Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
  • C01B33/023—Preparation by reduction of silica or free silica-containing material
  • C01B33/025—Preparation by reduction of silica or free silica-containing material with carbon or a solid carbonaceous material, i.e. carbo-thermal process
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F7/00—Compounds containing elements of Groups 4 or 14 of the Periodic Table
  • C07F7/02—Silicon compounds
  • C07F7/08—Compounds having one or more C—Si linkages
  • C07F7/12—Organo silicon halides
  • C07F7/16—Preparation thereof from silicon and halogenated hydrocarbons direct synthesis

Definitions

• the invention relates to a particular quality of metallurgical silicon with a controlled structure and containing aluminum, intended more particularly for the synthesis of alkyl or aryl-halosilanes used in the manufacture of silicones.
• Metallurgical silicon denotes the silicon obtained industrially by carbothermic reduction of silica in an electric furnace. It contains at least 98% silicon and, as main elements, iron, aluminum and calcium. It also contains a certain amount of oxygen and other elements, at a content ⁇ 0.1%, such as P, Ti, V, Ni, etc.
• the desired product being D
• selectivity of the reaction It is also important to produce the maximum quantity of silanes per unit of time, the value of the weight flow of silanes produced being called reactivity.
• Much work has been devoted to improving the reactivity and selectivity of the reaction. We have highlighted, in particular, the role played by metallic compounds present in the structure of metallurgical silicon used as raw material. This is the case for the publication of the plaintiff: T. MARGARIA, JC ANGLEZIO and C.
• the Applicant has therefore sought a means of improving the reactivity and the selectivity of the reaction by acting on the silicon grains themselves. This can be done by controlling their phosphorus content as described in international application WO 95/01303 filed by BAYER and the applicant.
• the silicone industry continues to demand silicon capable of further increasing the selectivity and reactivity of the ROCHOW reaction.
• the subject of the invention is therefore a metallurgical silicon intended for the synthesis of alkyl and aryl halosilanes, the structure of which consists of crystals of primary silicon and of intermetallic compounds essentially based on silicon, iron, aluminum and calcium and characterized in that more than 90% of the primary silicon grains have an aluminum content of between 50 and 1000 ppm.
• This structure is preferably obtained with a silicon containing overall between 0.12 and 0.30% by weight of aluminum and with a process for solidifying the silicon after casting making it possible to descend below 1200 ° C. in less than 10 s .
• the Applicant has found that, for a certain range of aluminum contents and under specific conditions for solidification of liquid silicon, it is possible to increase the aluminum content of the primary silicon crystals beyond the normal saturation threshold. 15 ppm, and to control the level of supersaturation by varying both the aluminum content of the liquid sihcium and its solidification speed, so as to obtain an increase in the reactivity of the sihcium in the ROCHOW reaction.
• a sensitivity factor RSF is determined for aluminum such that the concentration C (in atoms per cm 3 ) is equal to the product RSF x IAJ / IS I , c is to say the product of the sensitivity factor by the ratio of the intensities measured for aluminum and the silicon matrix.
• This RSF factor is obtained by averaging at least 5 measurements made on pre-implanted standards of known concentration and it is of the order of 3.3 10 23 .
• the aluminum supersaturation level of the primary sihcium increases with the aluminum content of the starting hydrous sihcium and with the speed of solidification.
• the cooling rate in particular between 1400 and 1200 ° C., also plays on the percentage of primary silicon crystals having an aluminum content of more than 50 ppm, very high speeds leading to more than 95% of supersaturated crystals. , or even at percentages close to 100%.
• a scanning electron microscope and X-ray diffraction examination of the aluminum supersaturated sihcium crystals reveals the existence of deformations in the crystals such as dislocations or shear planes. With a constant intermetallic content and identical phosphorus content in the primary silicon, it is found that the reactivity of the aluminum supersaturated sihcium is higher compared to that of a sihcium whose crystals contain the normal content of about 15 ppm solid solution.
• each of the samples was subjected to a methylchlorosilane manufacturing test under the following conditions: The tests were carried out in a glass reactor, in stirred ht, with a diameter of 30 mm, equipped with an agitator. The same amount of sihcium with the same particle distribution between 70 and 160 ⁇ m, was used in each test.
• the reaction mixture consisted of 40 g of sihcium, 3.2 g of partially oxidized copper as catalyst and 0.05 g of ZnO.
• the methyl chloride was sent to the reaction mixture, through a sintered glass disc under a pressure of 0.2 MPa. After heating the reaction medium and starting the reaction, the temperature of the system was adjusted and maintained at 300 ° C. and the quantity and the composition of the mixture of silanes formed was determined.
• P denotes the total quantity of silanes produced in g / h; MeH, Mono, T, D, PS, the respective percentages by weight of monomethyldichlorosilane (CH 3 HSiCl 2 ), tomethylchlorosilane ((CH 3 ) 3SiCl), methyltrichlorosilane (CH 3 SiCl 3 ), dimethyldichlorosilane ((CH3) 2 SiCl 2 ) and polysilanes.
• the desired product is dimethyldichlorosilane
• the selectivity of the reaction is assessed by D, while the reactivity is measured by P.
• the values indicated are the means of 4 individual measurements.
• sample 1 where the primary silicon is supersaturated with aluminum, has an increased reactivity of 6% for a selectivity identical to 0.2%.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Silicon Compounds (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1996
  • 1996-04-02 FR FR9604378A patent/FR2746785B1/fr not_active Expired - Fee Related
• 1997
  • 1997-03-24 WO PCT/FR1997/000514 patent/WO1997036821A1/fr not_active Ceased
  • 1997-03-24 AU AU22983/97A patent/AU2298397A/en not_active Abandoned
  • 1997-03-24 US US09/155,343 patent/US6391255B1/en not_active Expired - Fee Related
  • 1997-03-24 EP EP97915546A patent/EP0891297A1/de not_active Ceased

Non-Patent Citations (1)

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