EP3468938A1

EP3468938A1 - Spinel refractory granulates which are suitable for elasticizing heavy-clay refractory products, method for their production and use thereof

Info

Publication number: EP3468938A1
Application number: EP17713279.2A
Authority: EP
Inventors: Heinrich Liever; Hilmar Schulze-Bergkamen; Carsten Vellmer
Original assignee: Refratechnik Holding GmbH
Current assignee: Refratechnik Holding GmbH
Priority date: 2016-05-19
Filing date: 2017-03-23
Publication date: 2019-04-17
Also published as: RU2018144621A; RU2018144621A3; CN109153614A; CA3024486A1; MX2018014155A; KR20190009307A; JP2019519453A; US20190185378A1; WO2017198377A1; DE102016109254B4; DE102016109254A1; BR112018073646A2

Abstract

The invention relates to a granular refractory mineral elasticizing granulate for refractory products, in particular for basic refractory products, wherein the minerals consist of mono-phase sintered spinel mixed crystals of the ternary system MgO-Fe₂O₃-Al₂O₃ of the composition range MgO: 12 to 19.5, in particular 15 to 17 wt.-%, remainder: Fe₂O₃ and Al₂O₃ in a quantity ratio range of Fe₂O₃ to Al₂O₃ between 80 to 20 and 40 to 60 wt.-%, the respective mixed crystals having an Fe₂O₃ and Al₂O₃ content, starting from an MgO content between 12 and 19.5 wt.-%, from the limited ranges indicated for each case, to obtain 100% in the total composition. The invention also relates to a method for producing said elasticizing granulate and to the use of the same.

Description

Refractory spinel granules suitable for elastification of heavy clay fireproof products, process for their preparation and their

use

The invention relates to the refining of coarse ceramic, in particular basic, refractory products suitable refractory spinel elastomer granules, a process for their preparation and their use in spinelelastifizieriferous, coarse ceramic, especially basic refractory products.

Ceramic refractory products are based on refractory materials, eg. B. on basic refractory materials. Refractory basic materials are materials in which the sum of the oxides MgO and CaO clearly outweighs. They are z. B. in Tables 4.26 and 4.27 in "Paperback refractory materials, Gerald Routschka, Hartmut Wuthnow, Vulkan-Verlag, 5th edition" listed.

Elasticizing spinel granules - hereinafter also referred to as "spinel elastomers" or "elastifiers", which are usually used in the form of coarse granules - in a coarse ceramic, as a so-called main component at least one refractory mineral refractory material granules, z. B. basic, refractory products are mixed with a suitable content of the refractory products, randomly distributed in the refractory product structure, granular present, compared to the main component other mineral composition having refractory material granules, which in comparison to the main component z. B. have a different coefficient of thermal expansion and elasticize the structure of the refractory product by reducing the E and G module or reduce the brittleness of the refractory product and thereby, for. B. due to microcracking, increase the thermal shock resistance or thermal shock resistance. Usually determine the physical or mechanical and thermo-mechanical behavior of a z. B. basic refractory product, the main component at least one granular, z. B. basic, refractory mineral material. Such elastifiers are, for example, MA spinel, hercynite, galaxite, pleonast but also chromite, picrochromite. They are z. B. in the above-mentioned paperback in Chapter 4.2 in connection with various, z. As basic coarse ceramic refractory products described.

Usual grain sizes of granular spinel elastomers are known to be mainly z. B. between 0 and 4 mm, in particular between 1 and 3 mm. The grains of the main components of the refractory products of refractory, z. B. basic materials are known mainly z. B. between 0 and 7 mm, in particular between 0 and 4 mm. The term "granular" is used in the following in principle in contrast to the terms flour or powder or fine flour or fine powder, which is to be understood by flour or fines or finely divided grits below 1 mm, in particular below 0.1 mm However, each main component may also contain flour or powder fractions of up to, for example, 35% by weight, in particular 20% by weight and subordinately coarser, because these are industrially produced products which are only available with Limited accuracies are generated.

Crude ceramics refractory products are mainly shaped and unformed ceramically fired or unfired products produced by a heavy clay manufacturing process using refractory component grain sizes, e.g. B. to 6 mm or 8 mm or 1 2 mm are made (Paperback, page 21/22).

The refractory main component - also called Resistor - or the main refractory components of such z. B. basic refractory products essentially ensure the desired fire resistance and mechanical see or physical and chemical resistance, while the elastifiers in addition to their elasticizing effect also at least supportive of the mechanical and thermomechanical properties, but also possibly the corrosion resistance and a chemical resistance z. B. to ensure against alkalis and salts. As a rule, the proportion of the main refractory component predominates, ie it is more than 50% by mass in the refractory product, so that the content of elastifier is generally below 50% by mass.

Refractory elastifiers - also called micro crack images - are used for heavy clay fireproof products such. B. in DE 35 27 789 C3, DE 44 03 869 C2, DE 1 01 1 7 026 B4 described. It is therefore refractory materials that the resistance of the structure of the refractory, z. B. increase basic products against mechanical and thermo-mechanical stresses, in particular by reducing the modulus of elasticity and resistance to chemical attack, eg. B. against slag attacks, as well as salt and Alkalalienangriffe at least not worsen. As a rule, cause of the elastification microstructural disorders such as tensions and / or microcracks, which can lead to the fact that externally registered voltages can be reduced.

