FI69050B - ORGANISM SKUM - Google Patents

Description

69050

INORGANIC FOAM

The present invention comprises a process for preparing a light, water-resistant and completely non-combustible alkali silicate-based solid foam using the reaction result of reactive silica and alkali hydroxide solution and using zinc and boron compounds to provide water resistance in a flotation process at 400 to 450 ° C. The product contains less than 5% zinc compound, less than 10% boron compound, SiO 2: NagO is between 1-5.

It is known that an aqueous solution of alkali silicates, most commonly sodium silicate, can be foamed into a porous mass by several methods. The most commonly used method is to remove the water of the solution by rapid and efficient heating above 100 ° C, whereby the boiling water vapor swells the alkali silicate into a porous foam. The alkali silicate solution can also be foamed using efficient mechanical stirring or by adding a low temperature volatile liquid or a gas-releasing compound to the solution, the released gas forming foamable gas bubbles in the silicate solution, some methods to mention.

However, the foam prepared by the above methods is unusable for most purposes because it is completely water soluble as such. Various ways to improve the water resistance of alkali silicate foam have been proposed in the patent literature. They are generally based on the addition of certain water-resistant compounds, which may be either inorganic or organic, to the alkali silicate solution before foaming.

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The former group typically includes certain acids and their divalent or userapvalent metal salts, the latter generally organic acids and compounds which form acids in aqueous solution. The finished foam can also be subsequently protected against the effects of water by surface treatment or impregnation with a suitable substance.

In British Patent Publication 2008086, page 3, lines 48-55, it is shown that the product obtains optimal properties when various oxides are used in the following proportions: 55 p- $ SiO 2, about 10% boron oxide, about 15% sodium oxide, about 15% alumina and about 5% certain additives which confer specific characteristics on the product.

Other additives which increase the swelling of the product to a certain extent and which can be used to obtain products with a low bulk density are, for example, iron oxide, zinc oxide, lead oxide and magnesium oxide.

However, the result thus obtained is generally more or less unsatisfactory. In order to achieve sufficient water resistance, it is often necessary to use quite large amounts of additives, even in an almost stoichiometric ratio to the amount of alkali silicate used. In most cases, this means a significant increase in raw material costs, which in turn reduces the profitability of the product. Likewise, a large amount of additive impairs the foamability of the alkali silicate solution, in which case the product may become too heavy by volume to be used, for example, as a thermal insulation material.

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Depending on the flotation method and the composition of the substance, the alkali silicate solution can be flotated into products with very different bulk weights. With a bulk density of • 3 50 to 150 kg / m, the thermal conductivity of the product is typically λ = 0.04 to 0.05 W / m * C and the compressive strength is 100 to 2,300 kN / m. In this case, the product is very suitable for use as a non-combustible thermal insulation material, e.g. as a sheet, as a core material for sand-wich elements, etc., if its material composition is water-resistant.

The use of organic compounds to improve the water resistance of the alkali silicate foam is therefore not advantageous, since this has to compromise one of the essential properties of the product, complete non-combustibility.

As the alkali silicate solution, a sodium silicate solution having a SiO 2: Na 2 O ratio of between 2.5 and 5.0 is generally most preferred. A high SiO 2 content in the water resistance of the foam product is preferable, but disadvantageous in terms of foamability. The most commonly used commercial sodium water glass solution with SiO 2:

Na 2 O = 3.3 and with a dry matter content of 35-40%.

It was found that a product corresponding to a commercial water glass solution can be prepared by dissolving reactive silica in an amount corresponding to the desired SiO 2: Na 2 O ratio in a 10 to 15 L NaOH solution, most preferably at a temperature of 50 to 80 ° C. The use of more concentrated NaOH causes the resulting water glass solution to become very viscous, as its viscosity is very strongly dependent on the amount of water.

69050 4 The present invention comprises a method by which the above-mentioned weaknesses of alkali silicate foam products can be substantially eliminated. The efficiency of the method is based on the fact that by selecting the most effective additives and the optimal manufacturing conditions, very small amounts of additives can be obtained in a product which is practically water-resistant and low in bulk density, thus being an excellent non-combustible thermal insulation material.

