Refractory ceramic product, use of magnesia spinel hollow spheres, batch for producing refractory ceramic products, method for producing refractory ceramic products, kiln for producing cement clinker or lime, and method for producing cement clinker or lime

Abstract

The invention relates to a refractory ceramic product, to the use of magnesia spinel hollow spheres, to a batch for producing a refractory ceramic product, to a method for producing a refractory ceramic product, to a kiln for producing cement clinker or lime, and to a method for producing cement clinker or lime.

Description

[0001] Description The present invention relates to a refractory ceramic product, to the use of magnesia spinel hollow spheres, to a batch for producing a refractory ceramic product, to a method for producing a refractory ceramic product, to a kiln for producing cement clinker or lime, and to a method for producing cement clinker or lime.

[0002] A refractory ceramic product is a product which is able to withstand high temperatures. The term "refractory product" in the sense of the present invention particularly refers to refractory materials which have a working temperature of more than 600 °C, and preferably to refractory materials according to DIN 51060:2000-06, i.e. to materials having a cone equivalent > SK 17. The cone equivalent can be determined in particular according to DIN EN 993-12:1997-06.

[0003] The term "ceramic" refractory product, as is well known in the art, refers to a refractory product which consists of ceramic material, i.e. of particles which are sintered together.

[0004] Furthermore, a "batch" for producing a refractory ceramic product, as is well known from the prior art, consists of components which can produce a refractory ceramic product by firing.

[0005] A typical field of application of a refractory ceramic product is its use in a kiln for producing or firing cement clinker and lime. Such a kiln can in particular be a rotary kiln or a shaft kiln. Such a kiln is lined with a refractory ceramic product which can withstand the high temperatures within such a kiln.

[0006] Generally, such a refractory ceramic product for lining such a kiln for producing cement clinker and lime is based on magnesia, i.e. on the oxide MgO.

[0007] In principle, such a refractory ceramic product based on magnesia has proven suitable for use in the lining of such a kiln. However, it is an eternal task to improve such a refractory ceramic product in terms of its thermal insulation capacity and its strength. Thus, it is always pursued to make such a refractory ceramic product have a high strength while at the same time having a good thermal insulation effect. However, an increase in the thermal insulation effect of a refractory ceramic product of the prior art is often accompanied by a decrease in strength. The main reason is that an increase in the thermal insulation effect is associated with an increase in porosity, which leads to a decrease in strength. Furthermore, an increase in porosity, in particular also associated with an increase in open porosity, can lead to a decrease in the corrosion resistance of the refractory ceramic product, since components can penetrate the open porosity, leading to corrosion of the product.

[0008] In rotary kilns and shaft kilns for firing cement clinker and lime, the temperature is typically in the range of 1,400 to 1,500 °C. However, this is typically not the temperature that the refractory ceramic product lining the kiln is subjected to. This is due to the fact that on the hot side of the refractory ceramic product, the firing material (i.e. clinker or lime) typically creates a certain obstruction to the furnace atmosphere. In addition, the temperature inside the refractory ceramic product decreases from the hot side to the cold side. Thus, the average temperature inside the refractory ceramic product is much lower than the above-mentioned temperature, typically in the range of about 800 °C. Therefore, it is desirable that the refractory ceramic product has a good strength and a good thermal insulation effect at 800 °C.

[0009] It is an object of the present invention to provide a refractory ceramic product having a good thermal insulation effect and a high strength. At the same time, the refractory ceramic product should preferably also have a high corrosion resistance. In particular, the refractory ceramic product should have a good thermal insulation effect at about 800 °C and should also have a good strength.

[0010] It is a further object of the present invention to provide a batch for producing such a refractory ceramic product, and a method of producing such a refractory ceramic product.

[0011] To solve this problem, according to the present invention, a refractory ceramic product is provided which comprises the following features: a granulate matrix sintered together; the granulate sintered together comprises first granulate and second granulate; the first granulate is a magnesium oxide-based granulate; the second granulate is a magnesium oxide spinel hollow sphere; the proportion of the second granulate is in the range of 1 to less than 10 mass% based on the total mass of the matrix.

