Title of Invention | TEMPERED REFRACTORY CONCRETE BLOCK HAVING CONTROLLED DEFORMATION |
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Abstract | Refractory concrete comprising a refractory aggregate bound by a binding matrix, the concrete comprising at least 0.5 % by mass of SiC based on the mass of concrete, the matrix representing between 10 and 60% by weight of the concrete and having a composition such that, in percentages by weight based on the matrix: - Al2O3 + SiO2 > 70% 50%>SiO2>10% alkaline earth oxides: ≤ 0.2%. |
Full Text | The invention relates to an unmolded refractory concrete, to a molded concrete and to a prefabricated or finished refractory block which can be obtained from that unmolded concrete, and to their utilization for manufacturing metallurgical furnace linings and in particular linings of blast furnace crucibles or tuyeres. Refractory concretes normally consist of a mixture of an aggregate and a hydraulic binder based on alkaline earth oxides, in particular based on aluminate of lime. This latter binder is generally called "cement". However, the presence of alkaline earth oxides in these concretes, referred to as "castable" in English, is prejudicial to the refractory properties and increases the deformation under load. Moreover, these oxides react in a reducing medium. Thus, the refractory concretes described in EP 0 839 775, which exhibit an essentially zero content of lime (CaO) but contain at least 1% of fine particles of magnesia (MgO), are not suitable for blast furnace crucibles where the atmosphere is rich in carbon monoxide (CO). EP 0 030 181 describes concretes exhibiting a low content of alkaline earth oxides. These concretes thus exhibit good resistance to corrosion and oxidation. However, their deformation under load proves difficult to control. In general, linings based on refractory concretes with a low content of alkaline earth oxides, and even more so refractory concretes with no alkaline earth oxides, are well known to develop internal cracks when they are subjected to the temperature gradients and variations under the corrosive conditions of a blast furnace. These cracks favor erosion and thus limit the lifetime of these linings. The use of carbon-containing blocks for building the linings of blast furnaces is also known. These blocks are normally obtained by molding of a paste bound with resin or pitch, then firing at a temperature greater than 1200°C. The product is thus calcined and the organic binders pyrolyzed. However, carbon-containing blocks exhibit poor resistance to oxidation and to corrosion by the molten iron and erosion resistance which is all the weaker because they contain high proportions of carbon in the form of graphite. There is thus a need for a refractory concrete capable of solving, at least partially, one or more of the aforesaid problems. One purpose of the invention is to satisfy that need. In a first main implementation mode of a concrete according to the invention, this purpose is attained by means of a molded refractory concrete comprising a refractory aggregate bound by a binding matrix, the matrix representing between 10 and 60% by weight of the concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3 + SiO2 > 70% - 50%>SiO2>10% alkaline earth oxides: ≤ 0.2%. As will appear more clearly in the rest of the description, this composition surprisingly makes it possible to obtain excellent resistance to corrosion, in spite of a low content of alkaline earth oxides, particularly in case of use in a lining of a blast furnace crucible, and essentially linear deformability under load. Preferably the molded concrete according to the present invention further exhibits one or more of the following optional characteristics. - The matrix represents between 10 and 60% by weight of the concrete and exhibits a composition, in percentages by weight based on the matrix, such as: - 90% > Al2O3 > 60% - 40%>SiO2>10% alkaline earth oxides: ≤ 0.2%. - The alkaline earth oxides, and in particular the oxides CaO and/or MgO, are only present as impurities in the matrix. - The matrix contains more than 1%, preferably more than 1.5%, preferably more than 2%, or indeed more than 5% of hydratable alumina. Preferably, the matrix contains less than 50%, preferably less than 30%, more preferably less than 20%, or indeed less than 10%, of hydratable alumina. These contents are higher than those usually required when hydratable alumina is used to fluidize a starting charge. - Hydratable alumina contains a quantity of khi-Al2O3 and/or rho-Al2O3 alumina greater than 20%, preferably greater than 50%, preferably greater than 80%, as percentages by weight or volume. - Moreover, the inventors have discovered that aluminas other than aluminas of the crystallographic type khi-Al2O3 or rho-Al2O3 can be suitable, provided that they exhibit a moisture uptake, expressed by weight relative to the initial dry material, greater than 3%, preferably greater than 5%, more preferably greater than 8%. In the rest of the description, these aluminas are described as "high moisture uptake" aluminas. - The