GB1583441A

GB1583441A - Foamed ceramic elements and process of preparation

Info

Publication number: GB1583441A
Application number: GB2268578A
Authority: GB
Original assignee: Schneider GmbH and Co KG
Current assignee: Schneider GmbH and Co KG
Priority date: 1977-05-27
Filing date: 1978-05-25
Publication date: 1981-01-28
Also published as: BE867516A; FR2391969A1; DK223378A; JPS541309A; DE2724010C2; NL7805531A; DE2724010A1

Description

(54) FOAMED CERAMIC ELEMENTS AND PROCESS OF PREPARATION (71) We, SCHNEIDER GmbH & Co, a German body corporate, of Kolner Strasse 72,5020 Frechen 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates generally to a ceramic light construction element and for a process for making same.

Ceramics of lightweight construction materials are known. Typically such materials can be produced by placing granulated material of approximately uniform size into a molding box where the granulated material is swelled. Thereafter highly heated gas is blown through the mass until a ceramically binding condition of the surfaces of the granulated parts is reached, after the swelling has taken place. In such a process, the granulated parts are, as a rule, inflexibly supported to permit expansion into the free spaces where the particles are united to form a body of ceramically bound granulated parts.

However, in the known lightweight construction materials, the final product comprises a grainy structure, i.e. a structure where visible phase interfaces remain. Furthermore the pore structure in the finished product is not homogeneous with respect to the size and distribution of the pores so that the lightweight construction material does not have isotropic properties, particularly with regard to thermal conductivity and rigidity. In addition, the known construction materials have a high water adsorptive capacity and the processes for making same are technologically complicated and expensive.

It has been suggested to swell suitable massive bodies, e.g., briquettes and continuous long pieces of clay containing material, in a furnace. In this case, the swelled material separates from the unswelled material, falls onto the bottom of the furnace and is withdrawn from there. A homogeneous isotropic construction material with a low water absorptive capacity cannot be produced in this manner either.

In addition to the clay-mineral products, construction and insulating materials made of foamed glasses are known. In contrast to conventional clay-mineral insulation materials, foamed glass does not absorb water and has a diffusion resistance factor which is practically infinite. Such foamed glass products are made by mixing ground glass with a foaming agent and filling the admixture into steel molds. Foaming is induced in a tunnel kiln or compartment kiln and the foamed product is then cooled. As a rule, carbon or an organic compound decomposable to carbon at a temperature below the cell formation temperature are utilized as foaming agents. The foamed glass is practically free from crystals. However, an essential disadvantage of foamed glass lies in its low strength and its low compatibility with mortar.

Additionally, when porous structure is damaged there is evolved undesirable odors previously trapped in the closed pores.

Accordingly, there still remains a need for a light-weight ceramic material which does not have the aforementioned disadvantages of the known materials.

The present invention provides a foamed ceramic element derived from mineral raw materials, which comprises a solid portion having a crystalline phase portion of at least 10% by weight; a series of substantially spherical larger pores of substantially uniform size homogenously distributed throughout the element, the larger pores having a standard deviation from the average pore diameter which does not exceed + 50%; and distributed throughout the element a series of smaller pores, such that the distribution of pore diameters exhibits two distinct maxima.

A particularly preferred embodiment of the invention has a crystal phase portion of 15-30% by weight, a water absorption of practically zero and a water-vapour diffusion resistance factor which is practically infinite. The diffusion resistance factor is a measure of the water vapour passing through an element of given surface area under a given pressure gradient.

The foamed ceramic body according to the present invention is characterized by the fact that it has relatively large spherical pores of almost the same size which are homogeneously distributed. Solid material surrounds the pores in a web-like manner and depending on the kind of the raw material used, contains 10% by weight or more of a crystalline component (for example, anorthite), the remaining components of the solid material phase being X-ray amorphous. What is surprising is the fact that the webs of solid material are also porous and such pores have an average diameter which is much different to the relatively large pores surrounded by the web.An analysis of the pore distribution in the foamed ceramic element according to the present invention yields two maxima which differ distinctly from each other and which result from the fact that the large pores are always surrounded by small pores, i.e., the webs between the large pores are filled with small pores. It has been observed that the ratio of the average diameter of the large pores (1st maximum) to the average diameter of the small pores (2nd maximum) generally ranges from 3:1 to 8:1. A preferred ratio is from 4:1 to 5:1. The gross density of the foamed ceramic element is generally between 200 to 1,000 kg/m3 and preferably between 400 to 600 kg/m3. The compressive strength of the foamed element in these gross density ranges is usually from 4.0 to 8.0 (or from 2.5 to 12 N/mm2, respectively).

It is particularly advantageous that the relatively large pores in the foamed ceramic element are uniformly distributed and the standard deviation from the average pore diameter is not more than + 50%. An especially suitable foamed ceramic element has relatively large pores with a diameter in the range of from about 1.5 to 2.5 mm in homogeneous distribution whereby gross densities between about 300 to 600 kg/m3 are achieved. The foamed ceramic element according to the invention is to a large degree compatible with mortar and has a considerably higher fire resistance in comparison with conventional foamed glass. Furthermore, a shaped body of foamed ceramic according to this invention may have a low thermal conductivity of between 0.08 anf 0.2 kcal/m C and thus a high thermal insulation value.It is resistant to humidity, fouling and the effects of rodents and pests.

