PROCESS FOR PRODUCING CRYSTALS, PARTICULARLY POLYCRYSTALS

Abstract

The invention is a process for producing crystals (polycrystals) that comprises steps of: evacuating, melting a raw material in a container by means of a resistance heater to form a skull layer of 5-10 mm, crystallizing a melt of the raw material, annealing and cooling the crystal, separating the skull layer. The container is coated inside with a metal foil having a thickness of 0.04-0.15 mm; the steps of melting the raw material, crystallizing, annealing and cooling the crystal are performed in a double-layered shell composed of the metal foil and the skull layer; after the crystallization step, the crystal is annealed in a separate annealing furnace. The invention allows to: prevent crystal cracking, produce the crystal without any internal stresses; reduce the raw material mass consumed to form the skull layer; increase the size and the weight of the produced crystal; reduce energy consumption.

Claims

1. A process for producing crystals, the process comprises steps of loading a raw material into a container, placing the container loaded with the raw material into a cooling vacuum chamber that is evacuated to forevacuum, heating and melting the raw material in a skull to form an optimal thickness of a skull layer by means of a resistance heater positioned above the container and in parallel to a melt surface of the raw material, the resistance heater has a working heating surface having an area that is less than an area of an exposed upper part of the container and it has parameters that allow to produce the skull layer along inner surfaces of walls and bottom of the container having a thickness of 5-10 mm, further directional crystallizing the melt of the raw material by reducing a temperature of the resistance heater according to a given program, annealing the produced crystal, cooling the annealed crystal, separating the skull layer, wherein the process comprises, before the step of loading the container with the raw material, coating an inner surface of the container for growing the crystal with a protective metal foil layer having a thickness of 0.04-0.15 mm, and the steps of producing the melt of the raw material, directional crystallizing, annealing and cooling the annealed crystal are performed in a double-layered protective shell that is formed along the inner surfaces of the walls and the bottom of the container by the protective metal foil layer and the skull layer of the raw material, and the step of melting the raw material comprises adjusting a temperature T.sub.1 of the resistance heater based on controlling measurement values of a temperature T.sub.2 of a side wall of the container and a temperature T.sub.3 of the bottom of the container, while correspondingly fixing the temperature T.sub.1 of the resistance heater immediately after either one of the temperatures T.sub.2 or T.sub.3 or both temperatures T.sub.2 and T.sub.3 simultaneously reached a value that falls within an interval of values that corresponds to a temperature control criterion C.sub.tc that is 0.76-0.8 of a crystal melting temperature value T.sub.4 of the crystal being grown, namely, C.sub.tc=(0.76T.sub.4):(0.8T.sub.4), and after the step of directional crystallizing is completed, the step of annealing the crystal is performed in a separate annealing furnace at a temperature T.sub.5 having a value of 0.8-0.9 of the crystal melting temperature value T.sub.4 of the crystal being grown.

2. The process according to claim 1, wherein an aluminum foil layer having an aluminum content of at least 98.5% is used as a metal component of the double-layered protective shell.

3. The process according to claim 1, wherein the step of melting the raw material comprises controlling the temperature measurement value T.sub.2 of one of the side walls of the container that is performed in an upper external middle zone of the side wall of the container, while controlling the temperature measurement value T.sub.3 of the bottom of the container is performed in a central external zone of the bottom of the container.

4. The process according to claim 1, wherein the further melting the raw material for formation and maintaining the optimal thickness of the skull layer within 5-10 mm by adjusting the temperature T.sub.1 of the resistance heater based on controlling the temperature measurement values T.sub.2 and T.sub.3 according to the interval of values of the temperature control criterion C.sub.tc=(0.76T.sub.4):(0.8T.sub.4) takes place for 4-8 hours after pre-heating and pre-melting the raw material, and then the produced melt of the raw material having the formed skull layer is maintained for 1-2 hours.

5. The process according to claim 1, wherein an inner working volume of the separate annealing furnace is heated to the temperature T.sub.5 before the container with the crystal is loaded therein, and the crystal is annealed at this temperature for 1-5 hours.

6. The process according to claim 1, wherein after the steps of annealing and cooling the crystal, the double-layered protective shell is separated from the annealed and cooled crystal successively, namely, firstly, the aluminum foil layer is separated from the skull layer, and then, the skull layer is separated from the crystal.

Description

EXAMPLE 1

[0074] The claimed method is performed as follows.

