DE3805852A1 - Process for producing water-tight ceramic materials from clays without use of moulds - Google Patents

Abstract

The invention relates to a process for producing water-tight ceramic materials from clays, in which green bodies (blanks) having hollow spaces and produced without moulds are fired under exothermic processes and until expansion (bloating) by liberated gases occurs. To ensure a constant shape of the material, it is proposed according to the invention that stabilising materials be mixed into the ceramic formulation. These additives can be very widely differing materials, for example dry sulphite waste liquor and/or potato starch, ceramic fibres, pre-expanded or coarsely granular expanded clays, general granular or milled raw materials, such as quartz or amorphous SiO2 dust, slurried, alkali-free kaolins, etc.

Description

The invention relates to a method for producing water dense ceramic materials made of glauconite, illite or ben tonite-containing clays as well as blue shades, in which without forms joined blanks under exothermic processes and up to bloating be burned by released gases.

It is known to contain glauconite, illite or bentonite Tones as well as blues the approx. 8% iron oxide, 0.7% organic Components and 3 to 4% contain alkalis, in the ceramic Soften the fire at 1150 to 1230 ° C, forming it Inflate closed pores and increase in volume and after the Cool solid waterproof body with good thermal insulation ability  form. The fire can be reducing, as in DE-OS 34 17 851 executed or performed oxidizing according to DE-PS 8 14 865 will. In the first case, the iron oxide in the clays reacts the carbon of the organic substance according to the formula

Fe₃O₄ + C = 3 FeO + CO at 1150 ° C (1)

to form gaseous carbon oxide, which causes the bloat. In the second case, all organic constituents are burned out during heating and the iron oxides are oxidized to Fe ₂ O ₃ . If the heating process continues, the Fe ₂ O ₃ goes according to the formula

6 Fe₂O₃ → 4 Fe₃O₄ + O₂ (2)

in magnetite. The resulting oxygen gas causes the bloat. The swelling process also begins at around 1150 ° C, but only intensifies above 1200 ° C. In order to achieve bulk densities of 0.5 to 0.8 g / cm ³ , the temperature must be kept at 1220 ° C for a long time.

The process according to Eq. (1) can also be carried out in such a way that the blanks contain as much voids as required are due to the increase in volume that occurs during inflation just fill in. If this succeeds, after the Ab therefore cool a material that does not contain open pores is waterproof, its volume when heated to 1200 ° 1300 ° C changes little and keeps its shape unchanged.

Since the clay becomes soft when bloated, the viscous melt penetrates ze under the influence of the inflation pressure in all cavities and acts as a binder after cooling. About Surprisingly, it has been shown that the material is especially important stays in shape when you stabilize the stone offset de admixed substances. So dry sulfite waste liquor and / or Potato starch to be mixed in before heating through Water absorption becomes plastic, the remaining voids are filled and shrink when drying. This makes them counteractive  here and stabilize the shape.

To increase the strength, it is proposed to offset admix ceramic fibers, the quality of which from the pre see application temperature of the material. For Materials used at room temperature also suffice for fibers the application limit temperature AGT = 1260 ° C.

Furthermore, the offset can be additional substances according to the invention be mixed in according to the characteristics of the work Improve fabrics for intended uses. At for example, pre-expanded and coarse-grained expanded clay, which are to be referred to as "inflatable chamotte", then moved be mixed if the material has good thermal insulation should. The inflatable chamottes are appropriately manufactured in Muffle furnaces, the walls of which are covered with a fabric with low surface tension, e.g. Nextel Ultrafil ter are provided to eject after cooling facilitate.

To determine the expansion behavior, knowledge of the expansion value K _B = V _B / V _R ( V _B = volume of the expansion product, V _{R of} the raw material) is required. It is determined on pellets, which are used moist in an oven heated to 1150 ° C under an acid-free atmosphere. The maximum permissible percentage of clay volume in the material offset is ¹⁰⁰ / K _B %. The clays provided for the offsets have suitably low expansion values K _B = 1.4 to 1.8. If a batch contains, for example, 9 vol% expanded clay, it takes on a volume of 9 × 1.4 = 12.6% or 9 × 1.8 = 16.2% after expansion. From this, the volume of clay remaining at 9% by volume must be subtracted, so that 4 to 5% melt must be absorbed by the existing cavities. Excess or deficits cause open pores that can fill with water. If there is a lack of voids, it is proposed to add granular naphthalene C ₁₀ H ₈ . This substance melts at 80 ° C and evaporates at 218 ° C.

