SYSTEM AND PROCEDURE FOR REGULATING LIQUID SILICON CASTING.

Description

PLANT TITLE AND PROCEDURE FOR SLOTHING THE CASTING PI SILICON LI3JIDD . PRIORITY U. S .4 .- SUN. BREV. N.- ”41.409 OF 12 OCTOBER 1977 SEPTEMBER 1985 Rome, there................................................................................. >-e^« - T vgii 30814 AZ / fc Register A Protocol no 28434 A / 78 MINISTRY OF INDUSTRY, COMMERCE AND CRAFTS Provincial Office of Industry, Commerce and Crafts of Milan COPY OF THE MINUTES OF FILING FOR INDUSTRIAL INVENTION PATENT The year 1978 on the FIVEth day of the month of OCTOBER at ten o'clock and twenty-four minutes JaDina_ ffESTINGHOUSE ELECTRIC CORPORATION created: with US nationality in Pittsburgh, Pennsylvania (USA) jtajueum Via through the agent of the International Patent Technical Office Eng. A. ZINI and with domicile for legal purposes in Milan - Piazza Castello 1 at the agent's office has presented to me, the undersigned: r, 1 u . - MAIN - Stamped application for the granting of a patent for an INDUSTRIAL INVENTION xaatniBaxft having as its title: SYSTEM AND PROCEDURE FOR REGULATING THE CASTING OF LIQUID SILICON Priority of patent application in: USA No. 841,409 of October 12, 1977 duquesx&xxBESEsaixsBC accompanied by: - Description in duplicate of 16 pages of writing. - Drawings, plates no. 3 in duplicate. -1 hectaresTIJiÌRBBJBER - Declaration reference to Power of Attorney. - Document Oi priority' and Italian translation with reservation - Authorization or deed of transfer. with reservation - QiCbiaacxixKaaDBtseKxxaauuDxiDxxix^faaaeBsateaxaBXSBieBXzaeseaBC - Proof of payment into postal account no. 00668004 in the name of the Tax and Concession Registry Office of Rome of L7Q.5QQ issued by the Milan Post Office 15 on 5 October 197θ no. - Stamp duty of L. 2,000 The application, descriptions and drawings listed above have been signed by the applicant and countersigned by me and stamped with the official seal. THE DEPOSITOR For a copy compliant with the original The OFFljClAL Pietro Messine (for the Director Federico Nappi) THE HEAD OF THE OFFICE / sffcWl (Dr. Renato ob.u xuxsxxko «wmcjo τιπββτμγα μ^αβτι»ιαβατο Patent and Trademark Office of the United States, residing in Pittsburgh, Pennsylvania (USA), represented by Alessandro Zitti, Piasse Castello 1, Milan, where she has her domicile, hereby requests that the certificate for an industrial invention be granted for an invention entitled: •PEfi BSGOLABB POURING PLANT LIQUID SILICON The applicant declares that it intends to assert the priority rights of the U.S. patent application. I® 841.409 of 12 October 1977 ' Attach for this purpose: 1. Description in duplicate 2. Drawings No. 3 tables in duplo 3* Reference to the Attorney General's Office 4. Proof of payment of the taxes 5. A 2,000 L stamp duty for the certificate 6. A priority document with translation subject to reservation 7. An assignment of priority rights subject to reservation Milan, 5 October 1978 284 34A / 78 With perfect observance p. VSSXIlfi&ODSE ELSCTKIC CGRPQEXTIOI :C-| Ί η V'pfl »*. TP3';'.7'T ! 7 5' ;E':TT DESCRIPTION of the industrial invention entitled: SYSTEM AND PROCEDURE FOR REGULATING THE CASTING Li ί i {LIQUID SILICON THE I ! of the Westinghouse Electric Corporation, of U.S. nationality, with headquarters in Pittsburgh, Pennsylvania I .( 1' .5 . A,3 5 QT'f. 1978 'filed on: 284 34A / ig ZgS3o_mÌA .pbssrizmb The present invention relates to means for regulating the pouring of liquid silicon. When using electric air heaters! the trio for high-capacity silo production! However, there are certain problems with low-cost solar power. This is particularly true when higher production rates are required in advance. I ! I ! Π and 90 kg per hour. For example, means must be provided to regulate the flow of molten silicon in ingot casting machines as well as to act on the silicon flow without mechanically movable means. Furthermore, there is a problem of working in such a way as to regulate the flow rate at high temperatures. Finally, where sodium chloride is a gas produced in the production of liquid silicon, there is the problem of preventing this gas from contaminating the cast silicon ingot. —2~~ GEV-ΤΓ 'ί·\ΓΓ jaì < 1 j It has been discovered - according to the present invention that *L ì ! The above problems can be overcome by a liquid silicon melt control mechanism comprising an air heater having spaced upstream and downstream tubular electrodes forming the an arc chamber, means