Refractory material, method for producing same, and use thereof

Abstract

The invention relates to a refractory material which is thermally treated at a temperature of at least 1300 °C, preferably 1300 °C to 1750 °C, such that the material has an acicular structure and comprises a combination of a first phase, a second phase, and a third phase, wherein: the first phase comprises 2-10 wt.% C, <5 wt.% N, 30-40 wt.% O, 50-70 wt.% Al, and <5 wt.% Si, based on the total proportion of the first phase, the second phase comprises 1-7 wt.% C, 3-8 wt.% N, 25-35 wt.% O, 55-65 wt.% Al, and <5 wt.% Si, based on the total proportion of the second phase, and the third phase comprises <7 wt.% C, 14-28 wt.% N, 10-15 wt.% O, 52-63 wt.% Al, and <20 wt.% Si, based on the total proportion of the third phase, to a batch composition for producing a refractory material, to a green body produced from a batch composition, to a method for producing a refractory material, and to the use of such a refractory material.

Description

The present invention relates to a refractory material, to a batch for producing a refractory material, to a green body produced from a batch, to a method for producing a refractory material, and to the use of such. Refractory materials find their application in high-temperature industrial processes, for example, and are therefore required to remain stable even under adverse circumstances and at very high temperatures. They are used for example in the steel industry, where they serve purposes including the manufacture of products such as functional articles (e.g., perforated blocks or impact absorbers) and / or of products for the provision and / or maintenance of steel ladles, tundishes and other metallurgical assemblies. Such metallurgical assemblies provided with products made from refractory materials are used in turn for holding and processing molten steel and other liquid metal products. Refractory materials therefore secure other substances and mixtures during their combustion, conversion, smelting, detonation, burning, melting and molding, and are therefore required to withstand thermal, mechanical and chemical loading. It is therefore desirable to provide a refractory material having good physical properties, such as high strength and high thermal shock resistance, for example, that allows a host of different refractory products to be produced. It is therefore the object of the present invention to provide a refractory material which has very good physical properties, such as, in particular, very good heat resistance and / or hot abrasion resistance, good thermal shock resistance, and low thermal conductivity. Moreover, it is also to be possible to be able to utilize the refractory material for a host of different refractory products, including in particular more complex cast products. The object of the present invention, therefore, is also that the refractory material with its advantageous properties can be obtained starting from a batch which has advantageous processing properties, such as good flow properties in particular. The object of the present invention is likewise to produce a green body from a batch that has advantageous physical and mechanical properties, such as increased strength (high cold crushing strength and cold modulus of rupture, in particular) after drying, therefore accompanied by enablement of improved handling qualities and also enhanced capacity for processing of the green body to give the refractory material (and hence to give a host of different refractory products as described above). The invention achieves this object by means of a refractory material treated thermally at a temperature of at least 1300°C, preferably of 1300° to 1750°C, to have an acicular structure and to comprise a combination of a first phase, a second phase and a third phase, wherein the first phase comprises 2-10% by weight C, <5% by weight N, 30-40% by weight O, 50-70% by weight Al and <5% by weight Si, based on the total fraction of the first phase, the second phase comprises >1% by weight C, 3-8% by weight N, 25-35% by weight O, 55-65% by weight Al and <5% by weight Si, based on the total fraction of the second phase, the third phase comprises <7% by weight C, 14-28% by weight N, 10-15% by weight O, 52-63% by weight Al and <20% by weight Si, based on the total fraction of the third phase. To begin with, a number of terms used in the context of the invention should be explained. The term “refractory material” is used in the present application in the manner familiar to the skilled person from the prior art. It is accordingly a material which is fire-resistant and resistant to high temperature. The refractory material is preferably produced from inorganic raw materials. The material is able in particular to withstand high temperatures of at least 1500°C or more without softening. The material preferably has a pyrometric cone equivalent of greater than SC 17 (= ISO 150), corresponding roughly to a temperature of 1500°C (see DIN 51 060). The pyrometric cone equivalent can be determined according to ISO 528 and DIN EN 993-12. The material is therefore suitable for the possibility of being in contact with liquid metal products and steel products for a certain time period without itself losing its external shape. In the context of the present invention, a “batch” is a shapeless or unshaped formulation which is used for producing the refractory material. The term “green body” is used in the present application in the manner familiar to the skilled person from the prior art. It is accordingly a formulation which is molded or cast into shape, but unfired, and which can still be easily worked. The term “green body after drying” is used in the present application to refer to a green body which according to standard DIN EN ISO 1927-5 has been dried to constant mass at a temperature of (110 ± 5)°C. In the context of the present invention, a “phase” is a spatial region in a solid body which differs both chemically and morphologically (i.e., in shape, form and structure) from its surroundings. The