|Title of Invention||
CERAMIC BATCH FOR THE PRODUCTION OF FIREPROOF CERAMIC PRODUCTS
|Abstract||The invention relates to a ceramic batch for fireproof uses, comprising 83-99-5 Wt.% of at least one refractory base material in a grain fraction of < 8 mm and 0.5-12 wt.% of at least one separatE, granular SiO2 carrier and any remainder: other constituents. The invention also relates to a product using this batch.|
The invention relates to a ceramic batch and a associated product for fireproof (refractory) uses.
Ceramic batches comprising refractory base materials serve for the production of fireproof ceramic products and are used in many areas of industry, in particular for the lining and repair of metallurgical melting vessels or industrial furnace linings. Such base materials are furthermore employed for the production of so-called functional products/ for example for spouts, immersion pipes, shadow pipes, slide valve plates etc., such as are required in the melting units and furnaces mentioned.
The refractory base materials are both basic and non-basic types. MgO, in particular MgO sinter, is an essential constituent of all MgO and MgO-spinel products. The main constituent of MgO sinter is periclase. The essential base raw material for the preparation of MgO sinter is magnesite, that is to say magnesium carbonate, or a synthetic source of magnesia.
To adjust certain material properties, in particular to improve the chemical resistance to slag, to improve the ductility and the resistance to temperature changes and the heat resistance, various fireproof ceramic batches in combination with various additives are known, from which the corresponding non-shaped or shaped products are then produced.
These include, for example, chromium ore for the production of so-called magnesia chromite bricks. Their advantage lies in a low brittleness (or higher ductility) compared
with pure magnesia bricks. Nevertheless, there is an increasing demand for Cr2O3-free fireproof building materials in order to avoid the potential for the formation of toxic Cr6+.
Various batches which are free from chromium oxide have been proposed in this connection. According to DE 44 03 8 69 C2, such a batch comprises 50 to 97 wt.% sintered MgO and 3 to 50 wt.% of a spinel of the herzynite type. In contrast to pure MgO products, products fired from such a batch have a reduced brittleness.
Non-shaped products, for example casting compositions, are formed from batches which are brought into a desired processing consistency having a certain viscosity by means of water or other liquids and optionally additives (such as binders, liquefiers, dispersing agents). The compositions are then processed directly as monolithic compositions, for example for monolithic lining of a metallurgical melting vessel, or they are used for the production of so-called prefabricated components. In this case, the batches can also be processed, for example poured into moulds, as such or in combination with certain additives.
In the case of the casting compositions mentioned, which also include refractory concrete compositions, cracks can form on subsequent drying and/or shrinkage during later sintering, these reducing the life of the lining or of the prefabricated component.
Such cracks are often observed in the lining of casting ladles of the steel industry with non-basic casting compositions. In order to counteract this, spinel-forming
compositions have been proposed in the prior art. During the formation of spinel, an increase in volume occurs, which counteracts shrinkages. However, the formation of cracks often already occurs at temperatures which are below the temperatures for the formation of spinel. The desired longer service lifes then cannot be achieved.
The products mentioned which are based on MgO in combination with various spinels have proved themselves in principle. However, by introducing the spinels, additional oxides are introduced into the batch, which can lead to a reduction in the heat resistance of the fired products. Thus, for example, the invariant point, which is the temperature of the first formation of a fused phase, in a magnesia brick with an addition of MgAL2O4 can be only 1,325 °C. Calcium-rich infiltrates above all, such as, for example, basic slag or fused cement clinker, can then reduce the heat resistance and life.
In fired, shaped products also, the abovementioned influences, such as attack by slag, temperature changes etc., lead to an often inadequate life of the fireproof products. This applies in particular to uses where, for example, mechanical or thermomechanical stresses are to be expected. These include fireproof linings of units in which periodically changing deformations occur, for example, rotary kilns for the production of cement. However, fireproof products of reduced brittleness (or in other words: of increased "flexibility") are also required in furnace units in the area of the steel and non-ferrous metals industry.