for producing an electric arc in the space between the electrodes, means for injecting a gas into the arc chamber through the space extending within the arc chamber, means for feeding into the arc stream a quantity of a reducing metal or gas, means for introducing a silicon compound into the stream to produce a mixture of liquid elemental silicon and a salt of the reducing metal, means for separating the liquid silicon and the salt, a collection vessel for the liquid silicon and having a tapping hole for discharging liquid silicon therefrom, regulating means associated with the tapping hole for regulating the flow rate of silicon through the tapping hole and including a tubular constricted opening.Furthermore, in one version of the invention, the regulating means comprises cooling means for solidifying liquid silicon in the tapping hole and heating means for melting the liquid silicon. ··· ·-3AΑΈ7;A*. ·. . . ..Xà: ( i ! I give ael tapping hole. In another version of the[ In the invention, the control means comprises a liquid silicon opening having a cross-sectional area that is a function of the height of the liquid silicon above the opening, such that the silicon flows when the hydrostatic pressure exceeds the surface tension between the silicon and the opening. The present invention also comprises a method of regulating the function of liquid silicon consisting of ♦ ··· ( eee·' eee e • And · ·.·· • · e ·*· • · tee te,a) in providing an air heater having spaced electrodes and forming an air chamber in communication with a reaction chamber, b) in striking an electric arc in an axial gap between the electrodes, e) in introducing an arc gas OU. of hydr oe„o .d u. ... inert ettr.ver„ l-intef bspedines to form an arc current, d) in the ali I) try to feed into the air stream a quantity of a reductant selected from the group consisting of hydrogen and a quantity selected from the group consisting of a metal, dope, and a mixture thereof, e) feed into the air stream a quantity of silicon halide intended to react with the reductant to produce reaction products comprising liquid silicon or a gaseous salt of the reductant, f) separate the - ' 7 liquid silicon from the gaseous salt of the reducing agent, g) in ' 1 depositing the liquid silicon in a collection vessel which has a tapping hole, eh) in equipping the tapping hole with restrictors to regulate the flow rate of the liquid silicon coming from the vessel. The advantage of the mechanism and method of the present invention lies in the fact that a valve without moving parts is designed to tap Liquid silicon with the associated advantage of separating liquid silicon from the resulting by-products. THE The reduction of a material and which acts as a source of silicon dioxide. _______________ .....________________ Figure 1 is a working diagram for the prò • ··* eee and and liquid silicon solution; ________ _______________ Figure 2 is a perspective view with parts A cross-section showing a three-phase ar so heating system; ---------. Figure 3 is a partially axial elevation view. Figure 4 is a vertical sectional view of another embodiment of the present invention. According to the present invention the process consists of a) having an arc heater having elec; -5trodes spaced apart and forming -an air chamber in C£ prunic action with a reaction chamber, b) by striking an electric arc in an entire axial gap between the electrodes, e) in introducing an arc gas selected from the «group» consisting of hydrogen and a mixture of hydrogen and inert gas through the gap to form an arc surge, d) by feeding into the arc current a quantity of a reducing agent selected from the group consisting of a metal, hydrogen and their mixture, e) in feeding in the arc current uaa quan: The silicon halide tea so that it reacts with ι the LI reduces to produce reaction products that make liquid silicon a gaseous salt of the reducing agent, f) in separating the liquid silicon from the gaseous salt of the reducing agent, j g) depositing the liquid silicon in a collection vessel having a tapping hole, and h) in equipping the tapping hole with restrictors to regulate the flow rate of liquid silicon and coming from the container* ί eee ··. ! Although the above process describes the introduction of hydrogen with or without an inert gas such as argon -6_ p eli a fase (c), a l'uso di un reductante metallicap i like sodium or magnesium in step (d), it is understood that either step (e)—or step (d)—may be omitted. Using a