FR2963786A1 - Particulate mixture, useful to prepare sintered product, comprises a matrix fraction and aggregate respectively constituted of particles, and grains, where the particulate mixture comprises a chromium oxide - Google Patents

Abstract

Particulate mixture comprises a matrix fraction and aggregate respectively constituted of particles having a size of = 50 mu m, the matrix particles and particles having a size of greater than 50 mu m, grains, the matrix fraction having more than 10 mass% to less than 45 mass% of the particulate mixture, where the particulate mixture comprises a chromium oxide content of 10-80 wt.% on the oxide base of the refractory mixture, and the matrix fraction is such that as given specification. Independent claims are included for: (1) a sintered product obtained by sintering the particulate mixture; and (2) a device containing a glass furnace, reactor, preferably a gasifier reactor, regenerator, and glass distribution channel comprising a block and/or a coating of a sintered product obtained from the particulate mixture.

Description

Refractory product based on chromium oxide Technical Field The invention relates to a particulate mixture comprising chromium oxide, to a sintered product made from such a particulate mixture and to a process for the manufacture of a particulate mixture. such sintered refractory product. This refractory product can be used in particular in an environment in which. it is in contact with molten glass. STATE OF THE ART Among the refractory products, a distinction is made between molten and cast products and sintered products. Unlike sintered products, molten and cast products most often include a very abundant intergranular vitreous phase which fills the network of crystallized grains. The problems encountered in their respective applications by sintered products and by molten and cast products, and the technical solutions adopted to solve them. are therefore generally different. Moreover, due to the significant differences between the manufacturing processes, a composition developed to produce a molten and cast product is not a priori usable as it is to produce a sintered product, and vice versa. The sintered products are obtained by mixing appropriate raw materials and then raw shaping of this mixture and firing the resulting green part at a temperature and for a time sufficient to obtain the sintering of this green part. Sintered products. according to their chemical composition, are intended for a wide variety of industries.

Refractory products comprising chromium oxide are conventionally used in applications where they are subjected to extreme chemical attack, for example in glass furnaces, in particular as furnace blocks, or in furnaces in which they are are in contact with a slag. The use of such refractory products in contact with a slag or with a molten glass is for example known from US 6,352,951 (incineration furnaces containing blocks based on alumina and chromium) and from US 4,82 3,359 (furnaces of glassware with coatings made of alumina and chromium). However, there is a continuing need to increase the shelf life of these products. The aim of the invention is to satisfy this need.

Summary of the invention The invention provides a particulate mixture consisting of a matrix fraction and an aggregate consisting respectively of particles having a size less than or equal to 50 μm, called “matrix particles” and particles having a size greater than. 50 μm, called “grains”, the matrix fraction representing more than 10% and less than 45% of the mass of the particulate mixture, said particulate mixture having a chromium oxide content, denoted “CrT”, between 10% and 8O %, in percentage by mass on the basis of the oxides of the refractory mixture, the matrix fraction being such as 0.39. (CrT) +24 <CrM <O, 39. (CrT) +52 (I), - CrM denoting the mass content of chromium oxide of the matrix fraction, in mass percentage based on the oxides of the matrix fraction, and the aggregate being such that xn? 97%. xEE,? 70%, and xtv 5, xEEs - 70% Cro denoting the mass content of chromium oxide in a grain, as a percentage by mass based on the oxides of this grain, - xrs denoting the quantity. as a percentage by mass on the basis of the aggregate, of grains meeting the following condition (II): - if 10% ô <_ CrT 5 30%, then Crt, <_ 0.018. (CrT) 2 - O, 390. (Crr) +58.8; - if 30% <CrT <_ 60%. then Cro 12 22 (CrT) + 26.7; (II) - if 60% <CrT 5 80%. then Cro 5 100, xsE1 denoting the quantity, in percentage by mass on the basis of the aggregate, of grains complying with the following condition (III) - if 10% <_ Cri <_ 30%, then 0.018. (CrT) 2-0.390. (CrT) +9.10 <_ Cro <0.018. (CrT) 2-0.390. (CrT) +25.10; if 30% <60% CrT S, then 1.17. (CrT) -21.5 Cr6 5 1.17. (CrT) -5.5; (III) if 60% <CrT S 80%, then 1.17. (Cr ~) -21.5 <_ CrG 5 1.67. (CrT) -35.5, - xiv denoting the quantity, in percentage by mass on the base of the aggregate, of grains meeting the following condition (IV): - If 10% S CrT <_ 30%, then 0.018. (CrT) '- 0.390. (CrT) +9.10> Cr (- Si 30% < CrT <_ 60%. Then 1.17. (CrT) -21.5> CrG; (IV) - Si 60% <CrT S 80%, then 1.17. (CrT) -21.5> Crç, La The response traditionally proposed to increase the lifetime of products placed in contact with molten glass consists of improving corrosion resistance. However, the inventors have, following a new path, sought to make the wear of the products more uniform. have in fact observed that the “holes” on the surface in contact with the molten glass, corresponding to the zones in which the wear is maximum, limit the life of the products, whatever their composition. the conditions imposed on a product made from a particular mixture ire according to the invention advantageously lead to a particularly uniform corrosion profile. A particulate mixture according to the invention may also exhibit one or more of the following optional and preferred characteristics: 0.39. (CrT) +29 <CrM <0.39. (CrT) +47 (V) 0.39. (CrT) + 32 <Crm <0.39. (CrT) +44.5 (VIE); - x11 is greater than 98%, preferably greater than 99%, preferably substantially equal to 100%; - xui is greater than 85% and xiv is less than 1%. preferably substantially equal to 0%; At least 70% by mass of the grains have, in percentages by mass on the basis of the oxides, a chromium oxide content complying with the following condition (Vii): If 10% 5 CrT _ <30%, then 0.018. (C1T) 2-0.390. (CrT) +13.10 5 Crc <0.018. (CrT) 2-0.390. (CrT) +21.10; - If 30% <CrT <_ 60%, then 1.17. (CrT) -17.5 5 CrG _ <1.17. (CrT) -9.5; If 60% <CrT 5 80%, then 1.67. (CrT) -51.55 CrG 5 1.67. (CrT) -313.5 20 - At least 70% by mass of the grains present, as a percentage by mass on the oxide base, a chromium oxide content meeting the following condition (VIII): Si 10% 5CrT5.30%. then 0.018. (Crc) 2-0.390. (CrT) +13.10 5 Crc; 0.018 (CrT) 2-0.390 (CrT) +21.10; - If 30% <CrT 5 60%, then 1.17. (CrT) -17.5 c Cro <_ 1.17. (CrT) -9.5; 25 - If 60% <CrT <_ 80%, then I.67. (CrT) -47.5 5 Cro <1.67. (CrT) -39.5 - In a particular embodiment, the matrix fraction has a content of chromium oxide “CrM” complying with condition (VI) and at least 70% by mass of the grains have a content of chromium oxide “Cro” complying with condition (VIII); In a second particular embodiment, the matrix fraction has a content of chromium oxide “CrM” complying with condition (VI) and at least 99% by mass of the grains have a content of chromium oxide “CrM; »Respecting the condition (VIII); - At least 90%, preferably at least 95%, preferably at least 99%. preferably substantially 100% by mass of the grains have a content of chromium oxide “CrG” complying with condition (III) and / or condition (VII); The grains containing chromium oxide are preferably sintered particles. The invention also provides a method of manufacturing a sintered refractory product, comprising the following successive steps: A) preparation of a starting charge by mixing a particulate mixture according to the invention and water B) shaping of said starting charge so as to form a preform;

