Title of Invention	A COMPOSITION FOR FORMING POROUS BODIES IN PARTICULAR,CERAMIC AND METAL FOAMS,AND A PROCESS FOR THE PREPARATION THEREOF
Abstract	A composition for forming porous bodies comprising a ceramic or metal powder such as herein described, the ceramic or metal particulate loading being in the range of 10 to 80 volume percent, water, dispersant and at least a binder such as herein described in the range of 4 to 50 wt% on a dry powder weight basis.

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FIELD OF THE INVENTION This invention relates to a composition for forming porous bodies and a process for the preparation thereof This invention further relates to a composition for forming porous bodies, in particular, ceramic and metal foams, and a process for the preparation thereof BACKGROUND OF THE INVENTION Porous metal and ceramic solids have assumed great significance considering the wide number of applications in a large number of areas. Porous metals are being considered for use in terrestrial or space vehicles for their extremely high strength to weight ratios, for energy absorbing structure in situations of accidental impact experienced by vehicles, and for sound absorption applications. Porous ceramics made from the powder route are * considered to be superior over the fibrous ceramic, which pose health hazard The porous ceramics made with powders are extremely lightweight and can have better refractory properties than the fibrous refractories. Porous ceramics are also used for molten metal filtration, hot gas filtration, for making burners that achieve high combustion efficiency, substrates for catalysts, etc. OBJECTS OF THE INVENTION It is therefore an object of this invention to propose a composition for forming porous bodies, such as ceramic and metal foams and a process for the preparation thereof It is further object of this invention to propose a composition for forming porous bodies, such as ceramic and metal foams, which show minimum defects after casting. It is further object of this invention to propose ceramic and metal foams, which have extremely high green and sintered strength. Another object of this invention is to propose ceramic and metal foams, which in the green state can be machined easily or deformed into different shapes. : 2 : These and other objects of the invention will be more apparent from the ensuing description. BRIEF DESCRIPTION OF THE INVENTION Thus according to this invention is provided a composition for forming porous bodies comprising a composition for forming porous bodies comprising a ceramic or metal powder water, dispersant and at least a binder. Thus according to this invention is further provided a process for me preparation porous bodies comprising preparing an aqueous slurry by milling the binder and the ceramic or metal powder, optionally in the presence of a dispersant, followed by foaming the starry and pouring the same into moulds and coagulating the Blurry to obtain rigid foamed samples, drying the samples followed by subjecting the same to binder bum out and sintering. In accordance with this invention, the composition for forming porous bodies includes ceramic or metal powder, dispersant water and ovalbumin directly extracted from eggs or any other form such as dried flakes. The ceramic is such as alumina, zirconia, silicon carbide, silicon nitride, hydroxyapatite, silica, cement, fly ash, etc.) and metal such as aluminium, nickel, titanium, cobalt, steel, other alloys etc. The binder is selected from any of the following: ovalbumin, a mix of ovalbumin and sucrose or any other water soluble natural binder free from metal ions; ovalbumin with organic fugitives like starch in water, and sucrose or other water-soluble natural binder free of metal ions. The albumin acts as a binder which also promoted foaming of the participate slurries without any addition of foaming agent Albumin is environmental friendly, non-toxic and easily available and as extracted from eggs can be used directly with different dilutions with water. The foaming agent is used to create porous bodies wim varied pore volume and structure when using binder system(s) other than ovalbumin and is selected from compounds such as, for example, cetyl trimethyl ammonium bromide (CTMAB) Darvan : 3 : 821A (a polyscrylic acid ammonium salt), or dibasic ammonium citrate or any other aqueous based surfactants can be used for dispersion of ceramic or metal particles in the slurries. The microstructure of foams is most easily and effectively controlled by using different ceramic or metal particulate loading in the range of 10 to 60 volume % in the slurries