DE4102430A1 - Porous ceramic or metallic bodies of high, controlled pore content - mfd. by sedimentation of a solid-liquid dispersion, followed by calcination - Google Patents

Abstract

Mfr. of solid bodies with a large number of fine pores, involves subjecting mixt. comprising a coarse dispersion of a liq. phase and solid particles, which is capable of undergoing a sedimentation process, to sedimentation. The sediment is solidified by means of a chemical reaction between the sediment particles in the presence of a liq. phase to give a porous body which has sufficient stability of shape so that it can be heat-treated. The liq. phase may contain a polar component, a non-polar component, of a mixt. Ir may comprise a true soln. of a colloidal soln. of a substance. The initial solid particles have a size of 0.1-300 microns, most pref. 0.5-50 microns. The porous bodies formed have a pore content of 50-95 vol. %, most pref. 65-85 vol. %, with a pore dia. range of 0.1-500 microns, most pref. 0.5-100 microns, and similarly sized interconnecting channels. The green porous body is calcined at a temp. above 900-1000 deg.C. USE/ADVANTAGE - Solid bodies with fibre pores are produced, which can act as supports for liquids and melts. The process gives good control over the dia. of the pores and the channels linking them, as well as providing a large vol. of

Description

The invention relates to a method (according to the Preamble of claim 1) for the production of fine pores large solid with a high pore volume.

DE-OS 23 01 662 is a method for Her position known porous solid, in which one off Foam existing support body with a Auf slurry of a ceramic material soaked, ge dries and burns. Burns during the fire the foam out so that a porous ceramic Body arises. The disadvantage of this known Process the environmental pollution caused by the burning out Pore formers. It is also unfavorable that by Aus residues may remain nen, which negatively affects the quality of the porous solid influence.

DE-OS 38 04 884 is also a method knows, in which the pore-forming phase by a tem porous foam is formed. The disadvantage is in this method that the average pore size un below the acceptable limit for filter materials lies and the porosity largely from sack pores or closed pores. Is unfavorable furthermore, that this method is not a targeted one flow on pore size and porosity that can.

The subject of DE-OS 36 28 948 is still a Ver drive to the manufacture of filter bodies, in which the  Material into a colloidal solution and then through Polymerization is converted into a gel, the Ma material still in the state of the colloidal solution or in egg to a partially polymerized state be performed. After the polymerization is complete the porous gel body obtained is dried and burned if necessary. The disadvantage of this known Ver drive that there are no fine-pored solids with very high pore volume and that it in addition, the diameter of the pores is difficult and precisely control the channels connecting the pores.

The invention has for its object a method so according to the preamble of claim 1 form that it is possible without adding a pore bildners a fine-pored solid with high pores to produce volume, the solid in this Diameter of the pores and those connecting the pores Channels can be controlled.

This object is inventively characterized by nenden features of claim 1 solved. Appropriate Embodiments of the invention are the subject of the Un claims.

According to the solid particles in one single or multi-component liquid phase to a coarsely disperse, sedimentable mixture disper yaws. To do this, the solid particles are shaken or stirring (possibly also with the help of a disperser device) distributed homogeneously in the liquid phase.

This mixture is then brought to sedimentation. For this purpose the mixture can be made into a hollow form  non-absorbent walls in which the Sediment can form and solidify. The formation of the Pores occur here through sedimentation of the solid Particles. The primary grain size is for sedimentation and the grain shape of the solid particles is essential Importance.

In the method according to the invention, the sediment in the presence of the liquid phase by chemical reac tion between the sediment particles to a porous Solidified body, which has sufficient dimensional stability for a heat treatment. The liquid phase or the components dissolved in the liquid phase (which is a colloidal or a real lion solution) take part in this chemical reaction between the sediment particles.

If the sediment is sufficiently strong sits, the remaining liquid phase is decanted and the solidified sediment under a drying process pulled.

The dry product can increase the final strength be subjected to a burning process since that too sediment solidified into a porous body adequate chemical and mechanical stability for you Owns the burning process. The firing or sintering temperature depends on the type of raw materials used and is between 900 and 1800 ° C, preferably between between 1000 and 1700 ° C. By such a thermal The porous solidified sediment is still being treated an increase in its mechanical and chemical sta bility.  

Those produced by the process according to the invention fine-pored solids with a high pore volume are suitable is used as a lightweight building block, as a carrier material for other liquid or solid phases, as insulation, Construction, filling or filter material.