C) sintering of said preform. The invention also relates to a sintered product obtained by sintering a particulate mixture according to the invention, in particular according to steps A) to c) below.

Preferably, this product has a density greater than 3.1 g / m ', or even greater than 3.3 g / m' and / or less than 4.5 g / cm3, or even less than 4.3 g / cm3. Finally, the invention relates to a device chosen from a reactor, in particular a gasifier reactor. a glass furnace, a regenerator, and a glass distribution channel. also called "feeder channel", comprising a block and / or a coating of a sintered product according to

invention. Definitions The “matrix fraction” consists of particles of size less than or equal to 50 μm, called “matrix particles”. These particles are intended to constitute the matrix of the refractory product. The complementary fraction, made up of particles with a larger size

at 50 uni or "grains" is called "aggregate". The term “size of a particle” is understood to mean the dimension of a particle given conventionally by a characterization of the particle size distribution carried out with a laser particle size analyzer. The laser granulometer used for the examples is a Partita LA-950 from the company HORIBA. The term “circularity” of an observed particle is used as the PD / Pr ratio, Pr denoting the perimeter of the particle as observed, and PD denoting the perimeter of the disc having the same area as that of the particle as observed. The circularity depends on the direction of observation. As shown in FIG. 1b, in order to evaluate the circularity "Ci" of a particle P. the perimeter PD of the disk D having an area equal to the area AP of the particle P is determined on a photograph of this particle. The perimeter P. of this particle is also determined. 2 *. IM Circularity is equal to the ratio of PD / P, .. Thus Ci = Pr -. The more elongated the particle is, the lower the circularity. The SYSMEX FPIA 3000 user manual also describes this procedure (see “detailed specification sheets” at www.malvern.co.uk). The percentiles or "percentiles" 10 (Cil {) and 50 (Cis ") of a set of particles are the circularities of particles corresponding to the percentages, by number, of 10% and 50 respectively, on the cumulative circularity distribution curve particles of this set, the circularities of particles being classified in ascending order. For example, 10% by mass of the particles in this set have a circularity less than Ci10. The percentiles can be evaluated using an apparatus of the Morphology G3 type marketed by the company Malvem. Ci; o is also called “median circularity”.

By extension. these percentiles are used to characterize the distribution of circularities of the particles of a sintered material obtained from this powder. To determine the Cil () and Ciao percentiles, the set of particles is poured onto a flat plate and observed perpendicular to this plate. The number of particles counted is greater than 250, which makes it possible to obtain substantially identical percentiles, regardless of the way in which the particles have been poured onto the plate. A method of determination is described in more detail in the examples below.

We call “convexity” of an observed particle, the ratio Pe / Pr, P, designating the convex perimeter of the particle as observed and P ,. designating the perimeter of said particle as observed, as represented in FIG. 1a. The convexity of a particle depends on the direction of observation. The percentiles or "percentiles" 10 (Coc)) and 50 (Coco) of a set of particles are the convexities of particles corresponding to the percentages, by number, of 10% and 50%, respectively, on the convexity distribution curve cumulative number of particles in this set, the convexities of particles being classified in ascending order. For example, 10% by mass of the particles of this set have a convexity less than Col °. The percentiles can be evaluated using a device of the Morphologi® G3 type marketed by the company Malvem. Co5o is also called "median convexity". By extension, these percentiles are used to characterize the distribution of the convexities of the particles of a sintered material obtained from this powder. To determine the Cou) and Cos “percentiles, the set of particles is poured onto a flat plate and observed perpendicular to this plate. The number of particles is greater than 250, resulting in substantially identical percentiles regardless of how the particles were poured onto the plate. A method of determination is described in more detail in the examples below.

