EP1720812A1

EP1720812A1 - Ceramic batch and associated product for fireproof applications

Info

Publication number: EP1720812A1
Application number: EP05715686A
Authority: EP
Inventors: Harald Harmuth
Original assignee: Refractory Intellectual Property GmbH and Co KG
Current assignee: Refractory Intellectual Property GmbH and Co KG
Priority date: 2004-03-05
Filing date: 2005-03-03
Publication date: 2006-11-15
Also published as: RU2006134295A; RU2386604C2; ZA200607731B; CA2558526A1; US20070203013A1; CA2558526C; WO2005085155A1; BRPI0507341A

Abstract

The invention relates to a ceramic batch for fireproof applications, containing between 83 and 99.5 wt. % of at least one refractory base product in a grain fraction of less than 8mm, and between 0.5 and 12 wt. % of at least one separate granulated SiO2 carrier, and possible remnants i.e. other constituents. The invention also relates to a product using said batch.

Description

Ceramic offset and associated product for refractory applications

description

The invention relates to a ceramic substitute and an associated product for refractory applications.

Ceramic additives with refractory raw materials are used to manufacture refractory ceramic products and are used in many areas of technology, especially for lining

and repair of metallurgical melting vessels or industrial furnace linings. Furthermore, such basic materials are used for the production of so-called functional products, for example for spouts, immersion pipes, shadow pipes, slide plates, etc., as are required in the melting units and furnaces mentioned.

The refractory raw materials are both basic and non-basic varieties. MgO, in particular MgO sinter, is an essential component of all MgO and MgO spinel products. The main component of MgO sinter is periclase. The main raw material base for the production of MgO sinter is magnesite, i.e. magnesium carbonate, or a synthetic magnesia source.

To set certain material properties, in particular to improve the chemical resistance to slag, to improve ductility, as well as temperature change resistance and heat resistance, various refractory ceramic offsets in combination with various additives are known, from which the corresponding unshaped or shaped products are then produced.

This includes, for example, chrome ore for the production of so-called magnesia chromite stones. Their advantage lies in a low brittleness (or higher ductility) compared to pure magnesia stones. However, there is an increasing need for Cr O ₃ -free fire-resistant building materials in order to avoid the potential for the formation of toxic Cr ⁶⁺ . In this connection, various offsets that are free of chromium oxide have been proposed. According to DE 44 03 869 C2, such an offset consists of 50 to 97% by weight of MgO sinter and 3 to 50% by weight of a spinel of the Herzynit type. Products that are burned from such an offset have a reduced brittleness in contrast to pure MgO products.

Unformed products, for example casting compounds, are formed from batches which are brought to a desired processing consistency with a certain viscosity by water or other liquids and, if appropriate, additives (such as binders, plasticizers, dispersants). These masses are then processed directly as monolithic masses, for example for the monolithic lining of a metallurgical melting vessel, or they are used for the production of so-called prefabricated components. In this case, the offsets can also be processed as such or in combination with certain additives, for example cast in molds.

In the case of the above-mentioned casting compounds, which also include refractory concrete compounds, cracks may form during subsequent drying and / or shrinkage during the subsequent sintering, which reduce the durability of the infeed or the prefabricated component.

Such cracks are often observed in the delivery of ladles from the steel industry with non-basic casting compounds. In order to counteract this, spinel-forming masses have been proposed in the prior art Service. Spinel formation leads to an increase in volume that counteracts shrinkage. Cracking often occurs at temperatures below the temperatures for spinel formation. The desired longer shelf lives cannot then be achieved.

The mentioned products based on MgO in combination with various spinels have proven themselves in principle. However, the introduction of the spinels introduces additional oxides into the batch, which can lead to a reduction in the hot strength of the fired products. For example, the invariant point, which is the temperature of the first melting phase formation, can be only 1,325 ° C for a magnesia stone with the addition of MgAl ₂ O ₄ . Especially calcium-rich infiltrates, such as basic slags or cement clinker melts, can then reduce the heat resistance and durability.

