IL30700A - Process for making ceramics - Google Patents

Description

o»»ep» n wrip "m** -vwa PROCESS FOR MAJQHO CERAMICS This application relates to structural ceramic products like bricks, tiles, pipes, etc. to be fabricated by cementing together granular minerals by means of a unique colloidal mineral cement, under pressure and without sintering.

The invention is based upon the finding that certain mineral colloids are extremely effective cements for a group of granular mineral materials which may be suitably and economically applied as structural components or aggregate in making cex'amic products like bricks, tiles, etc. — It has also been found that a super atmospheric pressure applied to a mixture of granular mineral materials and a colloidal mineral cement produces extraordinary structural strength and water impervic-usness of the products. Furthermore, the setting reaction of said mixture has been found to be substantially proportional to said pressure.

In the prior industrial art of producing useful structural and decorative objects from mineral fragments essentially two types of methods were used to bind the mineral fragments together to yield solid aggregates. These two methods are known as sintering and cementing. An example of sintering is found in the conventional brick and tile industry where clays are formed into objects and heated to the point of sintering, i.e., to the point that at least some of the particles in the mass begin to soften and flow. This incipient melting produces a flux which binds the clay particles together in a solid aggregate. The strength of the bonds between the individual clay particles depends on the degree of sintering. An example of cementing is found in the conventional concrete industr in which particles of sand or sand and gravel are cemented together by means of a Portland type cement.

It is well known-that common bricks, if well sintered under high temperatures^and prolonged heating, are excellent building materials. However, it is equally well known that in order to reduce the high coast of heating in the production of "burned" bricks, heating, and therefore, sintering is often reduced below an adequate minimum with the result that bricks so produced are inadequate in structural strength and most important, they are not impervious to water. The result is that buildings made of > such "under burned" bricks are not weather-proof, hence, damp in rainy weather, and are often disfigured by leaching out of water soluble components in the bricks.

Bricks, tiles, etc., are also commercially produced of granular mineral materials, such as sand and certain types of clay, using a Portland type cement as the cementing medium. Whereas the structural strength and pipes,_ etc., may be' made from universally available raw materials, such as sand, clay, and crushed rock, and most significantly, may be made from industrial mineral waste products such as lime kiln dust, cement dust, rock. dust, and the like.

Still another object of the present invention is to provide a method whereby high quality cermaic products may be made economically in small local plant units as well as in large manufacturing .p.lants .

Finally, a major object of the present invention is to produce attractive top grade structural and decorative ceramic products at a low cost.

These objectives have been achieved primarily by devising a process which requires inexpensive raw materials, and a simple technique which may be practiced in small as well as in large production units.

In U.S. Patent No. 2,733,996, issued February 7, 1956, there is shown a method of making artificial stones. The invention is mainly characterized thereby that a mixture of clay, a magnesium-silicon-fluorine compound (MgSi F6.6H20) or a double salt of magnesium silicon fluoride and ammonium aluminum sulphate - .

(MgSi Fg.6H2O.NII4.Al (SO4) 2) and common salt or calcium is due to the fact that the colloidal, mineral cement of this invention forms an extremely thin film around the granular structural components of the mixture of the two, under the influence of pressure and cohere firmly by chemical and physical forces to the structural elements or aggregates.

It will be realised that the closer the granular materials in the product come together, the more rigid will be the structure of the whole, provided that the cementing material is sufficiently-Jfirm to prevent the granular particles from spatial movements. It is axiomatic that the firmness of the cementing material is inversely related to the thickness of the film it forms between the granular particles to be bound together by means of the cementing film. In other words, the thinner the film, the stronger the bond.

In this invention, the most flavour able requirements for obtaining maximum material strength in the products are achieved due to the fact that the colloidal mixture, forming an extremely thin film around the granular structure particles·, permits nearly theoretical packing of the structural particles, and permits maximum chemical and physical bonds to the structural particles and between the structural particles. product of the invention .can be removed from its mould by hand i-n a matter of a few seconds after the pressure is applied, and that the following curing requires no additiona expense.