sad different binder percent from 4 to 50 wt% according to dry powder weight basis. The microstructural parameters such as volume percent porosity, cell-size and connectivity of individual celts in the foams is also controlled by using different dispersant amounts or by adding antifoaming agents such as n-octanol in controlled amounts. The process tor fabrication of ceramic or metal foams from powders involved preparation of aqueous slurries by milling egg white or sucrose or combination of egg white and sucrose-water mix containing the metal or ceramic powder with or without amount of dispersed Homogeneous egg white water premix is prepared using magnetic stirrer at low RPM. The ceramic powder is added in steps as the milling progresses. The solids loading used for preparation of alumina foams were in the range of 15 - 80 volume %. Following milling, the slurry is foamed for different times to different extents. The foamed slurries are poured to molds coated with mold release agents Egg white and the suspended particles in the foamed slurries could be coagulated using acid, base like nitric acid, ammonium hydroxide, or any salts like alminum-nitrate or ammonium nitrate etc. The coagulation step yielded rigid foamed samples. The samples were initially slowly dried under ambient conditions. The samples were then placed in an oven and gradually heated and dried under vacuum. The parts were subjected to binder burn out and were sintered. Foams made from egg white sucrose mixtures could be prepared directly by temperature induced gelation and simultaneous drying. : 4 : For preparing metal foam, the process is similar except that instead of water-albumin mix, as extracted pure albumin is used to prepare the slurries. Use of water with albumin often results in separation of water from the oast This problem can be addressed by using combination of albumin with sucrose which can give better stability in case of foam made of coarser metal powder. Darvan 821A is used to stabilize the aluminium metal particles in the slurry. The rheological behaviour of the slurries is examined by use of parallel plate measurement geometry (40-mm diameter, 1mm gap) and it revealed that a wide range of viscosity such as 0.005 Pas at shear rate of 12.6 s4 of the powder loaded slurry can be used for foaming by this process. Foaming of the slurries can be done by mechanical agitation at different shear rate. For example, the slurries with viscosity values 2.5 pas and above (at shear rate 12.6 s4) can be foamed either by rolling or by tumbling. But the slurry with viscosity values below 2.5 pas (at shear rate 12.6 a4) can be foamed by tumbling at relatively higher shear rate. The foamed slurries are poured into petroleum wax coated molds. Albumin and the suspended particles in the foamed slurries can be coagulated using acid, base or any salts like nitric acid, ammonium hydroxide, aluminium nitrate or ammonium nitrate, etc. The coagulation step yields rigid foamed samples. The samples are initially slowly dried under ambient conditions. The samples are then placed in an oven and gradually heated and dried under vacum. The parts are subjected to binder burn out and are sintered In accordance with an embodiment of this invention, aqueous ceramic-slurries employing albumin (ovalbumin) as a binder, are foamed through mechanical agitation and are cast into moids. The cast-foamed slurries are then coagulated as mentioneld hereinbefore. The dried samples are then subjected to binder burn out and sintering. Foam samples produced by this route have exceptionally high green and sintered strength, the microstructure COD be controlled by the foaming time, the albumin-water ratio, ceramic solids loading in the slurries and the total porosity can be varied upto 90%. The : 5 : percentage of closed and open porosity can be produced easily. Samples produced through this route can be easily green machined to incorporate features that are difficult to cast directly. Use of ovalbumin avoids the problem of coagulating during foaming unlike when separate foaming agents, often ionic in nature, are added to induce foaming of slurries. The use of acid for coagulation of the structure following casting freezes the structure in the slurry. The sample thus produced can be dried rapidly without causing any cracks. In accordance with a further embodiment, aqueous ceramic slurries containing ovalbumin and sucrose are used to create porous bodies with varied pore volume and structure. After casting the samples are gelled initially at room temperature for few hours followed by faster drying nearly at 50°C under vacum which resulted in