DE2128845A1 - Process for the production of SiIi kat items - Google Patents

Description

ALEXANDER R. HERZFELD * l ^^ Lt £ ^W

LAWYER AT THE LAND COURT FRAN KFURTAM MAIN

entered on iLJLJZ. 2128845

Addition to patent application P 21 28 980.5

Applicant: Corning Glass Works
Corning, NT, USA

Process for the manufacture of silicate articles

The invention relates to a method for producing Silicate objects, in particular for the production of self-supporting, monolithic, porous silicate objects or also solid glass body.

The main patent (patent application P 21 28 980.5) describes a process for the production of said objects in which real solutions and / or colloid solutions and / or suspensions with pH 10-15 and 1-12 mol SiOp / l solution from the Silicate solutions of alkali metal silicates, organic ammonium silicates, colloidal silicates or mixtures thereof

2 -

203803 / 1SS4

> 1 E

prepared and with formaldehyde, paraformaldehyde, glyoxal, Formamide or mixtures thereof at one temperature

between the freezing and boiling point of the solution so long that the pH falls below 10 and that SiO «polymerized to form a gel.

The present invention is based on the surprising finding that the organic gelling agents of the main patent are wholly or partially by organic esters or inorganic Salts can be substituted. These esters or salts can therefore instead of the organic gelling agents formaldehyde, paraformaldehyde, Glyoxal or formamide occur, or can also be used together with this.

Based on this surprising finding, the inventive proposal provides that the formaldehyde, paraformaldehyde, Glyoxal or formamide is wholly or partially replaced by an ester with at most 5 "and preferably at most 4 carbon atoms, such as methyl formate, ethyl formate, methyl acetate or ethyl acetate or mixtures thereof or by an inorganic salt such as a carbonate and / or hydroxide and / or borate and / or phosphate of a cation with a Valence of at least 2, and that the gel is air dried on a self-supporting, monolithic, porous object, or if the softening point of the respective

2Ö9808 / 166A

igen composition lying temperature as long as fired until it is consolidated into a solid silicate glass body.

With regard to other more favorable, the invention Features refer to the further description and the subclaims referenced.

The invention is based on the surprising finding that certain organic esters and inorganic salts completely or partially substitute the gelling agents of the main patent can be.

The esters dissolved in the soluble silicates form an organic acid and an alcohol through hydrolysis and lower thus the pH value to a level that allows the polymerisation of the silica, usually about 8-10. The ester has to For this purpose, it must be soluble and hydrolyzable in the silicate solutions, and must be in a minimum amount of about 2% by volume are present. The most suitable are esters with up to A carbon atoms, possibly also up to 1r carbon atoms. Methyl or ethyl acetate or formate are preferred form methanol, ethanol, acetic acid or formic acid during hydrolysis. Empirically, a useful quantitative one Range of about 2-20% by volume of ester determined in the solution.

209608/1664

At more than 20% the gel tends to disintegrate because the reaction products crystallize out, while less than 2 % of the ester is insufficient for gelation. In practice, about 3-10 ¥ ol.% Ester, "with an optimum of 4%, is preferred. The specified amounts of ester are dissolved homogeneously and reacted evenly, so that a gel with a polymerized lattice is formed.

The effective reaction temperature range is between the freezing and boiling points of the solutions, with an increased Pressure even higher temperatures come into question. Usually normal pressure and 4-0-100 ° C with a treatment duration of about 5 seconds - 24 hours will be sufficient. Implementation times up to 720 hours were successfully tested, but did not bring any further improvement to the end product.

The reaction process can be viewed as a phase separation, whereby the ester neutralizes part of the alkali oxide and / or ammonium ion and the solution becomes weaker basic, so that the silica becomes polymerizable _o The polymerization is supported by the simultaneous replacement of the water of hydration of the silica with undissociated esters and alcohol released during ester saponification. The implementation product consists of a solid-phase body with a porous silica lattice, which after washing

209808/1666

with V / ater or a suitable solver already as such can be used for numerous purposes. However, it can also be essential through two different follow-up treatments to be changed.

