SYNTHESIS PROCESS FOR THE PRODUCTION OF A CALCIUM ZIRCONATE-CONTAINING MATERIAL

Description

[0001] The present invention relates to a synthesis process for producing a refractory oxide ceramic material from CaZrO 3 , in particular in the form of a refractory, preferably mechanically comminuted, in particular broken and / or ground, grain.

[0002] The term "refractory" in the context of the invention should not be limited to the definition according to ISO 836 or DIN 51060, which define a cone drop point of > 1500°C. Refractory products within the meaning of the invention have a compression softening point T 0.5 according to DIN EN ISO 1893: 2009-09 of T 0.5 ≥ 600°C, preferably T 0.5 ≥ 800°C. Accordingly, refractory or refractory granular materials or grains within the meaning of the invention are those materials or grains that are suitable for a refractory product with the above-mentioned compression softening point T 0.5. The refractory products according to the invention are used to protect aggregate structures in aggregates where temperatures between 600 and 2000°C, in particular between 1000 and 1800°C, prevail.

[0003] Coarse clay products are known to be products made from grains with grain sizes up to 6 mm, in special cases even up to 25 mm (see "Gerald Routschka / Hartmut Wuthnow, Practical Handbook "Refractory Materials", 5th edition, Vulkan-Verlag, (hereinafter referred to simply as "Practical Handbook"), Chapter 2).

[0004] The term "granulation" or "granular material" within the meaning of the invention encompasses a pourable solid consisting of many small, solid grains. If the grains have a grain size of ≤ 200 µm, the grain is a flour or powder. If the grains are produced by mechanical comminution, e.g., crushing and / or grinding, they are crushed granules or broken grains. However, a grain can also comprise granules or pellets, which are produced by granulation or pelletizing without mechanical comminution. The grain size distribution of the grain is usually adjusted by sieving.

[0005] In the case of heavy clay products, a distinction is also made between shaped and unshaped products.

[0006] Shaped heavy clay products are unfired, tempered, or ceramic-fired products, particularly bricks or slabs, preferably manufactured in a ceramic factory. They have a defined geometry and are ready for installation. Shaping is achieved, for example, by pressing, stamping, ramming, or slip casting. The shaped products, particularly bricks, are then laid with mortar or mortar-free ("crunching"), for example, to form a lining. The production process for shaped heavy clay products is typically divided into the following steps (Practical Handbook, page 15 / Section 2.1): Preparation Mixing Shaping Drying Thermal treatment up to 800 °C, firing or sintering Post-treatment (if necessary)

[0007] Unformed products are products that are formed into their final shape, usually by the user, from an unformed mass or lumps, e.g., by pouring, vibrating, poking, tamping, or spraying. Unformed products are usually placed behind formwork in larger sections at the site of use and, after hardening, form part of the lining. Examples of unformed products include shotcrete, tamping, casting, vibrating, or potting compounds.

[0008] Both the shaped and unshaped products are manufactured in a conventional manner from a coarse ceramic batch.

[0009] Calcium zirconate is the stable stoichiometric compound in the CaO-ZrO2 phase diagram. It has a high melting point of 2368 °C and is resistant to alkali corrosion. Because it is rarely found as a mineral in nature, calcium zirconate must be synthesized for technical applications. The goal of this pre-synthesis is to produce a phase-pure material, or a material made of 100% calcium zirconate. This ensures good properties of the refractory products made from the pre-synthesized material.

[0010] DE 10 2012 003 483 discloses a thermal shock- and corrosion-resistant ceramic product based on calcium zirconate, the structure of which consists of presynthesized crushed granules containing calcium zirconate. The crushed granules have a ZrO 2 / CaO ratio between 1.6:1 and 1:1.5 and a grain size of 100 µm to 6 mm. Furthermore, the crushed granules constitute a proportion of > 50 wt.%. Furthermore, the product comprises a binding matrix surrounding the crushed granules, sintered at > 1300 °C, consisting of fine-grained calcium zirconate and / or zirconium dioxide with grain sizes between 50 nm and 150 µm.

[0011] The calcium zirconate-containing crushed granulate can be a sintered and crushed crushed granulate based on synthesized CaZrO 3 from CaCO 3 and ZrO 2, wherein the sintered crushed granulate has been sintered at temperatures above 1300 °C.

