Particles for the production of sintered refractory products, batches for the production of sintered refractory products, method for the production of sintered refractory products and sintered refractory products

Abstract

1. Particles for producing a sintered refractory product, comprising the following characteristics: particles made from at least one of the following particles: particles made from magnesia having a zirconia coating on at least a portion of their surface, or particles made from magnesite having a zirconia coating on at least a portion of their surface, or particles made from doloma having a zirconia coating on at least a portion of their surface, or particles made from dolomite having a zirconia coating on at least a portion of their surface; and having a particle size of at least 2.8 mm.

Description

[Technical Field]

[0001] The present invention relates to particles for the production of sintered refractory products, to a batch for the production of sintered refractory products, to a method for the production of sintered refractory products and to sintered refractory products. [Background technology]

[0002] The term "refractory products" in the sense of the present invention particularly refers to refractory products having an operating temperature above 600°C, preferably refractory products according to DIN 51060:2006, i.e. materials having a pyrometric cone equivalent of >SK17. The fire resistance can be determined in particular according to DIN EN 993-12:1997-06.

[0003] The term "sintered" in the sense of the present invention denotes that the refractory product is a ceramic refractory product, ie a refractory product consisting of particles sintered together.

[0004] According to current practice, a "batch" is a composition of one or more ingredients or raw materials that can be subjected to a temperature treatment, i.e., in particular, by firing, for example in a furnace, to produce a sintered refractory product.

[0005] The components in the batch for producing sintered refractory products are routinely available in the form of raw materials based on metal oxides. Such common raw materials for producing sintered refractory products are, for example, doloma and magnesia. Doloma is well known to be a raw material based on the metal oxides calcium oxide (CaO) and magnesium oxide (MgO). Magnesia is well known to be a raw material based on the metal oxide magnesium oxide (MgO). Raw materials in the form of doloma can be, for example, in the form of dead-burned dolomite, synthetic doloma, or fused doloma. Raw materials in the form of magnesia can be in the form of sintered magnesia or fused magnesia.

[0006] It is well known that sintered refractory products are very brittle. This brittleness of sintered refractory products manifests itself in a low structural resilience and a correspondingly high modulus of elasticity of such sintered refractory products. Due to this low structural resilience, sintered refractory products are very sensitive to thermal stresses. In particular, such thermal stresses can lead to thermal spalling of the refractory products.

[0007] To improve the structural resilience of sintered refractory products with respect to thermal stress, it is known that certain components can be incorporated into the sintered refractory products in order to improve the structural resilience and correspondingly reduce the modulus of elasticity.

[0008] It is known to add a component in the form of zirconia (ZrO2) to the batch used to produce sintered refractory products containing calcium oxide to reduce their modulus of elasticity. When such batches are fired, the zirconia reacts in situ with the calcium oxide of the doloma to form calcium zirconate (CaZrO3). This reaction is associated with an expansion or volume increase during firing of the batch, thereby causing microcracks to appear in the matrix surrounding the zirconia particles of the product. These microcracks improve the structural resilience of the product, reducing its modulus of elasticity; therefore, thermal spalling of the refractory product is significantly reduced during temperature changes experienced by the product.

[0009] While this in-situ formation of calcium zirconate has a beneficial effect on the structural resilience of the sintered refractory product, as discussed above, the presence of zirconia in the product may have a detrimental effect on the slag resistance of the product. This is because zirconia may form a eutectic phase with iron oxide, which has a melting point of only 1,323°C, thereby significantly reducing the slag resistance of the product. For example, iron oxide may be present in the product as a minor component of the batch ingredients. However, iron oxide may also be a component of slag that the product comes into contact with, especially when the product is used to lining aggregates to hold molten metal.

[0010] Furthermore, the use of zirconia is disadvantageous from an economic point of view because the raw material cost of zirconia is relatively high.

[0011] In general, it can be said that it is known from the state of the art that the structural resilience of sintered refractory products containing calcium oxide can be improved by adding components in the form of coarse zirconia to the batch for producing the product. However, at the same time, this can reduce the slag resistance of the product. Furthermore, such products can only be produced at higher economic costs. Summary of the Invention [Problem to be solved by the invention]

[0012] It is an object of the present invention to provide a component for the production of sintered refractory products, in particular for the production of sintered refractory products comprising calcium oxide, whereby the structural resilience of the product can be improved without impairing the slag resistance of the product, in particular without substantially reducing the slag resistance of the product. In particular, it is an object of the present invention to provide a component that can be used in a batch for the production of such a product and that is capable of forming calcium zirconate in situ during firing of the batch to a sintered refractory product, but which component does not reduce the slag resistance of the product or reduce the slag resistance of the product to a lower extent than would be the case with the use of zirconia known from the state of the art. It is a further object of the present invention to provide such a component that can be provided more economically than state-of-the-art components in the form of zirconia.

[0013] It is a further object of the present invention to provide a batch containing such ingredients.

[0014] It is a further object of the present invention to provide a method for producing a sintered refractory product from such a batch.

[0015] It is a further object of the present invention to provide sintered refractory products produced by using such components. [Means for solving the problem]

[0016] In order to achieve the first object stated above, according to the present invention, a component in the form of particles for the production of sintered refractory products is provided, the particles having the following characteristics: (1) Particles of: Particles made from magnesia, the surface of which has at least a partial zirconia coating; or Particles made from magnesite, the surface of which is at least partially coated with zirconia; or Particles made from doloma, the surface of which has at least a partial zirconia coating; or Particles made from dolomite and having a zirconia coating on at least a portion of their surface and The particles have a particle size of at least 2.8 mm. A composition is provided having the following characteristics:

[0017] Here, the particles according to (1) can have at least one of the following characteristics according to (2) to (5): (2) Particles according to (1) having a particle size in the range of 2.8 to 8.0 mm. (3) Particles according to at least one of (1) to (2), in which the weight ratio of the zirconia coating to the total weight of the particles is in the range of 1 to 50 weight %. (4) Particles according to at least one of (1) to (3), wherein the zirconia coating has a thickness of at least 10 μm. (5) Particles according to at least one of (1) to (4), wherein the zirconia coating has a thickness in the range of 10 to 800 μm.

[0018] The particle characteristics according to (1) to (5) can be modified as described herein. The particle can include one or several of the additional characteristics described herein. Furthermore, all particle characteristics described herein can be combined with each other, individually or in combination. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention is based on several surprising findings.

