WO1993021126A1

WO1993021126A1 - Low-density inorganic moulding and process for producing it

Info

Publication number: WO1993021126A1
Application number: PCT/EP1993/000900
Authority: WO
Inventors: Theo Haack; Peter Randel
Original assignee: Hüls Troisdorf Aktiengesellschaft; F. Willich Dämmstoffe + Isoliersysteme Gmbh + Co.
Priority date: 1992-04-11
Filing date: 1993-04-13
Publication date: 1993-10-28
Also published as: AU4039893A; DE4391555D2; JPH07506326A; JP3563071B2

Abstract

The description relates to a process for producing light, at least largely inorganic mouldings with a density < 400 kg/m3. To this end a light microporous filler with a powder density < 150 kg/m3 is bonded with a geopolymer. The fillers used are, in particular, blown perlite and vermiculite. The geopolymer is produced by a stone-forming component, especially an oxide mixture containing silicon and aluminium oxides and an alkaline silicate solution as the hardener. The moulding compound consisting of the stone-forming component, the microporous filler and the hardener is poured into a possibly heated mould, pressed with a reduction in volume and removed from the mould after less than 3 min. The mouldings obtained contain a continuous phase of geopolymer with a dispersed phase of the light, microporous fillers. The mouldings have excellent resistance to temperature variations, a high temperature resistance, light weight and low heat conductivity.

Description

Inorganic shaped body with low density and process for its production

TECHNICAL FIELD The invention relates to a process for producing light, at least largely inorganic molded articles with a density <400 kg / m ³ and a molded article made from at least largely inorganic constituents with a density <400 kg / m ³ .

State of the art

It is known to produce inorganic moldings of low density by foaming and hardening a mixture containing a stone-forming component, an alkali silicate solution as hardener which brings about an exothermic hardening reaction with the stone-forming component, and a blowing agent. The so-called stone-forming components known from EP-A2 0 417 583, EP-Bl 0 148 280 and EP-Bl 0 199 941 are in particular:

I a finely divided oxide mixture with contents of amorphous silicon dioxide and aluminum oxide, obtained as filter dust from the production of corundum or mullite,

II glassy, amorphous electrostatic precipitator ash from high-temperature hard coal power plants,

III g & milled calcined bauxite, IV undissolved, amorphous SiO 2, in particular from an amorphous, disperse powder, dehydrated or water-containing silica or from high temperature processes (silica fume),

V ^■ Metakaolin.

To accelerate the hardening, lignite power plant filter ash in particular can be added. The stone-forming component reacts exothermically with an alkali silicate solution with 1.2 to 2.5 moles of SiO 2 per mole of K2O and / or Na2 O as hardener, a so-called geopolymer with a structure similar to zeolite or feldspar having a polycondensation or polyaddition reaction three-dimensional network structure. Although the foamed moldings produced by adding hydrogen peroxide as blowing agent in particular have sufficient strength and a relatively high temperature resistance for many purposes, the resistance to temperature changes is not sufficient for certain areas of application and the shrinkage is great when subjected to high temperatures. In the case of large-scale industrial use, the relatively long curing time is also disadvantageous, since the foamed moldings can only be removed from the mold after about 10 to 60 minutes (green strength).

EP-A2 0 071 897 discloses a lightweight building material and a process for its production in which perlite is bound as a light filler with a mixture of water glass, water and a water glass hardener. The binder is also foamed. K2SiFg or a CO2-releasing organic or inorganic agent is used as the hardener for the water glass. In this water glass hardening, which is based on a completely different reaction to the geopolymer bond, a drop in the silica and thus a solidification of the system is achieved by reducing the pH value of the water glass solution. These systems have the disadvantage of inadequate green strength and that they harden relatively slowly, so that short cycle times cannot be achieved when using expanded perlite as a light filler. In addition, these moldings have a relatively low resistance to temperature changes. The green strength is shortened by using expanded vermiculite instead of expanded pearlite, but the molded articles produced in this way have a significantly higher thermal conductivity.

task

It is therefore an object of the present invention to improve the process for the production of light inorganic moldings in such a way that the abovementioned disadvantages are avoided and moldings with high temperature resistance, temperature change resistance, low thermal conductivity and low shrinkage can be produced at elevated temperature. Presentation of the invention

This object is achieved by a method according to claim 1 or by a molded body according to claim 12 or 14, preferably in conjunction with one or more features of the subclaims. A preferred process product is a chimney or chimney element, produced in accordance with claim 15 or 16.