A “granule” is a particle having a circularity greater than 0.85.

The term “agglomerated particle” or “agglomerate” is used to refer to a particle formed by a set of other particles. Agglomerated particles can in particular be obtained by sintering or by means of a binder. Unless otherwise indicated, all percentages are percentages by weight. Chemical analyzes or chemical compositions of particles refer to the composition of each of said particles. The chemical analyzes or the chemical compositions of a “particulate mixture” or of a “powder” refer to the average composition, over all the particles concerned. Brief description of the figures Other characteristics and advantages of the invention will become apparent on reading the detailed description and on examining the drawing in which Figures la and lb illustrate the method used to measure the convexity and the circularity. , respectively ; FIG. 2 represents a photo of a section of a refractory product according to the invention. Detailed description The manufacture of a particulate mixture according to the invention can result from a mixture of powders of raw materials having compositions and suitable particle size distributions. Preferably, the particulate mixture has a Cr2O3 + Al2O3 content greater than 60%. preferably greater than 65%, preferably greater than 70%, preferably greater than 80%, or even greater than 90%, or even greater than 92%, or even greater than 94%, in percentage by mass based on the oxides. A particulate mixture according to the invention comprises. preferably. more than 15%, more than 20%. or even more than 25% and / or less than 40%, or even less than 35%, or even less than 30% of matrix particles, in percentage by mass on the basis of the particulate mixture.

The matrix fraction preferably consists of particles of chromium oxide on the one hand and. on the other hand, particles of alumina and / or particles of zirconia and / or particles of magnesia and / or particles of iron oxide and / or particles of titanium oxide and / or particles of silica and / or calcium oxide particles. Preferably, the matrix fraction consists of particles composed of chromium oxide on the one hand and, on the other hand. alumina and / or zirconia and / or magnesia and / or iron oxide and / or titanium oxide and / or silica and / or calcium oxide, or mixtures of such particles. For example, the matrix fraction can be a mixture of chromium oxide particles and alumina particles. but also consist of the particles of chromium oxide and alumina, for example in the form of a solid solution. Preferably, the matrix particles are composed of chromium oxide on the one hand and, on the other hand, of alumina and / or calcium oxide and / or zirconia and / or titanium oxide. The amount of zirconia matrix particles is preferably less than 10, preferably less than 8%, preferably less than 5%, preferably less than 3%, in percentage by mass based on the oxides of the particulate mixture. In one embodiment, the particulate mixture does not contain zirconia particles. A particulate mixture according to the invention preferably comprises less than 85%, or even less than 80%, or even less than 75% of grains, as a percentage by mass on the basis of the particulate mixture. The aggregate preferably consists of particles of chromium oxide on the one hand and, on the other hand, of particles of alumina and / or of particles of zirconia and / or of particles of magnesia and / or of particles of iron oxide and / or titanium oxide particles and / or silica particles. Preferably, the aggregate consists of particles composed of chromium oxide on the one hand and, on the other hand, of alumhia and / or zirconia and / or magnesia and / or iron oxide and / or titanium oxide and / or silica, or mixtures of such particles. For example, the aggregate can be a mixture of chromium oxide particles and alumina particles, but also be a mixture of chromium oxide and alumina particles, for example in the form of a solid solution. . Preferably, the grains are composed of chromium oxide on the one hand and. on the other hand. alumina and / or zirconia and / or titanium oxide. Also preferably, the particulate mixture does not contain zirconia particles of size between 50 μm and 500 μm, preferably does not contain zirconia particles in the aggregate. Advantageously, the resistance to stone release of the refractory product obtained from the refractory mixture in contact with molten glass is improved.

The standard deviation of the distribution of the chromium oxide content of the grains is preferably less than 8, preferably less than 4, preferably less than 1.5, preferably less than 1, more preferably less than 0, 75. The difference between the lowest and highest chromium oxide contents is preferably less than 9%, preferably less than 6%. preferably less than 4.5%. All the grains then have similar chromium oxide contents. More preferably, whatever the constituent considered, provided that its content is greater than 1% by mass percentage based on the oxides, the standard deviation of the distribution of its content between the different grains is less than 8, preferably less. 4, preferably less than 1.5, preferably less than 1, more preferably less than 0.75. All the grains then exhibit similar compositions. Preferably, the aggregate has a bulk density greater than 85% of the theoretical density. preferably greater than 88%, preferably greater than 90%, preferably greater than 91%. preferably greater than 92% of the theoretical density, or even greater than 93%, or even greater than 94%, or even greater than 95%, or even greater than 96% of the theoretical density. Preferably, the aggregate has an open porosity of less than 10%. preferably less than 6%, preferably less than 5%, preferably less than 3%, preferably less than 2%, preferably less than 1%, or even less than 0.7%, or even less than 0.6 %. The granulate may contain granules, that is to say substantially spherical particles. Preferably, the aggregate has a median circularity greater than 0.87. Preferably. the granules are agglomerated particles, in particular sintered particles.

In a particular embodiment, at least 80%, preferably at least 90%. preferably at least 95%. preferably at least 99%, or even substantially 100% by number of the grains are granules. Preferably, the aggregate and preferably at least 80% by mass of the granules of the aggregate have a chemical composition such that, in percentages by mass on the basis of the oxides and for a total of 100%: - Cr203 + Al203 + ZrO2 + MgO + Fe203 + SiO2 .f TiO2? 90%, preferably> 95%. and Cr203 + A1703 + MgO? 60%, and - Cr203 9% 'and 20% SiO2? 0.5%, and other oxides: <_ 10%, preferably S 5%. Preferably, at least 90% by mass of the granules have a size greater than 100 μm, preferably greater than 200 μm, preferably greater than 300 μm, preferably greater than 400 μm.