[0020] According to a surprising finding, it has been found that the zirconia particles known from the state of the art used in sintered refractory products produced from the aforementioned batches can be replaced by particles according to the invention in order to improve the structural resilience or reduce the modulus of elasticity of these products. In contrast to zirconia particles known from the state of the art, which are made entirely from zirconia, the particles according to the invention have at least one "core" of the raw material magnesia, magnesite, doloma, or dolomite, whereby the surface of this core is at least partially coated with zirconia. Surprisingly, it has been found in accordance with the invention that the elastifying properties of the particles coated according to the invention are such that a better elastifying effect can be achieved in the sintered refractory product than that achieved by solid zirconia particles. At the same time, the particles only surface-coated with zirconia according to the invention offer the possibility of introducing a lower proportion of zirconia into the sintered refractory product than that achieved by solid zirconia particles. Furthermore, finely divided zirconia can be used for coating the coated particles according to the present invention, which may be offered at a significantly lower economic cost than solid particles of zirconia. Furthermore, to the extent that the incorporation of zirconia into the product is reduced, the aforementioned negative effects of zirconia on the slag resistance of the product, particularly due to the formation of a eutectic phase with a low melting point, are also reduced.

[0021] In addition, it has been surprisingly found by the present inventors that the aforementioned beneficial effects of the coated particles, with regard to improved microstructural elasticity and reduced modulus of elasticity, only occur when the coated particles have a particle size of at least 2.8 mm. The basis of this effect has not been specified in detail. The inventors speculate that the elasticity-imparting effect of the coated particles according to the present invention is particularly noticeable only from particle sizes of at least 2.8 mm. Furthermore, the inventors speculate that from particle sizes of at least 2.8 mm (using a zirconia coating of a certain thickness on the coated particles according to the present invention), the mass ratio of zirconia to the core of the coated particles shifts in favor of the mass fraction of the core, so that from particle sizes of at least 2.8 mm, the coated particles actually achieve a low proportion of zirconia in the product according to the present invention, while at the same time achieving a sufficient elasticity-imparting effect of the coated particles.

[0022] The particles of the present invention having the zirconia coating of the present invention are hereinafter referred to as "coated particles."

[0023] The use of coated particles according to the invention "for the production of" a sintered refractory product means that the particles can be used in the context of a technique for the production of a sintered refractory product. In particular, the coated particles described herein can be used in a batch for the production of a sintered refractory product, and the coated particles described herein can be present in such a batch together with other components.

[0024] "Magnesia particles" in the sense of the present invention means particles of raw material magnesia, i.e. material consisting essentially of magnesium oxide (MgO). Such raw material in the form of magnesia can in particular be present in at least one form of raw material sintered magnesia or fused magnesia.

[0025] "Magnesite particles" in the sense of the present invention means particles of the raw material magnesite, i.e. a material consisting essentially of magnesium carbonate (MgCO3). Such raw material in the form of magnesite can in particular be present in the form of raw magnesite, i.e. uncalcined magnesite.

[0026] "Doloma particles" in the sense of the present invention means particles of raw doloma, i.e. a material consisting essentially of magnesium oxide (MgO) and calcium oxide (CaO). Such raw material in the form of doloma can in particular be present in at least one of the following forms: raw dead-burned dolomite, sintered doloma or fused doloma.

[0027] "Dolomite particles" in the sense of the present invention means particles of the raw material dolomite, i.e. a material consisting essentially of magnesium carbonate (MgCO3) and calcium carbonate (CaCO3). Such raw material in the form of dolomite can in particular be present in the form of raw dolomite, i.e. uncalcined dolomite.

[0028] "Zirconia" in the sense of the present invention refers to a material consisting essentially of zirconium oxide (ZrO2). Such raw material in the form of zirconia can in particular be present in at least one of the following forms: raw zirconia, baddeleyite, fused zirconia, calcia-stabilized zirconia or magnesia-stabilized zirconia.

[0029] In accordance with the present invention, it has been found that coated particles have their best elasticity-imparting effect when they have a particle size in the range of 2.80 to 6.63 mm, with only small amounts of zirconia being introduced into the sintered refractory product. Thus, according to a preferred embodiment, the coated particles should have a particle size of up to 8.0 mm, and even more preferably up to 6.63 mm. According to a preferred embodiment, the coated particles should have a particle size in the range of 2.8 to 8.0 mm, and even more preferably in the range of 2.80 to 6.63 mm.

[0030] The coated particles have a core of magnesia, magnesite, doloma or dolomite, the surface of which is at least partially coated with zirconia.

[0031] The fact that a coated particle has at least a partial zirconia coating indicates that the particle is completely or only partially coated with zirconia. When a coated particle has a partial but not complete zirconia coating, the zirconia completely surrounds the core of the particle, i.e., the magnesia, magnesite, doloma, or dolomite core of the particle, i.e., completely surrounds it like a shell inside which the magnesia, magnesite, doloma, or dolomite exists like a core. When zirconia only partially surrounds the magnesia, magnesite, doloma, or dolomite core, the zirconia coating may have, for example, gaps or cracks, or the zirconia coating may be only partially disposed on the particle, for example, in the form of separate parts or regions. The coated particle preferably has a zirconia coating over at least 50% of its surface area. In other words, the magnesia, magnesite, doloma, or dolomite has a zirconia coating on at least 50% of their surface. However, the coated particles preferably have a complete zirconia coating. In accordance with the present invention, it has been found that such particles, in particular those having a core of magnesia, magnesite, doloma or dolomite, completely coated with zirconia have a particularly strong elasticity-imparting effect in the sintered refractory product.

[0032] According to the present invention, it has been found that the elasticity-imparting effect of coated magnesite and dolomite particles, the surfaces of which are at least partially coated with zirconia, is slightly lower than that of coated magnesia or doloma particles, the surfaces of which are at least partially coated with zirconia. Therefore, the coated particles are preferably in the form of at least one of the following particles: magnesia particles, the surfaces of which are at least partially coated with zirconia, or doloma particles, the surfaces of which are at least partially coated with zirconia. Furthermore, according to the present invention, it has been determined that the elasticity-imparting effect of coated magnesia particles, the surfaces of which are at least partially coated with zirconia, is lower than that of coated doloma particles, the surfaces of which are at least partially coated with zirconia. Therefore, it is particularly preferred that the coated particles are in the form of doloma particles, the surfaces of which are at least partially coated with zirconia.