Even with fired, molded products, the above-mentioned influences, such as slag attack, temperature changes, etc., often lead to an inadequate service life for the refractory products. This applies in particular to applications in which mechanical or thermomechanical stresses are to be expected, for example. These include refractory linings for units that undergo periodically changing deformations, for example rotary kilns for the production of cement. Refractory products with reduced brittleness (or in other words: with increased "flexibility") are also required for furnace units in the steel and non-ferrous metal industry.

This problem is greater with basic materials than with non-basic grades. This is due, among other things, to the mostly lower thermal expansion and to a certain glass phase percentage of non-basic products. To reduce the brittleness, it is finally known to add a proportion of granular, stabilized zirconium oxide (zirconium dioxide; ZrO ₂ ) to the mixture. The disadvantage here is that only a relatively small reduction in brittleness is achieved and ZrO _{2 is} expensive.

The invention has for its object to offer a ceramic offset and associated products that have a symbiosis of the required property characteristics mentioned. In particular, the products formed from the offset should have reduced brittleness (ie improved ductility), good thermal shock properties, advantageous heat resistance and the best possible resistance to corrosion while at the same time being inexpensive to produce. The term “product” includes in particular unshaped and shaped products, those with and without heat treatment before use, sintered products and products that are / have been heat treated (heated) during use.

The invention is based on the knowledge that the brittleness of refractory products or products intended for refractory applications can be significantly reduced if the formation of macroscopically recognizable (large) cracks is avoided and the system is set so that it only serves to form microcracks in the Structure is coming. This is achieved by adding a separate SiO ₂ carrier to the offset. The crack density is increased (expressed, for example, as the number of cracks per square meter of the surface). However, the cracks have a much smaller crack width (in particular <20 μm), and are therefore significantly smaller than the macroscopically recognizable cracks in products in the prior art. These micro cracks do not have the same negative impact on the durability of the products. These products are also better able to withstand thermo-mechanical loads during use, for example due to thermal shocks. The fact that the SiO ₂ carrier as a largely independent component is retained and no melting phases form, the effects of microcracking are retained even after temperature treatment.

According to the invention, the physical changes in the structure can be achieved in certain mass fractions by adding a separate, grained SiO ₂ carrier. The term “SiO ₂ carrier” encompasses all crystalline SiO ₂ modifications which have sufficient stability at room temperature. These include primarily cristobalite (ß-form) and tridymite (γ-tridymite). Another possible SiO ₂ modification is coesite. Quartz (ß-shape) or quartz can also be used as SiO ₂ carrier. This also applies to substances that have been prepared from the above-mentioned SiO ₂ raw materials by physical and / or chemical processes (pretreatment). For example, quartz can be ground, compacted, sintered and then processed in a suitable grain. The pretreatment or preparation of the SiO ₂ carrier can be used to reduce its bulk density to values of <2.65 g / cm ³ , for example to values between 2.2 and 2.5 g / cm ³ . The chemical composition of the SiO ₂ carrier can also be varied by admixtures such as CaO.

The formation of microcracks is caused by a non-linear thermal expansion during phase transformations of the crystalline SiO ₂ carrier. Such a phase transformation is, for example, that of β-quartz to α-quartz at 573 ° C and the transformation of α-quartz to α-cristobalite at over 1050 ° C, often at around 1250 ° C. Ss-Cristobalite is already changing at 270 ° C in α-cristobalite, which is also associated with a volume expansion. Therefore, the desired effect can be seen in the product of Example 5 below after drying at 380 ° C.

In its most general embodiment, the invention then relates to a ceramic offset for refractory applications A: 83-99.5% by weight of at least one refractory base material in a grain fraction <8mm, and B: 0.5-12% by weight of at least one separate, granular SiO ₂ carrier, and C: any rest: other ingredients.

The offset can only consist of components A and B.

The refractory base material can be a basic substance such as doloma (i.e. burnt dolomite) or magnesia (ie MgO), or a non-basic substance, for example based on Al ₂ O ₃ or ZrO ₂ .