[0012] Furthermore, the binding matrix can be made from a mixture of calcium carbonate with a grain size of 50 nm to 150 µm and unstabilized zirconium dioxide with a grain size between 50 nm and 150 µm.

[0013] The crushed granulate is preferably produced using slip casting technology. However, it can also be produced using plastic forming or pressing technology.

[0014] DE 10 2012 003 478 A1 deals with the use of an oxide-ceramic material containing at least 75 wt.% CaZrO 3 and a maximum of 25 wt.% ZrO 2 as a lining material for coal gasification plants. The material is produced, for example, using slip casting technology. According to DE 10 2012 003 478 A1, ZrO 2 is mixed with CaCO 3 and other additives and processed into a slip with the addition of water. The molar ZrO 2 / CaCO 3 ratio is between 1.6:1 and 1:1.5. The slip is poured into a plaster mold, which removes the water from the slip to produce molded bodies. The molded bodies are dried and then sintered at temperatures between 800 and 1700 °C, preferably at 1300 to 1500 °C, under oxidizing or reducing conditions.

[0015] According to another process described in DE 10 2012 003 478 A1, the slip-cast CaZrO3 specimens are broken down into different grain sizes, and the grains are processed into a castable or vibratable mass using additional additives. This mass, which consists of coarse and fine-grained CaZrO3 and small amounts of ZrO2, is then dried and sintered. According to DE 10 2012 003 478 A1, large-format components with an open porosity of up to 20% can be produced in this way.

[0016] DE 10 2012 003 478 A1 also contains an embodiment in which the material obtained after sintering at 1400 °C has 64% CaZrO 3 and 36% Ca 0.15 Zr 0.85 O 1.85.

[0017] The article "Chemical Synthesis of Pure and Gd-doped CaZrO 3 Powders," by I. Erkin Gonenli and A. Cuneyt Tas, describes the synthesis of pure-phase CaZrO 3 powder. It is prepared from aqueous solutions of calcium chloride (CaCl 2 2H 2 O) and zirconium oxide chloride (ZrOCl 2 8H 2 O) in appropriate volumetric proportions. The formation of calcium zirconate was achieved by two different chemical synthesis routes: self-propagating combustion synthesis and precipitation in the presence of EDTA by acid-base titration.

[0018] JP 2 005 200 297 discloses a process for producing a calcium zirconate powder, ideally without requiring comminution after sintering. For this purpose, a calcium carbonate powder and a zirconium oxide powder are mixed with water to form a slurry. The slurry is spray-dried, and the spray-dried product is treated at a temperature of 600 to 900 °C. The solids content of the slurry is 5 to 50 mass%, e.g., 30 mass%.

[0019] CN 10 2001 705 discloses the production of calcium zirconate from a slurry with a high water content. 1.3 to 2.5 times as much water as solid is added. Even after drying, the water content of the slurry is still at least 40 mass%. According to CN 10 2001 705, the high water content is necessary to prevent the disadvantages of dry mixing. According to CN 10 2001 705, dry mixing results in uneven distribution, thus incomplete reaction, uneven particle size, and high energy consumption.

[0020] JP H09 142929 discloses the production of calcium zirconate from a pressed molded body consisting of calcium hydroxide powder and zirconium oxide powder. According to JP H09 142929, calcium hydroxide is used as the CaO source instead of quicklime. While the two powders can be pressed into molded bodies before firing, these molded bodies are preferably crushed before firing. JP H09 142929 does not disclose the addition of water to the mixture before pressing.

[0021] The object of the present invention is to provide a simple and cost-effective, economical and ecologically safe process for the synthesis of a, preferably phase-pure, calcium zirconate material, preferably in the form of a calcium zirconate-containing grain.

[0022] This object is achieved by synthesis processes having the features of claim 1.

[0023] The invention is explained in more detail below using a drawing as an example. The drawings show: Figure 1: An X-ray phase diagram of a grain made of phase-pure calcium zirconate material produced according to the invention in accordance with embodiment 1. Figure 2: An X-ray phase diagram of a shaped body produced according to embodiment 2.

[0024] Within the scope of the invention, it was surprisingly found that it is possible to produce a preferably phase-pure, calcium zirconate-containing material by means of press forming and sintering from a mixture which consists exclusively of at least one Ca-containing flour-like raw material component, at least one ZrO 2 -containing flour-like raw material component and water and has a water content of > 5 to 10 wt.%, preferably 7 to 8 wt.% water based on the dry mass of the mixture.