first phase preferably comprises 2-10% by weight C, 0.0015% by weight N, 30-40% by weight O, 50-70% by weight Al and 0.001-5% by weight Si, based on the total fraction of the first phase. The second phase preferably comprises 1-7% by weight C, 3-8% by weight N, 25-35% by weight O, 55-65% by weight Al and 0.001-5% by weight Si, based on the total fraction of the second phase. The third phase preferably comprises 0.001-7% by weight C, 1428% by weight N, 10-15% by weight O, 52-63% by weight Al and 0.001-20% by weight Si, based on the total fraction of the third phase. In accordance with the invention, the refractory material comprises a combination of the first phase, the second phase and the third phase. In accordance with the invention, the first phase preferably comprises Al4O4C or consists of Al4O4C. In accordance with the invention, further, the second phase preferably comprises Al28C6N6O21 or consists of Al28C6N6O21. In accordance with the invention, the third phase preferably comprises a compound selected from SiAl6O2N6, SiAl5O2N5, SiAl4O2N4, Si3Al7O3N9 and mixtures thereof. In accordance with the invention, further, the third phase preferably comprises SiAl6O2N6 or consists of SiAl6O2N6. The refractory material may comprise a fourth phase, in which case the fourth phase comprises <5% by weight C, 26-36% by weight N, <8% by weight O, 56-66% by weight Al and <5% by weight Si, based on the total fraction of the fourth phase, and the fourth phase preferably comprises AlN or consists of AlN. Further, the fourth phase may comprise 0.001-5% by weight C, 2636% by weight N, 0.001-8% by weight O, 56-66% by weight Al and 0.001-5% by weight Si, based on the total fraction of the fourth phase. The presence of the acicular structure or of phases with acicular structure may be determined preferably via scanning electron microscopy. The composition of the phases is determined preferably via scanning electron microscopy (SEM), with an excitation voltage of 10 kV and a probe current of 1 nA, using an energy-dispersive detector. The acicular structure preferably comprises needles with a length in a range of 0.1-50 pm, preferably 0.1-30 pm, more preferably 2-30 pm and / or with a thickness in a range of 0.01-8 pm, preferably 0.2-5 pm, measured via scanning electron microscopy, with an excitation voltage of 10 kV and a probe current of 1 nA. A minimal ratio of lengths to thicknesses (at least for some) of the needles is preferably at least 4:1. Preferably at least 20%, more preferably at least 40%, of the needles of the acicular structure have a minimal ratio of the lengths to thicknesses of at least 4:1. Preferably at least 20%, more preferably at least 40%, of the needles of the acicular structure in a region of at least 1000 pm x 1000 pm have a minimal ratio of the lengths to thicknesses of the needles of at least 4:1. This may be determined via scanning electron microscopy, with an excitation voltage of 10 kV and a probe current of 1 nA. The refractory material further preferably comprises holelike structures (or structures which appear circular at polished sections). The holelike structures or structures of circular appearance preferably comprise a (predominant) portion of the acicular structures. In one preferred embodiment, a (predominant) portion of the needles are formed at the surfaces of the holelike structures or structures of circular appearance. In accordance with the invention, preferably, a proportion of the phases with acicular structure is at least 0.01% by weight, preferably 0.1% by weight, based on the total fraction of the refractory material. The refractory material preferably has an open porosity in a range of 10.0-25.0% by volume, measured according to DIN EN ISO 1927-6, and / or a bulk density in a range of 2.95-3.70 g / cm3, measured according to DIN EN ISO 1927-6. The refractory material is preferably refractory functional articles, more preferably refractory castings and / or pressing products, even more preferably refractory products in the flow control sector, more preferably still slide gate plates, collector nozzles, shrouded tubes, stoppers, submerged tubes, inner nozzles, weirs, dams, impact absorbers and other nozzles. In the context of the present invention, the term “functional article” is to be understood to mean a product that is manufactured partly or entirely from the refractory material and has been subjected to shaping, by casting and / or molding. The invention has the advantage that the refractory material of the invention has very good physical properties. In particular, for example, the refractory material exhibits very good heat resistance / hot abrasion resistance and at the same time, too, very good thermal shock resistance. The refractory material of the invention is resistant to high temperature and is able to withstand temperatures of at least 1700°C without softening. It has an acicular structure with very stable phases which form in situ. The fine needles, which form in many regions of the material, are very likely responsible for the good thermal shock resistance. In addition, the refractory material of the invention displays low thermal heat conductivity. This not only has the advantage that the refractory material has good insulation properties but also results in an improvement in the pouring capacity of the products obtained from the refractory material. The reason is that, owing to low thermal heat conductivity of the material, an accumulation of solid constituents or particles on the refractory material, i.e., unwanted clogging, is avoided. One subject of the invention is also a batch for producing a refractory material of the invention, preferably as claimed in any of claims 1 to 8, wherein the batch comprises the following constituents: a) granular component as a coarse fraction having a particle size in a range of 0.5-10 mm, selected from MA spinel (magnesium aluminate spinel), sintered alumina, high-grade a-alumina, brown a-alumina, gray a-alumina, mullite, bauxite, andalusite, SiC, grog, zirconium-containing components and