DE1224655B - Process for the production of porous, ceramic materials from expanded clay - Google Patents

Description

Process for the production of porous, ceramic materials from expanded clay The invention relates to a porous ceramic material composed of a combination of substances that, when burned, form cavities when they swell.

The strength of a substance depends, among other things, on a certain one Porosity, on the size of the pores and the thickness of the pore walls. These properties are in turn a function of the viscosity and the surface tension of the Burning, mostly heterogeneous melts. The higher the viscosity, the smaller the pores become, all other things being equal, because of the gas pressure a greater resistance is opposed. With high surface tension arise fewer, but large pores with thick pore walls, since this way the surface less enlarged per unit of space than with the formation of many small pores.

Of those suitable for the manufacture of expanded porous fabrics Substances acts z. B. lowering silica, increasing alumina and iron oxide on the other hand on the surface tension (see Harders-Kienow, Feuerfestkunde, Berlin, 1960, P. 156). The naturally occurring clays suitable for puffing often have a very high silica content, namely 60 to 701 / o, their surface tension is therefore relatively low. When fired, such raw materials provide raw materials from this Basic expanded clay products with many pores and thin pore walls.

In the manufacture of this material, however, it has been shown that it is not possible to adapt the properties to the respective technical requirements adapt to a satisfactory extent. The firing temperature can probably do that Regulate the volume weight, because the pores become larger as the burning height increases, but all other properties, in particular strength, are then inevitable and depend on the raw material used.

Surprisingly, it was found that by adding change the properties of the red mud that occurs in the aluminum industry let that they can be largely adapted to the respective requirements. The red mud, which only contains 5 to 7% SiO2 in addition to 40 to 50 0/0 Fe203 and 20 to 25% A1203 contains, represents an annoying waste product that was previously difficult to use was. When mixing, however, care must be taken that this does not affect the surface tension the viscosity also increases too much, because then the swelling effect is too low or stops completely. It is known that e.g. B. glauconite-rich clays when fired 1100 to 1200 ° C form cavities and result in a high quality porous material, which is ideally suited as an aggregate for lightweight concrete.

As a characteristic value for the viscosity at a certain firing temperature one can look at the sail cone drop point in a crude approximation. This is included pure clay rich in glauconite at SK 4a / 5 a = 1225 ° C. By adding red mud up to 40 0/0 the Seger cone is lowered to SK 1 a / 2 a = 1155 ° C, the viscosity becomes less, the swelling effect increases at a firing temperature of 1180 ° C, and the Strength decreases.

Have mixtures of 50% glaconite-rich clay and 501 / o red mud on the other hand a Seger cone fall point of SK 4 a / 5 a = 1225 ° C, its viscosity is similar to that of pure glaconite-rich clay. But you have a higher one Surface tension, which is reflected in a greater thickness of the pore walls and in a greater strength.

In the case of mixtures that are even richer in red mud, the viscosity increases continue on. The cone fall point of a mixture of 15% glauconite-rich clay and 85% Red mud is at SK 9 = 1315 ° C; it only inflates very slightly at 1180 ° C.

Finally, pure red mud has a cone drop point of SK 14/15 = 1430 ° C and therefore does not swell at all, because at 1180 ° C there is still none to speak of Melt phase is present.

The low Seger cone fall point in the area of small red mud contents indicates the existence of a eutectic melting point. That The example described shows that by mixing. suitable substances for Glauconite-rich clay has considerable viscosity and surface tension when fired can change, so that porous, ceramic materials with for the respective purpose optimal properties arise.

Claims (3)

Claims: 1. Process for the production of porous, ceramic Fabrics with high strength due to the expansion of silica-rich expanded clays a firing temperature of 1100 to 1200 ° C, characterized in that the clay before burning, the red mud that occurs in the aluminum industry is mixed in. 2. The method according to claim 1, characterized in that when using glaconite-rich Clay red mud in amounts of 10 to 70 percent by weight, preferably 30 to 60 percent by weight, is admixed. 3. The method according to claim 1 and 2, characterized in that a high proportion in the production of small, highly pressure-resistant expanded clay granules is used on red mud.