Title of Invention

A COMPOSITION OF MAKING LIGHTWEIGHT CERAMIC ARTICLES AND A PROCESS OF MAKING THE SAME.

Abstract In the present invention there is provided a composition for making lightweight ceramic articles, a process for making the same and articles made thereby, wherein the synergistic composition has fibrous materials which are of similar composition to that of the main ceramic articles and a compatible composition is worked out so that the fibre continues to provide strength to the green article through out the intermediate stages from green upto the stage when ceramic bonds of sufficient strength are developed. The lightweight ceramic articles made from the composition and process, are such as translucent ceramic whiteware product, translucent ceramic bone china product and translucent vitreous ceramic whiteware product having a water sorbency of less than 0.5%.
Full Text The present invention relates to a composition for making lightweight ceramic articles, a process for making the same and articles made thereby.
This invention pertains to a composition for making lightweight ceramic ware products suitable for use as fine dinnerware and other low-expansion thermal shock resistant, non-porous (vitreous) ceramic whiteware such as cookware, ceramic tiles, sanitary ware, artware, electrical and technical porcelain. Contrary to expensive dinnerware, however, this invention provides a ceramic having very low thermal expansion. Acceptable translucency for fine dinnerware ordinarily requires at least about 0.9% light transmission per 0.1 inch thickness of test sample when measured by the test method of Shaw (Amer. Ceramic Soc. Bui., Vol. 37, No. 10 (1958), page 448). Non-porosity, conventionally referred to as "vitreous" in the whiteware nomenclature, specifies that the ceramic has less than 0.5% by weight water sorption. Thermal shock resistance refers to the ability of the ceramic to resist cracking and crazing due to rapid changes in temperature and is reported at the maximum temperature differential that a test sample can be rapidly subjected to without causing crazing or other physical defects. For cookware and fine dinnerware, the thermal shock resistance should be a differential of at least about 140°C. Still further, low thermal expansion is required wherein the coefficient of expansion must be less than about 50xlO~7cm./cm./.degree. C.
Vitrification in accordance with this invention produces a ceramic having the foregoing favorable physical characteristics as well as providing a feasible commercial process. To be commercially feasible, opaque, translucent, ceramic whiteware products must be fired within a reasonable vitrification range. Commercial firing kilns require a vitrification (firing) range of at least 40-50°C to allow for temperature variations within commercial equipment.
Conventionally ceramic materials particularly for whitewares related materials the raw materials are taken in participate form. The raw materials are mixed and articles are fabricated by various conventional ceramic fabrication processes as discussed above. To obtain sufficient strength of the fabricated articles the wall thickness cannot be reduced below a certain value. As a result translucency of the fired product reduces to a great extent. To increase the translucency to a desired level glass content of the fired product is increased which has a serious deleterious effect of reducing firing range. It becomes difficult to maintain such a low firing range in commercial kiln. This is precisely the reason for high firing damages of the articles which increases the cost of the produced materials. In addition, more wall thickness means more weight of the articles which not only affects the aesthetics but also contributes in the cost factor.
Although cordierite semicrystalline ceramics are known, none of the hitherto known prior art processes or products achieve all of the foregoing favorable physical and processing characteristics. For example: U.S. Patent No. 3,365,314 suggests a ceramic having several crystallizing phases which have mis-matched indices of refraction thereby precluding the production of a translucent ceramic.
Reference may also be drawn to U.S. Patent No. 3,480,452, which discloses crystalline cordierite from two different frits which similarly produce a cordierite crystalline phase coupled with a second BaO-based phase which results in opacity due to mis-matched indices of refraction of the two crystalline phases.
Further reference may be made to U.S. Patent No. 3,252,811, which suggests a lengthy process for nucleating with ZrOa to produce a multiplicity of inorganic crystals dispersed in a glass phase.
Reference may also be made to U.S. Pat. No. 3,499,787, wherein is disclosed a low-expansion porcelain cordierite body containing lithia to facilitate glazing; however the required lithia promotes a lithia containing crystalline phase which results in mismatched indices with the cordierite crystalline phase thereby causing opacity.
The foregoing patents all fail to suggest a lightweight low-expansion, thermal shock resistant, vitreous, semicrystalline ceramic whiteware body suitable for use to produce fine dinnerware and other low-expansion, thermal resistant, non-porous (vitreous) ceramic whiteware products.
Ceramic raw materials are made into a ceramic body by intimately mixing and usually wet milling the particulate ingredients so as to produce an aqueous slurry or slip suitable for casting in plaster molds; or at lower water content a plastic clay which may be molded or shaped. After drying to evaporate the water, such shaped objects in the "green" state are then fired to a temperature in the region of 1250°C. in order to produce unglazed "china biscuit" ware of low porosity and characteristic translucency. The biscuit ware is subsequently coated with a glaze slip and refired to a temperature of about 1100°C. to produce glazed china. One of the principal characteristics of ware produced in this way is the translucency, coupled with whiteness, for which bone china (sometimes called fine china or English bone china) is renowned. Because of its strength, it is also possible to produce objects of thinner wall section than is the case with other forms of pottery, which enhances lightness of weight, translucency and resistance to thermal shock.