For the first time, the method according to the invention enables the production of particularly light inorganic insulating materials with relatively high strength, in particular high compressive strength and a favorable average pore size. By admixing suitable water-storing substances in the insulating material, the method above all produces an end product which is advantageously suitable for tape protection. It is also advantageous that the insulating material has practically no shrinkage and low thermal conductivity values. Even under extreme temperature changes, there are no cracks and no shrinkage. It is particularly important to emphasize that for the first time, such an insulating material can be used to produce moldings from light fillers which have a quality which has hitherto been unknown. These insulating materials can also advantageously be processed further.

The method according to the invention differs in particular from the known method for producing lightweight moldings using lightweight fillers such as expanded pearlite or vermiculite in that a geopolymer known per se is used as the inorganic binder. It was not foreseeable that the use of this binding system would result in cycle times between the filling of the mixture into the mold or the pressing tool and demolding from a few minutes down to approximately 20 seconds and pure pressing times of a few seconds. the corresponding moldings have superior properties with regard to thermal conductivity, temperature resistance and resistance to temperature changes.

The quick release from the mold is surprising even when using expanded perlite as the only light filler reached. The cycle times can in particular be achieved by heating the mold to 40 to 250 ° C., preferably 100 to 170 ° C., and by pressing with volume reduction of 20 to 80%, preferably 30 to 50% of the initial volume at a pressure of approx. 1 to 4 bar be shortened. Without such pressing the cycle times significantly extend what but for be¬ approved applications, in particular in the production of moldings with lost forms, can be put into ^"buying. The strength of the Formkör- inventively prepared by can substantially increased and the need to use the alkali silicate solution as a hardener can be reduced if the microporous fillers are treated with a water-containing wetting liquid before mixing, in particular warm water with additions of components which reduce the surface tension, such as a suspension made of aluminum phosphate or polysilicate or a surfactant The wetting liquid is preferably injected into a stirred tank or the like, the light fillers being moved only carefully in order to damage the structure of the packing as little as possible If necessary, it can also be added after the light micro-porous components have been mixed with the stone-forming component, but before the alkali silicate solution is added as a hardener.

An alkali silicate solution with 20 to 25% by weight of 2O, 23 to 28% by weight of SiO 2 and 50 to 60% by weight of water is preferably used as the hardener. The molar ratio of SiO 2 to K2O (or when using Na2 O to Na2 O or to the sum of Na2 O and K2O) is preferably 1.4 to 1.9.

The thermal conductivity at high temperatures of around 400 to 1200 ° C can be reduced by adding opacifiers. Rutile, illmenite, carbon black or, preferably, vegetable ash with largely preserved flat silicate structure, such as, in particular, rice husk ash, are suitable for this. Rice husk ash also has the advantage of increasing the strength of the molded article produced. It is worth mentioning that the thermal conductivity of the finished molded articles does not decrease when using rice husk ash at temperatures up to approx. 200 ° C. is set, but that the effect of reducing the thermal conductivity occurs only at higher temperatures.

While both the solids and the fillers are usually ground as finely as possible in the known geopolymer systems, the rice husk ash is preferably cautious and mixed in while maintaining the structure of the rice husk ash and without a grinding process.

Expanded vermiculite and / or expanded pearlite is preferably used as the microporous filler with a bulk density of <150 kg / m ³ , pure pearlite or mixtures with up to 50% by volume pearlite being preferred.

Expanded vermiculite has a bulk density of approximately 75 to 200 kg / m ³ , while the bulk density of expanded perlite is approximately 30 to 100 kg / m ³ . The microporous fillers preferably have a grain size of 0 to 2 μm, in particular of 0 to 1 mm.

The total mixture preferably contains approximately 25 to 35% by weight of microporous filler, in particular

Perlite, approx. 25 to 35% by weight alkali silicate solution as hardener, approx. 10 to 20% by weight reactive solid, approx. 10 to 20% by weight rice husk ash, approx. 5 to 10% by weight wetting liquid.

In addition, customary fillers such as rock powder, basalt, clays, feldspar, mica powder, glass powder, quartz sand or quartz powder, bauxite powder, alumina hydrate and waste from the alumina, bauxite or corundum industry, ashes, slags and mineral fiber materials can be used. However, the total mixture preferably contains less than 20% by weight of these additional fillers, in particular less than a total of 10% by weight.

