Sintered Alumina Products

Abstract

A sintered product, Chemical analysis of the following as mass percentages relative to oxides: Al2O3: Remainder up to 100%, 0.26%≦Na2O≦4%, 0%≦Oxides other than Al2O3 and Na2O≦6%, but SiO2≦2%; The following crystalline phases, as a percentage by mass of the total amount of crystalline phases: 5%≦beta-alumina≦37%; less than 6% of crystalline phases other than beta-alumina and alpha-alumina; Remainder to 100%: Alpha-alumina The sintered product having:

Description

[Technical Field]

[0001] The present invention relates to sintered alumina products, methods for producing such products, particle mixtures and starting materials suitable for such methods, and preforms which upon sintering yield the alumina products. [Background technology]

[0002] Among refractory products, a distinction is made between fused cast products and sintered products.

[0003] Fused cast products, unlike sintered products, most often contain an intergranular glass phase that binds the grains together, as described, for example, in U.S. Patent Application Publication No. 2001 / 0019992. Therefore, the problems encountered by sintered and fused cast products, as well as the technical solutions employed to solve these problems, are generally different. Therefore, compositions developed to produce fused cast products cannot a priori be used to produce sintered products with the same properties, and vice versa.

[0004] The sintered product is obtained by mixing the appropriate starting materials and then forming the mixture into a preform and firing the preform at a temperature and for a time sufficient to achieve sintering of the preform, which can be carried out in situ in a furnace or, for products sold unsintered or in amorphous form, in a glass furnace.

[0005] Depending on their chemical composition and their mode of preparation, sintered products are intended for a wide variety of industries.

[0006] Among sintered products, alumina products are known to be used in installations for the manufacture of glass articles, in particular in distribution channels or "feeders".

[0007] There is a continuing demand for sintered alumina refractory products that have: - allowing for a reduced degree of bubbling when contacted with molten glass, thereby reducing the amount of defects in the produced glass article; It is less permeated by the molten glass, thereby making it possible to increase the service life of the product, in particular by avoiding any deterioration of its properties, and Low deformation during sintering, thereby making it possible to obtain dimensionally compliant parts and limit scrap and rework operations by machining.

[0008] One object of the present invention is to at least partially address this need. Summary of the Invention [Means for solving the problem]

[0009] According to the invention, this purpose is achieved by heating at 1350°C for 10 hours. Chemical analysis of the following as mass percentages relative to oxides: Al2O3: Remainder up to 100%, 0.26%≦Na2O≦4%, 0%≦Oxides other than Al2O3 and Na2O≦6%, but SiO2≦2%; The following crystalline phases, as a percentage by mass of the total amount of crystalline phases: 5%≦beta-alumina≦37%; less than 6% of crystalline phases other than beta-alumina and alpha-alumina; Remainder to 100%: Alpha-alumina This is accomplished by using a particle mixture of particles of a composition and crystallographic structure adapted to form a sintered article having

[0010] The particle mixture may include a binder in particulate form, preferably selected from hydraulic cement, resin, lignosulfonate, cellulose derivative, dextrin, gelatin, alginate, tylose, pectin, anhydrous phosphoric acid, aluminum phosphate, alumina hydrate, anhydrous sodium silicate, anhydrous potassium silicate, and mixtures thereof.

[0011] The particle mixture may include a shaping agent in particulate form, preferably selected from clays, plasticizers such as polyethylene glycol (or "PEG") or polyvinyl alcohol (or "PVA"), deflocculants such as alkali metal polyacrylates, polycarboxylates, polysulfonates, cement set accelerators, cement set retarders, and mixtures of these agents.

[0012] The particle mixture may preferably contain vinyl or polypropylene type fibers, preferably organic fibers, preferably in an amount of 0.01% to 0.1% by weight, preferably 0.01% to 0.03% by weight. Preferably, the average length (arithmetic mean) of these fibers is greater than 6 mm, preferably 18 to 24 mm. These fibers advantageously facilitate the removal of water during drying.

[0013] In a preferred embodiment, the particle mixture does not include fibers.

[0014] The particle mixture according to the invention can be packaged, for example, in drums or bags.

[0015] If the sintered product is sintered concrete, the particle mixture according to the invention preferably comprises: 1% to 8%, preferably 2% to 6%, of hydraulic cement, preferably alumina cement, preferably calcium aluminate cement, and 0.05% to 1%, preferably 0.1% to 0.8%, of a deflocculating agent, preferably a polycarboxylate, and / or 0% to 0.1% of a cement set accelerator and / or 0% to 0.1% of a cement set retarder Includes.

[0016] The particle mixture according to the invention advantageously makes it possible to produce a sintered product according to the invention, said sintered product having: Chemical analysis of the following as mass percentages relative to oxides: Al2O3: Remainder up to 100%, 0.26%≦Na2O≦4%, 0%≦Oxides other than Al2O3 and Na2O≦6%, but SiO2≦2%; The following crystalline phases, as a percentage by mass of the total amount of crystalline phases: 5%≦beta-alumina≦37%; less than 6% of crystalline phases other than beta-alumina and alpha-alumina; Remainder to 100%: alpha-alumina.

[0017] The inventors have discovered that sintered articles according to the invention behave very well in contact with molten glass, in particular exhibiting good resistance to bubbling and penetration by the molten glass. In addition, sintered articles according to the invention have good resistance to deformation during sintering.