According to one embodiment, the proportion of the refractory base material is 90-99% by weight. The proportion of the granular SiO ₂ carrier is, for example,> 1 and / or <7% by weight, in each case based on the total offset, the upper limit also being able to be set at <5% by weight or <4% by weight.

The mixture of refractory base material, for example an MgO base material and crystalline SiO _{2 support} , leads to expansion in the corresponding modification conversions of the SiO support during a temperature treatment (in particular in the case of fire) after shaping the offset, according to current knowledge, which leads to generation of micro-cracks in the structure. These micro cracks are responsible for reducing the brittleness.

In contrast to magnesia products with an addition of spinels, for example Herzynit, microcracks are formed when the crystalline SiO ₂ support is added during the heating phase of the firing process, while in the prior art microcracking can be observed in the cooling phase. If a glassy SiO ₂ carrier (quartz material) is used, the crack formation is due to the greater shrinkage of the refractory (refractory) basic component when cooling after the fire.

The principle of microcrack initiation by a separate, grained SiO ₂ carrier is basically independent of the raw material (the refractory basic component) and is therefore, for example, based on ceramic-bonded, chemically bonded, carbon-bonded, hydraulically bonded, shaped and unshaped, annealed, fired and unburned refractory displacements and products applicable.

The temperature can be a criterion for the selection of the SiO ₂ carrier.

For example, in the case of the prefabricated components, casting compounds or carbon-bonded refractory products mentioned, it can make sense to use cristobalite as an SiO ₂ carrier. In this way, the desired microcracks can be formed even at a very low temperature level, for example when the casting compounds are heated up. The unwanted shrinkage cracks can be avoided.

This also applies, for example, to the drying of monolithic masses or the hardening (tempering) of synthetic resin-bound or pitch-bound refractory products.

An important group for the application of the invention are unshaped products such as concrete masses or casting masses for the production of refractory linings or prefabricated components. These masses can be hydraulic or harden semi-hydraulically, e.g. be masses based on cement, especially alumina cement. The invention can also be applied to low-cement or cement-free casting compounds, for example those based on bauxite as a non-basic refractory base material.

The dry mix (e.g. bauxite and cristobalite) is mixed with the required amount of water to achieve a desired processing consistency. If necessary, additives such as plasticizers are added. The described conversion of ß-cristobalite to α-cristobalite takes place already during drying from 270 ° Celsius.

The mode of operation described is largely independent of the grain fraction of the refractory basic component. However, small maximum grain sizes (for example 2 mm) or small proportions (for example 5% by weight) of the coarse fraction (for example 2 to 4 mm) can have an unfavorable effect on the reduction in brittleness. However, it has proven to be advantageous if the SiO ₂ carrier has a grain size d ₅₀ or d ₀₅ which is larger than a maximum grain (or larger than at least 95% by weight) of the fine grain fraction of the refractory base material. Accordingly, 50 or 95% by weight of the SiO ₂ carrier is coarser than 95 or 100% by weight of the fine grain of the refractory base material.

The refractory base material is typically used in a relatively wide range of particles. In addition to a coarse grain fraction (<8mm), for example 1-6mm, the component can have a proportion of a medium grain, for example 0.25- <1mm and a fine grain fraction (flour fraction) <0.25mm.

The limit grain size between coarse grain and medium grain can also be set at 1, 5 or 2mm. Likewise, the proportion of flour grain can be determined, for example, to a grain fraction <0.125 mm (125 μm). According to various embodiments, the abovementioned fine grain fraction of the refractory base material is 10-30% by weight, 15-25% by weight or 25-30% by weight, in each case based on the total batch. The average grain fraction, as stated above, can be, for example, orders of magnitude of 5-30% by weight, 10-25% by weight or 10-20% by weight, again based on the total offset. The coarse grain fraction is calculated accordingly from the above proportions of fine grain or medium grain.

According to a further embodiment, the refractory, in particular oxidic, raw material is proposed in the following particle size distribution:

50-60% by weight l -6mm,

10-25% by weight 0.25- <lmm,

25-30% by weight <0.25mm, the sum being 100% by weight.

