DE4300538A1 - Mfr. of porous, refractory ceramic foams - Google Patents

Abstract

Porous refractory ceramic foams are mfd. from inorganic components mixed homogeneously at room temp. and simultaneously or subsequently moulded into a solidified form. The components being selected from (a) powdered AlSi and its alloys with e.g. Ca, Mg, Ba, B, Fe and Cr, (b) powdered oxides and/or hydroxides of the above metals, water-soluble powdered silicates, powdered aluminates, borates and chromates, (c) opt. powdered carbon-, boron-, silicon carbide- or silicon nitride-based modifiers, (d) opt. amorphous alumina, titanium or silicon oxides of rutile structure, activated carbon, carbon black or cellulose fibres as foam stabilisers, restricting the rheological behaviour of the mixt., and (e) an aq. soln. of pH 7.5-12 contg. at least one water-soluble silicate and at least one of Na2CO3, K2CO3 and NH3. Exothermic heat is produced during an autogenous reaction proceeding during foaming and heating whilst the end product forms.

Description

The invention relates to a method for producing porous, refractory ceramic foam bodies made from a mixture of organic components.

The prior art includes a number of manufacturing processes development of inorganic, porous materials, especially kerami body with different quality characteristics such as porosity, specific weight, strength, thermal conductivity, thermal Resistance etc.

Japanese Patent No. Sho-60-28786 describes a process for producing a silicon-rich, porous foam silicate body from a mixture of quartz and metal silicon melts, in which silicon is oxidized and forms a gaseous silicon monoxide, which foams the melt. A product is produced which contains glass-like SiO ₂ , has excellent heat resistance and thermal insulation properties and is non-crystallizable. In this process, an SiO ₂ raw material, preferably a high-purity quartz material with a low proportion of alkali oxides and / or alumina sand, is mixed, melted and foamed with metallic silicon and / or silicon nitride as the foamer, the foam silicate melt being formed. The SiO ₂ raw material preferably has particle sizes of <3 microns, and the frother <300 microns. As a result of the interactions that occur during heating between SiO ₂ and metallic Si of the foamer, gaseous silicon oxide and / or nitrogen are formed in a finely divided form within the melt, which causes uniform foaming.

This process can only be carried out at high temperatures and requires a disadvantageously high expenditure of energy.

As a result of the production at high temperatures, however, there is also a high degree of wear in the shaping of the ceramic body required metal molds.

German patent 25 17 380 describes a method for Production of ceramic silicon nitride foam bodies or silicon carbide foam bodies by molding one by reaction between a silicon powder and an inorganic substance Foam and burn the resulting moldings in nitriding or in a carburizing atmosphere. This invention teaches that Silicon powder with a grain size <63 micron with diluted Sodium hydroxide solution is treated, the stable foam formed in forms is poured and the resulting moldings are fired. Here there is a silicon oxidation in an alkali under hydrogen development which leads to foaming of the slip. Then A reaction takes place, the intermediate product obtained in Silicon nitride or carbide is implemented. The silicon oxidation runs over in a 0.3 to 5% sodium hydroxide solution with pH values 12.5.

Disadvantages arise in such a strong alkaline medium Response times of just a few minutes no water-insoluble Products that have strong bonds between the components of the Schlic can manufacture kers. Therefore, to stabilize the emerge the foam a drying process and a high temperature treatment required. Following this procedure, foam bodies are under extreme high energy and labor costs.

A method is also known from British patent GB 1 511 398 Known which foam body of high quality at room temperature are manufactured. After this procedure one becomes strong  acidic solution a cement material or anhydrous silicate Alkali metals are added and then silicon or boron is added. The acids that are added to this solution with water glass ultimately lead to the hardening reaction while silicon or boron serve as a foaming agent in the reaction with acids. The gas formation arises during a reaction due to metal dissolution in the acid, whereas the hardening in a neutralization reaction between acid and solid silicates of the alkali metals.