[0018] The particle mixture according to the invention preferably exhibits one or more of the following optional characteristics: the particle mixture comprises, as a percentage by mass, more than 15%, preferably more than 20%, and / or less than 35%, preferably less than 30%, of particles having a size of less than 10 μm (fraction F1), the particle mixture comprises, as a mass percentage, more than 15%, preferably more than 20% and / or less than 30% of particles having a size of less than 5 μm (fraction F2), more than 80%, preferably more than 85%, preferably more than 90%, preferably more than 95%, or even 100%, by mass, of said fraction F1 and / or of said fraction F2 consist of alpha-alumina particles, the particle mixture comprises, as a mass percentage, less than 20%, preferably less than 15%, and / or preferably more than 5% of particles having a size greater than 10 μm and less than 40 μm (fraction F3), more than 80%, preferably more than 90%, by mass of said fraction F3 consists of alpha-alumina particles, the particle mixture comprises, as a percentage by mass, more than 28%, preferably more than 30%, preferably more than 32%, and / or less than 50%, preferably less than 45%, of particles having a size less than 44 μm; the particle mixture comprises, by mass percentage, more than 20%, preferably more than 25%, preferably more than 30%, and / or less than 45%, preferably less than 40%, of alpha-alumina particles having a size less than 44 μm; the particle mixture comprises, as a percentage by mass, less than 60%, preferably less than 50%, and / or preferably more than 20%, preferably more than 25%, preferably more than 30%, of particles having a size greater than 500 μm; the particle mixture comprises, by mass percentage, less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 8%, preferably less than 5% of alpha-alumina particles having a size of more than 500 μm (fraction F4), preferably alpha-alumina particles having a size of more than 200 μm (fraction F5), preferably alpha-alumina particles having a size of more than 100 μm (fraction F6), the particle mixture comprises, as a percentage by mass, more than 10%, preferably more than 20%, preferably more than 30%, and / or less than 50%, preferably less than 45%, of alumina particles having a size of more than 500 μm relative to beta-alumina (fraction F7), the fraction of particles of the particle mixture having a size of less than 50 μm comprises, as a mass percentage relative to the mass of said fraction of particles, more than 80%, preferably more than 85%, of alpha-alumina; more than 60%, preferably more than 70%, preferably more than 75%, preferably more than 80% of the particles have a size less than 2 mm; more than 40%, preferably more than 50%, preferably more than 55% of the particles have a size less than 0.5 mm; the particle mixture comprises, as a percentage by mass of the particle mixture, less than 25%, preferably less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 5% of alpha-alumina particles having a size greater than 2 mm; the particle mixture comprises, as a percentage by mass of the particle mixture, more than 5%, preferably more than 10%, preferably more than 15%, and / or less than 35%, preferably less than 30%, preferably less than 25%, preferably less than 20%, of particles having a size greater than 2 mm for beta-alumina; the particle mixture comprises, as a percentage by mass of the particle mixture, less than 30%, preferably less than 25%, preferably less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 5% of alpha-alumina particles having a size greater than 0.5 mm; The particle mixture comprises, as a mass percentage of the particle mixture, more than 8%, preferably more than 10%, preferably more than 15%, preferably more than 20%, preferably more than 25%, preferably more than 30%, more than 35%, and / or less than 50%, preferably less than 45%, preferably less than 40%, of particles having a size greater than 0.5 mm relative to beta-alumina.

[0019] To produce a sintered product according to the present invention, the starting material, including the particle mixture according to the present invention, is formed into a preform.

[0020] The present invention also relates to the starting material and the preform.

[0021] In particular, the present invention relates to a starting material having the following composition, expressed as percentages by mass: The remainder up to 100%: particle mixture according to the invention, 1% to 15% of a solvent, preferably water, 0% to 10% liquid binder, 0% to 5% liquid molding agent.

[0022] The starting materials according to the present invention may be packaged in drums.

[0023] Preferably, the preform is dry, thereby facilitating handling of the preform.

[0024] The present invention also provides a method for producing a sintered product according to the present invention, comprising the steps of: a) mixing particulate starting materials to form a particle mixture according to the present invention; b) producing a starting material according to the present invention, comprising the particle mixture and a solvent; c) shaping said starting material to obtain a preform according to the invention; d) optionally drying the preform; e) sintering said preform to obtain said sintered product. The method comprises at least the following consecutive steps: the composition of the starting materials, in particular the particle mixture, is adapted so that the sintered product obtained after step e) is in accordance with the invention, Regarding the above method.

[0025] In one embodiment, the starting materials are formed in situ, i.e., at the operating location where the product according to the invention is intended to be brought into contact with molten glass.

[0026] In one embodiment, the preform, which is preferably dry, is placed in the operating position and then sintered in situ, preferably while the furnace temperature is increased.

[0027] In one embodiment, the preform is made from dried, at least partially machined, and hardened concrete, placed in the operating position, and then sintered in situ, preferably while the furnace temperature is elevated.

[0028] The invention also relates to a preform obtained on the basis of the outcome of step c) or d) of the manufacturing method according to the invention.

[0029] Preferably, the particle mixture or sintered product according to the invention also comprises one, preferably several, of the following optional features: the amount of beta-alumina is greater than 24% and less than 35% by mass relative to the total amount of crystalline phases; a NaO content, expressed as a mass percentage relative to the oxide, of more than 1.6% and less than 2.9%; the SiO2 content is less than 1% by mass relative to the oxide; The content of oxides other than Al2O3 and Na2O is less than 2% by mass relative to the oxides; a CaO content, expressed as a percentage by mass relative to said oxides, of more than 0.3%; the amount of amorphous phase present in the sintered product is less than 3% based on the weight of the sintered product; the sintered product being in the form of sintered concrete; The sintered product has the shape of a block of more than 1 kg, an open porosity of more than 10% and less than 25%, and a density of 2.8 g / cm 3 Ultra-thin and 3.2g / cm 3 having an apparent density of less than

[0030] The chemical analysis characteristics given above for the particle mixtures or sintered products according to the invention are based on the mass of all oxides, The crystalline phase characteristics described above for the particle mixture or sintered product according to the invention are relative to the total amount of crystalline phase, The particle size characteristics mentioned above for the particle mixture according to the invention are preferably relative to the mass of the particle mixture.

[0031] Finally, the present invention relates to a glass production unit, in particular a glass furnace, comprising a part, preferably consisting of a sintered product according to the invention, preferably produced according to the method of the invention, and / or a preform, preferably obtained based on the outcome of step c) or d) of the method of the invention, respectively.

[0032] In particular, and without limiting the invention, said parts may be: Blocking of feed channels, Burner block, Consumables, such as linings, plungers, stirrers, rotors, orifice rings, feeder spouts, Mandrels used in the manufacture of glass tubes according to the Danner process; Pool Block, Superstructure parts of the supply channel, especially the coated parts.

[0033] definition Unless otherwise specified, an "oxide" is an inorganic oxide.

[0034] The oxide content relates to the total content for each of the corresponding chemical elements expressed in their most stable oxide form according to standard industry practice.

[0035] Unless otherwise specified, all oxide contents of products according to the invention are mass percentages expressed based on the oxide.