The inventors have discovered that, remarkably, a refractory product based on chromium oxide using such granules has good thermal shock resistance and high corrosion resistance. Preferably, the composition of the aggregate is such that - the total Cr2O3 + Al203 + MgO content is greater than 65%. preferably greater than 70%, preferably greater than 80%, or even greater than 90%, or even greater than 92%, or even greater than 94%, in percentage by mass based on the oxides; and / or the SiO2 content is less than 16%, preferably less than 13%, preferably less than 10%, preferably less than 8%, preferably less than 6%, preferably less than 5%, or even less than 4%. or even less than 3% (advantageously, the densification is improved, without the corrosion resistance being reduced); and / or the TiO2 content is greater than 0.5% and / or less than 4%, preferably less than 3%, or even less than 2%; and / or the content of “other oxides” is less than 5%. preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than A. In some embodiments, the composition of the aggregate is such that Cr2O 3 + Al203> 80%, Cr203 + Al203> 90%, or even Cr2O 3 + Al203> 95%; Preferably, the granules of the granulate contain a solid solution Cr203-Al20 and / or a spinel based on Cr2O3-MgO, for example MgCr2O4, and / or a spinel based on Cr203-iron oxide, for example FeCr2O4, and / or or a spinel based on Al2O3-MgO, for example MgAl2O4, and / or a spinel based on Al2O3-iron oxide, for example FeAI2O4, and their solid solutions. Still preferably, the sum of the oxide contents in the granules of the granulate represents more than 90%, more than 95%, or even substantially 100% of the mass of said granules. Preferably, the granules of the aggregate are sintered particles. Preferably, the granulate has an apparent density greater than 3.0 g / cm 3, preferably greater than 3.3 glcm3, or even greater than 3.5 g / cm3, or even greater than 3.6 g / cm3; and / or - an apparent density greater than 85% of the theoretical density, preferably greater than 88%, preferably greater than 90%, preferably greater than 91%. preferably greater than 92% of the theoretical density, or even greater than 93%, or even greater than 94%, or even greater than 95%, or even greater than 96% of the theoretical density (advantageously, the flowability of the particulate mixture is improved thereby) and / or an open porosity of less than 10%, preferably less than 6%, preferably less than 5%, preferably less than 3%, preferably less than 2%, preferably less than 1%. or even less than 0.7%, or even less than 0.6%. The corrosion resistance of the refractory product obtained from the refractory mixture, in particular by contact with molten glass, is improved thereby. Always preferably more than 80%, preferably more than 90%, preferably more than 95%, preferably more than 99% by mass of the granules, or even of the grains, of the granulate, preferably substantially all of the granules of the granulate, or even substantially all of the grains of the aggregate have a size greater than 200 min. preferably greater than 300 μm, preferably greater than 400 μm, or even greater than 0.5 mm. and / or less than 10 mm, preferably less than 5 mm. Still preferably, the particulate mixture contains at least 10% of grains larger than 2 mm in size. in percentage by mass. Preferably, the aggregate has: a median circularity greater than 0.88, preferably greater than 0.90, preferably greater than 0.91, preferably greater than 0.92. preferably greater than 0.93; (advantageously, the thermal shock resistance is improved); and / or - a Cie circularity () greater than 0.72, preferably greater than 0.74, preferably greater than 0.76, preferably greater than 0.78, preferably greater than 0.80, preferably greater at 0.82; and / or a median convexity Cos "greater than 0.90, preferably greater than 0.92. preferably greater than 0.94. preferably greater than 0.95. preferably greater than 0.96; and / or - a Coi ° convexity greater than 0.80, preferably greater than 0.82, preferably greater than 0.85, preferably greater than 0.88, preferably greater than 0.90 and / or circularity median greater than 0.90, preferably greater than 0.92, and an open porosity less than 2%. preferably less than 1%. Preferably. the characteristics relating to the chemical composition of an aggregate as defined above, and in particular the optional characteristics above, are applicable to more than 80%. more than 90%, or even more than 95% or more than 99% by mass, or substantially 100% of the grains of this aggregate.

The particulate mixture can still contain at least 0.1% by mass of a shaping additive. The additive can in particular be chosen from the group consisting of: - clays; plasticizers, such as polyethylene glycol (or “PEG”) or polyvinyl alcohol (or “PVA”); cements, preferably with a high alumina content; - hydratable aluminas, such as boehmite; - binders including temporary organic binders such as resins, lignosulfonates, carboxymethylcellulose or dextrin deflocculants, such as alkali metal polyphosphates, alkali metal polyacrylates, polycarboxylates; and - mixtures of these products.

Preferably, the shaping additive is chosen from the group consisting of cements, deflocculants, clays, lignosulphonates, PVA and mixtures thereof. Preferably, the shaping additive content is less than 6%, as a percentage by mass on the basis of the particulate mixture. Manufacture of a Particulate Melan According to the Invention Sintered particles. and in particular a granulate of sintered particles, can be manufactured according to a conventional process comprising the following successive steps: a) preparation of a starting charge by mixing raw materials and water; b) firming said starting charge so as to form a set of particles; c) sintering of the particles obtained in step b). An example process is described in detail in the examples. In step a), the mixture of raw materials is adapted so as to obtain particles having the desired chemical composition. Any mixing means can be used, such as for example an intensive mixer or kneader.

In step b), preferably, the shaping does not include an atomization operation. Such a process in fact results in a low density. An atomization operation also results in particles having a small size, which makes it difficult to manufacture spherical grains.