[0025] The synthesis process according to the invention thus comprises the following process steps: a) Producing the mixture from the at least one Ca-containing flour-like raw material component, the at least one ZrO 2 -containing flour-like raw material component and the water with a water content of > 5 to 10 wt.%, preferably 7 to 8 wt.% water based on the dry mass of the mixture, b) Pressing the mixture to a green shaped body, c) Preferably drying the green shaped body, d) Sintering the shaped body, e) Optionally mechanical comminution, preferably breaking and / or grinding, of the sintered material to a grain.

[0026] According to the invention, the mixture thus contains a higher water content than is usual in conventional compression molding. Furthermore, according to the invention, the mixture contains no other components, in particular no binders and / or compression aids.

[0027] Within the scope of the invention, it was surprisingly discovered that the binders and / or pressing aids, even when present in very small quantities, nevertheless interfere with the synthesis of calcium zirconate. For example, it has been found that organic, temporary binders and / or pressing aids change the previously set CaO / ZrO 2 molar ratio during firing. It is suspected that the organic binders and / or pressing aids release CO and / or CO 2 during firing, which reduces the Ca contained in the raw materials. The reduced Ca, in turn, enters a gas phase and evaporates, so that the CaO / ZrO 2 molar ratio changes. These reactions take place above a temperature of approximately 550 °C.Thus, the synthesis is disturbed by the organic binders and / or pressing aids, even if they are present only in very small quantities, to such an extent that the production of a phase-pure material is not possible.

[0028] The high water content according to the invention ensures sufficient cohesion of the green molded body even without a binder. Furthermore, it has surprisingly been found that the high water content in the mixture also contributes to the production of a phase-pure material. Due to the high water content, a steam atmosphere prevails during the sintering process, which supports the sintering process. The steam atmosphere reduces the surface tension of the individual grains of the raw materials, which improves sinterability. Furthermore, the steam atmosphere surprisingly counteracts the evaporation of CaO.

[0029] To produce a phase-pure material, the CaO / ZrO 2 molar ratio in the mixture should also be essentially equimolar. This means that the CaO / ZrO 2 molar ratio in the mixture is preferably 1:1. However, according to the invention, the molar ratio is at least 1.5:1 to 1:1.6. When determining the molar ratio, an idealized pure raw material is assumed. Starting from the desired ratio, the weight ratio is calculated using the molar masses. Of course, this takes into account that the CaO carriers also contain other components, for example, CO 2 in CaCO 3.

[0030] The Ca raw material component used is preferably a raw material component containing CaCO 3 and / or CaO and / or Ca(OH) 2 and / or CaC 2 . A CaCO 3 raw material component is preferably used.

[0031] The CaCO 3 raw material component is preferably natural, ground limestone flour (GCC = ground calcium carbonate ) or synthetic, precipitated calcium carbonate (PCC = precipitated calcium carbonate ) or chalk. PCC is particularly preferred, particularly due to its high purity. PCC is preferably produced by reacting carbon dioxide with milk of lime or a hydrated lime suspension. The hydrated lime suspension is produced either by slaking quicklime or by dispersing calcium hydroxide in water.

[0032] The CaO raw material component is preferably quicklime.

[0033] Hydrated lime is preferably used as the Ca(OH) 2 raw material component.

[0034] Synthetically produced zirconium dioxide is preferably used as the ZrO2 raw material component. The zirconium dioxide is preferably unstabilized (monoclinic), but it can also be stabilized.

[0035] The raw material components preferably each have a purity of at least 96 wt.%, preferably at least 99 wt.%. This means that the minimum content of the respective compound (CaCO 3 , CaO, Ca(OH) 2 , CaC 2 or ZrO 2 ) is preferably at least 96 wt.%, preferably at least 99 wt.%, determined in each case by X-ray fluorescence analysis (XRF) according to DIN 51001:2003.

[0036] Furthermore, the Ca raw material component has a grain size of ≤ 200 µm, preferably ≤ 50 µm, particularly preferably between 200 nm and 10 µm according to DIN EN 725-5:2007. The average grain diameter of the Ca raw material component is preferably 500 nm to 5 µm, preferably 0.8 to 1 µm.

