Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
  • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/013—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics containing carbon
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
  • C04B35/101—Refractories from grain sized mixtures
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
  • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
  • C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
  • C04B35/573—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide obtained by reaction sintering or recrystallisation
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B7/00—Blast furnaces
  • C21B7/04—Blast furnaces with special refractories
  • C21B7/06—Linings for furnaces
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/10—Reduction of greenhouse gas [GHG] emissions
  • Y02P10/134—Reduction of greenhouse gas [GHG] emissions by avoiding CO2, e.g. using hydrogen
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to refractory products which can be used either in aluminum electrolysis cells - in particular in the form of blocks or slabs making up the edge of these cells -, either in the linings of blast furnaces or furnaces electrothermal energy.
• agglomeration and firing techniques are most often used, starting in particular from grains of silicon carbide in the case of the border blocks of the vats.
• aluminum electrolysis and in particular starting from alumina or aluminate grains in the case of lining blocks from blast furnaces and lining blocks from electrothermal furnaces.
• the methods of manufacturing refractory blocks having the essential constituent of silicon carbide aim to obtain either silicon carbide in the whole mass, or silicon carbide associated with nitride or silicon oxynitride, and these methods start from '' a mixture composed essentially of granular silicon carbide, powdered silicon and carbonaceous products, the quantity of silicon and the quantity of carbon liberated by coking being in a ratio which should promote the formation of silicon carbide associated or not with silicon nitride and oxynitride.
• the composition is normally adjusted so that the amount of silicon powder added to the starting material and the quantity of coke formed from the pitch, possibly supplemented by the addition of fine coke powder, correspond stoichiometrically, and the improvement in resistance of the refractory blocks baked in furnaces for baking carbonaceous products at final temperatures reaching 1100 to 1300 ° C is due to the fact that the framework baked binder consists of silicon carbide which arises at the higher temperatures of the baking process, by reaction of the silicon with the coke formed by coking.
• the silicon grains are protected from oxidation during heating thanks to a good covering of their surface by a binder of studied quality and the weight ratio between the silicon metal powder and the residual carbon of the pitch must be between 3/1 and 6/1.
• the heating is continued at high temperature in air or in a gas mixture containing nitrogen, and it leads to the formation of SiC from residual C and Sidebutbut at temperatures above 1100 ° C - and to the formation of Si 3 N 4 and Si 2 ON 2 - starting from from 1000 to 1100 ° C.
• the processes aiming to obtain, after firing, refractory products essentially consisting of silicon carbide - possibly associated with silicon nitride or oxynitride - from a mixture containing powdered silicon use various precautions to avoid or limit oxidation, improve the contact between the grains of silicon and the carbonaceous binder and adjust as well as possible the respective quantities of silicon and carbon resulting from coking, all this in order to favor the formation of silicon carbide, and these processes preferably use cooking temperatures over 1300 ° C, with treatment times that can exceed 24 hours.
• the methods of manufacturing refractory products composed of grains of silicon carbide agglomerated by a "carbon bond" usually employ more economical cooking conditions and in particular lower cooking temperatures of between 900 and 1150 ° C. and give usually less efficient products, for example in the case of border blocks of high intensity aluminum electrolysis cells.
• products are obtained essentially based on silicon carbide with a "carbon bond" starting from a mixture of SiC particles, from 4 to 12%. carbonaceous binder -especially brai- and from 0.5 to 10% sulfur, and by baking the products preferably between 900 and 1200 ° C.
• the role of the addition of sulfur would be twofold: the sulfur would make the pitch more fluid, and in addition it would combine with the hydrogen of the pitch in the form of H 2 S, which would promote the formation of a resin rich in carbon with from the carbon in the pitch.
• the present invention relates to a new refractory product with high crushing and tensile strength, with improved thermal conductivity, with increased electrical resistivity (100 to 300 m ⁇ .cm), with low porosity, good resistance to oxidation at air and the constituents of igneous electrolysis baths for the production of aluminum, as well as erosion by liquid iron in blast furnaces.
• This product is made up of a load of refractory grains and a binder.
• the refractory grains belong to the group comprising carbonaceous products such as anthracite, natural graphite, artificial graphite, amorphous carbon and coke, the refractory compounds usually designated by the abbreviation "RHM” (refractory hard metals), designating carbides and borides of so-called “transition” metals to which silicon is added (see, for example, BILLEHAUG.K and OYE, HA Aluminum (RFA), 56, Oct.
• RHM refractory hard metals
• RHM silicon carbide
• refractory oxides such as alumina and corundum, magnesia, silica and chromium oxide, taken separately, as a mixture or in combination, these grains being joined by a cement based on carbon residue, and metal silicon, the carbon residue coming from the coking of the base binder such as pitch or tar, thermosetting resin (formo-phenolic for example) or other organic pyrolysable binder with fo rmation of coke, and the silicon metal being in powder form, at a content of between 1 and 15.8%, and preferably between 3.2 and 10.5%.
• base binder such as pitch or tar, thermosetting resin (formo-phenolic for example) or other organic pyrolysable binder with fo rmation of coke
• the silicon metal being in powder form, at a content of between 1 and 15.8%, and preferably between 3.2 and 10.5%.
• the charge of the refractory grains can be constituted either entirely by carbonaceous grains, or by a mixture of 10 to 20% of RHM grains and 90 to 80% of carbonaceous product, or by a mixture of 45 to 100% of grains RHM and 55 to 0% carbonaceous grains. In both cases, at least part of the RHM grains and / or the carbonaceous grains can be replaced by grains of refractory oxides as defined above.
• silicon is not used in the present invention for the formation of silicon carbide as in the methods described by patent applications DE-OS 2,232,719 and FR-A 2,286,806, or for the formation of carbide silicon associated with silicon nitride and oxynitride as in the process described by patent application JP-A-55 80779/80, but the silicon remains present in the metallic state and seems to act as a reinforcing agent for the binder of the same way as gravel reinforces concrete. It is therefore understood that the present invention can be applied to the various qualities of refractory grains and in particular to carbonaceous grains, to RHM grains such as silicon carbide, to oxide grains refractory as previously defined.
• the present invention also relates to the process for manufacturing a refractory product, based on refractory grains and binder, process according to which a starting mixture is prepared, by kneading:
• R.H.M. such as silicon carbide, carbonaceous products such as anthracite, natural or artificial graphite, amorphous carbon, coke, refractory oxides such as alumina, corundum, magnesia, silica, chromium oxide, taken separately, as a mixture or in combination, the pitch or
• the manufacturing process is that used in the manufacture of carbon electrodes. It typically includes the following operations: mixing products at around 150 ° C, shaping at around 110 ° C, by a process such as press spinning, isostatic compression, pounding or vibrating, baking in an oven covered with granules of carbon. Cooking is preferably carried out between 1000 and 1090 ° C. The final silicon content is between 1 and 15.8%.
• the starting mixture consists of: - charge of refractory grains as defined above, in total 75 to 90% by mass
• metal powder 3 to 10% and the product obtained then has an Si content of between 3.2 and 10.5%.
• the invention relates to mixed refractory blocks, a part of which - for example on one side - consists of a first refractory product according to the invention and another part of which - for example the opposite face - consists of a second refractory product of a different known composition, or falling within the scope of the present invention, based on carbonaceous product or refractory oxidized compound, which makes it possible to produce linings in which each face is adapted to the particular conditions of temperature, of corrosion resistance or oxidation, or any other physical or chemical factor.
• the comparative tests in Table I below relate to four samples ⁇ 60 xh 100 mm kneaded at 150 ° C, compressed under 50 MPa and cooked 5 h at 1050 ° C under cover of carbon granules.
• Sample C outperforms Sample A which represents the industrial manufacture of carbon electrodes, both in terms of crush resistance and tensile strength as well as electrical resistivity " ⁇ ".
• sample D the major part of the crystallized SiC has been replaced by "amorphous" SiC of lower purity; the crushing resistance and the tensile strength obtained are then lower than those of C but better than those of A, which illustrates the possible advantage of using mixtures of refractory grains of various qualities for the sake of economic.
• a sample was prepared 0 60 xh 100 mm of binder baked 5h at 1050 ° C as above, starting from a mixture of 30% coal tar and 70% silicon metal powder (grains ⁇ 300 mesh, c (i.e. ⁇ 0.05 mm).
• the resistance to crushing of the cooked binder thus obtained was found to be 60.3 MPa.
• the comparative tests in Table II relate to samples ⁇ 60 x h 100 mm based on calcined alumina grains, kneaded and compressed as in Example 1 and baked 8 h at 1030 ° C under cover of carbon granules.
• SiC 14/24 (0.59 to 1.16 mm) 42.8% by mass SiC ⁇ 100 ( ⁇ 0.15 mm) 42.8%
• test piece "H” underwent a weight loss of 0.5% in this test while the carbon control test piece (like the reference sample “A” of Example 1) suffered a weight loss by 20%, c) finally, the resistance to the fluorinated bath was tested on another test tube taken from sample H: this is an electrolysis test in a bath of molten cryolite + alumina for 5 h.
• the test piece had no wear visible to the eye after this test, this result was considered excellent.
• the coefficient of expansion measured on H is close to that of the carbonaceous blocks, which allows the realization and the use in aluminum electrolysis tanks of mixed refractory blocks, for example of blocks of which a part of the volume on the inside side of the tank consists of the silicon carbide product containing silicon powder according to the invention and of which l the other part of the volume located on the side outside the tank is constituted by a conventional carbon product, the connection between the two parts being carried out by one of the connection methods known to those skilled in the art, for example by simultaneous compression of the layers of two starting mixtures (see examples 11 and 12).
• a sample I of ⁇ 235 xh 205 mm of the same composition as the sample H was kneaded and shaped in the same way, then was baked by maintaining at 1150 ° C. for 5 h, under cover of carbon granules, in the same carbon electrode baking oven.
• the crush resistance R E and I cooked at 1159 ° C and H cooked at 1050 ° C are close, which shows that the cooking of the refractory product of the invention can be carried out at a product temperature of 1150 ° C, usual maximum temperature for cooking carbon electrodes, keeping a high value of R E.
• Table III below relates to comparative tests relating to samples ⁇ 60 xh 100 mm kneaded and pressed as in Example 1 and cooked under different conditions:
• the samples JKL are all clearly better than the sample D of Example 1 prepared without adding silicon powder.
• Sample J cooked at 950 ° C is less good than sample K cooked at 1050 ° C, and L coked at 570 ° C and then cooked at 1050 ° C is a little better than K.
• This example first shows that , in the range of the usual firing temperatures of the carbon electrodes "900 ° C to 1150 ° C", the low temperatures are already of interest for the firing of the refractory product of the invention, and that taking into account the result of example 5 the whole interval "900C ° to 1150 ° C" is to be retained.
• This example also shows, in association with the previous examples, that a restricted range centered on 1050 ° C such as "1000 ° C to 1090 ° C" is preferable for the quality of the refractory product of the invention.
• Example 7 Table IV relates to a comparative test relating to samples ⁇ 60 xh 100 mm kneaded and compressed as in Example 1, and baked for 5 h at 1050 ° C., the starting mixtures of which comprise both silicon carbide and anthracite, the latter in grains ⁇ 0.2 mm with 45% of fines less than 74 ⁇ m.
• a series of blocks 165 ⁇ 165 mm in cross section and 800 mm long were made by spinning a dough having the following composition, in which the entire refractory grain consists of carbon products:
• the mixed sample "M'0 tested here is thus composed for half of a product" M “" - of the same composition as "M" - whose mixture of starting material contains both silicon carbide and anthracite with the addition of silicon powder -and for the other half of a product "0" whose starting mixture is based on silicon carbide with also a addition of silicon powder.
• the mechanical strength of the bond obtained is excellent.
• this second refractory product can for example be a product obtained from a mixture of carbon and carbon products.
• a series of mixed bricks of 668x275x120 mm was prepared by separate mixing of two mixtures P and Q (see table n ° 6), and pounding of two equal masses of P and Q, then baking for 5 hours at 1050 ° C under cover carbon granules.

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• 1982
  • 1982-12-08 FR FR8220893A patent/FR2537567B1/fr not_active Expired
• 1983
  • 1983-11-21 IN IN1430/CAL/83A patent/IN161625B/en unknown
  • 1983-12-06 EP EP19830903801 patent/EP0128165B1/fr not_active Expired
  • 1983-12-06 DE DE8383903801T patent/DE3373893D1/de not_active Expired
  • 1983-12-06 US US06/629,547 patent/US4544641A/en not_active Expired - Lifetime
  • 1983-12-06 AU AU22651/83A patent/AU578594B2/en not_active Expired
  • 1983-12-06 WO PCT/FR1983/000243 patent/WO1984002335A1/fr active IP Right Grant
  • 1983-12-06 IT IT2404683A patent/IT1167300B/it active
  • 1983-12-07 CA CA000442745A patent/CA1209593A/fr not_active Expired

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