Title of Invention	A NOVEL CERAMIC COMPOSITION USEFUL FOR MAKING THIN CERAMIC MICROFILTRATION MEMBRANES AND A PROCESS FOR MAKING THIN CERAMIC MICROFILTRATION MEMBRANES THEREOF.
Abstract	A novel ceramic composition useful for making thin ceramic microfiltration membranes and a process for making thin ceramic microfiltration membranes thereof by Ceramic Powder 60 to 85 wt%, Organic solvent 30 to 45 wt%, Dispersant 0.7 to 2.0 wt% of ceramic powder, Inorganic+Organic binder 5 to 30 wt% of ceramic powder, Additives 0.5 to 15 wt% of ceramic powder, Organic plasticizers 9 to 25 wt% of ceramic powder, Homogenizer 1 to 2.5 wt% of ceramic powder.

Title of Invention

A NOVEL CERAMIC COMPOSITION USEFUL FOR MAKING THIN CERAMIC MICROFILTRATION MEMBRANES AND A PROCESS FOR MAKING THIN CERAMIC MICROFILTRATION MEMBRANES THEREOF.

Abstract

A novel ceramic composition useful for making thin ceramic microfiltration membranes and a process for making thin ceramic microfiltration membranes thereof by Ceramic Powder 60 to 85 wt%, Organic solvent 30 to 45 wt%, Dispersant 0.7 to 2.0 wt% of ceramic powder, Inorganic+Organic binder 5 to 30 wt% of ceramic powder, Additives 0.5 to 15 wt% of ceramic powder, Organic plasticizers 9 to 25 wt% of ceramic powder, Homogenizer 1 to 2.5 wt% of ceramic powder.

Full Text	The present invention relates to a novel ceramic composition useful for making thin ceramic microfiltration membranes and a process for making thin ceramic microfiltration membranes thereof. The invention is useful for sterile filtration of liquids, pre-filtration of liquids with higher suspended matter and microbial impurities, harvesting and concentration of microbes. Ceramic microfiltration membrane discs developed by this process are suitable for reuse after cleaning by acids, dilute alkali covering pH range 0.1 to 14 and other organic solvents. Ceramic membrane discs can also be used after heat sterilization upto about 1000°C as such and upto 500°C when the membrane discs are sealed within a perforated support holder. Such membrane discs may be used for vacuum and/or pressure filtration wherein the trans-membrane pressure should be limited to a maximum of 2 Kg/cm2. For filtration application, the membrane discs sealed within a ceramic perforated disc should be housed in a filtration cell with a leak-proof fitting. The use of such porous discs may also be extended for separation of suspended particulate matter from gases, hot gases, flue gases, fumes etc. using appropriate sealing materials, gasket. Filter paper or cloth has been the traditional material for the separation of solids from liquids or gases. However, use of such materials is limited to relatively coarse particles only. Therefore porous membranes of smaller pore sizes have been fabricated using polymeric materials for filtration of fine particles and microbial impurities from liquids. The major drawbacks of polymeric membranes are : (1) The use of polymeric materials has been restricted to one time use for limited periods within narrow-pH and temperature range. (2) Polymeric materials are also susceptible to microbial attack, organic solvents, cleaning by strong acids, alkalis or organic solvents, deformation under the application of pressure thereby restricting the passage of filtering materials owing to their sponge like behaviour. In order to overcome the above inherent drawbacks of polymeric materials, use of ceramic materials for membrane preparation has gained much importance recently as described in Chan, K. K and Brownstein, A. M., "Ceramic membrane growth prospect and opportunities", Am. Ceram. Soc. Bull., 1991, 70, 703-707. The ceramic membranes are known in both discs and tubular configurations with multilayer structure consisting of a thin porous coating of smaller pore sizes over thicker (1.5 to 2 mm thickness) support of much higher pore sizes so that the thinner finer layer can withstand the filtration pressure during their applications. The drawbacks of the hitherto known ceramic filters are : (1) Higher thickness of existing ceramic discs has some disadvantages like lower permeation rate. (2) Mismatching of two layers causing internal strain resulting in cracks, fissures during pressure filtration applications. (3) The filtration rate is lower due to long tortuous path of the porous matrix through which the fluid needs to pass for producing filtered fluids. (4) The anisotropic property of the multilayered structure of ceramic membrane discs also poses problems during cleaning operation as the impurities retained over thin layer may penetrate into the macroporous layer of the opposite side. Reference may be made to Das, N., Bandyopadhyay, S., Chattopadhyay, D., and Maiti, H. S., "Tape-cast ceramic membranes for microfiltration applications", J. Mater. Sci., 1996, 31, 5221-5225 which is the closest and most relevant prior art wherein flexible tapes were prepared with the alumina powders, suspended in methylethyl ketone - ethyl alcohol azeotropic mixture using phosphate ester as dispersant. The suspension was milled for 4 hour for deflocculation. In the second milling step, polyvinyl butyral as binder and a mixture of polyethylene glycol and benzylbutyl phthalate as plasticizer were added to the suspension and milled for another 20 hour; the suspension after 24 hour milling was degassed and spread on a flat glass bed as a thin layer using a doctor blade which after drying overnight formed green tape. Dried tapes with sufficient strength and flexibility were cut into small pieces in the form of circular discs with diameter ranging from 25 to 50 mm and fired at different temperatures ranging from 1200° to 1500°C for different lengths of time (2 to 12 hour). Both heating and cooling rates were carefully controlled in order to avoid warpage or cracking of the fired discs. The drawbacks of this process are : 1. Presence of higher sized pores in the disc. 2. Poor strength of the porous disc. 3. Warpage of porous discs particularly with increase in size of the disc. From the available prior art, it is apparent that the thinner the porous disc the higher is the filtration rate. Therefore, it is necessary to prepare porous thin ceramic disc using appropriate technique to overcome the aforesaid drawbacks of the existing ceramic membrane discs conventionally prepared by slip casting or pressing process. Reference may be made to Mistier R. E, "Tape casting : the basic process for meeting the needs of the electronic industry", Am. Ceram. Soc. Bull., 1990, 69, 1022-1026 wherein tape casting technique is used as a precursor for fabrication of thin ceramic substrates in the form of sheets, discs required for microelectronic industry. The tape casting technique uses polymer bonded flexible ceramic sheets of thickness varying in the range of 25 to 1000 micron. In this method, ceramic powder of sufficient fineness is mixed with dispersant, binder and a plasticizer in an organic