It is known that alumina-containing basic refractory products for use z. B. in the cement, lime or dolomite industry at high operating temperatures around 1, 500 ° C generally have sufficient mechanical and thermo-mechanical properties. These products are usually elasticized by the addition of alumina and / or magnesium aluminate spinel (MA spinel) to calcined magnesia. Such magnesia-based refractory products require low levels of calcium oxide (CaO), which is only possible with well-prepared, expensive raw materials. In the presence of calcium oxide, aluminum oxide and MA spinel form CaO-Al ₂ O ₃ melts and thus adversely affect the brittleness of the ceramic products. In addition, arise in industrial furnace units, eg. As in cement kilns, at high temperatures reactions between alumina, in-situ spinel or MA spinel and the CaO-containing cement clinker melt minerals, z. B. Mayenite (Ca ₁₂ Al ₁₄ 0 ₃ 3) and / or Ye'elimit (Ca ₄ AI ₆ 0 ₁₂ (S0 ₄ )), which can lead to premature wear ß the furnace lining. In addition, dense and low-porous magnesia spinel bricks containing as elasticizing components either sintered or molten MA spinels (magnesium aluminate spinels), have little tendency to form a stable cladding layer which builds up from cement clinker melts during operation on the refractory lining and in the cement rotary kiln is desired.

These disadvantages have led to use hercynite (FeAI ₂ 0 ₄ ) as an elasticizer, in refractory products for the combustion zones in cement rotary kilns, which have a significantly improved reactivity due to the iron content of the elastifier and in the case of synthetic hercynite (DE 44 03 869 C2 ) or iron oxide-aluminum oxide granules (DE 1 01 1 7 026 A1) are added to the ceramic batch mass of the refractory product.

Varying redox conditions, the z. B. occur in furnaces of the cement, dolomite, lime and magnesite industry, lead in Hercynit-containing lining stones, however, to a disadvantageous exchange of aluminum and iron ions at high temperatures. Above 800 ° C, a complete solid solution within the material system FeAl ₂ 0 ₄ (hercynite) Fe ₃ 0 ₄ (magnetite) can take place in the hercynite crystal, with a two-phase system with excreted magnetite forming below 800 ° C undesirable chemical and physical vulnerability of hercynite in refractory products under certain redox conditions.

The use of alternative fuels and raw materials in modern rotary kilns z. As the cement, lime, dolomite or magnesite industry causes in their atmosphere considerable concentrations of alkalis and salts of various origins. Hercynite decomposes, as is known, at typical operating temperatures with access of oxygen and / or admission of air to FeAlO ₃ and Al ₂ O ₃ . These multiphase reaction products react with alkaline compounds and salts to form further secondary phases, which in turn lead to embrittlement of the refractory product and limit its use.

However, such a multiphase also arises in the production of hercynite during sintering or melting, namely by cooling by oxidation. After cooling, there is a multiphase product with hercynite as the main phase and, in addition, so-called secondary phases are present. Use of refractory products containing hercynite as elastifiers, d. H. in situ z. As in operated Zementdrehrohröfen, the production-related secondary phases act as the above-described, resulting in operating temperatures from hercynite secondary phases embrittling.

In order to avoid oxidation, according to CN 1 01 82 38 72 A, it has been proposed to produce hercynite in monophase by carrying out the ceramic firing in a nitrogen atmosphere. Although this measure is very time-consuming and can guarantee a monophase of the herbinite, it is still unstable in situ and has a lack of resistance under oxidizing conditions in a furnace aggregate.

The invention according to DE 1 01 7306 B4 describes an alternative to hercynite in that a synthetic refractory material of the pleonastic spinel type having the mixed crystal composition (Mg ²⁺ , Fe ²⁺ ) (Al ³⁺ , Fe ³⁺ ) ₂ 0 ₄ and MgO contents of 20 to 60 wt .-% is proposed. The literature describes the continuous exchange of Mg ²⁺ and Fe ²⁺ ions in the transition from spinel sensu stricto (ss) MgAI ₂ 0 ₄ to hercynite (FeAI ₂ 0 ₄ ), with members of this series containing Mg ² 7Fe ²⁺ ratios of 1 to 3 are referred to as pleonast (Deer et al., 1,985 Introduction to the Rock Forming Minerals). Compared to sintered or melted hercynite, these elastomers show improved resistance to alkali or clinker melt (Klischat et al., 201 3, Smart Refractory Solution for stress-loaded rotary kilns, ZKG 66, pages 54-60).

In the case of the resulting from the melt Pleonasts or pleonastic spinel with 20-60 wt .-% MgO z. B. the three mineral phases MgFe ₂ 0 ₄ ss, MgAI ₂ 0 ₄ and periclasic present. The existence of these mineral phases results from an energy-intensive manufacturing process of components from the ternary material system MgO-Fe ₂ O ₃ -Al ₂ O ₃ with interfering secondary phases. The sintering or melting in a melting unit, for. B. in an electric arc furnace, leads to considerable amounts of secondary phases such as dissolved FeO in MgO (MgOss, Magnesiowüstit) and results in a complex mixture of several mineral phases.

DE 1 01 1 7 026 B4 describes that the modulus of elasticity (modulus of elasticity) of investigated refractory bricks is directly proportional to increasing MgO contents of the pleonastic spinel used in them. Increasing from 20% to 50% by weight of MgO in the examples causes the modulus of elasticity to increase from 25.1 to 28.6 GPa. The quantities of pleonastic spinel selected in this case in many cases simultaneously determine the presence of mineral phases such as periclase (MgO), magnesiowüstite (MgO ss) and magnesioferrit (MgFe ₂ 0 ₃ ), which, as inherent constituents, influence the coefficient of linear expansion of the spinel and adversely affect the spinel Brittleness of spinel-containing refractory product.