These problems are greater in the case of basic materials than in the case of non-basic types. The reason is, inter alia, the usually lower thermal expansion and a certain glass phase content of non-basic products.
Finally, to reduce the brittleness it is known to admix to the batch a content of granular, stabilized zirconium oxide (zirconium dioxide; ZrO2) . Disadvantages of this are that only a relatively low reduction in brittleness is achieved and ZrO2 is expensive.
The invention is based on the object of providing a ceramic batch and associated products which show a symbiosis of the required property features mentioned. In particular, the products formed from the batch should have, during use, a reduced brittleness (that is to say an improved ductility), good thermal shock properties, advantageous heat resistances and the best possible resistance to corrosion, and here at the same time should be inexpensive to produce. The term "product" includes, in particular, non-shaped and shaped products, those with and without heat treatment before use, sintered products and products which are/were heat-treated (heated) during use.
The invention is based on the finding that the brittleness of refractory products or products envisaged for refractory uses can be reduced significantly if the formation of macroscopically detectable (large) cracks is avoided and for this purpose the system is adjusted such that merely the formation of microcracks in the structure occurs. This is achieved by the addition of a separate SiO2 carrier into the batch. By this means, the crack density (for example expressed as the number of cracks per square metre of the
surface) is indeed increased. However, the cracks have a considerably lower crack width (in particular The physical changes of the structure can be achieved according to the invention by addition of a separate, granular SiO2 carrier in certain amounts by weight. In this context, the term "SiO2 carrier" includes all crystalline SiO2 modifications which have an adequate stability at room temperature. These include, primarily, cristobalite form) and tridymite (γ-tridymite) . Another possible modification is coesite. Quartz (β form) or fused quartz can likewise be used as the SiO2 carrier. This also applies to substances which have been processed from the SiO2 base materials mentioned by physical and/or chemical processes (pretreatment). For example, quartz can be ground, compacted, sintered and then processed into a suitable grain size. In this context, the pretreatment or processing of the SiO2 carrier can be utilized to reduce its bulk density to values of
The formation of microcracks is caused by a non-linear thermal expansion during phase conversions of the crystalline SiO2 carrier. Such a phase conversion is e.g. that of β-quart2 into α-quartz at 573 °C and the conversion of a-quartz into a-cristobalite at above 1,050 °C, often at about 1,250 °C. β-Cristobalite is already converted into a-cristobalite at 270 °C, which is likewise associated with an expansion in volume. The desired effect is therefore already to be seen in the product of the following Example 5 after drying at 380 °C.
In its general embodiment, the invention accordingly relates to a ceramic batch for refractory applications comprising
A: 83-99.5 wt.% of at least one refractory base material in
a grain fraction of carrier, and C: any remainder: other constituents.
The batch may comprise only components A and B.
The refractory base material can be a basic substance, such as doloma (that is to say fired dolomite) or magnesia (that is to say MgO), or a non-basic substance, for example based on A12O3 or ZrO2
According to one embodiment, the content of the refractory base material is 90-99 wt.%. The content of the granular
SiO2 carrier is, for example, ≥ 1 and/or ≤ 7 wt.%, in each case based on the total batch, it also being possible for the upper limit to be set at
According to current findings, during a heat treatment (in particular during firing) after shaping of the batch, the mixture of refractory base material, for example an MgO base material and crystalline SiO2 carrier, leads to expansions during the corresponding conversions of the modification of the SiO2 carrier, as a result of which generation of microcracks in the structure occurs. These microcracks are responsible for a reduction in the brittleness.
In contrast to magnesia products with an addition of spinels, for example herzynite, the formation of microcracks in the case of addition of the crystalline SiO2 carrier takes place during the heating up phase of the firing process, while in the prior art a formation of microcracks is to be observed in the cooling down phase.
If a vitreous SiO2 carrier (fused quartz) is used, the formation of cracks is based on the greater shrinkage of the refractory (fireproof) base component during cooling down after firing.