Step b) can include a granulation operation. Such an operation cannot however guarantee obtaining a median circularity greater than 0.87 and a density greater than 85% of the theoretical density. To obtain such a result, an intensive type mixer is preferably used, preferably with a linear speed at the end of the vortex greater than 6 msec, and with a sequential supply of said mixer with starting charge. In step c). the particles are sintered, for example in a baking oven. All baking ovens can be used, such as intermittent ovens, but also rotary ovens. The sintering parameters are determined as a function of the composition of the particles.

The sintering temperature can be between 1400 ° C and 1700 ° C. The sintering can be carried out in air. but also in neutral condition (under nitrogen for example), or even in reducing condition (under excess carbon monoxide for example). Preferably. sintering is carried out in air. The dwell time can be between 1 hour and 10 hours, preferably between 2 hours and 5 hours. The open porosity can be adjusted by modifying the particle size distribution of the particulate raw materials used, or by acting on the temperature and / or the dwell time during sintering.

Process for manufacturing a refractory product A refractory mixture according to the invention can be advantageously used to manufacture products having an aggregate bound by a binder matrix. To this end, a method comprising steps A) to c) described above can be implemented. This process advantageously makes it possible to manufacture a sintered refractory product having an apparent density of between 3.1 and 4.5 g / cm3, preferably of between 3.3 and 4.3 g / cm3 The compaction models of Andréasen or Fuller-Bolomey can be used for modify the bulk density of sintered refractory products. Such compaction models are described in particular in the work entitled “Treaty of ceramics and mineral materials”, C.A. Jouenne, Editions Septima. Paris (1984), pages 403 to 405.

In step A), matrix particles and grains are mixed, preferably with a shaping additive, to form the starting charge.

Preferably, the grains comprise granules as described above. preferably thermally consolidated, preferably sintered. The granules can thus advantageously retain their spherical shape during handling. The particulate mixture can also be delivered ready to use. It is then sufficient to mix it with water to prepare the starting charge. The amount of water depends on the process used in step B). In the case of shaping by cold pressing, an addition of a quantity of water of between 1.5% and 4%, as a percentage by mass on the basis of the particulate mixture without the additives, is preferred. In the case of shaping involving a hydraulic connection. like for example a casting. an addition of an amount of water of between 3 and 7%, as a percentage by mass based on the particulate mixture without the additives, is preferred. Without being able to explain it theoretically, the inventors have discovered that the substantially spherical shape of the granules improves the resistance to thermal shocks, independently of the open porosity of the granulate.

The inventors have also discovered that the open porosity of the aggregate influences the flowability of the starting charge. Indeed, if the substitution of chamotte grains by an aggregate having an open porosity greater than 10% leads to a degradation of the flowability, in an unexplained manner, when the open porosity of the aggregate used is less than 6%, the flowability is greater. to that of classic chamotte grain products. The flowability is further improved when the open porosity is less than 2%. In step C), the sintering conditions, and in particular the sintering temperature, depend on the composition of the particulate mixture. Usually a sintering temperature between 1400 ° C and 1700 ° C. preferably between 1500 ° C and 1600 ° C is well suited. At the end of step C), a sintered refractory product according to the invention is obtained.

Such a product is shown in FIG. 2. The particles 10 according to the invention, which are substantially circular, are in particular clearly distinguished. and die 12. The properties of this product make it particularly well suited for use in a glass furnace, a regenerator, or a feeder channel. A sintered product according to the invention can be used in the form of a block or of a layer, for example in the form of a lining applied, by any known method, to a wall to be protected. The sintering can be carried out in situ, that is to say after the product has been placed in its service position.

Examples To make the grains “chromium oxide, alumina. silica, titanium oxide 'mentioned below, the following raw materials were used: - pigmentary chromium oxide Cr203 with a purity greater than 95%, having a specific surface area equal to 4 m' / g and a median size of 0 , 7 1Em; - Al 2 O 3 alumina with a purity greater than 99%, exhibiting a specific surface area equal to 7 μm / g, and a median size of 0.6 μm; - silica fume, with a purity greater than 92%; - titanium oxide. in the rutile form, with a purity greater than 93% and having a median size of 1.5 p.m. These raw materials were dosed and mixed so as to present the desired chemical composition. For each example, 3000 g of mixture of oxides, 350 g of water and 150 g of polyvinyl alcohol (PVA) are introduced into an Eirich RVO2 mixer.

The whole is then mixed for 1 minute, with a vortex rotating at 300 rpm and a tank set at 43 rpm in order to obtain a homogeneous mixture. The speed of rotation of the vortex is then increased to 1050 rpm, and an additional 900 grams of the mixture of oxides is then gradually added in one minute. The rotation is maintained for 2 minutes after the end of the introduction of the additional quantity of charge. The particles are then unloaded, dried in air for 24 hours at 110 ° C before being sintered at 1550 ° C for a dwell time of 3 hours, in air, with a temperature rise rate and a temperature fall rate of 50 ° C / h. After sintering, the particles are sieved and the 0.5 - 5 mm particle size range is retained.