[0012] Surprisingly, it was found in the context of the present invention that a refractory ceramic product having the above-mentioned features has both a good thermal insulation capacity (i.e. low thermal conductivity) and a good strength, and in particular a low thermal conductivity at 800 °C.

[0013] Of particular importance for these properties of the refractory ceramic product according to the present invention are the second granulate in the form of magnesium oxide spinel hollow spheres, which are present in the matrix in a proportion of 1 to less than 10 mass%.

[0014] Regarding the thermal conductivity of the refractory ceramic products according to the invention, it has been found within the scope of the invention that the proportion of the second particle according to the invention enables the provision of refractory ceramic products with excellent thermal insulation capabilities (i.e., low thermal conductivity, particularly less than 3.9 W / m·K at 800°C). However, in particular, it has been surprisingly found in the context of the invention that this low thermal conductivity decreases only slightly further when the proportion of hollow spheres is 10% by mass or higher, but at the same time the strength decreases significantly. In particular, when the proportion of magnesia spinel hollow spheres is 10% by mass or higher, the low-temperature crushing strength (CCS) drops sharply. However, for many applications, it is desirable for magnesia-based refractory ceramic products used for kiln linings, especially for kiln linings used in the production of cement clinker and lime, to have a low-temperature crushing strength higher than 60 MPa. However, it has been surprisingly found according to the invention that such strength values ​​are generally not achievable when the proportion of magnesia spinel hollow spheres in the matrix is ​​10% by mass or higher. Therefore, according to the present invention, it is envisioned to provide a magnesium oxide spinel hollow sphere in a matrix of less than 10% by mass.

[0015] Of particular importance to this invention is that the hollow spheres are composed of magnesia spinel (i.e., materials based on magnesia spinel (MgO·Al2O3, MgAl2O4)). According to the invention, this has been found to allow the use of elastomers in refractory ceramic products without compromising the integrity of the refractory ceramic product or reducing its properties. Elastomers are known to be components added to magnesia-based refractory ceramic products to reduce the brittleness of the product or to lower its elastic modulus. Typically, such elastomers are spinel-type materials, such as materials based on magnesia spinel (MgO·Al2O3, MgAl2O4), iron spinel (FeO·Al2O3, FeAl2O4), or magnesium-iron spinel ((Mg, Fe)(Al2O4)). However, by using hollow spheres made of magnesia spinel, the reaction of the hollow spheres with such elastomers is suppressed, thereby not compromising the integrity of the hollow spheres or their resulting effects in the refractory ceramic product.

[0016] As is well known, hollow spheres, sometimes referred to as "microspheres" in the prior art, are small hollow spheres or balloons composed of a substantially dense shell filled with gas (especially air). Because the shell is extremely small relative to the total volume of the hollow sphere, such hollow spheres have only an extremely low bulk density. Therefore, the use of such hollow spheres in refractory ceramic products can significantly reduce the thermal conductivity of such products. Typically, hollow spheres are prepared by first providing a melt of hollow sphere material, in this case, a melt of magnesium oxide spinel. The melt is then blown through a nozzle to form molten hollow spheres, which are then cooled in a fluid (especially water) or gas (especially air) to allow them to cool and solidify. Small hollow spheres are then obtained, which are called hollow spheres. The size of the spheres can be adjusted, specifically by adjusting the temperature of the melt, the shape of the nozzle, and the parameters during the blowing through the nozzle. For example, a method for producing hollow spheres is described in WO2012 / 122745A1 (PCT / CN2011 / 075096).

[0017] According to the present invention, a particular advantage of using hollow spheres to adjust the thermal conductivity of refractory ceramic products lies in the fact that these hollow spheres have a fairly dense surface, resulting in refractory ceramic products with only relatively low open porosity. This makes it possible to provide refractory ceramic products with very good corrosion properties according to the present invention.