The large amounts of acids or given by the recipe Salts and easily meltable Ver, containing alkali metals bindings, make it impossible to fire the resulting product to use solid material. Another disadvantage is that the use of acids and salts including halides the process make it environmentally harmful.

The invention has for its object a method for Her of porous, refractory ceramic foam bodies specify a mixture of inorganic components by which while avoiding the aforementioned difficulties and technical limits at working temperatures between room temperature or 100 ° C molded body with controllable porosity, pore ver division and a specified pore structure without emission of environmental pollution constituents that are harmful to the environment or with a minimum are particularly inexpensive to manufacture. Next towards the method it should be possible to aggregate or Kon structural elements consisting of a foam body according to the invention per with fiber blocks integrated into one unit, refractory Products such as stones or slabs and occasionally with metallic ones To produce fasteners in one process step. Also The inventive method should be able to do more to produce layered ceramic foam bodies, the individual Layers with different quality characteristics with regard to strength ability, thermal conductivity, heat resistance, specific weight etc. can be trained.  

A method is used to achieve the stated object proposed the features of claim 1.

In the method according to the invention, the work required essentially consists in metering and mixing the components mentioned under a) to e), this triggering the subsequent hydrogen development and oxidation of the metal powder. When reacting aluminum with the alkali, which contains Na and K ions, not only aluminum oxides and hydroxides are formed, but also sodium and potassium aluminates, which reduces their proportion of M ₂ · nSiO ₂ compounds. Here M means an alkali metal. In the course of the solution, this reaction initially leads to an increase in the viscosity of the solution and then to silicate hardening, n increasing more than four times. The same process results in the formation of borate. The silicon dissolution results in an immediate increase in the SiO ₂ content in the compound M ₂ O · nSiO ₂ . Interactions with Ca, Mg, Ba, Ti, Fe, Cr cause a partial exchange of the alkali metal oxide in the M ₂ O · nSiO ₂ compound for oxides of the aforementioned metals, water-insoluble complex silicates being formed and the mixture hardening. The metal oxides and hydroxides used become crystallization centers and continue to form the skeleton of the foam body.

The addition of modifiers according to component c) result thermal shock resistant body.

Foam stabilization by adding amorphous silicon, soot and especially reduce rutile silicon and titanium oxides the fluidity of the mixture due to a slight increase in viscosity. This favors an even pore distribution and the formation small pores, especially in the upper layers of the foamed body.

The foaming of the initially rheological mixture begins not immediately during or after the mixing process, but only after some time. This is believed to be due to the dissolution of the oxide film  caused on the metal surfaces in the alkaline medium. To this You can choose between the end of the mixing process and the beginning foaming takes 0.5 to 20 hours. The duration of this as Incubation period can be delayed by varying of the pH and the water content of the solution influenced within limits become. With a pH value of 12 and a water content of approx. 70% the incubation period takes 0.5 hours. At a pH between 8 and 9 and a water content of 150 to 200% on the weight of the components to be dissolved, there is an approx 20 hour incubation period. Then the actual opening takes place foam and harden for several seconds to several minutes. At this process becomes a solid, fire-resistant and water-insoluble Obtain foam body.

In addition to the evolution of hydrogen, the Water content of the mixture. The volatilization of the Hydrate water from the mixture of an autogenous heat development accompanied by the reaction. The proportion of water in the finished foam body is less than 3 percent by weight.

Refinements of the method according to the invention are corresponding provided the subclaims.

According to claim 2, the ratio of all masses Components a) to c) to the mass of the aqueous solution e) between 1: 3 and 7: 1. With a gradual increase in pH of 7.5 against 12, the proportion of metal component a) gradually increases from 5 to 95 percent by weight and the proportion of oxides or hydroxides b) is between 1 and 94 percent by weight; the proportion of modification rungsmittel c) between 1 and 4 percent by weight and the proportion of Foam stabilizers d) between 1 and 4 percent by weight. By Change the pH and the proportions a) to e) with the in the Claims 2 and 3 specified different proportions lead to the production of ceramic foam bodies with each  different quality characteristics, e.g. regarding strength, Thermal conductivity, heat resistance, pore volume and distribution or specific weight etc.