The method according to the invention is particularly important suitable for the production of depth filters because of Diameter of the pores and those connecting the pores Channels of the solid body to the respective requirements can be fitted.

Due to the high absorbency according to the fiction fine-pored solids produced by the process these are also particularly suitable as carriers material for nonpolar or polar liquids as well for solids that are introduced as a melt.

In the method according to the invention, the Verfe stabilization of the sediment on the reaction between the fe Most particles, the components of the liquid Phase can contribute to this reaction. The education of the pore space occurs exclusively through sedimenta tion of the solid phase; the addition of a pore former is not essential in the method according to the invention required.

In addition to water, the dispersion medium cannot either use aqueous polar and / or non-polar liquids be det. This is advantageous in systems in which the solidification of the sediment by hydrolysis, e.g. B. when using alkoxyalanes or -silanes comes out. The water required for hydrolysis can be caused by diffusing in air humidity  leads. It has also been shown that, for example wise with ternary alcohol / alkane / water mixtures, de water content precisely meets stoichiometric requirements corresponds, the hydrolysis proceeds sufficiently slowly.

With alumina powders you can do comparable Dispersity obtained analog results. Others too oxidic or silicate solids can according to the be specified for magnesium oxide embodiments acts and be further processed. The rheological However, properties of the solid powder are not only different from manufacturer to manufacturer, son it also occurs with one and the same manufacturer differences between the individual batches that influence the sedimentation considerably can.

With non-oxidic solids, sometimes also with ge ground quartz, is the preparation in non-aqueous Medium often an advantage because generally a good benet between the solid particles and the liquid Phase favors a homogeneous sediment structure.

In the method according to the invention can in the liquid phase at least one substance in real or col loidal solution. The pore size, the volume proportion of the pores as well as the size of the pore connecting Channels are determined by the choice of grain size division of the solid particles and that in the liquid Solute phase set.

As for the relationship between the solute and the porosity, the following is worth noting:
If the solid particles are dispersed in an aqueous electrolyte solution, two effects can occur:
On the one hand, the pore fraction of the sediment increases, and on the other hand, the sediment solidifies more quickly and the final strength is increased by a factor of 3 to 5.

For example, 2 g of sintered magnesium oxide in one Dispersed 0.1 molar zinc nitrate solution, so increased the sediment volume of 2.1 ml (in pure water) to 4.8 ml. This corresponds to an increase in the pore content partly from 73 to 88 vol .-%. With a 0.075 molar Zinc sulfate solution gives a sediment volume of 7.7 ml, which corresponds to a pore fraction of 93% by volume.

Although Kaustermagnesia is already highly porous with water This sediment forms, can be reached in a 0.075-mo laren zinc sulfate solution with 2 g solid a sediment volume of 18 ml, corresponding to a pore fraction of 97% by volume. In contrast, in pure water results a sediment volume of 11 ml, corresponding to a bottom Ren content of 95 vol .-%.

Additions of magnesium ni have a similar effect leaked or sulfate. With these above Electrolyte additives can also achieve higher final strength sediments. For comparable results you get z. B. with iron (III) nitrate, aluminum sulfate or zinc chloride. With other electrolytes, such as. B. Potassium nitrate, sodium sulfate or ammonium sulfate however, no improvement over the purely aqueous System reached.  

The sediment volume can be determined by the type and concentration tion of the dissolved substances by a factor of up to 10 above all be riied.

In the method according to the invention, at least 90%, preferably 95% of the solid particles, expedient a size between 0.1 and 300 microns, preferably between rule 0.1 and 100 microns, particularly preferably between 0.5 and 50 µm.

Those produced by the process according to the invention Solids expediently have a pore content of 50 to 95 vol .-%, preferably from 60 to 90 vol .-%, be particularly preferably from 65 to 85% by volume.

The pores are produced by the process according to the invention provided solid have a diameter expedient water between 0.1 and 500 microns, preferably between 0.3 and 200 µm, particularly preferably between 0.5 and 100 µm.

The channels connecting the pores according to the invented Solid process produced according to the invention expediently a diameter between 0.01 and 100 µm, preferably between 0.05 and 50 microns.

The volume of the sediment is appropriately 10 to 98%, preferably 25 to 90% of the volume of the grobdi Spersen, sedimentable mixture.

