Title of Invention

"LOW DENSITY FOAM CERAMIC AND PROCESS THEREOF"

Abstract

The present invention relates to low density foam ceramic with non porous strut having porosity greater than 92%, improved mechanical strength, and pore size in the range of 8 to 30 ppi and a process for preparation of the said foam ceramic by mixing carbohydrate resin to ceramic powder slurry, obtaining ceramic powder filled resin, drying it in air oven at a temperature ranging from 60° C to 120° C, cutting the foamed ceramic thus obtained into a desired shape, debinderising of foamed ceramic by heating up to 600 °C to remove the organics, followed by sintering up to a temperature of 1700 ° C, holding at this temperature for a period of 1 hr to 4 hr to obtained the required low density foam ceramic with non porous strut.

Full Text

LOW DENSITY FOAM CERAMIC AND PROCESS THEREOF FIELD OF INVENTION The present invention relates to low density foam ceramic with non porous strut and its process thereof. BACKGROUND OF INVENTION PRIOR ART Macroporous ceramics are used in applications such as high temperature thermal insulation, catalyst support, diesel engine exhaust filters, industrial hot gas filters and gas combustion burners. [1; 2] Macroporous ceramics are of two types namely reticulate ceramic and foam ceramic. Reticulate ceramics have completely interconnected open pore structure and foam ceramics have a combination of open and closed pores. Reticulate ceramics are usually prepared by polymer sponge impregnation method. US Patent No. 3,090,094 reported this method for the first time. The polymer sponge impregnation method comprises of following steps: (i) Impregnation of a polymer foam (polyurethane or cellulose acetate foam) having desired pore size with a ceramic slurry, (ii) squeezing the excess slurry out by rolling, (iii) drying the solvent in an oven,(iv) burning the polymer foam and (v) sintering of the resulting ceramic replica of the polymer foam. The slurry formulation for impregnation must have thixotropic flow characteristics and for producing the desired flow property some clay materials are also added along with alumina or other ceramic materials. Reticulated ceramics produced by this technique has There are many methods for the preparation of foam ceramics. US Patent No. 6,057,030 describes a method for dispersion of ceramic powder and an easily burnable second phase such as polymer and carbon particles are consolidated in to green body and then the second phase is burnt out carefully to produce porous ceramics [5]. The method is limited to ceramics of low porosities. In another method ceramic slurry containing a suitable foam stabilizer is foamed by in situ generation of gases such as hydrogen and carbon dioxide followed by setting to produce porous bodies. Reaction of acids or acidic phosphates with carbonates and metals is used for in situ generation of carbon dioxide and hydrogen respectively. Porous ceramics produced by this method have very low permeability. Recently, gelcasting process has been used for preparation of ceramic foams. In this method, an aqueous ceramic powder suspension containing a suitable surfactant, an organic monomer such as acrylamide and cross linking agent such as ethylene bisacrylamide is foamed by incorporating a gas like nitrogen or using a blowing agent such as Freon and the foam is stabilized by setting by in situ polymerization of the monomer and cross linking agent [6, 7, 8]. Foam ceramics have also been prepared by foaming an aqueous ceramic slurry containing egg white and other proteins such as albumin followed by setting by thermal coagulation of the protein molecules [9,10]. Most of these foam producing processes give porous bodies of porosity less than 90 %. United States Patent No 3,962,081 describes a process for preparation of an improved ceramic foam filter having a gradation of properties through out the thickness with respect to porosity and pore size by polymer foam impregnation method. United States Patent No 4,024,212 describes a polymer foam impregnation process for preparation of ceramic foam possessing controlled permeability and uniformity which are useful as filters for molten aluminium. United States Patent No 4,056,586 describes preparation of an improved ceramic foam filter for molten metals by polymer foam impregnation technique and a method of filtering molten metal. United States Patent No 4,075,303 describes a process for preparation of