BACKFILL FOR PRODUCING A BASIC HEAVY-CLAY REFRACTORY PRODUCT, SUCH A PRODUCT AND METHOD FOR PRODUCING SAME, LINING OF AN INDUSTRIAL FURNACE, AND INDUSTRIAL FURNACE

Abstract

A dry backfill for producing a basic molded heavy-clay refractory product, to such a product and a method for producing the same, to a lining of an industrial furnace, and to an industrial furnace.

Claims

1. Dry batch for the production of a coarse ceramic, refractory, shaped, fired or unfired magnesia spinel product, in particular for a working casing or a backing of a large-volume industrial furnace, preferably a cement kiln, a lime shaft or lime rotary kiln, a magnesite or dolomite kiln, or a heating kiln or a kiln for energy generation or a steel production kiln or a kiln of the non-ferrous metal industry, comprising a dry substance mixture consisting of: a) a granular magnesia component of at least one magnesia having an MgO content <91.5 ma. %, preferably <90 ma. %, particularly preferably <89 ma. %, as the main component in an amount of ≥70 ma. %, preferably in an amount of ≥85 ma. %, b) a granular elastifier component in an amount of 2 to 10 ma. %, preferably of 3 to 8 ma. %, particularly preferably of 4 to 6 ma. %, of at least one sintered bauxite, the elastifier component having a grain size according to DIN 66165-2:2016-08≤2.5 mm, preferably of ≤2 mm, and the elastifier component having grains with a grain size according to DIN 66165-2:2016-08 of ≤0.5 mm at most in an amount of ≤25 ma. %, preferably ≤20 ma. %, especially ≤15 ma. %, and c) optionally a further granular magnesia component of at least one magnesia with a higher MgO content than the main component.

2. Batch according to claim 1, wherein the elastifier component comprises grains with a grain size according to DIN 66165-2:2016-08 of ≤0.2 mm at most in an amount of ≤10 ma. %, preferably ≤7 ma. %, especially ≤5 ma. %.

3. Batch according to claim 1, wherein the elastifier component comprises grains with a grain size according to DIN 66165-2:2016-08 of >2 mm at most in an amount of ≤25 ma. %, preferably ≤20 ma. %, especially ≤10 ma. %.

4. Batch according to claim 1, wherein the MgO content of the at least one magnesia of the main component is 85 to <91.5 ma. %, preferably 85 to <90 ma. %, preferably 87 to <89 ma. %.

5. Batch according to claim 1, wherein the at least one sintered bauxite has an Al.sub.2O.sub.3 content of 70 to 92 ma. %, preferably of 78 to 91 ma. %.

6. Batch according to claim 1, wherein the averaged MgO content of all magnesia grades of the dry substance mixture taken together is 85 to 91.5 ma. %, preferably 87 to 90 ma. %, particularly preferably 87 to 89 ma. %.

7. Batch according to claim 1, wherein the averaged MgO content of all magnesia grades of the dry substance mixture taken together is ≤91.5 ma. %, preferably ≤90 ma. %, more preferably ≤89 ma. %.

8. Batch according to claim 1, wherein the CaO/SiO.sub.2 ratio of all components of the dry substance mixture taken together is 1.2 to 3.0, preferably 1.5 to 2.5.

9. Batch according to claim 1, wherein the dry substance mixture comprises the further magnesia component in an amount of 5 to 28 ma. %, preferably of 10 to 22 ma. %.

10. Batch according to claim 1, wherein the batch does not contain any MnO, or MnO.sub.2, or Mn.sub.2O.sub.3 raw material.

11. Batch according to claim 1, wherein the batch comprises at least one dry binder and/or at least one dry additive in addition to the dry substance mixture.

12. Batch according to claim 1, wherein the batch consists of at least 90% by weight, preferably of at least 95% by weight, more preferably of at least 98% by weight, particularly preferably of 100% by weight, of the dry substance mixture, in relation to the total dry mass of the batch.

13. Batch according to claim 1, wherein the elastifier component exclusively comprises crushed granular material(s).

14. Batch according to claim 1, wherein the dry substance mixture exclusively comprises crushed granular material(s).

15. Batch according to claim 1, wherein the grain size distribution of the main component and/or the grain size distribution of the elastifier component and/or the grain size distribution of the further granular magnesia component and/or the grain size distribution of all magnesia grades of the dry substance mixture taken together is continuous.

16. Coarse ceramic, refractory, shaped or unshaped, fired or unfired magnesia spinel product, in particular for a working casing or a backing of a large-volume industrial furnace, preferably a cement kiln, a lime shaft or lime rotary kiln, a magnesite or dolomite kiln, or a heating kiln or a kiln for energy production or a steel production kiln or a kiln of the non-ferrous metal industry, wherein the product is produced from a batch according to claim 1.

17. Product according to claim 16, wherein the product is produced from a press mass containing the batch and at least one liquid binder and/or water.

18. Product according to claim 17, wherein the liquid binder is a binder from the following group: thermosetting synthetic resin binder, in particular phenol-formaldehyde resin or molasses or lignin sulfonate, or a sulfur-free binder, in particular a binder on the basis of dextrose, an organic acid, an Al.sub.2O.sub.3 binder, phosphoric acid, a phosphate binder, water glass, ethyl silicate, or a sulfate, e.g. magnesium sulfate or aluminum sulfate, or a sol-gel system.

19. Product according to claim 16, wherein the shaped product is a green, in particular pressed, shaped body, preferably a brick.

20. Product according to claim 16, wherein the shaped product is a tempered shaped body, preferably a brick.

21. Product according to claim 16, wherein the shaped product is a fired shaped body, preferably a brick.

22. Product according to claim 21, wherein the fired shaped body, preferably the brick, has an E-modulus of 15 to 35 GPa, preferably of 18 to 30 GPa.