a strong green body. Samples made with combination of ovalbumin and sucrose exhibit negligible shrinkage and almost no defects (edge defects or cracks). The samples produced through this route have extremely high porosity of nearly 96%. The foam structure in the as foamed slurries is highly stable at room temperature for several days and homogeneous. The green ceramic or metal foam samples produced using mix of ovalbumin and sucrose have negligible shrinkage during drying and are exceptionally strong permitting easy demolding and can be mechanically deformed into different shapes. The foam samples dried under vacuum become hard and if exposed to ambient conditions, they regain moisture and become flexible. They can be pressed from surface to inside to get gradient in porosity and can be cut easily. In accordance with another embodiment of this invention, aqueous ceramic slurries containing sucrose as a binder with conventional foaming agents like Cetyl Tri Methyl Ammonium Bromide (CTMAB) are used to create porous bodies with varied pore volume and structure. Sucrose is environmental friendly, non-toxic and easily available. The microstructure of ceramic foams can be controlled by use of different dispersant amount, sucrose amount and the ceramic solids loading. A combination of foaming and antifoaming agent is used to control the homogeneity of the microstructure and the : 6 : connectivity between the pores and fugitives can be used to influence the pore connectivity. In this case, the similar gelation and drying step can be followed as described in previous paragraph - initial gelation at room temperature for few hours followed by fester drying nearly at 50°C under vacuum can be used. In accordance with yet another embodiment of this invention, a preraix containing albumin and a fugitive like starches is prepared and made into slurry with ceramic or metal powder, dispersant The slurry is foamed through mechanical agitation and cast to obtain the sample. In an alternative embodiment, use is made of oil-water emulsion along with albumin and the above procedure is repeated The use of oil water emulsion or fugitives will provide the additional advantage of contrpl over the microstructure especially the connectivity between individual cells of the foam. The foamed sample can be gelled and dried according to procedures described in preceding paragraphs above. The invention will now be explained in greater detail with the help of the following non-limiting examples. Example 1 Slurries with zirconia loading in the range of 15 - 55 volume % with different ovalbumin-water ratios were prepared. The freshly extracted ovalbumin was homogenized, before use in slurry preparation, using a magnetic stirrer at low RPM. A pre-optimized amount of dispersant was added The slurries were prepared by roll milling the above mix in the presence of spherical zirconia media in a polypropylene container. Following milling, the slurries were foamed via mechanical agitation and were cast into the molds. The cast-foamed slurries were then coagulated by addition of concentrated nitric acid The dried samples were then subjected to binder burn out and sintering. : 7 : Example 2 Aqueous alumina suspensions with 15 - 55 volume % were prepared by roll mixing/milling the constituents for 24 hours, in presence of zirconia milling media (2-3 nun diametre), in polypropylene containers. The suspensions were prepared using alumina powder in water or sucrose (30 wt%) solutions. A pre-optimized amount of the dispersant Darvan 821 A (polyacrylic acid ammonium salt, M.W. = 6,000 R-T. Vanderbilt Inc., USA) was used for the slurry preparation. Foaming of the suspensions was achieved by mechanical agitation in presence of the foaming agent cetyi trimethyl ammonium bromide (CTAB). For all suspensions, l?l of 10 wt % solution of (CTAB) was used per ml of the suspension. The foamed suspensions were cast into petroleum jelly-coated plastic rectangular molds. The cast samples were dried in an oven preheated to temperature 40°C up to a maximum of 24 hours subject to the water content (or ceramic loading). Since the sucrose containing green ceramic foams absorb moisture if left in ambient conditions, it is important to carry out the binder burn out step immediately after drying or the samples must be stored under low humidity conditions. Binder burn out followed by sintering was carried out to get the sintered ceramic foam. Sample made with 35 vol % ceramic and sucrose as binder (10 wt %) using Cetyl TYi Methyl Ammonium Bromide (CTMAB) as a foaming agent resulted in total porosity of 89 % mat included 84 % open porosity and the