With regard to the relationship between particle size and porosity, the following should be noted:
The porosity of the fine-pored solid is calculated using the formula

The porosity of the solidified sediment can be broken down into change wide borders. Is z. B. powdered sinter magnesia (95% of the particles have a diameter between 14 and 17 µm) dispersed in water, so forms a sediment with 73 vol.% porosity. Chooses on the other hand, as a solid, caustic burned magnesi umoxid with a particle size of 3 microns to 6 microns, so a sediment with 95% by volume of pores is obtained.

Regardless of the additives, the particle affects size of the sediment volume. If it exceeds An average of 15 µm gives Sedi ment porosities of maximum 70 vol .-%.

The grain size distribution is another, though not significant factor for the sediment procurement Ness. Polydisperse powders can be dissolved in electrolyte form solutions into highly porous sediments when through the electrolyte, e.g. B. by hydroxide formation or by electrostatic interactions with uploaded Io the adhesive forces between the grains are increased the. This is with the addition of magnesium, aluminum or iron (III) salts. For segregation according to different grain size during the sedimenta suppression should be done with polydisperse powders  the ratio of dispersion volume / sediment volume is not greater than 1.1 can be selected. This ratio leaves enlarge when the dispersion medium with Polyme ren is moved. So z. B. an addition of 1% Methyl cellulose that the aqueous dispersion of a po lydisperse magnesium oxide (55% <20 µm) 84 vol.% Po portion (compared to 67 vol.% porosity in Was ser). In addition to modified celluloses also polyglycol ethers, polyvinyl alcohols or poly ethyleneimine. By adding 0.3% polyethyleneimine (average relative molecular weight 26,000) the pore increases part in the sediment to 71 vol .-%. With almost monodisper These powders do not cause any significant polymer additives Increase in sediment volume.

The substance dissolved in the liquid phase is expedient in a concentration of 0.1 to 8%, preferably show 0.5 to 5%.

A useful development of the invention The process sees the combination of salt and polymer add before.

The used in the inventive method solid particles can be raw materials for ceramics, preferably at least one of the following compounds gen: aluminum oxide, magnesium oxide, silicon dioxide, zir condioxide, titanium dioxide, zirconium silicate, feldspar, cor dierid, clay, serpentine, talc, silicon carbide, silicon nitride, boron carbide and boron nitride.

Furthermore, the solid particles made of metal or Half metal consist, preferably of at least one of the following metals or an alloy thereof:  Aluminum, silicon, boron, zinc, titanium, copper, iron, Cobalt, nickel, chrome, molybdenum.

The liquid phase consists of at least one polar Component, so as a polar component at least one of the following connections should be provided: what water, mono- or polyvalent alkanols with 1 to 8 C-Ato men, mono- or multivalent ketones with 3 to 10 C-Ato men.

The liquid phase consists of at least one unpola ren component, as such can be non-polar component at least one of the following connections is provided be: n-iso- or cycloalkanes with 5 to 15 carbon atoms, Alkyl aromatics with 7 to 20 carbon atoms.

Under the designation "grobdispers" is part of the present application - in accordance with the Technical literature - a particle size of <0.1 µm ver stood (in contrast to the "colloid-disperse" grain size range from 0.1 to 0.001 µm). The particle size in coarsely dispersed area is a prerequisite for a Sedi mentation, while before with colloidal dispersities inflows brine occur.

The pores occur in the method according to the invention formation by sedimentation of the solid particles the scheme of pore formation in a bed of Ku apply. The ideal case here is a densest ball pac kung with a coordination number of 12 and a Po interior space of only 26% by volume. But already with one Ball packing with a coordination number of 8 increased the pore space to 32 vol .-%. In the present Invention, the pore space is further increased by the  Sedimentation for tight packing by electrostatic ces and adhesive forces between the solid parts prevented and the coordination number of each Solid particles is reduced. Through this metasta bile fixation of the solid particles becomes the training effect of the highly porous framework.

If the grain shape deviates from the spherical geometry, he gives way to a further increase in the pore space the house of cards as a contrary model presentation Ball pack.

The invention is also based on some execution examples explained in more detail.