[0037] The ZrO 2 raw material component preferably has a grain size of ≤ 200 µm, preferably ≤ 150 µm, particularly preferably between 200 nm and 10 µm according to DIN EN 725-5:2007. And the average grain diameter (d 50 ) of the ZrO 2 raw material component is preferably 500 nm to 5 µm, preferably 0.7 to 1 µm.

[0038] The grain sizes and mean grain diameter are determined using laser granulometry according to DIN EN 725-5:2007. The flour is dispersed using ultrasound, preferably in ethanol.

[0039] As already explained, the mixture consisting exclusively of the raw material components and water is formed into green molded bodies by pressing according to the invention. Pressing is preferably carried out at a pressure of 30 to 150 N / mm², preferably 50 to 80 N / mm². Furthermore, pressing is preferably carried out by uniaxial pressing. However, it can also be carried out by isostatic pressing, vibration pressing, briquetting, or pelletizing.

[0040] Mixing preferably takes place in an intensive mixer using a countercurrent process (whirlpool and plate rotate in opposite directions).

[0041] Preferably, cuboid-shaped green molded bodies are also produced, especially in conventional stone formats. The green pressed molded bodies preferably have the following dimensions: preferably Height 20 to 100 mm 25 to 75 mm length 20 to 300 mm 150 to 250 mm Width 20 to 150 mm 25 to 100 mm

[0042] The green molded bodies also preferably have a bulk density determined according to DIN EN 993-17:1999 of 2.0 to 3.0 g / cm 3< , preferably 2.1 to 2.5 g / cm 3< , and / or a porosity according to DIN 66133:1993-06 of 30 to 60 vol%, preferably 40 to 50 vol%.

[0043] In order for the green molded bodies to be handleable, they preferably have a cold bending strength according to DIN EN 993-6:1995-04 of at least 1 MPa.

[0044] After pressing, the green molded bodies are dried, as already explained. Drying is preferably carried out to a residual moisture content of between 0 and 2 wt.%, in particular between 0 and 0.5 wt.%, determined according to DIN 51078:2002-12. The green molded bodies are preferably dried between 25 and 110 °C, in particular between 100 and 105 °C, for a period of 4 to 24 hours, preferably 12 to 24 hours.

[0045] After drying, sintering takes place according to the invention. Sintering preferably takes place with a holding phase at a final temperature of 1200 to 1800 °C, preferably 1400 to 1650 °C, for a duration of 2 to 10 hours, preferably 4 to 6 hours. Heating is preferably carried out at a heating rate of 1 to 10 K / min, preferably 2 to 5 K / min. In addition, during heating, an intermediate holding phase is preferably carried out at a temperature of 400 to 1000 °C, preferably 550 to 900 °C, for a duration of 1 to 3 hours, preferably 1.5 to 2.5 hours. Cooling preferably takes place freely in the furnace.

[0046] Furthermore, sintering preferably takes place under neutral or oxidizing conditions.

[0047] Sintering is preferably carried out in an electrically heated or gas-fired furnace. Gas-fired furnaces have an adjustable oxygen content in the combustion air (excess or deficiency of oxygen), can achieve higher heating rates, and usually have a (different) gas flow field in the combustion chamber compared to electrically heated furnaces.

[0048] In addition, sintering takes place in a discontinuous or continuous process, preferably in a continuous process on an industrial scale.

[0049] As already explained, the process according to the invention makes it possible, in particular, to produce a very pure, in particular a pure-phase calcium zirconate material. The pure-phase calcium zirconate material produced according to the invention thus contains, in particular, no free raw materials and no mixed phases. Thus, complete conversion of the raw material components used to form calcium zirconate has taken place. At least the calcium zirconate material produced according to the invention has a CaZrO 3 content of at least 98 wt.%, preferably at least 99 wt.%, based on the dry mass of the calcium zirconate material.

[0050] An exemplary X-ray phase diagram of a phase-pure calcium zirconate material produced according to the invention in accordance with the exemplary embodiment is shown in Figure 1 shown.

[0051] Phase-pure in the context of the invention means that when analyzing the phase composition by X-ray diffraction, no other phases other than calcium zirconate are detected or detectable. This is Figure 1 clearly visible. Only peaks that can be attributed to calcium zirconate are present.