[0075] 1. The internal working surface of the side walls and the bottom of the aluminum container, where the crystal will be grown, is coated with the metal aluminum foil having a thickness of 0.1 mm before loading the raw material. Dimensions of the container may be, for example: 500 mm500 mm170 mm. The container may have any arbitrary geometric shape: the container may have rectangular, cylindrical or any other shape.

[0076] The aluminum soft (annealed) or hard (non-annealed) foil having an aluminum content of at least 98.5% is used; the hard (non-annealed) foil is annealed after being exposed to the temperature of not more than 500 C. and becomes soft.

[0077] 2. Then, the dry powdered raw material in a form of the mixture of sodium iodide NaI and thallium iodide TlI is loaded into the container in the general amount of 100 kg: 99 kg of NaI (99 wt. %) and 1 kg of the TlI activator (1 wt. %).

[0078] 3. The container with the loaded raw material is mounted in the vacuum water-cooling chamber.

[0079] 4. The thermocouples for measuring the temperature are secured to the bottom of the container and one of its side walls. At least two thermocouples are required: one thermocouple is to be located at the container bottom, while another thermocouple is to be located on one of its side walls. The thermocouples are connected to a temperature measurement unit.

[0080] 5. The resistance heater having dimensions of 400400 mm is positioned at a distance of 10 mm above the exposed upper part of the container with the raw material for melting this raw material and for subsequent temperature exposures onto the processing medium. The geometric shape of the heating working surface of the resistance heater corresponds to the shape of the exposed upper part of the container.

[0081] The resistance heater, particularly its heating working surface, is positioned horizontally and in parallel to the upper surface of the mass of the raw material loaded into the container, i.e., approximately in parallel to the surface of the future melt of this raw material. The area of the heating working surface of the resistance heater is less than the area of the exposed upper part of the container and, thus, the area of the heating working surface of the resistance heater is less than the area of the upper surface of the mass of the raw material loaded into the container (than the surface of the future melt of the raw material). Owing to this and to the heater parameters (its power), it becomes possible, during the subsequent melting of the raw material, to form and to maintain the partially unmelted layer of the raw material, i.e., the skull layer, along the internal surfaces of the walls and the bottom of the container, the skull layer prevents a contact between the melt of the raw material and the aluminum foil that coats the internal surfaces of the side walls and the bottom of the container.

[0082] 6. Then, the vacuum cooling chamber is evacuated to forevacuum (i.e., to pre-vacuum) for 48 hours, while simultaneously heating the container and the raw material loaded therein. The heating of the container with the raw material is started simultaneously with the start of the evacuation. During 1 (one) hour from the start of evacuation and heating, the temperature T.sub.1 of the resistance heater is increased up to the temperature of 300 C. and this temperature is fixed (maintained) for the next 23 hours of evacuation with the simultaneous heating at this temperature. Afterwards, i.e., 24 hours after the start of evacuation and the start of the simultaneous heating of the container and the raw material, the temperature T.sub.1 of the resistance heater is increased up to the temperature of 500 C. for 1 (one) hour, and this temperature is fixed (maintained) during the entire remaining evacuation period, i.e., for the next 23 hours.

[0083] 7. Producing the melt of the raw material.

[0084] 7.1. After the above-mentioned 48 hours have passed, the evacuation is stopped, and in order to reduce the rate of evaporation of the raw material being melted, the vacuum chamber is filled with argon until the pressure of 7 kPa is reached, and after the inflow of argon during 2 hours, the temperature T.sub.1 of the resistance heater is increased from 500 C. up to the temperature of 750 C.

[0085] 7.2. Fixing, i.e., maintaining this temperature T.sub.1 of 750 C. during the next 12 hours: during this time, the raw material is melted at this temperature. The raw material is melted and the processing media are formed, the processing media have various aggregate states, namely, the main melted mass of the raw material for growing the crystal and the skull layer, i.e., the partially unmelted layer of this raw material that is placed between the melted mass of the raw material and the aluminum foil layer that coats the internal working surface of the container. This skull layer is formed to avoid any contact between the melt of the main mass of the raw material and the aluminum foil layer. The skull layer and the aluminum foil layer together form the double-layered protective shell. However, the thickness of the skull layer that formed during the above-mentioned 12 hours at the temperature T.sub.1 of the resistance heater being 750 C. is 30-50 mm that is not the optimal thickness therefore, since it is too high.