The principle of initiation of microcracks due to a separate, granular SiO2 carrier is in principle independent of the raw material (the refractory base component) and therefore can be applied, for example, to ceramically bonded, chemically bonded, carbon-bonded, hydraulically bonded, shaped and non-shaped, tempered, fired and non-fired fireproof batches and products.
The temperature can be a criterion for the choice of the SiO2 carrier.
Thus, for example, for the prefabricated components, casting compositions or carbon-bonded fireproof products mentioned it may be appropriate to employ cristobalite as the SiO2 carrier. In this manner, the desired microcracks can already be formed at a very low temperature level, for example already during heating up of the casting compositions. The undesirable shrinkage cracks can thereby be avoided.
This also applies, for example, to the drying of monolithic compositions or the curing (tempering) of fireproof products bonded by synthetic resin or pitch,
Non-shaped products, such as concrete compositions or casting compositions for the production of fireproof linings or prefabricated components, are an important group for the use of the invention. These compositions can harden hydraulically or semi-hydraulically, that is to say, for example, compositions based on cement, in particular aluminous cement. The invention can likewise be used on low-cement or cement-free casting compositions, for example those based on bauxite as a non-basic refractory base material.
The dry batch (for example of bauxite and cristobalite) is mixed with the required amount of water in order to achieve a desired processing consistency. Additives, such as liquefier, are optionally admixed. The conversion of (3-cristobalite into a-cristobalite described already takes place from 270 ° Celsius during drying.
The mode of action described is largely independent of the grain fraction of the refractory base component. Low
maximum grain sizes (for example 2 mm) or low contents (for example 5 wt.%) of the coarse fraction (for example 2 to 4 mm) , however, can have an adverse effect on the reduction in brittleness. Nevertheless, it has proved to be favourable if the SiO2 carrier has a grain size d50 or dO5 which is greater than a maximum grain (or greater than at least 95 wt.%) of the fine grain content of the refractory base material, Accordingly, 50 or 95 wt.% of the SiO2 carrier is coarser than 95 or, respectively 100 wt.% of the fine grain of the refractory base material.
The refractory base material is typically employed in a relatively wide grain spectrum. In addition to a coarse grain content ( The grain size limit between coarse grain and medium grain can also be set at 1.5 or 2 mm. The flour grain content can likewise be specified at a grain fraction of According to various embodiments, the abovementioned fine grain content of the fireproof base material is 10-30 wt.%, 15-25 wt.% or 25-30 wt.%, in each case based on the total batch. The medium grain content such as has been mentioned above can be, for example, of the order of 5-30 wt.%, 10-25 wt.% or 10-20 wt.%, in turn based on the total batch. The coarse grain content is calculated accordingly from the above contents of the fine grain or medium grain.
According to a further embodiment, the refractory, in particular oxidic base material in the following grain distribution is proposed:
50-60 wt.% 1-6 mm,
10-25 wt.% 0.25- 25-30 wt.% the sum in each case being 100 wt.%.
According to one embodiment, the granular SiO2 carrier has a grain size of up to 6 mm, it also being possible for the grain upper limit to be chosen at 3.0 or 1.5 mm and the grain lower limit at 0.25, 0.50, 1 or 2 mm. The SiO2 carrier is typically present in a grain fraction of between 0.5 and 3 mm- Compared with grain sizes in the range below 1 mm, the increase in the grain size (> 1 mm) at the same amount leads to a higher effectiveness in the context of the invention. A grain size of 1 to 2 mm is thus more effective than a grain size of 0.5 to 1 mm.
At least one of the following components can be chosen as the non-basic refractory base material: chamotte, sillimanite, andalusite, kyanite, mullite, bauxite, corundum raw materials, such as fused corundum or brown corundum, tabular alumina, calcined alumina, base materials containing zirconium oxide, such as zirconium mullite, zirconium corundum, zirconium silicate or zirconium oxide, titanium oxide (TiC>2) , Mg-Al-spinel, silicon carbide.
Quartzite can also be used as the refractory base material, cristobalite, tridymite, coesite and/or the pretreated SiO2 carrier mentioned then being employed as an additive.