mixtures thereof; b) granular component as a fine fraction having a particle size in a range of <0.5 mm, selected from sintered alumina, high-grade a-alumina, zirconium-containing components and mixtures thereof; c) finely divided Al2O3, preferably calcined alumina as a fine fraction having a particle size in a range of <0.5 mm; d) carbon, preferably graphite and / or carbon black, more preferably a mixture of graphite and carbon black, more preferably still a mixture of graphite and carbon black with a mixing ratio in a range from 1:2 to 2:1, more preferably still a mixture of graphite and carbon black with a mixing ratio of 1:1; e) metallic aluminum powder (Al powder); f) dry phenolic resin binder, preferably dry pulverulent phenolic resin binder; and g) silica sol (silica in aqueous colloidal suspension), preferably silica containing SiO2 nanoparticles in aqueous colloidal suspension. The batch of the invention is produced preferably from a dry formulation (preferably comprising constituents a) to f)) by mixing with silica sol (silica in aqueous colloidal suspension; comprising constituent g)). In the dry formulation, the constituents are in chemically unaltered form. Binding of the formulation, based on what is called a sol-gel reaction, takes place only through addition of the silica sol (the silica in aqueous colloidal suspension). In the context of the present invention, therefore, the batch already contains all the constituents which must be present for production of the refractory material. The batch comprises the granular component as a coarse fraction having a particle size in a range of 0.5-10 mm, selected from MA spinel (magnesium aluminate spinel), sintered alumina, highgrade a-alumina, brown a-alumina, gray a-alumina, mullite, bauxite, andalusite, SiC, grog, zirconium-containing components and mixtures thereof. The granular component in the coarse fraction is preferably selected from a group of non-basic components. The use of non-basic components entails better processing qualities and also a more advantageous cure time after mixing with the silica sol (silica in aqueous colloidal suspension). The reason is that, generally, basic components greatly accelerate the binding process (what is called the solgel process), and so the use of suitable non-basic components here thus allows an optimal balance to be established between processing qualities and cure time. The batch also comprises the granular component as a fine fraction having a particle size in a range of <0.5 mm. This serves in particular for matrix filling. It was possible to determine, furthermore, that the granular component in the fine fraction has a positive influence on the flow properties of the batch, especially on casting. The batch further comprises carbon. Carbon is vital as a source for the formation of the phases formed in situ. In one preferred embodiment, there is a mixture of graphite and carbon black with a mixing ratio in a range from 1:2 to 2:1, more preferably a mixture of graphite and carbon black with a mixing ratio of 1:1. In this way, a very good trade-off is obtained between the physical properties achieved in the refractory material and the processing qualities of the batch. It was possible to determine here that graphite tends to have a positive influence on the wetting properties (and hence the resistance to infiltration and slag formation), while the more reactive carbon black positively influences the formation of the phases formed in situ. The batch further comprises metallic aluminum powder. The metallic aluminum powder has the advantageous function in particular of preventing the degradation (or the oxidation) of carbon. The aluminum powder preferably has a particle size <0.1 mm, more preferably <0.075 mm, more preferably still <0.065 mm. The batch further comprises dry (preferably pulverulent) phenolic resin binder. The dry (preferably pulverulent) phenolic resin binder has the advantageous function in particular of markedly increasing the strength of the green body after drying. The phenolic resin binder used is, for example, a standard commercial phenol-formaldehyde resin of the novolac type. One example of such a dry (preferably pulverulent) phenolic resin binder is Borofen BLR 3509. This addition of binder results in a significantly increased strength and thus facilitated handling qualities and improved transportability of the green body after drying. This is manifested in qualities including greatly increased cold crushing strength and cold modulus of rupture of the green body by comparison with a green body produced from a batch without such addition of binder. In this way, for instance, the failure rate due to disintegrated green bodies in the production of the refractory material can be markedly reduced. It has surprisingly emerged here that even a small addition of binder is sufficient to achieve a large advantageous effect for the strength of the green body. At the same time, the refractoriness of the refractory material is not adversely affected by this addition. The batch further comprises silica sol (silica in aqueous colloidal suspension), preferably silica containing SiO2 nanoparticles in aqueous colloidal suspension. This is a suspension of fine amorphous, nonporous and typically spherical silica particles in an aqueous phase. Colloidal silica is not the same as customary (dried) silica (e.g., (dried) fumed silica). The silica sol (the silica in aqueous colloidal suspension) serves in particular as a mixing fluid and binder for the refractory material. A solids fraction (fraction of SiO2 particles) in the silica sol (in the aqueous colloidal silica suspension) is preferably in a range from 20% to 50% by weight, more preferably 30% to 50% by weight, based on the total weight of the silica sol. Replacing a customary silica plus water with a silica sol, namely a silica in aqueous colloidal suspension, is a considerable advantage. The reason is that, when customary silica is used, in certain pH ranges the metal (aluminum) would react with water after the constituents were