When determining the ignition loss according to DIN EN ISO 26845: 2008-06 at 1 .025 ° C, Hercynit and Pleonast have an annealing gain of up to 4% and up to 2%, respectively. Under oxidizing conditions and corresponding temperatures, the crystal lattice of the hercynite breaks down. In the case of Pleonast, the magnesia resistance is converted into magnesia ferrite. The object of the invention is to provide a lower oxidation potential or oxidation-resistant, especially in basic refractory products better and more durable elastifying acting spinel, preferably in addition to the good elastification and a good thermochemical and thermomechanical resistance and the same elastification in comparison z. B. to hercynite or Pleonastgehalten relatively lower levels in particular basic refractory products, especially in the case of using the refractory products contained in cement rotary kilns, they also should cause a good formation of deposits. The object of the invention is also to provide coarse ceramic basic refractory products and uses therefor which are superior to the known coarse ceramic, in particular basic refractory products with respect to oxidation resistance as well as thermochemical and thermomechanical resistance and buildup in situ by a content of at least one Elastifizierergranulats of the type according to the invention.

These objects are achieved by the features of claims 1, 7 and 1 2. Advantageous developments of the invention are characterized in dependent on these claims dependent claims.

The invention relates to by a sintering process in neutral, especially oxidising forming atmosphere, particularly in an air atmosphere made Spinellelastifizierergranulate with selected compositions of spinels in the ternary system MgO Fe ₂ 03-AI ₂ 03. The sintering process is compared with the melting process much more energy efficient feasible. In addition, the sintering process brings about the surprising effect, in comparison to the melting process, that an oxidation-resistant spinel monophase forms practically without secondary phases, which is also resistant in situ and thus exposed to at least one spinel elasticizer according to the invention in an oxidizing atmosphere. B. in the form of granules containing coarse ceramic, especially basic refractory product remains stable and ensures its elasticity and also supports its thermochemical and thermomechanical resistance. In addition, the spinel monophase leads to a very good formation of deposits in a cement rotary kiln.

That in the ternary system MgO-Fe ₂ O 3 -Al ₂ O 3 a region with spinel monophases in the form of complex ternary mixed crystals exists, is by W. Kwestroo, in J. Inorg. Nucl. Chem., 1959, Vol. 9, pages 65 to 70, has been described on the basis of laboratory experiments. Accordingly, as shown in FIGS. 1 and 2, aaO, a relatively large molecular weight range was observed for samples fired and ground in air at the firing temperatures of 1 .250 and 1 .400 ° C. and X-ray analyzed, in which stable spinel monophases of different composition exist. It was determined that the magnetic saturation or the Curie temperature of the respective monophase can be a function of their chemical composition. Further properties of the monophases have not been investigated or indicated. The monophases had different amounts of (Al, Fe) ₂ 0 ₃ in solid solution in the spinel crystal.

Within the scope of the invention, in the ternary system MgO-Fe ₂ O ₃ -Al ₂ O _3, a narrow composition field of monophasic stable mixed crystal spinels in the known wide range of spinel monophases could be found with monophasic sintered spinel monocrystals of the following composition according to range of fields as elastifiers.

MgO: 12 to 19.5, especially 15 to 17 wt .-%

Rest: Fe ₂ 0 ₃ and Al ₂ 0 ₃ in the ratio range Fe ₂ 0 ₃ to Al ₂ 0 ₃ between 80 to 20 and 40 to 60 wt .-%.

The field of the ESS according to the invention is as follows: The minimum and maximum MgO content was within the scope of the invention with 12 wt .-% and 19.5% by weight determined. The lateral boundaries of the ESS field are in each case lines of constant Fe ₂ O ₃ / Al ₂ O ₃ ratios (% by weight).

Left limit: Fe ₂ 03 / Al ₂ 03 = 80/20

Right limit: Fe ₂ 0 ₃ / Al ₂ 0 ₃ = 40/60

Graphically, these boundaries represent a section of the connecting line from the apex of the triangle (MgO) to the base of the triangle. The above ratios are the coordinates of the points of the base of the triangle.

Starting from the MgO content between 1 2 and 1 9.5 wt .-%, the mixed crystals each contain a Fe ₂ 0 ₃ and Al ₂ 0 ₃ content in solid solution from the respective specified limited areas such that a total composition to Calculated 1 00 wt .-%. The compositions are thus always in the spinel field range of the ternary system with respect to MgO between 1 2 and 1 9.5 wt .-% MgO.

Particularly suitable as elasticizer are spinels from the inventive composition field region, which in granular form Kornrohdichten of at least 2.95, particularly at least 2.99, preferably at least 3.0 g / cm ^3, in particular up to 3.2 g / cm ^3, most especially up to 3.7 g / cm ³ , measured according to DIN EN 993-1 8. These elastifiers optimally elasticize in particular coarse ceramic basic refractory products offset therewith.

Monophasic for the purposes of the invention means that in the technical spinel mixed crystals according to the invention no, but at most less than 5, especially less than 2 wt .-% secondary phases, for. B. originating from impurities of the starting materials.

It is advantageous if the grain compressive strengths of the grains of the elastification granules are between 20 MPa and 35 MPa, in particular between 25 MPa and 30 MPa (measured in accordance with DIN EN 1 3055 - Appendix C). The inventive granular spinel elastomers are preferably prepared and used with the following grain distributions (determination by sieving):

0.5-1.0 mm 30-40% by weight

1, 0-2.0 mm 50-60 wt .-%, while in each case up to 5 wt .-% grain sizes smaller than 0.5 mm and greater than 2 mm are present, which reduce the other grain sizes accordingly.

The grain sizes are used with normal, customary grain distributions, in particular Gaussian grain distributions, or with certain conventional grain fractions in which certain grain fractions are absent (default grain size), as is common practice.

The monophasic sintered spinel elastomers according to the invention are clearly identifiable by means of X-ray diffractometry as exclusively monophasic present, as will be shown below.

In addition, the spinel monophases are analyzable as exclusively present in light micrographs and quantitatively the composition of the mixed crystals or monophases can be determined by X-ray fluorescence elemental analysis, e.g. with an X-ray fluorescence spectrometer z. B. with the type Bruker S8 Tiger.