[0018] According to the present invention, when the proportion of hollow spheres is about 5% by mass, the refractory ceramic product according to the present invention exhibits excellent strength, particularly excellent low-temperature crushing strength exceeding 60 MPa. Furthermore, when the proportion of hollow spheres in the product is about 5% by mass, the refractory ceramic product according to the present invention exhibits an excellent ratio of thermal conductivity to strength. Therefore, preferably, the proportion of the second particle in the matrix can be specified to be as close as possible to 5% by mass. It has also been found that when the proportion of the second particle in the form of magnesia spinel hollow spheres in the product is greater than about 5% by mass, i.e., in the range of 5% to less than 10% by mass, the thermal conductivity of the refractory ceramic product according to the present invention decreases only slightly. Therefore, according to a preferred embodiment, the proportion of the second particle in the refractory ceramic product can be specified to be at most 9% by mass, more preferably at most 8% by mass, even more preferably at most 7% by mass, even more preferably at most 6% by mass, in each case based on the total mass of the matrix. It can also be specified that in the refractory ceramic product according to the present invention, the proportion of the second particle is at least 2% by mass, more preferably at least 3% by mass, even more preferably at least 4% by mass, again based on the total mass of the matrix. Furthermore, it may be preferably specified that in the refractory ceramic product according to the invention, the proportion of the second particles is in the range of 2 to 9% by mass, more preferably in the range of 3 to 8% by mass, even more preferably in the range of 4 to 7% by mass, even more preferably in the range of 4 to 6% by mass, all based on the total mass of the matrix in each case.

[0019] Surprisingly, it was discovered in the context of this invention that the size or diameter of the magnesia spinel hollow spheres can significantly affect the properties of the refractory ceramic products according to the invention. Therefore, according to the invention, it was surprisingly found that when the diameter of the hollow spheres does not exceed 3 mm, the refractory ceramic products according to the invention exhibit particularly low thermal conductivity and high strength. Furthermore, it was found that the greater the proportion of hollow spheres made of magnesia spinel with a diameter not exceeding 1 mm, the lower the thermal conductivity and the higher the strength. This finding is even more surprising, considering that the volume-to-mass ratio decreases as the diameter of the hollow spheres decreases, it would practically be expected that the insulation capacity of the product would decrease as the product contains increasingly smaller hollow spheres. The reason why the thermal conductivity properties of the refractory ceramic products improve as the proportion of hollow spheres becomes less than 1 mm has not yet been definitively explained. The inventors believe that during the manufacturing process of the refractory ceramic products, most of the hollow spheres with a diameter greater than 3 mm are destroyed, and at least a considerable proportion of the hollow spheres with a diameter in the range of 1 to 3 mm are destroyed, resulting in reduced product strength, and the destroyed hollow spheres no longer function as insulation elements in the product. According to the preferred embodiment, in this respect, the diameter of the hollow sphere is specified to be no greater than 3 mm, even more preferably no greater than 2 mm, and particularly preferably no greater than 1 mm.

[0020] Furthermore, according to the present invention, it has been found that if the diameter of the hollow sphere is less than 100 μm, the thermal conductivity of the refractory ceramic product will only decrease slightly due to the hollow sphere. Therefore, according to a preferred embodiment, the diameter of the hollow sphere is specified to be in the range of 100 μm to 3 mm, more preferably in the range of 100 μm to 2 mm, and particularly preferably in the range of 100 μm to 1 mm.

[0021] The diameter of the hollow spheres is determined according to standard ISO 1927-3. The diameter of hollow spheres in refractory products can be determined, for example, using an electron microscope.

[0022] Magnesium oxide spinel hollow spheres are based on the mineral magnesium oxide spinel (MgO·Al2O3, MgAl2O4). Magnesium oxide spinel does not necessarily contain oxides MgO and Al2O3 in stoichiometric proportions.

[0023] According to one embodiment, the hollow sphere has a chemical composition comprising the following oxides in the following mass proportions relative to the total mass of the hollow sphere: MgO: 25 to 34% by mass; Al2O3: 66 to 75 by mass.