The invention also provides a process for the production of a foamed ceramic element according to claim 1 from mineral raw materials not ordinarily capable of being swelled, particularly clay-mineral-containing raw materials, with or without fluxing agents; which comprises the steps of providing a mixture of said mineral raw material with a sulfate and sulfide, heating the mixture until foaming occurs, and subsequently cooling the foamed ceramic.

A preferred process is characterized by the steps of (a) admixing a sulfate, a sulfide and water with the clay-mineral starting material which ordinarily cannot be swelled, (b) then heating the clay-mineral admixture until foaming occurs; (c) subsequently cooling the foamed product. It was very surpirsing that, when clay-mineral is combined with a sulfate and a sulfide, the foaming process of the ordinarily non-swelling clay-mineral material can be controlled to such an extent that an isotropic ceramic foam body can be produced.

From the production of expanded clay, it is actually known that material which cannot ordinarily be swelled can be swelled by adding a swelling adjuvant or agent and fluxing agent.

However, it is first desirable to provide relatively small granules, in comparison with a construction element, with a densely sintered outer skin, and, subsequently, to generate the gas from the swelling adjuvant so that the granules or grains can be swelled. As swelling adjuvants, gypsum or lignin sulfate are known. However, with these compounds and the known swelling adjuvants, gas evolution proceeds so fast after a certain temperature is reached that the foaming of large-format elements cannot be performed with the known swelling adjuvants.

It was unexpectedly discovered that when a mixture of sulfate and sulfide is used, gas evolution does not occur suddenly but rather gradually so that a temperature-dependent, adjustable and controllable foaming of clay-mineral-containing raw materials, which cannot ordinarily be swelled, becomes possible.

The swelling adjuvant preferably contains a mixture of a suitable sulfate and a sulfide at a ratio by weight of about 10:1 to about 1:1, preferably about 3:1. The mixture is added to the foamable clay-mineral-containing raw material preferably in amounts of 0.2 to 10%, by weight and preferably about 2 to 5% by weight, in relation to the solid phase.

A variety of suitable sulfate and sulfide compounds can be employed. A combination of iron sulfide and iron sulfate is particularly suitable but barium or calcium compounds cari also be utilized. It is also possible to use sulfate and sulfide compounds with different cations in combination. Furthermore, compounds can be utilized which are partially or entirely soluble in water. It is essential that the sulfate can get into contact with the sulfide during the foaming process which can, for example, be achieved by an intimate mixing of the clay-mineralcontaining raw materials with the foaming adjuvant.

The foaming adjuvants should not be pure compound but rather a mixture of other products compatible with the clay mineral-containing raw materials to be foamed. For example, sulfate or sulfide-containing products, particularly industrial or natural waste products, are usable. These can include slags, waste from the chemical industry, communal waste product ash from combustion systems, dusts, filter ash or residues from processing. If only one of the sulfur compounds is contained in these products, it is supplemented by a product containing the other sulfur compound and/or by a pure other sulfur compound.

It is of special advantage when the sulfate and sulfide is attached to each other in the primary grain or particles of the foaming adjuvant are desirably below 200 ym and preferably below 60 clam.

In mixing the clay-mineral-containing raw material with the foaming adjuvant it is also advantageous if, in addition to sulfate and sulfide, Sill, Al203, iron oxide and alkali oxide are also present. This particularly advantageous combination of the compounds is, as a rule, present in filtered sludge products, particularly in filtered sludge ash, so that such waste products are especially suitable for use as foaming adjuvant.

According to the process of the present invention foaming is preferably effected in an oxidizing atmosphere at a temperature between 1,000 and 1,200 C and for a time of between 10 and 180 minutes. It is possible to use raw material with large foaming temperature intervals and to control the foaming process which is dependent on temperature and time, in such a manner that foamed ceramic elements are produced with predetermined properties with regard to strength, porosity and thermal conductivity. This can be accomplished by, e.g., varying the sulfate/sulfide ratio and the quantity of foaming adjuvant. Clays, particularly stone clays, preferably with an illite portion, and loams are suitable clay-mineral starting materials. Fluxing agents can be added from the known alkali compounds. Such compounds can also be included with the foaming adjuvant.

Construction ceramic elements of any shape and size can be produced with the process according to the present invention to yield a higher strength in comparison with known products having the same porosity. At the same time, the ceramic element of the present invention has a lower thermal conductivity. This synergistic effect is probably due to the extraordinarily favorable influence on the structure of the foamed ceramic elements by the foaming adjuvant, i.e., the formation of two maxima of pore distribution. It is also possible to use this foaming adjuvant as a swelling adjuvant for the production of expanded granulated clay parts.

Having described the invention in general terms, the following examples are set forth to more particularly illustrate the invention. These examples, however, are not meant to be limiting. All percentages are by weight.

Example I A mixture of 70%stone clay, 20% ground basalt, 3% iron sulfide and 7% iron sulfate was prepared. Two parts by weight of water were added to one part by weight of the preparation and the mixture was intimately mixed in the ball mill for 4 hours. Subsequently, the mixture was poured into cups. This was followed by drying to a residual water content of below 2% water.The dried substance was then crushed and put into a mold 20 x 20 x 15 cm, 8 cm high and place in a furnace and heated to 1,1600C at 2"C/minute. The substance foamed uniformly in the temperature range of 1,140 to 1,1700C.After cooling, a foamed ceramic plate was obtained having a density of 500 kg/m3, a compressive strength of 8 N/mm2 and a thermal conductivity of 0.1 kcal/m h C. The average pore diameter of the relatively large pores amounted to 2 mm.