[0086] 7.3. In order to ensure the optimal thickness of the skull layer of 5-10 mm, any further melting of the raw material is performed in the following way: the processing media (the melt of the raw material, the skull layer) are heated by a gradual increase of the temperature T.sub.1 of the resistance heater, while controlling the temperature T.sub.2 of the side wall and the temperature T.sub.3 of the bottom of the container. The temperature T.sub.1 of the heater is increased until one of the temperatures T.sub.2 or T.sub.3 reaches the specific value, and then, the temperature T.sub.1 of the resistance heater is fixed, i.e., any further increase thereof is stopped. That is, while controlling the temperature T.sub.2 of the side wall and the temperature T.sub.3 of the bottom of the container, the temperature T.sub.1 of the resistance heater is gradually (at the rate of 5-30 C./hour) is increased from the value of 750 C. until the temperature T.sub.2 of the side wall and/or the temperature T.sub.3 of the bottom of the container reaches, i.e., falls within the interval (range) of 502-529 C., i.e., the value that is 0.76-0.8 of the crystal melting temperature T.sub.4 and is 661 C. (T.sub.2 and/or T.sub.3-(0.76661 C.=0.8661 C.), while avoiding falling beyond this range, i.e., lower than the limit of 0.76 of T.sub.4, namely, not lower than 0.76661 C., and higher than the limit of 0.8 of T.sub.4, namely, not higher than 0.8661 C.: i.e., the temperature T.sub.1 of the resistance heater is correspondingly fixed and its increase is stopped after one of the temperatures T.sub.2 or T.sub.3 or both temperatures T.sub.2 and T.sub.3 simultaneously reached the value that falls within the interval (the range) of values that corresponds to the temperature control criterion C.sub.tc of 0.76-0.8 of the value of the melting temperature T.sub.4 of the crystal being grown. In this Example 1, the values of the temperatures T.sub.2 and T.sub.3 fell within the interval of 502-529 C., but not simultaneously: firstly, the temperature T.sub.3 of the bottom of the container fell within this interval, thus, the temperature T.sub.1 of the resistance heater was adjusted based on the temperature value of the bottom of the container being T.sub.3=507 C. fixed after the threshold of the temperature entrance of 502 C.: the temperature T.sub.1 of the resistance heater was fixed and its further increase was stopped.

[0087] This adjusted increase of the temperature T.sub.1 based on controlling the values of the temperatures T.sub.2, T.sub.3 during further melting of the raw material was performed for 4 hours. In the provided example, the temperature T.sub.1 of the resistance heater reaches the value of 790 C. And the value of the temperature of the side wall of the container is T.sub.2=503 C.

[0088] 8. The fixed temperature T.sub.1 of the resistance heater of 790 C. at which the controlled temperatures are within the range of 502-529 C. are maintained for 2 hours: at this temperature and time mode, the melt of the raw material that is obtained by melting this raw material at the previous step is maintained.

[0089] The temperature T.sub.2 of one of the side walls of the container was controlled in the upper external middle zone, while the temperature T.sub.3 of the bottom of the container was controlled in the central external zone. Potentially, these areas are the hottest areas.

[0090] 9. After the melt of the raw material and the formed skull layer of the optimal thickness are obtained, the directional crystallization of the melt is performed by gradual reduction of the above-mentioned temperature of the resistance heater being 790 C. at the rate of 3 C./hour down to 680 C. At the temperature reduced down to 680 C., the melt is crystallized. The crystallization process of the melt starts from the bottom, i.e., the crystallization process continues from the container bottom being cooled and then to the top (towards the upper exposed part of the container towards the resistance heater) until the melt is completely crystallized.

[0091] 10. Preparing the container with the crystal for reloading into the annealing furnace.

[0092] After completion of the crystallization of the melt of the raw material, the temperature T.sub.1 of the resistance heater is reduced from 680 C. down to 550 C. in 20-30 minutes, and at this temperature of the resistance heater, the temperature of the container that is measured by the control thermocouples is within the interval of 350 C.-400 C.

[0093] The skull layer that is formed during melting the raw material maintains its thickness and aggregate state during the entire crystallization process and further reduction of the temperature after its completion.

[0094] 11. The hot container with the produced crystal that is coated with the double-layered shell, i.e., the skull layer in the aluminum foil, is reloaded to the separate annealing furnace having the internal working volume that is preliminarily heated to the temperature T.sub.5 being 0.832 of the crystal melting temperature T.sub.4. T.sub.5=0.832661 C., namely, to the temperature of 550 C.

[0095] 12. In the annealing furnace, the crystal is annealed, i.e., it is maintained at the above-mentioned temperature of 550 C. for 4 hours.