The present invention is based on the use of two compounds, one a zinc compound and the other a boron compound, as an additive to improve the water resistance of the product. Of the zinc compounds ZnO and the boron compounds H 2 BO 2 were found to be particularly effective. Both of these substances are compounds known in the art patent literature, which have been proposed for use in various mixtures, among other substances, with the aim of a water-resistant water glass foam. When used alone, they are both found to be quite effective additives in improving the water resistance of alkali silicates, but achieving really low water solubility requires larger amounts of substances. In this case, the previously mentioned problem caused by the use of additives is encountered: an increase in the amount of additives essential for water resistance impairs the foaming properties of the alkali silicate solutions, which is reflected in the increased bulk density of the product.

Surprisingly, it was found that by using both ZnO and boric acid simultaneously as additives under certain conditions, products with surprisingly good water resistance were obtained with very small amounts of substances, completely without other additives. Already amounts as low (based on the finished product) as <2.5% ZnO and <5% H 2 BO yielded products with a density of

• J O J

<120 kg / mJ and which were practically

II

5 69050 or almost insoluble in water (depending on the method of analysis, reference is made to the methods to be described later). The results suggest a clear synergistic effect between the mentioned substances.

The use of even small amounts of substances requires that their potency be fully utilized. Dissolving substances in a viscous aqueous glass solution is usually difficult and complete dissolution is difficult to ensure. Thus, the maximum efficiency of the additives was found to be achieved by preparing a water glass solution by dissolving reactive SiO 2 as previously described in a NaOH solution in which the additives had been previously dissolved. Furthermore, in order to obtain the maximum effect of the additives, it was found that the flotation step should take place at a sufficiently high temperature, preferably at 400-450 ° C.

The process according to the invention is presented step by step as follows: (1) Additives, most preferably boric acid and ZnO, were dissolved in a 10-15 $ NaOH solution together, corresponding to 0.5-10 l each in the foamed final product. The best result, taking into account the water resistance and volume weight of the final product, is obtained by using ZnOra 1 - 3% boric acid 3 - 7% · Dissolution can be carried out under the most comfortable stirring at a temperature of 50 - 80 * C.

(2) Dissolve reactive SiO 2 in the resulting NaOH solution in an amount corresponding to the desired NaO 2 Na 2 O ratio of the water glass.

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By reactive SiO 2 is meant here various high surface area silicic acids such as diatomaceous earth, various commercial gel-like, precipitated and pyrogenic silicas, some industrial wastes, for example leaching wastes from phlogopite mica. The dissolution is preferably carried out at a temperature of 50 to 80 ° C with constant stirring, the time required generally being 15 to 60 minutes, depending on the nature and amount of SiO 2 and the amount of additives used. The amounts of substances can be selected so that the SiO 2: Na 2 O ratio of the obtained water glass is e.g. between 1.0 and 5.0, but preferably between 3.0 and 4.0.

(3) The resulting water glass solution is foamed in an oven at high temperature by evaporating off the water. In order to obtain a body of the desired shape, the foaming should be carried out in a mold, which should preferably be detachable. Instead of an ordinary oven, a microwave oven, for example, can also be used. The water glass solution is already foamed at about 100 ° C, but in order to achieve a low bulk density and good water resistance, a sufficiently high temperature should be used, preferably 400-450 ° C.

The water glass solution obtained in step (2) described above generally contains an excess of water for flotation.

This excess can be removed by drying if desired. For example, a "water glass solution" containing 20 to 40% water is a hard and solid substance which, in many cases, is easier to handle as such or ground to the desired size than a solution containing more viscose than water.

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The water resistance quality of the foams prepared by the presented method was evaluated by two methods: (I) A 4 x 4 x 16 cm foam piece was crushed and ground and a 10 g sample (-0.5 + 0.1 mm) was taken and treated with 200 ml of boiling water. water for 1 h. The residual solid was filtered off and dried at 450 ° C, and the amount dissolved was calculated from the difference in weight.

(II) A 4 x 4 x 16 cm foam body was kept immersed in 50 ° C water for 24 h. The piece was crushed, washed, dried and the weight loss was determined.

Test (I) is very demanding in terms of conditions, since a similar method is used, for example, to determine the water solubility of glasses (standard SS 13632). Test (II), in turn, better reflects the extent to which water can in practice affect entire foam structures. Thus, the solubility values determined by the former method were higher than those of the latter.