Example 2 The preparation consisted of 50% stone clay and 50% of a filtered sludge ash product of a composition similar to a clay substance. This preparation contained 0.9% S and 2.6% S04-2. The processing and the foaming were effected according to Example 1. This resulted in a foamed ceramic plate having a density of 400 kg/ m3, a bending strength of 3 N/mm2 and compressive strength of 7 N/mm2. The gas permeability of the plate amounted to 10 nanoperms and its thermal conductivity was 0.1 kcal/m h "C. The average pore diameter of the relative large pores amounted to 2 mm.

Example 3 In accordance with Example 1, a mixture was made comprising 50% loam, 10% ground basalt and 40% of a filtered sludge ash product with the composition according to Example 2.

The mixture was heated to 1,150"C and the resulting foamed product then cooled. A foamed ceramic plate was obtained with a density of 400 kg/m3 and with the same properties as indicated in Example 2 with regard to bending strength, compressive strength, gas permeability, thermal conductivity, as well as pore distribution.

The new lightweight ceramic construction elements have the outstanding properties described above and are moreover fireproof to a certain extent. The object of a further embodiment of the present invention is to raise and ensure the fireproof property of foamed ceramic elements and indicate a way in which the fireproof property of such construction elements can intentionally advantageously be influenced. The fireproof level of construction elements is specified by DIN 4102. In other countries the specifications differ more or less from the German requirements. A further object of the present invention is to provide construction elements that can be quite generally classed as fireproof.

The known foamed glass and foamed ceramic elements when used as load-bearing walls are not fireproof for example within the meaning of DIN 4102. The reason for this is that in particular they are brittle, have a plurality of gas-filled closed pores, have a low thermal conductivity, and have a relatively high coefficient of thermal expansion. A considerable degree of large crack formation and chipping or spalling occurs when such elements are rapidly heated, and the latter may break up into many parts.

Theoretically there are several ways in which the construction elements can be made fireproof. Firstly, attempts can be made to reduce the coefficient of thermal expansion of the basic composition. Secondly, the desired objective can be achieved in some cases by raising the elastic properties while reducing the glass phase in the foamed ceramic element. This can be effected for example by increasing the proportion of the crystalline phase. Moreover, attempts can be made to increase the thermal conductivity and strength. Of the aforementioned possibilities, those involving the thermal conductivity and coefficient of thermal expansion are excluded for exonomic and technical reasons. Attempts to adopt the other methods were not successful in the case of foamed ceramic elements.

Accordingly, it is a further object of the invention to increase the fireproof level of foamed ceramic elements without having to relinquish the required other properties of construction elements.

Thus in a further preferred embodiment the invention provides a a foamed ceramic element, in particular one based on mineral raw materials, which has a pore distribution exhibiting two maxima, the first maximum being formed by average diameter large pores and the second maximum by average diameter smaller pores distributed throughout the web structure of the solid material between the large pores. characterised in that the element has microcracks in the solid material between the pores. Microcracks within the meaning of the invention are cracks that are formed on rapid heating and cooling, and wherein structural stresses caused by temperature differences are dissipated by crack formation.In the foamed ceramic element according to the invention some of these microcracks join the large and small pores and thereby produce a flow or open porosity that will enable gas diffusion or to some extent even gas flow to take place. Other microcracks are enclosed within the solid material between the large pores.

It has surprisingly been found that these microcracks are beneficial to the thermal shock resistance and the gas diffusion and gas flow in such a way that the required fireproof level can be ensured. It is advantageous if the proportion of microcracks is 0.3 to 1.1 volume %, giving an open porosity of about 10 to 25 volume %. It is particularly advantageous if the open porosity is 15 to 20 volume %.

The microcracks in the foamed ceramic element according to the invention correspond to the cracks that have been described for example by Griffith, and can easily be analysed by optical microscopy.

According to a particular embodiment of the invention, crystals and/or crystallites of anorthite and cristobalite are embedded in the solid connecting material containing the glass phase. which are surrounded by microcracks substantially parallel to the crystal face and/or from which microcracks extend more or less radially. In this connection, a cristobalite fraction of 2 to 20, in particular 5 to IS, and an anorthite fraction of 2 to 30, in particular 10 to 25 % by weight, are favourable. The open flow porosity is advantageously between 10 and 25 volume %, and the element advantageously has a diffusiion resistance factor of 60 to 160.In this connection, the microcracks should be about 10 to 30 ,u, in particular 16 to 20 , long, and 0.1 to 0.5 ,u, in particular 0.2 to 0.4,a wide. Such microcracks are on the one hand too small to form large macrocracks that could destroy the construction elements, and on the other hand prevent the propagation of macrocracks since the large cracks run into a large number of the microcracks and thereby "peter out". Since the microcracks are to some extent interconnected and also end in the large pores, an open flow porosity is thereby produced. The open flow porosity can be simply determined by the water absorption test. This is carried out determining the weight and volume of a test cube having the dimensions 10 x 10 x 10 cm boiling the test cube in distilled water for 2 hours, and then leaving it in distilled water for 24 hours. The water absorption can be calculated by determining the wet weight of the test cube.