According to one embodiment, the granular SiO ₂ carrier has a grain size of up to 6 mm, the upper grain limit also being selected at 3.0 or 1.5 mm and the lower grain limit at 0.25, 0.50, 1 or 2 mm can. The SiO ₂ carrier is typically present in a grain fraction between 0.5 and 3 mm. In comparison with grain sizes in the range below 1 mm, the increase in the grain size (> 1 mm) with the same amount leads to a higher effectiveness in the sense of the invention. A grain size of 1 to 2mm is therefore more effective than a grain size of 0.5 to 1mm.

At least one of the following components can be selected as the non-basic refractory base material: chamotte, sillimanite, andalusite, kyanite, mullite, bauxite, corundum raw materials such as high-grade corundum or brown corundum, Tabular alumina, calcined alumina, basic materials containing zirconium oxide such as zirconium mullite, zirconium corundum, zirconium silicate or zirconium oxide, titanium oxide (TiO ₂ ), Mg-Al spinel, silicon carbide.

Quartzite can also be used as a refractory base material, with cristobalite, tridymite, coesite and / or the aforementioned pretreated SiO 2 carrier being used as an additive.

An MgO base material with an MgO content of 83 to 99.5% by weight is proposed in particular as the basic refractory base material. According to various embodiments, the lower limit for the MgO content is 85, 88, 93, 94, 95, 96 or 97% by weight, the upper limit for example 97, 98 or 99% by weight.

In one embodiment, the MgO content is 94 to 99 or 96 to 99% by weight.

The MgO base material can consist of sintered magnesia, melted magnesia or mixtures thereof.

In one embodiment, the MgO content of the batch can be provided in a proportionate amount of 3 to 20% by weight (or 3 to 10% by weight) based on the total mixture, a spinel of the Herzynit type, the Galaxit type or mixtures thereof become. In this case, the microcracks initiated by the granular SiO ₂ carrier in the heating phase are supplemented by further microcracks by the spinel component during the cooling phase in the pyroprocess. In addition, the batch can contain other constituents in relatively small proportions, for example at least one of the following components: (elementary) carbon, graphite, resin, pitch, soot, coke, tar.

The offset can therefore be used to produce C-linked products. This applies in particular to applications of the offsets in carbon-bound products or products that are soaked in tar.

These include so-called ASC products, the names of which derive from the main components A (for Al O ₃ carriers), S (for SiC and / or Si metal) and C (for the carbon carrier). Magnesia carriers (for spinel formation) and Mg-Al spinels can also be part of the recipe. Such offsets are bound with a synthetic resin, for example a phenolic resin, as a binder. They are used for example for pig iron pans, but also for shadow pipes, dip pipes, etc.

For such resin-bonded products, the curing process can be carried out in such a way that, for example, the transition temperature from ß-cristobalite to α-cristobalite is reached or exceeded, so that microcracks are already present in the product when the pre-assembled molded parts are delivered. Alternatively, it is also possible to harden (temper) at a lower temperature (e.g. 160-220 °) and to postpone the process of microcracking until later use. The microcracking then occurs during the heating of the product after it has been delivered. As already stated, the offset described also serves in particular for the production of fired refractory products, in particular fired refractory molded parts. As usual, a binder, in particular a temporary binder, for example a lignin sulfonate solution, is mixed into the batch and the mixture is then pressed, for example into stones, dried and fired. A typical firing temperature is 1300-1700 ° Celsius. A typical firing temperature for a batch with 96% by weight of MgO and 4% of a granular SiO ₂ carrier is 1,400 ° C (+/- 50 ° C). The following experiences apply when choosing the firing temperature: Too high a firing temperature or application temperature can lead to a reduced effect of the SiO ₂ carrier and increase the brittleness again due to too intensive sintering (usually involving melting phases). In this respect, the reaction behavior, in particular the formation of melting phases, between the SiO ₂ carrier and the refractory base material must be taken into account without preventing sufficient sintering. The exact firing temperature is dependent on the specifically selected components of the offset and has to be determined empirically.