[0024] According to the present invention, it has been surprisingly found that when the magnesia spinel of the hollow spheres is present in a superstoichiometric proportion of Al2O3, the refractory ceramic product exhibits particularly good properties in terms of its thermal conductivity and strength. The stoichiometric composition of the magnesia spinel has a ratio of 71.67% by mass of Al2O3 and 28.33% by mass of MgO. According to a preferred embodiment of the present invention, the magnesia spinel of the hollow spheres can be specified to have a chemical composition comprising the following oxides in the following mass proportions based on the total mass of the hollow spheres: MgO: 25 to 28% by mass and Al2O3: 72 to 75% by mass, more preferably MgO: 25 to 27% by mass and Al2O3: 73 to 75% by mass, and even more preferably MgO: 25 to 26.5% by mass and Al2O3: 73.5 to 75% by mass.

[0025] According to one implementation, the hollow sphere has a mass of 0.5 to 1.0 g / cm³ based on the total mass of the hollow sphere. 3 The volume density within the range.

[0026] The refractory ceramic product according to the invention, like any ceramic product, comprises a sintered particulate matrix. In addition to second particles of magnesia spinel hollow spheres, these particles also comprise first particles based on magnesia.

[0027] In principle, such magnesium oxide-based particles can be any particles of magnesium oxide-based materials known in the art for use in refractory ceramic products. For example, magnesium oxide-based particles can include at least one of the following: sintered magnesium oxide particles or molten magnesium oxide particles. According to a particularly preferred embodiment, the magnesium oxide-based particles are in the form of sintered magnesium oxide particles.

[0028] According to a particularly preferred embodiment, the magnesium oxide-based particles are low-iron magnesium oxide particles. Particularly preferably, the low-iron magnesium oxide has a chemical composition with a Fe₂O₃ content of at most 1% by mass.

[0029] According to a preferred embodiment, the sintered particles include a first particle, a second particle, and a third particle, wherein the third particle is a particle based on at least one spinel-type material.

[0030] Other particles in this spinel-type material form can in particular act as elastomers, thereby reducing the ductility of the refractory ceramic products according to the invention.

[0031] According to a preferred embodiment, the third particle is a particle of at least one of the following spinel-type materials: magnesium oxide spinel, magnesium oxide spinel coated with magnesium oxide spinel, iron spinel, or magnesium-iron spinel. Even more preferably, the third particle is a particle of at least one of the following spinel-type materials: magnesium oxide spinel, iron spinel, or magnesium-iron spinel. Even more preferably, the third particle is a magnesium oxide spinel particle.

[0032] According to the preferred embodiment, the presence ratio of the third particle can be specified to be in the range of 0 to 20% by mass, more preferably in the range of 1 to 20% by mass, more preferably in the range of 3 to 17% by mass, and even more preferably in the range of 5 to 15% by mass.

[0033] According to the preferred embodiment, the presence ratio of the first particle is specified to make up the proportion of the second particle to 100% by mass, based on the total mass of the matrix.

[0034] According to the preferred embodiment, within the range where the matrix contains a third particle, the presence ratio of the first particle is specified to supplement the ratio of the second and third particles to 100% by mass, based on the total mass of the matrix.

[0035] According to one embodiment, the presence of the first particle is specified to be in the range of 99% to above 70% by mass, more preferably in the range of 98% to above 70% by mass, and even more preferably in the range of 90% to 80% by mass, in each case based on the total mass of the matrix.

[0036] As mentioned earlier, if the first particle contains not only particles based on magnesium oxide but also particles of spinel-type material based on magnesium oxide spinel, the second particle exhibits particularly good results in terms of the thermal conductivity and strength of the product, because in this case, the hollow spheres of the second particle have proven to be particularly stable and, in particular, can suppress reactions with the components of the refractory ceramic product.

[0037] Preferably, the refractory ceramic product according to the invention is based on magnesium oxide. Particularly preferably, the refractory ceramic product has a chemical composition based on magnesium oxide (MgO). In this respect, the magnesium oxide in the matrix of the refractory ceramic product according to the invention preferably represents the oxide present in the highest mass fraction relative to the total mass of oxides according to the chemical composition of the matrix.