23. Product according to claim 21, wherein the fired shaped body, preferably the brick, has a G-modulus of 7 to 16 GPa, preferably of 8 to 14 GPa.

24. Product according to claim 21, wherein the fired shaped body, preferably the brick, has a cold compressive strength according to DIN EN 993-5:1998-12 of 40 to 120 MPa, in particular of 50 to 90 MPa.

25. Product according to claim 21, wherein the fired shaped body, preferably the brick, has a cold bending strength according to DIN EN 993-6:1995-04 of 3 to 10 MPa, in particular of 4 to 7 MPa.

26. Product according to claim 21, wherein the fired shaped body, preferably the brick, has a refractoriness under load value T.sub.0.5 according to DIN EN ISO 1893:2008-09 of 1100 to 1750° C., preferably of 1200 to 1600° C.

27. Product according to claim 21, wherein the fired shaped body, preferably the brick, has an open porosity of 12 to 28 vol. %, preferably 13 to 20 vol. %, determined in accordance with DIN EN 993-1:1995-04.

28. Product according to claim 21, wherein the fired shaped body, preferably the brick, has a compression Z.sub.max at 1700° C. according to DIN EN ISO 1893: 2008-09 of 0.5 to 5 lin. %, preferably 1 to 4 lin. %.

29. Method for the production of a refractory shaped product according to claim 16, comprising the following method steps: a) mixing the batch with at least one liquid binder and/or water to form a press mass, b) shaping, in particular pressing, the press mass into a green shaped body, c) preferably drying the green shaped body, d) preferably tempering or firing the green shaped body.

30. Method according to claim 29, wherein drying is carried out to a residual moisture content of between 0.1 and 0.6 ma. %, in particular between 0.2 and 0.5 ma. %, determined in accordance with DIN 51078:2002-12.

31. Lining of a large-volume industrial furnace, preferably a burning kiln of the non-metal industry, preferably a cement kiln, a lime shaft or lime rotary kiln, a magnesite or dolomite kiln, or a heating kiln or a kiln for energy production or a steel production kiln or a kiln of the non-ferrous metal industry, wherein the lining comprises at least one product according to claim 16.

32. Lining according to claim 31, wherein the lining comprises a working casing comprising the at least one refractory product.

33. Lining according to claim 32, wherein the working casing is installed in a single-layer or multi-layer masonry.

34. Lining according to claim 31, wherein the lining comprises an insulating backing comprising the at least one refractory product.

35. Large-volume industrial furnace, preferably burning kiln of the non-metal industry, preferably cement kiln, lime shaft kiln or lime rotary kiln, magnesite kiln or dolomite kiln, or heating kiln or kiln for energy production or steel production kiln or kiln of the non-ferrous metal industry, wherein the industrial furnace comprises a lining according to claim 31.

36. Lining according to claim 31, wherein the product is produced by a method comprising the following method steps: a) mixing the batch with at least one liquid binder and/or water to form a press mass, b) shaping, in particular pressing, the press mass into a green shaped body, c) preferably drying the green shaped body, d) preferably tempering or firing the green shaped body.

Description

[0054] In the following, the invention is explained in more detail with the aid of a drawing by way of example. It shows:

[0055] FIG. 1: A light microscope image of an elastifier grain formed from sintered bauxite in a brick according to the invention after production firing

[0056] FIG. 2: Distribution of Al and Mg in an elastifier grain formed from sintered bauxite in a brick according to the invention (left) and in an elastifier grain formed from alumina in a brick not according to the invention (right)

[0057] FIG. 3: Distribution of Ca and Si in the elastifier grain formed from sintered bauxite in the brick according to the invention (left) and in the elastifier grain formed from alumina in a brick not according to the invention (right)

[0058] In the course of the invention, it was surprisingly found that it is possible to produce a magnesia spinel product with good mechanical and thermomechanical properties and sufficient refractoriness from a batch containing a mineral dry substance mixture, which contains an impure granular magnesia component as the main component, if an elastifier component of sintered bauxite is used for in situ elastification.

[0059] Here, impure means that the magnesia component consists of at least one magnesia with an MgO content of only <91.5 ma. %, preferably <90 ma. %, particularly preferably <89 ma. %. According to the invention, the granular, impure magnesia component is present in the dry substance mixture of the batch in an amount of ≥70 ma. %, preferably ≥85 ma. %.

[0060] The MgO content of the impure magnesia is thus preferably 85 to <91.5 ma. % according to the invention, preferably 85 to <90 ma. %, particularly preferably 87 to <89 ma. %.

[0061] Unless otherwise specified, the MgO content, the Al.sub.2O.sub.3 content, the SiO.sub.2 content and the content of the unwanted oxides of the raw materials are determined by X-ray fluorescence analysis according to DIN 12667:2013-2.

[0062] In addition, the at least one magnesia of the impure magnesia component is preferably a crushed granular material. Preferably, the magnesia of the impure magnesia component consists exclusively of crushed granular material(s).

[0063] Generally, the refractoriness decreases if impure raw materials are used. This is because the impure raw materials contain a relatively high amount of unwanted oxides or secondary constituents or impurities. Magnesia contains in particular CaO, SiO.sub.2 as well as Fe.sub.2O.sub.3 as unwanted oxides. These impurities can affect the reactions taking place in-situ during the firing process in a detrimental manner. Structural defects and reduced refractory strengths are the result. Cracking beyond the desired microcracks can lead to strength losses that cause spalling in service. Thus, the skilled man is generally discouraged from using impure raw materials, even though they are usually less expensive.

[0064] Within the scope of the invention, it has now surprisingly been found that a magnesia spinel product with good mechanical and thermomechanical properties and sufficient refractoriness can be obtained if a granular elastifier component of at least one sintered bauxite is used for in-situ MA spinel formation. According to the invention, the elastifier component is contained in the dry substance mixture of the batch in an amount of 2 to 10 ma. %, preferably of 3 to 8 ma. %, particularly preferably of 4 to 6 ma. %, in relation to the dry mass of the dry substance mixture.