Fig. 1 in wt .-% is in the ternary ternary system MgO-Fe ₂ 03-Al ₂ 03 according to the invention discovered composition field region of fizierer as an elastic appropriate monophasic Spinellmischkristalle as ESS limited rectangle, while the composition Field of the known pleonastic Spinellelastifizierer drawn limited rectangle as pleonaste is. In addition, on the composition line Fe ₂ O ₃ -Al ₂ O _{3 of} the ternary system, the typical spinel elasticizer composition of the commonly used hercynite is characterized as a limited rectangle Hercynite. The invention thus relates to sintered iron-rich spinels which are within the ternä- ren system MgO Fe ₂ 03-AI ₂ 03 and neither the spinels of Hercynit- are still made in which the pleonaste group. After sintering of correspondingly high-purity raw material or starting materials, the respective spinel product consists only of a synthetic mineral monophase and, due to the predominant existence of trivalent iron (Fe ³⁺ ), has no or hardly any oxidation potential. Reactive secondary phases as z. B. are often present in pleonastic or hercynitic spinel types are not present or not detectable by X-ray and can not affect the performance of refractory products containing the spinel products according to the invention in the spinel products according to the invention.

Spinels according to the invention as elastifying component even with lower initial weight in shaped and unshaped, especially basic refractory materials, eg. As used for kiln aggregates of the cement and lime industry or dolomite or magnesite industry, arise using conventional production methods ceramic refractory products with high corrosion resistance to alkalis occurring in the furnace atmosphere and salts. For putting these refractory products have excellent thermochemical and thermo-mechanical properties and a strong tendency to buildup in the mentioned industrial furnace aggregates at high temperatures, the latter properties are probably due to relatively high near-surface iron oxide contents of the refractory product.

Spinel granulates useful as elastomers in accordance with the present invention are in a limited ternary system which incorporates all the advantages of chemical resistance, ease of picking, elastification, and also good energy balance through an economical refractory production process. The invention thus closes a gap between Hercynit and Ple Onastspinellelastifizierern without having to fear the disadvantages of one or the other.

The monophase sintered spinels of the ternary material system MgO-Fe ₂ O ₃ -Al ₂ O ₃ used according to the invention in granular form differ essentially from the pleonastic spinels by the valence of the cations and by lower MgO contents. An excess of magnesium, which occurs only in the high temperature range, does not show up in the ternary system of iron-rich spinel used in the invention, but the latter consists only of a mineral monophase thanks to the absence of secondary phases such. B. Magnesioferrit, Magnesiowüstit. The monophasic spinels used according to the invention are therefore superior to the pleonastic spinel because the abovementioned secondary phases are missing, have the coefficients of linear expansion close to those of magnesia and thus have only a slight elasticizing effect.

It is ecologically and economically advantageous that the spinels used according to the invention can be prepared by a simple process which, after the preparation of three raw material components, provides for a sintering process at temperatures which are moderate compared to melting processes. In the context of the invention it has been found that z. B. from a mixture of sintered magnesia, naturally occurring iron oxide and / or mill scale and alumina after sintering forms a mineral monophase, wherein caustic magnesia, fused magnesia and metallurgical bauxite can also be used as starting materials.

The structural peculiarity of spinels employed in this invention as granules allows to include oxides such as Al ₂ 0 ₃ or Fe ₂ 0 ₃ in solid solution in the crystal, so that the end members represented by γ-ΑΙ ₂ 0 ₃ or Y-Fe ₂ 0 ₃ become. This circumstance allows the preparation of the mineral monophase in the ternary ternary system MgO-Fe ₂ 0 ₃ -AI ₂ 0 ₃ , whose electrical neutrality is ensured by cation defects in the spinel crystal lattice. In general, the difference in linear expansion coefficients of two or more components in a ceramic refractory product when cooled after a sintering operation results in the formation of microcracks mainly along the grain boundaries, thus increasing its ductility or reducing brittleness. The blending, shaping and sintering of burnt magnesia in admixture with spinel granules of the present invention using conventional production techniques results in basic refractory materials having reduced brittleness, high ductility and excellent alkali resistance which is superior to particularly basic products, sinter or melt hercynite or sintered or enamel bulk as an elasticizer component. In contact with cement clinker melt phases in the cement kiln, the iron-rich surface of inventive refractory products containing spinel granules causes the formation of the brownmillerite melting at 1 .395 ° C., which leads to a very good deposit formation and thus to a very good protection of the refractory material against thermomechanical stress by the kiln Contributes furnace.

The production of the sintered spinel used according to the invention as an elasticizer is described by way of example below. As already explained above, this is an iron-rich sintered spinel from the composition field ESS according to FIG. 1 in the three-substance system MgO-Fe ₂ O ₃ -Al ₂ O ₃ (in the following the sintered spinel is also referred to as ESS).

Starting materials are at least one magnesia component, at least one iron oxide component and at least one alumina component.

The magnesia component is in particular a high-purity MgO component and in particular fused magnesia and / or sintered magnesia and / or caustic magnesia.

The MgO content of the magnesia component is in particular above 96, preferably above 98 wt .-%. The iron oxide component is in particular a high-purity Fe ₂ O ₃ component and in particular natural or processed magnetite and / or hematite and / or mill scale, a by-product of iron and steel production.

The Fe ₂ 0 ₃ content of the iron oxide component is in particular more than 90, preferably more than 95 wt .-%.

The alumina component is in particular a high-purity Al ₂ O ₃ component and in particular alpha and / or gamma alumina.

The Al ₂ 0 ₃ content of the aluminum component is in particular more than 98, preferably more than 99 wt .-%.