matrix contains more than 1%, preferably more than 3%, preferably more than 5% and more preferably more than 10% of silica in micronic form, in particular in the form of silica fume or of ground or micronized silica and/or in the form of silica in colloidal form. Preferably however, the content of silica in micronic form and/or of silica in colloidal form, in the matrix, is less than 40%. - The matrix contains more than 25%, preferably more than 30%, more preferably more than 40%, and/or less than 85%, preferably less than 75%, more preferably less than 73%) of alumina, preferably about 50% of alumina (Al2O3). - The molar ratio, within the matrix, of alumina to silica (Al2O3/SiO2) is greater than 1, preferably greater than 1.3 and/or less than 2, preferably less than 1.7. A ratio of about 1.5. corresponding to the molar ratio of alumina to silica in mullite, is most preferred of all. - The matrix exhibits a content of chromium oxide (Cr2O3) and/or of zirconia (ZrO2) less than 0.5%, preferably less than 0.3%, more preferably less than 0.1%. Preferably, these oxides are only present in the binding matrix as impurities. - The matrix exhibits a total content of alkali metal oxides, in particular Na2O and K2O, of less than 1%. - The matrix represents at least 13% of the concrete, preferably at least 15% and/or less than 30%. - The matrix contains more than 15% of silicon carbide (SiC). - The concrete contains at least 0.5%, at least 1%, at least 2%, at least 3%, preferably at least 4% of silicon carbide and/or less than 10%, preferably less than 7% of silicon carbide, as percentages by weight based on the concrete. - The matrix is made up of alumina, silica and silicon carbide, the balance to 100% being made up of impurities and preferably representing less than 3%. or indeed less than 2% or less than 1 %. - The concrete contains at least 80% of alumina, and/or at least 1 % of silica, preferably more than 5% of silica, as percentages by weight based on the concrete. The concrete preferably contains less than 10% of silica, as percentage by weight based on the concrete. - The concrete exhibits a cold crushing strength greater than or equal to 55 MPa, or indeed greater than 60 MPa. - The aggregate is made up of grains the composition whereof contains aluminum (Al) and/or silicon (Si). Preferably, the aggregate is more than 80% made up of grains of corundum or of other forms of alumina, and/or of mullite or of precursors of mullite and/or of silicon carbide. The aggregate can also be formed of grains made up of non- oxide or carbon-based compounds. It can also be formed of grains consisting of a mixture of the above constituents. Finally, it can be formed of a mixture of the aforesaid grains. - At least 15% of the grains of aggregate exhibits a size between 1 and 15 mm, preferably between 2.5 and 10 mm. - The balance of the concrete to 100% is made up of impurities, in particular Fe, Ti, Na, K, Mg or Ca impurities. - The concrete has undergone tempering at a temperature less than 800°C, less than 700°C, or indeed less than 600 C and/or greater than 400°C. In a second main implementation mode of a concrete according to the invention, the invention also relates to a molded refractory concrete containing a refractory aggregate bound by a binding matrix, the matrix representing between 10 and 60% by weight of the concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3+SiO2>70%, - 50%>SiO2> 10%, alkaline earth oxides: ≤ 0.2%, the matrix containing more than 1% and less than 20% of hydratable or high moisture uptake alumina. In a third main implementation mode of the concrete according to the invention, the invention also relates to a molded refractory concrete, tempered at a temperature greater than 400°C, and non-sintered, containing a refractory aggregate bound by a binding matrix, the matrix representing between 10% and 60% by weight of the concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3 + SiO2 > 70% - 50%>SiO2> 10% hydratable or high moisture uptake Al2O3: > 1% alkaline earth oxides: This concrete can in particular contain at least 0.5% by weight of SiC. The hydratable alumina can in particular be of the kni-Al2O3 and/or rho-Al2O3 crystallographic type. A concrete according to the second main implementation mode or according to the third main implementation mode can also have one or more of the optional or necessary characteristics of a concrete according to the first main implementation mode, to the extent that these characteristics are not incompatible with these second or third main implementation modes. In the rest of the description, a concrete which is molded and according to any one of the three main implementation modes described above is called a "molded concrete according to the invention". The invention also relates to an unmolded concrete, in the dry or moist state, capable of solidification to constitute a molded concrete according to the invention or a block at least in part made up of such a concrete. "Capable of solidification" is understood to mean that the composition of the concrete enables it to harden by