Example 1: Porous molded articles made of mullite and / or sil limanite

100 g mullite and / or sillimanite powder (medium grain size 0.5 µm) with stirring or shaking in 150 up to 180 ml of an aqueous-alcoholic mixture of 11 g Aluminum tri-isopropylate and 4 g silicon tetra given ethylate. The homo by shaking or stirring genized dispersion is poured into a vessel, wel ches the desired shape of the body to be manufactured corresponds. The mixture will stand for sedimentation calmly. Depending on the ambient temperature has changed the sediment solidified for three to ten hours, that it can be demolded. The volume of the sediment is approx. 150 ml. The moist molded body becomes scho nend dried and slowly to the firing temperature of Heated to 1250 ° C.  

The linear shrinkage is about 2%, the pore volume is about 70% by volume. The moldings show a high absorbency against polar liquids and molten salts. The amount of liquid soaked up cannot be significantly increased by using a vacuum. It follows that sack and / or giant pores make no significant contribution to the pore volume. The compressive strength at room temperature is approximately 1 N / mm ² .

Similar results can be obtained if instead of Alkoxy metallates the correspondingly converted amounts of coarsely dispersed silica and aluminum salt (corresponding to 2 g silicon dioxide and 3 g aluminum oxide per 100 g mullite / sillimanite powder) are added and the mixture with ammonia to pH 8 until 10 is alkalized. The further procedure steps correspond to the above information.

Example 2: Porous molded articles made from calcium silicate those quartz grains

100 g quartz flour (grain size 1 to 6 µm) are in 150 ml dispersed in a 2% water glass solution. Under constant Dig stirring 30 ml of a 10% calcium nitrate solution quickly added. When left standing it forms a sediment with a volume of 140 ml This will solidify (approx. 6 hours at room temperature) Treated material in a similar manner as it be has already been described in embodiment 1).

The pore volume can be influenced via the firing temperature: after one hour at 1150 ° C it is 65 vol .-%, at 1250 ° C the porosity decreases to 55 vol .-%. The compressive strength increases from 1 N / mm ² to approximately 4 N / mm ² . The absorbency is equally good in both cases.

Example 3: Porous molded articles made of aluminum oxide

100 g of aluminum oxide (average grain size 4 µm) with 150 ml of an alcoholic solution of 20 g Alumi nium tri-ethylate stirred and then for sedimentation ditched. The sediment is consolidated by the hydrolysis rate of aluminum ethylate determined. they is between 3 and 12 hours. After drying it the fire follows at temperatures of 1500 ° C (3 hours Holding time) or 1650 ° C (1 hour holding time).

The pore volume is 60% by volume or 55% by volume.

Example 4: Porous molded articles made of nickel

Nickel powder with a particle size of about 3 µm is in one dispersed aqueous nickel salt solution and sedimen animals. The dispersion medium is one of the known Mi for the currentless deposition of metallic Nickel, whose redox potential is set so that the Deposition only on a nickel surface can. This leads to the fact that after 6 to 18 hours Sediment solidified into a dimensionally stable body becomes. This body can be made according to the known rules of Sintered metallurgy through thermal treatment in its Porosity and compressive strength can be modified.

The example described here provides porosities of maximum 65 vol .-%.  

Example 5: Porous molded articles made of silicon

Silicon powder (grain size 1 to 3 µm) is melted in zenem aluminum dispersed. The aluminum melt was before entering the silicon powder on silicon ge been satiated. After the sediment has solidified the aluminum melt is stripped off. Remaining alumi nium must be removed by acidic or basic extraction will. The shaped body has a porosity of approximately 75 % By volume. Its surface properties can be in wide limits can be varied depending on whether one Silicon oxide layer is generated or not.

In principle, Si can also be used instead of silicon Use silicon carbide in the above sense. The connection between the grains is also shot here silicon.

Example 6

a) 60 g of sintered magnesium oxide were slurried homogeneously in 200 ml of distilled water once without Mg (NO ₃ ) _{2 *} 6H ₂ O and once with 4 g Mg (NO ₃ ) _{2 *} 6H ₂ O. After a sedimentation time of 20 hours, the supernatant solution was decanted and the dimensionally stable sediment was removed from its shape. The Mg (NO ₃ ) _{2 *} 6H ₂ O additive shows its effect in better green strength, as well as in a larger sediment volume.

b) The samples are dried in a circulation con condensation system in slow temperature steps up to a final temperature of 120 ° C.  

c) The temperature treatment after drying was up to 300 ° C with a heating rate of 100 ° C / 1h, from 300 to 500 ° C with 40 ° C / 1h from 500 to 900 ° C with 100 ° C / 1h and from 900 to 1200 ° C with 50 ° C / 1h through guided. The final temperature of 1200 ° C was for 90 Minutes.

d) The porosity determination under normal pressure / water jet pump vacuum showed for the sample without Mg (NO ₃ ) _{2 *} 6H ₂ O 62/64 vol.% and for the sample with Mg (No ₃ ) _{2 *} 6H ₂ O 69/70 vol .-%.