These starting materials preferably have a fineness of fineness with particle sizes <1, in particular <0.5 mm. They are intimately mixed until a homogeneous to nearly homogeneous distribution of the starting materials in the mixture is present. It is expedient to mix the flours in a grinding unit and to apply a grinding energy which increases the fineness and consequently increases the reactivity of the flour particles for a sintering process. For example, the grinding and / or mixing in a z. B. a ton of millbase receiving ball mill or roll mill within z. B. 20 to 40 minutes. By simple mixing-mixing experiments, an optimization of the grinding-mixing process for a reaction activation of the starting materials for the sintering process can be determined. The meal is z. B. 1 5 to 30, especially 20 to 25 minutes.

However, the optimal fineness of the sintering reaction and mixture of the starting materials can also be advantageously produced in the grinding aggregate by grinding, by at least one granular starting material having grain sizes z. B. over 1, z. B. 1 to 6 mm is used, which is comminuted very fine during the grinding. After mixing or grinding, the fineness of the mixture z. B. 90 wt .-% <100 μιη, in particular <45 μιη amount.

The mixture of the starting materials is then in neutral or oxidizing atmosphere, in particular under air supply z. B. 3 to 8, in particular 4 to 6 hours z. B. sintered at temperatures between 1 .200 ° C and 1 .700 ° C, in particular between 1450 and 1550 ° C until reaching the desired monophase, wherein an ESS solid is formed or more solids are formed. It is then cooled and the solid crushed, z. B. with cone or roll crushers or the like. Crushing unit, so that usable as elastifiers, broken granules are formed. Subsequently, the crushed, granular material z. B. divided by sieving into certain granular ESS granule fractions. For sintering, e.g. Rotary kilns, bogies, shaft or tunnel ovens are used.

Conveniently, a compression of the mixture, for. By granulating, pressing or vibrating before sintering. Preferably, from the mixture compressed, in particular pressed moldings, for. As tablets, briquettes, spherical or angular shaped body produced. The granules have expediently a volume between 10 and 20 cm ³ , in particular between 12 and 15 cm ³ and densities between 2.90 and 3.20 g / cm ³ , in particular between 3.00 and 3.10 g / cm ³ . The density is determined according to DIN EN 993-18. Pressed moldings have z. B. volumes between 1 .600 to 2,000 cm ³ .

The compaction of the mixture accelerates the sintering reactions and favors the extra-phase freedom of the achievable monophases of the ESS.

After sintering and cooling, mixed crystals of Fe ₂ O ₃ in solid solution are present in the respective monophase, the iron preferably being present exclusively or with at least 90, in particular at least 95 mol%, in the trivalent oxidation state Fe ³⁺ . in the By contrast, in the case of a synthesis process with mixtures of the range according to the invention by melting, not insignificant proportions of divalent iron Fe ²⁺ and undesired mineral secondary phases are present.

To delineate clarification of the invention against pleonastic spinels according to DE 101 17 029 B4 mixtures of different compositions from the same starting materials have been prepared as examples according to a method according to the invention described above, the composition is characterized by the drawn points in the demarcated fields in Fig. 1st ,

The compositions at points 1, 2, 2-1 correspond to compositions of the ESS for the invention (hereinafter also referred to as composition according to the invention or spinel or inventive region according to the invention). The compositions at points 5, 5-1, as well as at points 6-1, 6-2, 6-3, 6-4, which are "6" in the drawn circle, correspond to pleonastic compositions according to DE 101 17 029 B4 ,

The chemical composition at the respective points is the following:

Compositions MgO Fe ₂ 0 ₃ Al ₂ 0 ₃ Si0 ₂ Loss on ignition [% by weight] [%]

1 17.49 63.33 17.37 0.80 0.14

2 17.64 33.02 48.22 0.40 0.19

2-1 19.41 32.06 47.42 0.37 0.1 1

5 21 .42 46.49 30.65 0.57 0.22 5-1 25.26 44.64 28.60 0.63 0.03

6-1 21 .01 32.54 45.30 0.38 0.12

6-2 25.86 30.37 43.69 0.26 0.03

6-3 21 .29 32.27 45.34 0.35 0.12

6-4 22.26 31 .73 44.91 0.35 0.17

Starting materials were an iron ore concentrate (magnetite) and high-quality fused magnesia and alumina. The sum of the oxides MgO, Fe ₂ 0 ₃ and Al ₂ 0 ₃ was 98 wt .-%. The following table contains the chemical analysis of the flour-like starting materials in% by weight:

The weighed starting materials were ground and mixed for 4 minutes in a rotary disk mill at 1 000 rpm, the resulting ground stock having a fineness of <45 μm. It was then moistened with denatured alcohol and the millbase into tablets with a Diameter of 2.54 cm and a thickness of 1 cm pressed (5.1 cm ³ ). After drying at 100 ° C, these tablets were fired for 12 hours at 1, 250 ° C in an electrically heated oven in air atmosphere. Subsequently, the fired tablets were ground and samples prepared for microscopic examinations and phase analyzes by means of X-ray powder diffractometry.

Of several distinguishing criteria of the iron-rich spinel according to the invention to the pleonastic spinel according to DE 101 17 029 B4, the monophase, which can be illustrated by X-ray powder diffractometry or light microscopy, a characteristic feature is. FIG. 2 shows each other X-ray diffractograms of the compositions 1, 2, 5 and 6-2. In the case of compositions 1 and 2, all reflexes can be assigned to a singular ESS mineral phase or ESS monophase, while compositions 5 and 6-2 clearly have at least one second crystalline mineral phase. Since the X-ray diffractometer images were carried out with the same parameters, it can be clearly seen from the peak height and peak configuration that in the case of compositions 5 and 6-2 there is multiphase, while the images of compositions 1 and 2 clearly show the single-phase nature.