Sintered refractory products were then made according to steps A) to C) above. In step A). the starting charge was prepared by mixing an amount of water between 4.1% and 4.7% with a particulate mixture suited to the desired chemical composition. The following raw materials were used: “AZS” grains of the electrofused refractory product ER-1681 manufactured and marketed by the European Society of Refractory Products, and containing as a percentage by mass on the basis of the oxides: 32.5% ZrO2, 51% d Al2O3, 15% SiO2 and 1.3% Na2O (used in the product of Example 1); 14 “AZS-Cr” grains of the electrofused refractory product ER-2161 manufactured by the European Society of Refractory Products, and containing as a percentage by mass on the basis of the oxides: 27% Cr203, 27% ZrO2. 28% A.12O3, 14.5% SiO2 and 1.1% Na2O (used in the product of Example 5); “High chromium” grains containing 92% Cr203 and having an open porosity of less than 3% (used in the product of Example 1 *): - “High chromium” grains containing 98% Cr203 and having an open porosity of less than 3% (used in the product of Example 5 *); Grains "chromium oxide, alumina, silica, titanium oxide" exhibiting, depending on the products of the examples considered, the characteristics appearing in the following table I: Grains "chromium oxide, alumina, silica, titanium oxide" used in the product of the example: 2 3 4 7 8 Cr203 (%) 13.9 16.1 21.4 39.6 57.5 87.3 Al203 (%) 83.9 81.7 74.7 53.7 37, 5 6.37 Si07 (%) 0.75 0.8 1 52 2.22 2.38! 3.78 TiO2 (%) 0.62 0.65 1.4 1.26 1.89 1.91 Others (° o) 0.83 0.75 0.98 0, 38 0.73 0.64 Porosity 4 , 02 3.58 5.08 1.56 0.9 0.6 open (%) Granules Yes Yes Yes Yes Yes Yes Table 1

- Pigmentary Cr203 chromium oxide with a purity greater than 95%, having a specific surface area equal to 4 m2lg and a median size of 0.7 .irn -Alumina Al203 with a purity greater than 99% , exhibiting a specific surface area equal to 7 m 2 / g, and a median size of 0.6 μm; Zirconia, with a purity greater than 98.5% having a median size of 3 μm; Titanium oxide, in rutile form, with a purity greater than 93% and having a median size of 1.5 Fin-i. 3% of a shaping additive (CA25 aluminous cement marketed by ALMATYS) was added to the starting charge. In step B), the starting charge was shaped by a vibrocasting technique in the form of a preform with dimensions suitable for the measurement to be carried out.

In step C). the preform obtained was then dried and then sintered in air at a temperature of 1550 ° C. for 10 hours. The following measurements were carried out: The measurement of the open porosity of a set of particles was carried out according to the following method: Dry at 110 ° C for at least 12 hours, 4 samples of 35 grams each consisting of particles whose size is between 2 and 5 mm. The dry mass of each of the samples is noted Psi, Pst. Psi and Psi .. We denote Ps = Psz + Ps7 + Ps3 + Ps4. Place each sample in a vial. - Using a vacuum pump, create a vacuum of at least 0.07 MPa in each of the flasks and maintain this vacuum for 7 minutes. Then introduce water into the flask so as to cover the particles with at least 2 cm of water, which allows the particles to always be covered with water during subsequent evacuations. Repeat a vacuum of 0.08 MPa in each flask containing the particles and the water, and maintain this vacuum for 7 minutes. Break the void. Repeat a vacuum of 0.08 MPa in each flask, and maintain this vacuum for 7 minutes. Break the void. - Repeat a vacuum of 008 MPa in each flask, and maintain this vacuum for 7 minutes. Break the void.

Determine the submerged weight of each sample, Pif, Pi2, Pi3 and Pi4. We denote Pi = Pis - + - Pi? -Pr3 + Pi4. Then pour the contents of the 4 flasks through a 2 mm square mesh sieve in order to remove the water. Then pour the particles onto a dry cotton cloth to remove excess water and wipe off the particles until the moisture sheen has disappeared from their surface. Determine the wet weight Ph of all the particles. The open porosity of the set of particles is equal to (Ph-Ps) 1 (Ph-Pi). These measurements are always carried out on sets of sintered particles. They correspond to average measurements on the material constituting the particles, that is to say do not take into account the interstices between the different particles. The measurements of the bulk density and the open porosity of a sintered product were carried out on samples of dimensions 125 x 25 x 25 mm 3. according to ISO 5017.

The Ci50 and Clio circularities and the Cos ° and Co10 convexities of a set of particles can be evaluated by the following method: A sample of particles with sizes between 0.5 and 2 mm is poured onto the glass plate provided at this effect of a Morphologi® G3 device marketed by the company Malvern. The chosen magnification is lx. The analysis is started. In order to avoid counting any scratches on the glass plate and dust, the measurements corresponding to particles with a width ("width") less than 0.4 mm are eliminated from the count by creating a filter ("width < 400 ”). The number of particles counted after filtering is greater than 250.

The apparatus provides an evaluation of the distribution of circularities (“Circularity”) and convexities (“Convexity”), the particles being counted in number. It is also possible to estimate the distribution of circularities and convexities of the particles present in a sintered product by an analysis of photographs of a section of said product, as represented in FIG. 2.

The chemical analyzes were carried out by X-ray fluorescence with regard to the constituents whose content is greater than 0.5%. The content of the constituents present in a content of less than 0.5% ô was determined by AES-ICP (“Atomic Emission Spectoscopy-Inductively Coupled Plasma”).