simple activation, preferably with no other prospective addition than addition of water. The unmolded concrete according to the invention can be poured on the spot to create a lining. In that case, it can be delivered in the dry or moist state, ready for use, for example packed either in big bags in the dry state, or in drums in the moist state. Alternatively, the concrete can be made into the shape of a finished or prefabricated block, which will be assembled on site. The invention thus also relates, in a first main implementation mode of a block, to a refractory block at least one part whereof, preferably the whole, is made up of a refractory concrete according to the invention. Preferably, the block according to the invention also exhibits one, and preferably several, of the following optional characteristics: - The block exhibits a weight of more than 50 kg, preferably of more than 300 kg and/or less than 2 tonnes. Preferably, it exhibits a weight of about 1 tonne. - The block is a prefabricated product. - After the preforming stage, the block has undergone no heat treatment other than tempering at a temperature lying between 400 and 600°C. The invention also relates to a finished block having preferably undergone firing at a temperature lying between 1300°C and 1500°C. The invention also relates, in a second main implementation mode of a block, to a refractory block exhibiting a weight of more than 50 kg and at least one part whereof is made up of a molded refractory finished or prefabricated concrete, containing a refractory aggregate bound in a binding matrix, the matrix representing between 10% and 60% by weight of concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3 + SiO2 > 70% - 50%>SiO2>10% alkaline earth oxides: This refractory block can have undergone tempering at a temperature greater than 400°C. It can contain at least 0.5% by weight of silicon carbide and/or more than 1% of hydratable alumina, and in particular of hydratable alumina of khi-Al2O3 and/or rho- Al2O3 crystallographic type or of high moisture uptake alumina. A refractory block according to a second main implementation mode can also have one or more of the characteristics of a block according to the first main implementation mode of a block, to the extent that these characteristics are not incompatible with that second main implementation mode. The invention also relates to a process for fabrication of a prefabricated refractory block according to the invention comprising the following steps: a) preparation of a starting charge; b) pouring of the starting charge into a mold and, preferably, vibration of the starting charge in that mold; c) drying and hardening so as to obtain a preform, d) tempering of the preform, preferably at a temperature lying between 400°C and 800°C, or indeed between 400°C and 600 C, so as to obtain a prefabricated block, the starting charge being determined such that at the end of step d), the prefabricated block is according to the invention. Finally, the invention relates to the utilization of a refractory concrete according to the invention or of a refractory block manufactured or capable of being manufactured by a process according to the invention in a lining of a furnace, in particular of a metallurgical furnace, or in a lining of a blast furnace, in particular in a lining of a crucible and/or of a tuyere of a blast furnace. Unless otherwise stated, all the percentages relating to the composition of the molded or unmolded, dry or moist concrete, or relating to the starting charge, are percentages by weight expressed relative to the weight of the dry mineral matter, including the possible silicon carbide. A dry or moist particulate mixture capable of solidification so as to constitute a molded concrete is called "unmolded concrete". A dry and solid material, the microstructure whereof is made up of an aggregate the grains whereof are held together by means of a matrix is called "molded concrete". A molded concrete can be of any shape. The molded concrete can in particular exhibit the shape of a block or of a layer, for example when it results from the solidification of an intended lining. Usually, the molded concrete is obtained by solidification of a particulate mixture which has undergone an activation step, generally by moistening with water. One or more subsequent heat treatments (tempering, firing) can improve the mechanical strength of the "molded concrete". A molded concrete is described as "prefabricated" when its microstructure is temporary. Otherwise, it is described as "finished". In the present invention, the microstructure of a prefabricated concrete of a lining of a reactor (furnace, blast furnace, ...) will thus develop further after installation of the concrete, under the action of a high operating temperature, typically of the order of 1300 to 1600°C, resulting from the firing up of that reactor. A collection of refractory grains at least 90% whereof by weight have a size lying between 150 um and 15 mm is called an "aggregate". The nature of the aggregate in the concrete according to the invention is