speed of the crystal holder 3 in manual mode.

System of automatic support of crystallization front and diameter

a growing crystal is included in the work

immediately before setting the herbal crystal and turning on the feed

1 charge, and turns off after reaching 3 of a given crystal length.

A system for automatically maintaining the crystallization front and the diameter of the growing crystal operates as follows.

0 When the X-ray source 11 is turned on as a result of transmission through the crystallization chamber, the image of the growing crystal 2 is projected onto the X-ray optical converter 12, read out by the transmitting television camera 13, and transmitted to the operator console 14 as a signal.

The operator at the TV signal processing unit sets the line number on which the crystallization front should be located during the growth process, while checking the correct selection on the monitor screen (the specified line is highlighted

5 on the monitor screen).

In the case of a change in the vertical crystallization front position relative to the selected one, the line number of the television image changes (when scanning

0 from top to bottom), on which the image of the growing crystal appears, and as a result of comparing the actual position of the crystallization front with the one set in the automatic operation mode of the system,

5, the signal is in block 10 and is supplied to the charge control subsystem 25 for correction in the direction of increasing or decreasing charge supply; Correction of the charge consumption for an increase in the case of a slowdown in the growth of the crystal (a tendency to position the image of the growing crystal below the selected row) and a decrease in feed in the case of an acceleration of growth (a tendency to position the image above the selected

5 lines).

The diameter of the growing crystal is measured on the line selected by the operator, located a predetermined number of lines below the line on which the crystallization front is located (the selected line is highlighted on the monitor screen when there is an image of the crystal or its simulator). To cut off the image of the walls - crystallization cameras, discriminators that highlight the useful part of the television image (set by the operator and highlighted on the monitor screen).

The diameter of the growing crystal is stabilized by controlling gas flow rates as follows.

Using the amplitude comparator 18, a signal from the crystal is extracted from the line on which the diameter of the growing crystal is measured. For the duration of this signal, the operation of the counter 20 is allowed, which reads stable counting pulses generated by the generator 19. Since the grown crystal may have a shape different from the cylindrical one due to different growth rates in different crystallographic directions (for example, when growing corundum crystals along the optical axis or perpendicular to the optical axis, or when growing strontium titanium crystals along one of the crystallographic planes), during the revolution of the crystal around its B (when the signal from the rotation sensor) is allocated the maximum value of the counter 20 (actual shape and dimensions of the crystal are visible on the screen).

This value, which is proportional to the maximum crystal diameter, is compared with the value set by the device for comparing the current value of the crystal diameter with a given 21 (generated as a function of time in the crystal diameter programmer 22).

The result of the comparison is fed to the input of the gas flow control subsystem 26. (using this subsystem, the gas flow (the amount of heat generated by the torch of the main or additional burner is corrected to exclude even small deviations of the crystal diameter from the set value that can occur as a result of changes in thermal forces growth in the working volume of the crystallization chamber, as well as during the transition from one material to another during one crystallization cycle when growing a multilayer crystal.

So. in the experiment it was found that when growing a complex crystal, for example, leucosapphire-ruby-leucosapphire, with a constant diameter when switching from one material to another, oxygen consumption, according to the automatic

regulation of gas flow, varies by 4-6% of the total flow, oxygen of the central burner and, accordingly, the larger the percentage of flow measurement is taken - 5 the larger the diameter of the grown crystal.

The process of growing crystals of increased optical uniformity with a diameter of from 10 to 100 mm using

0 newly developed heating systems and the location of the crystallization front are effectively implemented provided that they work in accordance with the following requirements:

5 Heating system.

For the main burner, the flow rate of oxygen (O2) through the internal channels is 0.3-2.5 m / s, and in each subsequent stream 1.1 to 3.4 times greater. The ratio of the rates of outflow of oxygen (Oa) and hydrogen (H) in the first stream is 0.1 - 0.85, and in the subsequent stream 0.21 - 1.2 with a flow ratio Oa / H2 in the first stream 1.8-2.75, length fronts of burning should not

5 vary by more than 15%. In this case, the design of the channels for the outflow of gas from the burner should ensure a difference in the perimeters of the initial contact of the reacting gases of each external and internal fronts

0 burning no more than 27%. Fulfillment of these conditions ensures that the torch is obtained with an effective size, where the torch diameter (m) is not less than 0.7 times the diameter of the crystal, and its length (mm) is 0.6 - 1.2 times

5 from the end of the burner to the location of the crystallization front.

For an additional burner, the flow rate of O2 (m / s) is 0.7-6.3, the ratio of the flow rates of 02 and H2 is 0.5 0 4.5, the optimal flame length (mm) is

1.1 - 2.0 distance between the end of the burner,

and the location of the crystallization front.

Plum and burning products of the main and

additional burners are not mixed;

5 For crystallization chamber:

- the diameter of the crystal holder D is equal to the diameter of the crystal Okr; the wall thickness of the muffles of the inner and outer doors is 5 n for da - (5 - 10), and for 60 - (10 0 15); the internal diameters of the muffles of the internal OVV and the external DHB at the place of their connection with the burners is determined by the design of the heating system, provided that the gas channels of both

5 burners should not be closer to the muffle ceramics closer than 2 mm.

The size of the inner muffle corresponds to the aspect ratio, provided that the inner diameter of the DCK crystallization section is D + (4 - 10) mm, and the height of this section HB2 is (1 - 2) 0, the height of the flame section HB1 is (0.75 - 5 , 4) D, the height of the cooling section НВз (5 - 20) 0, the lower diameter of the flame section and the upper diameter of the cooling section of these conical sections from the inside are equal to the diameter of the crystallization section Os.k, and the lower diameter of the cooling section is formed as a result of angle a equal to 0.5 - 1.5 ° at the apex of the cone starting at the junction with the cr lengths and lengths of the laying section ..