[0065] Furthermore, according to the invention, the elastifier component has a grain size according to DIN 66165-2:2016-08≤2.5 mm, preferably ≤20 mm.

[0066] In addition, it was found according to the invention that the fines content of the elastifier component must not be too high. This is because the reactive fines content can lead to a modified mineral phase composition in the binder phase.

[0067] According to the invention, the elastifier component comprises grains with a grain size according to DIN 66165-2:2016-08 of ≤0.5 mm at most in an amount of up to 25 ma. %, preferably up to 20 ma. %, particularly preferably up to 15 ma. %. Or the amount of grains with a grain size according to DIN 66165-2:2016-08 of ≤0.5 mm is 0 to 25 ma. %, preferably 0 to 20 ma. %, particularly preferably up to 0 to 15 ma. %.

[0068] Preferably, for the above-mentioned reason, the elastifier component also has grains with a grain size according to DIN 66165-2:2016-08 of ≤0.2 mm at most in an amount of up to 10 ma. %, preferably up to 7 ma. %, particularly preferably up to 5 ma. %. Or the amount of grains with a grain size according to DIN 66165-2:2016-08 of ≤0.2 mm is 0 to 10 ma. %, preferably 0 to 7 ma. %, particularly preferably 0 to 5 ma. %.

[0069] Furthermore, the elastifier component preferably has grains with a grain size according to DIN 66165-2:2016-08 of >2 mm at most in an amount 25 ma. %, preferably ≤20 ma. %, particularly preferably ≤10 ma. %. Or the amount of grains with a grain size according to DIN 66165-2:2016-08 of >2 mm is preferably 0 to 25 ma. %, especially 0 to 20 ma. %, particularly preferably 0 to 10 ma. %.

[0070] The above amounts refer, of course, to the total amount of elastifier component.

[0071] In addition, the at least one sintered bauxite is also preferably a crushed granular material. Preferably, the elastifier component comprises exclusively crushed granular material(s).

[0072] It was particularly surprising that it is possible to produce a magnesia spinel product with good mechanical and thermomechanical properties and sufficient refractoriness from two impure raw materials, namely an impure magnesia and an impure alumina raw material, namely the sintered bauxite. This is because the sintered bauxite in itself is an impure alumina raw material compared to alumina and preferably has an Al.sub.2O.sub.3 content of only 70 to 92 ma. %, preferably 78 to 91 ma. %. Thus, due to the high content of unwanted oxides in both the magnesia raw material and the sintered bauxite, it would actually have been expected that no good mechanical, thermomechanical properties and refractories could not achieved.

[0073] Surprisingly, it was also found in the context of the invention that no good properties can be achieved with purer alumina raw materials. This will be discussed in more detail within the exemplary embodiments.

[0074] Preferably, the at least one magnesia of the main component is sintered magnesia or fused magnesia. Preferably, it is sintered magnesia.

[0075] In addition, the at least one magnesia of the main component preferably comprises the following properties, which may be accomplished individually or in any combination according to the invention:

TABLE-US-00001 TABLE 1 Secondary oxide contents of the magnesia of the main component preferably SiO.sub.2 content [ma.-%] 0.5 to 3 0.7 to 2.5 CaO content [ma.-%] 0.5 to 4 1.0 to 3.5 Fe.sub.2O.sub.3 content [ma.-%] 0.2 to 10.0 0.5 to 9.5 MnO content [ma.-%] 0 to 1.5 0.1 to 0.7

[0076] Furthermore, the main component comprises a grain size distribution which is usual for the production of a coarse ceramic magnesia spinel product, preferably a magnesia spinel brick. That means, the main component comprises both a fine grain portion and a coarse grain portion. Thereby, both the fine grain portion and the coarse grain portion preferably comprise a continuous grain size distribution.

[0077] In the context of the invention, fine grain portion refers to all granular materials ≤1 mm. The coarse grain portion comprises grain sizes >1 mm.

[0078] Preferably, the main component also comprises a maximum grain size ≤7 mm, preferably ≤6.5 mm.

[0079] It is also advantageous if the impure magnesia has a high Fe.sub.2O.sub.3 content. This is because it has been found that the magnesioferrite contained in the magnesia is a stable phase which does not disturb the microstructure. This may have a favorable effect on strength and depositing behavior. Preferably, the impure magnesia has an Fe.sub.2O.sub.3 content of 0.2 to 10 ma. %, preferably 0.5 to 9.5 ma. %.

[0080] As already explained, the elastifier component consists of at least one sintered bauxite (=refractory bauxite). Sintered bauxite is a significantly less pure alumina raw material than, for example, alumina. It is therefore all the more surprising that it was found within the invention that significantly better properties of the products made from the batch can be achieved when sintered bauxite is used than when alumina is used. At the same time, sintered bauxite is also a relatively inexpensive alumina raw material.

[0081] The at least one sintered bauxite of the elastifier component preferably has the following properties, which can be accomplished individually or in any combination according to the invention:

TABLE-US-00002 TABLE 2 Properties of the sintered bauxite of the elastifier component preferably SiO.sub.2 content [ma.-%] 4 to 20 6 to 15 CaO content [ma.-%] 0.1 to 1.5 0.2 to 0.5 Fe.sub.2O.sub.3 -content [ma.-%] 0.5 to 4 0.9 to 2 TiO.sub.2 content [ma.-%] 0.5 to 4 2 to 3.5

[0082] In principle, it can be assumed that the refractoriness decreases with increasing CaO and/or SiO.sub.2 content, so that the skilled person is rather discouraged from using such a raw material as an elastifier component.

[0083] Furthermore, the elastifier component has a grain size distribution within the specified range. The grain size distribution is preferably continuous.