metallic reducing agent or hydrogen as an alternative to reduce silicon halide to the ί state |of liquid silicon. However, the preferred method is to use both hydrogen and a metallic reducing agent, because the process is more efficient. For example, when using hydrogen alone without the metallic reducing agent, excessive amounts of hydrogen are required. The means for carrying out this process are schematically described in figure.4 and acniprandana un separa·_· · '·? cyclone reactor 11 which is supported has associated structures which include a reactor reaction chamber 13, at least one and preferably one set of three-phase arc heaters 19, a first venting or outlet means 47 for the simultaneously produced gases, and a second venting or outlet means 19 for the liquid silicon. .......... ......................... ........... _ The arc gas is introduced into the plant at Inlet 21 into the arc heaters 15. The arc gas, together with the other products including HCl (g) or metal salt, exits the reactor through the vent and is connected to a cyclone or separator 23 of the typical dense core type to separate the arc gas from Hd. -7 0 metallic gale, The arc gas is returned through a .25 compressor in the ri ac to the arc processes... in inlet 21. The HC1 or metal salt comes out of the se The reactor 23 leads to an electrolytic cell 31 for dissociation into hydrogen or metal and chlorine. The hydrogen or metal is passed to inlet 35 where it is produced in reactor 13. The chlorine from cell 31 is conveyed to a chlorinator 37, where, together with a silica-bearing material, such as SiO2, and a carbonaceous material, such as coke, they react to produce silicon dioxide, impurity chlorides, and carbon oxides. The gas mixture produced in the chlorinator proceeds to a separator 43 to purify the silicon tetrachloride which is transferred to the reactors 13 in the furnace 51. ________ ... As shown in Figure 2, one or more, and preferably three, arc heaters 15__are of the same construction and operation as that described in U.S. Patent No. 3,765,870, entitled: Method of Directly Reducing Ore by Use of an Arc Heater, the inventors of which are M.G. Pey and Geòrgie A. Kemeny. Due to the completeness of that patent, the description of the arc heaters 1 is limited here to the construction and operation of the arc heaters 15__. - T-, » * ι -8!.. - Η - , :ìrì complain. The arc heaters 15 (figure 2) are each a self-contained alternating current device. scalable, single-phase capable of having power levels up to approximately 3500 Kilowatts, or up to 10,000 kW for a three-phase system insulation; In the practical implementation of the present invention, it is preferred to provide three arc heaters, one for each of the three phases of the AC power supply. ì n arc heater 15 has two electrodes of i annular copper 59* which are separated by a space or gap 63 of about one millimetre between them I receive a power source at a frequency, line, of approximately 4fcV; An arc 65 strikes in space 63 and the incoming supply gas 67 immediately blows the arc from the space into the interior of the arc chamber 69. The supply gas 67 must be compatible with the Silicon and may be one of the gases selected from the group consisting of inert gases, hydrogen, halides of ; f silicon, and their mixtures. The arc 65 rotates at a speed of about 1000 rpm by interaction with a magnetic field with a current ΐ te continues made from 71*73 field coils mounted] 23 internally. Speed ​​gives a workers' performance• · ·· ·· M' -L -9tive very high for an apparatus of this type and the elongated arc 65 is finally projected from the gap towards and possibly into the reaction chamber 13- The feed material is in- .... transduced through entrance ports 35, 51 which are generally downstream of electrode 61 so that the materials enter the elongated arc 65 as shown in FIG. 2. _______________________________ _____________________ , e e « :· i e · · « a metal reducing the red metals » such as sodium and magnesium, and / or a drug. However, silicon halide, silicon tetrachloride preferred, may be used; any other halide such as silicon tetrabromide may be used._______ The molten silicon product created by the arc heater in an exothermic reaction is in SCCOrd with the Sidl 4 + 4Na(-V-)----4 Nacl (v) + Si (1)___(1) .Sid£~*.~2H 2__Si » 4Ncl______________________(2) The reactor system, comprising the three arc heaters 15 (figure 2), directs the arc 65 into a pressure chamber 7 into which the... is injected. reducing gas or metal r <jome sodio o di prefj renna come spruzzo liquido attraverso un ingresso . 