solvent and the thick slurry is passed beneath a knife edge which is placed over a smooth glass plate and can be adjusted to control the thickness of the cast. Generally, minimum amount of organic binder is added to achieve the maximum green and fired density, which results in almost dense impermeable product. Such materials are unsuitable for use as microfiltration membrane. The present invention deals with the preparation of porous sheet and disc by controlling the grain size of ceramic, incorporating minor amount of inorganic binder, and/or burn out additives along with various organic compounds to provide flexibility and bond strength in the green stage and also selecting the sintering temperature to facilitate pore formation. The main object of the present invention is to provide a novel ceramic composition useful for making thin ceramic microfiltration membrane which obviates the above noted drawbacks. Another object of the present invention is to provide a novel ceramic composition wherein ceramic powder, inorganic binder, burn out additives and organic compounds are used to achieve desired fabricational advantage and physico-mechanical properties. Yet another object of the present invention is to provide a process for making thin ceramic microfiltration membrane from the novel composition. Still another object of the present invention is to provide thin ceramic membrane having a perforated dense ceramic support and guard ring. Another object of the present invention is to provide a thin ceramic microfiltration membrane and a perforated dense ceramic support as a base, both duly fixed by sealing to form a composite ceramic microfiltration membrane for pressure or vacuum filtration applications. Accordingly, the present invention provides a novel ceramic composition useful for making thin ceramic microfiltration membranes and a process for making thin 60 to 85 wt%Charactersed by man partice also in the range of 0.2 to 4 micro. 30 to 45 wt% Dispersant Inorganic+Organic binder Additives Organic plasticizers Homogenizer ceramic microfiltration membranes thereof which comprises : Ceramic Powder Organic solvent 0.7 to 2.0 wt% of ceramic powder 5 to 30 wt% of ceramic powder 0.5 to 15 wt% of ceramic powder 9 to 25 wt% of ceramic powder 1 to 2.5 wt% of ceramic powder In an embodiment of the present invention the ceramic powder used may be such as stable oxides, oxyhydroxides and hydroxides of metals and combination thereof. In another embodiment, the ceramic powder used may be of mean particle size/dso in the range of 0.2 to 4.0 micron with modal size dm ~ d50and having purity of at least 96% and containing at most 30% of fines d10 below 0.1 micron. In yet another embodiment of the present invention, the organic solvent used may be such as azeotropic mixture of methylethyl ketone - absolute alcohol, trichloroethylene-absolute alcohol, toluene-methanol system using a suitable dispersant like phosphate ester, menhaden fish oil, glycerol trioleate. In still another embodiment of the present invention, the inorganic binders used may be such as halides, sulphates, borates and phosphates of alkaline earth metals and aluminosilicates in the range of 0.1 to 5 wt % of ceramic powder. In another embodiment of the present invention, organic binders used may be such as poly vinyl butyral, polymethyl methacrylate, poly vinyl alcohol of molecular weight in the range of 36,000 to 1,00,000. In yet another embodiment of the present invention, the ratio of organic to inorganic binder may be in the range of 5 to 50. In still another embodiment of the present invention, the burn out additive used may he such us charcoal, starch, ultra high molecular weight polyethylene. In yet another embodiment of the present invention, dispersant used may be such as phosphate ester, menhaden fish oil, glycerol trioleate in the range of 0.7 to 2.0 wt% of ceramic powder. In another embodiment of the present invention, organic plasticizers used may be such as organic polyhydroxy compounds of molecular weight in the range of 400 to 600 and organic phthalates of molecular weight in the range of 250 to 400 wherein the ratio of the former to latter is 0.8 to 4. In still another embodiment of the present invention, the homogenizer used may be such as cyclohexanone in the range of 1 to 2.5 wt% of ceramic powder. Accordingly, the present invention provides a process for making thin ceramic microfiltration membranes using the abovesaid composition, which comprises dispersing ceramic powder in the organic solvent, in presence of the dispersant to form a slurry allowing the slurry to settle, decanting to separate the supernatant suspension, mixing the supernatant suspension with inorganic binder and burn out additive to obtain a homogeneous mixture, adding organic binder and plasticizers to the said mixture, followed by thorough mixing to obtain a casting slip having viscosity in the range ol' 1000 to 3000 ep, de-airing the slurry, casting in the form of thin sheets by known method and air drying to form a green flexible tape, cutting the said tape into desired shape such as discs, firing in an oxidizing atmosphere under a load of 7 to 50 gm at a temperature in the range of 1200° to 1500°C for 2 to 12 hours at the heating rate of 30° to 200°C per hour after maintaining at 800°C for 2 to 4 hours and cooling at the rate of 60° to 300()C per hour to make the membrane disc. In the drawings accompanying the specification, Fig 1 represents the fired V . sample of an embodiment of a porous thin ceramic membrane disc prepared using the composition and process of the present invention wherein the thickness and diameter are in the range of 100 to 500 micron and 12.5 to 77 laminated by which material not clear. mm. Fig 2 represents laminated and perforated ceramic holder wherein the size of the perforations may be varied from 1 to 4 mm dia and the gap between two perforations may be 1 to 2 mm. Fig 3 shows laminated guard ring of width and thickness between 3 to 4 mm and 200 to 2000 micron respectively. Fig 4a represents the top view and Fig 4b shows the side view of the porous thin ceramic membrane discs sealed within the perforated support. Accordingly, the present invention provides a thin ceramic microfiltration membrane system which comprises a thin ceramic microfiltration membrane disc prepared from the novel composition of the present invention by the abovesaid process, the said disc being provided with a perforated support base and a laminated guard ring, the said membrane disc support base and laminated guard ring being peripherally sealed using known sealants. In an embodiment of the present invention, the perforated support base and guard ring used may be such as dense ceramic tape cast materials prepared from known compositions by known methods. The detailed process steps of the present invention are : Processing of dry ceramic powder to separate oversize fraction in