The water absorption of the foamed ceramic elements according to the invention is preferably in the range from 8 to 30, in particular between 10 and 20 % by weight.

The foamed ceramic elements according to the invention can be produced in any conve nient manner. However, it is particularly effective to produce stresses in the solid connecting material and dissipate the stresses by microcracks. Accordingly, a further object of the invention is a process for producing fireproof foamed ceramic elements, wherein at least one raw material, in particular a clay-containing raw material optionally mixed with conventional fluxes, is made into a batch dry and/or with water, and the batch is preferably granulated, optionally dried, added to moulds and foamed by heating , and is then cooled, and wherein a sulphate and a sulphide are added to the batch as a foaming auxiliary, characterised in that stresses are formed in the solid connecting regions during the cooling stage and the said stresses are dissipated by microcrack formation.

The mineral raw materials and foaming procedures resulting in a foamed ceramic element have already been described.

The foaming process is strongly exothermic when the foaming auxiliary is added. It is therefore particularly favourable to produce a temperature equalisation by maintaining the temperature constant for a sufficiently long period, shortly before the commencement of swelling, and then initiate swelling by means of the exothermic reaction between the reac tants of the foaming auxiliary. In this way foamed ceramic elements having a swelling height of 50 cm and more with a uniform pore structure can be produced. The exothermic reaction is in particular initiated by using sewage sludge ash as foaming auxiliary, which basically contains sulphate and sulphides. The sewage sludge ash has a powerful effect on reducing the melting point by virtue of its chemical composition, and to this extent a synergistic effect is produced.

The exothermic reaction can also be brought about by starting with a raw material which already contains a foaming auxiliary component, and to which the second component is added. For example, a non-foaming, iron sulphate-containing clay can be made foamable by adding iron sulphide thereto. Conversely, a sulphide-containing clay can be converted into the foaming state by adding sulphate. It is also possible to use a swellable raw material and make it foamable by adding a foaming auxiliary. In this connection, the raw material may optionally contain a foaming auxiliary component, with the result that just the second component needs to be added. In all cases it is particularly favourable if an attempt is made to ensure that the foaming stage takes place on the basis of exothermic reactions.

The raw materials can be formulated dry or with water or another plasticising component, and the granulated raw materials can be added moist or dried to the moulds. The choice of these process parameters is governed by the requirements of the raw materials in each case.

Mixtures of pure sulphates and sulphides as well as natural and synthetic waste products containing the sulphur compounds as components can be used as foaming auxiliaries. If only one of the sulphur compounds is contained in such products, a foaming auxiliary can be prepared therefrom by admixing a product containing the other sulphur compound.

According to a particular embodiment of the invention the stresses and microcracks are produced by the temperature behaviour on cooling the foamed product, and from the point of view of the raw materials it is desirable that phase mixtures comprising at least two phases having different co-efficients of thermal expansion are formed in the solid connecting regions. Stresses arise at the phase boundaries or in the phase boundary regions on cooling, whose magnitude is determined by the difference in the coefficients of thermal expansion of the phases. The temperature on cooling is controlled in such a way that the stresses do not equalise in the melt phase by coalescence (melt flow) or other physical processes, but are dissipated to a certain extent and in the desired manner by the formation of microcracks.

A mixture of two phases in the solid connecting regions is preferably formed and provision is made to ensure that the mixture components or phases are almost homogeneously distributted.

In particular, the phase mixture is produced in accordance with the invention by precipitat ing crystals and/or crystallites having a higher coefficient of thermal expansion than the melt phase and the glass phase by devitrification from the melt phase on cooling. The crystals or crystallites are embedded in the melt and glass phases of the solid interconnecting regions. On cooling considerable stresses arise at the boundary surfaces of the glass and crystal phases, which are dispersed by microcrack formation around the individual crystals and/or crystal lites as well as by microcrack formation running from said individual crystals and/or crystal lites.In this connection. the number of crystals and/or crystallites as well as their size and thus the intensity of crack formation can be arbitrarily regulated with respect to the formation and growth of nuclei by controlling the temperature. and the optimum conditions can be deter mined empirically for a specific raw material composition. The intensity of crack formation is greater the larger the crystals or crystallites. and the greater the cooling rate.

It is advantageous to formulate a raw material mixture that will permit the formation of anorthite and cristobalite crystals. This is particularly simple if vitrified clays, preferably with a proportion of illite. are used as starting materials and sewage sludge ash is added as foaming auxiliary, the formation of cristobalite being promoted by using clays having a fairly high proportion of fine quartz. The cooling conditions are chosen so that 2 to 20 % by weight of cristobalite and 2 to 30%by weight of anorthite crystals precipitate in the solid interconnecting regions, and cooling is carried out at a rate of 2.0 to 5.0 C/minute up to the transformation interval of the glass phase, and at a rate of 0.4 to 1.2"C/ minute below the transformation interval.A particularly favourable formation of crystals and/or crystallites and a particularly suitable embedding effect in the glass phase of the solid interconnecting region is obtained if the raw materials are processed in a chaser mill or edge mill since a particularly favourable lodse and non-compacted raw material mixture structure is thereby formed.