[0084] Furthermore, the batch according to the invention may contain a further granular magnesia component in addition to the main component. The further magnesia component consists of at least one magnesia with a higher MgO content than the MgO content of the main component. Preferably, the further granular magnesia component is present in the dry substance mixture in an amount of 5 to 28 ma. %, preferably 10 to 22 ma. %, in relation to the dry mass of the dry substance mixture.

[0085] The averaged MgO content of all magnesia grades of the dry substance mixture taken together, that means of the main component and, if present, of the further magnesia component taken together, is thereby preferably 85 to 91.5 ma. %, especially 87 to 90 ma. %, particularly preferably 87 to 89 ma. %.

[0086] Or, the averaged MgO content of all magnesia grades of the dry substance mixture taken together, that means of the main component and, if present, of the further magnesia component taken together, is preferably ≤91.5 ma. %, especially ≤90 ma. %, in particular ≤89 ma. %.

[0087] In addition, the at least one magnesia of the further granular magnesia component is also preferably a crushed granular material. Preferably, the further granular magnesia component comprises exclusively crushed granular material(s).

[0088] Preferably, the dry substance mixture comprises exclusively crushed granular material(s).

[0089] In particular, all the magnesia grades taken together, i.e. the main component and, if present, the further magnesia component taken together, have a, preferably continuous, grain distribution which is usual for the production of a coarse ceramic magnesia spinel product, preferably a magnesia spinel brick. That means, the magnesia grades together have both a fine grain portion and a coarse grain portion. Thereby, both the fine grain portion and the coarse grain portion preferably comprise a continuous grain distribution.

[0090] Preferably, the magnesia grades also comprise a maximum grain size ≤7 mm, preferably≤6.5 mm.

[0091] The CaO/SiO.sub.2 ratio of all the components of the dry substance mixture taken together is preferably 1.2 to 3.0, preferably 1.5 to 2.5. To determine the CaO/SiO.sub.2 ratio of all the components, the CaO or SiO.sub.2 content of the individual components is added together respectively and the CaO/SiO.sub.2 ratio is calculated therefrom.

[0092] The averaged MnO content of all components of the dry batch is also preferably <1.0 ma. %, preferably <0.8 ma. %.

[0093] Preferably, the batch does not comprise a raw material consisting mainly of MnO or MnO.sub.2 or Mn.sub.2O.sub.3.

[0094] As already explained, it has surprisingly appeared that refractory products made from the batch according to the invention comprise a good thermal shock resistance (TSR), a low E- and G-modulus, as well as good cold compressive strength and good cold bending strength, while comprising at the same time a good refractoriness.

[0095] For the production of the refractory products, the batch according to the invention can comprise at least one dry or solid binder in addition or additive to the mineral dry substance mixture. Additive means the amount of binder is added additively and refers to the total dry mass of the dry substance mixture.

[0096] The batch according to the invention preferably contains the dry binder in a total amount of 0 to 4 ma. %, preferably 0 to 3 ma. %, in relation to the dry mass of the dry substance mixture.

[0097] The at least one dry binder is a binder suitable for refractory products. These binders are specified, for example, in the Practice Manual, page 28/item 3.2.

[0098] Furthermore, the batch may also contain, in addition or additive to the mineral dry substance mixture, at least one dry additive for refractory materials, preferably in a total amount <5 ma. % (=0 to <5 wt %), preferably <3 ma. % (=0 to <3 ma. %), in relation to the dry substance mixture.

[0099] The dry additive is an additive suitable for refractory products. The additive can be mineral or chemical. Suitable additives are specified, for example, in the Practice Manual, page 28/item 3.3. They are used to improve processability or formability or to modify the microstructure of the products and thus achieve special properties. Preferably, however, the batch does not contain any additive.

[0100] It goes without saying that the amount of the dry substance mixture in the batch is high enough so that a magnesia spinel product can be produced therefrom. Preferably, the batch according to the invention consists of at least 90% by weight, especially of at least 95% by weight, particularly preferably of at least 98% by weight, in particular of 100% by weight, of the dry substance mixture, in relation to the total mass of the batch.

[0101] For the production of shaped magnesia spinel products, in particular magnesia spinel bricks, from the batch according to the invention, a mixture or pressed mass or batch fresh mass is prepared from the dry batch with at least one liquid binder and/or water. If the batch contains a liquid binder, the addition of water is not necessary, but possible. In addition, the addition of liquid binder is not necessary but possible if the batch contains at least one dry binder.

[0102] The total amount of liquid binder in the batch fresh mass or pressed mass is preferably 2 to 6 ma. %, preferably 3 to 5 ma. %, in relation to the dry mass of the dry substance mixture.

[0103] Preferably, the at least one liquid binder is a binder from the following group: thermosetting synthetic resin binder, in particular phenol-formaldehyde resin, or molasses or lignin sulfonate, or a sulfur-free binder, in particular a binder on the basis of dextrose, an organic acid, saccharose, an Al.sub.2O.sub.3 binder, phosphoric acid, a phosphate binder, water glass, ethyl silicate, or a sulfate, for example magnesium sulfate or aluminum sulfate, or a sol-gel system. Magnesium sulfate or aluminum sulfate, for example, or a sol-gel system.

[0104] Optionally, at least one liquid additive can also be added, which is also added additively to the dry substance mixture.

[0105] The liquid additive is, for example, a wetting agent.

[0106] The total amount of liquid additive in the batch fresh mass is preferably <1.0 ma. % (=0 to <1 ma. %), especially <0.5 ma. % (=0 to <0.5 ma. %), in relation to the dry mass of the dry substance mixture.

[0107] For an optimal distribution of the binder(s) and/or the water and, optionally, the at least one additive, mixing is carried out for e.g. 3 to 10 minutes.

[0108] The mixture is placed in molds and pressed so that shaped bodies are formed. The pressing powers are in usual ranges, e.g. 60-180 MPa, preferably 100-150 MPa.