presence of a dispersant and an organic medium consisting of an azeotropic mixture of methyl ethyl kctonc - absolute alcohol or trichlorocthylene — absolute alcohol or toluene-methanol system using a suitable dispersant like phosphate ester or menhaden fish oil or glycerol trioleate and similar compounds, mixing with inorganic binders of 0.1 to 5 wt% of ceramic powder, burn out additives, organic binders, plasticizers and homogenizer for sufficient period to achieve a homogeneous mixture having appropriate viscosity 1000 to 3000 cp, de-airing the slurry to remove entrapped air, casting the slurry in the form of thin sheet with doctor blade, drying the green cast to form a flexible tape, punching of the dry green tapes in desired shape and size, making perforations of the support base, laminating the guard ring over the support base, sintering of the punched disc and perforated base laminated with guard ring, fixing the membrane disc within the fired perforated support base, filling the annular peripheral space with a sealant paste and finally firing the membrane disc and perforated base to develop a glassy bond to seal the two parts together to make the micro filtration membrane system for low volume laboratory filtration application under vacuum or positive pressure. The casting slurry for guard ring and perforated support holder is prepared using ceramic powder of various metal oxides, oxyhydroxides of purity more than 98% having a broad particle size distribution with ratio of d90 to d50 and d50 to d10within the broad range of 2 to 3, the concentration of inorganic binder of halides, sulphates, borates and phosphates of alkaline earth metals and also aluminosilicates being in the range of 0.1 to 5 wt% of ceramic powder, organic binders like polyvinyl butyral, polymethyl methacrylate, polyvinyl alcohols in the range of 5 to 15 wt% of ceramic powder and plasticizer 4 to 15 wt% of ceramic powder consisting a mixture of polyethylene glycol and benzyl butyl phthalate in the ratio of 0.8 to 3, cyclohexanone as homogenizer in the range of 1 to 2 wt% of ceramic powder to control the viscosity in the range 1000 to 3000 cp for casting with doctor blade following known technique. The green tape of support base of 200 to 800 micron thickness is laminated with a stack of 2 to 5 layers under a load of 50 to 100 Kg at varying temperature from ambient to 50°C for 1 to 15 min, subsequently punched and perforated by a ball press of 5 to 50 kg load depending on the size of the perforated base sheet of 15 mm to 100 mm dia and fired between 1500° and 1650°C with heating rate of 30° to 200°C per hour and cooled at the rate of 100° to 300°C per hour and maintaining 2 to 12 hours at 800°C and peak temperature. The present invention is based on the principle of relatively lower solid loading than used for fabrication of dense ceramic matrix using tape casting technique. The solid matrix consists of a mixture of primarily three components, viz. ceramic oxides or partially dehydrated material of metal hydroxide which forms the main matrix producing inter granular pores, inorganic binders which facilitate intergranular bonding and controlled grain growth and some burn out additives which increase the porosity of the matrix producing voids after their burning at higher temperature. The formation of porous thin ceramic matrix is based on the principle of fabrication of flexible tapes by adding organic binders and plasticizers in requisite proportion to produce a slurry of desired viscoelastic properties required for casting in the form of thin tape which retains its shape and form as hard sheet after firing under controlled condition. Presence of smaller particles d!0 is necessary to form a compact of larger size powders by filling the voids without increasing the overall volume of compact and thus reducing the total pore volume as well as the size of the pores. Therefore it is desirable to use powders of narrow particle size distribution with rounded or sub-rounded grains for formation of pores of almost spherical geometry. During sintering, material transport takes place because of the difference in curvature and surface energy leading to neck formation but producing open porosity. The novelty of the ceramic composition of the present invention lies in the introduction of porosity in the matrix and controlling the pore size of thin ceramic microfiltration membrane and providing sufficient strength of the porous matrix to withstand the pressure required for their application. The abovesaid novel features are as a result of the inventive steps : 1. The composition having ceramic powder of the particle size with mean particle size d50~dm, the modal size and containing at most 30 % of fines d]0 below 0.1 micron. 2. The ceramic composition having burn out additives and organic binder to control porosity for sufficient permeability. 3. The ceramic composition having inorganic binder to provide sufficient strength of the porous matrix. 4. The ceramic composition having lower loading of ceramic powder and higher loading of organic binders and plasticizers. The novel ceramic composition of the present invention is not a mere admixture but a synergestic mixture having properties which are not a mere aggregation of the properties of the individual component but distinctly different. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Example 1 67 gm of dry alumina powder of mean particle size d50 1.40 micron having purity of 99.6% alumina containing about 10% below 0.1 micron was taken in polyethylene bottle and 65 cc of azeotropic solvent mixture of methyl ethyl ketone and absolute alcohol containing 1.05 gm of phosphate ester as dispersant was added to form a slurry. After mixing the slurry in a pot mill for 20 hours, the slurry was transferred to a measuring cylinder and allowed to settle for about 20 minutes and the supernatant suspension was decanted out into n polyethylene bottle. 