mixed. This reaction is highly exothermic, and would also give rise to hydrogen gas (H2). Furthermore, when using aluminum, an aluminum oxide layer (Al2O3) would form in the marginal region. These are reactions to avoid. Firstly, the formation of H2 is disadvantageous on safety grounds; secondly, there would be less aluminum available for the phases formed in situ. Furthermore, however, because of the exothermic reaction and formation of gas, there would also be formation of cracks and layers in the green body. This is prevented by the use of a silica sol, that is a colloidal silica or a colloidal silica suspension. The batch may comprise one or more of the following constituents in the following amounts, based on the total fraction of the batch composition: a) 50-80% by weight, preferably 53-70% by weight, more preferably 55-67% by weight, more preferably still about 59% by weight, of granular component as a coarse fraction having a particle size in a range of 0.5-10 mm; b) 5-35% by weight, preferably 7-30% by weight, more preferably 10-30% by weight, more preferably still about 19% by weight, of granular component as a fine fraction having a particle size in a range of <0.5 mm; c) 0.05-15% by weight, preferably 2-12% by weight, more preferably 5-10% by weight, more preferably still about 7% by weight, of finely divided Al2O3; d) 2-10% by weight, preferably 3-8% by weight, more preferably 3.5-6% by weight, more preferably still about 4.5% by weight, of carbon; e) 3-10% by weight, preferably 4-9% by weight, more preferably 5-8% by weight, more preferably still about 5% by weight, of metallic aluminum powder (Al powder); f) 0.1-4% by weight, preferably 0.2-2% by weight, more preferably 0.3-1% by weight, more preferably still about 0.5% by weight, of dry (preferably pulverulent) phenolic resin binder; g) 4-15% by weight, preferably 5-12% by weight, more preferably 6-8% by weight, more preferably still about 7% by weight, of silica sol (silica in aqueous colloidal suspension), preferably silica containing    SiO2 nanoparticles in aqueous colloidal suspension, wherein the solids fraction (fraction of the SiO2 particles) is preferably in a range from 20% to 50% by weight, more preferably 30% to 50% by weight, based on the total weight of the silica sol (the aqueous colloidal silica suspension). Also one subject of the invention, moreover, is a green body produced from a batch of the invention, preferably a batch as claimed in claim 9 or 10, wherein the green body after drying preferably has an open porosity of about 10-25% by volume, measured according to DIN EN ISO 1927-6, and / or a bulk density in a range of 2.90-3.70 g / cm3, preferably about 2.98 g / cm3, measured according to DIN EN ISO 1927-6. The green body after drying preferably has a cold crushing strength of greater than 40 MPa, more preferably greater than 50 MPa, very preferably greater than 60 MPa, measured according to DIN EN ISO 1927-6, and / or a cold modulus of rupture of greater than 6 MPa, more preferably greater than 8 MPa, very preferably greater than 9 MPa, measured according to DIN EN ISO 1927-6. These properties of the green body lead to good strength and thus very good handling qualities and transportability of the green body. Also one subject of the invention is, moreover, a method for producing a refractory material of the invention, preferably a refractory material as claimed in any of claims 1 to 8, wherein the method comprises the following steps: i. providing a batch of the invention, preferably as claimed in either of claims 9 and 10; ii. producing a green body from the batch, and iii. heating the green body to a temperature of at least 1300°C, preferably to a temperature in a range from 1300°C to 1750°C. Here, the providing of the batch of the invention in step i. takes place preferably starting from a dry formulation (preferably comprising constituents a) to f)) which is produced by the mixing with silica sol (silica in aqueous colloidal suspension; comprising constituent g)). The producing of the green body from the batch in step ii. preferably involves casting and / or molding. In step iii. of the method, the green body is heated to a temperature of at least 1300°C. This preferably involves the green body being heated to a temperature in the range from 1300 to 1750°C. As a result, in particular, the refractory material can acquire the properties according to the invention. The green body is heated here preferably in a gas atmosphere of air with reduced oxygen content. The purpose of reducing the oxygen content in the air is to prevent the external oxidation of the green body. The reduction in the oxygen content can be achieved, for example, by embedding the green body in carbon particles. Also one subject of the invention, furthermore, is a refractory material which has an acicular structure and comprises a combination of a first phase, a second phase and a third phase, wherein the first phase comprises 2-10% by weight C, <5% by weight N, 30-40% by weight O, 50-70% by weight Al and <5% by weight Si, based on the total fraction of the first phase, the second phase comprises >1% by weight C, 3-8% by weight N, 25-35% by weight O, 55-65% by weight Al and <5% by weight Si, based on the total fraction of the second phase, the third phase comprises <7% by weight C, 14-28% by weight N, 10-15% by weight O, 52-63% by weight Al and <20% by weight Si, based on the total fraction of the third phase, produced by a method of the invention, preferably a method as claimed in claim 13. Likewise one subject of the invention is the use of a refractory material of the invention, preferably as claimed in any of claims 1 to 8, of a green body produced from a batch as claimed in either of claims 9 and 10 for producing refractory products for steel applications, especially steel ladles, tundishes, perforated blocks, CAS-OB bells, refractory products for the pig iron sector, especially casting products, and / or refractory products for the flow control sector, especially slide gate plates, collector nozzles, shrouded