One type of post-treatment occurs through leaching or drying in air and / or burning for the purpose of expulsion volatile constituents an essentially uniform nip porous object. The leaching; takes place with suitable solvents such as water, alcohol, ketones, or acids, which Dissolve out the soluble phases, in particular the gelling agent and the alkali oxide and / or ammonium ions, so that what remains is a body consisting essentially only of silica. Instead of leaching, the body can also do sufficiently higher but below the deformation point (and avoids filling the pores by sagging) Temperature to expel volatile components such as organic matter and ammonia. In both cases, a self-supporting, monolithic body is obtained with one that is sufficient for handling and deformation Strength. The pore size is, for example, from 100 - 20,000 S with a total porosity of about 30 - 85% adjustable. This is particularly important for use as a porous carrier material, as a filter and the like. If required, however strong the porous body

209808/1664

burns or sintered that the pores closed. and a dense silicate glass is created.

In a second type of post-treatment, the converted body is advantageously fired in one operation to expel volatile constituents for consolidation to form a solid glass body with a geometric shape corresponding to the initial body. While organics and ammonia are driven off, alkali metal oxide remains and acts as a flux that lowers the temperature required for consolidation. The latter is usually close to the softening temperature (temperature at which the viscosity is ίο '* ⁶ poise), around 500 - 1500 ⁰ . The heating rate is only limited by the formation of bubbles and cracks, which must be avoided, as well as any deformation of the body. A support that prevents deformation can be valuable here.

To prepare the real solutions or suspensions were Eolloidlösungen inorganic salts, methyl or ethyl formate or reagent grade's acetate used "The composition of the related trade of silicates was the following ι

Colloidal silicate - 30% SiO ₂ , remainder water, potassium silicate - 8.3% KgO, 20.8% SiO ₂ , remainder water,

~ 9 - 20d808 / 1664

quaternary ammonium silicate - 9> 8% quaternary ammonium ion,

4-5% SiO ₂ , remainder water,

Sodium silicate - 6.75% Na ₂ O, 25.3% SiO ₂ , remainder water, lithium polysilicate - 2.1% Li ₂ O, 20% SiO ₂ , remainder water.

Even gelation could not be achieved with potassium or sodium silicate solutions alone, but only in a mixture with colloidal silica and / or quaternary ammonium silicate solutions.

The inorganic salts which can be used instead of the esters or together with them as gelling agents lower during hydrolysis Surprisingly, too, the pH to such an extent that the silica is polymerized. These are common Salts the representation by precipitation from aqueous solutions with a pH value greater than 5 and cations one Valence of at least 2. They are insoluble in slightly acidic, neutral or alkaline aqueous media. Salts the cations of which do not form any anionic hydroxo complexes are also insoluble in a strongly alkaline aqueous medium. However, all salts can be dissolved in mineral acids.

Can be used e.g. B. carbonates, hydroxides, borates and phosphates of cations with a valence of at least 2 of their For the sake of low solubility, all these salts are

2Ö9SQ8 / 1664

Silicates, quaternary ammonium silicate, or colloidal silica solutions tolerated for "a limited time.

It is not necessary to adhere to stoichiometric amounts. The range of variation is therefore very large. on the other hand For this reason, the conversion cannot be explained by exact chemical equations. An explanatory hypothesis but was developed on the basis of the following laboratory tests with the relatively) water-insoluble salt 4- MgCO_ »Mg (OH) p3cHpO. According to A certain amount of basic magnesium carbonate becomes its solubility product in an aqueous medium to a state of equilibrium dissociated:

4MgOO ₅ "Mg (OH) ₂ XH ₂ O <-» ^ Mg ⁺² -4- 4CO, + 20H "+ 3H ₃ O. The hydrolysis results in a pH value of about 10.5 ·

This equilibrium is disturbed by an alkali silicate or an alkaline colloidal silica solution and the silica is polymerized for one or more of the following reasons;

1. Since the pH value of the alkaline silicate solutions is greater than 10, the hydrolysis of the inorganic salt causes partial neutralization of the alkali or ammonium ion.

209808/1 664

2. The magnesium ions in solution partially replace the alkali metal or ammonium ions surrounding the silicate ions or colloidal silica particles; Since the magnesium ions are divalent, the negative charge of the colloidal silica is neutralized and the colloid becomes unstable.

5. Dissociated magnesium ions require a certain amount Water for hydration; this can cause the polymerization set in motion a salting-out effect, which increases with increasing Silica concentration is becoming more and more important.

A series of measurements of pH as a function of time from the first addition of 4MgO (U «Mg (OH) pxH, /) to the onset of gelation have shown that the neutralization of the alkali silicate solution is not solely for the polymerization is crucial. An increase in the pH value indicating the release of OH ions was observed, which probably on the replacement of the alkali ions immediately surrounding the silicate ions by magnesium ions and the beginning Polymerization is based. The subsequent drop in pH can reduce the neutralization effect brought about by the hydrolysis of the salt; can be attributed.