0.8 gm of calcium fluoride, 0.5 gm of magnesium fluoride and 1.3 gm of aluminosilicate as inorganic binder and 6.7 gm of starch as burn out additive were added to the supernatant suspension to form a homogeneous mixture. Thereafter 6 gm of polyvinyl butyral as binder of molecular weight 1,00,000, a mixture of 5.4 gm polyethylene glycol of molecular weight 400 and 1.6 gm of benzyl butyl phthalate as plasticizer of molecular weight 312, 0.7 gm of cyclohexanone as homogenizer were added to the said mixture and thoroughly mixed for 22 hours when a casting slip of viscosity of 1800 cp was achieved. The casting slip was de-aired under vacuum for 1 minute and thereafter the vacuum was maintained for 15 minutes to remove entrapped air. This slip was cast on a smooth and clean glass plate with a laboratory batch type tape casting machine. The blade gap and speed were adjusted for 1.7 mm and 2.0 cm/sec respectively. After drying it in ambient atmosphere for 20 hours the green flexible tape of about 500 micron thick and about 2.37 gm/cc green density was obtained. The green tape was then punched into circular pieces of 40 mm dia with a sharp edged die punch fitted in a ball press. The punched disc was fired in an oxidizing atmosphere at a temperature of 1350°C for 4 hours at the peak temperature under a load of 10 gm in an electrically heated furnace hy healing ul a rate of (>oV per hour aller maintaining 'I hours ul H()()V and cooling at the rale of I()()°C pec hour to make the thin ceramic microfiltration membrane disc. The average shrinkage, bulk density and water absorption of the thin ceramic microfiltration membrane discs were found to be 6.5 %, 2.42 gm/cc and 15 wt% respectively. The casting slurry for support disc and guard ring was prepared using 70 gm of alumina powder of purity 98.2% of average particle si/e 3.2 micron in to an azeotropic solvent mixture of 42 cc methyl ethyl ketone and 21 cc of absolute alcohol containing 0.8 gm of phosphate ester as dispersant, 6 gm of polyvinyl butyral of molecular weight 72,000 as organic binder, a mixture of 6.4 gm polyethylene glycol of molecular weight 400 and 2.2 gm of benzyl butyl phthalate of molecular weight 312 as plasticizer, 0.7 gm cyclohexanone as homogenizer and a mixture of 0.9 gm of calcium fluoride, 0.5 gm of magnesium fluoride and 1.4 gm of aluminosilicate as inorganic binder, mixing to achieve a viscosity of 2200 cp and cast with a batch type tape casting machine following known technique. The dried cast tape was of average thickness of about 400 micron and average density 2.34 gm/cc. From the green tape, two pieces of support base of 55 mm dia and guard rings of outer diameter 55 mm and inner diameter 43 mm were punched, stacked and laminated under a load of 70 Kg. 19 numbers of perforations of 4 mm dia were punched in the central portion of support base leaving a distance of 2 mm between two perforations to prepare green perforated support base. Two punched guard rings were laminated and the laminated ring was subsequently fitted on to the periphery of the perforated support base and finally green perforated support base along with guard ring was fired at 1600°C under load of 25 gm following a schedule of heating at the rate of 30°C per hour maintaining 4 hours at 800°C and 1600°C each and cooling at a rate of 100°C per hour to make the perforated support base. The thin ceramic microfiltration membrane disc, prepared as above, was peripherally sealed within the annular space of the guard ring and perforated support base to make thin ceramic microfiltration membrane system. The filtration rate was found to be about 15 ml per minute using dry suction pump. The bacteriological test showed no colony growth in the filtrate compared to bacterial counts 20 to 50 per ml in control. Example 2 60 gm of dry alumina powder of mean particle size d50 0.52 micron having purity of 96.5% alumina containing about 15% below 0.1 micron was taken in polyethylene bottle and 80 cc of azeotropic solvent mixture of methyl ethyl ketone and absolute alcohol containing 1 gm of phosphate ester as dispersant was added to form a slurry. After mixing the slurry in a pot mill for 18 hours, the slurry was transferred to a measuring cylinder and allowed to settle for about 30 minutes and the supernatant suspension was decanted out into a polyethylene bottle. 0.09 gm of calcium fluoride, 0.06 gm of magnesium fluoride as inorganic binder and 0.6 gm of starch as burn out additive were added to the supernatant suspension to form a homogeneous mixture. Thereafter 8.5 gm of polyvinyl butyral as binder of molecular weight 1,00,000, a mixture of 9 gm polyethylene glycol of molecular weight 400 and 3.5 gm of benzyl butyl phthalate as plasticizer of molecular weight 312, 0.9 gm of cyclohexanone as homogenizer were added to the said mixture and thoroughly mixed for 20 hours when a casting slip of viscosity of 2000 cp was achieved. The casting slip was de-aired under vacuum for 1 minute and thereafter the vacuum was maintained for 15 minutes to remove entrapped air. This slip was cast on a smooth and clean glass plate with a laboratory batch type tape casting machine. The blade gap and speed were adjusted for 1.5 mm and 2.0 cm/sec respectively. After drying it in ambient atmosphere for 20 hours the green flexible tape of about 2.32 gm/cc green density was obtained. The green tape was then punched into circular pieces of 40 mm dia with a sharp edged die punch fitted in a ball press. The punched disc was fired in an oxidizing atmosphere at a temperature of 1300°C for 4 hours at the peak temperature under a load of 8 gm in an electrically heated furnace by heating at a rate of 30°C per hour after maintaining 2 hours at 800°C and cooling at the rate of 60°C per hour to make the thin ceramic microfiltration membrane disc. The average shrinkage, bulk density and thickness of the thin ceramic microfiltration membrane discs were found to be 13%, 2.35 gm/cc and 450 micron respectively. The casting slurry for support disc and guard ring was prepared using 70 gm of alumina powder of purity 98.2% of average particle size 3.2 micron in to an azeotropic solvent mixture of 42 cc methyl ethyl ketone and 21 cc of absolute alcohol containing 0.8 gm of phosphate ester as dispersant, 6 gm of polyvinyl butyral of molecular weight 72,000 as organic binder, a mixture of 6.4 gm polyethylene glycol of molecular weight 400 and 2.2 gm of benzyl butyl phthalate of molecular weight 312 as plasticizer, 0.7 gm cyclohexanone as homogenizer and a mixture of 0.9 gm of calcium fluoride, 0.5 gm of magnesium fluoride and 1.4 gm of aluminosilicate as inorganic binder, mixing to achieve a viscosity of 2200 cp and cast with a batch type tape casting machine following known technique. The dried cast tape was of average thickness of about 400 micron and average density 2.34 gm/cc. From the green tape, two pieces of support base of 55 mm dia and guard rings of outer diameter 55 mm and inner diameter 43 mm were punched, stacked and laminated under a load of 70 Kg. 19 numbers of perforations of 4 mm dia were punched in the central portion of support base leaving a distance of 2 mm between two perforations to prepare green perforated support base. Two punched guard rings were laminated and the laminated ring was subsequently fitted on to the periphery of the perforated support base and finally green perforated support base along with guard ring was fired at 1600°C under load of 25 gm following a schedule of heating at the rate of 30°C per hour maintaining 4 hours at 800°C and 1600°C each and cooling at a rate of 100°C per hour to make the perforated support base. The thin ceramic microfiltration membrane disc, prepared as above, was peripherally sealed within the annular space of the guard ring and perforated support base to make thin ceramic microfiltration membrane system. The filtration rate was found to be about 150 litre per sq. metre per hour using a positive pressure of 0.6 Kg per sq. cm. The bacteriological test showed no colony growth in the filtrate compared to bacterial counts 105 to 10 per ml in control. Example 3 140 gm of dry aluminium oxyhydroxide powder of mean particle size dso 1.60 micron having purity of 98% alumina containing about 5% below 0.1 micron was taken in polyethylene bottle and 140 cc of azeotropic solvent mixture of methyl ethyl ketone and absolute alcohol containing 2.3 gm of phosphate ester as dispersant was added to form a slurry. After mixing the slurry in a pot mill for 20 hours, the slurry was transferred to a measuring cylinder and allowed to settle for about 15 minutes and the supernatant suspension was decanted out into a polyethylene bottle. 