[0096] 13. Then, the temperature T.sub.5 of 550 C. in the annealing furnace is gradually reduced down to the room temperature, i.e., 16-25 C.

[0097] 14. After the gradual cooling of the crystal in the annealing furnace is completed, the container with the cooled crystal is transported from this furnace.

[0098] The cooled crystal that is coated with the skull layer and the aluminum foil layer is removed from the container.

[0099] 15. Then, the double-layered protective shell is removed from the crystal: firstly, the aluminum foil layer is removed from the skull layer, since the foil is easily separated from the skull layer after cooling, and then the skull layer is removed from the crystal.

[0100] Implementation of the technological steps of the claimed process results in production of the scintillation alkali-halide high-quality crystal based on sodium iodide that is dopped with thallium, has a weight of 81 kg and dimensions of 470 mm470 mm100 mm. The crystal has a polycrystalline structure having a single-crystal blocks diameter of 5-50 mm. The thickness of the skull layer along the side walls and the bottom of the container is 7-10 mm.

[0101] This crystal is produced from the melt of the raw material without any contact between the melt and the container material that ensured reduction of the level of the internal stresses and production of the crystal without formation of any internal stresses during implementation of the technological process. The produced crystal does not comprise any internal stresses and does not crack during further processing.

EXAMPLE 2

[0102] It is carried out in the same way as Example 1, but the raw material is used in the following quantitative ratio: 99.5 kg of NaI (99.5 wt. %) and 0.5 kg of TlI (0.5 wt. %), and after the internal surface of the container is coated with the aluminum foil having the thickness of 0.15 mm, the container is loaded with sodium iodide NaI in the amount of 99.5 kg, while thallium iodide (TlI) in the amount of 0.5 kg (0.5 wt. %) is loaded into the melted raw material before start of maintaining this melt of the raw material for 1 hour that is performed before the start of the crystallization process. TlI is loaded via a separate tube that is placed above the container center and passes through the resistance heater. The number of the thermocouples mounted on the container depends on the container structure and is as follows: two thermocouples at the bottom of the container and one thermocouple on either of the side walls. In this example, the controlled values of the temperatures T.sub.2 and T.sub.3 fell within the interval of 502-529 C. non-simultaneously: firstly, the temperature T.sub.3 of the bottom of the container fell within this interval, thus, the temperature T.sub.1 of the resistance heater was adjusted based on the temperature value of the bottom of the container being T.sub.3=510 C. fixed after the threshold of the temperature entrance of 502 C.: the temperature T.sub.1 was fixed and its further increase was stopped at the value of 795 C.

[0103] The crystal annealing time in the furnace is 5 hours.

[0104] The produced crystal has a polycrystalline structure having a single-crystal blocks diameter of 5-50 mm. The thickness of the skull layer along the side walls and the bottom of the container is 6-9 mm.

EXAMPLE 3

[0105] It is carried out in the same way as Example 1, but the crystals are grown based on cesium iodide that is dopped with thallium and by corresponding technological elements depending on the dimensions of the crystal being grown.

[0106] Growing the CsI(Tl) crystal.

[0107] Dimensions of the container: 500 mm500 mm170 mm.

[0108] Loading the powdered raw material of thallium-dopped cesium iodide CsI(Tl).

[0109] The overall weight of the raw material is 120 kg: 118.8 kg of CsI (99 wt. %) and 1.2 kg of TlI (1 wt. %).

[0110] The thickness of the aluminum foil layer is 0.09 mm.

[0111] T.sub.4 is the melting temperature of the crystal being grown, and it is 621 C.

[0112] T.sub.2, T.sub.3 are the temperatures of the side wall and the bottom of the container respectively: in the range of 472 C.-497 C., i.e., (0.76T.sub.4-0.8T.sub.4). In Example 3, the values of the temperatures T.sub.2 and T.sub.3 fell within the interval 472 C.-497 C. simultaneously, thus, the adjustment of the temperature T.sub.1 of the resistance heater was performed based on the values of the temperature T.sub.2 and T.sub.3 from the moment when they fell within the interval 472 C.-497 C.: and at this moment, the temperature T.sub.1 was fixed, i.e., its further increase above the value of 765 C. was stopped.

[0113] T.sub.5 is the annealing temperature in the internal working volume of the annealing furnace being 497 C., i.e., (0.8T.sub.4), the annealing time is 2 hours.

[0114] The crystallization is performed until the temperature of 640 C. is reached. The rate of the reduction of the temperature of the resistance heater down to 640 C. is 3 C./hour.