[0038] According to a preferred embodiment, the matrix has a chemical composition comprising the following oxides, respectively, in the following mass percentages based on the total mass of the matrix: MgO: 82 to 94% by mass; Al2O3: 4 to 14% by mass% Other oxides: 0 to 6 by mass.

[0039] More preferably, the matrix has a chemical composition comprising the following oxides, respectively, in the following mass percentages based on the total mass of the matrix: MgO: 84 to 90% by mass Al2O3: 8 to 13% by mass% Other oxides: 1 to 4 by mass.

[0040] The aforementioned "other oxides" are preferably at least one of the following oxides: SiO2, CaO, Fe2O3.

[0041] More preferably, the matrix has a chemical composition comprising the following oxides, respectively, in the following mass percentages based on the total mass of the matrix: MgO: 82 to 94% by mass; Al2O3: 4 to 14% by mass% Fe2O3: 0.3% to 1% by mass Other oxides: 0 to 5% by mass, wherein “other oxides” are preferably at least one of the following oxides: SiO2, CaO.

[0042] More preferably, the matrix has a chemical composition comprising the following oxides, respectively, in the following mass percentages based on the total mass of the matrix: MgO: 84 to 90% by mass Al2O3: 8 to 13% by mass% Fe2O3: 0.3% to 1% by mass Other oxides: 1 to 3% by mass, wherein "other oxides" are preferably at least one of the following oxides: SiO2, CaO.

[0043] More preferably, the matrix has a chemical composition comprising the following oxides, respectively, in the following mass percentages based on the total mass of the matrix: MgO: 84 to 90% by mass Al2O3: 8 to 13% by mass% Fe2O3: 0.3% to 1% by mass SiO2: 0.2 to 1.3% by mass; CaO: 0.8 to 1.8% by mass.

[0044] Therefore, the matrix of refractory ceramic products mainly includes oxides MgO and Al2O3, and the content of oxide Fe2O3 is preferably extremely low, and the preferred ratio is at most 1 by mass.

[0045] The chemical composition of the matrix of refractory ceramic products can be determined, in particular, by X-ray fluorescence analysis (XRF) and specifically according to the standard ISO 12677:2011.

[0046] The refractory ceramic products according to the present invention can have very low thermal conductivity, thereby providing excellent thermal insulation. According to a preferred embodiment, the thermal conductivity of the refractory ceramic product at 800°C is less than 5.0 W / m·K, and particularly preferably less than 4.5 W / m·K.

[0047] Thermal conductivity was determined according to standard ISO 8894-2:2007.

[0048] Despite its low thermal conductivity, the refractory ceramic product according to the present invention still exhibits good strength, particularly a very good low-temperature crushing strength (CCS). Specifically, the refractory ceramic product according to the present invention can have a low-temperature crushing strength of at least 60 MPa. According to a preferred embodiment, the refractory ceramic product according to the present invention has a low-temperature crushing strength higher than 60 MPa.

[0049] The low-temperature crushing strength was determined according to standard ISO 10059-1:1992.

[0050] Therefore, it can be specified that the refractory ceramic product according to the present invention has an excellent ratio of thermal conductivity to low-temperature crushing strength.

[0051] According to a preferred embodiment, the matrix of the refractory ceramic product according to the present invention has a content of 2.8 to 2.9 g / cm³ as determined according to standard ISO 5017:2013. 3 Density within the range.

[0052] Despite the relatively low density, the refractory ceramic products according to the invention can still have only low apparent porosity, particularly at most 18.5% by volume. This low apparent porosity and the simultaneous presence of low density can be achieved, in particular, by using hollow spheres in the matrix, thereby giving the product a low density without creating a porous matrix.

[0053] According to a preferred embodiment, the matrix of the refractory ceramic product according to the invention has an open apparent in the range of 17 to 18.5% by volume as determined by standard ISO 5017:2013.