tubes, stoppers, spouts, submerged pipes, inner nozzles, weirs, dams, impact absorbers and other nozzles. In the context of the invention, products in the flow control sector are understood to be refractory products which make it possible, for example, to obtain liquid metal or steel products or to guide or prevent the flow of such products. Products in the flow control sector require not only good physical properties, such as high strength, but also good processing properties in the formulation for processing, so as to be able to produce the components, some of which have complex shapes. A key advantage of the flow control products, preferably based on cast products, by comparison with products of isostatic pressing is seen as being a considerable cost reduction. A further advantage of the invention is therefore that with the batch of the invention and / or the method of the invention it is possible not only to obtain refractory materials having very good physical properties, such as high heat resistance, etc., but also to achieve good processing properties in the formulation for processing, for the production of relatively complex components, not least by casting. The invention is now described illustratively through a number of advantageous embodiments, with reference to the appended drawings, in which: Fig. 1:   shows an image of the refractory material of the invention via light microscopy. Fig. 2:   shows an image of a subregion shown in Fig. 1, generated via scanning electron microscopy. Fig. 3:   shows a further image of the refractory material of the invention via light microscopy. Fig. 4: shows an image of the other region marked in Fig. 3, generated via scanning electron microscopy. Fig. 5: shows the slag resistance of the refractory material of the invention (left) in comparison to that of a known refractory material (right). Fig. 6: shows the results of a test with the refractory material of the invention and comparison materials for softening characteristics under pressure (pressure softening). Production of a refractory material: Elucidated presently is how a refractory material of the invention can be produced starting from a batch of the invention. First of all, a batch comprising the following constituents was produced: 58.4 wt% granular component consisting of sintered alumina as a coarse fraction having a particle size in a range of 0.5-10 mm 9.4 wt% sintered alumina (<0.5 mm) 8.9 wt% high-grade a-alumina (<0.2 mm) 6.5 wt% calcined alumina 1A 2.3 wt% graphite, Hunan 80 / 200 GBK 2.3 wt% thermal carbon black, beaded 4.7 wt% metallic aluminum powder (Al met) (<0.063 mm) 0.5 wt% dry (pulverulent) phenolic resin binder 7.0 wt% silica sol (silica in aqueous colloidal suspension), with 40 wt% solids fraction (fraction of the SiO2 particles), based on the total weight of the silica sol (of the aqueous colloidal silica suspension). The batch was obtained by mixing a silica sol (silica in aqueous colloidal suspension), containing SiO2 nanoparticles, with a dry formulation that comprised the remaining constituents of the batch. A green body was then produced from this batch by casting. The green body was subsequently heated to a temperature of 1500°C in a gas atmosphere (air with reduced oxygen content). The reduction in the oxygen content in the gas atmosphere was achieved by embedding the green body in carbon particles. In this way, the refractory material of the invention was obtained. Physical properties: Reproduced below are the physical properties of a green body of the invention and of a refractory material of the invention, produced according to the method described above. They are contrasted for comparison, additionally, with the physical data of two non-inventive refractory materials. These are DELTEK A115 from RHI Magnesita, and a green body and a refractory material produced from a batch without addition of dry (pulverulent) phenolic resin binder according to the method described above. Table 1: Physical properties of a green body of the invention, of a refractory material of the invention and of two comparison materials. Green body Green body, Comparison of the or refractory material invention, material (DELTEK or without dry A115) refractory (pulverulent) material of phenolic the resin binder invention Green body after drying at 110°C, as per standard DIN EN ISO 1927-5 Bulk density (DIN EN ISO 1927-6) [g / cm3] 2.98 2.96 2.53 Open porosity (DIN EN ISO 1927-6) [vol%] 13.0 14.0 17.3 Cold crushing strength (DIN EN ISO 1927-6) [MPa] 50.0 35.0 - Cold modulus of rupture (DIN EN ISO 1927-6) [MPa] 8.0 5.0 8.4 Hot modulus of rupture at 1500°C in reducing atmosphere (with specimens cast as per DIN EN ISO 1927-5, format 130x20x20mm, measurement principle as per ISO 5013) [MPa] 15.0 17.0 8.0 After heating to 1000°C in reducing atmosphere, as per DIN EN ISO 1927-5 Bulk density (DIN EN ISO 1927-6) [g / cm3] 3.0 3.0 - Open porosity (DIN EN ISO 1927-6) [vol%] 12.0 13.0 - Cold crushing strength (DIN EN ISO 1927-6) [MPa] 150.0 170.0 - Cold modulus of rupture (DIN EN ISO 1927-6) [MPa] 23.0 24.0 - After heating to 1500°C in reducing atmosphere, as per DIN EN ISO 1927-5 Bulk density (DIN EN ISO 1927-6) [g / cm3] 3.0 3.0 - Open porosity (DIN EN ISO 1927-6) [vol%] 14.0 13.0 - Cold crushing strength (DIN EN ISO 1927-6) [MPa] 120 140 - Cold modulus of rupture (DIN EN ISO 1927-6) [MPa] 19.0 24.0 - Thermal conductivity (as per Dr. Klasse*) [W / mK]: 200°C 5.2 5.2 14.7 400°C 5.2 5.2 13.7 600°C 4.9 4.9 12.4 800°C 4.6 4.6 12.0 1000°C 4.7 4.7 11.7 *Klasse, F.; Heinz, A.; Hein, J.: Vergleichsverfahren zur Ermittlung der Warmeleitfahigkeit keramischer Werkstoffe [Comparative method for determining the thermal conductivity of 5 ceramic materials]. Ber. DKG 34 (1957), pp. 183 - 189. Table 1 shows that the green body of the invention after drying has a markedly higher strength than a green body after drying which has been produced from a batch without addition of dry 10 (pulverulent) phenolic resin binder. This is manifested in particular in the markedly elevated values for the cold crushing resistance and