It is believed that then the silicic acid grid in two stages arises. First of all, colloidal silica particles are formed,

10 -

209808/1684

which are surrounded by an inner layer of hydroxyl ions and a more scattered outer layer of alkali ions, so that the colloid has an overall negative charge and the sol is stabilized on the one hand magnesium ions are smaller than alkali ions, so ^{there is room for more Mg +} ions in the outer layer, and on the other hand the magnesium ions are doubly positively charged. By neutralizing the negative charge of the colloid, the silica becomes unstable. If this neutralization occurred suddenly, e.g. By adding hydrogen ions in the form of a readily soluble acid or an acidic salt, the silica would coagulate to form a gel in which the various particles are only loosely connected by a few Si-O-Si bridges Salt like 4MgOO, »Mg (OH) ρ so slowly in solution that the pebbles Acid quite uniformly polymerized. The colloid particles can coalesce and result in a uniformly polymerized silica lattice in which alkali and magnesium ions are built in a regular arrangement.

The uniform and complete dissolution of the 4MgCO ₃ .Mg (0H) ₂ crystals in an alkali silicate solution was determined by X-ray diffraction analysis of the air-dried

- 11 -

209808/1664

ten gels detected. The gel was non-crystalline, the alkali silicate solution was thus a homogeneous alkali-magnesium-silica Polymer implemented.

Thus, the reaction of 4MgOO, -Mg (OH) g with alkali silicate solutions results Surprisingly, not the glassy ones usually obtained when alkali silicate solutions are air-dried. Substances, but continuously porous bodies. Another difference is that the glassy substances when heated Foam to over 100 °, as the enclosed water then evaporates.

Example I.

A colloid solution was prepared by adding 50 ecm of the mentioned, commercially available potassium silicate solution with 50 ecm of the mentioned, commercially available colloidal silica solution mixed and mixed with 4 ecm methyl acetate. The sol was stirred vigorously for 1 minute and then up to a height of about 5 now in containers made of chemically inert, plastic material filled. The containers were closed and the solution was closed by heating to 50 ° for 15 min solidified into a hard, transparent body. With further When heated to 50 ° for an hour, the body shrank about 1%. After cooling to room temperature, the container was opened and the contents allowed to air dry 4 days.

- 12 209808/1664

The air-dried, self-supporting, porous, plate-like bodies were then placed on refractory bricks laid, which had previously been coated with calcined Al ^ O, powder to allow even shrinkage during consolidation. The items were with a Speed of 50 ° / h heated to 450 ° on this Maintained temperature for four hours and then further heated to 6 ^ 0 ° at the same rate. The consolidation Fe of the objects to a transparent glass took place at this temperature in about 20 minutes. The total shrinkage in one dimension from the original wet gel to the final glass article was about 4-0%; the geometric dimensions however remained true to life.

Example II

50 ecm of the potassium silicate and 50 ecm of the colloidal silica solutions were mixed to form a colloid solution and 20 ecm of methyl acetate were vigorously stirred into this for 1 min. The sol was poured into a plastic container according to Example I, the container was sealed and the solution was added Hardened at 50 ° for 1 hour to a hard, transparent body. After cooling to room temperature, the body air dried in about 4 days.

The air-dried material was made according to the firing schedule of example I to a transparent glass article

- 1? 209808/1664

consolidated. Because of the high methyl acetate content3 in the The consolidated glass object shrank in the starting sol Compared to the wet gel by more than 50% and several samples showed "a tendency to crack formation during drying and firing. An ester addition of 20% by volume therefore appears for the practical use as a maximum.

Example III

Example I was repeated, but only 2 ecm Methyl acetate added. The curing at 50 during 10 Hours produced a gel that was not as hard as in the previous one Examples. 2% by volume of the ester addition therefore appears to be a practical minimum addition. After air drying, the porous body consolidated into a glass object according to Example I.

Example IV

In 100 ecm of a silica sol according to Example I. 4 ecm of methyl formate were mixed in thoroughly. The solution solidified to one in about 15 seconds at room temperature hoard gel, the viscosity increasing noticeably after 2-3 seconds. The following treatment was the same as the example I.

