Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
  • B30B11/16—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using pocketed rollers, e.g. two co-operating pocketed rollers
  • B30B11/165—Roll constructions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
  • B30B11/18—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using profiled rollers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B3/00—Presses characterised by the use of rotary pressing members, e.g. rollers, rings, discs
  • B30B3/005—Roll constructions

Definitions

• roller compaction A well-known method for compacting powders is roller compaction.
• powder is compressed between two counter-rotating rollers.
• the specific contact pressures that occur are 5 N / cm to 50 kN / cm.
• Metal rollers are generally used for this application. Due to the high specific contact forces, which in some cases reach the flow limit of the metal roller, the rollers wear. The abrasion gets into the product. For applications in the photovoltaic, semiconductor, pharmaceutical and chemical industries, this metal abrasion is unfavorable to harmful, since metallic impurities in the ppm or ppb range sometimes lead to defective products.
• the invention is based on the object of creating a compaction device for the low-metal or metal-free compaction of a powder.
• the object is achieved by the features of claim 1.
• the essence of the invention is to provide compaction rollers in a compaction device which consists of ceramic at least on its jacket. This prevents metallic abrasion from occurring during compaction.
• FIG. 1 shows a section of a plant for producing silicon with a compression device according to a first exemplary embodiment
• Fig. 2 is an enlargement of a compaction roller of the compaction device according to Fig. 1 and
• Fig. 3 is an enlargement of a compaction roller according to a second embodiment.
• the structure of a system 1 for producing silicon powder according to a first exemplary embodiment is described below with reference to FIGS. 1 and 2.
• the plant 1 has, starting from above, a tubular, vertically running reactor 2 which encloses a cylindrical reaction chamber 3.
• a gas supply line 4 is arranged, which opens into the reaction chamber 3.
• the line 4 is designed such that a useful gas flow, for example made of monosilane, can be introduced in the middle.
• the useful gas flow is surrounded by a ring flow of an auxiliary gas.
• Approximately the upper half of the reactor 2 is surrounded by a ring-cylindrical heater 5 which surrounds the reactor 2 in such a way that the wall of the chamber 3 can be heated to temperatures of over 800 ° C.
• the lower half of the reactor 2 is surrounded by an annular cylindrical cooling device 6 which is directly adjacent to the reactor 2.
• the degassing device 31 consists of a housing 32, which runs obliquely upwards and is connected to the chamber 3, at the lower end of the reactor 2 is scheduled.
• an annular cylindrical sintered material filter 33 which is closed at the bottom and through which excess hydrogen can escape through an opening 34 located in the upper end of the housing 32.
• a roller breather 35 of known type and then a compression device 10, the construction of which is described in more detail below.
• the compression device 10 is connected to the reaction chamber 3 via the lock 7.
• a storage container 11 connected to it.
• the roller breather 35 has a cuboid housing 36, in which two breather rollers 38, 39 driven by a motor 37 are arranged.
• the rollers 38, 39 are rotatably mounted about associated axes of rotation 40, 41 running parallel to one another.
• the rollers 38, 39 are driven in opposite directions, so that both move downwards in the area of the gap 42 delimited by the rollers 38, 39.
• the roller 38 is hollow and has a porous jacket.
• a gas-permeable plastic film is applied to its outer surface. There is negative pressure within the roller 38. In this way, the gas remaining in the silicon powder 43 is drawn off.
• the surface of the roller 39 is smooth. Both rollers 38, 39 preferably have a non-metallic surface.
• the compression device 10 has a housing 12 which encloses an essentially cubic working space 13.
• the housing 12 has a feed opening 14 facing the lock 7 and connected to it, and a discharge opening 15 provided on the lower edge of the housing 12 and connected to the container 11.
• In the housing 12 there are two compacting rollers 18, 19, which can be driven in rotation about respective axes of rotation 16, 17, in the middle between the openings 14 and 15 are arranged adjacent to each other that a compression gap 20 is formed between them.
• the axes of rotation 16 and 17 run parallel to one another.
• the compression gap 20 has a width Bs.
• the compaction rollers 18, 19 can be driven in rotation by a motor 21, which is connected to the control device 9 via a connecting line 22.