The mixture can also be very advantageously 1 to 80 percent by weight Catalysts, e.g. B. powdery oxides of Ni, Pt, Mo, Co, CoMo, Ca or Al can be added.

One embodiment provides that the grain size of the powder Components a) and b) <150 micron and preferably <120 micron and the grain size of the powdery component d) <10 microns, is preferably <5 microns.

With the change in the ratio of the solid phase to the solution within wide limits, for example from 1: 3 to 7: 1, variations in one achieved a wide range of properties of the finished foam body be, especially with regard to porosity, density, thermal conductivity etc. Various metal and alloy powders can be used Aluminum and ferro alloy additives are used. The grain Size of the powdery components a) and b) largely influenced Limit the stability and completeness of the reaction process, it turned out that optimal heat insulation charak Teristics with metal powders with a grain size spectrum below 30 Micron can be reached.

One embodiment provides that when the components are mixed in the form of reinforcing or filling material is added, for example. 3 to 40 percent by weight of fibers or filler such as pearlite foam, Expanded clay, glass microspheres, plastic granules etc. The encore such reinforcing or filling material leads to an increase in The viscosity of the solution and a wide range differ mechanical properties. Occasionally, by interfering of filling material the end product in adaptation to lower mechani chemical or thermal resistance in manufacturing significantly ver approves.  

A design aiming in the same direction provides that the reinforcement or filling materials and occasionally support material like fabrics or nets or nonwoven-like tangled fiber structures made of inorganic material before pouring the component mixture or before the start of the reactive phase of the component mixture be introduced into the mold.

The production of complete construction elements or Ag The invention achieves glomerates by means of an embodiment characterized in that one or more of the walls of the mold with fittings made of inorganic fibers and / or refractory porous materials such as aluminum oxide and aluminum silicate fibers, silicon calcium, SiC, Mullite etc. can be occupied.

When the hardening has taken place, the finished product behaves after molding from the mold similar to a monolithic body. There are great advantages with the invention in that the mixing process and the subsequent autogenous foaming with the Shaping is combined in one step by this Operations are carried out in the same form.

Various reinforcing agents and fillers, ver reinforcing fibers or large-sized packing in the shape preferred be used before pouring the mixture. One or several mold walls can also be poured in before pouring the mixture refractory blocks are occupied. After foaming and hardening then the form content forms a firm bond with the inserted material or blocks. Manufactured in this way Aggregates of inorganic foam blocks were at 1100 ° C in Tested for 48 hours without any visible changes on the Foam body or changes in the quality characteristics could be put.  

One embodiment provides that the foaming of the mass and hardening of the molding in a tightly closed form Pressures up to 100 bar. This creates a very dense structure with extremely fine and finely divided pores within a very homogeneous structure achieved.

An embodiment provides that towards the end of the hardening process, shortly before reaching the final strength of the molding, the Pressure in the mold is reduced to 0.3 to 0.05 bar.

You can look for another design suggestion elastic shapes are used.

Shaping the foam into an elastic shape is therefore useful moderate because the volume of material changes during foaming reaction can increase by a factor of 8.

One embodiment provides that the shape during the reactive Phase of the component mixture in motion and preferably in Rotation is set.

This advantageously prevents the foaming when Pores essentially at preferred areas of the mass enrich and lead to an uneven structure. Through movement introduction into the mold and preferably by rotation becomes a uneven distribution of the pores in the mass is advantageously prevented.

One embodiment provides that the insertion and / or expiration the foam formation phase by heating the mixture at approx. 20 ° is accelerated up to 90 °. On the one hand, this makes the Incuba tion time and on the other hand also the phase of the through hardening. This can advantageously increase productivity can be achieved in the manufacturing process.