[0115] Before reloading the container with the crystal to the separate annealing furnace, the temperature of the resistance heater is reduced down to the temperature of 500 C.

[0116] The weight of the produced crystal is 100 kg and the dimensions are 470470100 mm.

[0117] The produced crystal has a polycrystalline structure having a single-crystal blocks diameter of 5-50 mm. The thickness of the skull layer along the side walls and the bottom of the container is 6-8 mm.

EXAMPLE 4

[0118] It is carried out in the same way as Example 1, but the crystals are grown based on cesium iodide that is dopped with sodium and by corresponding technological elements depending on the dimensions of the crystal being produced.

[0119] Growing the CsI(Na) crystal.

[0120] Dimensions of the container: 500 mm500 mm170 mm.

[0121] Loading the powdered raw material of cesium iodide CsI dopped with sodium iodide NaI.

[0122] The overall weight of the raw material is 120 kg: 119.7 kg of CsI (99.75 wt. %) and 0.3 kg of NaI (0.25 wt. %).

[0123] The thickness of the aluminum foil layer is 0.15 mm.

[0124] T.sub.4 is the crystal melting temperature of 621 C.

[0125] T.sub.2, T.sub.3 are the temperatures of the side wall and the bottom of the container respectively, and they must be within the range of 472 C.-497 C., i.e., (0.76T.sub.4-0.8T.sub.4). In Example 4, the values of the temperatures T.sub.2 and T.sub.3 fell within the interval of 472 C.-497 C., but not simultaneously: firstly, the temperature T.sub.2 of the side wall of the container fell within this interval, thus, the temperature T.sub.1 of the resistance heater was adjusted based on the temperature value of the side wall of the container being T.sub.2=478 C. fixed after the threshold of the temperature entrance of 472 C.: the temperature T.sub.1 was fixed and its further increase was stopped at the value of 775 C.

[0126] T.sub.5 is the annealing temperature in the separate annealing furnace being 497 C., i.e., (0.8T.sub.4), the annealing time is 1 hour.

[0127] The crystallization is performed until the temperature of 640 C. is reached. The rate of the reduction of the temperature of the resistance heater down to 640 C. is 1 C./hour.

[0128] Before reloading to the thermal insulation chamber, the temperature of the resistance heater is reduced down to the temperature of 500 C.

[0129] The weight of the crystal is 100 kg and the dimensions are 470 mm470 mm100 mm.

[0130] The produced crystal has a polycrystalline structure having a single-crystal blocks diameter of 5-50 mm. The thickness of the skull layer along the side walls and the bottom of the container is 5-8 mm.

EXAMPLE 5

[0131] It is carried out in the same way as Example 4, but the crystal is grown based on CsI without additives and by corresponding technological elements depending on the dimensions of the crystal being produced.

[0132] Growing the CsI crystal.

[0133] Dimensions of the container: 500 mm500 mm170 mm.

[0134] Loading the powdered raw material of cesium iodide CsI.

[0135] The overall weight of the raw material is 120 kg: 120 kg of CsI (100 wt. %).

[0136] The thickness of the aluminum foil layer is 0.14 mm.

[0137] T.sub.4 is the crystal melting temperature of 621 C.

[0138] T.sub.2, T.sub.3 are the temperatures of the walls or the bottom of the container, and it must be within the range of 472 C.-497 C., i.e., (0.76T.sub.4-0.8T.sub.4).

[0139] In Example 5, the values of the temperatures T.sub.2 and T.sub.3 fell within the interval of 472 C.-497 C., but not simultaneously: firstly, the temperature T.sub.3 of the bottom of the container fell within this interval, thus, the temperature T.sub.1 of the resistance heater was adjusted based on the temperature value of the bottom of the container being T.sub.3=475 C. fixed after the threshold of the temperature entrance of 472 C.: the temperature T.sub.1 was fixed and its further increase was stopped at the value of 770 C.

[0140] T.sub.5 is the annealing temperature in the annealing furnace being 497 C., i.e., (0.8T.sub.4), the annealing time is 3 hours.

[0141] The crystallization is performed until the temperature of 640 C. is reached. The rate of the reduction of the temperature of the resistance heater down to 640 C. is 1 C./hour.

[0142] Before reloading to the separate annealing furnace, the temperature of the resistance heater is reduced down to the temperature of 500 C.

[0143] The weight of the crystal is 100 kg, and the dimensions are 470 mm470 mm100 mm.