[0052] Phase analysis is performed according to DIN 13925-2:2003. For this purpose, the dried, ground substance (< 45 µm) is prepared in a sample holder. The testing instrument is preferably a PHILIPS PW1820. Evaluation is preferably performed using the X'Pert Pro MPD analysis software (PANalytical BV, Almelo, Netherlands). The background is determined according to Sonneveld & Visser. The program automatically identifies the reflections based on the selection of appropriate PDF maps (up to this point, this is a semi-quantitative analysis). Subsequently, the program also automatically converts the samples into phases, refines the scattering in semi-automatic mode, and then performs a Rietveld analysis.

[0053] Furthermore, the sintered shaped bodies made of the calcium zirconate material according to the invention preferably have an open porosity of 5 to 50 vol.%, preferably 8 to 40 vol.%, determined according to DIN EN 993-1:1995-04.

[0054] In addition, the sintered shaped bodies, in particular the sintered stones, preferably have a bulk density of 2.50 to 4.50 g / cm 3< , in particular of 2.60 to 4.30 g / cm 3< , determined according to DIN 993-1:1995-04.

[0055] As already explained, the sintered molded bodies are preferably mechanically comminuted, preferably crushed and / or ground, for further processing after sintering, and then classified into particle sizes by sieving. Sieving is carried out in a sieve tower using dry sieving according to DIN EN 933-1:2012. The Retsch AS 200 control sieving machine is preferably used, operating at an amplitude of 0.5 mm for 2 minutes.

[0056] The term "grain fraction" or "grain class" means that no grains remain on the upper sieve and none pass through the lower one. Thus, there are no oversize or undersize particles. Grain classes therefore have grain sizes between the two specified test grain sizes.

[0057] The presynthesized grain according to the invention has very good thermomechanical resistance.

[0058] In addition, the grain produced according to the invention preferably has a grain porosity (open porosity) according to DIN 66133:1993 of 5 to 50 vol.%, preferably 10 to 40 vol.%, and / or preferably an average pore diameter (d 50 ) according to DIN 66133:1993 of 0.5 to 2 µm, preferably 0.8 to 1.2 µm.

[0059] Furthermore, the grain produced according to the invention preferably has a true density, determined by helium pycnometry according to DIN 66137-2:2004, of 4.40 to 4.70 g / cm 3<, preferably of 4.65 to 4.70 g / cm 3<.

[0060] The grain according to the invention can then be used in a manner known per se in coarse ceramic batches for the production of shaped or unshaped, coarse ceramic refractory products.

[0061] If the sintered shaped bodies are pellets or granules or the like, they can be used directly as refractory grains without mechanical comminution.

[0062] Typically, a coarse ceramic batch comprises a dry material mixture consisting of at least one refractory grain and, as additives, preferably binder and / or water and / or liquid additives or admixtures. This means that the amount of binder (dry or liquid) and / or water and / or liquid additive is added additively and refers to the total dry mass of the dry material mixture (not to the total mass of the batch).

[0063] In the case of unshaped products, the liquid and / or solid or dry powdered binder and / or the liquid additive are preferably packed in a container separate from the other dry components of the batch.

[0064] The binder is a binder suitable for refractory products, preferably a temporary binder. These binders are listed, for example, in the practical handbook, page 28, section 3.2.

[0065] The additive is preferably a pressing aid.

[0066] The dry matter mixture comprises at least one coarse, pre-synthesized, calcium zirconate-containing grain with a grain size > 200 µm, preferably in an amount of 10 to 90 wt.%, preferably 80 to 90 wt.% based on the total dry matter of the dry matter mixture and / or at least one pre-synthesized, calcium zirconate-containing flour grain with a grain size ≤ 200 µm, preferably in an amount of 0 to 30 wt.%, preferably 10 to 20 wt.% based on the total dry matter of the dry matter mixture.

[0067] The grain sizes are determined by dry sieving according to DIN EN 933-1:2012.

[0068] Furthermore, instead of the calcium zirconate powder, or in addition to it, the dry material mixture may also contain at least one powdered Ca raw material component and at least one powdered ZrO2 raw material component, from which further calcium zirconate is formed in situ during firing of the product. The Ca raw material component and the ZrO2 raw material component are therefore the raw material components listed above. To form a pure-phase calcium zirconate, the raw material components are preferably present in the dry material mixture in an equimolar ratio.

[0069] Preferably, the dry material mixture comprises exclusively presynthesized calcium zirconate-containing grains according to the invention and optionally the at least one Ca raw material component and the at least one ZrO 2 raw material component, particularly preferably it consists thereof.