One embodiment provides that the insertion and / or expiration the foam formation reaction by cooling the mixture from about 20 ° is decelerated to -40 °.

A delay in the reaction can occur when producing large formats bodies or when pouring a finished mixture into a lot  number of small forms can be advantageous because then not that Premixing begins to thicken and foam before the Ver division in the form or forms has been completed. Such a case can be given if a large foam body such as carrier a furnace vault, made with a given profile should be, the execution of all operations in the form require a certain amount of work and time, then what but further processing of the manufactured body is unnecessary.

One embodiment provides for the production of moldings is carried out in layers, one at a time hardened layer another layer by pouring on a wide one Ren component mixture and its hardening in any repetition tion is applied. The individual can benefit from this Layers with different recipes their mixtures and therefore with different quality characteristics regarding Strength, thermal conductivity, heat resistance, specific weight etc. be trained.

The invention is explained below using an example.

example

Powdery AlSi alloys and Al-Si-M alloys in the grain size spectrum <120 microns were mixed. M is a metal selected from the group Ca, Mg, Ba, Fe, Cr, Ti. Powdered hydroxides of Ca, Mg, Ba and oxides of Ti and Fe were used as the oxide phase. Water-free Na ₂ CO ₃ , K ₂ CO ₃ , 3% NH ₃ and water solutions of Na and K silicates with water contents of 50 to 70% were used to prepare solutions. Powdery components crushed to 120 micron were used as modifying agents silicon nitride, silicon carbide, boron nitride and boron carbide. The components were mixed at 20 °. The resulting suspension was poured into a mold. In some cases, the mixing process was also carried out in the mold. The results are shown in Table 1.

Remarks

The ratio between solid and liquid phase is in the Patterns 1 to 4 = 3: 2, for patterns 5 and 6 = 2: 1.

After a 48-hour test, samples 2, 3, 4, 6 remained without visible changes. In pattern 1, the volume has changed Melting of the microspheres added as fillers ver changes. There were small cracks in pattern 5. These are on Gas evolution due to carbon oxidation and too little Share of modifiers. Pattern 2 foamed at 25 bar. At the beginning of foam formation, the pattern 3 was the Pressure initially reduced to 0.1 bar.

The method according to the invention is very advantageous for Manufacture of porous, refractory ceramic foam bodies a mixture of organic components. It stands out the following particularly advantageous properties:

• - The production requires a comparatively very small Effort,
• - The mixture of components can be immediately in one form but also in a separate mixing container,
• - the quality characteristics of those produced by the process Shaped bodies can be expanded by varying the recipe Influence borders in a targeted manner,
• - with the targeted adjustment of the quality characteristics to the given Ne requirements can also be the cost of materials can be influenced in a wide range. By given Use of modification and / or foam stabilization media can determine the pore volume, pore size and pore distribution and thus the specific weight of the foam body produced can be set within wide limits.
• - The process enables the production very advantageously complex composite body / laminate as well as large format Molded body.

In this respect, the invention provides an optimal solution at the beginning task.

Claims (16)

1. A process for the production of porous, refractory ceramic foam bodies from a mixture of inorganic components, characterized in that as components

• a) AlSi powder and its alloys with metals such as Ca, Mg, Ba, B, Fe, Cr;
• b) powdery oxides and / or hydroxides of these metals, water-soluble silicate powder, powdered aluminates, borates, chromates;
• c) optionally powdery modifiers based on carbon, boron or silicon carbide or silicon nitride, and
• d) if necessary, the rheological behavior of the mixture reducing foam stabilizing media such as amorphous alumina, rutile titanium or silicon oxides, activated carbon, carbon black or cellulose fibers;
• e) an aqueous solution with pH values between 7.5 and 12, which contains at least one water-soluble silicate and one of the compounds Na ₂ CO ₃ , K₂CO ₃ , NH, which cause an alkaline reaction when dissolved in water, and these Homogenized to a mixture at room temperature and given to a hardening mold during the mixing or afterwards and left to mature in the course of an autogenous reaction with foaming and heating by developing exothermic heat of reaction to the end product.