[0109] Preferably, drying is carried out after pressing, e.g. between 60 and 200° C., in particular between 90 and 140° C. Drying is preferably carried out to a residual moisture content of between 0.1 and 0.6 ma. %, in particular between 0.2 and 0.5 ma. %, determined in accordance with DIN 51078:2002-12.

[0110] The shaped bodies according to the invention, in particular the bricks, can be used unfired or tempered or fired. Preferably, however, they are used fired.

[0111] The green pressed bricks are tempered in a ceramic burning kiln, e.g. a tunnel kiln, between 200 and 800° C., in particular between 500 and 800° C.

[0112] For firing, the, preferably dried, pressed bricks are ceramically fired in a ceramic burning kiln, e.g. a tunnel kiln, preferably between >800 and 1800° C., in particular between 1400 and 1700° C. Preferably, it is being fired oxidizing, but depending on the material composition, reducing firing may also be advantageous.

[0113] The fired, shaped products, in particular the bricks, comprise a very good cold compressive strength according to DIN EN 993-5:1998-12 preferably of 40 to 120 MPa, in particular 50 to 90 MPa.

[0114] The cold bending strength according to DIN EN 993-6:1995-04 of the fired, shaped products according to the invention, in particular of the bricks, is preferably 3 to 10 MPa, in particular 4 to 7 MPa.

[0115] Furthermore, the fired, shaped products, in particular the bricks, preferably have a refractoriness under load value T.sub.0.5 according to DIN EN ISO 1893:2008-09 of 1100 to 1750° C., especially 1200 to 1600° C.

[0116] Furthermore, the fired, shaped products, in particular the bricks, preferably have a compression Z.sub.max at 1700° C. according to DIN EN ISO 1893:2008-09 of 0.5 to 5 lin. %, especially 1 to 4 lin. %.

[0117] In addition, the fired shaped products according to the invention, in particular the bricks, preferably have a E-modulus (modulus of elasticity) from 15 to 35 GPa, especially from 18 to 30 GPa.

[0118] The G-modulus (shear modulus) of the fired shaped products according to the invention, in particular of the bricks, is preferably 7 to 16 GPa, especially 8 to 14 GPa.

[0119] The E-modulus and G-modulus were determined with the GrindoSonic MK6.

[0120] The thermal shock resistance determined according to DIN EN 993-11:2008-03 with air at an elevated test temperature of 1200° C. of the fired, shaped products according to the invention, in particular the bricks, is preferably >30 quenching cycles, in particular >50 quenching cycles.

[0121] The fired, shaped products, in particular the bricks, also preferably have an open porosity of 12 to 28 vol. %, preferably 13 to 20 vol. %, determined according to DIN EN 993-1:1995-04.

[0122] And/or they preferably have a raw density of 2.60 to 3.15 g/cm.sup.3, in particular 2.75 to 3.10 g/cm.sup.3, determined according to DIN 993-1:1995-04.

[0123] All the above properties of the products according to the invention, including of the batch, are each individually and in any combination according to the invention.

[0124] The good mechanical and thermal properties result in particular from the fact that no microstructural disturbances occur during firing. This is also shown in particular by the fact that no significant volume increase occurs during firing.

[0125] The invention is illustrated by the following examples:

[0126] In a first series of tests, bricks were produced from two different pure magnesia grades with an MgO content >94 ma. % as comparative examples. Alumina (BSA=Brown Sintered Alumina) with an Al.sub.2O.sub.3 content of 96.5 ma. % was used as the elastifier component.

[0127] In a second series of tests, bricks were produced from an impure magnesia with an MgO content <88 ma. % as further comparative examples. Again, the alumina with an Al.sub.2O.sub.3 content of 96.5 ma. % was used as the elastifier component.

[0128] In a third series of tests, bricks were produced from the two pure magnesia grades and the impure magnesia as comparative examples. Two different sintered bauxites with an Al.sub.2O.sub.3 content of 90.5 ma. % and 79.6 ma. %, respectively, and in a grain fraction of 0-1 mm were used as elastifier component.

[0129] In a fourth series of tests, bricks according to the invention were produced from the impure magnesia and the two sintered bauxites with grain fractions according to the invention.

[0130] The properties of the raw materials used are listed in the tables below:

TABLE-US-00003 TABLE 3 Properties of the used magnesia raw materials DBM 1 DBM 2 DBM 3 grain bulk density D g/cm.sup.3 3.28 3.19 3.33 chem. analysis mass-% SiO.sub.2 0.89 2.11 0.58 Al.sub.2O.sub.3 0.14 0.48 0.26 Fe.sub.2O.sub.3 0.84 0.99 8.05 Cr.sub.2O.sub.3 0.01 0.02 0.01 MnO 0.08 0.07 0.46 TiO.sub.2 0.01 0.02 0.01 P.sub.2O.sub.5 0.18 0.11 0.05 GaO 2.20 1.68 2.57 MgO 95.58 94.48 87.95 Na.sub.2O 0.02 0.02 0.02 loss on ignition 0.11 0.12 0.18 C + S 3.09 3.79 3.15 C/S 2.47 0.80 4.43

TABLE-US-00004 TABLE 4 Properties of the used alumina raw materials alumina 96.5 bauxite 1 bauxite 2 grain bulk density D g/cm.sup.3 3.50 3.20 3.07 chem. analysis mass-% SiO.sub.2 0.90 4.57 13.57 Al.sub.2O.sub.3 96.50 90.47 79.64 Fe.sub.2O.sub.3 0.15 1.64 1.81 MnO 0.01 0.01 0.01 TiO.sub.2 1.20 2.90 3.20 P.sub.2O.sub.5 0.02 0.07 0.29 CaO 0.01 0.03 0.55 MgO 0.30 0.05 0.22 Na.sub.2O 0.30 0.02 0.06 loss on ignition 0.05 0.12 0.18

[0131] The production of the bricks was carried out as follows:

[0132] A press mass was prepared from the respective batch. Mixing was carried out for 4 minutes for an optimal distribution of the binder. The press mass was placed in molds and pressed so that bricks were formed. After pressing, drying was carried out at 110° C. for a time of 8 h to a residual moisture content of 0.1 ma. %, determined according to DIN 51078:2002-12. Subsequently, the bricks were fired oxidizing.