- 14 -

209808/166

The use of methyl formate as an ester promotes that extremely rapid gelation of the silica solutions and is therefore particularly favorable for technical operation Mixtures of different esters allow the conversion time to be regulated very precisely.

Example V

Ethyl acetate is basically usable, but the P production is due to its low solubility in water Solution and its comparatively slow hydrolysis take a long time. Thus 4 ecm of ethyl acetate were used as an emulsion in a mixture of 50 ecm of the sodium silicate solution and 50 ecm of the colloidal silica solution dispersed. In closed Containers formed hard gels after 15 hours at 85 °.

The further treatment for the creation of monolithic, porous bodies corresponds to Example I.

Example YI

A mixture of 50 ecm of the mentioned, commercially available quaternary ammonium silicate solution and 50 ecm of the mentioned Potassium silicate solution was added 4 ecm of ethyl formate. Gelation to a hard object occurred in about 2 minutes at room temperature. The further treatment Ms for Consolidation to a glass object corresponded to the example

209808 / 166A

Example VII

IJif »commercially available colloidal silica solution; is in the ρ.Π mean not strong enough alkaline to remove the added To hydrolyze esters in practically useful times. After all, an addition of up to about 10% by volume shortens Ammonia the gelation time of the silica brine after the ester has been added. The addition of ammonia also hardens the G-EL much faster, which is important for technical operation.

10 ecm of concentrated NILOH with reagent quality were in Stir in 100 ecm of the colloidal silica solution and add 4 ecm of methyl formate to the mixture. At room temperature Gel formation begins in three minutes and the gel has hardened well after 15 minutes. After treatment accordingly Example I resulted in a porous body which resulted in an opal glass body true to size, albeit shrunk by 50% was consolidated.

A clear glass article was made by treating the reacted gel with nitric acid to remove residual alkali and then air drying and firing.

Example VIII

The invention also enables the manufacture of articles that contain a filler material. Using

-16-209808 / 1664

Fillers, the mechanical strength is improved and the electrical and thermal characteristics can be influenced. · Catalysts can also be placed in the silica grid build in. Further advantages of using fillers are known to the person skilled in the art.

As an example of commercially available silica, HgSiO, -nHgO 50 g ^v n ° ecm gradually into a solution of 100

^ colloidal silica and 10 ecm of concentrated KH ^ OH with The reagent is stirred in. After stirring for 4 hours, the Suspension 4 ecm of methyl formate added. Started in about 2 minutes increase the viscosity. Once the viscosity was high enough to cause sedimentation of the suspended silica To avoid this (about 5 min.), the suspension was poured into plastic molds and began to close in about 15 min a hard, white gel to harden. The samples were allowed to cool to room temperature and in air coherent porous article dried, and then

by firing to 1500 ⁰ at 100 ° / hour. consolidated to form an opal glass containing the silicon compound. The one-dimensional shrinkage was around 20%, but here too the original geometric shape was retained.

The following examples illustrate the effectiveness of various inorganic salts for the polymerization of alkali silicate,

- 17 209808/1664

quaternary ammonium silicate and colloidal silica solutions to a coherent, porous body, which by subsequent heat treatment to a solid glass object can be consolidated. As the procedural steps for everyone Salts are essentially the same, these are discussed in advance.

The inorganic salts should be used in the form of fine-grained powder, since otherwise a completely uniform reaction product is difficult to achieve because of their poor solubility. The powder is slowly stirred into the silicate solution, namely ^ after the respective silicate solution and the readiness of the inorganic salt to react at a temperature lying between room temperature and the boiling point of the silicate solution. In addition, the mixing process is carried out in closed containers in order to avoid evaporation of water and a reaction with the COp present in the air. The viscosity of the suspension increases. As soon as there is no longer any risk of sedimentation even without stirring, the mixture is poured into plastic containers or suitable molds.

The hardening process is practically a continuation of the conversion of the inorganic salt and the silicate solution. After inserting: 0> e <\ er suspension Ln enters the plastic container ₍ depending on

- 18 20 9 000/16 64

the nature of the sol present, the gelation of the suspension. at room temperature or at a slightly higher temperature (up to to about 100) a. The wet gel will turn into a firm, translucent one Gel and thus shows the completeness of the implementation of the inorganic salt and its assimilation into the silica grid on. The curing usually takes 1-20 hours. Longer times are harmless but also without revealing To use.