not limiting. "Matrix" is understood to mean crystalline or non-crystalline phase, providing a continuous structure between the grains and obtained, during solidification, from the constituents of the starting charge. "Impurities" is understood to mean the unavoidable constituents necessarily introduced with the starting materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but are merely tolerated. "Silica in micronic form" is understood to mean a silica powder the particles whereof, partially amorphous, have a median diameter lying between 0.01 and 4 (am. Silica in colloidal form exhibits a median particle diameter which can be lower, generally of the order of a few nanometers. An alumina of the khi-Al2O3 or rho-Al2O3 crystallographic type obtained by flash calcination of hydrargilite gamma-Al(OH)3 is called "hydratable alumina". The hydratable aluminas are said to be "transitional" and have the property of hydrating in the presence of water (liquid or vapor). The transitional aluminas include the hydratable aluminas but are not limited to them. In particular, they include aluminas of the gamma and beta type. Reactive aluminas are aluminas which are calcined and usually ground so as to exhibit a median diameter of less than 10 µm. They are generally essentially in the alpha crystallographic form. The "moisture uptake" is measured by placing a sample, for example 100 g of alumina previously dried at 100°C and for a drying period of 5 hours, in a sealed enclosure saturated to 100% humidity at ambient temperature (20°C), at atmospheric pressure. The increase in the weight of the sample ("moisture uptake") until saturation, that is to say until stabilization of the weight, is then measured. The moisture uptake is stated as percentage by weight relative to the dry starting weight. Finally, elongated structures, typically of diameter from 0.1 µm to 2 mm and of length ranging up to about 3 cm are called "fibers". In a molded material, the average of the largest dimension of a particle or a grain and its smallest dimension, these dimensions being measured on a cross-section of the said material, is called the "size" of the particle or grain. A heat treatment of a moist mixture, preferably previously dried, at a temperature lying between 400 and 600°C is called "tempering". Zirconium oxide ZrO2 is called "zirconia". Aluminum oxide Al2O3 is called "alumina". Silicon oxide SiO2 is called "silica". To manufacture a molded refractory concrete according to the invention, the steps described above can be followed. In step a), the particulate materials are usually mixed until a homogenous mixture is obtained. The nature and the quantities of starting materials are determined in such a manner that the refractory concrete obtained at the end of step d) is according to the invention. The method of determining the proportions of the constituents of the starting charge is perfectly well known to the person skilled in the art. In particular, the person skilled in the art knows that the oxides of aluminum and of silicon and any silicon carbide present in the starting charge are also present in the molded concrete. He also knows how to determine which constituents will be transformed to constitute the matrix. Certain oxides can however be provided by the additives normally used to manufacture concretes, for example sintering agents, dispersants such as alkali metal polyphosphates or methacrylate derivatives. The composition of the starting charge can therefore vary, particularly depending on the quantities and the nature of the additives present, and the purity level of the starting materials used. Preferably, the starting charge is determined in order that silicon carbide, alumina and silica represent at least 80%, preferably at least 95% of the dry inorganic weight of the molded concrete. The aggregate can be made up of grains based on refractory oxides or non- oxide refractories, such as for example carbon, in particular anthracite or graphite, or for example carbides such as silicon carbide (SiC). In particular, the grains can be grains of alumina, zirconia, zircon, silicon carbide or silicon nitride, of a mixture of these latter, or indeed spherical granulated refractory particles. The silica can be provided in the form of micronic silica (for example in the form of silica fume or micronised silica) or colloidal silica. The matrix exhibits as low as possible a content of CaO and/or MgO, for example less than 0.15%, or indeed less than 0.1%. The content of CaO and/or MgO can even be reduced to less than 0.05%. Preferably, however, the content of zirconia (ZrO2) capable of constituting the matrix is limited such that, in the matrix, it is less than 2%, preferably than 1%, more preferably less than 0.5%. The presence of zirconia in fact leads to carbides or nitrides under the ambient conditions of a blast furnace. The chromium oxide (Cr2O3) content of the matrix is also limited such as to be, preferably, less than 0.5%, preferably less than 0.2%, in percentage by weight based on the matrix, more preferably essentially zero. In fact, under