[0036] The term "beta-alumina" refers to a compound having the formula 11Al2O3·XNa2O, where 1≦X≦1.6, and having a hexagonal crystallographic structure.

[0037] Particles or powders "based" on beta-alumina preferably contain, as a percentage by weight of the crystalline phase, more than 30%, more than 40%, more than 45%, more than 50% beta-alumina. In one embodiment, particles or powders "based" on beta-alumina contain, as a percentage by weight of the crystalline phase, less than 70%, or even less than 60% beta-alumina.

[0038] The term "particle mixture" is understood to mean a dry mixture of particles (not bonded together). The term "particles" is understood to mean the solids in the particle mixture.

[0039] The term "unformed concrete" is understood to mean a particle mixture comprising a hydraulic binder that is capable of hardening after activation.

[0040] Activation is a method of hardening. The activated state conventionally results from wetting of the cast concrete with water or another liquid. During this process, the cast wet concrete is referred to as "fresh concrete."

[0041] The solid mass obtained by hardening of fresh concrete is called "hardened concrete." Hardened concrete is typically composed of a collection of coarse particles having a size between 50 μm and 25 mm bound together by a matrix that ensures a substantially continuous structure between the coarse particles, which is obtained during the hardening of the starting material after activation.

[0042] "Sintering" is the heat treatment of a preform, whereby the preform forms a matrix that binds the coarse particles of the preform together. After sintering the hardened concrete, "sintered concrete" is obtained. The size of the coarse particles of the preform, especially of the hardened concrete, is not substantially altered when the preform is sintered. Thus, in sintered concrete, the coarse particles have a size of 50 μm to 25 mm.

[0043] The term "hydraulic binder" is understood to mean a binder that, when activated, causes setting and hydraulic hardening, generally at ambient temperature. Cement is a hydraulic binder. Aluminous cement is herein considered to be a cement containing more than 60%, preferably more than 65%, Al2O3, as a percentage by mass relative to the oxide. Calcium aluminate cement is one example of an aluminous cement.

[0044] The "size" of the particles is conventionally assessed by sieving using a square mesh sieve, characterizing the particle size distribution of the fraction of particles passing through the square mesh sieve with openings equal to 150 μm, and the fraction of particles larger than the sieve, using a laser particle sorter, which can be, for example, a Partica LA-950 from Horiba.

[0045] 50(D 50 ) and 99.5(D 99.5 ) percentiles or "centiles" are the sizes of powder particles corresponding to the 50% and 99.5% mass percentages, respectively, of the cumulative particle size distribution curve of the powder particles, the particles being sorted in increasing order of size. For example, 99.5% of the powder particles, by mass, fall within the D 99.5 and 50% by weight of the particles have a size less than D 50 The percentiles may be determined using particle size distributions generated using a laser particle sizer and / or sieving operations.

[0046] The "median diameter" is 50 (D 50 ) percentile.

[0047] "Maximum size" is 99.5(D 99.5 ) percentile.

[0048] The expressions "containing a", "comprising a" or "having a" are understood to mean "comprising at least one", unless otherwise specified.

[0049] Other features and advantages of the present invention will become more apparent upon reading the following detailed description and examining the accompanying drawings. [Brief explanation of the drawings]

[0050] [Figure 1] FIG. 1 shows a schematic diagram of a device for measuring thermal deformation. DETAILED DESCRIPTION OF THE INVENTION

[0051] Manufacturing method The method for producing a sintered product according to the present invention comprises steps a) to e), which are conventional but adapted for the present invention.

[0052] In step a), a particle mixture is prepared that includes particles of a refractory oxide (ie, "refractory particles").

[0053] The particle size of the particle mixture is particularly adapted to the shaping in step c). The Andreasen or Fuller-Bolomey packing models can be used. Such packing models are described in particular in the publication entitled "Treatise on Ceramics and Inorganic Materials", CAJouenne, published by Septima, Paris (1984), pages 403 to 405.

[0054] In a preferred embodiment, the particle size of the particle mixture is adapted so that the sintered product is sintered concrete.

[0055] Preferably, in particular when the sintered product is sintered concrete, the particle mixture according to the invention preferably comprises, as a mass percentage, more than 10%, preferably more than 15%, preferably more than 20%, and less than 50%, preferably less than 40%, or even less than 35%, or even less than 30%, of particles having a size of less than 50 μm.

[0056] Preferably, at least 90% by weight of the particles of the particle mixture according to the invention having a size of less than 50 μm, especially when the sintered product is sintered concrete, have a size of less than 40 μm, preferably less than 30 μm, preferably less than 20 μm, or even less than 10 μm.

[0057] Preferably, the fraction of particles of the particle mixture having a size of less than 50 μm comprises, as a mass percentage relative to said fraction, less than 30%, preferably less than 25%, preferably less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 5% of particles based on beta-alumina.

[0058] In one embodiment, particularly when the sintered product is sintered concrete, the fraction of particles of the particle mixture having a size less than 50 μm preferably comprises alpha-alumina particles, cement particles and molding agent particles, preferably alpha-alumina particles, cement particles and deflocculating agent particles.

[0059] The particle mixture preferably contains, as a percentage by mass, less than 90%, preferably less than 85%, preferably less than 80%, of particles having a size between 50 μm and 25 mm.

[0060] Preferably, at least 90% by weight of the particles having a size of 50 μm or greater have a size greater than 100 μm, preferably greater than 200 μm, preferably greater than 300 μm, preferably greater than 400 μm.

[0061] Even more preferably, more than 80% by weight, preferably more than 90% by weight, preferably more than 95% by weight, preferably more than 99% by weight of the particles having a size of 50 μm or more have a size of more than 200 μm, preferably more than 300 μm, preferably more than 400 μm, or even more than 0.5 mm and / or less than 10 mm, preferably less than 5 mm.

[0062] Even more preferably, the particle mixture contains at least 10% by mass of particles having a size greater than 2 mm.

[0063] In a manner well known to those skilled in the art, the composition of the particle mixture is adapted to the composition desired for the sintered product to be produced. In particular, the oxides present in the particle mixture are found substantially in their entirety in the sintered product. Therefore, the composition based on the oxides is substantially the same in the particle mixture, the preform, and the sintered product.

[0064] The binder and / or the molding agent present in finely divided form which may be present in the particle mixture according to the invention are chosen in particular depending on the molding technique used during step c) of the process of the invention.