[0070] However, the dry material mixture may also comprise at least one further coarse grain with a grain size > 200 µm and / or at least one further fine grain with a grain size ≤ 200 µm made of other common refractory materials.

[0071] Furthermore, the dry material mixture can contain at least one dry additive for refractory materials, preferably in a total amount of < 5 wt.%, and / or at least one dry additive for refractory materials, preferably in a total amount of < 5 wt.%. The dry additive is an additive suitable for refractory products. These additives are listed, for example, in the practical handbook, page 28 / section 3.3. They are used to improve processability or formability or to modify the structure of the products and thus achieve special properties.

[0072] The coarse grain portion (=all coarse grains contained in the batch) of the dry material mixture preferably has a grain size of up to a maximum of 8 mm, preferably up to a maximum of 6 mm, particularly preferably up to a maximum of 4 mm.

[0073] The grain distribution of the coarse grain portion of the dry matter mixture is preferably continuous.

[0074] The grain distribution of the flour grain portion (=all flour grains contained in the batch) of the dry matter mixture is preferably also continuous.

[0075] And the grain distribution of the entire dry matter mixture is preferably continuous.

[0076] The coarse grain portion serves as a supporting grain in the usual way. During firing, the fine grain portion forms the binding matrix in which the coarse grain portion is embedded.

[0077] As already explained, the backfill is used to produce unshaped or shaped, coarse ceramic products.

[0078] For the production of pressed products, especially bricks, a mixture or plastic mass is created from the dry matter mixture of the backfill with at least one liquid and / or solid binder and / or water and / or a pressing aid. If the backfill contains a liquid binder and / or pressing aid, the addition of water is not necessary, but possible. However, water alone can also be added.

[0079] For optimal distribution of the binder(s) and / or water and / or pressing aid, mix for 3 to 10 minutes.

[0080] The mixture is poured into molds and pressed to form molded bodies. The pressing pressures are within the usual range, e.g., 50 to 150 MPa, preferably 100 to 150 MPa.

[0081] Preferably, drying is carried out after pressing, e.g., between 40 and 110 °C, in particular between 100 and 105 °C. Drying is preferably carried out to a residual moisture content of between 0 and 2 wt.%, in particular between 0 and 1 wt.%, determined according to DIN 51078:2002-12.

[0082] The dried, pressed stones can be used unfired or fired.

[0083] For firing, the preferably dried, pressed bricks are ceramically fired in a ceramic kiln, e.g., a tunnel kiln, preferably between 1200 and 1800 °C, especially between 1400 and 1700 °C. Oxidative firing is preferred, but depending on the material composition, a reducing firing may also be advantageous.

[0084] However, the molded products can also be formed by other conventional methods, preferably by slip casting or strand or extrusion processes of a plastic mixture, or by manual or mechanical ramming or ramming. Slip casting allows the mixture to flow accordingly.

[0085] Preferably, the fired, shaped products, in particular the bricks, have a bulk density of 4.00 to 4.70 g / cm 3< , in particular of 4.40 to 4.60 g / cm 3< , determined according to DIN 993-1:1995-04.

[0086] The cold bending strength according to DIN EN 993-6:1995-04 of the fired, shaped products, in particular the bricks, is preferably between 10 and 40 MPa.

[0087] In addition, the fired, shaped products, in particular the bricks, preferably have an E-modulus according to DIN EN ISO 12680-1:2007-05 of 80 to 200 GPa, preferably 90 to 120 GPa.

[0088] For the production of unmolded products, especially compounds, preferably injection molding compounds, vibratory compounds, casting compounds, or slurry compounds, a mixture of the dry material mixture with at least one dry and / or liquid binder and / or water and / or at least one liquid additive is also prepared, and the mixture is introduced, for example, behind a formwork. If the batch contains a liquid binder and / or additive, the addition of water is not necessary, but possible. However, water alone can also be added.

[0089] As already explained, the synthesis process according to the invention makes it possible to produce a preferably phase-pure calcium zirconate-containing material in a simple, economical, and ecologically safe manner. The manufacturing process (mixing, pressing, firing, preferably crushing) is very complex. Furthermore, the grain properties can be easily controlled via the sintering temperature. A higher sintering temperature leads to lower porosity. Grains with lower porosity are particularly suitable for casting materials. Grains for casting materials are preferably sintered at temperatures > 1550 °C. The higher the bulk density of the presynthesized grain, the lower the shrinkage during firing of the resulting material.