[0054] Another object of the present invention is to use magnesia spinel hollow spheres to reduce the thermal conductivity of magnesia-based refractory ceramic products, wherein the magnesia spinel hollow spheres are used in such a way that, based on the total mass of the magnesia-based refractory ceramic product, the magnesia-based refractory ceramic product contains magnesia spinel hollow spheres in a proportion ranging from 1% to less than 10% by mass.

[0055] In other respects, the use of magnesium oxide spinel hollow spheres according to the invention can be carried out under the conditions of the features of the invention disclosed herein.

[0056] In the context of the present invention, "based on magnesium oxide" means that the refractory ceramic product contains MgO as the main oxide.

[0057] According to another aspect of the present invention, a batch material for producing refractory ceramic products is provided, comprising the following features: First component and second component; The first component is at least one magnesium oxide-based raw material; The second component is hollow spinel spheres of magnesium oxide; Based on the total mass of the first and second components, the proportion of the second component is in the range of 1% to less than 10% by mass.

[0058] This batch of material is preferably used for the production of refractory ceramic products according to the present invention.

[0059] According to one implementation scheme, the batch also includes a third component, which is a raw material based on at least one spinel-type material.

[0060] Another objective of this invention is to provide a method for producing refractory ceramic products, comprising the following steps: Provide batch materials according to the present invention; The batch of materials was fired.

[0061] This method is preferably used for producing refractory ceramic products according to the present invention.

[0062] By firing the batch, the first particles of the refractory ceramic product according to the invention are formed from the first component of the batch according to the invention, and the second particles of the refractory ceramic product according to the invention are formed from the second component. When the third component is present in the batch, the third particles of the refractory ceramic product according to the invention are formed from the third component. Thereafter, the first component enables the formation of the first particles of the refractory ceramic product, the second component enables the formation of the second particles of the refractory ceramic product, and the third component enables the formation of the third particles of the refractory ceramic product.

[0063] Subsequently, the composition of the first component may preferably correspond to the composition of the first particles, that is, particularly including the proportion of magnesium oxide-based particles as disclosed above. Their proportion in the batch may correspond to the proportion of these particles in the matrix of the refractory ceramic product according to the invention.

[0064] Furthermore, the second component of magnesium oxide spinel hollow spheres may have the characteristics of second particles of magnesium oxide spinel hollow spheres, and may be present in the batch in proportion to the presence of the second particles in the matrix of the refractory ceramic product according to the present invention.

[0065] Furthermore, the third component may thereafter preferably correspond to the composition of the first particles, that is, particularly include the proportion of spinel-type material-based particles as disclosed above.

[0066] According to the method of the invention, the duration and temperature of firing the batch should be such that the first component, the second component, and the third component (if included in the batch) sinter together to form a sintered particulate matrix. For example, firing can be carried out at a temperature in the range of 1,500 to 1,800°C for a duration in the range of 3 to 8 hours.

[0067] Another object of the present invention is to provide a kiln for producing cement clinker or lime, which includes the following features: The kiln includes a refractory lining; The refractory products include refractory ceramic products according to the present invention.

[0068] The kiln according to the present invention is preferably a rotary kiln or a vertical kiln, and is particularly preferred to be a rotary kiln.

[0069] Another object of the present invention is to provide a method for producing cement clinker or lime, comprising the following steps: A kiln according to the present invention is provided; It provides raw materials that can be used to produce cement clinker or lime through firing; Raw materials are fired in a kiln.

[0070] The production of cement clinker or lime can also be carried out using existing and known technologies.

[0071] Further features of the invention will be apparent from the claims and the exemplary embodiments described below.

[0072] All features of the present invention may be combined individually or in combination as needed.

[0073] Exemplary Implementation First, exemplary embodiments of the batch materials according to the present invention are provided, for producing refractory ceramic products according to the present invention.

[0074] Each of the exemplary embodiments of the batch material includes a first component, a second component, and a third component.