For the exact determination of the cavity volume one is heated Sample up to just below the temperature of the beginning of inflation, at for example to 1100 ° C and measures the hollow after cooling space using ultrasound.

If a material with very good thermal insulation is to be produced, an expandable chamotte with a high expandability must be used. This requires cylindrical pellets with a triangular cross section, as described in German patent application P 36 13 546.1. The carefully dried pellets are poured into the muffle furnace and heated up as quickly as possible. At the expansion temperature, an exothermic process begins, in which a completely uniform structure is created under an overpressure of 2 to 4 mbar and the temperature rises until all expansion gases CO + CO _{2 have} escaped. The process can be used to produce expanded chamotte with bulk densities down to 0.2 g / cm ³ .

The fact that according to patent application P 36 13 546.1 in cylin bodies with a triangular cross section when inflating the cavities but don't close in a circular cross section, you can take advantage of this in carefully dried Blanks of materials to drill tubes into the stone fire for the passage of gases or liquids, and can also be used to hold cables. The finished masonry then no longer needs to be costly to be broken to make room for the cables.

In the production of large format e.g. storey-high Components with good thermal insulation properties must be in parallel triangular cavities are provided for the longitudinal axis, where the ratio of cross-sectional area to solid Area is set so that according to the rules of the German Patent application P 36 13 546.1 for the desired stone fire Bulk density is achieved. In the edge zones of the components circular cylindrical tubes are provided, which after the Fire can accommodate the supply lines.  

Such components can best be used on modern vacuum Manufacture extrusion presses. You will be in the hearth car fire Furnaces arranged so that the fuel gases pass horizontally through the Cavities can paint until the triangular channels close evenly under the influence of exothermic processes eat.

If no thermal insulation is required, other granular or ground raw materials can be added to the mixture instead of expanded refractory material, e.g. quartz material, preferably in the grain size 0.5 to 1.0 mm or the amorphous SiO ₂ obtained in the manufacture of silicon in an electric arc furnace - Dust with the particle size 0.1 to 10 µm and the specific surface 20 to 22 m ² / g, which is not subject to volume changes when heated. This method is particularly suitable for the repair of historic buildings, especially domes, whose outer walls have been damaged by environmental toxins. Since the materials are waterproof, no liquids can penetrate and the gas permeability is so low that gases can only penetrate from outside if their vapor pressure is significantly higher than the vapor pressure inside the building. The vapor diffusion resistance number is µ = 12 to 22. In order to match the color of the material to that of the building, the surfaces of the material are covered with a waterproof colored glaze.

If a very high strength is required and the material is to be used at high temperatures, it is advisable to use glauconite-rich clay. In the semi-dry pressing process with 5 to 9% moisture, this raw material gives a product with a bulk density of 0.7 to 0.9 g / cm ³ and a pore size of 1 to 3 mm under an oxidizing atmosphere according to Eq. (2) at 1220 ° C firing temperature and 15 min holding time. Its volume increases by 14 to 30%. Due to the low moisture content, the clay develops its plastic properties and binding power only incompletely. In order to be able to distribute it evenly in the mass, it must be finely ground and the components of the batch must be fed to the mixer separately in the following order:

1.) Moistened chamotte grain
2.) Half of the tone
3.) Rest of the sound and water.

Eirich mixers with heavy, light are suitable for mixing raised pan or planetary mixer. The blanks must sen with high pressure, which is slow or in several stages is applied to the trapped air expel and distribute the moisture evenly.

Particularly suitable as chamotte are slurried, practically alkali-free kaolins with the composition Al ₂ O ₃ × 2 SiO ₂ × 2 H ₂ O. When drying, these raw materials shrink linearly by 4.5% to the shrinkage limit, the firmly adsorbed residual water evaporating and A vacuum of 0.9 bar is created in the pores. In stone firing, the kaolins shrink linearly by 3% up to 1100 ° C without any cavities, rather the lattice particles approach each other up to the metakaolinite stage at 700 ° to 800 ° C, which causes a loose bond. The formation of the stable mullite 3 Al ₂ O ₃ × 2 SiO ₂ phase begins at 900 ° C and at 1100 ° C the kaolins only consist of mullite and the remaining silica SiO ₂ in the form of the cristobalite phase:

This mixture sinters at 1500 ° C to form a Melting phase in which the cristobalite dissolves. The bulk density reaches its maximum, the porosity with 3 to 10% by volume Minimum.

As the temperature rises above 1500 ° C, the mullite crystals become larger and more compact and therefore resistant to dissolution due to corrosive melts. With slow cooling between 1300 ° and 900 ° C, the cristobalite separates out again and creates the risk of cracking. Therefore, the kaolin must be rapidly cooled above 900 ° C with 4 ^K / min, which is intended for the offsets discussed here.

The quantitative ratio between the flatulent clay and the kaolin must be set so that the resulting at 1220 ° C Volume increase by 14 to 30% from the pores or other void clear in the kaolin. At this tempera The kaolin is not yet solidified and contains 3 to 10 vol% pores that are open up to 1500 ° C. After that the Ratio clay to kaolin on average 1: 4 vol% 1: 6.5 % By weight.

The following are proposed as additional offset components:

1. high-quality ceramic fibers with a classification temperature of 1600 ° C, which, however, can only be used in continuous operation up to 1450 ° C, 1 to 2 vol .-%;
2. The stabilizers dry sulfite waste liquor and potato starch, each 3% by volume;
3. Al₂O₃ powder, type Ker 710 with 99% Al₂O₃

An offset from

The addition of Al ₂ O ₃ powder converts all cristobalite into mullite and the existing melt into solid substance. After cooling, the material is the only mineral phase containing mullite 3 Al ₂ O ₃ × 2 SiO ₂ + 2 Al ₂ O ₃ × SiO ₂ , which melts congruently at 1850 ° C. It expands linearly by approx. 1.0% from its formation temperature at 1100 ° C to 1800 ° C.

The stabilizing agents added to the batch evaporate when heated and provide cavities for absorbing the expanded products. Experience has shown that the bodies retain their shape up to at least 1220 ° C. At this temperature, the body consists of solid mullite due to its high Al ₂ O ₃ content.

Also the enamel to be expected from the kaolin at 1500 ° C phase cannot develop. The body therefore stays up 1850 ° C dimensionally stable.

In order to prevent the brittle material from tearing when the temperature changes sharply, it is proposed to add small amounts of high-melting substances, such as aluminum phosphate AlPO ₄ or apatite Ca ₅ (PO ₄ ) ₃ F or burnt gypsum CaSO ₄ , if necessary. that can serve as a lubricant. This gives the material a high resistance to temperature changes and can dissipate heat generated in a machine, eg a ceramic motor, or in an oven to the outside without being damaged. It is therefore also suitable for lining heat exchangers and regenerators in the high temperature range, as well as for systems for heat recovery.

If such high demands are placed on the material that they cannot be satisfied by mullite alone, the content of Al ₂ O ₃ powder can be increased at the expense of the kaolin. Then, in addition to mullite, the highly refractory corundum phase is formed and the melting temperature can be increased to 2000 ° C with a mixture of 78% mullite and 15% corundum. The corundum increases the thermal conductivity and the thermal expansion.

Since it does not make sense to use the stones in masonry To connect with mortar that is permeable to water, the Connection made by a tongue and groove system what requires a high degree of dimensional accuracy. This is true apparently only to be achieved with the semi-dry pressing method.

Claims (9)

1. A process for the production of watertight ceramic materials from clays, in which blanks having cavities produced without molds are burned under exothermic processes and up to expansion by released gases, characterized in that stabilizing substances are mixed in with the stone offset. 2. The method according to claim 1, characterized in that Dry sulfite waste liquor and / or potato starch are added will. 3. The method according to claim 1, characterized in that ceramic fibers are added. 4. The method according to claim 1, characterized in that pre-expanded and coarse-grained expanded clay are added. 5. The method according to claim 1, characterized in that granular or ground raw materials, such as quartz or amorphous SiO ₂ dust, in particular with a particle size of 0.1 to 10 microns and a specific surface of 20 to 22 m ² / g admixed will. 6. The method according to claim 1, characterized in that the slurried, alkali-free kaolins with the composition Al ₂ O ₃ × 2 SiO ₂ × 2 H ₂ O are added. 7. The method according to claim 1, characterized in that the mixture, apart from expanded clay, kaolin and stabilizers, is mixed with as much Al ₂ O ₃ powder with 90% Al ₂ O ₃ that the end product consists only of mullite melting at 1850 ° C. 8. The method according to claims 1 and 7, characterized in that the content of Al ₂ O ₃ powder is increased so much that corundum is formed in addition to mullite during firing and the end product melts at 2000 ° C. 9. The method according to any one of the preceding claims, since characterized in that as a tone a glauconite tone, Clay or blue clay containing illite or concrete becomes.