cold modulus of rupture and therefore enables intact transport of such green bodies of the invention to the customer and also reliable usage of such green bodies of the 15 invention by the customer. Moreover, the thermal heat conductivity of the refractory material of the invention is low by comparison with the known material DELTEK A115. The considerably lower thermal heat conductivity of the refractory material of the invention provides better insulation properties and so has a positive influence on the flow properties of the material, as unwanted clogging can be prevented. Clogging is understood as the accumulation of solid constituents and / or particles in a component or spout system, leading possibly to disruption to casting and hence to reduced pouring capacity of the refractory material. Measurement methods: For the measurements of the properties as per DIN EN ISO 19276, geometry D specified in that standard was used. The refractory material was investigated by light microscopy and scanning electron microscopy. Light-microscopic investigations were performed using a NIKON Eclipse LV150. Analyses using the scanning electron microscope were performed using a JEOL JSM-6460 or using a JEOL JSM-7900F scanning electron microscope. The composition of the individual phases was able to be determined via scanning electron microscopy with an excitation voltage of 10 kV and a probe current of 1 nA, using an energy-dispersive detector. The scanning electron microscope images were generated using a BSE detector. Fig. 1 shows an image of a refractory material of the invention via light microscopy, in which the acicular structure of the material is evident. In particular, regions that can be seen include those with structures having a holelike or circular appearance, in which the acicular structures of the material are preferentially formed. The needles preferably have a low thickness in a range of 0.01-8 pm, more preferably 0.2-5 pm. It is assumed that the fine needles which form in many regions are very likely responsible for the very good thermal shock resistance of the refractory material. It is additionally assumed that the circular structures in the refractory material may prevent crack propagation. Fig. 2 shows an image, generated via scanning electron microscopy, of the refractory material from Fig. 1, with Fig. 2 depicting the region marked in Fig. 1. The acicular structure of the material is evident even more markedly from Fig. 2. Marked in Fig. 2 are the regions 1 to 4, which contain accordingly the four phases described in this application. Fig. 3 shows a further image of the refractory material of the invention via light microscopy, in which further regions of holelike structure are evident, in which the acicular structures of the material have formed in situ. Fig. 4 shows an image, generated via scanning electron microscopy, of the region marked in Fig. 3. In this region as well, the refractory material has an acicular structure. Additionally marked in Fig. 4 are the regions 1 to 4, which contain accordingly the four phases described in this application. Test for slag resistance: The refractory material of the invention was tested against both an acidic (C / S = 0.8) and a basic (C / S = 3.2) slag composition for slag resistance. The slag resistance is the capacity of the refractory material to withstand the detrimental effect of molten slags. The refractory material of the invention here showed very good slag resistance, not least in comparison with a known refractory material for steel ladles (comparison material COMPRIT 185HMV from RHI Magnesita) (see Fig. 5, showing on the left the material of the invention and on the right the comparison material COMPRIT 185HMV from RHI Magnesita). Test for pressure softening (softening characteristics under pressure): Furthermore, a test for the softening characteristics under pressure (pressure softening) was carried out with the refractory material. Used for this test were, firstly, the refractory material of the invention and, secondly, a refractory material produced from a batch without addition of dry (pulverulent) phenolic resin binder according to the method described above, along with a known refractory material (ANKO 85MR5A from RHI Magnesita), as comparison materials. The test was carried out with a sample cast as per DIN EN ISO 1927-5. The sample was dried to constant mass as per DIN EN ISO 1927-5 at a temperature of 110°C. Test specimen: cylinder (height (h): 50 mm, diameter (d): 40 mm, internal hole: 16 mm, measurement method as per ISO 5013) The measurements for the softening characteristics under pressure (pressure softening) were carried out as per DIN EN ISO 1893. In this case an applied load of 0.2 MPa and a heating rate of 5°C / min in reducing atmosphere were selected. The result obtained was a T0.5 of >1700°C. That is to say, this figure is the temperature at which the maximum thermal expansion of the specimen has decreased by 0.5%. The maximum temperature of the measurement is limited to 1700°C. For the material of the invention, in contrast to the known refractory material ANKO 85MR5A, no softening was able to be found up to a temperature of 1700°C. The addition of dry (pulverulent) phenolic resin binder had no adverse influence on the softening characteristics under pressure, as evident in particular in the comparison with the material produced without addition of phenolic resin binder (Fig. 6). Test for measuring the thermal conductivity as per Dr. Klasse: 5 The thermal conductivities reported in Table 1 for the material of the invention and for the comparison materials (DELTEK A115 from RHI Magnesita and the material produced without addition of dry (pulverulent) phenolic resin binder) were determined by the method of Dr. Klasse (Klasse, F.; Heinz, A.; Hein, J.: 10 Vergleichsverfahren zur Ermittlung der Warmeleitfahigkeit keramischer Werkstoffe [Comparative method for determining the thermal conductivity of ceramic materials]. Ber. DKG 34 (1957), pp. 183 — 189). The values reported for 1000°C were extrapolated here.