It is also possible to replace part of the reactive solid with higher use of rice husk ash, with all However, the time required for curing is extended. Possibly. However, this effect can be partially compensated for by a higher temperature during processing, ie during pressing.

To carry out the method, a system is preferably provided which has a first mixer in which the solids, ie. H. the reactive solid, the microporous fillers and possibly other additives are mixed, with this mixer being followed by a counterflow mixer with injection nozzles for the wetting liquid. This makes it possible with such a system to separate the individual components, ie. H. above all, mix the light filler with the wetting liquid carefully and evenly, in order to then mix the correspondingly pre-mixed solid with the hardener so that the even and easy-to-use "earth-moist" molding compound results.

According to a particularly expedient embodiment of the invention, it is provided that a further post-mixer is connected downstream of the countercurrent mixer, or that both mixers form a unit having several mixing sections. In the case of a system or a corresponding mixer designed in this way, it is possible to gradually and uniformly mix the individual components, the gentle treatment of the light fillers, in particular pearlite and vermiculite, being ensured. In order to bring the correspondingly produced molding compound into the desired shape, it is particularly provided that a press is arranged downstream of the counterflow mixer. This press is used to form plates and moldings which are ideally suited to a wide variety of operating conditions and have high insulating properties.

According to a particularly preferred embodiment of the method according to the invention, the mixture containing the microporous fillers, the reactive solid and the hardener is filled into a mold or a pressing tool and reduced in volume to 20 to 80%, preferably 30 to 50% of the Initial volume pressed at a pressure of about 1 to 4 bar. By This pressing in the mold or between two pressing plates ensures that the molded bodies are solidified after a very short time to such an extent that they can be removed from the mold and then hardened further. The reduction in volume is associated with a certain destruction of the structure of the light fillers, but the moldings obtained are nevertheless extremely light and have outstanding thermal insulation properties. With a particularly preferred mixture of approx. 30% by weight pearlite, approx. 30% by weight hardener, approx. 15% by weight reactive solid, approx. 10% by weight rice husk ash and approx. 7.5 % By weight of wetting liquid, moldings with a density of approx. 250 to 270 kg / m ³ and a thermal conductivity of 0.051 W / mK at 30 ° C. are achieved.

According to an alternative embodiment of the method according to the invention, it is also possible to fill the mixture containing the microporous fillers, the reactive solid and the hardener into a lost form, wherein, depending on the desired properties, pressing with volume reduction can also be dispensed with entirely . In this way, in particular chimneys or chimney elements can be produced by filling the molding compound into an annular gap between two walls and then curing it. The walls preferably consist of two stainless steel tubes arranged concentrically to one another.

It is particularly advantageous that the molding compound adheres to the walls despite its low specific weight due to its low shrinkage and its high resistance to temperature changes, without later showing any unacceptable cracking or shrinkage.

In principle, it is also possible to additionally add a known foaming agent to the mixture containing the microporous fillers, the reactive solid and the hardener, with about 10% by weight H2O2 in amounts of 2 to 6% by weight. , based on the overall approach, are sufficient. This additional foaming leads to even slightly lighter end products with further improved thermal insulation, but these products have te lower strength and higher shrinkage, so that non-foamed products are preferred.

In a further preferred embodiment of the invention it is provided that the moldings are constructed in multiple layers with a light core with a density below 400 kg / m ³ and at least one outer layer or coating of a geopolymer with a density between 400 kg / m ³ and 1200 kg / m ³ , the outer coating having a much higher strength and temperature resistance than the core. The lightweight molded articles as previously prepared may be¬ written to after the escape and possibly with a hardening molding composition, comprising a stone-forming component _^ an alkali silicate solution as a curing agent and optionally smaller amounts of perlite and / or be coated Vermicu- lit. However, the coating is preferably achieved by prior to pressing the mixture for the core, this mixture in the mold with a thin layer of a molding compound containing a stone-forming component, an alkali silicate solution as hardener and, if appropriate, smaller proportions of pearlite and / or vermiculite, and the two layers are pressed together. Alternatively or additionally, the denser film mass can also be filled into the mold in a thin layer first, whereupon the light layer is then filled with the higher proportion of light fillers.

Brief description of the invention

Further details and advantages of the subject matter of the invention emerge from the following description of the associated drawing, in which a preferred exemplary embodiment is shown with the necessary details and individual parts with regard to the production systems. It shows:

Fig. 1 is a schematic sketch of the system provided for the production of plates.

Best way to carry out the invention

The production plant 1 initially has a plurality of storage containers 2, 3, 4. The individual components for the solid are stored in these storage containers 2, 3, 4. namely a reactive solid, a temperature change-resistant aluminum silicate or aluminum titanate or aluminum oxide as filler, and rice husk ash to reduce the thermal conductivity at elevated temperatures. The solid components removed from these storage containers 2, 3, 4 are mixed together in the mixer 5 to form a solid mixture which is then further processed with the light fillers and the hardener to give a molding composition. The mixing can be carried out, for example, discontinuously in what are known as Eirichmisers or in suitable continuous mixers.

The light fillers perlite and vermiculite, which are kept in the containers 7 and 8, first reach the countercurrent mixer 6, where intensive mixing is carried out. In this countercurrent mixer 6, the wetting liquid, which consists of a suspension of aluminum phosphate or polysilicate in water, is fed from the tank 10 in countercurrent via the injection nozzle 9. Here, too, it is conceivable to keep the individual constituents separately and then to add them mixed or uniformly via the injection nozzle 9.

In the embodiment shown in FIG. 1, a post-mixer 11 is provided which is constructed like the counterflow mixer 6 and to which both the mixture of light fillers and wetting liquid and the solid are fed. The hardener is then injected into the post-mixer 11 via the nozzle 12 from the tank 13 and is mixed in during the stirring in the post-mixer 11.

The uniform molding compound thus obtained then reaches the press 14, where appropriate shaping takes place, whereupon, for example, insulating plates 15 are then stacked up and then sent for sale.

In the example shown, a mixture is formed as a solid

15 parts by weight of an amorphous, powdery oxide mixture with contents of amorphous silicon oxide and aluminum oxide, which as a dusty deposit from the Exhaust gas is produced during the production of corundum (commercial product: WILLIT® solid) 8.5 parts by weight of a temperature change-resistant aluminum silicate or aluminum titanate or aluminum oxide as filler

10 parts by weight of rice bowl ash produced. This is done in an appropriately trained mixer.

7.5 parts by weight of a suspension of aluminum phosphate in water are used as the wetting liquid.

29 parts by weight of an alkali silicate solution with a density of 1.53 kg / dm ³ with 25.2% by weight SiO 2, 22.1% by weight K 0 and 52.7% by weight H2O (WILLIT ® hardener E 61059) and as light fillers 20 parts by weight of expanded perlite and 10 parts by weight of expanded vermiculite.

The light fillers are placed in a countercurrent mixer, the wetting liquid (aluminum phosphates in water) is sprayed in while stirring, the solid mixture is added and finally the hardener (alkali silicate solution) is metered in with stirring.

Sheets with a density between 280 and 400 kg / m ^{3 were produced} by pressing from the earth-moist molding compound. The compressive strengths were between 0.9 to 1.2 N / mm ² , the shrinkage (linear) at 800 ° C to approx. 1%. The thermal conductivity at 400 ^{C was} 0.07 to 0.10 W / mK. When the samples were subjected to changes in temperature (heating to 800 ° C., cooling to 20 ° C.), there were no changes such as cracks or shrinkage.

Claims

1. Process for the production of light, at least largely inorganic molded articles with a density of <400 kg / m ³ using a solid stone-forming component, a liquid hardener which effects the hardening reaction of the stone-forming component, and microporous fillers with a bulk density <150 kg / m ³ , which contains the solid stone-forming component

I a finely divided oxide mixture with contents of amorphous silicon dioxide and aluminum oxide and / or

II a glassy, amorphous electrostatic precipitator and / or

III ground calcined bauxite and / or IV electrostatic precipitator ash from lignite-fired power plants and / or

V undissolved, amorphous SiO 2, in particular from an amorphous, disperse powder, dehydrated or water-containing silica or from high-temperature processes (silica fume) and / or

VI metakaolin, and an alkali silicate solution with 1.2 to 3.0 moles of SiO 2 per mole of K2O and / or Na2 O and a density of 1.4 to 1.7 kg / dm ³ is used as the liquid hardener The following process steps: the microporous fillers are mixed with the stone-forming component, if appropriate after wetting with a water-containing liquid, and if appropriate after admixing further solid components with the liquid hardener, the macrostructure of the light fillers being at least largely is preserved, the mixture is filled into a mold and - then the mixture is cured to form the shaped bodies.