[0033] The "particle size" of coated particles in the sense of the present invention is determined in accordance with DIN 66165-2:2016-08.

[0034] The cores of coated magnesia particles consist primarily of magnesia (MgO), the cores of coated doloma particles consist primarily of magnesia (MgO) and calcium oxide (CaO), and the cores of coated dolomite particles consist primarily of magnesium carbonate (MgCO3) and calcium carbonate (CaCO3). In addition to these primary materials, the usual secondary oxides and impurities typically contained in the raw materials may be present. In this regard, coated particles with a magnesia core may contain secondary oxides in the form of CaO, SiO2, Al2O3, or Fe2O3, while coated particles with a doloma or dolomite core may contain secondary oxides in the form of SiO2, Al2O3, or Fe2O3. However, these secondary oxides or impurities are preferably present in a proportion of less than 10% by weight based on the weight of the core of the coated particle.

[0035] The zirconia coating that each coated particle contains consists of zirconia (ZrO) and, in addition to the pure oxide ZrO, may contain common secondary oxides and impurities, such as secondary oxides in the form of CaO, SiO, AlO, or FeO. In addition, the coating has the common secondary oxide HfO, which is usually associated with ZrO. Preferably, however, these secondary oxides are present in a proportion of less than 10% by weight, based on the weight of the coating of the coated particle.

[0036] According to the invention, it has been found particularly advantageously that coated particles can exert their elasticity-imparting effect if the coating is present in a mass fraction of at least 1% by mass, based on the total mass of the coated particles. Furthermore, according to the invention, it has been found that the amount of zirconia in the sintered refractory product due to the coated particles may be too high if the coated particles have a mass fraction of zirconia coating of more than 50%. Therefore, according to the invention, it is preferred that the mass fraction of the zirconia coating of the coated particles should be in the range of 1 to 50% by mass. Furthermore, according to the invention, it has been found particularly advantageously that coated particles can only exert their elasticity-imparting effect if the coated particles have a mass fraction of 20% by mass of coating while simultaneously providing as little zirconia as possible in the sintered refractory product. Therefore, according to the invention, the mass fraction of the zirconia coating of the coated particles may have to be as close to this fraction as possible. Thus, preferably, the mass fraction of the zirconia coating of the coated particle may be at least 5% by mass, even more preferably at least 10% by mass, and even more preferably at least 15% by mass. Furthermore, according to the present invention, the mass fraction of the zirconia coating of the coated particle may be at most 45% by mass, even more preferably at most 30% by mass, and even more preferably at most 25% by mass. Thus, preferably, according to the present invention, the mass fraction of the zirconia coating of the coated particle may be in the range of 5 to 45% by mass, even more preferably in the range of 10 to 30% by mass, and even more preferably in the range of 15 to 25% by mass. The mass specifications given above for the mass fraction of the zirconia coating of the coated particle are in each case based on the total mass of the coated particle.

[0037] In each case, it is preferred that at least 50% by weight, and even more preferably at least 90% by weight, of the coated particles, relative to the total weight of the coated particles, have the aforementioned weight proportion of zirconia coating.

[0038] According to the present invention, it has been found that a zirconia coating of a coated particle having a layer thickness of about 10 μm or more can form calcium zirconate, in particular together with calcium oxide originating from further components of the batch in which the coated particle is present or from the core of the coated particle. Therefore, according to a preferred embodiment, the zirconia coating is intended to have a thickness of at least 10 μm. Additionally, according to the present invention, it has been found that from a zirconia coating thickness of more than 800 μm, the zirconia as a whole can no longer react with calcium oxide to form calcium zirconate, and therefore, after firing the product, a significant portion of the zirconia coating remains on the product, which, as explained above, may impair the thermal properties of the product. Therefore, according to one embodiment, it is intended that the zirconia coating should have a thickness of at least 10 μm, more preferably in the range of 10 to 800 μm. In accordance with the present invention, the optimum thickness of the zirconia coating has been found to be in the range of 60 to 500 μm, because such a thickness provides sufficient zirconia to form calcium zirconate while leaving only a small amount, or none, of the zirconia coating remaining in the sintered refractory product. Therefore, according to a preferred embodiment, it is contemplated that the zirconia coating should have a thickness of at least 20 μm, even more preferably at least 40 μm, and even more preferably at least 60 μm. It may also be preferred that the zirconia coating have a thickness of 800 μm or less, more preferably 600 μm or less, and even more preferably 500 μm or less. According to a preferred embodiment, it is contemplated that the zirconia coating has a thickness in the range of 20 to 700 μm, even more preferably in the range of 40 to 600 μm, and even more preferably in the range of 60 to 500 μm.

[0039] Preferably, each coated particle has a zirconia coating thickness of at least 50% of the coated particles, more preferably at least 90% of the coated particles, based on the total weight of each coated particle.

[0040] It is particularly preferred that the zirconia coating of the coated particles is in the form of a powder, i.e., in the form of fine particles. In particular, the zirconia of the coating of the coated particles is not sintered. Such a coating of the coated particles in the form of a zirconia powder has the advantage, in particular, that zirconia is highly reactive, and can therefore particularly advantageously react with calcium oxide in situ during firing to give calcium zirconate.

[0041] To improve the adhesion of such zirconia powder coatings to the coated particles, the zirconia powder can be applied to the surface of the coated particles via an adhesion promoter, for example, in the form of water or a binder. A particularly preferred type of coating is zirconia in the form of zirconia powder bound by an organic binder. The organic binder can be, in particular, a temporary binder that burns or evaporates when the batch containing the coated particles is fired. In this regard, temporary binders known in the state of the art, such as aqueous polyvinyl alcohol solutions, can be used.

[0042] The zirconia powder preferably has a particularly fine or small particle size in the coating. According to a preferred embodiment, the zirconia is present in the zirconia coating of the coated particles with a particle size of less than 45 μm (325 mesh), in an amount of at least 90% by weight, even more preferably at least 97% by weight, and even more preferably at least 99% by weight, in each case relative to the total weight of zirconia in the zirconia coating.