According to a further embodiment of the invention a phase mixture having different coefficients of thermal expansion is produced in the solid interconnecting regions by foaming and cooling a predominantly homogeneous granulate mixture consisting of at least two types of granulate i.e. two different materials, each type of granulate forming a metl and glass phase having a coefficient of thermal expansion different to that of the other glass phase. In this connection, a granulate mixture of two dry and/or moist crude granulate types or a granulate mixture of two pre-swelled granulate types may be used. It is also possible to mix homogeneously a crude granulate type with a pre-swelled granulate type. It is particularly expedient to mix a crude granulate or pre-swelled granulate type with a foamed and comminuted granulate type.Moreover, it is particularly favourable to prepare a crude granulate from raw materials, foaming auxiliaries and comminuted, pre-swelled granulate or comminuted, foamed ceramic product according to the invention by intimate mixing in such a way that a grain for the second phase is embedded in a homogeneously distributed manner in the granules consisting of the conventional raw materials and foaming auxiliaries. The last two process variants are particularly suitable if the pre-swelled or pre-foamed product has the larger coefficient of thermal expansion.Foamed ceramic waste material, e.g. cutting waste, can be economically re-used in these cases if it has preferably been precomminuted to a size of less than 8 mm and in particular has the following grain distribution: 7.0 - 0.8 mm 11 - 14 % by weight in particular 12.83 % by weight 3.0 - 7.0 mm 40 - 44 tf " 42.6Q 2.0 - 3.0 mm 9 - 12 " " 10.87 1.0 - 2.0 mm 3 - 5 " " 3.60 0.5 - 1.0 mm 8 - 10 " " 8.47 0.25 - 0.5 mm 6 - 7 " " 6.10 0.10 - 0.25 mm 7 - 8 " " 7.20 0.063 - 0.1 mm 2 - 4 " " 2.93 < 0.063 mm 4 - 6 " " 5.40 It has been found that is advantageous for the purposes of the invention if a granulate type having a coefficient of thermal expansion after foaming of 4.2 to 5.0 x 10-6 C- is mixed with a granulate type having a coefficient of thermal expansion after foaming of 5.0 to 7.0 x 10-6 0C '. Care should however be taken to ensure that the difference in the coefficient of thermal expansion of the two types of granulates or glass phases is in the range from 0.5 to 2.5 x 106 0C in particular between 0.8 and 2.0 x 10- "C- . Microcrack formation then takes place by dissipating the stresses in the boundary phase regions. In this connection it is also favourable to cool at a rate of 2.0 to 5 .00C/ minute before the transformation interval, and at a rate of 0.4 to 2.0"C/minute after the transformation interval.

According to a further process variant it is particularly recommended to form two glass phases and one or two crystal phases in the solid interconnecting regions. This can be achieved with a raw material batch of the first process variant by mixing with a second granulate or foamed waste grain, a glass phase with crystals being formed from the raw material batch and a second glass phase being formed from the waste grain. The crack formation is then particularly easy to control because both the crystals and also the glass phases produce stresses and promote crack formation.

It is furthermore advantageous to use granulate mixtures that have a different transformation region or a different transformation interval after the foaming. This has a favourable effect on the shape. number and size of cracks. The transformation interval should in particular exhibit a difference of 5 to 25"C.

A semi-wet processing of the raw materials, in particular with slightly moist clays, in the chaser mill should also be employed for these process variants, and a heating rate up to the foaming temperature of about 1180 to 12000C of two to four hours should be selected.

A composition having a fairly high coefficient of thermal expansion can be prepared in a simple manner by employing the raw material basic composition and adding quartz powder, The quartz powder should preferably have the following grain distribution: > 63 ,u 18 - 20 % by weight in particular 19 % by weight 5() - 63 " 7 - 9 " 8 40 - 50 " 6 - 8 ,, 7 25 -40 " 18-22 " " 20 " 16 - 25 " 14 - 16 " " 15 If) - 16 " 10 - 12 " " ll 6.3 - 10 " 6- 8 " " 7 ,, 7 4 - 6.3 " 3 - 5 " ,, q 2.5- 4 2 2- 5 " ,, 4 < 2.5 " 3- 5 " ,, 5 A clay having a high content of fine quartz, for example having the following grain distribution can also be added to the raw material basic composition for preparing the second granulate type: > 63 ,u 18 - 20 % by weight in particular 1.6 % by weight 50 - 63 " I - 2 " " 1.3 " 40 - 50 " I - 2 " " 1.4 " 25 - 40 ' 2 - 4 " " 2.7 16 - 25 " 3 - 6 ,, 5.4 10 - 16 2 4 4 " 3.8 6.3 -10 " 8 - 10 " " 9 9.2 4 - 6.3 " 3- 6 " 5.1 2.5 - 4 " 7 7 " 6.2 < 2.5 " " " 63.3 " The following examples serve to illustrate the process according to the invention still further.

Example 4 A mixture is prepared from 70%by weight of stoneware (vitrified) clay containing at least 50% by weight of fine quartz. 20% by weight of basalt powder. 3% by weight of iron sulphide and 7% by weight of iron sulphate. 0.25 part by weight of water is added to one part by weight of this batch and the constituents are intimately mixed for 20 minutes in a chaser mill. The composition is then dried until ths residual water content is below 2% by weight. The dried material is next comminuted into granules having a boundary grain size of about 10 mm. and the granules are added to moulds and foamed. The foaming process itself is carried out in fireproof moulds provided with an insulating layer.Heating is carried out for approximately 10 hours to a final firing temperature of 1180"C. The material foams uniformly in the temperature range from 1140 to 1180 C.