[0133] The batches used and the properties of the bricks produced from them, as well as the firing temperature, are given in the following tables. In the case of the sintered bauxite and alumina, the indicated grain sizes are grain fractions, and in the case of the magnesia grades, they are grain groups:

TABLE-US-00005 TABLE 5 Batches and results of test series 1 firing temperature 1430° C. 1430° C. batch No.: V1a V1b binder lignosulfonate 3.6 3.6 (45% conc.) format mm 70/65 × 200 × 220 70/65 × 200 × 220 pressing power MPa 180 180 DBM 1 2-4 27.0 DBM 1 1-2 20.0 DBM 1 0-1 14.0 DBM 1 meal 34.0 DBM 2 2-4 27.0 DBM 2 1-2 20.0 DBM 2 0-1 14.0 DBM 2 meal 34.0 alumina 96.5 0.5-1.0 5.0 5.0 comment prior art prior art no cracks no cracks finished bulk density g/cm.sup.3 2.92 2.80 E modulus GPa 24.02 16.04 G modulus GPa 11.41 8.15 cold compr. strength MPa 87.25 51.45 cold bending strength MPa 6.14 4.36 porosity Vol.-% 16.68 19.23 TSR, air, 1200° C. cycles 1/—/>30 1/—/>30 shrinkage lin.-% −0.28 −1.84 refractoriness under load: D.sub.max lin.-% 1.79 1.51 T.sub.0 ° C. 1556 1331 T.sub.0.5 ° C. — 1471 T.sub.1 ° C. — 1523 T.sub.2 ° C. — 1601 T.sub.5 ° C. — — Z.sub.max (1700° C.) lin.-% 0.21 4.76

TABLE-US-00006 TABLE 6 Batches and results of test series 2 firing temperature 1430° C. 1430° C. 1430° C. 1430° C. batch No.: V2a V2b V2c V2d binder lignosulfonate 3.6 3.6 3.6 3.6 (45% conc.) format mm 70/65 × 200 ×220 70/65 × 200 × 220 70/65 × 200 × 220 70/65 × 200 × 220 pressing power MPa 180 180 180 180 DBM 2 meal 20.0 20.0 20.0 20.0 DBM 3 2-4 28.0 28.0 28.0 28.0 DBM 3 1-2 23.0 23.0 23.0 23.0 DBM 3 0-1 14.0 15.0 16.0 17.0 DBM 3 meal 10.0 10.0 10.0 10.0 bauxite 1 0.5-1.6 bauxite 1 0.5-1.0 alumina 96.5 0.5-1.0 5.0 4.0 3.0 2.0 comment instable brick microstructure/brick damages light cracks cracks cracks cracks finished bulk density g/cm.sup.3 2.93 2.92 2.92 2.98 E modulus GPa 14.11 14.78 15.38 23.27 G modulus GPa 7.43 7.67 8.09 11.67 cold compr. strength MPa 47.00 48.65 44.15 62.30 cold bending strength MPa 3.91 3.40 3.95 4.56 porosity Vol.-% 17.45 17.39 18.15 16.62 TSR, air, 1200° C. cycles 1/—/>30 1/—/>30 1/—/>30 1/—/>30 shrinkage lin.-% −1.06 −1.64 −1.44 −0.56 refractoriness under load: D.sub.max lin.-% 1.51 n.b. n.b. n.b. T.sub.0 ° C. 1298 (because of the microstructure failures/cracks not determined) T.sub.0.5 ° C. 1449 T.sub.1 ° C. 1499 T.sub.2 ° C. 1565 T.sub.5 ° C. Z.sub.max (1700° C.) lin.-% 4.72