[0144] The produced crystal has a polycrystalline structure having a single-crystal blocks diameter of 5-50 mm. The thickness of the skull layer along the side walls and the bottom of the container is 8-10 mm.

[0145] The above-mentioned Examples 1, 2, 3, 4, 5 of the specific practical implementation of the claimed process are the most preferred exemplary embodiments of the invention within the industrial technology.

[0146] The claimed process, according to the provided Examples 1, 2, 3, 4, 5, has been reproduced in the experimental and manufacturing conditions for the required number of times in order to obtain average testing results of this technology that have confirmed the achievement of the technical effects upon implementation of the present process.

[0147] Comparative characteristics of weight of the crystal, weight, and thickness of the skull layer which were obtained during experimental tests of the claimed process, namely, during implementation of the technologies according to the closest analog and according to the claimed process, are provided in Table 2.

TABLE-US-00002 TABLE 2 Electrical energy Electrical energy consumption, kW consumption, kW Step of the The closest The claimed technological process analog process 1 2 3 Evacuation 72 64.8 Melting the raw material 115 103.5 Growing the crystal 192 172.8 Annealing the crystal 14 8 Cooling the crystal 180 60 IN TOTAL at the 573 409.1 above-mentioned steps, kW IN TOTAL at the 100% 71% above-mentioned steps, %

[0148] The number of technological cycles (%) implemented to ensure the thickness of the formed skull layer of 5-10 mm:

[0149] Along the internal side surface of the container: [0150] 65% for the closest analog; [0151] 100% for the claimed process.

[0152] Along the internal surface of the bottom of the container: [0153] 20% for the closest analog; [0154] 100% for the claimed process.

[0155] The number of technological cycles (%) implemented to ensure the thickness of the formed skull layer of greater than 10 mm:

[0156] Along the internal side surface of the container: [0157] 35% for the closest analog; [0158] 0% for the claimed process.

[0159] Along the internal surface of the bottom of the container: [0160] 80% for the closest analog; [0161] 0% for the claimed process.

[0162] The number of technological cycles (%) implemented to ensure complete melting of the skull layer along the side wall or the bottom of the container that resulted in a discharge of the melt from the container (emergency situation): [0163] 10% for the closest analog; [0164] 0% for the claimed process.

[0165] The claimed process allows to increase the efficiency of the process for growing the crystal, namely, to increase the crystal weight by up to 10% as compared to the closest analog. This became possible due to control of the thickness of the skull layer along the bottom of the container, thereby allowing to assuredly reduce its thickness down to the optimal thickness of 5-10 mm.

[0166] Comparative values of electrical energy consumption which were obtained during experimental tests of the claimed process, i.e., during implementation of the technologies according to the closest analog and according to the claimed process, are provided in Table 3.

TABLE-US-00003 TABLE 3 Electrical energy Electrical energy consumption, kW consumption, kW Step of the The closest The claimed technological process analog process 1 2 3 Evacuation 72 64.8 Melting the raw material 115 103.5 Growing the crystal 192 172.8 Annealing the crystal 14 8 Cooling the crystal 180 60 IN TOTAL at the 573 409.1 above-mentioned steps, kW IN TOTAL at the 100% 71% above-mentioned steps, %

[0167] Owing to use of the aluminum foil as well as conduction of annealing and cooling of the crystal in the separate annealing furnace, electrical energy consumption for production of the crystal according to the claimed process are reduced by 29% as compared to the closest analog.

[0168] Industrial applicability and achievement of the technical effects upon application of the claimed process have been confirmed many times during conduction of experimental and manufacturing tests.

[0169] The conducted tests of the claimed technology have confirmed the achievement of the technical effects upon implementation of the present process.

[0170] The implementation of the novel technological cycles, the novel set of the technological steps of the claimed process resulted in: [0171] production of crack-free crystals, i.e., polycrystals, having the assured high quality without any internal stresses due to elimination of accumulation of these stresses and cracking of the polycrystal along boundaries of the single-crystal blocks; [0172] production of the crystals, i.e., polycrystals, having the increased dimensions and the increased weight, and, thus, increase of the process efficiency by up to 10% due to reduction of the raw material mass that is consumed for the formation of the skull layer; [0173] reduction of energy consumption for conduction of the process by down to 29%.

[0174] The claimed process meets all the requirements of equipment operation and usage, as well as the common safety rules.

[0175] Use of the claimed process will also allow to expand the range of modern technologies for producing crystals of various sizes, including large-sized crystals, namely, large-area polycrystals.