[0090] The unshaped and shaped products are used, for example, for the refractory lining, preferably for the working lining or the safety lining, of a coal gasification plant.

[0091] They can also be used as heat protection tiles in gas turbines, as inlays in slide plates, crucibles for titanium castings / titanium alloys (VIM), crucibles for other non-ferrous metals (e.g. nickel-based alloys).

[0092] The following examples further illustrate the superiority of the process according to the invention and the heavy clay products: Example 1 (production of CaZrO 3 grains from CaCO 3 and unstabilized ZrO 2 ): Table 1 shows an example of a composition for the production of a molding compound. Calcium carbonate (PreCarb 400) from Schäfer Kalk GmbH & Co. KG, Diez, and monoclinic zirconium dioxide (ZirPro CS02) from Saint-Gobain, Le Pontet Cedex, France, were used. Table 1: Composition for the production of a molding compound material Percentage in wt.% based on dry mass ZrO2 55,2 CaCO3 44,8 Water 8,0

[0093] First, the dry raw materials were weighed and placed in an intensive mixer. After a 10-minute mixing process, the water was added. The mixer was operated in a countercurrent mode (whirlpool and plate rotate in opposite directions). The wet mass was mixed for a further 10 minutes. The resulting mass was then poured into the press cavity of the hydraulic press. Shaped bodies were pressed from it at a pressure of up to 50 MPa. After demolding, they were dried at 100 °C for 24 hours. The samples were then sintered at 1400 °C for 5 hours, with a holding time during the ramp-up phase of 2 hours at 900 °C. The heating rate was 3 K min -1 . Cooling in the furnace was carried out freely. The resulting material was then coarsely pre-crushed and subsequently crushed into various grain sizes in a jaw crusher and subsequently classified. An XRD analysis showed exclusively peaks attributable to CaZrO 3 (see Figure 1 ). The material thus contained 100% CaZrO 3 .

[0094] Example 2 (production of a thermal shock and corrosion-resistant molded body based on the phase-pure calcium zirconate from Example 1 with different grain fineness): Table 2 below shows a composition for the production of a coarse-grained refractory molded body from CaZrO 3 synthesized for this purpose. Table 2: Composition for the production of a coarse-grained refractory molded body from CaZrO 3 synthesized for this purpose material specification Percentage in wt.% CaZrO3 <0.16 mm 33,4 0.16 - 0.63 mm 34,1 0.63 - 1.0 mm 9,8 1.0 - 2.0 mm 15,4 2.0 - 3.15 mm 7,3 Binder: polyvinyl alcohol Optapix PAF 60, ZSCHIMMER & SCHWARZ GmbH & Co KG - CHEMICAL FACTORIES, Lahnstein 3,5

[0095] To produce the molding compound, the dry raw materials were first weighed and poured into the mixing container from fine to coarse. A ToniMix building material mixer from Toni Technik Baustoffprüfsysteme GmbH was used for mixing. The dry raw materials were mixed for 5 minutes. The binder was then added and everything was mixed for another 5 minutes. The material was then compression-molded in a hydraulic uniaxial press. Test specimens were produced at 150 MPa. After brief drying at 100 °C for 4 hours, they were sintered at 1650 °C for 6 hours with a holding time during the ramp-up phase at 900 °C for 2 hours. The heating rate was 2 K min -1< . Table 3 shows selected properties of the material produced in this way. Table 3: Properties of the manufactured material Unit Value Bulk density, according to DIN 993-1:1995 g / cm -3< 4,30 True density g / cm -3< 4,66 open porosity, according to DIN 993-1:1995 Vol.-% 7,28 Total porosity, according to DIN 993-1:1995 Vol.-% 8,52 Cold bending strength, based on DIN 993-6:1995 (with a support distance of 100 mm) MPa 35,54 Cold bending strength after 5 thermal shock cycles, according to DIN 993-11:2008 and based on DIN 993-6:1995 (with a support distance of 100 mm) MPa 4,89 Loss of strength after 5 thermal shock cycles % 86 Young's modulus after 0 1 GPa 95,70 3 84,18 5 thermal shock cycles, according to DIN EN ISO 12680-1:2007 40,47 31,39 Elastic modulus loss after 5 thermal shock cycles % 67

