Device for growing single crystals of sapphire

 

The invention relates to the cultivation of molten sapphire crystal and is aimed at improving thermal protection system. The essence of the invention: a device for growing single crystals of sapphire, including a vacuum chamber, a crucible former, mounted coaxially to the cylindrical crucible resistive heater made of tungsten rods, cylindrical reflector, a vertical screen in the form of bonded between a molybdenum cylinder, and upper and lower horizontal screens, the reflector is made of two pairs of coaxially arranged cylinders of molybdenum, the cavity inside the steam filled with refractory material, and the ratio of the outer diameter of the crucible and the inner diameters of the cylindrical pairs of reflector is 1:(1,6-1,8):(2,0-2,2) accordingly, the distance from the heater rods to the axis of the camera is 0.65 to 0.75 radius from the camera. In addition, a pair of cylinders reflector made of composite height; cavity pairs of cylinders reflector filled with tungsten rods, and/or tungsten powder, and/or molybdenum sponge, and/or molybdenum sponge with a mixture of powders of molybdenum and tungsten. Technical resuli quality and reducing the cost of system thermal protection. 2 C.p. f-crystals, 3 ill.

The invention relates to the cultivation of molten sapphire crystal by the method of crystallization from the melt and is aimed at improving thermal protection system.

A device for growing monocrystalline ribbons sapphire from the melt on a seed crystal containing mounted in the chamber of the crucible former, placed inside a graphite heater, screens mounted above the crucible, and the outer surface of the crucible has a coating of tungsten, and the inner surface of the heater has a coating of molybdenum carbide.

The device allows to increase the wear resistance of elements of construction while increasing product yield. However, its disadvantage is a special process operations for coating of tungsten and molybdenum carbide. (see A. S. No. 1213781, With 30 In 15/34, 29/20, 1984).

A device for growing single crystals of sapphire, containing installed in a vacuum chamber resistive heater made of tungsten rods, suspended on a copper current leads are made in the form of half-rings, the crucible former, structurally attached to the t heater, vertical screen, which represents a set of 17 molybdenum cylinder, coaxially arranged to each other with a gap, the upper and lower horizontal screens, a reflector mounted coaxially to the crucible height below the upper edge of the crucible between the upper and lower horizontal screens and between the heater and vertical screen.

The reflector is made of a sintered mixture of powders of tungsten and other refractory metals such as molybdenum, or copper, or graphite coated on their surface by plasma spraying a mixture of powders of the same composition.

The reflector has the shape of a cylinder with an internal diameter of 1.6-1.8)D and wall thickness (0,03-0,06)D, where D is the external diameter of the crucible. (see A. C. of the USSR №1132606, With 30 17/ 00 from 11.08.83. Blacken N. And. and others).

The specified device is adopted for the prototype.

The reflector in the known device performs the following function.

In single crystals of sapphire, the most common defect are gas inclusions in the form of bubbles that fall in the volume of the growing crystal. Necessary to prevent capture of bubbles curvature of the solidification front is provided by the uniformity of the crystallization rate, which is controlled by an automatic system pre Latter varies from process to process, and during each process as a result of samostalni due to condensation of vapors melt on the cold parts of crystallization site. Change leads to the violation of the stability fields and to intermittent advancement of the crystallization front. This causes the formation of defects in the crystal. Installation of reflector as an additional element of thermal shielding contributes to the stabilization of thermal field and the resources of heat shields.

The presence of the reflector increases the service life of thermal snap-in devices in General, including the most vulnerable element - vertical screen.

The reflector of the prototype is made by sintering a mixture of powders of tungsten, other refractory metals, such as molybdenum. The height of the reflector in the known device is not below the upper edge of the crucible due to the possibility to avoid direct exposure of the screens from the walls of the crucible.

At the same time, as shown, the use of the known device, it does not provide sufficient heat shielding, and therefore, despite the presence of the reflector, due to violations of thermal field in the cycle of cultivation there is a gradual decline in the quality of the crystals. Krichene by volume of the crucible allows you to grow crystals weighing less than 12 kg while there is a need manufactured using standard vacuum chambers and equipment, described in the prototype, to obtain crystals with a mass of 20 kg or more.

The technical result of the invention consists in providing the possibility of obtaining crystals of 20 kg or more for the preservation of their quality and at lower cost thermal protection.

The technical result is achieved by the fact that in the known device for growing single crystals of sapphire, including a vacuum chamber, a crucible former, mounted coaxially to the cylindrical crucible resistive heater made of tungsten rods (slats), a cylindrical reflector, a vertical screen in the form of bonded between a molybdenum cylinder, and upper and lower horizontal screens, according to the invention, the reflector is made of two pairs of coaxially arranged cylinders of molybdenum, the cavity inside the steam cylinder is filled with refractory material, and the ratio of the outer diameter of the crucible to the inner diameters of the pairs of cylindrical reflector is 1:(1,6-1,8):(2,0-2,2) accordingly, the distance from the heater rods to the axis of the camera is 0.65 to 0.75 radius from the camera. In addition, a pair of cylinders reflector made of composite height; cavity pairs of cylinders reflector for which bcoi with the addition of a mixture of powders of molybdenum and tungsten.

The essence of the claimed invention with the proposed design of the reflector is that it provides substantial thermal discharge on the second pair of cylinders of the reflector and thereby stabilize thermal field, and these same design features allow you to increase the diameter of the heater and reduce the number of vertical screens, thereby increasing the free volume, creating the opportunity to place in the device is increased by the volume of the crucible, in which grow the crystals weighing 20 kg without compromising product quality and lower costs for thermal shielding.