[0043] The object of the present invention is also a method for preparing coated particles according to the invention, comprising the steps of: The following particles: Magnesia particles, or Magnesite particles, or droma particles, or Dolomite particles providing particles having a particle size of at least 2.8 mm; providing zirconia; coating at least a portion of the surface of the particles with zirconia; The method includes:

[0044] The features of the method can be modified as described herein. The method can include one or more of the additional features described herein. Furthermore, all features of the method described herein can be combined with each other, individually or in combination.

[0045] The particles produced, available for carrying out the method, will be referred to hereinafter as "particles to be coated".

[0046] The particles to be coated provided by this method can have the particle size of the coated particles shown above. Furthermore, the particles to be coated can have the chemical composition of the core of the coated particles described above.

[0047] The zirconia used in the present method can have the particle size and chemical composition of the zirconia coated particles described above.

[0048] The particles to be coated are preferably coated with zirconia in such a way as to obtain a coating thickness equal to the thickness of the zirconia coating on the coated particles. For this purpose, the particles to be coated can be mixed with zirconia. Preferably, the particles to be coated and zirconia are mixed in a mixer, preferably a compulsory mixer. The particles to be coated and zirconia are preferably mixed together for such a period that the particles to be coated are coated with zirconia to a thickness corresponding to the thickness of the zirconia coating on the coated particles.

[0049] Furthermore, in order to coat the particles to be coated with zirconia, the particles to be coated and the zirconia are preferably mixed together with a binder, preferably an organic binder, particularly preferably a temporary binder, as described above.

[0050] The proportion by weight of binder relative to the total weight of the particles to be coated, not including binder, can be, for example, between 1 and 2% by weight.

[0051] The zirconia is preferably provided as a powder, especially a dry powder, as described above, especially having the particle size of the coated particles of zirconia described above.

[0052] The particles to be coated are preferably coated with a proportion of zirconia such that the mass proportion of the zirconia coating, relative to the total mass of the particle to be coated and the coating applied thereto, is present in a mass proportion corresponding to the mass proportion of the aforementioned zirconia coating of the coated particle.

[0053] The present invention also refers to: (6) A batch for the production of a sintered refractory product, the batch comprising coated particles according to the invention.

[0054] Here, the batch according to (6) can have at least one of the following characteristics according to (7) to (13): (7) A batch according to (6) containing at least 1% by weight of particles relative to the total weight of the batch. (8) A batch according to at least one of (6) to (7), containing 1 to 15 wt. % of particles with respect to the total weight of the batch. (9) A batch according to at least one of (6) to (8), which contains at least one component containing calcium oxide. (10) A batch according to at least one of (6) to (9), wherein the at least one calcium oxide-containing component is at least one of the following calcium oxide-containing components: doloma or dolomite. (11) A batch according to at least one of (6) to (10), wherein at least one calcium oxide-containing component is present in particulate form. (12) A batch according to at least one of (6) to (11) for producing a sintered refractory dolomite product. (13) A batch according to at least one of (6) to (12), having a chemical composition containing 38 to 90 mass% MgO, 8 to 60 mass% CaO, and the remainder being ZrO2, SiO2, Fe2O3, and Al2O3.

[0055] The chemical composition is determined in accordance with DIN EN ISO 12677:2013.

[0056] The batch characteristics according to (8) to (13) can be modified as described herein. The batch can include one or several of the additional characteristics described herein. Furthermore, all the characteristics of the methods described herein can be combined with each other, individually or in combination.

[0057] It has been found in accordance with the present invention that coated particles according to the present invention, when present in a batch in an amount of at least 1% by weight, can exert their elasticity-imparting effect in the sintered refractory product to be produced from the batch to a certain extent. In this regard, according to a preferred embodiment, the batch according to the present invention must contain coated particles in a proportion of at least 1% by weight. Furthermore, it has been found in accordance with the present invention that if the batch contains coated particles according to the present invention in a proportion of more than 15% by weight, the coated particles according to the present invention may incorporate excess zirconia into the sintered refractory product to be produced from the batch. In a preferred embodiment, the batch must contain coated particles according to the present invention in a proportion by weight ranging from 1 to 15%. In this regard, a proportion of coated particles in the batch according to the present invention of 3% by weight has proven optimal. In this regard, according to a preferred embodiment, the batch according to the present invention may contain coated particles in a proportion ranging from 1 to 10% by weight, even more preferably in a proportion ranging from 1 to 8% by weight, even more preferably in a proportion ranging from 1 to 6% by weight, and even more preferably in a proportion ranging from 2 to 4% by weight. The preformulated data in % by weight relate in each case to the total mass of the batch.

[0058] In addition to the coated particles, the present invention can include a refractory basic material, which can consist of one or more components, which can include, in particular, known prior art batches for the production of sintered refractory products.

[0059] The components of the refractory basic material may consist of one or more non-metallic inorganic materials that sinter together when subjected to temperatures to form a sintered or ceramic refractory product.

[0060] Preferably, the refractory basic material or components of the refractory basic material are present in the form of particles, preferably with a particle size in the range of >0-8 mm.

[0061] The refractory basic material is preferably available in the form of a basic refractory basic material, i.e., it consists of one or more basic components. As is well known, a "basic" refractory component is a component based on at least one of the oxides calcium oxide (CaO) and magnesium oxide (MgO).

[0062] Particularly preferably, the batch or refractory basic material comprises at least one component containing calcium oxide as such a basic component. Calcium zirconate can be formed in situ during firing of the batch from the calcium oxide of such a component and the zirconia of the zirconia coating of the coated particles. The at least one calcium oxide-containing component can contain calcium oxide, for example as bound calcium oxide, for example in the form of calcium carbonate (CaCO). However, the calcium oxide-containing component particularly preferentially contains calcium oxide in free form. According to a particularly preferred embodiment, the at least one calcium oxide-containing component is present in the form of at least one of the following calcium oxide-containing components: doloma or dolomite. Calcium oxide-containing components in the form of doloma are particularly preferred. Doloma can preferably be present in the form of at least one of the following components: sintered doloma or fused doloma.

[0063] In addition to at least one calcium oxide-containing component, the refractory basic material may preferably contain at least one magnesium oxide-containing component as a further basic component. According to a preferred embodiment, the at least one magnesium oxide-containing component is in the form of magnesia. The magnesia may preferably be in the form of at least one of the following components: sintered magnesia or fused magnesia.