5. Within chamber 75 the metal 77 enters the arch 65 Tcrq;P|A -10-- '•'Π· .ί where it combines with the gas 67 of the arc current; which is preferably a mixture of hydrogen and argon, from where it is pushed downstream (to the right as seen in figure 2). As shown in figure 3, the pressure chamber i I :75 is connected by the reaction chamber or reactor | ί ί to a cyclone separator 11. Inlet ports 51 are arranged in a veil of the chamber 75 for the injection of the silicon halide. The halide Silicon combines with sodium or hydrogen in con Γ* forms with formulas (1) and (2). 'ii The resulting products of the above reactions; are projected tangentially into the cyclone separator 11 from where the gaseous products including sodium chloride and hydrochloric acid are discharged at Through the outlet means 17. The liquid silicon j is collected on a liner 87 within the separator and flows downward into the lower end where it is collected in the vessel 89. In accordance with the present invention, the vessel 89 comprises a bottom wall having an inclined surface 91 and a constricted tubular opening 93 which serves as a tapping hole for the vessel 89.' i A means for melting silicon within the aperture 93 which includes an HF coil 97 is provided to raise the temperature of the silicon to a value above the • a_a· ·* '**· · . ··* ·* * ·· ·· • •tea ae ••aa a · ···· ♦ ··· a · aaa -11' 'l· IMG. melting point for discharging silicon from the reactor 89. Additionally, the RF coil 97, being water-cooled, is also available for cooling the reactor. ^silicon within the 93 aperture at a temperature below the melting point. As shown in fig. THE In |ra 3, a solidified layer 99 of silicon can be extended from the inner wall of the vessel towards the i low above the inclined surface 91 and through the opening 93. The control of the silicon casting is maintained by solidifying or melting a central portion 101 of silicon within the opening 93 by the operation of the water-cooled coil 97 and the RF coil 99, whereby the liquid silicon 95 can be poured or tapped from the vessel 89 into an ingot mold (not shown). As the size of the solid silicon axis increases, the resistance to the coil Β.E. increases to improve the coupling. The Rf* coil thus heats the center of the solidified silicon where the field lines converge, allowing the silicon outlet orifice to vary in diameter, thus regulating the flow rate. The opening is thus always filled with solid or liquid, Eoa aai open to the movement of NaCl vapor towards the the silicon ingot formed below, and so are THE THE I prevented the harmful effects of the contaminants of the si·· ♦ · •r '· ·· « « ♦ ♦ · ·· *··· ···· a · aa · -12'XX 1 lyceum for solar cells. i ί | Another version of the invention is shown in i Figure 4, where like numbers refer to like parts, A plate 105 having circular holes 107 is disposed across the cross-section of the tubular opening 93. The surface tension of the I i molten silicon 95, indicated by a protruding portion 109 of the liquid silicon, prevents its passage through the holes 107 until a sufficient hydrostatic pressure of liquid silicon builds up above the plate 105. The expression in play, I is the formula: . « ·· • . ··· • ·· ·. and « * and « • * · · · • • • • ··.. . ; · • _· • * and · · • and « • • .. . • * • 4 (3) where * surface tension of silicon ..... rc = radius of the hole __________ Θ = wetting angle ........ _ —.density of silicon ......... ... g » gravity constant h = height of the silicon where the hydrostatic pressure exceeds the surface tensile pressures, and the silicon flow begins. During operation, the plate 105 prevents the liquid silicon 95 from flowing through the aperture into the ingot below. Once 'VFtTl ι i [As the critical height h* is exceeded, liquid silicon will flow out until the height falls below the critical height h. Thus* there is always a molten silicon bath in the casting mouth or opening maintained by the RE 99 coil. In this way* the bypass passage of silicon vapours is prevented NaCl and contaminants . . .... Therefore this silicon flow rate regulation mechanism avoids problems that would be encountered if more complex means were used! Traditional flow control systems* such as a gate valve. Avoiding mechanical parts in contact with the liquid silicon prevents contamination of the final product by sodium chloride and other contaminants.