By preparing the foams as described above using a foaming temperature of 450 ° C, a SiO 2: Ν3 £ £ ratio of 3.0 to 3.75, ZnO 1-2.5% and boric acid 2 to 6% by weight of the final product, foams were obtained, having a density of typically 100 to 120 kg / m 2, a solubility of 3 to 10% as determined by method (I) and 0 to 3% as determined by method (II). In particular, the latter figures show that the products prepared by the method of the present invention have excellent water resistance.

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The prepared foam bodies were also tested for the effect of air vapor. The test pieces were kept for a long time in different weather conditions (weather cabinet, protected from rainwater in room air) and their weight and length extractions were monitored.

The following examples illustrate the invention: Example 1 1.75 g of ZnO was dissolved in 183.6 g of 11% NaOH solution at 75 ° C. While maintaining the solution at said temperature, 53.3 g of phlogopite mica dissolution waste (93.8% SiO 2, 5.7% H 2 O, impurities 0.5%) was added thereto with constant stirring. Stirring was continued for 60 min, by which time all of the SiO2 had dissolved. The resulting solution was cloudy due to partial precipitation of zinc as silicates. The amounts of substances used corresponded to a SiO 2: 2: Na 2 O ratio of 3.3 (molar ratio) in the obtained water glass solution. The resulting viscous solution was transferred to a 4 x 16 cm bottom steel mold which was placed in an oven at 450 ° C. In the oven, the solution foamed and after 1.5 h of heat treatment, all the water was considered to have evaporated, at which point the mold was removed from the oven. A 4 x 4 x 16 cm piece was cut from the resulting foam,

O

whose density was determined to be 78 kg / m 2. The body was crushed and its solubility in boiling water was determined according to method (II) above. The solubility was 59%.

Example 2

Example 1 was repeated using 4 g of H-B0 * instead of ZnO. Otherwise, the procedure was as above.

5 j o

The foam obtained had a density of 83 kg / mJ and a solubility in boiling water of 45 ° as determined according to method (I).

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Example 3

Examples 1 and 2 were combined using simultaneously 1.75 g of ZnO and 4 g of H 2 BO 4. Otherwise, the procedure was as described in Example 1. The foam obtained had a density of 103 kg / m 3 and a solubility in boiling water, determined according to method (1), of only 5.5 Ϊ, which can be considered very low given the complexity of the test.

Example 4

Example 1 was repeated using 2.5 g of ZnO and 2.5 g of H 2 O 2 · · 2 · Otherwise, the procedure was as described in Example I. The density of the obtained foam body was 116 kg / m 2. The solubility of the body was determined according to the above method (II) by immersing it in water at 50 ° C for 24 h. As determined, the solubility of the body was 0.2%.

Example 5

In the same manner as in Example 1, 4 similar batches of solution were prepared using 5 g of ZnO, 201.9 g of II% NaOH solution and 53.3 g of phlogopite leach waste. The amounts of substances in the obtained water glass solution corresponded to a SiO 2: Na 2 O ratio of 3.0. Foaming was performed at temperatures of 290, 340, 410 and 440 * 0. The densities of the foam bodies obtained were 193, 178, 83 and 69 kg / m 2, respectively, and the solubilities determined according to method (II) were 23.1%, 7.3%, 2.9% and 2.8%. The results clearly show the beneficial effect of high temperature in terms of both bulk density and solubility.

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Example 6

According to Example 1, two pieces were prepared,

in which 1.5 g of ZnO was used in the amounts of additives

and 3 g H_B0o and in the other 1.5 g ZnO and 4 g 1 j 3.

H ^ BO ^ · The densities of the bodies were 93 kg / m 3 and 98 kg / m 2. The bodies were kept in the open air exposed to normal ambient temperature and humidity fluctuations, but protected from rainwater. After a one-year exposure period, the weight gain of the bodies was 7.5% and 2.9%, and the elongations were 0.075% and 0.012%.

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Claims (2)

69050 A process for preparing a water-resistant alkali silicate-based foaming product, wherein the spent alkali silicate is prepared by dissolving reactive silica in an alkali hydroxide solution and using one zinc compound and one boron compound at the same time The process takes place in the temperature range from 400 to 450 ° C, the product obtained having less than 5% of a zinc compound, less than 10% of a boron compound and a SiO 2: Na 2 O ratio of 1 to 5. Process according to Claim 1, characterized in that the zinc compound is ZnO. Process according to Claim 1, characterized in that the boron compound is H 2 BO 2.