Claims

1. A refractory material treated thermally at a temperature of at least 1300°C, preferably of 1300°C to 1750°C, to have an acicular structure and to comprise a combination of a first phase, a second phase and a third phase, wherein:the first phase comprises 2-10% by weight C, <5% by weight N, 30-40% by weight O, 50 -70% by weight Al and <5% by weight Si, based on first phase, the total fraction of the the second phase comprises 1-7% by weight C, 3-8% by weight N, 25-35% by weight O, 55 -65% by weight Al and <5% by weight Si, based on the total fraction of thesecond phase, andthe third phase comprises <7% by weight C, 14-28% by weight N, 10-15% by weight O, 52-63% by weight Al and <20% by weight Si, based on the total fraction of the third phase.

2. The refractory material as claimed in claim 1, characterized in that the first phase comprises Al4O4C or consists of Al4O4C.

3. The refractory material as claimed in claim 1 or 2, characterized in that the second phase comprises Al28C6N6O21 or consists of Al28C6N6O21.

4. The refractory material as claimed in any of claims 1 to 3, characterized in that the third phase comprises a compound selected from SiAl6O2N6, SiAl5O2N5, SiAl4O2N4, Si3Al7O3N9 and mixtures thereof or consists of SiAl6O2N6.

5. The refractory material as claimed in any of claims 1 to 4, characterized in that the refractory material comprises a fourth phase, in which case the fourth phase comprises <5% by weight C, 26-36% by weight N, <8% by weight O, 56-66% by weight Al and <5% by weight Si, based on the total fraction of the fourth phase, and the fourth phase preferably comprises AlN or consists of AlN.

6. The refractory material as claimed in any of claims 1 to 5, characterized in that the acicular structure comprises needles with a length in a range of 0.1-50 pm, preferably 0.1-30 pm, more preferably 2-30 pm and / or with a thickness in a range of 0.01-8 pm, preferably 0.2-5 pm, measured via scanning electron microscopy, with an excitation voltage of 10 kV and a probe current of 1 nA.

7. The refractory material as claimed in any of claims 1 to 6, characterized in that a minimal ratio of lengths to thicknesses at least for some of the needles is at least 4:1.