The invention is explained in more detail below with the aid of various exemplary embodiments. A total of 5 batches (No. 1 -5) with non-basic basic components, one batch (No. 7) based on MgO and one comparative example according to the prior art (No. 6, 8) are listed below, the raw material composition and the chemical composition in the form of an oxide analysis are given.

The offsets of Examples 1-3 are used to produce fired, shaped products based on non-basic raw materials. It goes without saying that a temporary binder must be added to the offset components. This can be, for example, sulfite waste liquor, phosphoric acid or monoaluminum phosphate. A binding tone can also be used in the recipe be included. At the usual pressures (e.g. 65-130 MPa), stones or other molded parts can be produced from the offsets, which are then fired. The firing temperature should be selected so that the sintering is sufficient, but not so high that excessive sintering counteracts the effect of reducing the brittleness. For a given composition of the components, the granulometry of the fine-grain fraction of the non-basic raw material and the binder are decisive.

For example 1, a firing temperature of 1450 ° Celsius was chosen. The (pressed) stones produced from offsets 2 and 3 were fired at 1550 ° Celsius.

Offset No. 4 is used to manufacture a so-called ASC product, i.e. a C-linked product, as was presented above, with an addition of cristobalite. Via the cristobalite conversion, microcracks in the structure are initiated during the tempering (400 ° Celsius) of the products made from the offset.

Example 5 shows an offset for a casting compound with a proportion of alumina cement. The batch was mixed with water and molded parts were made from it, which were dried or tempered at temperatures up to 380 ° Celsius. In addition, a comparison mass (No. 6) was produced, but without the addition of cristobalite, and analog samples were produced and also dried or tempered at 380 ° Celsius. In order to compensate for the missing 4% by weight of cristobalite in batch No. 6, all other basic components of batch No. 5 were increased by 4% each. Example 1)

Example (2)

Example (3)

Example (4)

* based on oxidized sample

Example (5)

Fracture mechanical tests have shown that microcrack initiation can reduce brittleness. Measurements of the brittleness of a product can be made in different ways. Such a measure is, for example, the characteristic length

_ G _F - E ^l ch (I) f In this equation, G _F denotes this specific breaking energy (N / m), E the modulus of elasticity (Pa), and f _t (Pa) the tensile strength. The greater the characteristic length, the lower the brittleness of the refractory building material. As a rule, a decrease in brittleness is observed with increasing quotient Gp / ft of the specific breaking energy G _F to the tensile strength f _t . The ratio G _F / O _{Z is} used to characterize products according to the invention. A basic wedge gap test to determine the specific breaking energy G _F and the nominal notch tensile strength σκ_z is described in K. Rieder et.al. "Fracture mechanical cold and hot testing of refractory coarse ceramic materials", progress reports of the German Ceramic Society, Materials - Process - Application - Volume 10 (1995), Book 3, ISSN 0177- 6983, 62-70. The test method is explained further below:

The wedge gap test is carried out after a temperature treatment of the product (for example after drying, tempering or fire of the product) at room temperature.

The table at the end of the description lists the conditions for the wedge gap test depending on the starting product. “Unformed product” denotes an offset, if appropriate after adding a binder and / or a mixing liquid. The term “molded product” includes all shapes and shaping processes, the product having to be at least the size of the test specimen described below. A distinction is made between molded products without and after temperature treatment and according to their different types of bonds. An "originally unshaped product", for example a casting or injection molding compound, can become Solidification of the creation of a monolithic body (for example a furnace lining) solidifies during use and thus virtually becomes a “molded” part. This also applies analogously to prefabricated components which are exposed to higher temperatures at least during use.

At least three test specimens of each product are tested and the average of the results is used for the assessment. The shape of the test specimen is shown in FIG. 1. The cuboid test specimen has the following dimensions: width W: 1 10 mm, length L: 75 mm, height H: 100 mm. A recess A with the following dimensions can be seen on the upper side: width b: 24 mm; Length 1: 75 mm, height h: 22 mm. The recess A is used to hold strips, rollers and a wedge for power transmission. From the bottom of the recess A, a notch Kl extends with a width b 'of 3 mm and a height h' of 12 mm downwards in the direction of the base area G. In each case, another notch adjoins the notch Kl

Notch K2, K3 on, which run to the base G of the test specimen. K2, K3 each have a width b "of 3 mm and a height h" of 6 mm. For the test, two strips LS are inserted into the receptacle A on the outside, the shape and size of which can be seen in FIG. A wedge K1 according to FIG. 3 (above) is placed in the middle between the strips LS and is supported against the strips LS via two rollers R (FIG. 3 below), as shown in FIG. If the shaping process of product manufacture is done by uniaxial pressing, the sample is taken so that the direction of the pressing force is parallel to the plane of the ligament surface (that is the surface where the fracture is generated during the test). The length of the wedge K and the strips LS corresponds to the sample length of 75 mm. The rolls R are a little longer. Wedge Kl, strips LS and rollers R are made of steel. During the test, the test specimen rests on a linear support. This is a square steel rod S, which has an edge length of 5 mm and whose length corresponds at least to the specimen width of 75 mm and extends over the entire length of the specimen. The bar S covers the width of the Notches K2, K3 even on both sides. The course of the test is shown in FIG. 5. A load cell KM can be seen in the upper image area. The vertical force V exerted by the testing machine on the wedge Kl causes horizontal forces which lead to a steadily progressing crack formation during the test. Meanwhile, the vertical load F _v and the vertical displacement δ _{v are} determined. These sizes are registered until the load drops to 10% or less of the maximum load. The fracture energy GF is determined as the area under the load / displacement diagram. It is therefore

In this equation (II), A is the ligament area of 66 x 63 mm [(100-22-12) x (75-6-6)], δ _max is the maximum displacement during the measurement. The nominal notch tensile strength is calculated using the following equation:

= ^ ≡- + ^{6 'Ffl} ^ ^{' y} (III) ^κz B - WB - W ²

In this equation (III), B is the ligament length (63mm) and W is the ligament height (66mm). The size y denotes the vertical distance of the line of action of the horizontal force introduced by the rollers from the center of gravity of the ligament surface. A value of 62 mm is used as a sufficient approximation for this (FIGS. 1 and 4). The horizontal maximum load FH _max used in this relationship (III) can be determined from the vertical maximum load Fy _ma according to the following relationship:

FV max r H max ~ 2 • t, an (/ i2rΛ) (^ N In this relation (IN), α means the wedge angle that was chosen to be 10 °. The test is carried out in a feed-controlled manner with a vertical speed of the stamp of the testing machine of 0.5 mm / min.

In the event that these test parameters cannot be met for a certain product - e.g. because a sufficiently large sample cannot be produced or for other reasons that raise doubts as to the accuracy of the determined absolute values - the quotient G _F / Ü _RZ for the product according to the invention and an analogue manufactured and tested product without SiO ₂ carrier determined. The missing SiO ₂ content is added proportionally to all other components of the product. The reduction in brittleness is then determined using the ratio of the quotient Gp / σκz for the product according to the invention to the quotient Gp / σκz for the analogously produced product without SiO ₂ carrier. The ratio is> 1, mostly> 1, 5 or> 1, 8. Values> 2 are aimed for. As the following examples (7), (8) show, values of almost 3 are achieved.

The following table shows the comparison values for the specific breaking energy G _F , the nominal notch tensile strength σj z and the quotient of the two. Products according to the invention are characterized by a ratio G _F / Ü _Z > 40. Values> 50 are aimed for.

The product according to the invention shows a more than doubled quotient of specific breaking energy and nominal notch tensile strength, from which a significantly reduced brittleness can be read.

The wedge gap test mentioned was also carried out here to demonstrate the reduction in brittleness.

FIG. 6 shows the load / displacement diagrams of the wedge gap test (carried out at room temperature) and demonstrates the significantly less brittle behavior of the offset (7) according to the invention. In the table above, this can be seen from the higher quotient of the specific breaking energy G _F by the nominal notch tensile strength σκ: z.

Furthermore, the dynamic modulus of elasticity E _{yn was determined} from the resonance frequency of the expansion wave [Hennicke, Leers: The determination of elastic constants with dynamic methods, Tonindustrie-Zeitung 89 No. 23/24, 539-543 (1976)].

As the table above shows, the addition of the granular SiO ₂ support to the magnesia component causes a significant reduction in the modulus of elasticity, namely from 75.8 GPa to 14.9 GPa. The table also shows that the ratio of the nominal notch tensile strength to the dynamic modulus of elasticity is significantly higher in the variant according to the invention. This leads to an increase in the thermal stress parameter R according to Kingery [WD Kingery et.al. : Introduction to Ceramics, John Wiley & Sons, 1960; ISBN 0-471 -4786C- 1].

Although the invention manages with a simple, inexpensive additive (granular SiO 2 carrier) in addition to the refractory basic component, the said offset proves to be a good basis for the production of refractory products which have a relatively low brittleness, so that they show good thermal shock resistance, are corrosion resistant, but also do not cause a reduction in the heat resistance in comparison to other products from the prior art. The selection of the offset components and manufacturing conditions is such that the product gives a ratio Gp / σκz> 40.

Compared to magnesia products without granular SiO ₂ carriers, the product according to the invention has the advantage of a higher mechanical or thermomechanical resistance to thermal shock or impressed deformations. In comparison to magnesia chromite products, there is the advantage of a chromium-free delivery material, whereby the risk of Cr ⁶⁺ formation can be avoided. Compared to spinel products, there is a cost advantage due to the relatively inexpensive SiO ₂ carrier available. On the other hand, building materials in the CaO-MgO-SiO _{2 system} with mass ratios of CaO to SiO ₂ (C / S ratios) below 0.93, as can be expected for products according to the invention, have an invariant point of at least 1502 ° C., which at C / S ratios below approx. 0.25 (presence of a forsterite mixed crystal as the only silicatic secondary phase) can be increased further with a decreasing C / S ratio up to a maximum of approx. 1860 ° C. In contrast, a magnesia stone containing spinel (MgAl ₂ O ₄ ) with a C / S ratio above 1.87, as it corresponds to the prior art, has an invariant point of 1325 ° C. The higher invariant point in the product according to the invention can be used to improve the hot properties if, taking into account the product composition and any infiltrates in use, the amount of melting phase is also more favorable. Compared to products with the addition of ZrO _{2 there} is in any case an economic advantage due to the lower cost of the SiO ₂ carrier.

In the case of non-basic products, there is the advantage over the use of mullite or zircon mullite that no component is introduced which contains the glass phase and thus has an unfavorable influence on the softening behavior. The product according to the invention allows a material composition that consists exclusively of crystalline phases. Another advantage is that when using cristobalite, microcrack initiation and thus a reduction in brittleness already occurs at a temperature of 270 ° C. This allows unburned products to be manufactured or used even at low temperatures with reduced brittleness. These include, for example, casting compounds and prefabricated components. It is also possible, for example, to reduce the brittleness of carbon-bound unbaked products in this way.

Mean:

1: A test specimen is formed from the batch, optionally after adding a binder and / or water (for example: chemical or hydraulic binder), and this is heat-treated at 350 ° C.

2: A test specimen is formed from the batch, optionally after adding a binder and / or water (for example: chemical or hydraulic binder), and this is heat-treated at 650 ° C., alternatively> 1350 ° C.

3: A test specimen is cut from the product and this is heat-treated at 350 ° C., provided that the product has not previously been heat-treated at a temperature> 350 ° C.

4: A test specimen is cut from the product and this is heat-treated at 650 ° C, alternatively 1350 ° C, provided the product has not previously been heat-treated at a temperature> 650 C, alternatively> 1350 ° C.

5: A test specimen is cut from the product formed during use and this is heat-treated at 350 ° C., provided the product has not already been temperature-treated during use> 350 ° C.

6: A test specimen is cut from the product formed during use and this is heat-treated at 650 ° C, alternatively 1350 ° C, provided the product has not already been heat-treated during use> 650 C, alternatively> 1350 ° C.