The final microstructure of bone china results from reactions during firing, the crystalline materials originally produced having been dissolved and new crystals formed. Bone china after firing consists of about 70% crystals and 30% of a glassy phase. The crystals are mainly beta-tricalcium phosphate and anorthite (a lime
felspar). The high crystal content of bone china accounts for its good mechanical strength.
Bone china of substantially the above type and composition has been produced for some two hundred years and changes in formulation and fabrication have been evolutionary. The composition requires a higher firing temperature than is needed for earthenware and consequently the firing cycle is comparatively prolonged and the costs of both the kilns and the fuel used are higher. The firing time is also lengthened relative to earthenware in order to allow formation of the calcium phosphate-based phases which impart the characteristic strength and translucency.
Methods for making the ceramic clayware called "white ware", from clay, flint and a flux, in which certain boron-containing compositions are used as the flux are known. According to U.S. Patent No. 3,532,522, a borate other than an alkali metal borate is used as the flux, e.g., calcium borate. According to U.S. Patent No. 3,704,146, a ground vitreous frit which includes 8203 in its oxide analysis is used as the flux. However, thin green unfired products are difficult to handle and as a result excessive breakage is a common phenomenon with such type of materials. This limits the wall thickness of the articles which in turn adversely affect the translucency of the materials. Moreover, to obtain translucency of desired value requires the increasing glass content in the microstructure which again causes more damage due to sagging of the articles during firing.
The primary object of this invention is to provide a composition for making lightweight ceramic articles, which provides strength to a ceramic body during fabrication.
Another object of the present invention is to provide a composition for making lightweight ceramic articles, wherein the composition has compatible fibrous materials.
Yet another object of the present invention is to provide a composition having a vitrification range of at least about 40 to 50°C suitable for firing in a conventional kiln.
Still another object of the present invention is to provide a composition for making lightweight ceramic articles, which is not a mere admixture but a synergistic mixture having properties which are not a mere aggregation of properties of the individual ingredients.
Still yet another object of the present invention is to provide a process for making lightweight ceramic articles from the said composition.
A further object of the present invention is to provide a process for making lightweight ceramic articles, wherein homogenous mechanical mixing of the composition ingredients including fibrous materials is carried out.
A still further object of the present invention is to provide a commercially viable process for producing translucent ceramic whiteware product.
A yet further object of the present invention is to provide a method for producing terra-cotta articles.
Another object of the present invention is to provide a translucent ceramic whiteware product.
Still another object of the present invention is to provide translucent ceramic bone china product.
Yet another object of the present invention is to provide translucent vitreous ceramic whiteware product having a water sorbency of less than 0.5%.
The green strength of the articles may be increased by incorporating high temperature resistant inorganic fibrous materials into the composition in a proportion so that the fired properties of the materials are not affected adversely. If the fibre remains even after firing the translucency of the materials is likely to be reduced and the visibility of fibres will affect the aesthetics of the articles as well. The other disadvantages that may arise due to fibre inclusion into the ceramic body is lowering of mechanical strength if the compatibility of the fibres materials and the ceramic composition is not maintained. Therefore, the best fibrous materials may be of similar chemical composition of the ceramic body and preferably the fibrous materials should chemically react and ultimately become part of the homogenous microstructure developed in the fired articles. During dissolution of the fibres the liquid phase if generated should have high viscosity so that sagging of the articles during firing is prevented.
In the present invention there is provided a composition for making lightweight ceramic articles, a process for making the same and articles made thereby, wherein the synergistic composition has fibrous materials which are of similar composition to that of the main ceramic articles and a compatible composition is worked out so that the fibre will continue to provide strength to the green article upto the stage of complete dissolutions of the fibre into the metrics. In other words fibre should provide strength in the ceramic body through out the intermediate stages from green upto the stage when ceramic bonds of sufficient strength are developed. Therefore,
the main novelty of the present invention lies in providing strength to a ceramic body during fabrication. The novelty is realised by the non-obvious inventive steps of incorporating compatible fibrous materials in the composition and subjecting the composition ingredients to homogeneous mechanical mixing.
Accordingly, the present invention provides a composition for making lightweight
ceramic articles which comprises:
Clay : 20 to 99.5 wt%;
Bone ash : 0 to 50 wt%;
Feldspar : 0 to 20 wt%;
Alumina silicate fibre : 0.5 -10 wt%.
In an embodiment of the present invention, the clay is of generic variety such as china clay, illitic clay, montmorillonitic clay.
In another embodiment of the present invention, the bone ash is of commercial variety.
In still another embodiment of the present invention, the alumino silicate fibre is of commercially available type having composition such as alumina 40 to 60 wt% and silica 60 to 40 wt%.
The composition of the present invention for making lightweight ceramic articles, is not a mere admixture but a synergistic mixture having properties which are not a mere aggregation of properties of the individual ingredients.
Accordingly, the present invention provides a process for making lightweight ceramic articles from the composition as described herein above, which comprises