industrial conditions, chromium oxide leads to very stringent constraints as regards hygiene, safety and the environment. It is also useful to limit the content of alkali metal oxides such that the total quantity thereof in the molded concrete is less than 1% relative to the inorganic weight of the dry molded concrete. Advantageously, in this way latent swelling associated with the formation of phases made up of alumina Al2O3, silica SiO2 and alkali metal oxides (K2O, Na2()) of the leucite or kaliophyllite type is avoided. Preferably, the oxides of chromium, zirconium, calcium, magnesium and alkali metals are only introduced into the starting charge as impurities. Preferably, the base mixture contains between 0.1% and 2%, preferably less than 0.5% of a dispersant, as percentages by weight relative to the weight of the dry starting charge. The dispersant can for example be selected from the polyphosphates of alkali metals or the methacrylate derivatives. All known dispersants can be envisaged, pure ionic, for example sodium hexametaphosphate (HMPNa), pure steric. for example of the sodium polymethacrylate type, or in combination. The addition of a dispersant makes it possible to distribute the fine particles, of size less than 150 microns, better and thus benefits the mechanical strength of the matrix. Preferably, the starting charge also contains between 0.01% and 0.1% of organic fibers of the vinylic or polypropylene type, as percentages by weight based on the dry starting charge. These fibers advantageously facilitate the removal of water during drying. In order further to improve the fracture resistance during use, the starting charge can also contain metallic or ceramic fibers, the content by weight of these fibers in the starting charge preferably lying between 0.01 and 5%, as percentages by weight based on the dry starting charge. The dry starting charge constitutes an unmolded concrete according to the invention, which can be packed and delivered in this form. After dry mixing sufficiently to obtain a homogenous mixture, water is normally added to the starting charge. Preferably, at least 2%, preferably at least 3% and less than 10%, preferably less than 6%, more preferably less than 5%. of water is added, in percentages by weight relative to the inorganic weight of the starting charge, excluding the water. The water is added progressively to the mixer while it is running until an essentially homogenous moist mixture is obtained. The addition of water causes the activation of the starting charge, that is to say starts its solidification process. The moist mixture constitutes an unmolded concrete according to the invention, which can be packed, for example in drums, and delivered in this form. In step b), the moist mixture is poured into a mold so as to obtain a block of the desired dimensions, for example 1.0 x 0.8 x 0.4 m3 Preferably, at least one of the dimensions of the block is greater than 0.4 m, preferably than 0.6 m, preferably than 0.8 m. The utilization of large blocks advantageously makes it possible to reduce the number of joints compared to an assembly of refractory bricks. In this way, corrosive attack via the joints is limited. The utilization of large blocks also allows rapid installation of the refractory lining. The utilization of refractory blocks in fact avoids the need to carry out drying before installation of the lining. In order to improve the placing of the mixture in the mold, a vibrating pin like those utilized in civil engineering is normally used. The vibration of the pin within the moist mixture is preferably maintained for a period lying between 3 and 20 minutes, depending on the size of the block. At the end of the vibration step, the mold is preferably covered with a covering sheet in order to reduce surface drying In step c), the drying is performed so as to harden the moist mixture. To facilitate the hardening, the mold is preferably immediately placed in an oven, from the end of step b), preferably at a temperature lying between 40 and 70°C and for a period which is variable depending on the dimensions of the block, in general from a few minutes to 24 hours. After hardening, the preform can be removed from the mold. In step d), tempering is performed in order to eliminate the hydrates. This tempering is preferably effected in air, more preferably at a temperature greater than 400°C, preferably greater than 450 C and, more preferably, less than 800°C, or indeed less than 600 C. The rate of temperature increase and the plateau duration at the maximum temperature are normally adapted depending on the dimensions of the block and the charge of the tempering furnace. The tempering period can be greater than 3 hours, greater than 10 hours, or indeed greater than 20 hours, or indeed greater than several days, depending on the weight of concrete to be tempered and on the tempering temperature. It is considered that the tempering is finished when essentially all the hydrates have been eliminated. Routine tests make it possible to determine the optimal tempering period. At the end of the tempering, the