ceramic foams with controlled permeability and uniformity by impregnation of open celled organic polymer foam with slurry of thixotropic ceramic composition followed by rolling and heat treatment. The ceramic foams prepared by this invention are useful as filters for molten metals especially aluminium and its alloys. United States Patent No 4,084,980 describes a process for preparation of foamed body from a pasty mixture of aqueous acidic phosphate, a metal blowing agent, a cement material and foam stabilizer such as silica gel, talc and mica. United States Patent No 4,207,113 describes a process for preparation of inorganic foam with cell diameter United States Patent No 4,343,704 describes a process for preparation of an improved foam filter for molten metals from ceramic slurry composition consisting of alumina, montmorillonite, ceramic fibers and ceramic binders by polymer foam impregnation technique. United States Patent No 4,610,832 describes a process for making ceramic foam material having superior strength and durability by a polymer foam impregnation technique using thixotropc ceramic slurry containing alumina hydrate binder. United States Patent No 4,885,263 describes a process for preparation of an improved ceramic foam filter from slurry containing silicon carbide and a colloidal silica binder by polymer foam impregnation technique. United States Patent No 5,441,919 describes a process for preparation of open celled ceramic foam from open celled metal foam coated with a supporting layer followed by oxidation by heat treatment. United States Patent No 5,998,317 describes a phase inversion process for preparation of open celled porous ceramics. In this, a flowable slurry containing ceramic powder, a polymer and dispersant is poured in to a precipitation tank where the polymer coagulates to non flowable mass. This is then dried and heat treated to produce open celled ceramics. United State Patent No 6,171,532 describes a process for preparation of ceramic foam from an inorganic sinterable powder such as alumina, zirconia etc., a blowing agent such as ammonium carbonate and ammonium bicarbonate which liberate carbon dioxide in acidic pH, a pH control material such as phthalic anhydride, Pyromellitic anhydride and maleic anhydride which produce H3O+ and a frame work former such as urea formaldehyde. There are many limitations associated with the reticulate and foam ceramics of the prior art. 1) Porosity of ceramics obtained is less than 92 %. 2) Possess porous strut. 3) Limited mechanical strength of the ceramic obtained. 4) High density of ceramics obtained. 5) Process of preparation utilizes blowing agents and setting agents enabling it to be costly and complicated. 6) Use of organic polymer in the process leads to neurotoxicity. 7) Use of Freon gas as blowing agent causes depletion of ozone layer. Hence, there is a need to develop a ceramic product which is devoid of above limitations and a process to prepare such ceramic products. Therefore it is necessary to develop alternative product and the process technique for preparation of open cell ceramic foams with porosity greater than 92 % and having non porous strut. Accordingly, there is a need for development of low density ceramic foams having non porous strut with porosity greater than 92 % having improved mechanical strength and an inexpensive process for obtaining such ceramic foam. The surprising results of the present invention is achieved by obtaining low density ceramic foam with non porous strut by using hydrophilic resin derived preferably from carbohydrate which provides a medium for uniform distribution of the ceramic powder used. The density of the ceramic powder is lowered up to 30 % of its theoretical density in the ceramic foam with non-porous strut obtained OBJECTS OF THE INVENTION Main object of the invention is to provide low density foam ceramic having non porous strut. An object of the invention is to provide low density foam ceramic having porosity greater than 92 % Another object of the invention is to provide low density foam ceramic having improved mechanical strength. Still another object of the invention is to provide a process for the preparation of low density foam ceramic which finds application in high temperature thermal insulation, molten metal filtration, catalyst support, diesel engine exhaust filters and industrial hot gas filters. Yet another object of the invention is to provide a low cost process