Whereas the material is cooled for about 3 hours down to the transformation region of the cooling procedure of 780"C. 24 hours are required for the cooling down to room tempera ture.

After the cooling procedure a foamed ceramic element is obtained having anorthite and cristobalite crystals in the solid interconnecting regions, a density of 500 kg/m', a compres sive strength of 5.5 N/ mm2. a bending strength of 2.5 N/mm2. and a thermal conductivity of 0.1 kcal/m.h C. The average pore diameter in the region of the larger pores is 2.5 mm and the water absorptibn is 16% by weight..

Example 5 The batch is formulated from 50%by weight of clay or a clay batch containing at least 50% by weight of fine quartz. and 50%by weight of a sewage sludge product having a composition similar to that of clay. The batch contains 0.9%by weight of S2- and 2.6% by weight ofSO42.

The processing and foaming are carried out in the basic steps according to Example 4. with the exception that the granules are already prepared in a plastic state by means of a pelleting apparatus. These are added after having been dried or directly in the plastic state to insulated fireproof trays. A foamed ceramic element having a density of 450 kg/m and a compressive strength of 5.0 N/mm2 is formed after the foaming procedure and cooling according to Example 4. The bending strength is 2.5 N/mmZ and the thermal conductivity is 0.1 kcal/ m.h.0C.

Values of around 14% by weight are found for the water absorption for the fireproof elements. The average pore diameter is 2.5 mm for the larger pores.

Example 6 Pcllets are produced according to Examples 4 and 5 from a batch containing a normal illite stoneware clay, and also from a batch containing a high quartz content clay. These are dried and then mixed in the weight ratio of 2:1, added to a fire proof tray, heated and foamed. and finally cooled according to Example 4. 3 Aftcr cooling. a foamed ceramic element having a density of 450 kg/m , a compressive strength of 5.5 N/mm is formed. The thermal conductivity is 0.15 kcal/m.h. C. and the water absorption is I by weight. The average pore diameter of the large pores is 2.5 mm.

The structure of the foamed ceramic element will be described in more detail with the aid of Fig. 1: in this connection, Fig. I is a section of foamed ceramic element produced according to Example 2, and shows the pore distribution of the element. which consists of the solid interconnecting material I , the relatively large pores 2, and the relatively small pores 3. in this connection, the ratio of the average pore diameter of the large pores to the averuge pore diameter of the small pores in the solid interconnecting material is about 4.5 to 1.

A foamed ceramic clement according to the invention will be described bricfly with the aid of Fig. 2. The solid interconnecting material 1 surrounds the large diameter pores 2. Pores 3 of small diameter and microcracks 4 are homogeneously distributed throughout the interconnecting regions 1. Some of the microcracks go from a large pore 2 to another large pore. or from a smaller pore 3 in the interconnecting region to another smaller pore, without reaching the large pores 2. Crack intersections are also present. The cracks produce an open flow porosity by connecting largcr and smaller pores.

The present invention thus also indicates a way by which foamed ceramic elements can be made fireproof by intentional microcrack formation. It has also shown by what means microcrack formation can be produced. It is obviously also possible to make foamed glass and other foamed ceramic elements fireproof by microcrack formation. using similar means WHAT WE CLAIM IS: 1.A foamed ceramic element derived from mineral raw materials. which comprises a solid portion having a crystalline phase portion of at least 10% by weight; a series of substantially spherical larger pores of substantially uniform size homogeneously distributed throughout the element. the larger pores having a standard deviation from the average pore diameter which does not exceed + DO6Sc; and distributed throughout the element a series of smaller pores. such that the distribution of pore diameters exhibits two distinct maxima.

2. A foamed ceramic element according to claim 1. wherein the ratio of the average diameter of the large pores to the average diameter of the small pores is from 3:1 to 8:1.

3. A foamcd ceramic element according to either preceding claim which contains residues of a suitable sulphate sulphite mixture which has been heated to induce foaming.

A. A foamed ceramic element according to any preceding claim. having a water absorption of substantially zero and a water vapour diffusion resistance factor which is substantially infinite.

5. A foamed ceramic element according to any preceding claim. wherein said crystalline phase is anorthite and the remaining solid portion is X-ray amorphous.

6. A foamed ceramic element according to any preceding claim. having a density of from '()() to 1.()()() kg m 7. A foamed ceramic element according to claim 6. which has a compressive strength between 2.5 and 12 N/ mm2.

S. A foamed ceramic clement according to claim 6. which has pores of a diameter in the range of from 1.) to '.5 mm and a density of from 300 to 6()(1 kg m 9 A foamed ceramic element according to any preceding claim. characterized by the fact that it has a thermal conductivity of between 0.08 to 0.' keal m h C.

10. A foamed ceramic element according to any of claims I to 3. which has microcracks that partially join the large and small pores to form an open porous structure.

11. A foamed ceramic element according to claim 10. wherein the proportion of microc- racks is ().3 to I . I Cj( hv volume and an open porosity of 1() to 25 c/C by volume is thereby produced.

17. A foamed ceramic element according to claim 1() or I I. wherein crystals and or crystallitcs of anorthite and cristobalite surrounded by microcracks are embedded in the solid inierconnecting regions.

13. A foamed ceramic element according to claim 12. having a cristobalite content of 2 to 20% by weight. and an anorthite content of 2 to 30% by weight.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Example 4. The bending strength is 2.5 N/mmZ and the thermal conductivity is 0.1 kcal/ m.h.0C.