block is a prefabricated block according to the invention which advantageously exhibits a mechanical strength sufficient for it to be capable of manipulation, transport and assembly to form a lining of a furnace, tuyere or crucible. The prefabricated refractory block, after tempering and before firing, advantageously exhibits the following characteristics: remarkable corrosion resistance; a coefficient of free thermal expansion, in other words with no load, which varies essentially linearly under the action of an increase in the temperature between 20°C and 1600°C; a mean coefficient of free thermal expansion, between 20 and 800°C, C20-800, less than 10.10-6/°C, corresponding to a free thermal expansion of less than 1.25% between the ambient temperature of 20°C and the temperature of 800°C; a ratio between the mean coefficient of free thermal expansion (C800-1500) between 800 and 1500°C to that (C20-800) between 20 and 800°C lying between 0.7 and 1.3, or indeed between 0.8 and 1.2, and even lying between 0.9 and 1.1; remarkable performance under load, and in particular a mean coefficient of thermal expansion under a load of 2 bars lying between 2.10-6 and 9.10-6 /°C, corresponding to a thermal expansion under load lying between 0.3 and 1.4% between 20 and 1600°C; a thermal expansion such that, for any temperature T lying between 600 and 1600°C, L-20-600 ≤ L'20-T ≤ L'20-600 + 1,3 * L'20-600*(T - 600)/(600 - 20) where L'20-600 and L'20-T designate the thermal expansion values under a load of 2 bars between 20 and 600°C and between 20 and T°C, respectively; an open porosity of the finished concrete of less than 15%; a median pore diameter in the finished concrete less than 0.5 µm. or indeed less than 0.1 µm; very low permeability, which improves the corrosion resistance. In particular, the permeability in air and at ambient temperature (20°C) can be less than 0,5 mDarcy (lmDarcy=0.987*10-l2m2). Surprisingly, the inventors have found that the median pore diameter can be less than 0.05 urn, or indeed less than 0.02 µm. Advantageously, such pore diameters confer very good resistance to infiltration and hence good resistance to corrosion. Surprisingly, the inventors have also found that the specific surface area, normally measured by the B.E.T. method (this method, by adsorption of inert gas, was developed by S. Brunauer, P.H. Emmet and J. Teller and is well known to the person skilled in the art) can be greater than 2 m2/g, greater than 2.5 m2/g, or indeed greater than 4m2 /g or than 5 m2 /g. The specific surface area can vary depending on the quantity of matrix. These median pore diameter and specific surface area values are particularly high, conventional concretes typically exhibiting a median pore diameter of the order of 0.1 to lum and a specific surface area of the order of 1 m2/g. The thermal expansion, expressed as a percentage, corresponds to the elongation (if change positive) or contraction (if change negative) of a test piece under the action of the increase in the temperature, in the sense of the standard NFB40308 in the absence of load or of the standard ISO1893 in the case of the application of a load, the state "(T being the starting state of the test piece before the application of heat. The coefficient of thermal expansion represents the change in elongation between two reference temperatures and is expressed in 10 -6 /°C. The linearity of the free deformation curve during the development of the concrete advantageously makes it possible to position the expansion joints precisely in the lining to be manufactured, which makes it possible efficiently to reduce the occurrence of expansion stresses in this lining and/or in a possible external metallic envelope in contact with the lining. The prefabricated block can be installed in its working position without having been fired. The characteristics of the prefabricated concrete will then develop following the firing up of the furnace or blast furnace, under the action of temperatures typically lying between 1300 and 1650°C. The final characteristics of the refractory lining are then obtained after the firing up of the reactor, which enables an appreciable energy saving and contributes to the preservation of the environment. The following tests are provided for purposes of illustration and do not limit the invention in any way. For these examples, different prefabricated blocks were manufactured following the steps a) to d) of the process described above. The following materials were utilized: - mixture of brown electro-fused corundum grains marketed by Alcan, less than 30% of the grains, by weight, exhibiting a size lying between 1 and 15 mm. and 60%, by weight, exhibiting a size lying between 0.2 and 5 mm; - black electro-fused corundum powder of size less than 150 microns, marketed by Alcan, - mullite precursor powder based on andalousite exhibiting a size less than 500 microns, marketed by Damrec; - silicon carbide powder (SiC) exhibiting a size less than about lOOum; - silica fume of the 983 U type, marketed by Elkem; - calcined alumina powder exhibiting a median diameter