for obtaining low density foam ceramics using a carbohydrate resin. Another object of the invention is to provide a process for obtaining low density foam ceramic having porosity > 90 % and a density of up to 30% of theoretical density of the ceramic powder. Further object of the invention is to provide a process for low density foam alumina ceramics with pore size in the range 4 to 30 pores per linear inch (ppi). SUMMARY OF INVENTION The present invention relates to low density foam ceramic with non porous strut having porosity greater than 92 %, improved mechanical strength, and pore size in the range of 4 to 30 ppi and a process for preparation of the said foam ceramic by mixing carbohydrate resin and ceramic powder slurry, obtaining ceramic powder filled resin, drying it in air oven at a temperature ranging from 60°C to 120°C, cutting the foamed ceramic thus obtained into a desired shape, debinderising of foamed ceramic by heating up to 600°C to remove the organics , followed by sintering up to a temperature of 1700°C, holding at this temperature for a period of 1 hr-4 hr to obtained the required low density foam ceramic with non porous strut The invention further relates to a low density foam alumina ceramic and a process thereof. BRIEF DESCRIPTION ACCOMPANYING DRAWING Figure 1 Low density foam ceramic with non porous strut DETAILED DESCRIPTION OF THE INVENTION In accordance with the object, the invention provides low density foam ceramic with non porous strut as represented in figure 1 In an embodiment of the invention provides a process for the preparation of low density foam ceramic comprising steps of: a) treating an aqueous solution of carbohydrate and nitrate salt with acid to adjust the pH of the solution between 1 and 4, preferably 1.5, concentrating the solution to attain viscosity of up to 400 mPa.s. to obtain a carbohydrate resin, b) dispersing ceramic powder having particle size in the range of 0.1 to 5 \xm in an aqueous acidic medium of pH ranging from 1.0 to 4.0, preferably 3.5, for a period of 2 hr to 24 hr to obtain ceramic powder slurry, c) pouring ceramic powder slurry of step (b) to resin of step (a), mixing to obtain ceramic powder filled resin, drying in an air oven at a temperature ranging from 60°C to 120°C in open mould to obtain foamed ceramic, d) cutting foamed ceramic of step (c) into desired shape, debinderising by removing organics from the foamed ceramics by adapting slow rate of heating up to 600°C, e) sintering the debinderised foam ceramic by heating up to a temperature of 1300°C to 1700°C, holding at this temperature for 1 hr to 4 hr to obtain low density foam ceramic with non porous strut. The invention uses ceramic powder selected from a group consisting of alumina, zirconium oxide, silicon carbide and aluminosilicate to obtain ceramic slurry. The invention uses aqueous solution of carbohydrate selected from the group consisting of sucrose, fructose, lactose, glucose and galactose to obtain resin. The invention uses acid selected from the group consisting of hydrochloric acid, nitric acid and acetic acid preferably nitric acid. The invention uses nitrate salt selected from the group consisting of aluminium nitrate, ammonium nitrate, zirconium nitrate, magnesium nitrate and calcium nitrate as one of the ingredient to obtain the resin. The low density foam ceramic with non porous strut of the invention has porosity in the range of 92 % to 98 %, mechanical strength in the range of 0.1 to 3.2 MPa and pore size in the range 4 to 30 ppi. The molar ratio of sucrose to nitrate salt used is in the range of 1:0.028 to 1:0.40 and the molar ratio of sucrose to ceramic powder is in the range of 1:1.5 to 1:7.0. The ceramic slurry of the invention has solid content in the range of 30 to 55 volume %. Debinderising of foamed ceramic of desired shape is achieved by removing organics by heating up to 600°C at slow rate preferably in the range 30°C /h to 120°C/ h. Sintering of the debinderised foamed ceramic, by heating at a rate in the range 60° C /h to 300° C/h up to temperature ranging between 1300 ° C and 1,700 ° C and holding for 1 hr to 4 hrs at this temperature. Porosity and pore size of low density foam ceramic with non porous strut depends on carbohydrate to nitrate mole ratio and carbohydrate to ceramic powder mole ratio. Foam ceramic of the present invention has interconnected voids surrounded by web of ceramics suitable for applications such as molten metal