7: A test specimen is cut from the product.

8: The SiO ₂ carrier consists of at least 50% by weight of cristobalite and / or tridymite.

9: The SiO ₂ carrier consists of less than 50% by weight of cristobalite and / or tridymite.

For the 4th and 6th, the temperature treatment is usually carried out at 1350 ° C. If the temperature of 1350 ° C is too high to reduce brittleness, the temperature treatment is carried out alternatively at 650 ° C, which is higher than the temperature for the quartz crack.

*: with a reducing atmosphere during temperature treatment

Claims

7 £ -Patentansprüche

1. Ceramic offset for refractory applications with

A) 83-99.5% by weight of at least one refractory base material in a grain fraction <8 mm and B) 0.5-12% by weight of at least one separate, granular SiO ₂ carrier, and C) any rest: other constituents

2. Batch according to claim 1, the refractory base material is at least partially a non-basic base material.

3. Batch according to claim 1, the refractory base material of which consists at least partially of doloma and / or magnesia.

4. Batch according to claim 1 with A) 90-99% by weight of the refractory base material, and B) 1 -7% by weight of the granular SiO 2 carrier

5. Batch according to claim 1, whose granular SiO ₂ carrier consists of at least one of the following SiO ₂ modifications: cristobalite, tridymite, coesite, a pretreated product with a bulk density <2.65 g / cm ³ .

6. Batch according to claim 1, whose SiO ₂ carrier has a grain size d ₅ o which is greater than 95% by weight of the fine grain fraction of the refractory base material.

7. batch according to claim 1, the SiO ₂ carrier has a grain size d ₀₅ , which is greater than 95 wt.% Of the fine grain fraction of the refractory base material.

8. Batch according to claim 1, the refractory base material of which has a fine grain fraction with 95% by weight <250 μm.

9. batch according to claim 1, the refractory base material has a fine grain content with 95 wt .-% <125μm.

10. Batch according to claim 8 or 9, whose fine grain fraction of the refractory base material is 10-30% by weight of the total batch.

1 1. Offset according to claim 1, the SiO ₂ carrier has a grain size up to 6mm.

12. Batch according to claim 1, whose SiO ₂ carrier has a grain size of up to 3 mm.

13. Batch according to claim 1, the SiO ₂ carrier has a grain size between 0.5 and 3mm.

14. Batch according to claim 1, whose refractory base material has a grain size <6mm.

15. Batch according to claim 1, whose refractory base material has the following particle size distribution: a) 50-60 wt .-% l -6mm, b) 10-25 wt .-% 0.25- <lmm, c) 25-30 wt. -% <0.25mm, the sum being 100% by weight.

16. Batch according to claim 1, with a non-basic refractory base material from at least one of the following components: chamotte, silimanite, andalusite, kyanite, mullite, bauxite, corundum raw materials such as high-grade corundum or brown corundum, tabular clay, calcined alumina, quartzite, zirconium oxide-containing basic materials such as zirconium mullite , Zirconium corundum, zirconium silicate or zirconium oxide, titanium oxide, Mg-Al spinel, silicon carbide.

17. Batch according to claim 1, with a MgO base material, which consists of 3 to 20 wt .-%, based on the total mixture, of a spinel of the Herzynit type, the Galaxit type or mixtures thereof.

18. Batch according to claim 1, which comprises at least one of the following components as other constituents: carbon, graphite, resin, pitch, soot, coke, tar.

19. Product based on an offset according to one of claims 1-18, with a quotient of specific breaking energy G _F (N / m) and nominal notch tensile strength σj_z (MPa)> 40 μm, in each case determined by means of a wedge gap test on a test specimen as described herein.

20. Product based on an offset according to one of claims 1-18, with a quotient of specific breaking energy G _F (N / m) and nominal notch tensile strength σ z (MPa), each determined by means of a wedge gap test on a test specimen as described herein, the at least is 1.5 times the equally determined quotient for an analog product without a separate, grained SiO ₂ carrier, the remaining basic components of which are proportionally adjusted by the missing SiO proportion to a total of 100% by weight.