Figures 3 to 6 show the light micrographs of compositions 1, 2, 5 and 6-2. The photographs in Figs. 3 and 4 show only the Spinellmonophase "S" of the compositions 1 and 2 of the inventive Sinterspinellbereich of the ternary system MgO, Fe ₂ 0 _3, Al ₂ 0 _3. The photographs in Figs. 5 and 6 show as Main phase the spinel phase "ST and to a lesser extent the spinel phase" S2 ". A single monophase is therefore not available.

An X-ray powder diffractometer from Panalytical X'Pert Pro was used with an X'Cellerator detector. The measurements were done with a Copper X-ray tube, with the excitation of the X-ray at 45 kV and 40 mA.

The oxidation resistance of ESS according to the invention is shown in FIGS. 7a and 7b. FIG. 7 a shows the X-ray diffractogram after the preparation of an ESS with the composition 1. FIG. Fig. 7b shows the X-ray diffractogram after treatment of the ESS at 1, 250 ° C and 12 hours in an air atmosphere in an electrically heated oven. It can be seen that the original spinel structure has been preserved despite the influence of temperature and the presence of oxygen. A new formation of mineral phases could not be determined by X-ray powder diffractometry.

For comparison, a hercynite sample according to DE 44 03 869 A1 was melted and an X-ray diffractogram was created (FIG. 8 a). Thereafter, the hercynite sample was also treated at 1250 ° C for 12 hours in an air atmosphere in the electrically heated furnace. The result is shown in FIG. 8b. It can be clearly seen that the original spinel structure was disturbed by the effect of temperature and oxidation of divalent iron (Fe ²⁺ ). The divalent cations necessary for the crystal lattice of the hercynite spinel are no longer available. The newly formed phases are hematite (Fe ₂ 0 ₃ ) and corundum (Al ₂ 0 ₃ ).

The invention also relates to the production of basic refractory products, e.g. As basic refractory moldings and basic refractory materials. For example, basic refractory products according to the invention have the following composition:

50 to 95 wt .-%, in particular 60 to 90 wt .-% of at least one granular basic refractory material, in particular magnesia, in particular fused magnesia and / or sintered magnesia with particle sizes z. B. between 1 and 7, in particular between 1 and 4 mm, 0 to 20 wt .-%, in particular 2 to 18 wt .-% of at least one flour-shaped basic refractory material, in particular magnesia, in particular fused magnesia and / or sintered magnesia with grain sizes <1 mm, in particular <0.1 mm,

5 to 20 wt .-%, in particular 6 to 15 wt .-% of at least one granular ESS according to the invention with particle sizes z. B. between 0.5 and 4, in particular between 1 and 3 mm,

0 to 5, in particular 1 to 5 wt .-% of at least one flour-like ESS according to the invention as an additive with grain sizes <1 mm, in particular <0.1 mm,

0 to 5, in particular 1 to 2 wt .-% of at least one known for refractory products binder in particular at least one organic binder such as lignosulfonate, dextrin, methyl cellulose.

Which binders are suitable for which refractory products can be found in the above-mentioned paperback, page 28/29.

The following example shows that very good solid properties can nevertheless be achieved with refractory products according to the invention which have lower addition amounts of elastifier compared to addition amounts with hercynite or pleonast. The example composition was as follows:

43.1% by weight sintered magnesia with particle sizes between 1 and 4 mm

44.4% by weight of sintered magnesia flour with grain sizes below 1 mm

10.5 wt .-% ESS with the composition 1 with particle sizes between 1 and 3 mm

2% by weight of organic binder From the mixture stones were pressed with a pressing force of 180 MPa and this burned in a tunnel oven in an air atmosphere at 1 .520 ° C for 6 hours.

The chemical composition of the fired refractory product is given in the following table:

The physical and thermochemical properties include the following table:

With the same composition under the same treatment, a sample having a pleonast granule having the composition 6-2 of spinel as an elasticizer was produced in place of the ESS elastifier. The fired sample showed a considerably higher modulus of elasticity, which is shown in the following table:

The result of the above example shows that with smaller amounts of ESS elastifiers, moduli of elasticity can be ensured which, with pleonast as elastifiers, can only be achieved with significantly higher addition quantities.

Based on basic magnesia moldings containing ESS, it is shown below that these refractory products are more resistant to alkalis than the same refractory products with hercynite spinel granules or Pleonastspellell granules. For this purpose, after the crucible process at 1 .400 ° C (residence time 3 hours) was tested with potassium carbonate as a reaction agent. The test was carried out by the method "Test method for dense refractory products - Guidelines for the examination of fluid-induced corrosion of refractory products; German version CEN / TS 1 541 8: 2006 ".

The result is shown in FIG. 9. Compared to the "hercynite sample" (right image) and the "pleonite sample" (center), the ESS-containing moldings (left image) show a significantly improved alkali resistance with the same weight of components ESS (left image), Pleonast (center) and Hercynit (right picture).

Finally, Fig. 1 0 shows the superiority of refractory products according to the invention with ESS compared with refractory products of the same composition with Pleonast. The left image in Figure 10 shows a sample made with 8.5% ESS. In each case the same particle size distribution is used. tions of the main component, namely fused magnesia and the spinel component has been used. In addition, the firing conditions were the same. After the ceramic firing, the samples were subjected to a standardized thermal shock resistance test at 1 .200 ° C. (30 cycles, 30 minutes each in accordance with DIN EN 993-1 1).

The thermal shock resistance of the left ESS-containing undestructed sample is clearly visible, while the sample containing the right pleonast is cracked.

In the following, advantageous features according to the invention are specified, wherein all features can be combined individually or in different combinations with the features of the main claim, regardless of their list in the respective subclaims.