Values of around 14% by weight are found for the water absorption for the fireproof elements. The average pore diameter is 2.5 mm for the larger pores.

Example 6 Pcllets are produced according to Examples 4 and 5 from a batch containing a normal illite stoneware clay, and also from a batch containing a high quartz content clay. These are dried and then mixed in the weight ratio of 2:1, added to a fire proof tray, heated and foamed. and finally cooled according to Example 4. 3 Aftcr cooling. a foamed ceramic element having a density of 450 kg/m , a compressive strength of 5.5 N/mm is formed. The thermal conductivity is 0.15 kcal/m.h. C. and the water absorption is I by weight. The average pore diameter of the large pores is 2.5 mm.

The structure of the foamed ceramic element will be described in more detail with the aid of Fig. 1: in this connection, Fig. I is a section of foamed ceramic element produced according to Example 2, and shows the pore distribution of the element. which consists of the solid interconnecting material I , the relatively large pores 2, and the relatively small pores 3. in this connection, the ratio of the average pore diameter of the large pores to the averuge pore diameter of the small pores in the solid interconnecting material is about 4.5 to 1.

A foamed ceramic clement according to the invention will be described bricfly with the aid of Fig. 2. The solid interconnecting material 1 surrounds the large diameter pores 2. Pores 3 of small diameter and microcracks 4 are homogeneously distributed throughout the interconnecting regions 1. Some of the microcracks go from a large pore 2 to another large pore. or from a smaller pore 3 in the interconnecting region to another smaller pore, without reaching the large pores 2. Crack intersections are also present. The cracks produce an open flow porosity by connecting largcr and smaller pores.

The present invention thus also indicates a way by which foamed ceramic elements can be made fireproof by intentional microcrack formation. It has also shown by what means microcrack formation can be produced. It is obviously also possible to make foamed glass and other foamed ceramic elements fireproof by microcrack formation. using similar means WHAT WE CLAIM IS: 1.A foamed ceramic element derived from mineral raw materials. which comprises a solid portion having a crystalline phase portion of at least 10% by weight; a series of substantially spherical larger pores of substantially uniform size homogeneously distributed throughout the element. the larger pores having a standard deviation from the average pore diameter which does not exceed + DO6Sc; and distributed throughout the element a series of smaller pores. such that the distribution of pore diameters exhibits two distinct maxima.
2. A foamed ceramic element according to claim 1. wherein the ratio of the average diameter of the large pores to the average diameter of the small pores is from 3:1 to 8:1.
3. A foamcd ceramic element according to either preceding claim which contains residues of a suitable sulphate sulphite mixture which has been heated to induce foaming.
A. A foamed ceramic element according to any preceding claim. having a water absorption of substantially zero and a water vapour diffusion resistance factor which is substantially infinite.
5. A foamed ceramic element according to any preceding claim. wherein said crystalline phase is anorthite and the remaining solid portion is X-ray amorphous.
6. A foamed ceramic element according to any preceding claim. having a density of from '()() to 1.()()() kg m
7. A foamed ceramic element according to claim 6. which has a compressive strength between 2.5 and 12 N/ mm2.
S. A foamed ceramic clement according to claim 6. which has pores of a diameter in the range of from 1.) to '.5 mm and a density of from 300 to 6()(1 kg m
9 A foamed ceramic element according to any preceding claim. characterized by the fact that it has a thermal conductivity of between 0.08 to 0.' keal m h C.
10. A foamed ceramic element according to any of claims I to 3. which has microcracks that partially join the large and small pores to form an open porous structure.
11. A foamed ceramic element according to claim 10. wherein the proportion of microc- racks is ().3 to I . I Cj( hv volume and an open porosity of 1() to 25 c/C by volume is thereby produced.
17. A foamed ceramic element according to claim 1() or I I. wherein crystals and or crystallitcs of anorthite and cristobalite surrounded by microcracks are embedded in the solid inierconnecting regions.
13. A foamed ceramic element according to claim 12. having a cristobalite content of 2 to 20% by weight. and an anorthite content of 2 to 30% by weight.
14. A foamed ceramic element according to any of claims 10 to 13 having a diffusion