rest as closed porosity. Linear shrinkage of the sample was around 13 %. Example 3 The processing of alumina foams under this example follows similar steps as in example 1. A special gelation procedure was followed which simplified the overall processing of ceramic foams. The foams were prepared by temperature-induced gelation followed by drying in a single step. In the present case, sucrose was added to the aqueous ceramic : 8 : slurries containing egg white to create the porous bodies with varied pone volume and structure. Samples made with combination of egg white and sucrose exhibited negligible shrinkage and almost no defects (edge defects or cracks). This is unlike samples made with egg white as in example 1, where use of extremely low solids loading (like 20 volume % or below) and high binder content (like 75 volume % or more of egg white in water) resulted in cracking, large shrinkage and the maximum porosity is limited to 92 volume %. The high alumina loading slurry was difficult to achieve with egg white based premise Use of only 1 to 10 wt % sucrose resulted in decrease in viscosity and easier to make 55 and higher solids loading. The samples made from oavlbumin-sucrose mix are homogeneous in microstructure. Using 15 volume % solids loading powder, the porosity of the samples can be made as high 96%. Shaping can be done by a saw in green state. It must be noted that the benefits from addition of sucrose could be utilized for making from slurries with any solids loading. Example 4 A premix containing egg white or egg white and sucrose along with fugitive materials like potato starch was made. Using the above premix a Blurry with silicon carbide powders, dispersant was prepared following the procedures mentioned in the previous examples. The slurries were foamed through mechanical agitation and cast The as cast foams were dried, subjected to binder burn out followed by sintering. Examples A different route was followed in the present case. A foamed ovalbumin-sucrose mix was prepared and was mixed with cement slurry. The mixing resulted in a homogeneous foamed cement slurry which was cast into blocks and allowed to set This resulted in preformed lightweight cement blocks, which could be used in structural applications. : 9 : Example 6 Similar to the preparation of ceramic foams as described in example 3, metal foams were prepared using aqueous premix of ovalbumin-sucrose. Foams with homogeneous microstructure could be prepared even with relatively coarse aluminum powders as large as 50 ?l. These samples were made with 45 volume % aluminum particle slurries. The foams made with these slurries were highly stable and the foam structure could be set simply by temperature induced gelation with simultaneous drying. Example 7 Slurry preparation began with a 15-wt % premix of methacrylamide (MAM) and methylene bisacrylamide (MBAM) in 6:1 ratio and 5 wt % sucrose in water. Dispereant was added to the premix contained in a polypropylene bottle in accordance with the intended alumina solids loading. All slurries were milled and then foamed by mechanical agitation. The foam was gelled rapidly by using about 3 ml of 10 wt % ammonium persulphate (APS) initiator solution and 3 ml of n, n, n', n'-Tetra methyl ethylene di-amine (TEMED) catalyst solution per gm of slurry. The gelled alumina foams were dried and subjected to binder burn out followed by sintering. Hybrid structures such as alternate layers of dense and porous ceramic or graded porosity or porous ceramic blocks coated with dense ceramic layers can be produced by using slurries foamed to different extents or unfoamed as prepared slurries (containing no foaming agent but antifoaming agents to suppress air bubbles. The porosity of samples using albumin as the binder has been tested and the results are shown in Table-1 : 10 : Table-I The linear shrinkage for the above samples from dried to sintered ranged from 16 to 20 %. The Rheology of ceramic and metal slurries prior to foaming is depicted in Fig. 1 of the accompanying drawing where A: 40 vol% ceramic with 2: 1 albumin: water ratio, B: 35 vol% ceramic with 1:1 albumin: water ratio, C: 46 vol% metal with pure albumin, D: 43 vol% metal with 8.3:1 albumin: water ratio. Fig. 2 shows a typical microstructure of a sintered ceramic foam sample. We Claim 1. A composition for forming porous bodies comprising a ceramic or metal powder such as herein described, the ceramic or metal particulate loading being in the range of 10 to 80 volume percent, water, dispersant and at least a binder, such as herein described in the range of 4 to 50 wt % on a dry powder weight basis. 