[0064] In accordance with the above-mentioned preferred proportions of coated particles in the batch according to the invention, the batch according to the invention preferably comprises a proportion in the range of 85 to 99% by weight, more preferably a proportion in the range of 90 to 99% by weight, more preferably a proportion in the range of 92 to 99% by weight, more preferably a proportion in the range of 94 to 99% by weight, more preferably a proportion in the range of 96 to 98% by weight of refractory basic material, each based on the total weight of the batch.

[0065] The refractory basic material should preferably consist of one or more basic components, in particular in the form of the calcium oxide and magnesium oxide-containing components specified above. According to a preferred embodiment, the refractory basic material consists of one or more basic components, and is intended to consist of at least 50% by weight, more preferably at least 70% by weight, of one or more basic components in the form of the calcium oxide-containing components mentioned above.

[0066] According to a preferred embodiment, a batch is provided that can be used for the production of sintered refractory dolomite products. As is well known, refractory "dolomite" products are in fact based on "doloma" rather than "dolomite", i.e., on the oxides MgO and CaO. Preferably, the batch has a chemical composition comprising 38-90% by weight of MgO and 8-60% by weight of CaO, with the remainder up to 100% by weight being one or more of the oxides ZrO2, SiO2, Fe2O3 and Al2O3. Preferably, the total mass of MgO and CaO is at least 96% by weight. The mass percentage data provided in each case relate to the total mass of the batch.

[0067] In addition to the coated particles and the refractory basic material, the batch according to the invention can also contain at least one clay, in particular at least one binding clay, as a further component. In particular, such binding clays can be used to improve the sintering properties of the batch. The batch according to the invention can contain, for example, such clays in proportions in the range of >0 to 2% by weight, in particular 0.1 to 2% by weight, in each case relative to the total weight of the batch.

[0068] The present invention also provides a method for producing a sintered refractory product, comprising the steps of: Providing a batch according to the invention; firing the batch to form a sintered refractory product; The present invention relates to a method including:

[0069] The features of the method can be modified as described herein. The method can include one or several of the additional features described herein. Furthermore, all of the particle features described herein can be combined with each other, individually or in combination.

[0070] The batch according to the invention, which is provided for carrying out the method of the invention, is preferably mixed before firing, preferably in a mixer, particularly preferably a forced-mixing mixer. During mixing of the batch, a binder, particularly an organic binder, especially a temporary organic binder, can be added to the batch. In this regard, temporary binders known from the state of the art can be used, in particular for binding the batch for producing a sintered refractory product. For example, the batch can be mixed with a temporary binder, such as a non-aqueous organic binder. Preferably, the batch is mixed with a binder in a proportion ranging from 1 to 2% by weight, based on the total weight of the batch without binder.

[0071] The mixture, optionally mixed with a binder, can then be formed into a batch, optionally including a binder, by compacting, preferably at a pressure in the range of 70-200 MPa. For example, the batch can be pressed into a shaped green body in the form of a so-called green compact.

[0072] The shaped batch can then be fired in such a way that the components of the batch, particularly the coated particles and the refractory basic material, are sintered together to form a sintered refractory product. In this regard, the firing is a so-called ceramic firing, in which a sintered, i.e., ceramic refractory product is fired from the batch. The firing temperature and duration should be selected by those skilled in the art in such a way that such a sintered refractory product is fired from the batch. Suitable firing conditions can be easily determined by those skilled in the art. According to the present invention, a firing temperature in the range of 1,450 to 1,600°C can be provided. Furthermore, according to the present invention, a firing time (at the temperature in the above range) in the range of 4 to 8 hours may be preferred.

[0073] As explained above, the zirconia coating of the coated particles reacts in situ with calcium oxide during firing. This calcium oxide can be present, for example, as a minor component of one of the batch components. However, calcium oxide is particularly preferred as at least one component of the refractory basic material, particularly at least one component containing calcium oxide. The zirconia coating reacts in situ with calcium oxide during firing to form calcium zirconate. This, as mentioned above, is associated with an increase in volume and, as a result, the formation of microcracks in the sintered refractory ceramic product produced by firing during batch firing, thereby reducing the product's brittleness and increasing its microstructural resilience. This is indicated by a decrease in the product's elastic modulus.

[0074] The object of the present invention is also a sintered refractory product having the following characteristics: the product comprises particles that are sintered together; the particles include first particles and second particles; the first particles include particles containing calcium oxide; The second particle is a particle: Magnesia particles having a calcium zirconate coating on at least a portion of their surface; or Magnesite particles having a calcium zirconate coating on at least a portion of their surface; or Doloma particles, the surface of which has at least a partial calcium zirconate coating; or Dolomite particles having a calcium zirconate coating on at least a portion of their surface At least one of the following characteristics: the second particles having a particle size of at least 2.8 mm; A sintered refractory product comprising:

[0075] The characteristics of the sintered refractory product can be modified as described herein. The sintered refractory product can include one or several of the additional characteristics described herein. Furthermore, all of the characteristics of the sintered refractory product described herein can be combined with each other, individually or in combination.

[0076] This sintered refractory product according to the invention is preferably produced by the aforementioned method according to the invention, wherein the coated particles of the batch according to the invention form the second particles and the refractory basic material component of the batch according to the invention form the first particles.

[0077] Therefore, the first particles should preferably consist of a basic material. The first particles preferably comprise particles containing calcium oxide. The first particles may preferably be in the form of doloma particles or doloma and magnesia particles. At least 50% by weight, or more preferably at least 70% by weight, of the first particles may be in the form of doloma particles, based on the total weight of the first particles.

[0078] The first particles can be present in the product in a proportion by weight that corresponds to the proportion by weight of the refractory basic material in the batch according to the invention. The product according to the invention therefore preferably comprises a proportion in the range of 85 to 99% by weight, even more preferably a proportion in the range of 90 to 99% by weight, even more preferably a proportion in the range of 92 to 99% by weight, even more preferably a proportion in the range of 94 to 99% by weight, even more preferably a proportion in the range of 96 to 98% by weight of first particles, in each case relative to the total weight of the product.

[0079] The second particles may preferably have the particle size of the coated particles according to the present invention. Therefore, it may be preferred that the second particles have a particle size of at least 2.80 mm, and not more than 8.0 mm, more preferably not more than 6.63 mm. According to one embodiment, the second particles should have a particle size in the range of 2.80 to 8.0 mm, and even more preferably in the range of 2.80 to 6.63 mm.

