Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Patent
1995-01-27
1998-09-22
Speer, Timothy M.
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
428 98, 428172, 428446, 428688, 428697, 428702, 264 28, 264660, B32B 900
Patent
active
058111719
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to ceramic products, and in particular it relates to ceramic products with high unfired, or "green", strength, especially for use in buildings.
BACKGROUND OF THE INVENTION
It is known to produce fire resistant products for use in buildings and many of these comprise inorganic material such as asbestos bound together into a board or duct. Asbestos is no longer recommended for many applications. These products may take the form of board for use in partitioning or in cladding steel structures. It is important that this material is itself non-flammable and must exhibit poor thermal conductivity so that the temperature of the flame is dropped across the thickness of the material to an acceptable level. This is particularly important when encasing steel structures since in some cases the steel can reach a temperature where it will soften and deform.
As ceramic products are fire resistant (although not necessarily having the low thermal conductivity of fireboard) they are useful as cladding products. However the green strength of most ceramic material limits the size and complexity of shape that can be made owing to handling problems before firing and/or glazing.
It is an object of the present invention to provide a ceramic material which can be formed into boards or other products which have good fire resistance, and to provide a method of making the same.
SUMMARY OF THE INVENTION
According to the first aspect of the present invention there is provided a method of producing a ceramic product comprising the steps of preparing an aqueous slurry of a silica sol with a refractile material comprising a calcium silicate and/or zirconium silicate, causing the slurry to gel by physical or chemical means to form a solid structure, and drying said structure to form a porous ceramic product.
The gelation may be induced by means of a chemical gelling agent, but it is currently preferred to use physical means such as pressure moulding and, in particular, freeze moulding to set the slurry.
Preferably the refractile material, which should be insoluble in water, is a calcium meta-silicate. Preferably, the material includes both calcium and zirconium silicates.
The product can be tailored, or explained more fully hereinafter, to produce a relatively lightweight fireboard or a high green strength ceramic board in large or complex shapes suitable for subsequent firing into a `tilc` (which term is to include moulded three-dimensional shapes as well as simple square or rectangular sheets).
When the resultant product is a ceramic board, it has been found to have unexpectedly high green (unfired) strength and, in addition, the surface of the product produced using this method is particularly suitable for application of ceramic glaze, due to its smoothness, porosity and the absence of materials in the composition which would damage the glaze when burned out during firing. Preferred products are large flat or cornered tiles primarily, but not exclusively, for use as internal or external decorative architectural wall cladding material.
We believe, although the utility of the invention does not depend on the variety of this belief, that the high green strength may be due to one or a combination of the following factors: a) the introduction of divalent, as opposed to trivalent (such as Al.sub.2 O.sub.3), cationic refractile material; b) the change in pH caused by the addition of acid-neutral zirconium silicates into the alkaline sol; and c) the range of refractile particle sizes used, and the total specific surface area of these particles in relation to the silica particles, available for bonding. These may all or in part contribute to the formation of stronger bonds between the silica particles during the gelation process and confer the enhanced green strength properties of the product.
Where a fireboard is required, the product may be of relatively low density, advantageously no more than 850 kg/m.sup.3, ideally 500 or even 250 kg/m.sup.2.
The step of drying may be carried by firing th
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Brown Richard Allan
Jones Ronald
Osborne Martin
S.D. Investments Limited
Speer Timothy M.
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