To measure the average corrosion rate and the roughness index, samples in the form of cylindrical bars having an initial radius ro equal to I l mm and 100 mm in height were taken and subjected to a test consisting of rotating the samples immersed in a bath of molten glass, brought to a temperature T determined as a function of the composition of said glass. The speed of rotation of the samples was 6 revolutions per minute. The. samples were kept immersed for a period "t". At the end of this period and after cooling, the part of a sample which has soaked in the glass (of height H equal to 30 mm) has a section in the form an ellipse with a minor axis Pa and a major axis Ga. For each sample, the minimum value of Pa (Pm) in mm is determined. the maximum value of Pa (PaM) in mm, the minimum value of Ga (Gai) in mm and the maximum value of Ga (GaM) in mm. We fix Pamoyet, _ (Pam + PaM) 12 and Ga, nucle, = (Gam + GaM) l2. For each sample, the mean remaining volume Vrmoy'en is determined by the formula Vrmoyen- (n. H. Pamoyen. Garnoyen) 14- For each sample, the mean corroded volume Vcmoyen is determined by the formula 10 Vc, ye ' - [(iE. H. 22) / 4] - Vr ,,, oye ,,. For each sample, the average corrosion rate Vu. r 'rr, expressed in lm / h, is determined by the formula: Vu = t The average corrosion rate "Vu" of a sample gives an assessment of the corrosion resistance of the sample tested. Thus, the lower the corrosion rate of a sample, the higher its resistance to corrosion by molten glass. The roughness index Ir of sample i, I. is determined by the following formula: lri = [100. (Vcmoye ,, reference sample) / (Veinoye 'reference sample - AV sample i)] - 100. where dV = (Vc ,,,,, y 'VcM). The characteristics of the particulate mixtures tested and the results of the tests are given in Table 2 below: Table 2 Example 1 * 4 5 * 6 J7 '8 Particulate mixture '10 Cri 33.1 20.1 25.4 31 61.8 43.7 62 80.5 Matrix Composition Cr 03 Cr2O3 Cr2O; Cr2Cl3 Cr2O3 Cr2O 3 Cr2O Cr2O, A1-20, Al20 Al20 A103 'Al203 Al203 A1.0; Al203 Cement Cement Cement Cement Cement Cement Cement Cement - - ZrO2 TiO2 Quantity of matrix (°, "31 24 24 28 35 32 37 32% Cr, tij 50 40.6 53.4 55.7 67 68 63 64 Condition respected (VI) ( VI) (VI)) (VI) (VI) (VI) (VI) (VI) Grains Quantity of grains 69 76 76 72 65 68 63 68 Composition AZS strong Chromium oxide AZS- strong Chromium oxide, chromium alumina. silica, Cr chromium oxide alumina, silica, titanium oxide titanium% Cro 0 92 13.5 16 20 27 .98 40 58 88 Condition met None (II) and (H) and (II) and None (II) and ( II.) And (II) and (V III) (VIII) (VIII) (VIII) (VIII) (VIII) of grains respecting 100 100 100 100 100 100 said condition Sintered part obtained after sintering of the particulate mixture `?: N Cr203 33.1 20.1 25.4 31.0 61.8 43.7 62.0 80.5% Al-, O 38.5 77.3 72 65.3 16.5 52.9 29.6 .5.75% ZrO2 17.4 0.05 0.05 0.07 11.8 0.1 4.43 7.81 °, ~ SiO2 8.78 0.71 0.78 I, 30 7.10 0.85 1.28 2.59% TiO2 0.46 0.48 0.53 1.04 0.70 1 1.38 2, 08% CaO 0.95 0.59 0.59 0.61 0.90 0.91 0.93 09 3% Other s elements 0.81 0.77 0.65 0.68 1.2 0.54 0.38 0.33 Apparent density (g / cm3) 3.30 3.30 3.38 3.51 3.65 3.60 3.81 4.10 Porosity, open (° ,%) 16 16.3 14.7 14 14.5 15.8 15.5 14.7 Glass c, Average speed 27.7 28.2 24.8 20.1 - - - - T = 1450 ° C, of corrosion Seen, in. tm / h t-100 h Roughness index 25 5 4 3 - - Ir Glass C, Medium speed - - - 8.4 7.5 6 T-1450 ° C. of corrosion Vu, _ t = 120 h in gtfl / h Roughness index - 20 6 Ir Glass C. Average speed - - - - 10.1 - - 7.2 of corrosion Vu. in l.tm. h T = 1480 ° C. t- = 100 h Roughness index - - - 18 - - 7 Ir: Outside the invention A roughness index of less than 15 is representative of regular and uniform wear. 19 A comparison of the products of Examples 1 * and 4 shows that for similar total chromium oxide contents, the product according to Example 4 presents, after corrosion test. a roughness index more than three times lower than that of Example 1 * as well as a remarkable corrosion resistance. A comparison of the products of Examples 5 * and 7 leads to a similar conclusion, Example 7 however comprising zirconia. A comparison of the products of Examples 1 * on the one hand and 2 and 3 on the other hand shows that the products according to Examples 2 and 3 have a roughness index much lower than that of the product of Example 1 *. In addition. despite a lower chromium content. the products according to Examples 2 and 3 exhibit a resistance to corrosion by molten glass similar or superior to that of Example 1 *. The same observation can be made by comparing the products of Examples 6 and 5 *. Finally. a comparison of the product of Example 5 * with the product of Example 8 shows that the latter, which comprises titanium oxide, has a much lower roughness index. As is now clearly apparent, the invention provides a particulate mixture making it possible to manufacture refractory products which are particularly well suited to being in contact with molten glass. In use, these products wear out remarkably evenly, which considerably increases their service life. Of course, the invention is not limited to the examples provided for illustrative purposes.