After hardening, the gel is, if necessary, at room temperature left to cool, then opened the plastic container and allowed the gel to air dry. In some cases However, drying in the air can lead to hoisting, so that in these cases drying is carried out in a known manner Steam or other regulated atmosphere, or with the help of organic solvents is made · The duration of air drying usually depends on the shape, dimensions and in particular the thickness of the object and lies usually in the range of 2-5 days.

The air-dried porous body can then become a solid porous object fired or consolidated into a non-porous glass object. When burning is first make sure that the water absorbed in the silica grid escapes without bubbles. When using quater-

- 19 2098ÜÖ / 1664

ner ammonium silicate as the starting material must also complete the decomposition and oxidation of the organic Carbon components are ensured. The burning schedule can be adjusted in such a way that the pore size continuously changes from the size of the air-dried Materials up to the finished, consolidated, non-porous glass can be modified. The burning process also influences the activity of the porous material, so that this too Feature can be modified.

The differential heat analysis is used to determine the consolidation temperature suitable. Empirically, the preferred consolidation temperature was approximately 10-100 ° below the The devitrification temperature of the respective glass is determined. the to compress the porous material into a solid glass The time required is inversely proportional to the temperature maintained in the consolidation area. Usually times of 5-60 minutes in the consolidation temperature range are very satisfactory. As the glasses in question are capable of devitrification, the duration of the treatment is best not exceeded.

However, it has been found that glass compositions with a high silica content and a low alkali or oxide content are less easily devitrified and therefore less precisely regulated

- 20 -

209808/1664

Get along with consolidation conditions. As these glass compositions are difficult to manufacture at the same time as conventional glass manufacturing processes, this results in a special feature surprising and favorable field of application of the invention.

The following non-limiting examples further illustrate the invention. In principle, the implementation time increases increasingly with the listed silica solutions in the order: colloidal silica, quaternary ammonium silicate, Lithium silicate, potassium silicate, sodium silicate. To prevent cracks and cracks in the finished glass object, in Fired in a controlled atmosphere, initially in an atmosphere with 100% humidity, which then gradually becomes linear was reduced to the ambient conditions. In the following examples, the required moisture Delivered by steam. Atmospheres are also suitable, however from methanol, ethanol or other solvents.

Example IX

A solution of 50 cc of the above-mentioned potassium silicate ιινΛ 50 cc of the quaternary ammonium silicate was prepared in a closed plastic container and into the solution: stirred 10 g 4MgOO ₅ .MG (OH) ₂ · ηΗ ₂ 0 (40 wt% MgO content.). The resulting suspension was 30 min. In a bath of boiling

- 21 -

209808/1664

Water stirred; the viscosity had then increased so that settling of the salt was no longer to be feared even without stirring. The suspension was then placed in plastic molds, covered and cured for 16 hours at 80 °. The molded body consisted of a translucent gel in which the Salt was dissolved.

The gel in the closed mold was brought into contact with absolute methanol at 50 ° for four days, and thereby Most of the water in the body's structure is replaced with methanol. Compartment cooling to room temperature was the gel in Controlled atmosphere dried for 5 days and resulted in a cohesive, self-supporting, air-dried porous body.

If a consolidated glass object is desired, the air-dried body is first removed from the plastic mold at a speed of 25 ° / hour. heated to 450 ° and at this temperature 8 ° t. held to ensure complete oxidation of the organic ammonium complex. Then it is heated to 870 ° - 930 ° for about 1/4 1/2 hour until it has consolidated. The heating rate for this second stage is arbitrary, because the volatile constituents escape already on the first stage. In general, a heating rate of 50-100 ° / ßtd. chosen.

209303/1664

The consolidated object was a see-through one . K ^ O-MgO-SiO ^, glass that has an isotropically shrunk true to shape Possessed shape corresponding to the molded body.

Example X

5 g of PbGO were stirred in 100 ecm of the sodium silicate solution. The reaction of the PbCO ₇ with the sodium silicate solution proceeded so rapidly that after 5 minutes of stirring the viscosity "had already reached a level excluding the precipitation of FbOO- even without stirring. The suspension was then placed in a plastic mold, covered and cured for 16 hours at 80. The resulting gel was then cooled to room temperature, treated with absolute methanol as in the previous example and air-dried for 5 days in a regulated atmosphere to form a coherent, monolithic, porous body.