filtration, diesel engine exhaust filters, catalyst support and high temperature thermal insulation. Foam ceramics of the present invention has combination of open and closed pores suitable for high temperature thermal insulation and catalyst support. Aqueous acidic carbohydrate solution when concentrated by heating undergoes polymerization by condensation. The carbohydrate polymer resin containing nitrate on drying undergoes foaming due to nitrous gases generated by the decomposition of the nitrate. The foam obtained showed well defined foam structure. Foam structures obtained by careful heat treatment is highly fragile and even do not have handling strength. Ceramic powder filled resin prepared by mixing the carbohydrate resin with ceramic powder slurries also undergo foaming in to foam structures depending on the carbohydrate to nitrate mole ratio and carbohydrate to ceramic powder mole ratio when heated at temperature in the range 60 to 120° C. Sintering of these foams after careful burn out of organics produce strong foam ceramics. The porosity, pore size and interconnectivity of pores depend on carbohydrate to nitrate mole ratios and carbohydrate to ceramic powder mole ratios. The carbohydrate resin referred to in this application comprises essentially carbohydrate and a nitrate salt. Ceramic powder slurry referred to in this application comprises essentially ceramic powder and an acid. The density of the ceramic powder is lowered up to 30 % of its theoretical density in the ceramic foam with non-porous strut obtained The invention is illustrated by the following examples and should not be construed to limit the scope of the present invention. The present invention is described in term of its specific embodiments and any modifications and equivalents to a person skilled in the art should be included within the scope of the present invention. EXAMPLES Example 1 Ceramic slurry was prepared by dispersing 1.13 moles alumina powder in 35 ml water at pH 3.5 and ball milling for 12 hrs to obtain alumina slurry. Separately preparing carbohydrate slurry from 0.30 moles sucrose and 0.017 moles aluminium nitrate dissolved in water and adjusting the pH of the solution to 1.5 using nitric acid. This solution was concentrated by heating on a hot plate to form a resin. The alumina slurry was poured in to the resin and mixed thoroughly by stirring. The powder filled resin was dried in a Teflon mould at 100°C for 46 hrs. The foam body obtained was cut in to rectangular bodies and heated up to 600°C at rate of 30°C/h and then up to 1600°C at a rate of 300°C/h and held for 2 hrs at the final temperature. Example 2 Ceramic slurry was prepared by dispersing 1.32 moles of alumina powder in 35 ml water at pH 3 and ball milling for 12 hours to obtain alumina slurry. Separately preparing carbohydrate slurry from 0.30 moles sucrose and 0.017 moles aluminium nitrate dissolved in water and pH of the solution was adjusted to 1.5 using nitric acid. The solution was concentrated by heating in on a hot plate to obtain a resin. The alumina slurry was poured in to the resin and mixed thoroughly by stirring. The powder filled resin was dried in an open Teflon mould at 100° C for 48 hrs. The foam body obtained was cut in to rectangular pieces and heated up to 600°C at rate of 30°C/h in air atmosphere and then up to 1600°C at a rate of 300°C/h and held for 2 hrs at the final temperature. Example 3 Ceramic slurry was prepared by dispersing 1.42 moles of zirconium oxide powder in 35 ml water at pH 3 and ball milling for 12 hours to obtain zirconium oxide slurry. Separately preparing carbohydrate slurry from 0.34 moles sucrose and 0.024 moles zirconium nitrate dissolved in water and pH of the solution was adjusted to 1.5 using nitric acid. The solution was concentrated by heating in on a hot plate to obtain a resin. The zirconium oxide slurry was poured in to the resin and mixed thoroughly by stirring. The powder filled resin was dried in an open Teflon mould at 100° C for 47 hrs. The foam body obtained was cut in to rectangular pieces and heated up to 600°C at rate of 30°C/h in air atmosphere and then up to 1600°C at a rate of 300°C/h and held for 2 hrs at the final temperature. Example 4 Ceramic slurry was prepared by dispersing 1.64 moles of zirconium oxide powder in 35 ml water at pH 3 and ball milling for 12 hours to obtain zirconium oxide slurry. Separately preparing carbohydrate slurry from 0.34 moles sucrose and 0.024 moles