[0080] The calcium zirconate coating of the second particles can have a thickness equivalent to that of the zirconia coating of the coated particles according to the present invention. Because the zirconia coating of the second particles can grow during firing, the calcium zirconate coating of the second particles may have a thickness somewhat greater than that of the zirconia coating of the coated particles according to the present invention. Preferably, the calcium zirconate coating may have a thickness of at least 10 μm, even more preferentially at least 40 μm, even more preferentially at least 60 μm, and even more preferentially at least 100 μm. Preferably, the calcium zirconate coating has a thickness of 800 μm or less, more preferably 700 μm or less, and even more preferably 600 μm or less. According to a preferred embodiment, calcium zirconate coatings are provided having thicknesses in the range of 10 to 800 μm, more preferably 40 to 700 μm, more preferably 60 to 600 μm, and more preferably 100 to 600 μm.

[0081] The second particles can be present in the product in a proportion by weight that corresponds to the proportion by weight of the coated particles in the batch according to the invention. Thus, the product according to the invention preferably comprises a proportion of second particles in the range of 1 to 15% by weight, even more preferably in the range of 1 to 10% by weight, even more preferably in the range of 1 to 8% by weight, even more preferably in the range of 1 to 6% by weight, even more preferably in the range of 2 to 4% by weight, in each case relative to the total weight of the product.

[0082] In the sintered refractory product, the first particles can preferably form a matrix in which the second particles are embedded. The calcium zirconate coating can be arranged like a shell around the second particles, and the second particles are in contact with the matrix of the product, and in particular with the first particles, via this calcium zirconate coating.

[0083] The calcium zirconate coating acts as an elasticizer in the sintered refractory product, increasing the structural resilience of the product and reducing its brittleness, which is particularly evident in the low elastic modulus of the product.

[0084] At the same time, the present invention allows the incorporation of only a small proportion of zirconia into the product, despite the presence of calcium zirconate, since the second particles do not have a core of zirconia, but rather a core of magnesia, magnesite, doloma, or dolomite. As explained above, this results in products according to the present invention having such good slag resistance, since the second particles introduce only small amounts of zirconia into the product. In this regard, products according to the present invention can have both good thermal properties and good microstructural elasticity.

[0085] The proportion of zirconia in the sintered refractory product according to the invention is preferably less than 1% by weight of the total weight of the product.

[0086] In addition, the sintered refractory product according to the invention may have an elastic modulus of less than 110 GPa, more preferably less than 100 GPa, the elastic modulus being determined in accordance with DIN EN ISO standard 12680-1:2007.

[0087] The sintered refractory product according to the invention is particularly preferably characterized by a proportion of zirconia of less than 1% by weight and an elastic modulus as mentioned above.

[0088] The sintered refractory product should preferably have second particles in the form of at least one of the following particles: magnesia particles having at least a partial coating of calcium zirconate on their surface, or doloma particles having at least a partial coating of calcium zirconate on their surface, since these particles are able to improve the microstructural elasticity particularly well. In particular, the sintered refractory product according to the invention has second particles in the form of doloma particles having at least a partial coating of calcium zirconate on their surface, since these particles are able to improve the structural elasticity to the greatest extent.

[0089] According to the invention, it has been found that the product according to the invention is particularly suitable for lining an aggregate for holding molten metal, in particular molten steel. This is particularly true when the product is made from a batch whose refractory basic material consists of a basic component, and accordingly the first particles of the product consist of the basic material. In this regard, the invention also provides for the use of the product according to the invention for lining an aggregate for holding molten metal, in particular molten steel. In this regard, the invention also provides for an aggregate for holding molten metal, in particular molten steel, having a lining of the product according to the invention.

[0090] Further features of the invention emerge from the claims and from the following exemplary embodiments of the invention.

[0091] All features of the invention can be combined with one another in any way, individually or in combination.

[0092] Exemplary embodiments of the invention are described in more detail below.

[0093] In the exemplary embodiments of the present invention and the comparative examples, the chemical composition is determined in accordance with DIN EN ISO standard 12677:2013, the particle size is determined in accordance with DIN 66165-2:2016-08, the particle size of the zirconia powder is determined in accordance with DIN 66165-2:2016-08, and the elastic modulus is determined in accordance with DIN EN ISO standard 12680-1:2007. [Example]

[0094] Exemplary Embodiment 1 Example of a method for producing coated particles First, magnesia particles having particle sizes ranging from 2.80 to 6.63 mm were provided for carrying out the present method.

[0095] The magnesia particles had the following chemical composition relative to the total mass of the magnesia particles: MgO: 98.4% by mass CaO: 0.8% by mass Fe2O3: 0.5% by mass Al2O3: 0.1% by mass SiO2:0.1% by mass Mn2O3: 0.1% by mass.

[0096] A zirconia powder was also provided, having the following chemical composition, based on the total mass of the zirconia powder: ZrO2:92.5% by mass HfO2:2.0% by mass CaO:2.6% by mass Fe2O3:0.1% by mass Al2O3: 1.9% by mass SiO2: 0.9% by mass.

[0097] The zirconia powder had a particle size of less than 45 μm (325 mesh), and accounted for 99.5 mass % of the total mass of the zirconia powder.

[0098] The magnesia particles were placed in a mixer, which was then started. A binder was then added to the magnesia particles in the mixer in an amount of 1.5% by weight, based on the total weight of the magnesia particles without the binder. The binder consisted of an aqueous polyvinyl alcohol solution.

[0099] Next, zirconia powder was slowly added to the magnesia particles prepared with the binder in the mixer. As a result, a zirconia coating was formed on the magnesia particles. The addition of this zirconia powder to the mixer was continued until coated particles with a mass ratio of 80% magnesia to 20% zirconia were achieved. The thickness of the zirconia coating on the magnesia particles was approximately 80-250 μm.

[0100] Coated particle examples The previously described embodiment of the method for producing coated particles produced coated magnesia particles whose surfaces were completely coated with a zirconia coating. At thicknesses of 80-250 μm, the mass fraction of the zirconia coating was approximately 20% by mass relative to the total mass of the coated particles. In other words, the method produced coated particles having a magnesia core, with the surface of the particle completely coated with a zirconia coating. The mass ratio of the core to the coating was 80% by mass to 20% by mass.

[0101] Batch Example Exemplary embodiments of batches according to the present invention were produced that included coated particles according to the exemplary embodiments described above.