Since the batch did not contain any quaternary ammonium silicate, it was unnecessary the heat treatment to remove the organic complex according to the previous example · The porous The body was therefore only at moderate speed (usually around 50 - 100 ° / hour) on the consolidation area of 600 - 700 ° heated and held for 10 minutes.

The final product was a NagO-FbO-SiO ^ glass article manufactured by the original shape had shrunk isotropically.

- 23 209808/1664

Example XI

10 g of ZnOO "were stirred into 100 ecm of the above-mentioned potassium silicate solution"! After stirring for about 15 minutes, the viscosity had reached the level that prevented ZnOO from settling. The gel was then hardened as in Example X and air-dried. The porous body was consolidated by heating to 700 ° for 1 hour to form an isotropically shrunk, that is to say true-to-shape, image of the porous shape. The glass consisted of K ₂ O

Example XII

5 g of basic chromium carbonate were dissolved in 100 ecm colloidal silicate solution, stabilized by adding ammonia, stirred. The slow reaction of the chromium carbonate with the solution required continuous stirring for 30 minutes in a water bath, to bring about a sufficient increase in viscosity and avoid sedimentation of the salt.

During the subsequent curing in a covered plastic container at 80 ° and for 16 hours, this came off Chromium salt in the silicate structure. The gel was then used to Formation of a coherent, self-supporting, porous body in a controlled atmosphere for 4 days air dried. Since the ammonia content was low (about 5% by weight), a heat treatment at an intermediate temperature as in Example IX, not required.

- 24- _ 209Θ08 / 1 8βΛ

Opaque CroO ^ -SiCL bodies, which had shrunk isotropically from their original shape, were obtained by consolidating the porous bodies at 1500 ° for 1/2 hour. when the GTpO ₇ content is kept below 3% by weight.

Example XIII
By precipitating a lanthanum nitrate solution with an excess

W shot ammonium carbonate was prepared a basic lanthanum carbonate. The precipitate was filtered, washed repeatedly with hot water and dried at 110 °. 10 g of this lanthanum carbonate were suspended in 100 ecm of the quaternary ammonium silicate and the mixture stirred at water bath temperatures until the viscosity was high enough to allow transfer to plastic molds (usually about 1 hour). The molds were covered and the gel cured for 16 hours at 80 °, cooled to room temperature and for 5 days

^ in a regulated atmosphere to a cohesive, porous body air-dried.

The air-dried body was at 25 ° / ßtd. heated to 450 ° and 8 hours to remove the carbon constituent of the to oxidize quaternary ammonium silicate. The resulting porous object of the La ^ O ^ -SiOp system is particularly favorable

209808 / 16.64

Can be used as a catalyst because it is in the silica lattice the rare earth ion is very evenly distributed.

Example XIV

A slurry of 5 S 3ZnO-2BpO, with 20 ecm HpO was made stirred into 100 ecm of the potassium silicate solution. After 10 min. With stirring time, the viscosity was high enough to prevent the zinc borate from settling. The material was in plastic molds transferred, covered and cured for 1 hour at 85 °. The resulting gel was cooled to room temperature and in air-dried in a controlled atmosphere to form a cohesive porous body. Long curing times affect the Strength of the body, but on the other hand allow the pore sizes of the air-dried material to be modified. The porous body can optionally be consolidated into a glass of the system ΚρΟ-ΖηΟ-ΒρΟ -, - SiOp. This is a True-to-shape, isotropically shrunk image of the original molding. The consolidation takes place by heating up 700 ° - 800 ° for 1/2 - 1 hour

Example XV

10 g Fb (BOg ^ HpO were added 30 ecm HpQ and the resulting Thickening in 100 ecm of the sodium silicate solution mixed in. After only 3 minutes of stirring, strong gel formation began. The gel was placed in a plastic

- 26 209808 / 166A originally inspected

shape transferred, covered, cured for 15 min. at 70 ° and in 2nd Air-cooled for days in a regulated atmosphere at room temperature. The monolithic, porous body thus formed could to a glass object of the composition NaoO-FbO-BpO ^ -SiO be consolidated by heating to 700 ° for 1/2 hour.

Example XTI

A slurry of 10 g of aluminum borate in 20 ecm HpO and w 10 ecm concentrated NH ^ OH was suspended in a mixture of 50 ecm of the potassium silicate solution and 50 ecm of the quaternary ammonium silicate solution. After about 4 hours of stirring in a water bath, gelation occurred. The material was transferred to plastic molds, covered and cured for 16 hours at 85 °. After cooling to room temperature, the gel was air-dried in a controlled atmosphere in four days to form a cohesive, porous body.