0.3 gm of calcium fluoride, 0.8 gm of magnesium fluoride and 2.0 gm of aluminosilicate as inorganic binder and 0.7 gm of charcoal as burn out additive were added to the supernatant suspension to form a homogeneous mixture. Thereafter 35 gm of polyvinyl butyral as binder of molecular weight 72000, a mixture of 26 gm polyethylene glycol of molecular weight 400 and 9 gm of benzyl butyl phthalate as plasticizer of molecular weight 312, 3.5 gm of cyclohexanone as homogenizer were added to the said mixture and thoroughly mixed for 22 hours when a casting slip of viscosity of 1500 cp was achieved. The casting slip was de-aired under vacuum for 1 minute and thereafter the vacuum was maintained for 15 minutes to remove entrapped air. This slip was cast on a smooth and clean glass plate with a laboratory batch type tape casting machine. The blade gap and speed were adjusted for 1.4 mm and 2.0 cm/sec respectively. After drying it in ambient atmosphere for 20 hours the green flexible tape of about 300 micron thick and about 1.80 gm/cc green density was obtained. The green tape was then punched into circular pieces of 40 mm dia with a sharp edged die punch fitted in a ball press. The punched disc was fired in an oxidizing atmosphere at a temperature of 1500°C for 2 hours at the peak temperature under a load of 10 gm in an electrically heated furnace by heating at a rate of 60°C per hour after maintaining 4 hours at 800°C and cooling at the rate of 150°C per hour to make the thin ceramic micro filtration membrane disc. The average porosity of thin ceramic micro filtration membrane discs was found to be 45%. The casting slurry for support disc and guard ring was prepared using 70 gm of alumina powder of purity 98.2% of average particle size 3.2 micron in to an azeotropic solvent mixture of 42 cc methyl ethyl ketone and 21 cc of absolute alcohol containing 0.8 gm of phosphate ester as dispersant, 6 gm of polyvinyl butyral of molecular weight 72,000 as organic binder, a mixture of 6.4 gm polyethylene glycol of molecular weight 400 and 2.2 gm of benzyl butyl phthalate of molecular weight 312 as plasticizer, 0.7 gm cyclohexanone as homogenizer and a mixture of 0.9 gm of calcium fluoride, 0.5 gm of magnesium fluoride and 1.4 gm of aluminosilicate as inorganic binder, mixing to achieve a viscosity of 2200 cp and cast with a batch type tape casting machine following known technique. The dried cast tape was of average thickness of about 400 micron and average density 2.34 gm/cc. From the green tape, two pieces of support base of 55 mm dia and guard rings of outer diameter 55 mm and inner diameter 43 mm were punched, stacked and laminated under a load of 70 Kg. 19 numbers of perforations of 4 mm dia were punched in the central portion of support base leaving a distance of 2 mm between two perforations to prepare green perforated support base. Two punched guard rings were laminated and the laminated ring was subsequently fitted on to the periphery of the perforated support base and finally green perforated support base along with guard ring was fired at 1600°C under load of 25 gm following a schedule of heating at the rate of 30°C per hour maintaining 4 hours at 800°C and 1600°C each and cooling at a rate of 100°C per hour to make the perforated support base. The thin ceramic rnicrofiltration membrane disc, prepared as above, was peripherally sealed within the annular space of the guard ring and perforated support base to make thin ceramic microfiltration membrane system. The filtration rate was found to be about 200 litre per sq. metre per hour using dry suction pump. The bacteriological test showed no colony growth in the filtrate compared to bacterial counts 270 to 300 per ml in control. The main advantages are : (1) Minimum thickness of porous membrane disc. (2) Higher surface smoothness of disc. (3) Strong guard ring and perforated support base for protection of membrane disc. (4) Very smooth (0.5 to 1 µm) and flat surface of guard ring for leak- proof fitting. (5) Control of crack or debonding and stickiness, flatness, surface smoothness and homogeneity of greensheet as well as controlling deformation of the greensheet after firing. Claim : 1. A novel ceramic composition useful for making thin ceramic microfiltration membranes and a process for making thin ceramic microfiltration membranes thereof which comprises : Ceramic Powder 60 to 85 wt%Charactersed by man partice also in the range of 0.2 to 4 micro.Organic solvent 30 to 45 wt% Dispersant 0.7 to 2.0 wt% of ceramic powder Inorganic+Organic binder 5 to 30 wt% of ceramic powder Additives 0.5 to 15 wt% of ceramic powder Organic plasticizers 9 to 25 wt% of ceramic powder Homogenizer 1 to 2.5 wt% of ceramic powder 2. A novel ceramic composition as claimed in claim 1 wherein the ceramic powders used are stable oxides, oxyhydroxides and hydroxides of metals and combination thereof. 3. A novel ceramic composition as claimed in claims 1 to 2 wherein Saide ceramic powder not reaction 85 have with modal size dm-dso containing 30% of the fines dio below 0.1 micron and having a purity of at least 96%. 4. A novel ceramic composition as claimed in claims 1 to 3 wherein the saisd organic solvents used are azeotropic mixture of methyl ethyl ketone- absolute alcohol, trichloroethylene-absolute alcohol, toluene-methanol 5. A novel ceramic composition as claimed in claims 1 to 4 wherein the said inorganic binders are halides, sulphates, borates and phosphates of alkaline earth metals and aluminosilicates in the range of 0.1 to 5.0 wt% of ceramic powder. 6. A novel ceramic composition as claimed in claims 1 to 5 wherein the said organic binder used are polyvinyl butyral, polymethyl methacrylate, polyvinyl alcohol of molecular weight in the range of 36000 to 1 ,00,000. 7. A novel ceramic compositon as claimed in claims 1 to 6 wherein the ratio of organic to inorganic binders is in the range of 5 to 50. 8. A novel ceramic compositon as claimed in claims 1 to 7 wherein the additives used are charcoal, starch, ultra high molecular weight polyethylene in the range of 0.5 to 15 wt% of ceramic powder. 