Claims

1. A synthesis method for the synthesis of a refractory oxide-ceramic, calcium zirconate-containing material, in particular in the form of a refractory calcium zirconate-containing granular material that is preferably mechanically comminuted, in particular crushed and / or ground, having the following method steps: a) producing a mixture exclusively of at least one mealy Ca raw material component, at least one mealy ZrO2 raw material component, and water, with a water content of > 5 to 10 wt.-% relative to the dry mass of the mixture and with a molar ratio CaO / ZrO2 in the mixture of 1.5:1 to 1:1.6, preferably 1:1, b) pressing the mixture exclusively consisting of the raw material components and water to form at least one green shaped body, c) preferably drying the green shaped body, d) sintering the shaped body, e) if applicable, mechanical comminution, preferably crushing and / or grinding, of the sintered shaped body to form the granular material.

2. The synthesis method according to Claim 1, characterized in that a calcium zirconate-containing material having a content of at least 98 wt%, preferably at least 99 wt%, CaZrO3, relative to the dry mass of the material and / or a phase-pure calcium zirconate-containing material is produced.

3. The synthesis method according to one of the preceding claims, characterized in that a raw material component containing CaCO3 and / or a raw material component containing CaO and / or a raw material component containing Ca(OH)2 and / or a raw material component containing CaC2 is used as Ca raw material component, wherein preferably natural, ground limestone meal and / or synthetic, precipitated calcium carbonate and / or chalk is used as CaCO3 raw material component and / or quicklime is used as CaO raw material component and / or hydrated lime is used as Ca(OH)2 raw material component.

4. The synthesis method according to one of the preceding claims, characterized in that synthetically produced, preferably monoclinic, zirconium dioxide is used as ZrO2 raw material component.

5. The synthesis method according to one of the preceding claims, characterized in that the raw material components each have a purity of at least 96 wt%, preferably of at least 99 wt%.

6. The synthesis method according to one of the preceding claims, characterized in that a) the at least one Ca raw material component has a grain size of ≤ 200 µm, preferably ≤ 50 µm, particularly preferably between 200 nm and 10 µm, according to DIN EN 725-5:2007 and / or the average grain diameter of the Ca raw material component is 500 nm to 5 µm, preferably 0.8 to 1 µm, and / or b) the at least one ZrO2 raw material component has a grain size of ≤ 200 µm, preferably ≤ 150 µm, particularly preferably between 200 nm and 10 µm, according to DIN EN 725-5:2007 and / or the average grain diameter of the ZrO2 raw material component is 500 nm to 5 µm, preferably 0.7 to 1 µm.

7. The synthesis method according to one of the preceding claims, characterized in that the pressing takes place with a molding pressure of 30 to 150 N / mm2, preferably 50 to 80 N / mm2 and / or the pressing takes place by uniaxial or isostatic pressing.

8. The synthesis method according to one of the preceding claims, characterized in that a cuboidal green shaped body is produced.

9. The synthesis method according to one of the preceding claims, characterized in that a green shaped body having a) a bulk density, determined according to DIN EN 993-17:1999, of 2.0 to 3.0 g / cm3, preferably 2.1 to 2.5 g / cm3, and / or b) a porosity according to DIN 66133:1993-06 of 30 to 60 vol%, preferably 40 to 50 vol% and / or c) a cold bending strength, according to DIN EN 993-6:1995-04, of at least 1 MPa, is produced.

10. The synthesis method according to one of the preceding claims, characterized in that a) the green shaped body is dried to a residual moisture between 0 and 2 wt%, in particular between 0 and 0.5 wt%, determined according to DIN 51078:2002-12, and / or b) the green shaped body is sintered with a holding phase at a final temperature of 1200 to 1800° C, preferably 1400 to 1650° C, for a duration of 2 to 10 h, preferably 4 to 6 h, and / or c) during the heating, an intermediate holding phase is carried out at a temperature of 400 to 1000° C, preferably 550 to 900° C, for a duration of 1 to 3 h, preferably 1.5 to 2.5 h.

11. The synthesis method according to one of the preceding claims, characterized in that a) during the sintering, heating takes place at a heating rate of 1 to 10 K / min, preferably 2 to 5 K / min, and / or b) the sintering takes place in an electrically fired kiln or a gas-fired kiln.