[0075] The first component is a raw material in the form of sintered magnesium oxide. The chemical composition of sintered magnesium oxide is as follows: MgO: 96.7% by mass; Al2O3: 0.2% by mass; Fe2O3: 0.8% by mass; SiO2: 0.8% by mass% CaO: 1.4% by mass; Other: 0.1% mass.

[0076] The third component is a raw material in the form of molten magnesium oxide spinel, which acts as an elastomer. The chemical composition of molten magnesium oxide spinel is as follows: MgO: 32.5% by mass; Al2O3: 62.9% by mass; Fe2O3: 0.6% by mass; SiO2: 0.4% by mass% CaO: 0.8% by mass% Other: 2.8% mass.

[0077] The second component exists in the form of hollow magnesium oxide spinel spheres. These hollow magnesium oxide spinel spheres have the following chemical composition: MgO: 24.6% by mass; Al2O3: 74.0% by mass Fe2O3: 0.2% by mass; SiO2: 0.4% by mass% Other: 0.8% mass.

[0078] The bulk density of the hollow sphere is 1 g / cm³. 3 .

[0079] Subsequently, three batches, labeled V1 to V3 in Table 1 below, were produced from these components. Accordingly, the first component of these three batches V1 to V3 is identical. For the second component, each of batches V1 to V2 contains 5% by mass of the second component. However, the hollow spheres in batch V1 are present only with a particle size of 1 mm or smaller, while in batch V2 they are present with particle sizes up to 1 mm and up to 2 mm, respectively. In batch V3, hollow spheres are present at 8% by mass with particle sizes up to 1 mm and up to 2 mm.

[0080] Table 1 All component proportions in Table 1 are expressed as mass %

[0081] Batch V4 and V5 are examples of batches not according to the invention. Batch V4 contains hollow spheres, but in a proportion greater than 10% by mass, i.e., 16% by mass. Batch V5 contains only the first component and therefore does not contain the second component in the form of hollow magnesium oxide spinel spheres.

[0082] To ensure similar chemical compositions across all batches from V1 to V5, varying amounts of molten magnesium oxide spinel (with a chemical composition almost identical to that of hollow spheres and a particle size up to 5 mm) were added as a third component to the batches. The addition of the third component resulted in a total ratio of 16% by mass for both the second and third components across all batches.

[0083] According to an exemplary embodiment of the method of the present invention, batches V1 to V3 are respectively mixed with a binder in the form of lignin sulfonate, wherein the proportion of binder is 4 by mass based on the mass of the batch without binder.

[0084] Subsequently, the blanks are pressed from the batch material at a pressure of 140 MPa.

[0085] The pressed blanks are then fired in a tunnel kiln at 1,600°C for 5 hours.

[0086] After firing, exemplary embodiments of refractory ceramic products according to the present invention, made from batches V1 to V3, are provided.

[0087] Non-inventory batch V4 is produced in the same manner, and non-inventory batch V5 is fired in the same manner to produce refractory ceramic products.

[0088] The result of firing is that the particles of the first and second components of each batch are sintered together to form a sintered particle matrix. The particles of the first component in each batch form the first particles of the refractory ceramic product, and the particles of the second component form the second particles of the refractory ceramic product. Subsequently, the material and particle size of the first component of each batch correspond to the material and particle size of the first particles of the refractory ceramic product made from it. Therefore, the material and particle size of the magnesia spinel hollow spheres of the second component of each batch correspond to the magnesia spinel hollow spheres of the second particles in the refractory ceramic product made from it. Table 2 below shows the chemical and physical properties of the refractory ceramic products made from batches V1 to V5, respectively, where products V1 to V5 are labeled according to the batches in which they were manufactured.

[0089] Table 2 Exemplary embodiments of the refractory ceramic products V1 to V3 according to Table 2 exhibit particularly low thermal conductivity at 800°C, at only 3.64, 3.93 and 4.40 W / m·K, respectively.

[0090] Despite having only low thermal conductivity, the products from V1 to V3 also exhibit excellent low-temperature crushing strengths of 74, 70 and 61 MPa, respectively.