• the tubular reactor 2 has a vertical central longitudinal axis 23, which runs centrally through the gap 20.
• the rollers 18, 19 are driven in opposite directions, ie the roller 18 rotates clockwise, the roller 19 counterclockwise. As a result, the surfaces of the rollers 18, 19 move downward together in the region of the gap 20.
• the rollers 18, 19 have a roller core 24 made of steel, which is circular cylindrical in shape.
• a roller jacket 25 with an annular cross section, which completely surrounds the roller core 24 on the circumferential side.
• the roller shell 25 is formed in one piece and consists of a non-metal material, that is, a non-metallic material. In particular, these are glass, graphite or ceramic materials. Ceramic is particularly preferred. The ceramics used consist mainly of silicon nitride.
• the roll shell 25 is fixed on the roll core 24 in the axial and tangential direction, for example by gluing or tongue and groove connections.
• the roller jacket 25 has the shape of a circular cylinder. It is possible to form the entire roller 18 or 19 from a ceramic material.
• FIG. 2 shows a second exemplary embodiment. Identical parts are given the same reference numerals as in the exemplary embodiment according to FIG. 2. Structurally different, but functionally similar parts are given the same reference numerals with a suffix a.
• the main difference compared to the exemplary embodiment according to FIG. 2 is that the roller jacket 25a is not formed in one piece, but consists of two half-shells 27, 28 which completely and completely enclose the roller core 24.
• the gaps 29 between the half-shells 27 and 28 are completely and completely closed, so that material which reaches the surface 26 does not come into contact with the roller core 24.
• the half-shells 27, 28 were subjected to an exact mechanical processing after the ceramic production. As part of the mechanical processing, the surface of the half-shells 27, 28 was profiled.
• the surface of the half-shells 27, 28 can also be designed in such a way that the compressed silicon has the shape of rods, pillows, almonds etc.
• the combination of ceramic and metal materials withstood the machining It is also possible to use partial shells with a center angle of ⁇ 180 ° on the circumference. In particular, three partial shells with a center angle of 120 ° or four partial shells with a center angle of 90 ° can be provided on the circumference. Other divisions are also possible.
• a gas mixture of monosilane and hydrogen in a volume or molar ratio of 1: 3 was converted into silicon powder and hydrogen in the reactor 2 with a wall temperature of the wall 30 of> 800 ° C. and a production rate of 200 g silicon per hour implemented.
• the addition took place in such a way that the monosilane was introduced centrally into the reaction chamber 3 from above.
• the hydrogen surrounded the monosilane in the form of a ring flow in order to prevent the silicon from being deposited directly on the walls of the reaction chamber 3.
• the silicon powder 43 was partially degassed after the decomposition by means of the degassing device 31 arranged on the lock 7.
• the powder obtained had a bulk density of about 50 g / l.
• the degassing in the degassing device 31 was carried out automatically in relation to the ambient pressure.
• the deaerated and pre-compressed product with a bulk density of approx. 200 g / dm 3 was compressed to a bulk weight of 450 g / dm 3 by means of the compression device 10. 6 kg of this compressed silicon powder were placed in an induction melting plant IS30 from Leybold. The system was then evacuated. An argon atmosphere with a pressure between 1 and 100 mbar was generated.
• the silicon powder was heated to a melting temperature of 1415 ° C.
• the silicon powder was then melted without residues at 1450 ° C. in 30 minutes with a melting capacity of 70 kW.
• the silicon melt was then poured off and the silicon solidified in a directed manner.
• the solidified polycrystalline silicon block showed a homogeneous polycrystalline structure of the silicon, and no residues of silicon powder or silicon-containing slag.
• a gas containing silicon can be decomposed in the reactor. Examples of these are trichlorosilane or monosilane. Other gases containing silicon can also be used.
• the gas containing silicon is introduced into the center of the tubular reactor 2 and is surrounded by a ring flow of an auxiliary gas so that the gas containing silicon is not deposited directly on the reactor walls.
• the auxiliary gas can generally be an inert gas. Hydrogen is particularly advantageous because it also forms during the decomposition of monosilane, for example. However, noble gases such as argon and other gases such as e.g. B. nitrogen or carbon dioxide can be used.