This contrasts strikingly from the conventional operating procedure in the art in which the products have to be removed from the moulds on trays, and then cured for several weeks in humidity controlled air, or for 24 hours, or more, in steam chambers.

It has been demonstrated that for a given formula of composition, the strength of finished 'product is proportional to. the pressure applied, and so is the speed of setting of the binding material used. This latter item is arf important economic factor in the production and distribution of the product. Whereas, ordinary concrete bricks, blocks and pipes require a comparatively long period of time for curing prior to shipment, the products of this invention can be transported and used 24 hours after leaving the press.

A preferred pressure for compressing the composition is in excess of 50 Kg per square centimetre.

An extraordinary phenomenon of this invention is the fact that after drying for a day or two, the bricks "ring" jjust like sintered bricks of the highest quality. It is well known that the more or less clear ring of common bricks The fact that the bricks produced according to the present invention have a distinct ring, . indicates that the . bonds between the granular structural components of the bricks, produced by the colloidal binding material under the substantial pressure employed, are in fact of the same order as the bonds between the individual clay particles in well sintered bricks, produced by the heat sintering process. The property of the ring of the products of the present invention is, therefore, a distinction which sets the product apart from- all known ceramic products produced by means of cementing together granular materials.

Whereas, some products require only moderate pressure for adequate structural strength, the better grades of structural ceramics require pressure in the range of 100 to 350 Kg per square centimetre (1422-5000 pounds per square inch depending on the desired strength and hardness of the products to be made. It will be understood, therefore, that the optimum pressure applied may vary from moderate to several hundred atmospheres, depending upon the results desired or required.. . .

In the following table, Table II, several examples are given in compositions of formulas for producing the mineral colloids of this invention. However, it will be understood that these are given by the way of illustration^ . In conjunction with the formulae in Table II, we prefer to use hydrochloric acid as a catalyst in the amount of 0.5 - 1.5%.

The speed-up of the setting reaction due. to the catalytic action of acids is of substantial economic significance since it speeds up the entire production cycle and thus, reduces the production cost.

Table III gives the preferred formula for preparation of the colloidal binder-f,or_ the purpose of producing high grade bricks. ____ Table III Calcium Chloride - 8% Aluminium Chloride - 2% Hydrochloric Acid - 0.5% Water - 89.5% Whereas, the exact chemical reaction or reactions taking place upon mixing of these formulae with the granulous components, i.e., the structural components of the ceramic products to be made, are obscure, it is certain that a substantial portion of the reaction products, whether crystalline or amorphous are colloidal in nature, and have strong chemical and physical affinities for the surfaces of the granular structural or aggregate components of the class as herein specified.

Observation of the products of this invention under on the granular interphases of the structural components, and that the extent of this crystal formation is a function, of both the catalytic action of the acid and the pressure applied.

The chemicals used to produce the colloidal cement in this invention are mixed in water to produce a solution or suspension prior to mixing with the structural components, i.e., the granular, mineral components. In this disclosure and claims, the mixture of the required chemicals in water' will be referred to as the colloidal aqueous solution, regardless of whether the reaction of the chemicals have fully or partly taken place prior to mixing of the aqueous * chemicals to the structural components, or whether the chemical reactions take place v/holly after such mixing has been made.

The amount of colloidal aqueous solution used in compounding a formula depends somewhat on the composition of the structural components used, and upon the product to be made; preferably 8-18% of the weight of the structural components is used. However, these figures may not be taken as limitations, since in some cases the moisture content of the structural components, for instance clay, requires adjustment of the water content of the colloidal solution downward to maintain a preferred total moisture content of the mixture of about 12%.

The preparation of the colloidal aqueous solution involves merely mechanical mixing of the required chemicals in the required amount of water. Heating or cooling is optional. Preferably the colloidal aqueous solution is kept agitated to maintain uniform distribution of the reaction products prior to addition to the structural components of the product to be made, The structural component, or components, may be one, or a judicious combination of several of the following mineral materials: A naturally occurring mineral like sand, clay, diatomaceous earths and the like, or it may be a ground mineral like limestone, sandstone, granite and the like, or it may be' an industrial waste product like cement dust, lime kiln dust, etc.

