DE1015734B - Process for making a calcium silicate product - Google Patents

Description

Process for Making a Calcium Silicate Product The invention refers to the manufacture of a calcium silicate product made from a combination of compounds 4 Ca0. 5 Si02. 5 H20 and 5 Ca0. 5 Si02. 1120 exists.

From US Pat. No. 2,547,127 it is known that equimolar Amounts of lime and silica dispersed in water at increased Temperatures and pressures with binding of the crystalline xonotlite, 5Ca0. 5S102. 11.0, respond. The crystals of this calcium silicate hydrate have a latte-like shape Structure and can grow together to form molded bodies in a wide range of bulk density, which, among other things, depends on the concentration or the water-solid volume ratio depends in the starting and reaction mixture. The molar ratio Ca0: Si02 of the starting material must be 1 here.

The other component of the combination product made according to the invention is the naturally occurring silicate tobermorite, 4Ca0. 5Si02.5H20, in which the Ca0: Si02 molar ratio = 0.8. Its crystals have thinner structure Dandruff. According to the present invention it has been found that in mixtures of finely divided reactive lime and finely divided reactive silicon dioxide and water, in which the Ca0: Si02 ratio is above 0.8 and below 1 and the water-solids ratio (Weight) is about 3: 1 to 9: 1, at temperatures of about 125 to a little above 200 ° C and appropriate pressures to prevent boiling, d. H. about 3 up to 16 atm, essentially the entire lime component gradually dissolved and can be reacted with the silica component and become a integrated intimate and uniform mixture of a dispersion of flaky tobermorite crystals and long, thin slat-like xonotlite crystals leads. Both connections arise in fine-grained crystalline structure, which is evenly made up of finely divided cavities is interspersed.

To achieve this reaction it is necessary that calcium oxide and Silicon dioxide is in finely divided reactive form. In particular that Silica must have a particle size such that the diameter of the particles 44 microns or smaller. An even finer degree of division can be achieved, for. Am a colloid mill. This shortens the time needed to solve and react necessary time. The lime can also advantageously be finely ground; but that seems less necessary, especially when he's in shape freshly slaked lime is used, which is mixed with hot water, the fineness and the degree of division and dispersity as well as the solubility to increase.

As a further condition, the reaction must be carried out in an aqueous dispersion of the reacting solids so that they can react unhindered with one another and with the intermediate products formed in the course of the reaction during the entire reaction time. Such a dispersion is intended, for example, to achieve a distance between the dispersed particles which is at least equal to their average diameter in each direction, which corresponds to a volume ratio of water to solid of about 7: 1 (weight ratio 3: 1). It is advantageous to choose a greater distance between the particles, ie a higher water-solids volume ratio, specifically up to about 26: 1 (weight ratio 9: 1). The water content of the mixture is chosen depending on the desired density of the end product.

The S'02 used for the reaction is expediently in the form of Quartz, because it makes the response time relatively short. One can also use other forms of SiO 2 such as silica, kieselguhr, tripoli, and the like; but this may be due to the physical effect of the originally hydrated and the more gelatinous state of these Si 02 forms have a longer reaction time become necessary until the conversion is completed.

Instead of or in addition to free Ca0 and 502, a material can also be used in which these two constituents are already bound to one another, e.g. B. in Portland cement and in the blast furnace slag. In this case the rate is calculated taking into account the reactive lime and silicon dioxide contained in the cement. So z. B., 100 parts Portland cement mixed with 62 parts of quartz to provide a ratio of 0.80 Ca 1.0 Si 0 to produce 0, or with 60 parts of quartz for a ratio of 0.825 to 1.0 Si02 Ca0. Such a combination of lime and silicon dioxide, as is found in Portland cement, seems to make both components particularly reactive, especially in a very finely ground state. In a corresponding manner, compounds with a different lime / silicon dioxide ratio, in which lime and silicon dioxide are similarly reactive with reactive quartz or reactive silicic acid in an aqueous medium, can also be used.

As for the reaction temperature, it is under optimal conditions a value of 175 'is high enough for the conversion to be complete in about 8 hours is done. Another increase in temperature speeds up the reaction, but it does it is advisable not to significantly exceed the temperature of 200 °, because over 200 ° the formation of xonotlite predominates too much. The practical range is therefore between about 125 and 203 °. The pressure is increased accordingly to accommodate the To prevent boiling, e.g. B. in an autoclave.