An MgO base material having an MgO content of from 83 to 99.5 wt.% is proposed in particular as a basic refractory base material. In this case, according to various embodiments the lower limit for the MgO content is 85, 88, 93, 94, 95, 96 or 97 wt.% and the upper limit is, for example, 97, 98 or 99 wt.%.
According to one embodiment, the MgO content is 94 to 99 or 96 to 99 wt.%.
The MgO base material can comprise sintered magnesia, fused magnesia or mixtures thereof.
According to one embodiment, a proportion of the MgO content of the batch can be provided by 3 to 20 wt.% (or 3 - 10 wt.%), based on the total mixture, of a spinel of the herzynite type, the galaxite type or mixtures thereof. In this case, the microcracks initiated by the granular SiO2 carrier in the heating up phase are supplemented by further microcracks due to the spinel component during the cooling down phase in the pyroprocess.
The batch can moreover comprise other constituents in relatively small amounts, for example at least one of the following components: (elemental) carbon, graphite, resin, pitch, carbon black, coke, tar.
The batch can accordingly be employed for the production of C-bonded products. This applies in particular to uses of the batches in carbon-bonded products or products which are impregnated with tar.
These include so-called ASC products, the name of which originates from the main components A (for AI2O3 carrier) , S (for SiC and/or Si-metal) and C (for the carbon carrier) . Magnesia carriers (for formation of spinel) and Mg-Al-spinels can also be constituents of the recipe. Such batches are bonded with a synthetic resin, for example a phenolic resin, as a binder. They are employed, for example, for pig iron ladles, but also for shadow pipes, immersion pipes etc.
For such products bonded with synthetic resin, the curing process can be carried out such that, for example, the conversion temperature of (3-cristobalite into a-cristobalite is reached or exceeded, so that on delivery of the prefabricated shaped parts, microcracks are already present in the product. Alternatively, however, it is also possible to carry out the curing (tempering) at a lower temperature (for example 160-220°) and to shift the process of formation of microcracks to the later use. The formation of microcracks then takes place during heating up of the product after its installation.
As already stated, the batch described also serves in particular for production of fired refractory products, in particular fired refractory shaped parts. In this context, a binder, in particular a temporary binder, for example a ligninsulphonate solution, is admixed to the batch - as is conventional - and the mixture is then, for example, pressed to bricks, dried and fired. A typical firing temperature is 1,300-1,700 ° Celsius. A typical firing temperature for a batch comprising 96 wt.% MgO and 4 % of a granular SiO2 carrier is 1,400 °C (+/- 50 °C). The following findings apply when choosing the firing
temperature: Too high a firing temperature or application temperature can lead to a reduced effect of the SiO2 carrier due to too intensive sintering (usually with involvement of fused phases) and can increase the brittleness again. In this respect, the reaction behaviour, in particular the formation of fused phases, between the SiO2 carrier and refractory base material is to be taken into account, without preventing adequate sintering. The precise firing temperature depends in this respect on the components chosen concretely for the batch and is to be determined empirically.
The invention is explained in more detail below with the aid of various embodiment examples. In total, 5 batches (no. 1-5) with non-basic base components, one batch (no. 7) based on MgO and in each case one comparison example according to the prior art (no. 6, 8) are described, the raw material composition and the chemical composition in each case being stated in the form of an oxide analysis.
The batches of Examples 1-3 serve for the production of fired, shaped products based on non-basic base materials. It goes without saying that a temporary binder must be admixed to the batch components. This can be, for example, sulfite waste liquor, phosphoric acid or monoaluminium phosphate. A binder clay can also be included in the recipe. Bricks or other shaped parts can be produced from the batches under conventional pressing conditions (for example 65-130 MPa) and are then fired. The firing temperature is to be chosen such that the sintering is sufficient, but is not so great that too intensive a sintering counteracts the effect of the reduction in brittleness. For this, at a given composition of the
components, in particular the grain size distribution of the fine grain content of the non-basic base material and the binder are decisive-
A firing temperature of 1,450° Celsius was chosen for Example 1. The bricks produced (pressed) from batches 2 and 3 were fired at 1,550 ° Celsius.