2. The composition as claimed in claim 1, wherein said ceramic is such as alumina, zirconia, silicon carbide, silicon nitride, hydroxyapatite, silica, cement and flyash. 3. The composition as claimed in claim 1, wherein said metal is such as aluminium, nickel, titanium, cobalt, steel and other alloys. 4. The composition as claimed in claim 1, wherein said dispersant is a polyacrylic acid ammonium salt, a dibasic ammonium citrate or any other aqueous based surfactant. 5. The composition as claimed in claim 1, wherein said binder is selected from ovalbumin, a mix of ovalbumin and sucrose or any other water soluble natural binder free form metal ions, ovalbumin with organic fugitives like starch in water, and sucrose or other water soluble natural binder free of metal ions. 6. The composition as claimed in claim 1, wherein a foaming agent is optionally used in combination with a binder other than ovalbumin. 7. The composition as claimed in claim 6, wherein said foaming agent is selected from compounds such as for example cetyl trimethyl ammonium bromide (CTMAB). 8. A process for the preparation of porous bodies comprising preparing an aqueous slurry by milling the binder such as herein described in the range of 4 to 50 wt % based on dry powder wt. and the ceramic or metal powder such as herein described in the range of 10 to 80 volume percent optionally in the presence of a dispersant, followed by foaming the slurry and pouring the same into moulds and coagulating the slurry to obtain rigid foamed samples, drying the samples followed by subjecting the same to binder burn out and sintering. 9. The process as claimed in claim 8, wherein a premix of the binder is first prepared followed by adding the ceramic or metal powder in steps thereto, while milling the mixture. 10. The process as claimed in claim 8, wherein the slurry is foamed for different times to different extents. 11. The process as claimed in claim 8, wherein the foamed slurry is powdered into moulds coated with mold release agents. 12. The process as claimed in claim 8, wherein the slurry is coagulated with a compound such as acid or base like nitric acid, ammanium hydroxide or any other salts like aluminium nitrate, ammonium nitrate. 13. The process as claimed in claim 8, wherein the samples are dried initially slowly dried under ambient conditions followed by heating in an oven at 50-80° C and drying in a vacuum. 14. The process as claimed in claim 8, wherein the binder is added at the beginning of slurry preparation of just prior to completion of the milling / mixing process. 15. The process as claimed in claim 8, wherein the foam is produced through any form of mechanical agitation including roll milling, tumbling in presence of hard ceramic media, high speed stirring or by bubbling or turbulent mixing of gas through the slurry. 16. The process as claimed in claim,8, wherein the slurry is produced by bail milling or . by other high shear mixing / milling arrangements to break down agglomerates in the powders and to mix all constituents homogenousry. 17. The composition as claimed in claim 1, comprising egg white and sucrose or other water soluble natural binder, ceramic or metal powder, water, dispersant and a foaming agent. 18. The composition as claimed in claim 1, comprising egg whire with oil-water emulsion, ceramic or metal powder, water, dispersant. 19. The composition as claimed in claim 1, comprising egg white, organic fugitives like starches in water, ceramic or metal powder, water, dispersant. 20. The composition as claimed in claim 1, comprising" sucrose or other water soluble natural binder, ceramic or metal powder, water, dispersant and a foaming agent. 21. The composition for forming porous bodies substantially as herein described. 22. The process for the preparation of porous bodies substantially as herein described. A composition for forming porous bodies comprising a ceramic or metal powder such as herein described, the ceramic or metal particulate loading being in the range of 10 to 80 volume percent, water, dispersant and at least a binder such as herein described in the range of 4 to 50 wt% on a dry powder weight basis.

Documents:

00331-cal-2002-abstract.pdf

00331-cal-2002-claims.pdf

00331-cal-2002-correspondence.pdf

00331-cal-2002-description(complete).pdf

00331-cal-2002-description(provisional).pdf

00331-cal-2002-drawings.pdf

00331-cal-2002-form-1.pdf

00331-cal-2002-form-18.pdf

00331-cal-2002-form-2.pdf

00331-cal-2002-form-3.pdf

00331-cal-2002-form-5.pdf

00331-cal-2002-g.p.a.pdf

00331-cal-2002-letters patent.pdf

331-CAL-2002-CORRESPONDENCE.pdf

331-CAL-2002-FORM 15.pdf

331-CAL-2002-PA.pdf