subjecting the composition ingredients consisting of clay : 20 to 99.5 wt%; bone ash : 0 to 50 wt%; feldspar : 0 to 20 wt% and alumina silicate fibre : 0.5 -10 wt%, to homogeneous mechanical mixing; followed by mixing the resultant composition ingredients mixture with 35 to 40 wt% water for a period in the range of 0.5 to 35 hours; shaping by known ceramic fabrication technique such as slip casting to obtain a green cast body; drying the green and cast body so obtained for a period in the range of 12 to 30 hours in air followed by drying at a temperature in the range of 110 to 120°C for a period in the range of 24 to 30 hours; firing the dried green body at a temperature in the range of 1000 to 1250°C for a period of in the range of 1 to 2 hours followed by glazing by conventional methods.
In an embodiment of the present invention, the homogeneous mechanical mixing of the composition ingredients, such as alumina silicate fibre and the ceramic materials is done by conventional ceramic processing such as ball milling, attrition milling, vibratory milling.
Accordingly, the present invention provides lightweight ceramic articles made from the composition and process, such as herein described.
In an embodiment of the present invention, the lightweight ceramic articles made from the composition and process, are such as translucent ceramic whiteware product, translucent ceramic bone china product.
In another embodiment of the present invention, the lightweight ceramic articles made from the composition and process, are such as translucent vitreous ceramic whiteware product having a water sorbency of less than 0.5%.
The novelty of the composition and process of the present invention resides in:
1. Uniform fibre reinforcement of matrix and improved green strength of the
body, thus providing strength to a ceramic body during fabrication.
2. A composition having a vitrification range of at least about 40 to 50°C
suitable for firing in a conventional kiln.
3. A translucent ceramic whiteware product.
4. A translucent ceramic bone china product.
5. A translucent vitreous ceramic whiteware product having a water sorbency of
less than 0.5%.
6. A process of making translucent ceramic articles.
7. A commercially viable process for producing translucent ceramic whiteware
products.
The novelty of the composition and process of the present invention has been enabled by the non-obvious inventive steps of providing a composition wherein fibrous materials used are of similar composition to that of the main ceramic articles and homogenous mechanical mixing of the composition ingredients. Thereby providing a compatible composition in which the fibre continues to provide strength to the green article upto the stage of complete dissolution of the fibre into the matrix. Thus the novelty of the composition and process of the present invention in providing strength to a ceramic body during fabrication is realized by the non-obvious inventive step of incorporating compatible fibrous materials in the composition and homogenous mechanical mixing of the composition ingredients.
The following examples are given by way of illustration in actual practice of making lightweight ceramic articles by the process from the composition of the present invention and should not be construed to limit the scope of the present invention in any way.