Batch no. 4 serves for the production of a so-called ASC product, that is to say a C-bonded product, as has been described above, having an addition of cristobalite. Microcracks are initiated in the structure via the cristobalite conversion during tempering (400 ° Celsius) of the products produced from the batch.
Example 5 shows a batch for a casting composition having a content of aluminous cement. The batch was prepared by mixing with water and shaped parts were produced therefrom and were dried or tempered at temperatures of up to 380° Celsius. In addition, a comparison composition (no. 6) was produced, but without addition of cristobalite, and analogous specimens were produced and likewise dried or tempered at 380 °Celsius. In order to compensate for the missing 4 wt.% cristobalite in batch no. 6, all the other base components of batch no. 5 were increased relatively by in each case 4
Mechanical fracture tests have shown that the initiation of microcracks can reduce the brittleness. Dimension figures for the brittleness of a product can be obtained in various ways. Such a dimension figure is, for example, the characteristic length
In this equation, GF designates this specific fracture energy (N/m), E the modulus of elasticity (Pa) and ft (Pa) the tensile strength. The brittleness of the fireproof building material is lower/ the higher the characteristic length. As a rule, a decrease in brittleness is observed with an increasing quotient Gr/ft of the specific fracture energy GF to the tensile strength ft- For characterization of products according to the invention, the ratio GF/oKz is used. A wedge split test for determination of the specific
strength oKz is described in its fundamental mode of functioning in K. Rieder et el., "Bruchmechanische Kalt-und Heiftpriifung feuerfester grobkeramischer Werkstoffe [Cold and hot testing of mechanical fracture of fireproof ordinary ceramic materials]", Progress Reports of the Deutsche Keramische Gesellschaft, Werkstoffe - Verfahren -Anwendung [Materials - Methods - Use] - volume 10 (1995) , issue 3, ISSN 0177-6983, 62-70. The test method is explained in more detail in the following:
The wedge split test is carried out at room temperature after a heat treatment of the product (for example after drying, tempering or firing of the product).
The table given at the end of the description states the conditions for the wedge split test depending on the starting product. "Non-shaped product" designates a batch, where appropriate after addition of a binder and/or a mixing liquid. The term "shaped product" includes all shapes and shaping processes, where the product must have at least the size of the test specimen described in the following. A distinction is made here between shaped products without and after heat treatment and according to their different types of bonding. An "originally non-shaped product", for example a casting or injection composition, can become compacted during use after establishing a monolithic body (for example a furnace lining) and thus becomes virtually a "shaped product". This 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 mean of the results is used for the evaluation. The shape of the test specimen is shown in Fig. 1. The ashlar-like test specimen has the following dimensions: breadth B: 110 mm, length L: 75 mm, height H: 100 mm. A recess A having the following dimensions can be seen on the upper side: breadth b: 24 mm, length 1: 75 mm, height h: 22 mm. The recess A serves to accommodate bars, rollers and a wedge for transmission of energy. A notch Kl having a breadth b' of 3 mm and a height h1 of 12 mm extends from the base of the recess A downwards in the direction of the base area G. At the end in each case a further notch K2, K3 follow on from the notch Kl, running down to the base area G of the test specimen. K2, K3 each have a breadth b" of 3 mm and a height h" of 6 mm. For the test, two bars LS, the shape and size of which can be seen from Figure 2, are inserted in mirror image fashion on the outside into the recess A. A wedge Kl according to Figure 3 (top) which is supported against the bars LS, as shown in Figure 4, via two rollers R (Figure 3 bottom) is placed centrally between the bars LS. When the shaping process of the production of the product takes place by uniaxial pressing, the specimen is removed such that the direction of the pressing force is parallel to the plane of the ligament area (which is that area in which the fracture is generated during testing). The length of the wedge K and of the bars LS corresponds to the specimen length of 75 mm. The rollers R are somewhat longer. Wedge Kl, bars LS and rollers R are made of steel. During testing, the test specimen rests on a linear support. This is a four-edged steel rod S which has an edge length of 5 mm and the length of which corresponds at least to the test specimen breadth of 7 5 mm and extends over the entire length of the
test specimen. The rod S overlaps the breadth of the notches K2, K3 uniformly on both sides. Fig. 5 shows the course of the test. A load cell KM can be seen in the upper area of the diagram. The vertical force V applied by-loading the wedge K1 by the test machine causes horizontal forces, which lead to a stably progressing formation of cracks during the test. During this, the vertical load Fv and the vertical displacement 5V are determined. These parameters are recorded up to a drop in load to 10 % or less of the maximum load. The fracture energy GF is determined as the area under the load/displacement curve. It is therefore
In this equation (II), A is the ligament area of 66 x 63 mm2 [100-22-12)x (75-6-6), 5max is the maximum displacement during the measurement. The nominal notched tensile strength is calculated according to the following equation:
In this equation (III), B is the ligament length (63 mm) and W the ligament height (66 mm). The parameter y designates the vertical distance of the line of action of the horizontal force introduced by the rollers from the centre of gravity of the ligament area. A value of 62 mm is used for this as an adequate approximation (Fig. 1 and 4). The horizontal maximum load FHmax used in this
relationship (III) can be determined from the vertical maximum load FVmax according to the following relationship:
In this relationship (IV), a denotes the wedge angle, which was chosen as 10 °. Testing is carried out with a regulated advance at a vertical speed of the die of the test machine of 0.5 mm/min.
In the case where these test parameters cannot be adhered to for a particular product - e.g. because no specimen of adequate size can be produced or for other reasons which raise doubts as to the exactness of the absolute values determined - the quotient GF/oKZ is determined for the product according to the invention and a product without an SiO2 carrier produced and tested analogously. In this context, the missing SiO2 content is added proportionally to all the other components of the product. The reduction in brittleness is then determined from the ratio of the quotient GF/OKZ for the product according to the invention to the quotient GF/oKZ for the product without an SiO2 carrier produced analogously. The ratio is > 1, usually > 1.5 or > 1.8. Values of > 2 are aimed for. As the following Examples (7), (8) show, values of almost 3 are achieved.
The comparison values for the specific fracture energy GF, the nominal notched tensile strength oKZ and the quotient of the two are shown in the following table. Products according to the invention are distinguished by a ratio GF/OKZ of > 40. Values of > 50 are aimed for.
The product according to the invention shows a more than doubled quotient of the specific fracture energy and nominal notched tensile strength, from which a significantly reduced brittleness can be deduced.
Here also, the wedge split test mentioned was carried out to demonstrate the reduction in brittleness.
Figure 6 shows the load/displacement graphs of the wedge split test (carried out at room temperature) and demonstrates the significantly less brittle behaviour of the batch (7) according to the invention. In the above
table, this can be seen from the higher quotient of the specific fracture energy GF divided by the nominal notched tensile strength oKz-
The dynamic modulus of elasticity Edyn was furthermore determined from the resonance frequency of the extensional wave [Hennicke, Leers: Die Bestimmung elastischer Konstanten mit dynamischen Methoden [Determination of elastic constants by dynamic methods], Tonindustrie-Zeitung 89 no. 23/24, 539-543 (1976)].
As the above table shows, the addition of the granular SiO2 carrier to the magnesia component causes a significant reduction in the modulus of elasticity, namely from 75.8 GPa to 14.9 GPa.
It can be furthermore seen from the table that the ratio of the nominal notched tensile strength to the dynamic modulus of elasticity is significantly higher in the variant according to the invention. This suggests an increase in the thermal stress parameter R according to Kingery [W. D. Kingery et al.: Introduction to Ceramics, John Wiley & Sons, 1960; ISBN 0-471-47860-1].
Although the invention manages with a simple, inexpensive additive (granular SiO2 carrier) alongside the refractory base component, the batch mentioned proves to be a good basis for the production of fireproof products which have a relatively low brittleness, and therefore have a good resistance to thermal shock, are corrosion-resistant, but also show no reduction in heat resistance compared with other products from the prior art. The choice of the batch
components and production conditions is made such that the product results in a ratio GF/oKz of > 40.
Compared with magnesia products without a granular SiO2 carrier, the product according to the invention has the advantage of a higher mechanical or thermomechanical resistance under thermal shock or pronounced deformations. Compared with magnesia chromite products, the advantage of a chromium-free lining material results, as a result of which the risk of the formation of Cr6+ can be avoided. Compared with spinel products, on the one hand a cost advantage results due to the relatively inexpensively available SiO2 carrier. On the other hand, building materials in the CaO-MgO-SiO2 system at weight ratios of CaO to SiO2 (C/S ratios) of below 0.93, such as are to be expected for products according to the invention, have an invariant point of at least 1,502 °C, which at C/S ratios of below approx. 0.25 (existence of a forsterite mixed crystal as the sole silicatic secondary phase) can be increased further to a maximum of approx. 1,860 °C as the C/S ratio decreases.
In contrast, a magnesia brick comprising spinel (MgAl2CU) and having a C/S ratio above 1.87, such as corresponds to the prior art, has an invariant point of 1,325 °C. The higher invariant point in the product according to the invention can be utilized for improving the heat properties if the amount of fused phase is also more favourable, taking into consideration the product composition and any infiltrates during use. Compared with products with addition of ZrC>2, there is at any rate a more economical advantage on the basis of lower costs of the SiO2 carrier.
In the case of non-basic products, there is the advantage over the use of mullite or zirconium mullite that no component which comprises a glass phase and therefore results in an adverse influencing of the softening properties is introduced. The product according to the invention allows a material composition which comprises exclusively crystalline phases. A further advantage is that if cristobalite is used, an initiation of microcracks and therefore a reduction in brittleness already occurs at a temperature of 270 °C. Non-fired products can therefore also already be produced or employed with a reduced brittleness at a low temperature. These include e.g. casting compositions and prefabricated components. It is also possible, for example, to reduce the brittleness of carbon-bonded non-fired products in this manner.
In this table, the meanings are as follows:
1: A test specimen is shaped from the batch, where appropriate after addition of a binder and/or water (for example: chemical or hydraulic binder), and this is heat-treated at 350 °C.
2: A test specimen is shaped from the batch, where appropriate after addition of a binder and/or water (for
example: chemical or hydraulic binder), and this is heat-treated at 650 °C or alternatively > 1,350 °C.
3: A test specimen is cut out of the product and this is heat-treated at 350 °C if the product has not already been
heat-treated at a temperature of > 350 °C beforehand.
4: A test specimen is cut out of the product and this is heat-treated at 650 °C or alternatively 1,350 °C if the product has not already been heat-treated at a temperature
of > 650 °C or alternatively > 1,350 °C beforehand.
5: A test specimen is cut out of the product formed during use and this is heat-treated at 350 °C if the product has
not already been heat-treated at > 350 °C during use.
6: A test specimen is cut out of the product formed during use and this is heat-treated at 650 °C or alternatively 1,350 °C if the product has not already been heat-treated
at > 650 °C or alternatively 1,350 °C during use. 7: A test specimen is cut out of the product.
8: The SiC>2 carrier comprises cristobalite and/or tridymite to the extent of at least 50 wt.%.
9: The SiO2 carrier comprises cristobalite and/or tridymite to the extent of less than 50 wt.%.
In 4. and 6., the heat treatment is conventionally carried out at 1,350 °C- If the temperature of 1,350 °C is too
high to achieve a reduction in brittleness, the heat
treatment is alternatively carried out at 650 °C, which is above the temperature for the quartz crack.
*: with a reducing atmosphere during the heat treatment
1. Ceramic batch for fireproof uses, comprising
A) 83-99.5 wt.% of at least one refractory base
B) material in a grain fraction of C) 0.5-12 wt.% of at least one separate, granular
D) SiO2 carrier, and
C)any remainder: other constituents.