In some cases where exceptional density and strength of product is required, for instance for SW (severe weather) bricks, a certain percentage of Portland cement may be used in the formula. The Portland cement probably serves both as a cement and as a structural material. However, since this invention is based on the unique application of a colloidal mineral cement as disclosed- above, Portland cement will be classified as structural in the following examples of structural material formulae. See Table IV.

It will be understood that the degree of granulation of the structural mineral matter will depend largely upon content and adjusted for distribution of the granular material and thoroughly blended in a dry-mix machine.

The colloidal aqueous solution is prepared by mixing the chemicals in water in an open tank with an impeller type mixer. Account is made of the water content of the dry-mix materials so as to arrive at a preferred total moisture content of the formula of about 12%. Finally, the dry mix and the aqueous mix are fed simultaneously to a powerful wet-mix machine, thoroughly homogenized, fed to a moulding machine, and compressed into solid aggregates. The pressure is applied quickly and only momentarily, after which the moulded product is ejected from the mould and air dried for more or less 24 hours.

It is obvious that all the above related operations lend themselves to continuous operation, and automatic performance under instrumental control.

In Table 1, the quality of products obtained according to the present invention is given. The Table shows test results reported by a commercial testing laboratory on bricks produced on a pilot plant scale, about 800 bricks per hour capacity, and according to the preferred method disclosed in this specification. The testing results on bricks prepared according to this invention are compared with Changes may. be made in the above without depart from the essential characteristics of the invention as defined in the ensuing claims.

Claims (1)

1. 30700/lV IS CLAIMED IS t « A process for making a ceramic product such as a building brick or tile without heat curing comprising dry mixing at least one mineral aggregate such as sand, crushed rocks, clay and cement dust with Portland cement, adding to such dry mixture a sufficient amount of an aqueous solution of at least one member of the group of alkaldLne earth metal chlorides, earth metal chlorides and their mixtures with hydrogen chloride to provide a plastic mouldable mixture, said chloride group member being present in said solution in a concentration of from 2*5 to 335-», introducing the plastic mouldable mixture into a mould and moulding the same therein under increased pressure of at least 5© atmospheres. The process of making a ceramic product according to Claim 1, in which said alkaline earth metal chloride is a calcium chloride* The process of making a ceramic product according to Claim 1 or Claim 2, in which said earth metal chloride is aluminium chloride* The process of making a ceramic product according to Claim 1, in which said chlorides consist of calcium chloride, aluminium chloride and hydrogen chloride* The process of making a ceramic product as claimed in any of Claims 1 to ^ in which the components include a water soluble mineral acid and/or a water soluble organic acid and/or an acid salt to accelerate the cementing reaction* 30700/ιν * 'Vhe process of making a ceramic roduct as claimed in Claim 5» in which the chloride group member ie a mixture as defined, of hydrochloric acid and a metal chloride /and wherein said acid ie present in said solution in an amount of 0.5 to 1,3£» » A method of making a building brick characterized in that a mixture of mineral aggregate, Portland cement* water and at least one chloride seieoted from the group consisting of alkaline earth metal chloride* earth metal their mixtures with chloride and/hydrogen chloride* is formed in a mould and subjected to a pressure of at least 50 kg per square centimetre in said mould* thqbrick ejected from the mould and exposed to the atmosphere for about 2¾ hours prior to use* * A method of making a building tile characterized in that a mixture of mineral aggregate* Portland cement* water and at least one chloride selected from the group consisting alkaline earth metal chloride* earth metal 'their mixtures with chloride and/hydrogen chloride* is formed in a mould and subjected to a pressure of at least 50 kg per square centimetre in said mould* the tile ejected from the mould and exposed to the atmosphere for about 2h hours prior to use* · Ceramic products when made by the process claimed in any of Claims 1 to 6· 0* Bricks made by the method claimed in Claim 7· 1· Tiles made by the method claimed in Claim 8. 2· Ceramic products made by the method claimed in Claim 1 Ceramic products made by the method claimed in Claim 1 and employing as mineral afjg egates the formulae epeoified in any of the Examples of Table TV herein* Regd. Paienf Aitorneys P. O. Box 33116, TEL-AVIV, ISRAEL