Claims (10)

CLAIMS 1. Particulate mixture consisting of a fraction CLAIMS1. Particulate mixture consisting of a matrix fraction and a granulate consisting respectively of particles having a size less than or equal to 50 μm, called “matrix particles” and particles having a size greater than 50 μm, called “grains”, the fraction matrix representing more than 10% and less than 45% of the mass of the particulate mixture, said particulate mixture comprising a chromium oxide content, denoted "CrT", of between 10% and 80%, in percentage by mass on the basis of the oxides of the refractory mixture, the matrix fraction being such that 0.39. (CrT) +24 <CrM <0.39. (Crr) +52 (1), CrM denoting the mass content of chromium oxide in the matrix fraction: in mass percentage based on the matrix oxides, and the aggregate being such that x11? 97%. x1? 70%, and xIv ç xIII - 70% Cr (, denoting the mass content of chromium oxide in a grain, in percentage by mass on the basis of the oxides of this grain, xi denoting the quantity, in percentage by mass on the basis of the aggregate, of grains meeting the following condition (II.): - if 10% CTT 30%. then CrG 5 0.018. (CrT) '0.390. (CrT) +58.8; - if 30% <CrT <_ 60 %, then CrG 1.22. (CrT) + 26.7; (II) - if 60% <CrT <80%, then CrG 100, xiii designating the quantity. in percentage by mass on the basis of the aggregate, of grains respecting the following condition (III): if 10%. CrT ç 30%, then 0.018. (CrT) 2-0.390. (CrT) +9.10 Cru <_ 0.0 1 8. (CrT) 2-0.390. (CrT) +25.1 0; if 30% <CrT- <_ 60%, then 1.17. (CrT) -21.5 <_ Cri, <1.1 7. (CrT) -5.5; (III. ) if 60% <CrT 80%, then l, l 7. (Cr-r) -21.5 S CrG S 1.67. (CrT) -3 5, S, xIv denoting the quantity, in percentage by mass on the basis of the aggregate, of grains meeting the following condition (IV): - If 10% CrT <30%. then 0.018. (CrT) 2-0.390. (CrT) + 9.10> Cru; - If 30% <CrT S 60%, then 1.17. (Cr-r) -21.5> Cru; (IV) Si 60% <CrT 80%. then 1.17. (Crr) -21.5> Cru. 2. Particulate mixture according to the preceding claim, in which xlr 99%. 3. Particulate mixture according to any one of the preceding claims, in which 0.39. (CrT) +29 <CrM <0.39. (Crr -) + 47 (V) 4. Particulate mixture according to the preceding claim, in which 0.39. (CrT) +32 <CrM <0.39. (CrT) +44.5 (VI) 5. Particulate mixture according to any one of the preceding claims, in which at least 70% by weight of the grains present. as a percentage by mass based on the oxides, a chromium oxide content complying with the following condition (VII): If 10% 5_ Cri- 5 30%, then 0.018. (CrT) 2-0.390. (CrT) +13, 1.0 5 Cr6 <0.018. (CrT) 2-0.390. (CrT) +21.10; If 30% <CrT <_ 60%, then 1.17. (CrT) -17.5 <_ CrT; <_ 1.17. (Cr1) -9.5; If 60% <CrT 5 80%. then 1.67. (Cn) -51.5 Cri; 1.67. (CrT) -39.5. 6. Particulate mixture according to the preceding claim, wherein, in said condition (VU), if 60% <_ CrT <_ 80%, then I.67. (CrT) -47.5 5 Cri ,. 7. Particulate mixture according to any one of the preceding claims, in which at least 90% by mass of the grains have a content of chromium oxide "Cri;" »Respecting condition (III) If 10% <_ CrT 5 30%, then 0.018. (CrT) 2-0.390. (CrT) +9.105 Crc <_ 0.018. (CrT) 2-0.390. (CrT) +25, 10; - If 30% <CrT <60%, then I, 17. (CrT) -21.55 Cro 5 1.17. (CrT) -5.5 Si 60% <CrT 5 80%. then 1.17. (CrT) -21.55, Cro <1.67. (Crr) -35.5; and / or condition (VII) Si 10% 5 CrT 5 30%. then 0.018. (CrT) 2-0.390. (CrT) +13.105 Cro <0.018. (CrT) 2-0.390. (CrT) +21.10; If 30% <CrT <_ 60%, then 1.17. (CrT) -17.55 Cro 5 1.17. (CrT) -9.5; If 60% <Cr '<_ 80%. then 1.67. (Crr) -51.5 <_ Cro 5 1.67. (CrT) -39.5. 8. Particulate mixture according to any one of the preceding claims, in which, whatever the constituent considered, provided that its content is greater than 1% by mass percentage based on the oxides, the standard deviation of the distribution of its. content between the different grains is less than 8. 9. Particulate mixture according to any one of the preceding claims, having a Cr 2 O 3 + Al 2 O 3 content of greater than 60%, as a percentage by mass on the basis of the oxides. 10. Particulate mixture according to the preceding claim, having a Cr2O3 Al2O content; greater than 90%, as a percentage by mass based on the oxides. 1.1. Particulate mixture according to any one of the preceding claims, wherein the matrix fraction consists of particles composed of chromium oxide and / or alumina and / or zirconia and / or magnesia and / or iron oxide and / or titanium oxide and / or silica and / or calcium oxide, or consists of a mixture of such particles and / or the aggregate formed by the grains consists of particles composed of oxide of chromium and / or alumina and / or zirconia and / or magnesia and / or iron oxide and / or titanium oxide and / or silica, or consists of a mixture of such particles . 12. Particulate mixture according to any one of the preceding claims, in which the aggregate has a bulk density greater than 85% of the theoretical density and / or an open porosity less than 3%. 13. A particulate mixture according to any preceding claim, wherein the grains containing chromium oxide are sintered particles. 14. Particulate mixture according to any one of the preceding claims, in which the aggregate has a median circularity greater than 0.87. 15. Sintered product obtained by sintering a particulate mixture according to any one of the preceding claims. 16. Device chosen from among a glass furnace, a reactor, in particular a gasifier reactor, a regenerator, and a glass distribution channel comprising a block and / or a coating of a sintered product obtained from a mixture. particulate according to any one of claims 1 to 14.