Example 7

a) 54 g of sintered magnesium oxide, 6 g of Kauster magnesium oxide and 4 g of Mg (NO ₃ ) _{2 *} 6H ₂ O were slurried to a homogeneous suspension in 200 ml of distilled water. After 20 hours, the solid part formed a dimensionally stable sediment. The supernatant solution was decanted, the sediment removed from its shape and dried as described in Example 6 b).

b) The temperature treatment is carried out as in the example 6c).

c) The porosities determined as in Example 6 d) gave 78/80 vol .-%.

Example 8

a) 60 g of Kauster magnesium oxide with 4 g of Mg (NO ₃ ) _{2 *} 6H ₂ O were homogeneously suspended in 200 ml of ethanol. After 10 hours the sedimentation is complete and the amount of solid has solidified.

b) After demolding, as in Example 6b) dries.

c) The temperature treatment is carried out as in the example 6c).

d) The porosity determinations according to Example 6d) erga ben 64/65 vol .-%.

Example 9

a) 40 g of caustic burned magnesium oxide were in 50 ml of distilled water at 25 ° C in a mold slurried with non-absorbent walls. After 50 ml of petroleum was added to the mixture using egg a stirrer (speed <8000 / min) in 60 seconds suspended to a homogeneous mass. After unge for about 6-7 hours the hardening will turn green strength that allows removal of the shape.

b) The samples are dried in a circulation con condensation system with slow temperature increase up to a final temperature of 120 ° C.

c) The temperature treatment after drying was up to 300 ° C with a heating rate of 100 ° C / 1h, from 300 to 500 ° C with 40 ° C / 1h, from 500 to 900 ° C with 100 ° C / 1h and from 900 to 1150 ° C with 50 ° C / 1h through guided. The final temperature of 1150 ° C was for 90 Min.  

d) The porosity determinations for normal pressure / water jet pump vacuum gave 67/76 vol .-%.

Example 10

a) 20 g of caustic fired magnesium oxide and 20 g of sintered magnesium oxide were suspended with 11 g of Mg (NO ₃ ) _{2 *} 6H ₂ O as described in Example 1 a).

b) After about 7 hours, the green strength was great enough to remove the mold. The temperature treatment was as in example points 9b) and 9c) described.

c) The porosity determinations for normal pressure / water jet pump vacuum gave 68/78 vol .-%.

Example 11

a) 10 g of caustic magnesium oxide and 30 g of pre-annealed, caustic magnesium oxide were mixed with 2.60 g of Mg (NO ₃ ) _{2 *} 6H ₂ O in 70 ml of distilled water and 30 ml of petroleum with a stirrer (number of revolutions <8000 min. ^-1 ) Sus pendulum in 60 seconds.

b) After the sample had solidified and their Form could be removed, the further tem temperature treatment carried out as under the Example points 9b) and 9c) is described.  

c) The porosity determinations for normal pressure / water pump vacuum resulted in 70/74 vol .-%.

Example 12

a) 40 g of caustic magnesium oxide and 2.60 g of Mg (NO ₃ ) _{2 *} 6H ₂ O were in a dispersion phase, consisting of 10 ml of petroleum, 5 ml of distilled water and 85 ml of ethanol, with a stirrer (number of revolutions < 8000 min. ^-1 ) in 60 seconds.

b) 5 hours after the dispersion had been prepared Mass solidified and could in the Umwälztroc can be dried.

c) The sintering process was carried out with the same temperature Rablauf (as described under Example 9c) taken.

d) The porosity determinations for normal pressure / water jet pump vacuum gave 71/73 vol .-%.  