As a result of the use of quaternary ammonium silicate in the Approach the organic carbon component had to be burned out before the consolidation, according to the Example XIII. The article was then turned into an isotropic conformal body by heating to 7 ° O ° for 45 min. consolidated·

- 27 -

209808/1664

Example XVII

A suspension of 10 g Fb (OH) ₂ in 100 ecm potassium silicate solution was stirred into a water bath until the viscosity increased considerably, which is usually the case after about 1 hour. The material was placed in a plastic foil, covered and cured for 2 hours at 85 °. The resulting gel was cooled to room temperature and air-dried in a controlled atmosphere for four days. The self-supporting, porous body can optionally be consolidated into a solid glass with the composition KpO-PbO-SiOp by heating to 700 ° for 15 minutes.

Example XVTII

The previous example was repeated, but 10 g of Zn (OH) _{2 were} used instead of Pb (OH) 2. Here, too, a porous body and, if desired, a solid glass could be produced,

Example XIX

A suspension of 10 g of Mg (OH) ρ in 60 ecm of the potassium silicate solution and 40 ecm of the quaternary ammonium silicate solution was stirred into a water bath for 3 hours until the viscosity prevented the _{Mg (OH) 2 from settling.} The suspension was then transferred to plastic molds, covered and cured for 16 hours at 85 °. The hardened gel was cooled to room temperature and air-dried in a controlled atmosphere in 3 days to form a coherent, porous body.

- 28 209808 / 166A

After reheating to expel the organic Carbon component of the quaternary ammonium silicate !? corresponding the porous material was added to example XIII by heating to 700-800 ° for about 1/4 to 1 hour. one Consolidated isotropically shrunk true to shape image of the original shape. The glass had the composition

Example XX

10 g of Zn -, (PO ^) 2 were in a mixture of 50 ecm of the colloid Stir in silica and 50 ecm of the potassium silicate solution. Considerable gel formation occurred after a stirring time of 4 minutes. The gel was in 10 hours at 85 ° in a covered plastic container cured and in four days at room temperature in a controlled atmosphere to a cohesive, porous Body air dried. By heating to about 4-50 ° a solid body with an open structure was created, which z. B. as Filter or catalyst is very suitable.

Example XXI

A slurry of 10 g AlPO ^ in 20 ecm HpO and 10 ecm concentrated NH ^ OH was in 100 ecm of the potassium silicate solution suspended. The suspension was stirred on a water bath for 3 hours to induce appreciable gel formation. To The material was transferred into covered plastic molds

- 29 -

16 hours "cured at 85 °. The cured gel was in four Air-dried for days in a regulated atmosphere at room temperature, whereby a coherent porous body was created. By burning the porous body at 800 ° during For 15 minutes, a solid glass article of the composition became

generated.

The examples clearly show that certain inorganic salts when added to silicate solutions, colloid solutions or Hydrolyze suspensions and form products that lower the pH of the solution in question and polymerize the silica. One of the main advantages of using inorganic salts instead of organic esters for polymerisation is that specific, including a number of reasons valuable metal oxides can remain in the solid phase as a product of hydrolysis after gel formation. These oxides are z. B. cheap as a glass-forming agent, as an opalizing agent, to change certain physical properties of the Final product, etc. These oxides remain in the glass article when the reacted or porous body is fired, so that a glass with certain properties can be produced.

In the selection of suitable inorganic salts that Kiene acid! Is the eighth% u primarily on polymerislept and no herewith in W "htbewerb kicking substances, such as

209808/166 4 bath ORIGINAL

ζ. B. crystalline silicates arise. The same applies to the silicate solutions as to the reaction with organic esters, ie the silica must have a minimum concentration of 1 mol / l and a pH greater than 10.

To better regulate the implementation process, the salt do not cause immediate gel formation, as this would not take place evenly in the solution. In summary the salt should meet the following requirements: once the solution, colloid solution or suspension of the

/on

Salts' a little below that causing the polymerization pH value so that a uniform and sufficiently slow conversion takes place. On the other hand, there is also a salt with very low solubility but with the ability to become one Can be used to hydrolyze pH values significantly below 10, because its slow speed of resolution determines the speed of implementation. Second is the inorganic Salt is also said to be a functional part of the final Glass composition and should therefore be able to be converted to form glass at a low temperature. In general, divalent or trivalent oxides and those acting as network modifiers in the glass are therefore favorable Salts. Examples IX-XXI show the beneficial use of the carbonates, borates, hydroxides and phosphates of various types two- and three-terminal metal ions.