[0091] Furthermore, despite having very low densities, at 2.86, 2.87, and 2.83 g / cm³ respectively. 3 However, products V1 through V3 exhibited only relatively low open porosity, at 18.4, 18.7, and 19.7 volumes, respectively.

[0092] Table 2 shows that although product V4 has a low thermal conductivity (within the range of products V1 to V3) due to its high hollow sphere ratio of 16% by mass, its CCS is also drastically reduced, making it unsuitable for many applications.

[0093] Products V1 to V3 produced according to the exemplary embodiments can be used excellently as linings for cement rotary kilns used for firing cement clinker.

Claims

1. A refractory ceramic product, comprising the following characteristics: 1.1 Sintered particle matrix; 1.2 The sintered particles include the first particle and the second particle; 1.3 The first particle is a magnesium oxide-based particle; 1.4 The second particle is a hollow sphere of magnesium oxide spinel; 1.5 The proportion of the second particle is based on the total mass of the matrix, ranging from 1% to less than 10% by mass.

2. The refractory ceramic product according to claim 1, wherein the diameter of the hollow sphere is not greater than 3 mm.

3. The refractory ceramic product according to at least one of the preceding claims, wherein the diameter of the hollow sphere is in the range of 100 μm to 3 mm.

4. The refractory ceramic product according to at least one of the preceding claims, wherein the hollow spheres have a chemical composition comprising the following oxides in the following mass proportions relative to the total mass of the hollow spheres: MgO: 25 to 34% by mass; Al2O3: 66 to 75 by mass.

5. The refractory ceramic product according to at least one of the preceding claims, wherein the bulk density of the hollow spheres is between 0.5 and 1.0 g / cm³ relative to the total mass of the hollow spheres. 3 Within the range.

6. The refractory ceramic product according to at least one of the preceding claims, wherein the sintered particles comprise a first particle, a second particle, and a third particle, and wherein the third particle is a particle based on at least one spinel-type material.

7. The refractory ceramic product according to claim 7, wherein the third particle is a particle of at least one of the following spinel-type materials: magnesium oxide spinel, magnesium oxide spinel coated with magnesium oxide, iron spinel (herzynite) or magnesium iron spinel.

8. The refractory ceramic product according to at least one of the preceding claims, wherein the proportion of the first particles is supplemented to the proportion of the second and third particles to 100 by mass based on the total mass of the matrix.

9. The refractory ceramic product according to at least one of the preceding claims, wherein the matrix has a chemical composition comprising the following oxides in the following mass proportions relative to the total mass of the matrix: MgO: 82 to 94% by mass; Al2O3: 4 to 14% by mass% Other oxides: 0 to 6 by mass.

10. The refractory ceramic product according to at least one of the preceding claims has a thermal conductivity of less than 5.0 W / m·K at 800°C.

11. Use of magnesium oxide spinel hollow spheres to reduce the thermal conductivity of magnesium oxide-based refractory ceramic products, wherein the magnesium oxide spinel hollow spheres are used in such a manner that the proportion of magnesium oxide spinel hollow spheres contained in the magnesium oxide-based refractory ceramic product is in the range of 1% to less than 10% by mass of the total mass of the magnesium oxide-based refractory ceramic product.

12. Batches used for the production of refractory ceramic products, including the following characteristics: 12.1 First component and second component; 12.2 The first component is at least one magnesium oxide-based raw material; 12.3 The second component is magnesium oxide spinel hollow spheres; 12.4 The proportion of the second component is in the range of 1% to less than 10% by mass based on the total mass of the first and second components.

13. A method for producing refractory ceramic products, comprising the following steps: A. Providing the batch material as described in claim 12; B. Firing this batch of materials.

14. A kiln used for producing cement clinker or lime, comprising the following characteristics: 14.1 Kilns include refractory linings; 14.2 The refractory products include refractory ceramic products according to at least one of claims 1 to 10.

15. A method for producing cement clinker or lime, comprising the following steps: A. To provide the kiln according to claim 14; B. Provide raw materials that can be used to produce cement clinker or lime through firing; C. Firing the raw materials in a kiln.

Images