[0065] The particle mixture comprises: The following chemical analyses, expressed as percentages by mass relative to the oxides: Al2O3: Remainder up to 100%, 0.26%≦Na2O≦4%, 0%≦Oxides other than Al2O3 and Na2O≦6%, but SiO2≦2%; The following crystalline phases, as a percentage by mass of the total amount of crystalline phases: 5%≦beta-alumina≦37%; less than 6% of crystalline phases other than beta-alumina and alpha-alumina; Remainder to 100%: Alpha-alumina may have.

[0066] The particle mixture may also have one or more of the following optional characteristics relating to the composition of the sintered product according to the invention:

[0067] In a preferred embodiment, Al2O3 is preferably provided exclusively by one or more powders of alpha-alumina, beta-alumina, and optionally the hydraulic cement, and the alpha-alumina and beta-alumina crystallographic phases are substantially retained during production of the sintered product.

[0068] The starting powders are preferably mixed thoroughly to obtain a particle mixture according to the invention.

[0069] In step b), a starting material is preferably prepared from the particle mixture at ambient temperature, comprising the particle mixture according to the invention, a solvent, preferably water, and optionally a liquid binder, especially if the particle mixture according to the invention does not contain a binder in particulate form, and / or one or more liquid forming agents.

[0070] As examples of liquid binders that can be used, mention may be made, without limitation, of phosphoric acid solutions, ethyl silicate, and colloidal silica.

[0071] In one embodiment, the particle mixture according to the present invention does not contain cement. In a preferred embodiment, the particle mixture according to the present invention contains cement, and the starting material does not contain a liquid binder.

[0072] The particle mixture preferably contains, as a percentage of the mass of the particle mixture, more than 1%, preferably more than 2%, and / or less than 8%, preferably less than 6%.

[0073] In one embodiment, the starting material does not include a liquid binder.

[0074] The solvent is preferably water.

[0075] As known to those skilled in the art, the amount of solvent, preferably water, will vary depending on the shaping technique, especially in step c).

[0076] In step c), when a molding technique by casting or vibrocasting is used, the amount of solvent, preferably water, is greater than 4%, preferably greater than 5%, and / or less than 7%, preferably less than 6%, as a mass percentage relative to the mass of the particle mixture.

[0077] In step c), when a uniaxial pressing technique is used, the amount of solvent, preferably water, is greater than 2%, preferably greater than 3%, and / or less than 6%, preferably less than 5%, as a mass percentage relative to the mass of the particle mixture.

[0078] If the particle mixture includes hydraulic cement, the addition of water activates the hydraulic cement, i.e., causes it to begin to set.

[0079] When the particle mixture comprises hydraulic cement, the amount of solvent, preferably water, is preferably greater than 3%, preferably greater than 4%, preferably greater than 5%, and preferably less than 9%, preferably less than 8%, preferably less than 7%, as a mass percentage relative to the mass of the particle mixture.

[0080] The starting materials are conventionally mixed in a mixer.

[0081] In step c) the starting material is shaped.

[0082] All of the conventional methods that are used to manufacture preforms made in particular from hardened concrete can be envisaged.

[0083] The molding may involve isostatic pressing, slip casting, uniaxial pressing, gel casting, vibrocasting, or a combination of these techniques.

[0084] Preferably, the starting materials are poured into a mold.

[0085] Preferably, when the sintered product according to the invention is sintered concrete, the starting materials are poured into a mold, and the starting materials harden in the mold, in particular by solidification resulting from the reaction of the hydraulic cement with a solvent, preferably water.

[0086] Preferably, the mould is shaped so that the sintered product has the shape of a block, with all dimensions of the block being greater than 1 mm, greater than 5 mm, greater than 5 cm, and preferably less than 500 cm in all dimensions.

[0087] Preferably, the mould is shaped so that the sintered product has a mass of more than 1 kg, more than 5 kg, more than 10 kg or even more than 100 kg, and / or less than 2500 kg, or even less than 2000 kg.

[0088] After demolding, a block called a "preform" is obtained.

[0089] During molding, and in particular during solidification when the sintered product is sintered concrete, the amount of oxides, in particular the amount of alpha-alumina and beta-alumina, and their crystallographic structure are not substantially modified.

[0090] Thus, the preform according to the invention The following chemical analyses, expressed as percentages by mass relative to the oxides: Al2O3: Remainder up to 100%, 0.26%≦Na2O≦4%, 0%≦Oxides other than Al2O3 and Na2O≦6%, but SiO2≦2%; The following crystalline phases, as a percentage by mass of the total amount of crystalline phases: 5%≦beta-alumina≦37%; less than 6% of crystalline phases other than beta-alumina and alpha-alumina; Remainder to 100%: Alpha-alumina may have.

[0091] The preform may also have one or more optional characteristics relating to the composition of the sintered product according to the invention.

[0092] In step d), the preform may be subjected to a drying step to remove part of the water used for the shaping. Preferably, the drying results in a preform with a residual moisture content of less than 2%. Such steps are fully known to those skilled in the art. Any drying technique can be envisaged.

[0093] In step e), the preform is sintered to obtain a sintered product according to the invention.

[0094] The sintering is preferably carried out at atmospheric pressure, preferably with a steady temperature phase at a temperature above 1100° C. and / or below 1700° C., of duration greater than 5 hours and / or less than 15 hours.

[0095] Sintering can be carried out in situ in the glass manufacturing facility, ie after the hardened block is placed in its operating position.

[0096] In this embodiment, the mold can also be positioned so that the hardened block is in its operating position after demolding. The hardened block is then molded in situ and at least partially sintered in situ. In situ molding allows for the production of large blocks that are impossible or difficult to move later.

[0097] Sintering results in a sintered product according to the present invention.

[0098] The sintered product preferably comprises more than 98%, preferably more than 99%, preferably substantially 100% oxides based on the weight of the sintered product.