[0102] These coated particles were mixed with a refractory basic material, a binding clay and a binder to form a batch.

[0103] The refractory basic material consisted exclusively of basic components in the form of sintered doloma and sintered magnesia, each of which was provided in a particle size range of >0 to 6.63 mm.

[0104] The binder was in the form of a non-aqueous organic binder, a temporary organic binder.

[0105] The ingredients, except for the binder, were placed in a mixer in the following proportions by weight relative to the total mass of the batch to form batches: Coated particles: 4% by mass Droma: 86% by mass Magnesia: 9.6% by mass Bonding clay: 0.4% by mass.

[0106] A binder was then added to the batch at a rate of 2% by weight based on the batch without the binder.

[0107] The ingredients were then mixed in a mixer to form a batch.

[0108] Example of a method for producing a sintered refractory product The mixed batch was removed from the mixer and compressed in a press at a pressure of 100 MPa to obtain a green compact.

[0109] The green compact or pressed batch was then fired at a temperature of 1,450° C. for 8 hours.

[0110] During firing, the components of the batch were sintered together to form a sintered or ceramic refractory product.

[0111] Furthermore, during firing, the zirconia coating of the coated particles reacted in situ with the calcium oxide of the doloma particles to form calcium zirconate, a reaction associated with an increase in volume, which resulted in microcracks in the structure of the product during firing.

[0112] After firing, the product was in the form of a sintered refractory product according to the invention.

[0113] The product had first sintered particles in the form of sintered doloma and sintered magnesia particles, these first particles being formed from particles of the refractory basic material component.

[0114] The product also contained secondary particles formed from the coated particles. These secondary particles were in the form of magnesia particles, each bearing a coating of calcium zirconate. The thickness of this calcium zirconate coating was somewhat greater than the thickness of the zirconia coating on the coated particles, i.e., approximately 100-300 μm.

[0115] The microstructure of the sintered refractory product had a matrix of sintered first particles with second particles embedded in the matrix.

[0116] The elastic modulus of the product was determined to be 88.0 GPa.

[0117] At the same time, the chemical content of ZrO2 in the product was 0.7% by mass relative to the total mass of the product, which is expected to give the product good resistance to FeO-rich slag.

[0118] Comparative Example Comparative Example 1 For comparison purposes, sintered refractory products were produced that differed from those produced in accordance with the exemplary embodiments in that the coated particles were replaced by zirconia particles having particle sizes in the range of 0.6 to 3.35 mm, and the products were made from the following batches: Zirconia particles: 0.87% by mass Droma: 89.13% by mass Magnesia: 9.6% by mass Bonding clay: 0.4% by mass.

[0119] The resulting sintered refractory product had an elastic modulus of only 91.3 GPa. However, it had a chemical zirconia content of 0.8 wt. %. Due to this relatively high zirconia content, it is expected that this product will be relatively less resistant to FeO-rich slag than the product according to Exemplary Embodiment 1.

[0120] At the same time, the production of this product was associated with an economic disadvantage in that the provision of zirconia particles was significantly more expensive than the provision of coated particles according to the invention.

[0121] Comparative Example 2 To determine the effect of coated particle size on the microstructural resilience of sintered refractory products produced using such coated particles, two sintered refractory products were produced for comparison purposes, which differed from the product produced according to the exemplary embodiment only in that the coated particles had a particle size of less than 2.8 mm.

[0122] According to the product of Comparative Example 2, coated particles having particle sizes ranging from 0.85 to 2.8 mm were provided.

[0123] Next, the product according to Comparative Example 2 had an elastic modulus of 100.6 GPa.

[0124] According to Comparative Example 2, the elastic modulus of the product was significantly higher than that of the product of Exemplary Embodiment 1 according to the present invention, which indicates significantly lower structural elasticity.

[0125] Exemplary Embodiment 2 Example of a method for producing coated particles First, doloma particles having particle sizes ranging from 2.80 to 6.63 mm were provided for carrying out the present method.

[0126] The doloma particles had the following chemical composition relative to the total mass of the doloma particles: MgO: 39.8% by mass CaO:58.2% by mass Fe2O3:0.8% by mass Al2O3: 0.5% by mass SiO2:0.7% by mass Mn2O3: 0.0% by mass.

[0127] A zirconia powder was also provided, which had a chemical composition and particle size according to Exemplary Embodiment 1.

[0128] To provide a zirconia layer on the doloma particles, the doloma particles were treated in the same manner as the magnesia particles according to Exemplary Embodiment 1. Thus, zirconia-coated doloma particles were provided having a mass ratio of 80% by weight doloma to 20% by weight zirconia, and further having a thickness of the zirconia coating on the doloma particles of about 150-500 μm.

[0129] Coated particle examples The previously described embodiment of the method for producing coated particles resulted in coated doloma particles whose surfaces were completely coated with a zirconia coating. At thicknesses of 150-500 μm, the mass fraction of the zirconia coating was approximately 20% by mass relative to the total mass of the coated particles. In other words, this method produced coated particles having a doloma core and whose surfaces were completely coated with a zirconia coating. The mass ratio of the core to the coating was 80% by mass to 20% by mass.

[0130] Batch Example Exemplary embodiments of batches according to the present invention were produced that included coated particles according to the exemplary embodiments described above.

[0131] These coated particles were mixed with a refractory basic material, a binding clay and a binder to form a batch.

[0132] The refractory basic material consisted exclusively of basic components in the form of sintered doloma and sintered magnesia, each of which was provided in a particle size range of >0 to 6.63 mm.

[0133] The binder was in the form of a non-aqueous organic binder, a temporary organic binder.

[0134] The ingredients, except for the binder, were placed in a mixer in the following proportions by weight relative to the total mass of the batch to form batches: Coated particles: 4% by mass Droma: 86.1% by mass Magnesia: 9.5% by mass Bonding clay: 0.4% by mass.

[0135] A binder was then added to the batch at a rate of 1.8% by weight based on the batch without the binder.

[0136] The ingredients were then mixed in a mixer to form a batch.

[0137] Example of a method for producing a sintered refractory product The method was carried out according to exemplary embodiment 1.

[0138] After firing, the product was therefore in the form of a sintered refractory according to the invention.

[0139] The product had first sintered particles in the form of sintered doloma and sintered magnesia particles, these first particles being formed from particles of the refractory basic material component.