The invention is particularly characterized by a granular Elastifi- Painters in the form of a broken granulate for refractory products, in particular for basic refractory products, mineral each consisting of a single-phase sintered Mischkristallspinell of the ternary system MgO-Fe ₂ 03-AI ₂ 03 from the composition range

MgO: 12 to 19.5, especially 15 to 17 wt .-%

Rest: Fe ₂ 0 ₃ and Al ₂ 0 ₃ in the ratio range Fe ₂ 0 ₃ to Al ₂ 0 ₃ between 80 to 20 and 40 to 60 wt .-%. starting from a MgO content between 12 to 19.5 wt .-%, the respective mixed crystals each containing a Fe ₂ 0 ₃ - and Al ₂ 0 ₃ content in solid solution from the respective specified limited areas such that a Total composition to 100 wt .-% results.

It is furthermore advantageous if the elasticizer has: a grain density> 2.95, in particular> 2.99, preferably> 3.2 g / cm ³ , very preferably up to 3.7 g / cm ³ , measured 5 according to DIN EN 993-18 or less than 5, in particular less than 2 wt .-% secondary phases or

Corneal strengths between 20 MPa and 35 MPa, in particular between 25 MPa and 30 MPa, measured on the basis of DIN EN13055 - Appendix C or linear expansion coefficients between 8.5 and 9.5, in particular between 8.8 and 9.2 · 10 ^"6 K ^"1 or

Grain size distribution between 0 and 6, in particular between 0 and 4 mm, preferably with the following grain distributions, in each case with normal customary grain distributions, in particular Gaussian grain distributions, or with certain selected grain fractions or grain bands.

0.5-1.0 mm 30-40% by weight

1, 0-2.0 mm 50-60% by weight

The invention is also characterized in particular by a process for producing a monophasic sintered spinel, wherein

- At least one high purity, in particular flour-shaped MgO component

- At least one high purity, especially flour-shaped Fe ₂ 0 ₃ - component - Mixed at least one high purity, in particular flour-shaped Al ₂ 0 ₃ - component in certain, in the composition range according to claim 1, based on the oxides amounts and the mixture is sintered in a neutral or oxidizing atmosphere in a ceramic firing process until reaching the respective monophasic Sinterspinellmischkristallausbildung , then the sintered material is cooled, resulting in a sintered solid or a plurality of sintered solids, which is or are comminuted into granules, after which from the granules, z. B. by screening, a Elastifizierergranulat is created with a predetermined grain composition.

Furthermore, it is advantageous if the following process parameters are used: as MgO component at least one starting material from the following group is used: sintered magnesia, caustic magnesia, in particular with MgO contents above 96, preferably above 98 wt.

as Fe ₂ 0 ₃ component is used at least one starting material from the following group: hematite or magnetite, and in particular with Fe ₂ 0 ₃ contents above 90, preferably above 95 wt .-%

as AI ₂ 0 ₃ component is at least used a starting material from the following group: alpha and / or gamma alumina, in particular Al ₂ 0 ₃ content above 98, preferably above 99 wt .-%, preferably alpha and gamma alumina ,

Instead of the pure commonly used high quality primary raw materials, granules of recycled materials such as mill scale (Fe ₂ 0 ₃ ) or recycled magnesia (MgO) or magnesia spinel (Al ₂ 0 ₃ , MgO) can be used at least in part. It is furthermore advantageous if the components are comminuted and mixed with grinding energy in a grinding unit, preferably up to a fineness <0.10, in particular <0.05 mm, or the mixtures at temperatures between 1.200 and 1, 700, in particular be sintered between 1400 and 1600, preferably 1450 to 1550 ° C, in particular 5 to 7 hours, or the mixtures before sintering z. B. be compacted by granulation or pressing, in particular to granules z. B. with volumes between 10 and 20, in particular between 12 and 15 cm ³ , and bulk densities z. B. between 2.90 and 3.20, in particular between 3.0 and 3.1 g / cm ³ determined to DIN EN 993-18 are pressed preferably with pressing pressures between 40 MPa and 130 MPa, in particular between 60 and 100 MPa. Pressed moldings have z. B. Volumes between 1 .600 and 2,000 cm ³ .

The invention also relates to a basic, ceramically fired or unburnt refractory product in the form of refractory shaped bodies, in particular pressed refractory shaped bodies or unshaped refractory masses, in particular consisting of:

50 to 95 wt .-%, in particular 60 to 90 wt .-% of at least one granular, basic, refractory material, in particular magnesia, especially fused magnesia and / or sintered magnesia with particle sizes z. B. between 1 and 7, in particular between 1 and 4 mm

0 to 20, in particular 2 to 18 wt .-% of at least one flourförmi- basic, refractory material, in particular magnesia, especially fused magnesia and / or sintered magnesia with grain sizes <

1 mm, in particular <0.1 mm 5 to 20, in particular 6 to 1 5 wt .-% of at least one granular Elastifizierergranulats invention with grain sizes z. B. between 0.5 and 4, in particular between 1 and 3 mm

0 to 5, in particular 1 to 5 wt .-% of at least one flour-shaped additive, for. Example, from a flour-shaped sintered spinel according to the invention with particle sizes <1 mm, in particular <0.1 mm

0 to 5, in particular 1 to 2 wt .-% of at least one known for refractory binder, in particular with at least one organic binder such as lignosulfonate, dextrin, methylcellulose, etc.

The refractory products according to the invention containing the elastification granules are particularly suitable for use as the fire-side lining of industrial large-volume furnace units, which are operated with a neutral and / or oxidizing furnace atmosphere, in particular for the lining of cement rotary kilns.