of about 4 microns, marketed by Almatis; - cement based on aluminate of lime CA 270, marketed by Alcoa; - reactive hydratable alumina of the Alphabond 300 type, marketed by Almatis; - powdered dispersant HMPNa, marketed by Rhodia. The permeability was measured in air and at ambient temperature, according to the standard ISO 8841. The corrosion tests were performed by rotating test pieces of dimensions 30 x 30 x 150 mm3 at a linear speed of 2 cm per second, in a blast furnace and pig iron slag, at 1500°C. for 6 hours under argon. The degree of attack at the interface between the pig iron and the slag, and in contact with the pig iron, that is to say the reduction in thickness of the test piece, is measured as a percentage relative to the initial thickness. The measurements of the coefficients of free thermal expansion were performed on cylindrical test pieces of 50 mm diameter and 50 mm height, according to the standard NFB 40308. The measurements of the coefficients of thermal expansion under load were performed on test pieces of the same size, according to the standard ISO 1893. The open porosity was measured according to the standard ISO 5017. The median pore diameter was determined from measurements of the pore diameter distribution made by mercury porosimetry. The permeability measurements were made on cylindrical test pieces of 50 mm diameter and 30 mm thickness. The measurements of mechanical cold crushing strength were performed on cylindrical test pieces of 50 mm diameter and 50 mm height according to the standard NFB 40322. The oxidation tests were performed on test pieces of 30 x 30 x 150 mm3- under steam, at a temperature of 1000°C, for 24 hours, according to the standard ASTM C863. Tables 1 and 2 below summarize the results obtained. (*): Almost complete destruction of the test piece It is considered that the coefficient of free thermal expansion varies linearly when there is a straight line such that the linear regression coefficient (R2) of the expansion curve, with no load, relative to that straight line is greater than or equal to 0.95 over the range 20°C-1600°C. Examples 1 and 2 are provided as comparison examples. Example 1 is representative of products with very low alumina cement content, whereas Example 2 is representative of carbon-containing products. Table 1 shows clearly that the refractory concretes A and B according to the invention exhibit a lower permeability to air and a lower median pore size, also relative to the carbon-containing product of Example 1. The concretes according to the invention also exhibit a resistance to corrosion by the slag and the pig iron greater than that of the products containing aluminous cement and a resistance to oxidation in steam markedly greater than that of the carbon-containing products of Example 2. In the applications under consideration, the concretes according to the invention constitute an optimal compromise. Of course, the invention is not limited to the implementation modes described, which are provided by way of illustration and are non-limiting. In particular, the concrete according to the invention can be constituted on the spot, the moist mixture being projected, by a standard technique, onto the wall to be covered. The concrete of the invention can also be used in applications other than blast furnaces, for example as the lining of a furnace used for the melting of metals. WE CLAIM : 1. Molded refractory concrete containing a refractory aggregate bound by a binding matrix, the concrete containing at least 0.5% by weight of SiC as percentage by weight based on the concrete, the matrix representing between 10 and 60% by weight of the concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3 + SiO2 > 70% - 50%>SiO2>10% - Al2O3 which is hydratable and/or exhibits a moisture uptake greater than 3%:>1% alkaline earth oxides: ≤ 0.2%. 2. Concrete as claimed in the previous claim, characterized in that the matrix contains less than 50% of hydratable alumina. 3. Concrete as claimed in the previous claim, characterized in that the matrix contains more than 5% and less than 10% of hydratable alumina. 4. Concrete as claimed in any one of the previous claims, characterized in that the matrix contains more than 1% and less than 40% of micronic silica and/or of silica in colloidal form. 5. Concrete as claimed in the previous claim, characterized in that the matrix contains more than 10% of silica fume and/or of silica in colloidal form. 6. Concrete as claimed in any one of the previous claims, characterized in that the alkaline earth oxides are only present as impurities. 7. Concrete as claimed in the previous claim, characterized in that the matrix contains more than 40% of alumina Al2O3. 8. Concrete as claimed in any one of the previous claims, characterized in that the matrix contains more than 15% of silicon carbide SiC. 9. Concrete as claimed in any one of the previous claims, characterized in that the molar ratio within the matrix of alumina to silica AlO3/SiO2 is greater than 1 and less than 2. 