[0140] The product also contained secondary particles formed from the coated particles. These secondary particles were in the form of doloma particles, each bearing a coating of calcium zirconate. The thickness of this calcium zirconate coating was somewhat greater than the thickness of the zirconia coating on the coated particles, i.e., approximately 200-600 μm.

[0141] The microstructure of the sintered refractory product had a matrix of sintered first particles with second particles embedded in the matrix.

[0142] The elastic modulus of the product was determined to be 96.4 GPa.

[0143] At the same time, the chemical content of ZrO2 in the product was 0.8% by mass relative to the total mass of the product, which is expected to give the product good resistance to FeO-rich slag.

[0144] Comparative Example Comparative Example 3 For comparison purposes, sintered refractory products were produced that differed from the product produced in accordance with Exemplary Embodiment 2 in that the coated particles were replaced by zirconia particles having particle sizes in the range of 2.80 to 6.63 mm, and the products were made from the following batches: Zirconia particles: 0.87% by mass Droma: 89.23% by mass Magnesia: 9.5% by mass Bonding clay: 0.4% by mass.

[0145] The resulting sintered refractory product had an elastic modulus of only 102.0 GPa. However, it had a chemical zirconia content of 0.9 wt. %. Due to this relatively high zirconia content, it is expected that this product will be relatively less resistant to FeO-rich slag than the product according to Exemplary Embodiment 2.

[0146] At the same time, the production of this product was associated with an economic disadvantage in that the provision of zirconia particles was significantly more expensive than the provision of coated particles according to the invention.

[0147] Scanning electron microscope images were made of cross sections of sintered refractory products produced in accordance with exemplary embodiments.

[0148] Two of these images are shown in the accompanying figures. [Brief explanation of the drawings]

[0149] [Figure 1] 1 shows a scanning electron microscope image of a region of a sintered refractory product according to Exemplary Embodiment 1. [Figure 2] 10 shows another scanning electron microscope image of a region of a sintered refractory product according to Exemplary Embodiment 2.

[0150] In Figures 1 and 2, the white scale at the bottom indicates a length of 1 mm. In this regard, it should be noted that the second particle shown in Figures 1 and 2, respectively, has an average particle size of greater than 2.8 mm. To the extent that particles appear to have an average particle size smaller than 2.8 mm in Figures 1 and 2, this is due to the particles extending vertically from the cut surface.

[0151] 1 and 2 each show a second particle in a sintered refractory product according to a respective exemplary embodiment.

[0152] FIG. 1 shows a second particle of magnesia coated with calcium zirconate. The calcium zirconate coating appears as a light area surrounding a dark area. The dark area represents the magnesia particle, i.e., the magnesia "core." The second particle shown in FIG. 1 is embedded in a matrix of sintered first particle of sintered doloma and sintered magnesia, which surrounds the outer light area of ​​calcium zirconate.

[0153] Figure 2 shows a second particle of doloma coated with calcium zirconate. The calcium zirconate coating appears as a light area surrounding a dark area. The dark area represents the doloma particle, i.e., the "core" of the doloma. The second particle shown in Figure 2 is embedded in a matrix of sintered doloma and sintered magnesia from the sintered first particle, surrounding the outer light area of ​​calcium zirconate.

Claims

1. Particles for the production of sintered refractory products, comprising: The particles are Particles made from magnesia, the surface of which has at least a partial zirconia coating; or Particles made from magnesite, the surface of which is at least partially coated with zirconia; or Particles made from doloma, the surface of which has at least a partial zirconia coating; or Particles made from dolomite and having a zirconia coating on at least a portion of their surface and The particles have a particle size of at least 2.8 mm. A particle having the following characteristics.

2. 10. The particles of claim 1 having a particle size in the range of 2.8 to 8.0 mm.

3. 2. The particle according to claim 1, wherein the weight percentage of the zirconia coating is in the range of 1 to 50 wt. % relative to the total weight of the particle.

4. 10. The particle of claim 1, wherein the zirconia coating has a thickness of at least 10 μm.

5. 10. The particle of claim 1, wherein the zirconia coating has a thickness in the range of 10 to 800 μm.

6. 1. A batch for the production of a sintered refractory product, said batch comprising particles, said particles comprising: Particles made from magnesia, the surface of which has at least a partial zirconia coating; or Particles made from magnesite, the surface of which is at least partially coated with zirconia; or Particles made from doloma, the surface of which has at least a partial zirconia coating; or Particles made from dolomite and having a zirconia coating on at least a portion of their surface and The particles have a particle size of at least 2.8 mm. A batch having the following characteristics.

7. 7. The batch of claim 6, comprising at least 1 wt. % of particles, based on the total weight of the batch.

8. 7. The batch of claim 6, comprising 1 to 15 wt. % of particles, based on the total weight of the batch.

9. 7. The batch of claim 6, comprising at least one calcium oxide-containing component.

10. 7. The batch of claim 6, wherein the at least one calcium oxide-containing component is at least one of doloma or dolomite.

11. 7. The batch of claim 6, wherein the at least one calcium oxide-containing component is present in particulate form.

12. 7. The batch of claim 6, which is a batch for the production of a sintered refractory dolomite product.

13. 38 to 90% by mass of MgO and 8 to 60% by mass of CaO, the remainder being ZrO ２ , SiO ２ , Fe ２ O ３ and Al ２ O ３ 7. The batch of claim 6 having a chemical composition:

14. 1. A method for the production of a sintered refractory product, comprising: providing a batch, said batch comprising particles, said particles comprising: Particles made from magnesia, the surface of which has at least a partial zirconia coating; or Particles made from magnesite, the surface of which is at least partially coated with zirconia; or Particles made from doloma, the surface of which has at least a partial zirconia coating; or Particles made from dolomite and having a zirconia coating on at least a portion of their surface and The particles have a particle size of at least 2.8 mm. providing a method for producing a pharmaceutical composition comprising the steps of: firing the batch to form a sintered refractory product; A method comprising:

15. 1. A sintered refractory product comprising: the product comprises particles sintered together; the particles include first particles and second particles; the first particles include particles containing calcium oxide; The second particles are Magnesite particles having a calcium zirconate coating on at least a portion of their surface; or Doloma particles, the surface of which has at least a partial calcium zirconate coating; or Dolomite particles having a calcium zirconate coating on at least a portion of their surface At least one of The second particles have a particle size of at least 2.8 mm. A sintered refractory product characterized by:

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