The reaction time depends on the type and condition of the starting materials such as on the reaction temperature. If you're working at 175 degrees or above, that's how hot it is the reaction mixture is generally in about 1 to 2 hours to the desired Worth it, it will last about 6 to 8 hours or 16 hours at this level and cool then to room temperature, e.g. B. in an hour or less for the long ones Try or in 8 to 10 hours for the shorter attempts. At lower temperatures the reaction speed is slower; she is ; at 162 ° to about half decreased and amounts to 15 to 20 hours for a comparable degree of conversion and at 125 ° 2 to 4 weeks.

Since the various reaction conditions described above one must usually depend on one another if one changes one of these conditions, Change another condition to allow the response to be the desired state and / or the desired composition leads.

When using the porous molded body according to the invention from quartz, one can use the finely divided quartz and the finely divided lime Mix together dry and then add the necessary amount of water to the mixture disperse. You can also slurry the lime in water first and then it add a separately prepared aqueous dispersion of the quartz. The lime slurry can be at an elevated temperature, as can the quartz dispersion. That in this A mixture of both ingredients made fresh and at an elevated temperature is now brought into shape.

The solids can during the reaction and eventual integration the batch by stirring or by adding inert, finely divided fibrous Material can be kept in the state of dispersion. Asbestos fibers are particularly effective, which are frayed so far along their length that the diameter of the individual fibers on the order of 0.1 to 3 microns while their length varies, but is always noticeably greater than the thickness, d. H. the characteristic fiber shape is preserved. The asbestos fiber is prepared for this purpose by making it in the form of a 5 to 10% aqueous suspension in a slurry device treated. Cellulose fibers are also suitable as dispersants. While Fiber asbestos is particularly suitable as a dispersant, the additive imparts of asbestos any form of mass internal cohesion and prevents it from breaking apart while drying.

The still hot dispersion is now at the desired reaction temperature (about 125 to 203 °), the pressure being increased accordingly to one To prevent boiling, e.g. B. in an autoclave. The one for taking up the dispersion certain containers to be brought into the autoclave can be open or through a lid to be introverted. If necessary, the container or the entire autoclave can be used Mixture is to be stirred, added in revolutions.

The atmosphere of the autoclave advantageously contains a slight excess of water and is kept in a saturated or slightly oversaturated state, thus essentially no loss of water and thus shrinkage of the melt entry.

The porous shaped body can, depending on the density of the product, at temperatures be dried between 149 and 177 °. As a result of the integration of the The high porosity and strength achieved can be achieved even before the chemical has finished Reaction with integration progressing from the outside in, as soon as the outside Parts have become dimensionally stable, the water will evaporate as long as the evaporation takes place does not happen too quickly and does not run ahead of integration. You can also do that Drying by repeated washing in acetone, then in ether and finally Effect drying for 1 hour at 100 °.

To z. B. to obtain a molded body with a density of 0.32 g / cm3, one uses quicklime (94% Ca0), quartz flour (99.8% Si 02), of which about 96 to 98 ° / a a sieve no. 325 pass, or lime and silicon dioxide in the form of portland cement and various types and types of asbestos in the following: Quantities: Ca0: Si0 .; = 0.825 Quick lime (Ca0), kg .......... 90; 80 Quartz, kg ......................... 118.04 Chrysotile, 60 degrees, kg ............... 6.44 Amosite, kg ......................... 6.44 Water, kg ........................ 665.11 Water-to-solid ratio ......... 3: 1 The quick lime is hydrated with four times the weight of hot water (about 54 to 77 °) while stirring. The remaining part of the water is then added in the form of a 5-10% slurry with asbestos, after which the quartz flour is added. After all ingredients have been added, the mixture is stirred for an additional 5 minutes. The slurry is then poured into dishes of the desired size and shape and autoclaved at a steam pressure of 8.8 kg / cm2 (178.3 °) for 8 hours or at 15.4 kg / cm2 (201.9 °) for 5 hours.

To make a molded article of low density, e.g. B. 0.16 g / cm3, to produce you can use the procedure described above with the proviso that the asbestos is shredded to a high degree of separation. In addition, a relatively high Percentage of up to 20% long-fiber asbestos may be necessary or advantageous, to achieve the desired internal cohesion and sufficient strength. The water-solids ratio in the mixture must then be 6.0 to 6.2 parts by weight Water per part by weight of solid can be increased.

For moldings of lower bulk density, the reaction mixtures of lime, silica and inert pulverized fiber product and / or ordinary, to the For the purpose of increasing the internal cohesion of added fibers, etc. to such high water-solids ratio can be set so that the crystals formed to a uniform body of the desired uniform composition and Strength grow together.