resistance factor of 60 to 160.
15. A foamed ceramic element according to any of claims 10 to 14, having microcracks 10 to 30 CL long, and 0.1 to 0.5 ,u wide.
16. A foamed ceramic element according to any of claims 10 to 15, wherein some of the microcracks are connected to one another and some terminate in large and/or small pores.
17. A foamed ceramic element according to any of claims 10 to 16, having a water absorption of 10 to 25% by weight.
18. A foamed ceramic element substantially as herein described in any of the Examples, or as described with reference to and as illustrated in either of Figures 1 and 2.
19. A process for the production of a foamed ceramic element according to claim 1 from mineral raw materials not ordinarily capable of being swelled, particularly clay-mineralcontaining raw materials, with or without fluxing agents; which comprises the steps of providing a mixture of said mineral raw material with a foaming adjuvant comprising a sulfate and sulfide, heating the mixture until foaming occurs, and subsequently cooling the foamed ceramic.
20. A process according to claim 19, wherein the mixture contains water, which further comprises the steps of drying the mixture to be foamed and then placing the dried mixture into a mold prior to foaming.
21. A process according to claim 19 or 20, wherein a foaming adjuvant of sulfate and sulfide is added in a ratio by weight of sulfate: sulfide of 10:1 to 1:1.
22. A process according to any of claims 19 to 21, wherein the foaming adjuvant is added in relation to the solids content of the mineral raw materials in an amount ranging from 0.2 to 10% by weight.
23. A process according to any of claims 19 to 22, employing a combination or iron sulfate and iron sulfide as the foaming adjuvant.
24. A process according to any of claims 19 to 23, wherein the foaming adjuvant added is at least partially soluble in water.
25. A process according to either of claims 19 and 20, wherein the mineral raw material already contains one of the sulfur compounds and a foaming adjuvant component is added which contains the other of the sulfur compounds.
26. A process according to claim 25, wherein the foaming adjuvant comprises natural and industrial waste products.
27. A process according to claim 26, wherein said foaming adjuvant is a filtered sludge ash having particles of size below 200 im.
28. A process according to any of claims 19 to 27, wherein the foaming step is effected at between 1,000 and 1,200"C.
29. A process according to claim 28, wherein the foaming step is carried out for 10 to 180 minutes.
30. A process according to any of claims 19 to 29, wherein the starting material employed is stone clay with an illite portion.
31. A process according to claim 19 for producing an element having microcracks.

wherein at least one raw material is mixed dry and/or with water, optionally granulated and dried, added to moulds and foamed by heating and then cooled, a sulphate and a sulphide being included as foaming auxiliary in the mixture, and wherein on cooling stresses are produced in the solid interconnecting regions and the stresses are dissipated by microcrack formation.
32. A process according to claim 31, wherein the foaming is carried out by means of an exothermic reaction of the foaming auxiliary.
33. A process according to claim 32, wherein before swelling a temperature equalisation is produced by maintaining the temperature constant for a certain period, and then swelling is initiated by exothermic reaction between the reactants of the foaming auxiliary.
34. A process according to claim 31 or 32, wherein sewage sludge ash is used as foaming auxiliary.
35. A process according to any of claims 31 to 34, wherein a swellable raw material is used as raw material.
36. A process according to any of claims 30 to 35, wherein a raw material is used which already contains one foaming auxiliary component, and the second component is added.
37. A process according to any of claims 30 to 36, wherein the microcracks are formed by regulating the temperature during the cooling of the foamed product, raw materials being chosen such that phase mixtures of at least two phases having different coefficients of thermal expansion are formed in the solid interconnecting regions.
38. A process according to claim 37, wherein a mixture of two phases is produced in the interconnecting regions and the phases are homogeneously distributed adjacent to one another.
39. A process according to claim 38, wherein the phase mixture is produced by devitrification from the melt phase during cooling, the crystals and/or crystallites in the devitrified regions having a higher coefficient of thermal expansion than the melt phase therein.
40. A process according to claim 39, wherein anorthite and cristobalite crystals are produced.
41. A process according to claim 40, wherein a stoneware clay containing illite is used as raw material, and sewage sludge ash is used as foaming auxiliary.
42. A process according to claim 41, wherein the components are cooled at a rate of 2.0 to 5.0 C/ minute down to the transformation interval of the glass phase, and at a rate of 0.4 to 1.2"C/minute below the transformation interval.
43. A process according to claim 42, wherein the raw materials are processed in a chaser mill.
44. A process according to claim 37, wherein a homogeneous granulate mixture of at least two granulate materials is foamed and cooled, each granulate material forming a melt and glass phase having a coefficient of thermal expansion different to that of the other glass phase.
45. A process according to claim 44, wherein a crude granulate material is homogeneously mixed with a pre-swelled granulate material.
46. A process according to claim 44, wherein a crude granulate or pre-swelled granulate material is mixed with a foamed and comminuted granulate material.
47. A process according to claim 44, wherein a crude granulate is prepared from raw materials, foaming auxiliaries and a comminuted foamed ceramic product by intimate mixing, the grain for the second phase being embedded in a homogeneously distributed manner in the granules.
48. A process according to claim 47, wherein the prefoamed granulate has a larger coefficient of thermal expansion.
49. A process according to any of claims 37 to 48, wherein a granulate type having a coefficient of thermal expansion after foaming of 4.2 to 5.0 x 10-6 "C-' is mixed with a granulate type having a coefficient of thermal expansion after foaming of 5.0 to 7.0 x lo-60C- I
50. A process according to claim 49, wherein cooling is performed at a rate of 2.0 to 5.0 C/minute before the transformation interval, and at a rate of 0.4 to 1.2"C/minute after the transformation interval.
51. A process according to any of claims 31 to 50, wherein two glass phases and one or two crystal phases are produced in the solid interconnecting regions.
52. A process according to claim 37, wherein a granulate mixture consisting of two granulate types is used, whose glass phases have different transformation regions.
53. A process according to claim 52, wherein the difference in the transformation interval is 5 to 25"C.
54. A process according to any of claims 37 to 53, wherein in order to produce the glass phase having a higher coefficient of thermal expansion, a granulate from the raw material basic composition is employed to which quartz powder has been added.
55. A process according to any of claims 37 to 53, wherein to produce the glass phase having a higher coefficient of thermal expansion, a granulate from the raw material basic composition is used to which a high quartz content clay has been added.
56. A process for the production of a foamed ceramic element substantially as herein described in any of the Examples. - -