TABLE-US-00007 TABLE 7 Batches and results of test series 3 firing temperature 1430° C. 1430° C. 1430° C. 1430° C. 1430° C. 1430° C. batch No.: V3a V3b V3c V3d V3e V3f binder lignosulfonate 3.6 2.6 2.6 2.6 2.6 2.6 (45% conc.) format 70/65 × mm X X X X X X 200 × 220 pressing power MPa 180 180 180 180 180 180 DBM 1 2-4 27.0 27.0 27.0 27.0 27.0 DBM 1 1-2 20.0 15.0 18.0 18.0 18.0 DBM 1 0-1 14.0 19.0 16.0 16.0 16.0 DBM 1 meal 34.0 34.0 34.0 34.0 34.0 DBM 2 2-4 27.0 DBM 2 1-2 20.0 DBM 2 0-1 14.0 DBM 2 meal 34.0 DBM 3 2-4 DBM 3 1-2 DBM 3 0-1 DBM 3 meal bauxite 1 0-1 5.0 3.0 5.0 bauxite 1 1-2 5.0 2.0 bauxite 1 0.5-1.6 5.0 bauxite 2 0-1 3.0 bauxite 2 1-2 2.0 comment finished bulk density g/cm.sup.3 2.93 2.90 2.89 2.89 2.87 2.93 E modulus GPa 29.62 23.32 20.91 23.99 23.90 23.37 G modulus GPa 14.32 11.51 10.35 11.58 12.27 13.05 cold compr. strength MPa 112.30 79.00 70.60 77.60 74.20 111.20 cold bending strength MPa 7.68 5.16 5.36 6.27 6.14 6.39 porosity Vol.-% 15.86 17.65 17.54 17.37 17.08 16.37 TSR, air, 1200° C. cycles 1/—/>30 1/—/>30 1/—/>30 1/—/>30 1/—/>30 1/—/>30 shrinkage lin.-% −0.21 0.14 0.00 0.00 0.00 −0.14 refractoriness under load: D.sub.max lin.-% 1.90 1.81 1.68 T.sub.0 ° C. 1462 1463 1383 T.sub.0.5 ° C. 1678 1668 1533 T.sub.1 ° C. — — 1594 T.sub.2 ° C. — — 1658 T.sub.5 ° C. — — — Z.sub.max (1700° C.) lin.-% 0.64 0.74 3.25 T.sub.f/Z.sub.f ° C./lin.-% firing temperature 1430° C. 1430° C. 1430° C. 1430° C. 1430° C. 1430° C. batch No.: V3g V3h V3i V3j V3k V3l binder lignosulfonate 2.6 2.6 2.6 2.6 2.6 2.6 (45% conc.) format 70/65 × mm X X X X X X 200 × 220 pressing power MPa 180 180 180 180 180 180 DBM 1 2-4 DBM 1 1-2 DBM 1 0-1 DBM 1 meal DBM 2 2-4 27.0 27.0 27.0 27.0 DBM 2 1-2 15.0 18.0 18.0 18.0 DBM 2 0-1 19.0 16.0 16.0 16.0 DBM 2 meal 34.0 34.0 34.0 34.0 20.0 20.0 DBM 3 2-4 28.0 28.0 DBM 3 1-2 23.0 21.0 DBM 3 0-1 14.0 16.0 DBM 3 meal 10.0 10.0 bauxite 1 0-1 3.0 5.0 3.0 bauxite 1 1-2 5.0 2.0 2.0 bauxite 1 0.5-1.6 5.0 bauxite 2 0-1 3.0 bauxite 2 1-2 2.0 comment finished bulk density g/cm.sup.3 2.93 2.95 2.93 2.92 3.02 3.04 E modulus GPa 24.46 25.83 23.93 26.59 22.95 24.82 G modulus GPa 13.85 14.48 13.15 14.81 12.94 13.67 cold compr. strength MPa 108.30 112.01 113.00 110.70 96.30 102.70 cold bending strength MPa 5.41 5.94 6.21 6.74 6.04 5.51 porosity Vol.-% 16.30 15.49 16.42 16.57 15.24 14.71 TSR, air, 1200° C. cycles 1/—/>30 1/—/>30 1/—/>30 1/—/>30 1/—/>30 1/—/>30 shrinkage lin.-% 0.00 −0.07 −0.04 0.11 0.28 0.42 refractoriness under load: D.sub.max lin.-% 1.73 1.69 1.74 T.sub.0 ° C. 1371 1349 1358 T.sub.0.5 ° C. 1521 1448 1496 T.sub.1 ° C. 1579 1502 1571 T.sub.2 ° C. 1653 1571 1639 T.sub.5 ° C. — 1638 — Z.sub.max (1700° C.) lin.-% 3.26 failure! failure! T.sub.f/Z.sub.f ° C./lin.-% 1638 1686

TABLE-US-00008 TABLE 8 Batches and results of test series 4 firing temperature 1430° C. 1430° C. 1430° C. 1430° C. 1430° C. 1430° C. 1430° C. batch No.: V4a V4b V4c V4 d V4e V4f V4g binder lignosulfonate 3.6 3.6 3.6 3.4 3.6 3.6 3.6 (45% conc.) format mm 70/65 × 70/65 × 70/65 × 70/65 × 70/65 × 70/65 × 70/65 × 200 × 220 200 × 220 200 × 220 200 × 220 200 × 220 200 × 220 200 × 220 pressing power MPa 180 180 180 120 180 180 180 DBM 2 meal 20.0 20.0 20.0 20.0 20.0 20.0 20.0 DBM 3 2-4 28.0 28.0 28.0 28.0 28.0 28.0 28.0 DBM 3 1-2 23.0 23.0 21.5 23.0 22.0 23.0 23.0 DBM 3 0-1 15.0 14.5 14.5 15.0 12.0 14.0 14.0 DBM 3 meal 10.0 10.0 10.0 10.0 10.0 10.0 10.0 bauxite 1 2-2.5 1.0 bauxite 1 1-2 1.0 bauxite 1 0.5-1.6 6.0 bauxite 1 0.5-1 4.0 4.5 4.0 8.0 2.0 bauxite 1 0.2-0.5 1.0 bauxite 2 2-2.5 1.0 bauxite 2 1-2 1.0 bauxite 2 0.5-1 2.0 bauxite 2 0.2-0.5 1.0 bricks according to the invention no cracks no cracks no cracks no cracks no cracks no cracks no cracks finished bulk density g/cm.sup.3 3.04 3.03 3.02 2.97 2.99 3.03 3.02 E modulus GPa 25.36 22.28 19.10 21.06 16.43 23.37 23.38 G modulus GPa 12.88 11.58 10.18 10.68 9.46 13.74 14.08 cold compr. strength MPa 102.95 95.50 83.40 75.30 85.55 99.35 95.10 cold bending strength MPa 5.88 5.23 4.68 4.63 4.71 5.70 5.58 porosity Vol.-% 14.92 14.56 14.85 17.02 16.05 14.91 14.86 TSR, air, 1200° C. cycles 1/—/>30 2/—/>30 2/—/>30 1/—/>30 1/—/>30 1/—/>30 1/—/>30 shrinkage lin.-% 0.13 0.25 0.08 0.33 −0.28 0.21 0.28 refractoriness under load: D.sub.max lin.-% 1.76 1.71 1.63 1.80 1.68 1.67 1.65 T.sub.0 ° C. 1358 1342 1340 1324 1364 1332 1328 T.sub.0.5 ° C. 1578 1481 1524 1481 1513 1542 1511 T.sub.1 ° C. 1653 1550 1593 1549 1572 1613 1581 T.sub.2 ° C. — 1647 1676 1633 1667 1700 1637 T.sub.5 ° C. — — — — — — — Z.sub.max (1700° C.) lin.-% 1.53 2.95 2.49 3.83 3.36 2.04 3.47

[0134] The results of test series 1 show that bricks with good mechanical properties and good refractoriness could be readily produced from the two pure magnesia grades and the alumina.