2. Batch according to claim 1, at least some of the
3. refractory base material of which is a non-basic base
5. Batch according to claim 1, at least some of the
6. refractory base material of which comprises doloma
7. and/or magnesia.
8. Batch according to claim 1, comprising
A) 90-99 wt.% of the refractory base material, and
B) 1-7 wt.% of the granular SiO2 carrier.
5. Batch according to claim, 1, the granular SiO2 carrier
of which comprises at least one of the following SiO2
modifications: cristobalite, tridymite, coesite, a
pretreated product having a bulk density of
6. Batch according to claim 1, the SiO2 carrier of which
has a grain size d50 which is greater than 95 wt.% of
the fine grain content of the refractory base
7. Batch according to claim 1, the SiO2 carrier of which
8. has a grain size dO5 which is greater than 95 wt.% of
9. the fine grain content of the refractory base
11. Batch according to claim 1, the refractory base
12. material of which has a fine grain content with
13. 95 wt.% 14. Batch according to claim 1, the refractory base
15. material of which has a fine grain content with
16. 95 wt.% 17. Batch according to claim 8 or 9, of which the fine
18. grain content of the refractory base material is
19. 10-30 wt.% of the total batch.
20. Batch according to claim 1, the SiO2 carrier of which
21. has a grain size of up to 6 mm.
22. Batch according to claim 1, the SiO2 carrier of which
23. has a grain size of up to 3 mm.
24. Batch according to claim 1, the SiO2 carrier of which
25. has a grain size of between 0.5 and 3 mm.
26. Batch according to claim 1, the refractory base
27. material of which has a grain size of 28. Batch according to claim 1, the refractory base
29. material of which has the following grain
a) 50-60 wt.% 1-6 mm,
b) 10-25 wt.% 0.25- c) 25-30 wt.% d) the sum being 100 wt.%.
16. Batch according to claim 1, comprising a non-basic
17. refractory base material of at least one of the
18. following components: chamotte, sillimanite,
19. andalusite, kyanite, mullite, bauxite, corundum raw
20. materials, such as fused corundum or brown corundum,
21. tabular alumina, calcined alumina, quartzite, base
22. materials containing zirconium oxide, such as
23. zirconium mullite, zirconium corundum, zirconium
24. silicate or zirconium oxide, titanium oxide, Mg-Al-
25. spinel, silicon carbide.
26. Batch according to claim 1, comprising an MgO base
27. material which comprises a spinel of the herzynite
28. type, the galaxite type or mixtures thereof to the
29. extent of 3 to 20 wt. %, based on the total mixture.
30. Batch according to claim 1, which comprises as other
31. constituents at least one of the following components:
32. carbon, graphite, resin, pitch, carbon black, coke,
34. Product based on a batch according to one of
35. claims 1 - 18, having a quotient of the specific
36. fracture energy GF (N/m) and nominal notched tensile
37. strength oKZ (MPa) of > 4 0 μm, in each case determined
38. by means of the wedge split test on a test specimen as
39. described herein.
20. Product based on a batch according to one of
claims 1 - 18, having a quotient of the specific fracture energy GF (N/m) and nominal notched tensile strength oKZ (MPa), in each case determined by means of the wedge split test on a test specimen as described herein, which is at least 1.5 times the quotient, determined in the same way, for an analogous product without a separate, granular SiO2 carrier, the other base constituents of which are adjusted proportionally by the missing SiO2 content to give 100 wt.% in total.
|Indian Patent Application Number||3681/CHENP/2006|
|PG Journal Number||7/2010|
|Date of Filing||05-Oct-2006|
|Name of Patentee||REFRACTORY INTELLECTUAL PROPERTY GMBH & CO. KG|
|Applicant Address||WIENERBERGSTRASSE 11, AT-1100 WIEN, AUSTRIA|
|PCT International Classification Number||C04B 35/01|
|PCT International Application Number||PCT/EP05/02226|
|PCT International Filing date||2005-03-03|