The claimed range of the ratio of the diameters of the crucible and the pairs of cylinders of the reflector, and the claimed range is the distance from the slats of the heater to the axis of the camera allow you to maximize the weight of the grown crystal, providing stabilization of thermal field.

Fill the steam cylinder reflector tungsten rods, or tungsten powder or molybdenum sponge, or molybdenum sponge and a mixture of powders of tungsten and molybdenum allows to improve the insulating quality of the reflector while reducing the cost of thermal snap.

The implementation presented is authorized to burnout.

The claimed device shown in Fig. 1.

In a vacuum chamber (1) has a cylindrical shape inserted along the periphery of the vertical screen (2), which represents a set of coaxially arranged to each other and bonded to each other cylinders of the molybdenum sheet. On a vertical screen (2) has an upper horizontal screen (3) of molybdenum. At the bottom of the camera (1) is lower horizontal screen (4) in the form of a molybdenum disk with an axial bore in which is inserted molybdenum stand (5) of the crucible (6). Coaxial stand (5) and the crucible (6) on two copper semirings-current (7) is suspended from a cylindrical resistance heater (8), collected from a bent U-shape tungsten rods (slats), and the distance from the slats to the axis of the camera is 0.65 to 0.75 radius from the camera.

Directly above the crucible (6) posted by set top horizontal screens (9) of molybdenum. At the lower end of the stem, the seed-holder (10) is fixed to the seed crystal (11), Coaxial to the crucible (6) and with height above the level of the top edge, a bottom horizontal screen (4) has a reflector in the form of two pairs of coaxial cylinders (12) and wall thickness (0,03-0,06)D, the inner diameter of the pairs of cylinders extending t the E. also shown is placed in the crucible (6) shaper (13), representing a cylinder made of molybdenum or tungsten, and the part grown from the seed crystal (11) single crystal (14).

As a result of execution of the reflector in the form of two pairs of coaxially arranged cylinders thermal field is stabilized at the desired level and there is the possibility of reducing the number of molybdenum cylinder comprising a vertical screen, from 17 in the prototype to 13-14. This reduction, combined with increasing distance from the slats to the axis of the camera from 0.5 to 0.65 to 0.75 on the radius of the camera allows you to increase the inner diameter of the crucible from 155 mm to prototype to 200 mm

Mainly, the reflector is movable and consists of three parts (Fig.2). The length of the middle part is determined by the height of the crucible. During the operation of the middle part of the cylinder reflector (12) if necessary replace, not bringing up of impacts associated with burning.

Cavity pairs of cylinders reflector filled with tungsten rods, or tungsten powder or molybdenum sponge or molybdenum sponge and a mixture of powders of molybdenum and tungsten, which provides reliable thermal protection in conjunction with the availability and low cost of the materials used.

One of the variants of Her on the example of growing a single crystal sapphire as follows.

Preparing the device for operation carried out as follows. In a vacuum chamber (1) has a cylindrical shape placed vertical screen (2), which represents a set of 13 coaxially arranged to each other with a gap of 8-10 mm and clamped between a cylinder height of 510 mm of molybdenum sheet thickness of 0.3-0.6 mm Above the vertical screen (2) install the upper horizontal screen (3) of molybdenum. At the bottom of the camera (1) install the lower horizontal screen (4) in the form of a molybdenum disk with an axial bore in which is inserted molybdenum stand (5) of the crucible (6). Coaxial stand (5) and the crucible (6) on two copper semirings-current (7) establish a cylindrical resistance heater (8), collected from 10-12 pairs of bent U-shape tungsten rods, and the distance from the slats to the axis of the camera is 0.65 to 0.75 radius from the camera. Between the heater (8) and a vertical screen (2) establish a cylindrical reflector (12), made of two pairs of coaxially arranged cylinders of molybdenum, cavity inside pairs supplemented pereplavleni materials. In the crucible (6) is placed coaxially with the shaper (13) and fill the entire volume of the crucible to the original charge, for example, in the form of crushed pieces sapphirina screens (9). Insert and center in structurale (10) the seed crystal (11). Heat the crucible to a temperature of 2100With, melt the charge and maintain the melt within 2-4 hours for homogenization. Then, reduce the temperature of the melt until 2050C (melting point of aluminum oxide 2040C) and lower the seed crystal before contact with the melt. After soaking in 1-3 min seed crystal slowly raise up. After 20-30 minutes the rise of the seed crystal with the growing crystal (14) is stopped. Further growth of the crystals to the walls of the shaper (13) and into the crucible provide a predetermined temperature profile, the magnitude of the temperature gradient. After complete solidification of the melt supplied to the heater power is uniformly reduced to zero, the crystal is cooled in vacuum and unloaded from the chamber and crucible.

The result is a single crystal sapphire weighing 20 kg or more with a yield of over 50%.

Claims

1. Device for growing single crystals of sapphire, including a vacuum chamber, a crucible former, mounted coaxially to the crucible, the cylinder is ideal fastened by a molybdenum cylinder, as well as the upper and lower horizontal screens, characterized in that the reflector is made of two pairs of coaxially arranged cylinders of molybdenum, the cavity inside the steam filled with refractory material, and the ratio of the outer diameter of the crucible and the inner diameters of the cylindrical pairs of reflector is 1:(1,6-1,8):(2,0-2,2) accordingly, the distance from the heater rods to the axis of the camera is 0.65 to 0.75 radius from the camera.

2. The device under item 1, characterized in that the pair of cylinders reflector made of composite height.

3. Device according to any one of paragraphs.1 and 2, characterized in that the cavity pairs of cylinders reflector filled with tungsten rods, and/or tungsten powder, and/or molybdenum sponge, and/or molybdenum sponge with a mixture of powders of molybdenum and tungsten.

 

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