Claims

claims

1 . Granular refractory mineral Elastifizierergranulat for refractory products, especially for basic refractory products, mineral consisting of a monophasic sintered spinel mixed crystal of the three-component system MgO-Fe ₂ 0 ₃ -AI ₂ 0 ₃ from the composition range

MgO: 12 to 19.5, especially 15 to 17 wt .-%

Rest: Fe ₂ 0 ₃ and Al ₂ 0 ₃ in the ratio range Fe ₂ 0 ₃ to Al ₂ 0 ₃ between 80 to 20 and 40 to 60 wt .-% starting from a MgO content between 12 to 19.5 wt. % of the respective mixed crystals each contain a Fe ₂ 0 ₃ - and Al ₂ 0 ₃ content in solid solution from the respective specified limited ranges such that a total composition results in 100%.

2. Elastifizierergranulat according to claim 1,

marked by

a bulk density> 2.95, in particular> 2.99, preferably> 3.2 g / cm ³ , very particularly up to 3.7 g / cm ³ , measured according to DIN EN 993-18.

3. Elastifizierergranulat according to claim 1 and / or 2,

marked by

less than 5, in particular less than 2 wt .-% secondary phases.

4. Elastifizierergranulat according to one or more of claims 1 to 3, characterized by

Corneal strengths between 20 MPa and 35 MPa, in particular between 25 MPa and 30 MPa, measured on the basis of DIN EN 13055 (Appendix C).

5. Elastifizierergranulat according to one or more of claims 1 to 4, characterized by

a linear expansion coefficient between 8.5 and 9.5, in particular between 8.8 and 9.2 · 1 CT ⁶ K ^{~ 1} .

6. Elastifizierergranulat according to one or more of claims 1 to 5, characterized by particle sizes with normal customary grain distributions, in particular Gau ß'schen grain distributions, or with certain grain fractions between 0 and 6, in particular between 0 and 4 mm, preferably with the following particle size distributions:

0.5-1 .0 mm 30-40 wt.%

1 .0-2.0 mm 50-60% by weight.

7. A process for producing a monophasic elastifying granule according to one or more of claims 1 to 6,

characterized in that

- At least one high purity, in particular flour-shaped MgO component

- At least one high purity, especially flour-shaped Fe ₂ 0 ₃ - component

- Mixed at least one high purity, in particular flour-shaped Al ₂ 0 ₃ - component in certain, in the composition range according to claim 1, based on the oxides amounts and the mixture in a neutral or oxidizing atmosphere in a ceramic firing process until reaching the respective monophasic Sinterspinellmischkristallausbildung is sintered, then the sintered material is cooled, resulting in a sintered solid or more sintered solids, which is comminuted into granules or be, from which from the granules, z. For example, by sieving, a Elastifizier- is granules made with certain grain composition.

8. The method according to claim 7,

characterized in that

at least one raw material material from the following group is used as the Mg O component: fused magnesia, sintered magnesia, caustic magnesia, in particular with MgO contents above 98, preferably above 98 wt.%, or an iron-rich, alpine sintered magnesia

- as Fe ₂ 0 ₃ component at least one raw material material from the following group is used: magnetite, hematite, mill scale, in particular with Fe ₂ 0 ₃ levels above 90, preferably above 95 wt .-%

- As Al ₂ 0 ₃ component at least one raw material material from the following group is used: alumina, in particular in the form of alpha or gamma alumina, in particular with Al ₂ 0 ₃ levels above 98, preferably above 99 wt .-%, or calcined metallurgical bauxite.

9. The method according to claim 7 and / or 8,

characterized in that

the components are mixed and / or comminuted in a grinding unit, preferably up to a fineness <0.5, in particular <0.1 mm.

10. The method according to one or more of claims 7 to 9,

characterized in that

the mixtures are sintered at temperatures between 1 .200 and 1 .700, in particular between 1400 and 1600, preferably 1450 to 1550 ° C., in particular 4 to 8 hours.

1 1. Method according to one or more of claims 7 to 10, characterized in that

the mixtures before sintering z. B. be compacted by granulation or pressing, in particular to granules z. B. with volumes between 10 and 20 cm ³ , in particular between 12 and 15 cm ³ , and bulk densities z. B. between 2.90 and 3.20, in particular between 2.95 and 3.1 0 g / cm ³ , determined according to DIN EN 993-18, are pressed, preferably with pressing pressures 5 between 40 MPa and 130 MPa, in particular between 60 and 100 MPa.

12. Basic, ceramically fired or unburnt refractory product in the form of refractory moldings, in particular pressed refractory moldings, or in the form of unshaped refractory compositions, in particular consisting of:

50 to 95 wt .-%, in particular 60 to 90 wt .-% of at least one granular, basic, refractory material, in particular magnesia, in particular fused magnesia and / or sintered magnesia, with grain sizes z. B. between 1 and 7, in particular between 1 and 4 mm

0 to 20 wt .-%, in particular 2 to 18 wt .-% of at least one flour-shaped, basic, refractory material, in particular magnesia, in particular fused magnesia and / or sintered magnesia with grain sizes <1 mm, in particular <0.1 mm

5 to 20, in particular 6 to 15 wt .-% of at least one granular Elastifizierergranulats invention with particle sizes z. B. between 0.5 and 4 mm, in particular between 0.5 and 3 mm

0 to 5 wt .-%, in particular 1 to 5 wt .-% of at least one flour-shaped additive z. B. from a sintered material according to the invention with particle sizes <1 mm, in particular <0.1 mm 0 to 5 wt .-%, in particular 1 to 2 wt .-% of at least one binder commonly used for refractory products, in particular at least one organic binder such as dextrin, methyl cellulose, lignosulfonate.

3. Use of a refractory product according to claim 1 2 containing an elastifying granule according to one or more of claims 1 to 6, which is prepared according to one or more of claims 7 to 1 1, as a fire-side lining of large-volume, industrial operated with neutral or oxidizing furnace atmosphere Furnace aggregates, in particular for lining cement rotary kilns.