- 31 2098 08/1664

" ⁵¹ ". 21288Λ5

Thus, the usable inorganic salts result in solutions, colloid solutions or suspensions with a pH below 10, which show no tendency to form crystalline precipitates instead of the desired polymerization

As the examples ΙΣ - 3XE show, the polymerized First of all, water and volatile components are removed from the gel. It is then burned into a glass. The various non-volatile oxides, such as di- and trivalent oxides and alkali metal oxides, remain in the produced porous body or the glass object and affect its properties. If desired, the hardened Gel can also be leached or selectively volatilized with a suitable solvent, so that a porous Silica body remains. Depending on the solvent used, the porous body then contains the two and trivalent oxides or alkali metal oxides or is free from these. The total porosity and pore size of these objects is similar to the products reacted with esters. The porous glass body can be sintered into a solid glass are, of course, at much higher temperatures than with the more favorable burning of the body that has not been exhausted.

To ensure the lowering of the pH value below 10 and to polymerize the SiO £ to form a gel, the proportion of

- 52 -209808/1664

inorganic salt are at least 2 wt.% ". The preferred Amount is 5 - 10% · Additives of more than 20% are for the desired implementation is not necessary per se, but can be beneficial if the salt in the end product does the job a filler should meet.

In a further modification of the end product produced, the starting approach can be mechanical or electrical or chemical Properties influencing fillers are added, such as. B. inorganic fibers, vrie SiG or AIpO-zur Improving mechanical strength or metal particles to improve electrical or thermal Characteristics.

209808 / T 664

Claims (10)

Process for the production of solid oil bodies or self-supporting, monolithic, porous silicate objects in which real solutions and / or colloid solutions and / or suspensions with pH 10-15 and 1-12 mol SiO ₂ Zl solution from the silicate solutions of alkali metal silicates, organic ammonium silicates, colloid silicates or Mixtures of the same are prepared and reacted with formaldehyde, faraformaldehyde, glyoxal, formamide or mixtures thereof at a temperature between the freezing and boiling point of the solution (the pH value falls below 10 and the SiO ^ polymerizes to the gel, according to the patent (patent application P% 1ZΫ'βStV, £}> characterized in that the formaldehyde, paraformaldehyde, glyoxal or formamide is completely or partially replaced by an ester with a maximum of 5 "and preferably a maximum of 4 carbon atoms, such as methyl formate, ethyl formate, methyl acetate or Ethyl acetate or mixtures thereof or by an inorganic salt such as a carbonate and / or hydroxide and / or borate and / or phosphate of a cation with an advertising d humidity of at least 2, and that the gel in air at a self-supporting, monolithic, porous article dried or at a temperature near the softening point of the respective composition temperature It is fired until it is consolidated into a solid Sililcat glass body. ^H f } .- fii, ORfGfNAL INSPECTED 209Ö08 / .1664 2. The method according to claim 1, characterized in that
that the ester is 2-20 % by volume and preferably 3-10 % by volume
of the solution. 3 · The method according to claim 1, characterized in that gel single leaning,
that the real solutions, colloid solutions and / or suspensions contain 3-12 mol SiO ^ / l solution. 4 ·. Process according to claim I _1, characterized in that the alkali metal silicates are lithium, potassium, sodium silicate
or mixtures thereof. 5. The method according to claim 1, characterized in that the organic ammonium silicate is a quaternary ammonium silicate is. 6. The method according to claim 1, characterized in that * the reaction temperature between room temperature and 100 °
lies. 7. The method according to claim 1, characterized in that the lowering of the pH value below 10 and for the polymerization of the SiOp sufficient time is 5 seconds - 24 hours. ÖBK »NAL INSPECTED 2 O <) 8 O 8/1664 8. The method according to claim 1, characterized in that the at least divalent cation is magnesium, lead, zinc, ohrom, lanthanum or aluminum. 9 · The method according to claim 1, characterized in that the air drying is carried out between room temperature and the deformation temperature of the object, or that at 500 - 1500 ° is burned. 10. The method according to claim 1, characterized in that the time sufficient for consolidation is 5-60 minutes. 209808/1664 ORKSINAL INSPECTED