8. The refractory material as claimed in any of claims 1 to 7, characterized in that a fraction of the phases with acicular structure is at least 0.01% by weight, preferably 0.1% by weight, based on the total fraction of the refractory material.9.A batch for producing a refractory material as claimedin any of claims 1 to 8, wherein the batch comprises thefollowing composition:a) granular component as a coarse fraction having a particle size in a range of 0.5-10 mm, selected from MA spinel (magnesium aluminate spinel),sintered alumina, high-grade a-alumina, brown a-alumina, gray a-alumina, mullite, bauxite, andalusite, SiC, grog, zirconium-containing components and mixtures thereof;b) granular component as a fine fraction having a particle size in a range of <0.5 mm, selected from sintered alumina, high-grade a-alumina, zirconium-containing components and mixtures thereof;c) finely divided Al2O3, preferably calcined alumina as a fine fraction having a particle size in a range of <0.5 mm;d) carbon, preferably graphite and / or carbon black, more preferably a mixture of graphite and carbon black, more preferably still a mixture of graphite and carbon black with a mixing ratio in a range from 1:2 to 2:1, more preferably still a mixture of graphite and carbon black with a mixing ratio of 1:1;e) metallic aluminum powder (Al powder);f) dry phenolic resin binder, dry preferably pulverulent phenolic resin binder; andg) silica sol (silica in aqueous colloidalsuspension), preferably silica containing SiO2nanoparticles in aqueous colloidal suspension.10.The batch as claimed in claim 9, characterized in that one or more of the following constituents are present in the following amounts, based on the total fraction of the batch composition:a) 50-80% by weight, preferably 53-70% by weight, more preferably 55-67% by weight, more preferably still about 59% by weight, of granular component as a coarse fraction having a particle size in a range of 0.5-10 mm;b) 5-35% by weight, preferably 7-30% by weight, more preferably 10-30% by weight, more preferably still about 19% by weight, of granular component as a fine fraction having a particle size in a range of <0.5 mm;c) 0.05-15% by weight, preferably 2-12% by weight,more preferably 5-10% by weight, more preferablystill about 7%, by weight of finely divided Al2O3;d) 2-10% by weight, preferably 3-8% by weight, more preferably 3.5-6% by weight, more preferably still about 4.5% by weight, of carbon;e) 3-10% by weight, preferably 4-9% by weight, more preferably 5-8% by weight, more preferably still about 5% by weight, of metallic aluminum powder;f) 0.1-4% by weight, preferably 0.2-2% by weight, more preferably 0.3-1% by weight, more preferably still about 0.5% by weight, of dry (preferably pulverulent) phenolic resin binder;g) 4-15% by weight, preferably 5-12% by weight, more preferably 6-8% by weight, more preferably still about 7% by weight, of silica sol (silica in aqueous colloidal suspension), preferably silica containing SiO2 nanoparticles in aqueous colloidal suspension, wherein the solids fraction (fraction of the SiO2particles) is preferably in a range from 20% to 50% by weight, more preferably 30% to 50% by weight, based on the total weight of the aqueous colloidal silica suspension.

11. A green body produced from a batch as claimed in claim 9 or 10, characterized in that the green body after drying preferably has one or more of the following properties:- an open porosity of about 10-25% by volume, measured according to DIN EN ISO 1927-6;- a bulk density in a range of 2.90-3.70 g / cm3, preferably about 2.98 g / cm3, measured according to DIN EN ISO 1927-6.

12. A green body produced from a batch as claimed in claim 9 or 10, characterized in that the green body after drying preferably has one or more of the following properties:- a cold crushing strength of greater than 40 MPa, preferably greater than 50 MPa, very preferably greater than 60 MPa, measured according to DIN EN ISO 1927-6;- a cold modulus of rupture of greater than 6 MPa, preferably greater than 8 MPa, very preferably greater than 9 MPa, measured according to DIN EN ISO 1927-6.

13. A method for producing a refractory material as claimed in any of claims 1 to 8, wherein the method comprises the following steps:i. providing a and 10; batch as claimed in either of claims 9 ii. producing a green body from the batch, and iii. heating the green body to a temperature of at least5 1300°C 1300°C , preferably to a temperature in a to 1750°C. range from 10 14. The use of claims 1 to claimed in refractory a refractory material as claimed 8, of a green body produced from either of claims 9 and 10 for products for steel applications, in any of a batch as producing especiallysteel ladles, tundishes, perforated blocks, CAS-OB bells, refractory products for the pig iron sector, especially casting products, and / or refractory products for the flow control sector, especially slide gate15           plates, collector submerged pipes, nozzles, shrouded tubes, stoppers, inner nozzles, weirs, dams, impactabsorbers and other nozzles.

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