2. The method according to claim 1, characterized, that the ratio of all masses of components a) to c) to Mass of the aqueous solution e) is between 1: 3 and 7: 1, with a gradual increase in pH of 7.5 against 12 the proportion of metal component a) gradually from 5 to 95 % By weight increased and the proportion of oxides or hydroxides b) between 1 and 94% by weight; the proportion of modifiers c) between 1 and 4% by weight and the proportion of foam stabilizer ren d) is between 1 and 4 wt .-%. 3. The method according to claim 1, characterized, that the ratio of the mass of all solid components a) to d) to the mass of the aqueous solution e) between 1: 1 and 3: 1 is, with a gradual increase in the pH of 9.5 against 12 the proportion of metal component a) gradually from 10 increased to 80 wt .-% and the proportion of oxides or hydroxyl den b) between 1 and 5% by weight, based on the mass powdery components, and the proportion of foam stabilization is between 1 and 4% by weight. 4. The method according to one or more of claims 1 to 3, characterized, that the mixture 1 to 80 wt .-% catalysts, for. B. powder shaped oxides of Ni, Pt, Mo, Co, CoMo, Ca or Al added become. 5. The method according to one or more of claims 1 to 4, characterized, that the grain size of the powdery components a) and b) <150 micron and preferably <120 micron and the grain size of the powdery component d) <10 microns, preferably <5 Micron is.   6. The method according to one or more of claims 1 to 5, characterized, that when the components are mixed in the form of reinforcing or filler material is added, for example 3 to 40% by weight of fibers or filler such as pearlite foam, expanded clay, glass microspheres, Plastic granules etc. 7. The method according to one or more of claims 1 to 6, characterized, that the reinforcing or filling materials and occasionally Support materials such as fabrics or nets or non-woven Tangled fiber structures made of inorganic material before pouring the component mixture or before the onset of the reactive Phase of the component mixture are introduced into the mold. 8. The method according to one or more of claims 1 to 7, characterized, that one or more of the walls of the mold with fittings inorganic fibers and / or refractory porous materials such as aluminum oxide and aluminum silicate fibers, silicon calcium, SiC, mullite, etc. 9. The method according to one or more of claims 1 to 8, characterized, that the mixing process and the subsequent autogenous foaming is combined with the shaping in one work step, by performing these operations in the same form become. 10. The method according to one or more of claims 1 to 9, characterized, that the foaming of the mass and the hardening of the molding in a tightly closed form under pressures up to 100 bar he follows.   11. The method according to one or more of claims 1 to 10, characterized, that towards the end of the hardening process, shortly before reaching the final strength of the molding, the pressure in the mold to 0.3 is lowered to 0.05 bar. 12. The method according to any one of claims 1 to 11, characterized, that elastic shapes are used for the shaping. 13. The method according to one or more of claims 1 to 12, characterized, that the shape during the reactive phase of the component mi is set in motion and preferably in rotation. 14. The method according to one or more of claims 1 to 13, characterized, that the onset and / or expiration of the foaming phase accelerated by heating the mixture from approx. 20 ° to 90 ° becomes. 15. The method according to one or more of claims 1 to 14, characterized, that the onset and / or expiration of the foaming reaction delayed by cooling the mixture from 20 ° to -40 ° becomes.   16. The method according to one or more of claims 1 to 15, characterized, that a production of moldings carried out in layers is, a white on each previously hardened layer tter layer by pouring another component mixture and their hardening applied in any repetition the individual layers with different Recipes of their mixtures and therefore with different quality features such as strength, thermal conductivity, Heat resistance, etc. can be formed.