[0135] The bricks of test series 2 from the impure magnesia and the alumina, on the other hand, surprisingly did not comprise good mechanical strengths. The bricks grew significantly during firing. This resulted in significant microstructural defects (cracks). The bricks did not have good strengths due to the microstructural defects.

[0136] In test series 3 it appeared that when the sintered bauxites were used in form of too fine granular materials in combination with the impure magnesia, it was not possible to achieve sufficient refractoriness.

[0137] In test series 4, numerous bricks according to the invention with good mechanical properties and good refractoriness were produced. Thereby, the content of sintered bauxite was varied. In addition, according to the invention, only grain fractions according to the invention with a low amount of granular material <0.5 mm were used.

[0138] During production firing, the bricks according to the invention shrank moderately. The strengths of the bricks according to the invention correspond to typical magnesia spinel bricks. The refractoriness (refractoriness under load) is advantageous for a brick for the firing zone of an industrial furnace, since such thermoplastic behavior can be utilized when used in mechanically loaded furnaces.

[0139] In the context of the invention, it is assumed that the surprisingly good properties of the bricks according to the invention result, among other things, from the formation of a transition zone (=reaction zone) between the MgO matrix and the elastifier grains. To prove this, the bricks were examined by light microscopy, X-ray diffraction and micro X-ray fluorescence spectrometry. The analysis of the individual elastifier grains with micro X-ray fluorescence spectrometry allows a spatial resolution of the elemental distribution.

[0140] FIG. 1 shows a light microscope image of an elastifier grain 1 formed from the sintered bauxite with 90.5 ma. % Al.sub.2O.sub.3 in an MgO matrix 2 of a brick according to the invention. An inner ring 3 and an outer ring 4 formed around the elastifier grain 1 and forming the transition zone or reaction zone, can be clearly seen. In addition, pores 5 can be seen.

[0141] The results of X-ray powder diffraction are shown in the following table:

TABLE-US-00009 mineral phase content (qualitative) test V2a V4b comment not according to the invention according to the invention periclase (M) ++++ ++++ spinel (MA) + + corundum (A) ± ± magnesioferrite (MF) + + belite (C.sub.2S) ± ± merwinite (C.sub.3M.sub.S2) ± ± hibonite (CA.sub.6) ± − ++++ = main phase + = detected ± = trace − = not detected

[0142] From the results of X-ray diffraction and micro-X-ray fluorescence spectrometry it can be deduced that the inner ring 3 contains spinel, which was formed during firing by a reaction of the magnesia with the elastifier grain 1 at its edge region. The outer ring additionally contains the impurities or unwanted oxides contained in the sintered bauxite. It is assumed that the reaction of the elastifier grain 1 with the magnesia is stopped due to the formation of the outer ring 4 and, as a result, the increase in volume during firing is prevented and the bricks are therefore not damaged.

[0143] X-ray powder diffraction also showed that not only in-situ spinel but also hibonite (CA.sub.6) formed due to the high CaO contents in the brick with the alumina. The formation of hibonite (CA.sub.6) is usually undesirable because it leads to an increase in volume. From the results of micro X-ray fluorescence spectrometry, it can be derived that hibonite (CA.sub.6) was formed in the transition zone. In contrast, no hibonite (CA.sub.6) was detectable in the brick according to the invention.

[0144] FIGS. 2 and 3 show the distribution of Al, Mg, Ca and Si in and around an elastifier grain of sintered bauxite containing 90.5 ma. % Al.sub.2O.sub.3 (left) and in and around an elastifier grain of the alumina (left) after ceramic firing at 1430° C., as determined by micro X-ray fluorescence spectrometry. For comparability, the same scaling (At. %) was used for the representation of the respective elements in both cases.

[0145] Depending on the alumina raw material used, differences can be seen in the formation of the respective transition zone.

[0146] In the case of the alumina, the area between the chemically hardly modified core and the outer ring of spinel is significantly wider than when using the sintered bauxite. In the case of the alumina, an enrichment of CaO and SiO.sub.2 is particularly noticeable in the transition zone.

[0147] In the case of the alumina, a zone of calcium aluminate has also developed (10-14% CaO), which in turn is surrounded by a CaO-free rim of MA spinel (34% MgO). In the zone of calcium aluminate SiO.sub.2 is enriched (up to 2.8%), but not in the surrounding ring of MA spinel.

[0148] In the case of sintered bauxite, a continuous decrease in the SiO.sub.2 content can be observed from the center to the edge. The enrichment of CaO in the transition region is to a significantly lesser extent than in the case of the alumina. Here, too, a ring of MA spinel adjoins. The SiO.sub.2 content within the elastifier grain varies in the range of 12-22% for the sintered bauxite. Comparatively low Al.sub.2O.sub.3 contents indicate that, in addition to the radiographically detected MA spinel phase, significant amounts of melilite (C.sub.2AS) and merwinite (C.sub.3MS.sub.2) were formed, which may be present as a melt phase at the selected firing temperatures. Thus, in the case of sintered bauxite, the activity of CaO is probably reduced by the SiO.sub.2 content in the raw materials due to the formation of melt phases and/or calcium-magnesium silicates or calcium-aluminum silicates. This prevents the undesirable formation of hibonite (CA.sub.6) and prevents an increase in volume during firing. The sintered bauxite buffers the reaction to hibonite (CA.sub.6) via the formation of secondary phases and is consequently less reactive.