10. Concrete as claimed in any one of the previous claims, characterized in that the molar ratio within the matrix of alumina to silica Al2O3/SiO2 is greater than 1.3 and less than 1.7. 11. Concrete as claimed in any one of the previous claims, characterized in that the matrix exhibits a content of chromium oxide Cr2O3 and/or of zirconia ZrO2 of less than 0.5%. 12. Concrete as claimed in any one of the previous claims, containing at least 80% of alumina and/or at least 1 % of silica, as percentages by weight. 13. Concrete as claimed in any one of the previous claims, characterized in that the aggregate is made up of grains the composition whereof contains aluminum Al and/or silicon Si and/or carbon, 14. Concrete as claimed in any one of the previous claims, characterized in that the hydratable alumina contains more than 20% of alumina of khi-Al2O3 and/or rho-Al2O3 crystal lographic type. 15. Concrete as claimed in any one of the previous claims, exhibiting a median pore diameter less than 0.05 µm and/or a specific surface area greater than 2 m2/g. 16. Concrete as claimed in the previous claim, exhibiting a median pore diameter less than 0.02 ^m and/or a specific surface area greater than 4 m2/g. 17. Finished or prefabricated refractory block, exhibiting a weight of more than 50 kg and at least one part whereof is made up of a molded refractory concrete as claimed in any one of the previous claims. 18. Unmolded concrete capable of solidification so as to constitute a concrete as claimed in any one of claims 1 to 16 or a block as claimed in claim 17. 19. Utilization of a refractory concrete as claimed in any one of claims 1 to 16 or of a block as claimed in claim 17 in a lining of a furnace or in a lining of a blast furnace. 20. Molded refractory concrete containing a refractory aggregate bound by a binding matrix, the matrix representing between 10 and 60% by weight of the concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3 + SiO2 > 70% - 50%>SiO2>10% - alkaline earth oxides: ≤ 0.2%, the matrix containing more than 1% and less than 20% of hydratable alumina and/or of alumina exhibiting a moisture uptake greater than 3%. 21. Concrete as claimed in the previous claim, the hydratable alumina containing more than 20% of alumina of khi-Al2O3 and/or rho-Al2O3 crystallographic type. 22. Molded refractory concrete tempered at a temperature greater than 400°C, and non- sintered, containing a refractory aggregate bound by a binding matrix, the matrix representing between 10 and 60% by weight of the concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3 + SiO2 > 70% - 50%>SiO2>10% Al2O3 which is hydratable and/or exhibits a moisture uptake greater than 3%:> 1% alkaline earth oxides: ≤ 0.2%. 23. Concrete as claimed in the immediately preceding claim, containing at least 0.5% by weight of SiC. 24. Concrete as claimed in either one of the two immediately preceding claims, the hydratable alumina containing more than 20% of alumina of khi-Al2O3 and/or rho- Al2O3 crystallographic type. 25. Finished or prefabricated refractory block, exhibiting a weight of more than 50 kg and at least one part whereof is made up of a molded refractory concrete containing a refractory aggregate bound by a binding matrix, the matrix representing between 10 and 60% by weight of the concrete and exhibiting a composition, in percentages by weight based on the matrix, such as: - Al2O3 + SiO2 > 70% - 50%>SiO2>10% alkaline earth oxides: ≤ 0.2%. 26. Refractory block as claimed in the previous claim, containing at least 0.5% by weight of SiC. 27. Refractory block as claimed in either one of the two immediately preceding claims, containing more than 1% of Al2O3 which is hydratable or exhibiting a moisture uptake greater than 3%. 28. Refractory block as claimed in the previous claim, the hydratable alumina containing more than 20% of alumina of kni-Al2O3 and/or rho-Al2O3 crystallographic type. Refractory concrete comprising a refractory aggregate bound by a binding matrix, the concrete comprising at least 0.5 % by mass of SiC based on the mass of concrete, the matrix representing between 10 and 60% by weight of the concrete and having a composition such that, in percentages by weight based on the matrix: - Al2O3 + SiO2 > 70% 50%>SiO2>10% alkaline earth oxides: ≤ 0.2%. |
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Patent Number | 270780 | |||||||||
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Indian Patent Application Number | 3328/KOLNP/2009 | |||||||||
PG Journal Number | 04/2016 | |||||||||
Publication Date | 22-Jan-2016 | |||||||||
Grant Date | 19-Jan-2016 | |||||||||
Date of Filing | 18-Sep-2009 | |||||||||
Name of Patentee | SAINT-GOBAIN CENTRE DE RECHERCHES ET D'ETUDES EUROPEEN | |||||||||
Applicant Address | LES MIROIRS, 18 AVENUE D'ALSACE-F-92400, COURBEVOIE, FRANCE | |||||||||
Inventors:
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PCT International Classification Number | C04B35/103; C04B35/101 | |||||||||
PCT International Application Number | PCT/FR2008/050519 | |||||||||
PCT International Filing date | 2008-03-26 | |||||||||
PCT Conventions:
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