9. A novel ceramic composition as claimed in claims 1 to 8 wherein the said dispersarits used are phosphate ester, menhaden fish oil, glycerol trioleate in the range of 0.7 to 2.0 wt% of ceramic powder. 10. A novel ceramic composition as claimed in claims 1 to 9 wherein the organic plasticiers used are mixture of organic polyhydroxy compounds of molecular weight 400 to 600 and organic phthalates of molecular weight 250 to 400 wherein the ratio of former to latter in the range of 0.8 to 4. 11. A novel ceramic composition as claimed in claims 1 to 10 wherein the homogenizer used is cyclohexanone in the range of 1 to 2.5 wt% of ceramic powder. 12. A process for making thin ceramic microfiltration memtranes using the novel ceramic composition as claimed in claims 1 to 11, which comprises dispersing ceramic powder in the organic solvent in presence of the dispersant to form a slurry allowing the slurry to settle, decanting to separate the supernatant suspension, mixing the supernatant suspension with inorganic binder and additive to obtain a homogeneous mixture, adding to the said mixture organic binder and plasticizers, followed by thorough mixing to obtain a casting slip having viscosity in the range of 1000 to 3000 cp, de-airing the slurry, casting in the form of thin sheets by known method and air drying to form a green flexible tape, cutting the said tape into desired shape such as discs, firing in an oxidizing atmosphere under a load to 7 to 50 gm at a temperature in the range of 1200° to 1500°C for 2 to 12 hours at the heating rate of 30° to 200°C per hour after maintaining at 800°C for 2 to 4 hours and cooling at the rate of 60° to 300°C per hour to make the membrane disc. 13. A novel ceramic composition useful for making thin ceramic microfiltration membranes and a process for making thin ceramic microfiltration membranes thereof substantially as herein described with reference to the examples.

Full Text

The present invention relates to a novel ceramic composition useful for making thin ceramic microfiltration membranes and a process for making thin ceramic microfiltration membranes thereof.
The invention is useful for sterile filtration of liquids, pre-filtration of liquids with higher suspended matter and microbial impurities, harvesting and concentration of microbes. Ceramic microfiltration membrane discs developed by this process are suitable for reuse after cleaning by acids, dilute alkali covering pH range 0.1 to 14 and other organic solvents. Ceramic membrane discs can also be used after heat sterilization upto about 1000°C as such and upto 500°C when the membrane discs are sealed within a perforated support holder. Such membrane discs may be used for vacuum and/or pressure filtration wherein the trans-membrane pressure should be limited to a maximum of 2 Kg/cm2. For filtration application, the membrane discs sealed within a ceramic perforated disc should be housed in a filtration cell with a leak-proof fitting. The use of such porous discs may also be extended for separation of suspended particulate matter from gases, hot gases, flue gases, fumes etc. using appropriate sealing materials, gasket.
Filter paper or cloth has been the traditional material for the separation of solids from liquids or gases. However, use of such materials is limited to
relatively coarse particles only. Therefore porous membranes of smaller pore sizes have been fabricated using polymeric materials for filtration of fine particles and microbial impurities from liquids. The major drawbacks of polymeric membranes are :
(1) The use of polymeric materials has been restricted to one time use for
limited periods within narrow-pH and temperature range.
(2) Polymeric materials are also susceptible to microbial attack, organic
solvents, cleaning by strong acids, alkalis or organic solvents, deformation
under the application of pressure thereby restricting the passage of filtering
materials owing to their sponge like behaviour.
In order to overcome the above inherent drawbacks of polymeric materials, use of ceramic materials for membrane preparation has gained much importance recently as described in Chan, K. K and Brownstein, A. M., "Ceramic membrane growth prospect and opportunities", Am. Ceram. Soc. Bull., 1991, 70, 703-707. The ceramic membranes are known in both discs and tubular configurations with multilayer structure consisting of a thin porous coating of smaller pore sizes over thicker (1.5 to 2 mm thickness) support of much higher pore sizes so that the thinner finer layer can withstand the filtration pressure during their applications.
The drawbacks of the hitherto known ceramic filters are :
(1) Higher thickness of existing ceramic discs has some disadvantages
like lower permeation rate.
(2) Mismatching of two layers causing internal strain resulting in cracks,
fissures during pressure filtration applications.
(3) The filtration rate is lower due to long tortuous path of the porous
matrix through which the fluid needs to pass for producing filtered fluids.
(4) The anisotropic property of the multilayered structure of ceramic
membrane discs also poses problems during cleaning operation as the
impurities retained over thin layer may penetrate into the macroporous layer
of the opposite side.
Reference may be made to Das, N., Bandyopadhyay, S., Chattopadhyay, D., and Maiti, H. S., "Tape-cast ceramic membranes for microfiltration applications", J. Mater. Sci., 1996, 31, 5221-5225 which is the closest and most relevant prior art wherein flexible tapes were prepared with the alumina powders, suspended in methylethyl ketone - ethyl alcohol azeotropic mixture using phosphate ester as dispersant. The suspension was milled for 4 hour for deflocculation. In the second milling step, polyvinyl butyral as binder and a mixture of polyethylene glycol and benzylbutyl phthalate as plasticizer were added to the suspension and milled for another
20 hour; the suspension after 24 hour milling was degassed and spread on a flat glass bed as a thin layer using a doctor blade which after drying overnight formed green tape. Dried tapes with sufficient strength and flexibility were cut into small pieces in the form of circular discs with diameter ranging from 25 to 50 mm and fired at different temperatures ranging from 1200° to 1500°C for different lengths of time (2 to 12 hour). Both heating and cooling rates were carefully controlled in order to avoid warpage or cracking of the fired discs. The drawbacks of this process are :
1. Presence of higher sized pores in the disc.
2. Poor strength of the porous disc.
3. Warpage of porous discs particularly with increase in size of the disc.
From the available prior art, it is apparent that the thinner the porous disc the
higher is the filtration rate. Therefore, it is necessary to prepare porous thin
ceramic disc using appropriate technique to overcome the aforesaid
drawbacks of the existing ceramic membrane discs conventionally prepared
by slip casting or pressing process.
Reference may be made to Mistier R. E, "Tape casting : the basic process for meeting the needs of the electronic industry", Am. Ceram. Soc. Bull., 1990, 69, 1022-1026 wherein tape casting technique is used as a precursor for
fabrication of thin ceramic substrates in the form of sheets, discs required for microelectronic industry. The tape casting technique uses polymer bonded flexible ceramic sheets of thickness varying in the range of 25 to 1000 micron. In this method, ceramic powder of sufficient fineness is mixed with dispersant, binder and a plasticizer in an organic solvent and the thick slurry is passed beneath a knife edge which is placed over a smooth glass plate and can be adjusted to control the thickness of the cast. Generally, minimum amount of organic binder is added to achieve the maximum green and fired density, which results in almost dense impermeable product. Such materials are unsuitable for use as microfiltration membrane. The present invention deals with the preparation of porous sheet and disc by controlling the grain size of ceramic, incorporating minor amount of inorganic binder, and/or burn out additives along with various organic compounds to provide flexibility and bond strength in the green stage and also selecting the sintering temperature to facilitate pore formation.
The main object of the present invention is to provide a novel ceramic composition useful for making thin ceramic microfiltration membrane which obviates the above noted drawbacks.
Another object of the present invention is to provide a novel ceramic composition wherein ceramic powder, inorganic binder, burn out additives
and organic compounds are used to achieve desired fabricational advantage and
physico-mechanical properties.
Yet another object of the present invention is to provide a process for making thin
ceramic microfiltration membrane from the novel composition.
Still another object of the present invention is to provide thin ceramic membrane
having a perforated dense ceramic support and guard ring.
Another object of the present invention is to provide a thin ceramic microfiltration
membrane and a perforated dense ceramic support as a base, both duly fixed by
sealing to form a composite ceramic microfiltration membrane for pressure or
vacuum filtration applications.
Accordingly, the present invention provides a novel ceramic composition useful for
making thin ceramic microfiltration membranes and a process for making thin
60 to 85 wt%Charactersed by man partice also
in the range of 0.2 to 4 micro.
30 to 45 wt%
Dispersant
Inorganic+Organic binder
Additives
Organic plasticizers
Homogenizer
ceramic microfiltration membranes thereof which comprises : Ceramic Powder Organic solvent
0.7 to 2.0 wt% of ceramic powder 5 to 30 wt% of ceramic powder
0.5 to 15 wt% of ceramic powder 9 to 25 wt% of ceramic powder 1 to 2.5 wt% of ceramic powder
In an embodiment of the present invention the ceramic powder used may be
such as stable oxides, oxyhydroxides and hydroxides of metals and
combination thereof.
In another embodiment, the ceramic powder used may be of mean particle
size/dso in the range of 0.2 to 4.0 micron with modal size dm ~ d50and having
purity of at least 96% and containing at most 30% of fines d10 below 0.1
micron.
In yet another embodiment of the present invention, the organic solvent used
may be such as azeotropic mixture of methylethyl ketone - absolute alcohol,
trichloroethylene-absolute alcohol, toluene-methanol system using a suitable
dispersant like phosphate ester, menhaden fish oil, glycerol trioleate.
In still another embodiment of the present invention, the inorganic binders
used may be such as halides, sulphates, borates and phosphates of alkaline
earth metals and aluminosilicates in the range of 0.1 to 5 wt % of ceramic
powder.
In another embodiment of the present invention, organic binders used may
be such as poly vinyl butyral, polymethyl methacrylate, poly vinyl alcohol of
molecular weight in the range of 36,000 to 1,00,000.
In yet another embodiment of the present invention, the ratio of organic to
inorganic binder may be in the range of 5 to 50.
In still another embodiment of the present invention, the burn out additive
used may he such us charcoal, starch, ultra high molecular weight
polyethylene.
In yet another embodiment of the present invention, dispersant used may be
such as phosphate ester, menhaden fish oil, glycerol trioleate in the range of
0.7 to 2.0 wt% of ceramic powder.
In another embodiment of the present invention, organic plasticizers used
may be such as organic polyhydroxy compounds of molecular weight in the
range of 400 to 600 and organic phthalates of molecular weight in the range
of 250 to 400 wherein the ratio of the former to latter is 0.8 to 4.
In still another embodiment of the present invention, the homogenizer used
may be such as cyclohexanone in the range of 1 to 2.5 wt% of ceramic
powder.
Accordingly, the present invention provides a process for making thin
ceramic microfiltration membranes using the abovesaid composition, which
comprises dispersing ceramic powder in the organic solvent, in presence of
the dispersant to form a slurry allowing the slurry to settle, decanting to
separate the supernatant suspension, mixing the supernatant suspension with
inorganic binder and burn out additive to obtain a homogeneous mixture,
adding organic binder and plasticizers to the said mixture, followed by
thorough mixing to obtain a casting slip having viscosity in the range ol' 1000 to 3000 ep, de-airing the slurry, casting in the form of thin sheets by known method and air drying to form a green flexible tape, cutting the said tape into desired shape such as discs, firing in an oxidizing atmosphere under a load of 7 to 50 gm at a temperature in the range of 1200° to 1500°C for 2 to 12 hours at the heating rate of 30° to 200°C per hour after maintaining at 800°C for 2 to 4 hours and cooling at the rate of 60° to 300()C per hour to make the membrane disc. In the drawings accompanying the specification, Fig 1 represents the fired
V .
sample of an embodiment of a porous thin ceramic membrane disc prepared using the composition and process of the present invention wherein the
thickness and diameter are in the range of 100 to 500 micron and 12.5 to 77
laminated by which material not clear.
mm. Fig 2 represents laminated and perforated ceramic holder wherein the
size of the perforations may be varied from 1 to 4 mm dia and the gap between two perforations may be 1 to 2 mm. Fig 3 shows laminated guard ring of width and thickness between 3 to 4 mm and 200 to 2000 micron respectively. Fig 4a represents the top view and Fig 4b shows the side view of the porous thin ceramic membrane discs sealed within the perforated support.
