A POROUS CERAMIC MATERIAL

Abstract: A porous ceramic material comprising mineral fibres and clay in a weight ratio of 9:1 to 3:7, having open porosity from 75 to 90 %, the coefficient of thermal conductivity at room temperature less than 0.2 W/mK, bulk density between 350 and 800 kg/m<3>, the length of mineral fibres less than 6 mm, compressive strength from 2.0 to 10 MPa, bending strength from 0.1 to 3 MPa. Said material can be used for thermal insulation, for acoustic decorative linings and fire-proof linings. Its manufacture consists of mixing raw materials, forming crude products, drying and firing.

Description: Λ POROUS CERAMIC MATERIAL The present invention relates to a porous ceramic material, to a process for the preparation thereof as well as to its use. More particularly, the present invention relates to a ceramic material on the basis of mineral fibres and clay as ceramic binder, said material having a low density, from 350 to 800- g/m 3 , a low thermal conductivity at room temperature, from 0.10 to 0.16 W/mK, and non-Inflammability according to British Standard BS -476 part . . Its resistance to elevated temperatures depends on the starting materials used and amounts, e.g. when using diabase rock wool and ball clay, to max. 1050 C and when using ceramic fibres and refractory clay e.g. to 1600 C. Said material exhibits convenient strengths with regard to low bulk density - bending strength from 0.1 to 3-0 MPa, compressive strength from 2.0 to 10 MPa - and has open porosity from 75 to 90 %. Final products can be formed by hand-operated tools . The novel material according to the invention can be used for non-supoorting heat-insulating walls and as heat-insulating filler for supporting walls; for heat insulating and non-inflammable linings of walls, floors and ceilings; for interior acoustic decorative linings; for insulation of thermic devices up to a certain high temperature with regard to the starting materials employed; fo.r fire-proof linings of steel constructions and other building constructions; for fire-proof linings in furniture parts as well as in shipbuilding. Until now ..mineral fibres in combination with clay ' have-; only been employed in order tυ improve the drying rate of clay articles. Mineral fibres are added to clay in an amount up to 15 wt. % (reported at Conference of Silicate Industry and Silicate Science, Budapest 1981, East-German Patent 126 -441). The objective of the present invention, however, is not the improvement of the drying rate of clay articles, but the manufacturing of a novel thermoinsulating material with determined physical properties. The porosity of ceramic clay articles can be affected by adding different inorganic as well as organic substances (cf. H. Schmidt, Ziegelindustrie Int., 9, 500 (1978) and British patent 1 -478 904). Among inorganic insulating materials expanded perlite, expanded vermiculite, diatomaceous earths, asbestos fibres are cited as additives, whereas the addition of mirH'al fibres is not mentioned. Thus the objective of the present invention is a porous ceramic material, which consists of mineral fibres and clay, the weight ratio of mineral fibres/clay being from 9:1 to 3:7. Said ~atio relates to the composition of raw materials as to dry weight of components as well as in the final product. As mineral fibres all known mineral fibres can be used, such as rock wool (basalt type and diabase type), slag wool, glass wool, ceramic fibres and also waste fibres obtained in the production of articles made of mineral fibres. Ba3ic characteristics of some fibres, useful in th present invention, are evident from Table 1. Table 1 Ceramic Analysis Mineral Fibres Ceramic Fibres Glass Fibres Si0 2 42,5 49 62,2 15,6 A1 2°3 49 3,5 7,8 0,8 0,1 Fe 2°3 CaO 16,8 - 8,6 MgO 12,4 - 2,9 Ti0 2 1,7 1,0 - MnO 0, 16 - (B 2 0. 3 > , K 2 0+Na 2 0 3,0 0,2 13,6 mean fibre diameter 4,4 urn 3,0 .urn 7,9 / ura fibre length frcm 3 to 100 nm frcm 3 to 100 ι run fYm 3 to 100 rrm % of pearls to 30 % to 30 % - Different kinds of clays can be used (ball clays, ceramic and refractory clays , bentonite , kaolin). Typical ch emical composition of ball clay IS as follows : Si0 2 - 50 - 85 % - 10 - 25 A1 2°3 % - 2 - 10 Fe 2°3 % CaO - 0.5 - 20 % MgO - 0.5 - 5 % SO, - 0. 01 - 0.02 % 2 0+Na 2 0 - 2 - 5 % The weight ratio of mineral fibres/clay from 7:3 to 6:4 is specially preferred. The length of mineral fibres in th-e. final article is less than 6 mm. The technological process for manufacturi g ceramic material consists of mixing ' raw materials, forming crude products, drying and firing, and it is also an object of the present invention. The process is characterized in that a pumpable aqueous suspension of clay is prepared, mineral fibres and optionally water are added up to the ratio of mineral fibres/clay from 9:1 to 3:7, the suspension is kept homogeneous by stirring, then the raw mixture is formed by means of sucking off the excess of water by vacuum in moulds with reticular bottom until no significant amounts of water can be removed any more, the formed pieces are dried, conveniently at about 100 °C, and fired at temperatures between 800 and 1000 °C. The production can take place in existing tile industry. The process can be carried out continuously and automated to the desired degree. Said process provides that the fibres are homogeneously dispersed in materials and equally oriented in all directions. Thus better mechanical properties of products are achieved. Owing to their porosity crude products are very quickly dried in comparison with tile articles. The aqueous suspension of clay should have such a density that it is appropriate for decanting or pumping. Suitable compositions are in weight ratio of clay to water 1* 1 to 1:2. The suspension can be made from wet worked up clay or dry ground clay. When using wet clays, tilery working-up process is sufficient, all admixtures in clay being crushed under 2 mm. When using dry clays, the exploited crude clay should be dried and then ground to a fineness of -Less than 0.5 mm. The aqueous suspension in water is prepared in both cases in a vessel with a propeller mixer. The obtained suspension is then decanted into a larger collecting vessel, equipped with a stirrer for maintaining the homogeneity of suspension. Into the stirring vessel there are fed the suspension, mineral fibres and additional water. For stirring there are used fast hollow stirrers, e.g. with 2800 rpm. Stirring is continued until there is obtained a pumpable suspension, capable of being cast. As an example there is given the stirring of rock wool on the basis of diabase with fibres of a length up to 3 cm. The materials are fed into a stirring vessel in following quantities: suspension clay.water (weight ratio 1: 1) 180 kg rock wool 120 kg water 400 kg The above composition will result in the composition of a final product, taking into account losses at work, of 40 % of clay and 60 % of mineral fibres, by weight. The quantities fed into the stirring vessel can be varied as to the desired final composition of the formed article. Semi-manufactured articles are then moulded as sche¬ matically represented by Fig. 1 The slurry is pumped from a collecting reservoir, equipped with a stirrer, into a mould where it spreads like a liquid. The mould consists of a frame 1 and a metal net 2 and is placed on a plate 3 of a moulding device. In the.. * plate there is an opening 4, which leads ' into a chamber 6, which chamber is connected to a rotatory vacuum pump with water sealing as ' it is used e.g. in the technology of asbestos-cement products. Over the metal net there is stretched a net 5, made of plastic fabric with apertures between 0.25 and 0.5 mm. Of great importance is a rubber seal 7 between the plate 3 and the frame 1 of the mould, which secures minimum losses of underpressure at sucking off the excessive water from the slurry. The underpressure is switched on by a valve 8 on the tube coming from the vacuum pump. For the above composition, the weight of materials after sucking off water reduces for 45 %, i.e. from 100 1 of slurry there is obtained a semi- manufactured product of 55 1. Hence at moulding, the volume of the raw mixture of fibres/clay/water should be foreseen with regard to the volume of the formed article. Sucking off is continued until no water can be seen on the surface and for a further period until no significant amounts of water percolate any more. E.g. a layer of a thickness of 7 cm has proved to be sucked off to said degree within about a minute. After the sucking off is complete, the frame is separated from the formed product and the raw article is transferred mechanically or by means of a vacuum handle to drying nets. Results of experimetal work according to the present process have shown that a continuous process can be designed, wherein the raw mixture is poured on to an endless net passing through an evacuating zone, then the strip is cut into appropriate sizes and tranr.fer pd to drying nets. Subsequently, semi-manufactured articles are dried. They dry t. a substantially quicker rate than raw products made only of clay. Plates of a thickness of 6 cm with., dry bulft density of about 700 kg/m dry 'for 8 hours at 100 C. In comparison with standard clay products, the drying is complete.y . uπcomp] i C ted with no risk of the cracking of the products. Conventiona. drying rooms as used in tilery are suitable for drying, e.g. drying chambers or drying tunnels with internal hot-air recirculation. Dry semi-manufactured products achieve sufficient strength for further manipulation at being put into the kiln. For firing the products there may be used the conven- tional kilns for tilery, such as circular kilns, chamber kilns or tunnel kilns. The firing temperature and the firing period are the same as used in firing tile products, i.e. between 800 and 1000 °C, and the complete cycle period lasts from 50 hours on, depending upon the kiln. All phases of the technological process re schemati¬ cally shown in Fig. 2. A picture taken by a scanning electronic microscope (Fig. 3) shows a broken surface area of the material, wherein there can be seen a well preserved fibrous texture and the ceramic binding phase over it. ri the stirring phase each fibre is soaked with the clay suspen ion, whereby in the firing phase there is achieved a good ceramic bond between individual fibres or flocks of fibres. This results in a compact porous ceramic material with satisfactory mechanical properties and good thermal characteristics. The invention is illustrated by the following Examples . Example 1 In a stirring vessel of a high rotor rate (2800 rpm) there are stirred 1500 g of waste rock wool, 2250 g _>f an aqueous suspension of clay in a weight ratio of 1:1 and 5000 g of water. After about 5 minutes of stirring, the obtained slurry is poured into a mould with a reticular bottom and excessive water is sucked off. The raw product is released from the r-.--.-uld, dried for 8 hours at 100 °C and fired for 3 hours at 900 C. After cooling the product exhibits the following properties: bulk density 650 kg/m 3 coefficient of thermal conductivity at room temperature λ = 0.13 W/mK bending strength 2.0 MPa compressive strength 5.0 MPa melting point 1120 °C Example 2 1500 g of rock wool granules are given, within 10 to 20 sec. under intensive stirring (I44u rpm), into 3000 g of a 25 % aqueous suspension of clay. Uniformly impregnated granules of rock woll are filled wet into a mould, uniformly distributed by means of vibrating and pressed by means of low pressure to such an extent "that the formed product maintains its shape. The formed product is dried for 2 hours at a temperature of 110 C and fired for 2 hours at a temperature of 900 °C. After cooling the product exhibit,:, the following properties : bulk densi ty 650 kg/ m 3 coefficient ofi thermal ^ conductivity at room temperature Λ - 0. 1 W / mK bending strength 0. 9 MPa .compress ive strength 3 . 0 MPa Example 3 The procedu re i s the same as i n Examp le ?. wi th the only exception that there are taken 1000 g of granules of ceramic fibres and 2000 g of a 25 % aqueous suspension of clay . There is obtained a product wi th the following properties : bulk dens ity 700 kg/ m 3 coefficient of thermal conductivity at room temperature Λ = 0.13 W/mK bendi ng strength 1 . 0 MPa compressive strength 3.5 MPa Example 4 The procedure is the same as in Example 2 with the only exception that there are taken 350 g of granulated glass wool and 1400 g of a 25 % aqueous suspension of clay. Firing takes place at '300 C. There is obtained a product with the following properties: bulk density 7O kg/m 3 coefficient of thermal conductivity at room temperature __ 0.13 W/mK bending strength 0.7 MPa compressive strength 2.8 MPa According to the present process there can be manu¬ factured articles of larger dimensions, e.g. 500 x 1000 mm. and of thicknesses up to 90 mm.

Claims: CLAIMS 1. A porous ceramic material comprising mineral fibres and clay, the weight ratio of mineral fibres to clay being from 9:1 to 3:7. 2. A material according to claim 1, characterized in that all known mineral fibres, rock wool of basalt or diabase type, slag wool, glass wool, ceramic fibres or wastes at the production of articles from mineral fibres are employed as mineral fibres. 3. A material according to claim 1, characterized in that ball clay, ceramic and refractory clays, bentonite and kaolin are used as clays. 4. A material according to claim 1, characterized in that the weight ratio of mineral fibres to clay is from 7:3 to 6:4. 5. A material according to claim 1, characterized in that it has open porosity from 75 to 90 %. 6. A material according to claim 1, characterized in that the coefficient of thermal conductivity thereof is less than 0.2 W/mK, preferably between 0.13 and 0.16 W/mK, at room temperature. 7. A material according to claim 1, characterized in that bulk density thereof is between 350 and 800 kg/m 3 . 8. A material according to claim 1, characterized in that the length of " mineral fibres is under 6 mm. 9. Process for manufacturing a porous ceramic material as defined in claim 1 , characterized in that a pumpable aqueous suspension of clay is prepared, mineral fibres and optionally water are added to the ratio of mineral fibres/clay from 9: 1 to 3:7, the suspension is kept homogeneous by tirring, then the raw mixture is formed by means of sucking off the excess of water by vacuum in moulds with reticular bottom until no significant amounts of water are removed, the formed pieces are dried, conveniently at about 100 °C, and fired at temperatures between 800 and 1000 °C. 10. A process according to claim 9, characterized in that it is carried out continuously. 11. Use of the porous ceramic material according to claim 1 for thermal and high-temperature insulation, for acoustic decorative lining and Tor fire-proof linings .

Inventors: DROLJC STANE, ELERSEK ANDREJ, FERJAN MARJAN, KLADNIK EDO, MAKAROVIC DUSAN, MALI EDVARD, SOBA JURIJ, STADLER ZMAGO, ZAUCER MATJAZ, DROLJC, STANE, ELERSEK, ANDREJ, FERJAN, MARJAN, KLADNIK, EDO, MAKAROVIC, DUSAN, MALI, EDVARD, SOBA, JURIJ, STADLER, ZMAGO, ZAUCER, MATJAZ
Applicants: TERMIKA IND IN MONTAZA IZOLACI, TERMIKA ISOLIERBAU GMBH, Z RAZISKAVO MAT KONST LJUBLJAN, TERMIKA, INDUSTRIJA IN MONTAZA IZOLACIJ, N. SOL. O, ZAVOD RAZISKAVO MAT KONST LJUBLJANA N.SOL.O
Application year: 1985
Main classification: C04B38
IPC codes: C04B14, C04B33, C04B38, E04B1