Example 13

a) 10 g of caustic magnesium oxide and 30 g of pre-annealed magnesium oxide were homogeneously dispersed with 2.60 g of Mg (NO ₃ ) _{2 *} 6H ₂ O in a solution of 15 ml of distilled water, 75 ml of ethanol and 10 ml of petroleum. The mold could be removed after 16 hours.

b) drying as described under Example 9b).

c) The temperature treatment after drying was up to 300 ° C with a heating rate of 100 ° C / 1h, from 300 to 500 ° C with 40 ° C / 1h, from 500 to 900 ° C with 100 ° C / 1h and from 900 to 1200 ° C with 50 ° C / 1h through guided. The final temperature of 1200 ° C was for 90 Minutes.

d) The porosity determinations for normal pressure / water jet pump vacuum resulted in 73/76 vol .-%

Claims (19)

1. A process for producing fine-pored solids with a high pore volume, characterized in that a coarsely disperse, sedimentable mixture of egg ner liquid phase and solid particles for sedimentation brought and the sediment in the presence of the liquid phase by chemical reaction between the sediment particles to a porous body verfe is Stigt, which has sufficient dimensional stability for a heat treatment. 2. The method according to claim 1, characterized in that that the liquid phase has at least one polar compo contains. 3. The method according to claim 1, characterized in that the liquid phase at least one non-polar com component contains. 4. The method according to claim 1, characterized in that the liquid phase is at least one polar and contains at least one non-polar component. 5. The method according to claim 1, characterized in that in the liquid phase at least one substance in real or colloidal solution. 6. The method according to claim 1, characterized in that at least 90%, preferably 95%, of the solid Particles between 0.1 and 300 microns in size preferably between 0.1 and 100 microns, especially before preferably between 0.5 and 50 microns.   7. The method according to claims 1 and 5, characterized ge indicates that the pore size, the volume fraction of the pores as well as the size of the pore connecting Channels by choosing the grain size distribution of the solid particles and dissolved in the liquid phase most substance is set. 8. The method according to claim 1, characterized in that the Herge according to the inventive method solids had a pore content of 50 to 95 Vol .-%, preferably from 60 to 90 vol .-%, particularly preferably from 65 to 85% by volume. 9. The method according to claim 1, characterized in that the pores of the process according to the invention ren manufactured solid a diameter between 0.1 to 500 microns, preferably between 0.3 to 200 µm, particularly preferably between 0.5 and 100 µm, exhibit. 10. The method according to claim 1, characterized in that the the pore connecting channels of the after Solids produced according to the method of the invention a diameter between 0.01 and 100 microns, preferred have between 0.05 and 50 microns. 11. The method according to claim 1, characterized in that the volume of the sediment is 10 to 98%, preferably wise 25 to 90% of the volume of the coarsely disperse sedimentable mixture. 12. The method according to claim 5, characterized in that that the solute by a salt, preferably at least one magnesium, aluminum, iron, zinc  or ammonium salt of formic acid, acetic acid, Hydrochloric acid, sulfuric acid or nitric acid formed becomes. 13. The method according to claim 5, characterized in that that the solute by at least one distributor ter from the group methyl celluloses, polyvinyl alcohol hole, polyolefin waxes, polyolefinimines formed becomes. 14. The method according to claim 5, characterized in that that the solute in a concentration of 0.1 up to 8%, preferably 0.5 to 5%. 15. The method according to claim 1, characterized in that the solid particles are raw materials for ceramics are, preferably at least one of the following Compounds: aluminum oxide, magnesium oxide, silicon Umoxid, zirconium dioxide, titanium oxide, zirconium silicate, Feldspar, cordierite, clay, serpentine, talc, silicon carbide, silicon nitride, boron carbide, boron nitride. 16. The method according to claim 2 or 4, characterized records that as a polar component at least one of the following compounds is provided: water, mono- or polyvalent alkanols with 1 to 8 carbon atoms, mono- or polyvalent ketones with 3 to 10 carbon atoms. 17. The method according to claim 3 or 4, characterized records that as a non-polar component at least one of the following connections is provided: n-, iso-, or cyclo-alkanes with 5 to 15 carbon atoms, Al kylaromatics with 7 to 20 carbon atoms.   18. The method according to claim 1, characterized in that the solid particles of metal or semi-metal consist, preferably of at least one of the fol metals or an alloy thereof: Alumi nium, silicon, boron, zinc, zircon, titanium, copper, Iron, cobalt, nickel, chromium, molybdenum. 19. The method according to claim 1, characterized in that that the sediment solidified into a porous body a firing process at a temperature of over 900 ° C, preferably above 1000 ° C, is subjected.