• the mixture ratio, ie volume or molar ratio, of monosilane to hydrogen can be between 1: 0 and 1: 100.
• the specific energy requirement per 1 kg of solid silicon for the process steps of thermal decomposition and mechanical compression was less than 20 kWh.
• the space-time yield per tubular reactor 2 was more than 1 kg of silicon powder per hour.
• the wall temperature of the reactor 2 is more than 400 ° C., in particular more than 800 ° C.
• the silicon powder can be compressed in one or two stages, advantageously in two stages.
• the contact forces in the compression device 10 were between 5 N / cm and 50 kN / cm.
• the silicon powder comes into contact only with the roller jacket 25 made of ceramic, so that this is ensured.
• the high-purity powdered silicon produced by the process according to the invention has good handling properties despite its powdery ground state and is suitable for the production of pure silicon melts from which silicon blocks or silicon crystals can be produced. It was found that with the defined composition of the pyrolysis gas consisting of hydrogen and monosilane, it is possible to produce silicon in powder form with high yields and very low energy consumption.
• the process is particularly characterized in that the silicon powder can be handled, packaged and shipped separately after the process has been carried out and can thus be used with a time delay for the production of silicon blocks or silicon crystals.
• the silicon is characterized by a good melting behavior and a high purity despite the large surface and an unfavorable, small volume / surface ratio in comparison to Prime Poly silicon.
• the silicon powder produced by the thermal decomposition had a bulk density of 10 to 100 g / dm 3 .
• the silicon powder finally compacted by the device 10 had a bulk density of 100 to 1500 g / dm 3 , in particular from 200 to 1200 g / dm 3 , in particular from 250 to
• the total silicon powder contained no more than 10 19 atoms of foreign elements per 1 cm 3 silicon.
• the silicon powder consisted of crystalline particles with a primary particle size of 10 nm to 10000 nm, preferably 50 nm to 500 nm, typically about 200 nm.
• the compacted silicon powder consisted of aggregates with an aggregate size of 500 nm to 100000 nm, in particular 1000 nm to 10000 nm, typically about 4000 nm.
• the compressed silicon pieces from silicon aggregates had a largest dimension of 1 to 200 mm. They were irregular in shape, which could also be chopsticks.
• the silicon powder had a surface area of 1 to 50 m 2 / g.
• the compacted silicon powder had a total of no more than 10 17 atoms of transition metals per 1 cm 3 silicon.
• the silicon powder according to the invention has a brown color, whereas silicon granules produced by conventional processes are gray.
• the compressed silicon powder can be used for the production of polycrystalline silicon blocks for photovoltaics or for the production of silicon single crystals. Silicon wafers can be produced from the silicon according to the invention.
• the metal content of the compacted silicon powder corresponded to that of the starting product. No contamination was found. Due to the manufacturing process, the silicon did not contain any silicon oxide compounds on the surface of the silicon particles, which would have significantly increased the melting temperature of the silicon powder.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Silicon Compounds (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Mechanical Treatment Of Semiconductor (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Road Repair (AREA)
• Disintegrating Or Milling (AREA)
• Road Paving Machines (AREA)

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• 2004
  • 2004-06-04 DE DE102004027564A patent/DE102004027564A1/de not_active Withdrawn
• 2005
  • 2005-05-10 WO PCT/EP2005/005019 patent/WO2005118272A1/fr not_active Application Discontinuation
  • 2005-05-10 JP JP2007513735A patent/JP2008501528A/ja active Pending
  • 2005-05-10 DE DE502005006878T patent/DE502005006878D1/de active Active
  • 2005-05-10 EP EP05750911A patent/EP1750931B8/fr not_active Not-in-force
  • 2005-05-10 US US11/569,783 patent/US7584919B2/en not_active Expired - Fee Related
  • 2005-05-10 AT AT05750911T patent/ATE425868T1/de not_active IP Right Cessation
  • 2005-05-10 ES ES05750911T patent/ES2321016T3/es active Active
  • 2005-05-10 CN CN2005800179025A patent/CN1960852B/zh not_active Expired - Fee Related

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