Example 1
995 gms of clay, 5 gms of alumina silicate fibre was thoroughly mixed with 400 cc of water for a period of 30 minutes in a pot mill. The slip thus obtain poured in a plaster mould to get a lightweight ceramic article. The article released from the mould was air dried for 12 hrs. followed by drying at 110°C for 24 hrs. Dried body has a green MOR of 16.8 kg/cm2. Finally, the dried article was fired at 1000°C for one hour soaking. Fired body has a MOR value of 310 kg/cm2 and water absorption of 15.7%.
Example 2
200 gms of clay, 500 gms of bone ash, 200 gms of feldspar and 100 gms of alumina silicate fibre was thoroughly mixed with 350 cc of water for a period of 35 hrs in a pot mill. The slip thus obtain poured in a plaster mould to get a lightweight ceramic article. The article released from the mould air dried for 30 hrs. followed by drying at 110°C for 30 hrs. Dried body has a green MOR of 24.7 kg/cm2. Finally, the dried article was fired at 1250°C for one hour soaking. Fired body has a MOR value of 576 kg/cm2 and water absorption of Example 3
1000 gms of clay was thoroughly mixed with 350 cc of water for a period of 60 minutes in a pot mill. The slip thus obtain poured in a plaster mould to get a lightweight ceramic article. The article released from the mould was air dried for 15 hrs. followed by drying at 120°C for 30 hrs. Dried body has a green MOR of 9.5 kg/cm2. Finally, the dried article was fired at 1010°C for one hour soaking. Fired body has a MOR value of 295 kg/cm2 and water absorption of 16.3%.
Example 4
990 gms of clay, 10 gms of alumina silicate fibre was thoroughly mixed with 375 cc of water for a period of 45 minutes in a pot mill. The slip thus obtain poured in a plaster mould to get a lightweight ceramic article. The article released from the mould was air dried for 20 hrs followed by drying at 110°C for 24 hrs. Dried body has a green MOR of 21.6 kg/cm2. Finally, the dried article was fired at 1020°C for one hour soaking. Fired body has a MOR value of 326 kg/cm2 and water absorption of 15.6%.
Example 5
300 gms of clay, 500 gms of bone ash and 200 gms of feldspar was thoroughly mixed with 350 cc of water for a period of 32 hrs in a pot mill. The slip thus obtain poured in a plaster mould to get a lightweight ceramic article. The article released from the mould air dried for 28 hrs. followed by drying at 110°C for 30 hrs. Dried body has a green MOR of 12.6 kg/cm2 . Finally, the dried article was fired at 1230°C for two hour soaking. Fired body has a MOR value of 559 kg/cm2 and water absorption of Example 6
250 gms of clay, 500 gms of bone ash, 200 gms of feldspar and 50 gms of alumina silicate fibre was thoroughly mixed with 380 cc of water for a period of 34 hrs in a pot mill. The slip thus obtain poured in a plaster mould to get a lightweight ceramic article. The article released from the mould air dried for 30 hrs. followed by drying at 110°C for 30 hrs. Dried body has a green MOR of 19.3 kg/cm2. Finally, the dried article was fired at 1240°C for one hour soaking. Fired body has a MOR value of 565 kg/cm2 and water absorption of The results of the examples detailed herein above are shown in the following table:

(Table Removed)
The results obtained in the examples, as tabulated above shows that the addition of alumino silicate fibre in the composition has improved the strength properties of the compositions both at the green stage as well as in the fired condition.
The main advantages of the present invention are:
1. To provide a composition having a vitrification range of at least about 40 -
50°C suitable for firing in a conventional kiln.
2. To provide a translucent ceramic whiteware product.
3. To provide a translucent ceramic bone china product.
4. To provide a translucent vitreous ceramic whiteware product having a water
sorbency of less than 0.5%.
5. To provide a process of making translucent ceramic articles.
6. To provide a commercial method for producing a translucent ceramic
whiteware product.
7. To provide a method for producing terra-cotta articles.





We claim:
1. A composition for making lightweight ceramic articles which comprises:
Clay : 20 to 99.5 wt%;
Bone ash : 0 to 50 wt%;
Feldspar : 0 to 20 wt%;
Alumina silicate fibre : 0.5 -10 wt%.
2. A composition as claimed in claim 1, wherein the clay is of generic variety such as
china clay, illitic clay, montmorillonitic clay.
3. A composition as claimed in claim 1-2, wherein the bone ash is of commercial
variety.
4. A composition as claimed in claim 1-3, wherein the alumino silicate fibre is of
commercially available type having composition such as alumina 40 to 60 wt% and
silica 60 to 40 wt%.
5. A process for making lightweight ceramic articles from the composition as
claimed in claims 1-4 above, which comprises subjecting the composition
ingredients consisting of clay : 20 to 99.5 wt%; bone ash : 0 to 50 wt%; feldspar : 0
to 20 wt% and alumina silicate fibre : 0.5 -10 wt%, to homogeneous mechanical
mixing; followed by mixing the resultant composition ingredients mixture with 35 to
40 wt% water for a period in the range of 0.5 to 35 hours; shaping by known ceramic
fabrication technique such as slip casting to obtain a green cast body; drying the
green and cast body so obtained for a period in the range of 12 to 30 hours in air
followed by drying at a temperature in the range of 110 to 120°C for a period in the
range of 24 to 30 hours; firing the dried green body at a temperature in the range of
1000 to 1250°C for a period of in the range of Ito 2 hours followed by glazing by conventional methods.
6. A process as claimed in claim 5, wherein the homogeneous mechanical mixing of
the composition ingredients, such as alumina silicate fibre and the ceramic materials
is done by conventional ceramic processing such as ball milling, attrition milling,
vibratory milling.
7. Lightweight ceramic articles made from the composition and process as claimed in
claims 1-6 above.
8. Lightweight ceramic articles made from the composition and process as claimed in
claims herein above, such as translucent ceramic whiteware product, translucent
ceramic bone china product.
9. Lightweight ceramic articles made from the composition and process as claimed in
claims herein above, such as translucent vitreous ceramic whiteware product having
a water sorbency of less than 0.5%.
10. A composition for making lightweight ceramic articles, a process for making the
same and articles made thereby, substantially as herein described with reference to
the examples.

Documents:

673-del-2006-abstract.pdf

673-del-2006-Claims-(19-10-2012).pdf

673-del-2006-claims.pdf

673-del-2006-correspondence-others 1.pdf

673-del-2006-Correspondence-Others-(19-10-2012).pdf

673-del-2006-correspondence-others.pdf

673-del-2006-description (complete).pdf

673-del-2006-description (provisional).pdf

673-del-2006-form-1.pdf

673-del-2006-form-18.pdf

673-del-2006-form-2.pdf

673-del-2006-Form-3-(19-10-2012).pdf

673-del-2006-form-3.pdf

673-del-2006-form-5.pdf


Patent Number 255285
Indian Patent Application Number 673/DEL/2006
PG Journal Number 07/2013
Publication Date 15-Feb-2013
Grant Date 09-Feb-2013
Date of Filing 10-Mar-2006
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address ANUSANDHAN BHAWAN,RAFI MARG, NEW DELHI-110001,INDIA
Inventors:
# Inventor's Name Inventor's Address
1 MAITI HIMADRI SEKHAR CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O JADAVPUR UNIVERSITY, KOLKTA 700 032, INDIA.
2 MUKHOPADHYAY TAPSAS KUMAR CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O JADAVPUR UNIVERSITY, KOLKTA 700 032, INDIA.
3 DAS SWAPAN KUMAR CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O JADAVPUR UNIVERSITY, KOLKTA 700 032, INDIA.
4 DANA KAUSIK CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O JADAVPUR UNIVERSITY, KOLKTA 700 032, INDIA.
5 SARKAR RITWIK CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O JADAVPUR UNIVERSITY, KOLKTA 700 032, INDIA.
6 GHATAK SANKAR CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O JADAVPUR UNIVERSITY, KOLKTA 700 032, INDIA.
PCT International Classification Number C04B 35/16
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA