Compositions: ceramic – Ceramic compositions – Pore-forming
Patent
1991-02-20
1993-01-05
Bell, Mark L.
Compositions: ceramic
Ceramic compositions
Pore-forming
119171, 502 80, C04B 3802
Patent
active
051770369
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to porous ceramic materials and to methods for their production. In particular, the present invention provides a porous ceramic material having absorbent properties which, at least when in a granular form, make it suitable for such end uses as animal litter or industrial absorbent for liquids.
The present invention provides a porous granular ceramic material having a granule size predominantly within the range of from 1 to 5 mm, a bulk density within the range of from 200 to 700 g/l, a porosity within the range of from 55 to 80% v/v, and a liquid absorbency within the range of from 20 to 200% of water based on the weight of granular material. The material preferably has a bulk density within the range of from 350 to 700 g/l, and a liquid absorbency within the range of from 40 to 150%, more preferably 70% to 150%, of water based on the weight of granular material. More preferably, the material has a bulk density of from 350 to 550 g/l, and a porosity of from 65 to 80% v/v.
In one aspect of the invention, in such a porous granular ceramic material the pores are constituted by voids derived from the combustion of a combustible material previously contained therein. The said combustible material is advantageously lignite. The ceramic material is preferably a clay-based material.
The present invention further provides a method for the preparation of a porous ceramic material comprising calcining a mixture of clay and a particulate combustible material, the temperature and time of calcination being such that a substantial amount of the clay minerals remain unvitrified and at least a part of the combustible material is burned off. Preferably, when the product is to be used as an animal litter, substantially all the combustible material is burnt off.
The temperature of calcination is preferably in the range from 800.degree. C. to 1100.degree. C., more preferably from 1000.degree. C. to 1100.degree. C.
As examples of clays suitable for use in the invention there may be mentioned ball clay, especially carbonaceous clay.
When the porous material of the invention is produced from a mixture of clay and lignite the ratio of clay:lignite is preferably within the range of from 1:9 to 9:1, more preferably from 1:2 to 2:1.
The mixture of clay and a combustible material may be obtained by mixing particulate or powdered clay and combustible material with sufficient water to cause the particles to form agglomerates, and drying the agglomerated mixture.
If desired or required, a surfactant or deflocculating agent may be employed to assist in forming a satisfactory mixture.
The aqueous material is preferably dried to a moisture content of not more than 5%, wet basis. The mixture is preferably dried at a temperature of not greater than 200.degree. C. Advantageously, the conditions of the calcination step are such that the weight loss of the mixture is from 40 to 65%, preferably 40 to 55%, based on the weight of the dried mixture.
In a preferred process according to the invention the moist mixture is shaped prior to drying and, if necessary, the dried mixture is divided into granules. The mixture may, for example, be shaped by extrusion, for example using a pug mill or brick extruder, and the extrudate dried, broken and screened to recover granules within the desired size range. Any material screened out may be recycled for use so that the process produces very little waste.
In a particularly advantageous manner of operation the mixture is extruded onto a flat surface so that the granules have at least one flat surface. This allows more efficient packing of the granules in a bed and, when used as animal litter, the improved packing reduces liquid penetration through the bed.
Alternatively, the moist mixture may be formed directly into granules. Granulation may occur in the mixer or the mixture may be subjected to pelletisation for example on a drum or pan pelletiser.
Preferably, the particle sizes of the clay and of the combustible material in the starting mixture are each not greater than 2 mm.
Some
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patent: 491764 (1883-02-01), Butler
patent: 4159008 (1979-06-01), Bavaueas
patent: 4187803 (1980-02-01), Valenta
patent: 4275684 (1981-06-01), Kramer et al.
patent: 4671208 (1982-06-01), Smith
patent: 4824810 (1989-04-01), Lang et al.
Sprechsaal, vol. 103 #19 Oct. 10, 1970 H. Schmidit.
Kunst Franz D.
Payne Arthur F.
Wilkinson Paul A.
Bell Mark L.
Wright Alan
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