The reaction between Ca0 and quartz takes place in such a way that first Lime goes into solution and acts on the dispersed quartz particles. This creates first a soluble product, which in a gelatinous precipitating phase of the Composition 2.0 Ca0. 1.0 Si0,. x 1320 (x = 2 or more) and, if applicable less watery hydrates of the same Ca0: Si02 ratio passes over. With advancing Reaction, the phase of the solid lime disappears, whereupon the remaining Si0, enters into reaction until over a number of intermediates with lower and lower As the Ca0: Si0 ratio, the final composition is reached that corresponds to the Ca 0 : Si 02 corresponds to the ratio of the starting mixture. Because the reaction is always about Leads to intermediate products with a higher CaO content, it is not absolutely necessary to that all Si0 is contained in the compensation mixture from the start, but one can first add the amount necessary to form one of the intermediate products and only later the remaining portion of Si02.

If one uses silica in place of quartz, the reaction progresses similar; Here, too, the final composition is based on a number of intermediate products achieved by a higher Ca0: Si02 ratio. Because of the hydrated state of the However, as already mentioned above, silica requires a longer reaction time. Sometimes, even after a long reaction time, you can still find small amounts of silica, Gyrolit or Xonotlit. This is based on the slower and correspondingly delayed one Effect of the silica, which leads to a stabilization of the intermediate, 1 Ca0 . 1 Si0,. x H20, leads. By increasing the lime content of the original raw mixture of lime and silicon dioxide by only 0.25 per cent the conversion of the charge takes place in the essential completely.

The growing together of the crystals of 4 Ca0. 5 Si0,. 5 H20 and 5Ca0-5Si02.H20 to a shaped body can be made without any binder. This creates a three-dimensional one Network that is interspersed with voids. The total pore volume can be smaller or be far larger than that of the crystals. The porous, cell-like, crystalline Structure is firm and elastic and resistant to high temperatures. These properties are based in part on the physical properties of the crystals, their disperse properties Growing together as well as their chemical composition, the unique thermal Properties and low thermal conductivity. The highly hydrated scaly Tobermorite has a high thermal capacity and a high resistance to it the absorption and transmission of heat. The less hydrated, slat-like Xonotlit is stable, solid and both chemically even at very high temperatures as well as physically relatively inert. Both compounds arise in a fine-grained manner crystalline structure, which is evenly interspersed with finely divided cavities is. This combination product, which is free from by-products and binders, combines the advantageous properties of the two hydrates mentioned in and works well for construction purposes or as a thermal insulation material, with the two components in predetermined amounts adapted to the respective purpose can be connected.

Since the practical implementation of the invention has been described above essentially only using quartz as a SiO 2 component, the use of tripoli as a SiO 2 component is shown in the table below. The times given apply to an ordinary hardening cylinder. It can be seen from the table that with an increasing molar ratio of Ca 0: Si 02, the time required for conversion into a completely crystalline product at a given pressure also increases in a certain proportion. A curing pressure of 15.8 to 16.9 atm seems technically and economically suitable for all Ca0: Si02 ratios, but you can also choose pressures and corresponding temperatures outside this range.

The time it takes for a given pressure to acquire a completely crystalline product is slightly shorter if you use quartz in place of Tripoli or silica used as a source of silica.

A number of modifications are possible within the scope of the invention. So you can also do that for the hardening and drying of the integrated molding in U.S. Patent 2,534,303 use the method according to which the raw mixes are hardened and dried in a considerably shorter time than possible with a separate autoclave treatment and drying stage is.

Claims (1)

PATENT CLAIMS: 1. Process for the production of a calcium silicate product, that of intergrown mixtures of calcium silicate hydrates 4 Ca0. 5 Si0, # 5 1120 and 5Ca0 # 5Si02.H20, characterized in that lime and Si 0, in a molar ratio of more than 0.8 and less than 1.0 in an aqueous dispersion, whose water-to-solids ratio (weight) is about 3: 1 to about 9: 1, at a temperature of about 175 to a little above 200 ° C and a pressure of about 8 to 16 atm and the resulting mixture of intergrown crystals freed from its free water content by drying. 2. Procedure according to claim 1, characterized in that the reaction is carried out at a temperature of 203 ° and a pressure of 16 atm. 3. The method according to claim 1 to 2, characterized in that the starting materials are dispersed by adding finely divided fibers such as shredded asbestos. Into consideration Drawn Documents: U.S. Patent No. 2,547,127.