The size of the outer muffle corresponds to the aspect ratio provided that the inner diameter DI of the cooling and flare sections at their junction is DC.K + 2 5V (3 - 32) the length of the flare section HH1 is (0.75 - (6.3) 0 , and the total length of the muffles of the external heating chamber Hi is HB- (1 - 7) 0.

- Layer-by-layer distribution of the lining materials is carried out so that the inner boundary of each layer is within the temperature limit of use of the material with a 10% margin.

As the experiment showed, the use of lining, for example corundum, foam corundum, foam weight, ultralight weight and asbestos board in series, provides the opportunity to optimize heat transfer from the inner wall of the muffle to the outer wall of the casing and to produce the casing of the optimal size, the ability to quickly, accurately process, design and long the term of its operation.

It has been experimentally confirmed that the system for automatically maintaining the crystallization front provides, as determined by the technology, the location of the crystallization front with an accuracy of no worse than 1/2 - 1/4 of the thickness of the melt layer, depending on the material being crystallized.

PRI me R. On a crystallization installation for growing crystals of increased optical uniformity with an inner diameter of the crystallization section of the inner muffle Os.k equal to 40 mm with a three-way main burner with a diameter of the outer annular channel for gas supply equal to 24.8 mm and two-way additional burner, blockless crystals were grown up to 160 mm long and diameter up to 30 mm. with a dislocation density of 103-104 cm2, a radial gradient of the exponent, refractions in such crystals A, (3.1 - 3.3), which is two times

less than in previously known crystals. Crystals grown under the proposed conditions have deviations in diameter of no more than 2%, which is 6.0 times better

grown, the total gas consumption decreased by 12.7%, the charge consumption decreased by an average of 9.4%. energy intensity of the process decreased by 2-5 times.

As shown by experiments, crystals,

grown on the proposed installation have increased optical uniformity, which ensures the manufacture of high-quality active elements for lasers, structural parts for mechanical engineering, instrument making, optical, watch and jewelry industries.

Claims (6)

1. A method of growing crystals by the Verneil method, comprising feeding the charge into the crystallization chamber through the central channel of a multi-channel burner, simultaneously supplying oxygen and hydrogen flows through its channels, melting the charge in the zone of the crystallization front and growing on the seed crystal, characterized in that, for the purpose of increasing the size of the grown crystals with high optical uniformity, the outer wall of the crystallization chamber is heated with additional oxygen and hydrogen flows supplied from above Res additional burner ports. . 2. The method according to item T, wherein the maximum temperature on the inner wall of the crystallization chamber is located above the zone of the crystallization front and above the temperature in this zone by 30-250 ° C, the temperature difference between the crystal and the inner wall of the crystallization chamber is DT 10 - 100 ° C, and the temperature of the wall of the crystallization chamber at a distance of no more than 4D below the zone the crystallization front has a smooth decrease of no more than 10% of the temperature in the region of the crystallization front, where D is the diameter of the crystal holder equal to the diameter of the crystal. 3. The method is no pp, 1 and 2, with the exception that the rate of expiration of the oxygen flow through the internal channel of the main burner is 0 0.sub.O2 0.3 - 2.5 m / s, in in each subsequent channel, the flow rate is 1.1 to 3.4 times greater, the ratio of the rates of oxygen and hydrogen flow in the first stream is VOCH. 0.1 - 0.85, and in the subsequent stream is equal to v2ocH. 0.21 - 1.2 in relation to expenses oxygen and hydrogen in the first stream QIOCH .. "1.8 - 2.75, the torch has a diameter of not less than 0.7 of the diameter of the crystal and the length of the LOCH. 0.6 - 1.2 distance from the end of the main burner to the crystallization front, the rate of oxygen outflow through the additional burner is vRon.O2 - 0.7 - 6.0 m / s, the ratio of the rates of outflow of oxygen and hydrogen is Odop. 0.5 - 4.5, and the optimal torch length is LRon. 1.1 - 2.0 shots between the end of the auxiliary burner and the crystallization front. 4. Installation for growing crystals by the Verneil method, comprising a crystallization chamber, a crystal holder mounted therein for rotation and vertical movement, a main multi-channel burner placed above it, an additional burner, a hopper provided with means for supplying the charge to the crystallization chamber, and control means so that, in order to increase the size of the grown crystals with high optical uniformity, the crystallization chamber is made in the form of two isolated coaxial muffles surrounded by a multilayer lining, an additional burner is installed coaxially with the main one and connected to the outside With a muffle, the hopper is equipped with a dispenser located under it, and the control means is made in the form of an automatic system for maintaining the crystallization front and the diameter of the crystal associated with the dispenser and means for supplying gases to the burners. 5. Installation according to claim 4. characterized in that the inner muffle is made of three sections, the height of the upper section of which is Hei (0.75 - 5.4) D, the height of the middle section is HB2 ° (1 2) 0 and the height of the lower section is HBZ (5 - 20) D, the outer the muffle has a length of Нн HBi + Н82 + НВз - (1 - 7р and is made of two sections, the height of the upper section is (0.75 - 6.3) D, and the lower section is made in the form of a truncated cone with an angle of inclination of the generatrix to the vertical axis 0.5 -1.5 °. 6. Installation according to claims 4 and 5, characterized in that in order to stabilize the growth process, the automatic system for maintaining the crystallization front and crystal diameter includes an x-ray source mounted outside the crystallization chamber, diametrically opposed to the information conversion and processing subsystems accordingly with the subsystems of the charge and gas flow. 2-gpf 5Sh) Sh AND Fig.Z