zirconium nitrate dissolved in water and pH of the solution was adjusted to 1.5 using nitric acid. The solution was concentrated by heating in on a hot plate to obtain a resin. The zirconium oxide slurry was poured in to the resin and mixed thoroughly by stirring. The powder filled resin was dried in an open Teflon mould at 100°C for 47 hrs. The foam body obtained was cut in to rectangular pieces and heated up to 600°C at rate of 30°C/h in air atmosphere and then up to 1600°C at a rate of 300°C/h and held for 2 hrs at the final temperature. REFERENCES 1. Saggio-Woyansky et al. Am.Ceram.Soc. Bull. 71 (1) 1674-82 (1992); 2. Innocentini et al. Am.Ceram.Soc. Bull 78(9) 78-84 (1999) 3. Brown et.al J.Am.Ceram Soc, 77(6) 1467-72 (1994) 4. Innocentini et.al. J.Am.Ceram.Soc, 81(12) 3349-52(1998) 5. Lopes et.al. Mat.Sci. & Eng., 1996, A209, 149-155 6. Sepulved, Am.Ceram.Soc. Bull. 1997, 76 (10) 61-65 7. Binner, Brit.Ceram. Trans. 1997, 96 (6) 247-249 8. Sepulveda et.al J. Euro. Ceram. Soc, 1999, 19 (12) 2059-66 9. Duck et.al. J. Mater. Sci. Lett. 1999(18)1003-1005 10. Garrn et.al. J. Euro. Ceram. Soc. 2004, 24, 579-587 We Claim: 1. A low density foam ceramic with non porous strut comprising of an interconnected ceramic web of porosity in the range of 92% to 98% wherein size of the pore is in the range 8 to 30ppi and the mechanical strength of said foam ceramic is in the range of 0.1 to 3.2 MPa. 2. The foam ceramic as claimed in claim 1 obtained from a ceramic powder, which is selected from a group consisting of alumina, zirconium oxide, silicon carbide and aluminum silicate. 3. A process for the preparation of foam ceramic as claimed in claim 1, said process comprising steps of: a. treating an aqueous solution of carbohydrate and a nitrate salt with an acid to adjust the pH of the solution between 1.0 and 4.0, preferably 1.5, concentrating the solution to attain viscosity of up to 400mPa s, to obtain a carbohydrate resin, b. dispersing ceramic powder having particle size in the range of 0.10 to 5.0 preferably 3.5, for a period of 2 hr to 24 hr to obtain ceramic powder slurry, c. pouring ceramic powder slurry of step( b) to resin of step ( a), mixing to obtain ceramic filled resin, drying in air oven at a temperature ranging from 60° C to 120 ° C up to 48 hours in open mould foamed ceramic, d. cutting foamed ceramic of step (c ) into desired shape, debindersing by removing organics from the foamed ceramics by adapting slow rate of heating up to 600° C, e. sintering the debinderising foam ceramic by heating up to a temperature of 1300 ° C to 1700 ° C, holding at this temperature for 1 hr to 4 hr to obtain low density foam ceramic. 4. The process as claimed in claim 3, wherein the carbohydrate used in step(a) is selected from the group consisting of sucrose, fructose, lactose, glucose, and galactose. 5. The process as claimed in claim 3, wherein the acid used in steps(a) and (b) is selected from the group consisting of hydrochloric acid, nitric acid and acetic acid preferably nitric acid. 6. The process as claimed in claim 3, wherein the nitrate salt used in step(a) is selected from the group consisting of aluminum nitrate , ammonium nitrate , zirconium nitrate , magnesium nitrate and calcium nitrate. 7. The process as claimed in claim 3, wherein the ceramic powder used in step (b) is selected from a group consisting of alumina, zirconium oxide, silicon carbide, and aluminosilicate. 8. The process as claimed in claim 3, wherein the molar ratio of carbohydrate to nitrate used is in the range of 1: 0.028 to 1: 0.400. 9. The process as claimed in claim 3, wherein the molar ratio of carbohydrate to ceramic powder is in the range of 1:1.5 to 1:7.0. 10. The foam ceramic and its process for preparation as herein substantially described with reference to the figure and examples.

Documents:

135-DEL-2005-Abstract-(06-08-2012).pdf

135-del-2005-abstract.pdf

135-DEL-2005-Claims-(06-08-2012).pdf

135-del-2005-claims.pdf

135-DEL-2005-Correspondence Others-(06-08-2012).pdf

135-del-2005-Correspondence-Others-(22-09-2011).pdf

135-del-2005-correspondence-others.pdf

135-del-2005-description (complete).pdf

135-DEL-2005-Drawings-(06-08-2012).pdf

135-del-2005-drawings.pdf

135-del-2005-form-1.pdf

135-del-2005-form-18.pdf

135-del-2005-form-2.pdf

135-del-2005-form-26.pdf

135-del-2005-form-3.pdf

135-del-2005-form-5.pdf

135-del-2005-GPA-(06-08-2012).pdf

135-del-2005-GPA-(22-09-2011).pdf

135-del-2005-petition-137.pdf