[0099] Preferably, said shaping and said sintering are carried out in a known manner by the open porosity of the sintered product is greater than 8%, preferably greater than 10%, preferably greater than 12%, preferably greater than 14%, or even greater than 15%, or even greater than 17%, and / or less than 25%, preferably less than 20%, preferably less than 18.5%; and / or The apparent density of the sintered product is 2.8 g / cm 3 More than 2.9 g / cm 3 and / or 3.2 g / cm 3 less than 3.1 g / cm 3 is less than It can be adapted to:

[0100] Preferably, in the sintered product: the Al2O3 content, expressed as a percentage by mass relative to the oxide, is greater than 94%, preferably greater than 95%, preferably greater than 95.5%, and / or less than 98.5%, preferably less than 98%, preferably less than 97.5%, and / or the NaO content, expressed as a percentage by mass relative to the oxide, is more than 0.35%, preferably more than 0.5%, preferably more than 0.78%, preferably more than 1%, preferably more than 1.4%, preferably more than 1.6%, preferably more than 1.8%, preferably more than 2%, and / or less than 2.9%, preferably less than 2.6%; and / or More than 85%, preferably more than 90%, preferably more than 93%, preferably more than 95% of the NaO is in the form of beta-alumina, and / or the content of oxides other than Al2O3 and Na2O is, as a percentage by mass relative to the oxides, less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1.8% and / or more than 0.1%; and / or the SiO2 content, expressed as a percentage by mass relative to the oxide, is less than 1.5%, preferably less than 1%, preferably less than 0.8%, preferably less than 0.7%, preferably equal to or less than 0.6%, and / or In particular when the sintered product is sintered concrete, the CaO content, expressed as a percentage by mass relative to the oxides, is more than 0.3%, preferably more than 0.5%, preferably more than 0.6%, and / or less than 2%, preferably less than 1.8%, preferably less than 1.5%, preferably less than 1.3%, preferably less than 1%, and / or the amount of beta-alumina is, as a percentage by mass relative to the total amount of crystalline phases, more than 7%, preferably more than 10%, preferably more than 15%, preferably more than 20%, preferably more than 24%, preferably more than 27%, and / or less than 35%, preferably less than 32%; and / or the amount of crystalline phases other than beta-alumina and alpha-alumina is less than 5%, preferably less than 4%, preferably less than 3%, as a percentage by mass relative to the mass of crystalline phases; and / or The amount of amorphous phase present in the sintered article is less than 5%, preferably less than 4%, preferably less than 3%, based on the weight of the sintered article.

[0101] Example The following non-limiting examples are given for the purpose of illustrating the present invention.

[0102] The following starting materials were selected for use in these examples, and the percentages given are percentages by weight. T60 tabular alpha-alumina powder, sold by Almatis Powder based on beta-alumina with the following chemical analysis, as percentages by mass: Al2O3: 95%, Na2O: 4%, other compounds: 1%, and the following crystallographic analysis, as percentages by mass relative to the crystalline phase: beta-alumina: 53%, alpha-alumina: 45%, in which the amount of amorphous phase, as percentages by mass relative to the powder under consideration, is equal to 2%. The following chemical analysis, as percentages by mass: Al2O3: 95%, Na2O: 4%, other compounds: 1%, and the following crystallographic analysis, as percentages by mass relative to the crystalline phase: beta-alumina: 53%, alpha-alumina: 45% (the amount of amorphous phase, as percentage by mass relative to the powder, is equal to 2%), and a median diameter (D) equal to 23 μm. 50 ), a fine-grained powder based on beta-alumina, Al2O3 with a mass content of more than 99.7% and a median diameter (D 50 ), a calcined alpha-alumina powder having Al2O3 with a mass content of more than 99.7% and a median diameter (D 50 ), a reactive alpha-alumina powder having Al2O3 with a mass content of more than 95%, a median diameter (D 50 ) and diameter D equal to 100 μm 90 a fine alpha-alumina powder having Median diameter (D 50 ) CA270 cement sold by Almatis, Modified polycarboxylate ether.

[0103] The part is manufactured according to the method according to the invention.

[0104] In step a), the oxide powder and the modified polycarboxylate ether are weighed and mixed to form a particle mixture.

[0105] In step b), the particle mixture and water are introduced into a mixer. After mixing for a duration of 20 minutes, the starting material is obtained.

[0106] In step c), the starting material is cast into wooden moulds to obtain preforms in the form of bricks having a length equal to 230 mm, a width equal to 115 mm and a thickness equal to 115 mm, and preforms in the form of bars having a length equal to 500 mm and a cross section equal to 40 mm x 40 mm.

[0107] After drying, the bars are used to characterize the deformation during sintering.

[0108] In step d), after demoulding and drying at 110° C. for 24 hours, the preform in the form of a brick is sintered in the following thermal cycle: Ramp from ambient temperature to 1350°C at a rate of 30°C / hour. Maintain at 1350°C for 10 hours The temperature is reduced to 500° C. at a rate equal to 30° C. / hour and then allowed to decrease naturally to ambient temperature (20° C.).

[0109] Table 1 below summarizes the composition of the particle mixture in step a) and the starting material in step b) for each example.

[0110] [Table 1]

[0111] The chemical analysis is carried out by X-ray fluorescence.

[0112] Crystallographic analysis is carried out on powdered samples using the Rietveld method on a Bruker D5000 instrument sold by Bruker.

[0113] The bubbling behavior of the sintered products of the examples when in contact with molten glass is evaluated by the following method.

[0114] outer diameter equal to 50 mm, total height equal to 50 mm, a hole concentric with the outer diameter and having a diameter equal to 30 mm; and bottom with a thickness equal to 20 mm A crucible having a sintered product brick of the example to be tested is machined.

[0115] Each crucible is filled with 30 grams of soda-lime glass powder, the median diameter of which is equal to 1 mm and the maximum size of which is equal to 5 mm and which has the following chemical analysis by mass: SiO2: 71.6%, CaO: 12.5%, Al2O3: 2%, Na2O+K2O: 12.3%, other oxides: 1.6%.

[0116] The entire crucible and glass are then placed in an electric furnace and subjected to the following heat treatment in air. Ramp to 1250°C at a rate equal to 500°C / hour, Maintain at 1250°C for 30 hours Decrease to 800°C at a rate equal to 500°C / hour, Decrease to 660°C at a rate equal to 20°C / hour, Maintain at 660°C for 5 hours The temperature is decreased to ambient temperature at a rate equal to 8°C / hour.

[0117] The ratio of the area of ​​bubbles generated during the test to the area of ​​the observed glass can be evaluated using the following non-limiting method.

[0118] After cooling, the resin is poured into the crucible so as to completely fill it, which is then cut to obtain slices having a thickness equal to 7 mm, said slices containing the vertical axis of symmetry of the crucible and having a height equal to the height of the crucible.

[0119] The section is then polished to make the glass transparent and facilitate observation, said polishing being carried out with abrasive paper of at least 1200 grit, preferably diamond paste.

[0120] An image is then taken with the aid of an optical microscope, where a light source illuminates the glass section from the backside of the microscope (backlighting). This backlighting reveals any bubbles contained in the glass. In particular, the aperture is focused so that all bubbles contained in the observed portion of the glass section are clearly visible.

[0121] The magnification used is 0.5 mm above the surface of the glass of the section. 2 is the highest magnification that allows obtaining images corresponding to , the total number of images being equal to the number of images necessary to be able to observe the entire glass surface of the section without overlap.

[0122] Next, for each section, each image is analyzed using imageJ software available at http: / / rsbweb.nih.gov / ij / according to the following method. Open the image in imageJ, Delete any past results using the "Analyze > Clear Results" function, Define the size to be measured, in other words the area, by checking only the "Area" box in "Analyze>Set measurements" and then confirming with "OK" Adjust the brightness with the "Image > Adjust > Brightness / Contrast" function, and then click "Auto"; Use the "Process > Filters > Gaussian blur" function to apply a "Gaussian blur" with a sigma (or radius) value equal to 2.00, and then confirm with the "OK" button. Convert the color / gray level values ​​to 8-bit using the "Image > Type > 8-bit" function. The image is binarized using the "Image > Adjust > Threshold > Auto" function, the "Dark Background" box is checked, the drop-down menu corresponding to the thresholding type is set to "Default", and the red thresholding color is selected using the "Red" drop-down menu ("Stack histogram" is unchecked, "Apply" is pressed, and then the window is closed); Using the "Freehand" tool, selected using the dedicated icon, define with the mouse the zone of glass to be analyzed (this zone does not have any bubbles in contact with the inner surface of the crucible); Use the "Analyze > Measure" tool to find the area of ​​the above region, i.e., Z At Measure the area value, which will be displayed in the "Area" column of the open window, record the value, and close the window. using the "Edit > Clear outside" tool to erase the image parts located outside the area of ​​the glass to be analyzed, and then using the "Edit > Selection > Select None" tool to deselect the area of ​​the glass to be analyzed that was already selected, and using the "Analysis > Clear Results" tool to erase the results; Within the area of ​​the glass to be analyzed, select areas that should not be taken into account, such as cracks that may appear during the cooling of the glass. These selections are made using the "Freehand" tool and its dedicated icon. The area Z of each of the regions i that should not be considered in the image t is calculated using the following command sequence: "Analyze > Measure", then "Analyze > Clear Results", then "Edit > Clear", then "Edit > Select > Deselect". itThis sequence is repeated i times. BT is the area Z it The sum of Use the "Process > Binary > Make Binary" tool to invert the black and white areas of the image. The bubbles will then appear black on a white background (value 255 for white, 0 for black). Some bubbles may appear as empty circles (white circles with black centers). For these bubbles, use the "Process > Binarize > Fill holes" function to convert the black center to white. Use the following command to determine the area of ​​the bubble: "Analyze > Analyze Particles..." - "Size" range: 0 to infinity, "Circularity" range: 0.00 to 1.00, "Show" range: "Nothing", then check only the boxes: "Display results", "Clear results", and "In situ Show", and click "OK". Save the results file "Results.xls" using the command "File>Save As..." Open the result file "Results.xls" and calculate the sum Z of the values ​​in the "Area" column, which represents the area of ​​each bubble in the analyzed area. Ct Forming Calculate the area of ​​the observed glass that is taken into account (the observed glass area Z At From the area of ​​the excluded area, Z Bt minus Z At -Z Bt ), Calculate the total area Zc of the bubbles (the sum of the areas determined for each image t, Z Ct ), Total area of ​​glass considered Z A -Z BCalculate the sum of the observed areas (Z) determined for each image t At -Z Bt )), Area of ​​the bubble Z C and the area Z of the glass under consideration A -Z B The ratio of Z C / (Z A -Z B ) is calculated.

[0123] This ratio characterizes the bubbling behavior of the sintered product when in contact with the molten glass.

[0124] The ability of the molten glass to penetrate the sintered product is assessed by measuring the average penetration of the molten glass into the crucible wall thickness present in the section after a bubbling test and the creation of the sections required to quantify the bubbling.

[0125] The deformation during sintering of the products of the examples was evaluated by the following method: A bar of the dried product of each example, with a length equal to 500 mm and a cross section equal to 40 mm x 40 mm, was placed in an electric furnace in a 40 x 40 x 40 mm chamber, arranged as shown in Figure 1a. 3 (the inner distance between the two supports, ie e, is equal to 400 mm).

[0126] The bars are subjected to the following heat treatment in air: Ramp to 1350°C at a rate equal to 30°C / hour, Maintain at 1350°C for 10 hours The temperature is decreased to ambient temperature at a rate equal to 30°C / hour.

[0127] The deformation during sintering is the deflection f (mm) measured for each bar, as shown in Figure 1b.

[0128] Table 2 below summarizes the characteristics obtained after sintering.

[0129] [Table 2]

[0130] A measured glass penetration equal to 20 mm means that the glass penetrated through the thickness of the bottom of the crucible.

[0131] The ratio of the area of ​​the bubbles to the area of ​​the observed glass, expressed as a percentage, is low for the products of Examples 2-5.

[0132] The ratio of the area of ​​the bubbles to the area of ​​the observed glass, expressed as a percentage, could not be determined for the product of Example 1 because there was not enough glass left in the crucible after the test.

[0133] The average penetration of the glass into the bottom of the crucible is lower for the product of Example 2 according to the invention (8% beta-alumina, average penetration of the glass into the bottom of the crucible of 15 mm), the product of Example 3 according to the invention (17% beta-alumina, average penetration of the glass into the bottom of the crucible of 10 mm), the product of Example 4 according to the invention (30% beta-alumina, average penetration of the glass into the bottom of the crucible of 3.3 mm), and the product of Example 5 not according to the invention (42% beta-alumina, average penetration of the glass into the bottom of the crucible of 2.8 mm) than for the product of Example 1 not according to the invention (0% beta-alumina, average penetration of the glass into the bottom of the crucible of 20 mm).

[0134] Finally, the deformation during sintering, measured by the deflection f, is lower for the product of Example 2 according to the invention (8% beta-alumina, deflection f equal to 6 mm), for the product of Example 3 according to the invention (17% beta-alumina, deflection f equal to 5.2 mm) and for the product of Example 4 according to the invention (30% beta-alumina, deflection f equal to 7.5 mm) than for the product of Example 5 not according to the invention (42% beta-alumina, deflection f equal to 12 mm).

[0135] Therefore, the products of Examples 2, 3 and 4 according to the invention are the best products, showing a low degree of bubbling when in contact with soda-lime glass, a low average glass penetration value and little deformation during sintering.

[0136] Of all these, the product of Example 4 is the preferred product.

[0137] Of course, the invention is not limited to the described embodiments, which are provided by way of illustrative and non-limiting examples.

[0138] In particular, products according to the present invention are not limited to any particular shape or size. The present invention may be configured as follows. [Section 1] A sintered product, Chemical analysis of the following as mass percentages relative to oxides: Al 2 O 3 : Remaining up to 100%, 0.26% or less Na 2 O≦4%、 0%≦Al 2 O 3 and Na 2 Oxides other than O≦6%, except for SiO 2 ≦2%、 The following crystalline phases, as a percentage by mass of the total amount of crystalline phases: 5%≦beta-alumina≦37%; less than 6% of crystalline phases other than beta-alumina and alpha-alumina; Remainder to 100%: Alpha-alumina Over 10% open porosity The sintered product having [Section 2] Item 1. The sintered product of item 1, wherein the amount of beta-alumina is greater than 15% and less than 35% by mass relative to the total amount of crystalline phases. [Section 3] Item 3. The sintered product of item 2, wherein the amount of beta-alumina is greater than 24% and less than 32% by mass relative to the total amount of crystalline phases. [Section 4] Na 2 Item 4. The sintered product according to any one of items 1 to 3, wherein the O content is greater than 1.4% and less than 2.9% by mass relative to the oxide. [Section 5] SiO 2 Item 5. The sintered product according to any one of items 1 to 4, wherein the content is less than 1% by mass of the oxide. [Section 6] Al 2 O 3 and Na 2 6. The sintered product according to any one of items 1 to 5, wherein the content of oxides other than O is less than 2% by mass relative to the oxides. [Section 7] 7. The sintered product according to any one of items 1 to 6, wherein the CaO content is greater than 0.3% by mass relative to the oxide. [Section 8] Item 8. The sintered product according to any one of items 1 to 7, wherein the amount of amorphous phase present in the sintered product is less than 3% based on the mass of the sintered product. [Section 9] Item 9. The sintered product according to any one of items 1 to 8, which is in the form of sintered concrete. [Section 10] Block shape over 1 kg, open porosity less than 25%, and 2.8 g / cm 3 Ultra-thin and 3.2g / cm 3 Item 10. The sintered product according to any one of items 1 to 9, having an apparent density of less than 1000 kJ / cm. [Section 11] 11. The sintered product of any one of claims 1 to 10, having an open porosity of more than 12%. [Section 12] Na 2 Item 12. The sintered product according to any one of items 1 to 11, wherein the O content is less than 2.6% by mass percentage relative to the oxide. [Section 13] Na 2 Item 13. The sintered product according to any one of items 1 to 12, wherein the O content is greater than 1.6% by mass percentage relative to the oxide. [Section 14] A method for producing a sintered product according to any one of items 1 to 13, a) mixing particle starting materials to form a particle mixture; b) forming a starting material comprising the particle mixture and a solvent; c) shaping the starting material to obtain a preform; d) optionally drying the preform; e) sintering said preform to obtain said sintered product. The method comprises at least the following consecutive steps: The composition of the starting materials is adapted so that the sintered product obtained after step e) complies with any one of items 1 to 13; The method. [Section 15] 15. The method of claim 14, wherein the preform is placed in the operating position and then sintered in situ, preferably while the furnace temperature is increased. [Section 16] 16. The method of claim 14 or 15, wherein in the particle mixture, the fraction of particles having a size less than 50 μm comprises, as a mass percentage of the fraction, less than 30% of particles relative to beta-alumina. [Section 17] 17. The method of claim 16, wherein the fraction of particles having a size less than 50 μm comprises, as a mass percentage of the fraction, less than 20% of particles relative to beta-alumina. [Section 18] 18. The method of claim 17, wherein the fraction of particles having a size of less than 50 μm comprises, as a mass percentage of the fraction, less than 10% of particles relative to the beta-alumina. [Section 19] Item 19. The method according to any one of items 14 to 18, wherein the particle mixture comprises more than 20% of the sintered product, preferably sintered concrete, by mass, particles having a size of less than 50 μm. [Section 20] Item 20. The method according to any one of items 14 to 19, wherein the particle mixture comprises, by mass percentage, more than 28% of particles having a size of less than 44 μm. [Section 21] Item 21. The method of item 20, wherein the particle mixture comprises, by mass percentage, more than 30% and less than 50% of particles having a size less than 44 μm. [Section 22] 22. The method of any one of paragraphs 14 to 21, wherein the particle mixture comprises, by mass percentage, more than 20% alpha-alumina particles having a size of less than 44 μm. [Section 23] 23. The method of claim 22, wherein the particle mixture comprises, by mass percentage, more than 25% and less than 45% alpha-alumina particles having a size less than 44 μm. [Section 24] 24. The method of claim 22 or 23, wherein the particle mixture comprises, by mass percentage, more than 30% alpha-alumina particles having a size less than 44 μm. [Section 25] 25. The method of any one of paragraphs 14 to 24, wherein the particle mixture comprises less than 25% alpha-alumina particles having a size greater than 2 mm, as a mass percentage of the particle mixture. [Section 26] 26. A preform obtained as a result of step c) or step d) of the method according to any one of items 14 to 25. [Section 27] 26. The preform of claim 25, wherein the preform is made from dried, at least partially machined, and hardened concrete. [Section 28] A glass producing unit, particularly a glass furnace, comprising or consisting of a part comprising the sintered product according to any one of items 1 to 13, or produced by sintering the preform according to item 26 or 27. [Section 29] The parts are: Channel blocks of supply channels, Burner block, Linings, plungers, stirrers, rotors, orifice rings, feeder outlets, Mandrels used in the manufacture of glass tubes according to the Danner process; Pool Block, Supply channel superstructure parts Item 29. The glass producing unit according to item 28, selected from the group consisting of:

Claims

1. A sintered product, Chemical analysis of the following as mass percentages relative to oxides: Al ２ O ３ : Remaining up to 100%, 0.26%≦Na ２ O≦4%、 0%≦Al ２ O ３ and Na ２ Oxides other than O≦6%, except for SiO ２ ≦2%, The following crystalline phases, as a percentage by mass relative to the total amount of crystalline phases: 5%≦beta-alumina≦37%, less than 6% of crystalline phases other than beta-alumina and alpha-alumina; Remainder to 100%: alpha-alumina Over 10% open porosity The sintered product having

2. 2. The sintered product of claim 1, wherein the amount of beta-alumina is greater than 15% and less than 35% by mass as a percentage of the total amount of crystalline phases.

3. 3. The sintered product of claim 2, wherein the amount of beta-alumina is greater than 24% and less than 32% by mass as a percentage of the total amount of crystalline phases.

4. Na ２ 4. The sintered product of claim 1, wherein the O content, expressed as a percentage by mass relative to the oxide, is greater than 1.4% and less than 2.9%.

5. SiO ２ 5. The sintered product according to claim 1, wherein the content, as a percentage by mass relative to the oxide, is less than 1%.

6. Al ２ O ３ and Na ２ 6. The sintered product according to claim 1, wherein the content of oxides other than O is less than 2% by mass relative to the oxides.

7. 7. A sintered product according to any one of claims 1 to 6, wherein the CaO content, as a percentage by mass relative to said oxides, is greater than 0.3%.

8. 8. The sintered product of claim 1, wherein the amount of amorphous phase present in the sintered product is less than 3% based on the mass of the sintered product.

9. The sintered product according to claim 1, the sintered product is composed of a collection of coarse grains having a size between 50 μm and 25 mm bound by a matrix that ensures a continuous structure between the coarse grains, and the CaO content, as a percentage by mass relative to the oxide, is greater than 0.3% and less than 2%. The sintered product.

10. Block shape of more than 1 kg, open porosity less than 25%, and 2.8 g / cm ３ Over 3.2 g / cm ３ 10. The sintered product of any one of claims 1 to 9, having an apparent density of less than 1000 kJ / cm.

11. A sintered product according to any one of claims 1 to 10, having an open porosity of more than 12%.

12. Na ２ 12. A sintered product according to any one of the preceding claims, wherein the O content, as a percentage by mass relative to the oxide, is less than 2.6%.

13. Na ２ 13. The sintered product of any one of claims 1 to 12, wherein the O content, as a percentage by mass relative to the oxide, is greater than 1.6%.

14. A method for producing a sintered product according to any one of claims 1 to 13, comprising the steps of: a) mixing particle starting materials to form a particle mixture; b) forming a starting material comprising the particle mixture and a solvent; c) shaping the starting material to obtain a preform; d) optionally drying the preform; e) sintering the preform to obtain the sintered product. The method comprises at least the following consecutive steps: The composition of the starting materials is adapted so that the sintered product obtained after step e) is in accordance with any one of claims 1 to 13. The method.

15. The method of claim 14, wherein the preform is placed in an operating position and then sintered in situ.

16. 16. The method of claim 14 or 15, wherein the particle mixture comprises a fraction of particles having a size of less than 50 μm, said fraction comprising less than 30% by mass percentage of particles based on beta-alumina.

17. 17. The method of claim 16, wherein the fraction of particles having a size less than 50 μm comprises less than 20% by mass percentage of the fraction of particles based on beta-alumina.

18. 18. The method of claim 17, wherein the fraction of particles having a size less than 50 μm comprises less than 10% by mass percentage of the fraction of particles based on beta-alumina.

19. 19. The method according to any one of claims 14 to 18, wherein the particle mixture comprises more than 20% by mass of particles having a size of less than 50 μm.

20. 20. The method of any one of claims 14 to 19, wherein the particle mixture comprises, as a mass percentage, more than 28% of particles having a size less than 44 μm.

21. 21. The method of claim 20, wherein the particle mixture comprises, by mass percentage, more than 30% and less than 50% of particles having a size less than 44 μm.

22. 22. The method of any one of claims 14 to 21, wherein the particle mixture comprises, as a mass percentage, more than 20% of alpha-alumina particles having a size less than 44 μm.

23. 23. The method of claim 22, wherein the particle mixture comprises, by mass percentage, greater than 25% and less than 45% alpha-alumina particles having a size less than 44 μm.

24. 24. The method of claim 22 or 23, wherein the particle mixture comprises, by mass percentage, more than 30% of alpha-alumina particles having a size less than 44 μm.

25. 25. The method of any one of claims 14 to 24, wherein the particle mixture comprises, as a mass percentage of the particle mixture, less than 25% of alpha-alumina particles having a size greater than 2 mm.

26. A method for producing a preform, comprising: a) mixing particle starting materials to form a particle mixture; b) forming a starting material comprising the particle mixture and a solvent; c) shaping the starting material to obtain a preform; The method comprises at least the following consecutive steps: The composition of the starting materials is adapted so that the preform is adapted to give, after sintering, a sintered product according to any one of claims 1 to 13. The method.

27. The method comprising: After step c), d) drying the preform; and at least partially machining; The process includes the steps of: and obtaining a hardened concrete composed of a collection of coarse particles having a size between 50 μm and 25 mm bound by a matrix. wherein the matrix ensures a continuous structure between the coarse grains, and the CaO content is greater than 0.3% and less than 2% by mass relative to the oxides; 27. The method of claim 26.

28. A glass producing unit comprising a part comprising or consisting of a sintered product according to any one of claims 1 to 13.

29. The parts are: Channel blocks for supply channels, Burner block, Linings, plungers, stirrers, rotors, orifice rings, feeder outlets, Mandrels used in the manufacture of glass tubes according to the Danner process; Pool Block, Supply channel superstructure parts 29. The glass producing unit of claim 28 selected from the group consisting of:

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