2. The method according to claim 1, characterized in that the microporous fillers - optionally together with the stone forming component - be wetted with a water-containing liquid before adding the liquid hardener.

3. The method according to claim 2, characterized by the addition of a substance reducing the surface tension to the water-containing wetting liquid.

4. The method according to claim 1, characterized by the addition of an opacifying agent to reduce the thermal conductivity at elevated temperatures.

5. The method according to claim 4, characterized by the use of a vegetable ash with largely preserved flat silicate structure as an opacifier.

6. The method according to claim 5, characterized by the use of rice husk ash as plant ash.

7. The method according to claim 1, characterized by the end of expanded vermiculite and / or perlite as a microporous filler.

8. The method according to claim 1, characterized in that the total mixture contains a) 25 to 35 wt .-% miroporous filler,

^• b) 25 to 35% by weight hardener, c) 10 to 20% by weight reactive solid, d) 10 to 20% by weight rice husk ash, e) 5 to 10% by weight wetting liquid.

9. The method according to claim 1, characterized by the fact that the mixture containing the microporous fillers, the reactive solid and the hardener are filled into a mold or a pressing tool and reduced in volume to 20 to 80%, preferably 30 to 50% of the Output volume is pressed at a pressure of 1 to 4 bar.

10. The method according to claim 9, characterized in that the mold or the pressing tool to a temperature of 40 to 250 ° C, preferably 100 to 170 ° C, is preheated.

11. The method according to claim 9 or 10, characterized in that the molded body is removed from the mold within 3 min after the pressing and then cured at an ambient temperature of 40 to 300 ° C, preferably 100 to 200 ° C.

12. Shaped articles composed of at least largely inorganic constituents with a density of <400 kg / m ³ , characterized by a continuous phase of geopolymer formed by the exothermic reaction of a hardener with a reactive solid and having zeolite- or feldspar-like ones Structure and a disperse phase made of light, microporous fillers.

13. Shaped body according to claim 12, characterized by a content of rice husk ash of 10 to 30 wt .-%, based on the weight of the shaped body, in the continuous phase.

14. Molded articles with at least two layers of at least largely inorganic constituents, at least one layer having a density of <400 kg / m ³ and at least one outer layer having a density of 400 kg / m ³ to 1200 kg / m ³ , characterized in that the layer or layers with a density <400 kg / m ³ a continuous phase of geopolymer formed by exothermic reaction of a hardener with a reactive solid with a zeolite- or feldspar-like structure and a disperse phase of light, has or have microporous fillers and that the layer or layers with a density of 400 kg / m ³ to 1200 kg / m ^{3 is} made of a light, possibly microporous filler containing geopoly there is or exist a structure similar to zeolite or feldspar.

15. Process for the production of chimneys or chimney elements using a solid stone-forming component, a liquid hardener, which effects the hardening reaction of the stone-forming component, and microporous fillers with a bulk density <150 kg / m ³ ,

- The solid stone-forming component contains

10 I a finely divided oxide mixture with contents of amorphous silicon dioxide and aluminum oxide and / or II a glass-like, amorphous electrostatic filter ash and / or

15 III ground calcined bauxite and / or

IV electrostatic precipitator ash from lignite-fired power plants and / or

V undissolved, amorphous SiO 2, especially from an amorphous, disperse powdery, dewatered

20 or water-containing silica or from high-temperature processes (silica fume) and / or

VI metakaolin,

- And where as a liquid hardener an alkali silicate solution with 1.2 to 3.0 moles of SiO 2 per mole of K2O and / or

25 a2θ and a density of 1.4 to 1.7 kg / dm ³ is used, comprising the following process steps: the microporous fillers are - if necessary after wetting with a water-containing liquid - together

30 mixed with the stone-forming component and, if appropriate, after admixing further solid components with the liquid hardener, the macrostructure of the light fillers being at least largely retained,

^• 35 - the mixture is then poured into an annular gap between two walls and cured.

16. The method according to claim 15, characterized in that the walls are formed by two concentrically arranged stainless steel tubes.