Claims

1. CLAIMS -13> · · · • and - ». T. · · · · · · · 1. Liquid silicon casting mechanism comprising an arc heater which has electrodes spaced upstream and downstream forming an arc chamber, means for producing an electrical arc. [With the space between the electrodes of the means for injecting gas into the reaction chamber through the space to form an arc current extending into and downstream of the chamber, the means for supplying gas into the reaction chamber - to bent into the arc current a quantity of a reducing agent, some means for introducing a compound of silos. this in the arc stream to produce a mixture of liquid elemental silicon and a reducing salt, means for separating the liquid silicon and the salt, a collecting vessel for liquid silicon having the hole. tapping to discharge liquid silicon therefrom, and the regulating means associated with the gold. tapping to regulate the flow rate of the silicon through this hole. .........

2. Mechanism according to rev. 1 wherein the tapping hole comprises a ribbed tubular opening.

3. Mechanism according to rev. 2 wherein the adjusting means comprises cooling means for solidifying the liquid silicon in the bore. tapping, and heating means, for melting the liquid silicon in the tapping furnace. _______ ....

4. Mechanism according to rev. 2, in which the adjustment means comprises a passage opening for the liquid silicon having a cross-sectional area which is an anointing of the height of the liquid silicon above the opening whereby the silicon flows out when the hydrostatic pressure exceeds the surface tension force of the silicon that is across the aperture. -15UfHSìj ’HG G-ii.'i ... do you Γ? IMG. ALESSAÌNLG. λ.,. ί 5. Mechanism according to rev. 3, wherein the silicon compound is silicon tetrachloride. ! the 6. Mechanism according to rev. 5, in which the ridup. The bridge is selected from a group consisting of an alkali metal, alkaline earth metal, hydrogen and mixtures thereof. | 7 "Mechanism according to rev. 6, wherein the cooling medium comprises walls cooled with li. liquid.

8. Mechanism according to claim 6, in which the heating medium comprises a means of heating by induction.

9. Method for regulated casting of silicon Ιίςιμί. do consistent; _ ________ ... ... ... ............. a) in providing an arc heater having and r readrodes spaced apart and forming an arc chamber in communication with a reaction chamber , b) in striking an electric arc in an axial space between the electrodes, c) in introducing an arc gas selected from the g * u £ po consisting of hydrogen and a mixture of hydrogen and an inert gas through the space to supply an elongated arc current, d) in feeding into the arc current a quantity of a reducing agent chosen from the consistent group. · · · • * ·· ·· ··· fi -16UFHCIO ΤΕΤΝ'ΤΌ ί \ ί ~. \ 'Λ7Ι τ ·. LoSΑι'ί lj' IV. E EEEVETP RO ΖίΝί of a metal, hydrogen, and a mixture thereof, a) in feeding into the arc current a quantity of silicon halide which can react with the reductant to produce reaction products comprising liquid silicon and a gaseous salt of the reductant, f) in separating the liquid silicon from the gaseous salt of the reductant, and from the arc gas r g) in depositing the liquid silicon in a collection vessel having a tapping hole, and il) in providing the tapping hole of a medium. ii choke to regulate the flow of liquid silicon from the vessel. _ 10. A method according to claim 9 wherein the constricting means comprises an opening or constricted openings whose area in. cross section is a function of the height of the silicon, where the silicon flows out when the hydrostatic pressure exceeds the surface tension forces of the silicon penetrating (between through the opening or openings.

11. Method according to rev. 9, wherein the constriction means comprises means for heating the silicon to a liquid state and cooling the silicon to a solid state. UFHCIO TE'IN ·· · · • ♦ ·· a · · * / / · * ···· • j * 1 * ·· * * • · • a a · a a a a • · · ”· aaaa r. ·: · · ·. . · · · ·. .... · •. · · ·, · • · ««. ····· .... ..— · .. ..... . .... ····. «« ... * p. WEJTINGHOUSE ELECTRIC CORPORATION ππππππ * 843 4A / , no