Accordingly, the present invention provides a thin ceramic microfiltration membrane system which comprises a thin ceramic microfiltration membrane disc prepared from the novel composition of the present invention by the abovesaid process, the said disc being provided with a perforated support base and a laminated guard ring, the said membrane disc support base and laminated guard ring being peripherally sealed using known sealants. In an embodiment of the present invention, the perforated support base and guard ring used may be such as dense ceramic tape cast materials prepared from known compositions by known methods. The detailed process steps of the present invention are : Processing of dry ceramic powder to separate oversize fraction in presence of a dispersant and an organic medium consisting of an azeotropic mixture of methyl ethyl kctonc - absolute alcohol or trichlorocthylene — absolute alcohol or toluene-methanol system using a suitable dispersant like phosphate ester or menhaden fish oil or glycerol trioleate and similar compounds, mixing with inorganic binders of 0.1 to 5 wt% of ceramic powder, burn out additives, organic binders, plasticizers and homogenizer for sufficient period to achieve a homogeneous mixture having appropriate viscosity 1000 to 3000 cp, de-airing the slurry to remove entrapped air, casting the slurry in the form of thin sheet with doctor blade, drying the
green cast to form a flexible tape, punching of the dry green tapes in desired shape and size, making perforations of the support base, laminating the guard ring over the support base, sintering of the punched disc and perforated base laminated with guard ring, fixing the membrane disc within the fired perforated support base, filling the annular peripheral space with a sealant paste and finally firing the membrane disc and perforated base to develop a glassy bond to seal the two parts together to make the micro filtration membrane system for low volume laboratory filtration application under vacuum or positive pressure.
The casting slurry for guard ring and perforated support holder is prepared using ceramic powder of various metal oxides, oxyhydroxides of purity more than 98% having a broad particle size distribution with ratio of d90 to d50 and d50 to d10within the broad range of 2 to 3, the concentration of inorganic binder of halides, sulphates, borates and phosphates of alkaline earth metals and also aluminosilicates being in the range of 0.1 to 5 wt% of ceramic powder, organic binders like polyvinyl butyral, polymethyl methacrylate, polyvinyl alcohols in the range of 5 to 15 wt% of ceramic powder and plasticizer 4 to 15 wt% of ceramic powder consisting a mixture of polyethylene glycol and benzyl butyl phthalate in the ratio of 0.8 to 3, cyclohexanone as homogenizer in the range of 1 to 2 wt% of ceramic
powder to control the viscosity in the range 1000 to 3000 cp for casting with doctor blade following known technique.
The green tape of support base of 200 to 800 micron thickness is laminated with a stack of 2 to 5 layers under a load of 50 to 100 Kg at varying temperature from ambient to 50°C for 1 to 15 min, subsequently punched and perforated by a ball press of 5 to 50 kg load depending on the size of the perforated base sheet of 15 mm to 100 mm dia and fired between 1500° and 1650°C with heating rate of 30° to 200°C per hour and cooled at the rate of 100° to 300°C per hour and maintaining 2 to 12 hours at 800°C and peak temperature.
The present invention is based on the principle of relatively lower solid loading than used for fabrication of dense ceramic matrix using tape casting technique. The solid matrix consists of a mixture of primarily three components, viz. ceramic oxides or partially dehydrated material of metal hydroxide which forms the main matrix producing inter granular pores, inorganic binders which facilitate intergranular bonding and controlled grain growth and some burn out additives which increase the porosity of the matrix producing voids after their burning at higher temperature. The formation of porous thin ceramic matrix is based on the principle of fabrication of flexible tapes by adding organic binders and plasticizers in
requisite proportion to produce a slurry of desired viscoelastic properties required for casting in the form of thin tape which retains its shape and form as hard sheet after firing under controlled condition. Presence of smaller particles d!0 is necessary to form a compact of larger size powders by filling the voids without increasing the overall volume of compact and thus reducing the total pore volume as well as the size of the pores. Therefore it is desirable to use powders of narrow particle size distribution with rounded or sub-rounded grains for formation of pores of almost spherical geometry. During sintering, material transport takes place because of the difference in curvature and surface energy leading to neck formation but producing open porosity. The novelty of the ceramic composition of the present invention lies in the
introduction of porosity in the matrix and controlling the pore size of thin

ceramic microfiltration membrane and providing sufficient strength of the
porous matrix to withstand the pressure required for their application.
The abovesaid novel features are as a result of the inventive steps :
1. The composition having ceramic powder of the particle size with mean
particle size d50~dm, the modal size and containing at most 30 % of fines d]0
below 0.1 micron.
2. The ceramic composition having burn out additives and organic binder to
control porosity for sufficient permeability.
3. The ceramic composition having inorganic binder to provide sufficient
strength of the porous matrix.
4. The ceramic composition having lower loading of ceramic powder and
higher loading of organic binders and plasticizers.
The novel ceramic composition of the present invention is not a mere
admixture but a synergestic mixture having properties which are not a mere
aggregation of the properties of the individual component but distinctly
different.
The following examples are given by way of illustration and therefore
should not be construed to limit the scope of the present invention.
Example 1
67 gm of dry alumina powder of mean particle size d50 1.40 micron having purity of 99.6% alumina containing about 10% below 0.1 micron was taken in polyethylene bottle and 65 cc of azeotropic solvent mixture of methyl ethyl ketone and absolute alcohol containing 1.05 gm of phosphate ester as dispersant was added to form a slurry. After mixing the slurry in a pot mill for 20 hours, the slurry was transferred to a measuring cylinder and allowed
to settle for about 20 minutes and the supernatant suspension was decanted out into n polyethylene bottle. 0.8 gm of calcium fluoride, 0.5 gm of magnesium fluoride and 1.3 gm of aluminosilicate as inorganic binder and 6.7 gm of starch as burn out additive were added to the supernatant suspension to form a homogeneous mixture. Thereafter 6 gm of polyvinyl butyral as binder of molecular weight 1,00,000, a mixture of 5.4 gm polyethylene glycol of molecular weight 400 and 1.6 gm of benzyl butyl phthalate as plasticizer of molecular weight 312, 0.7 gm of cyclohexanone as homogenizer were added to the said mixture and thoroughly mixed for 22 hours when a casting slip of viscosity of 1800 cp was achieved. The casting slip was de-aired under vacuum for 1 minute and thereafter the vacuum was maintained for 15 minutes to remove entrapped air. This slip was cast on a smooth and clean glass plate with a laboratory batch type tape casting machine. The blade gap and speed were adjusted for 1.7 mm and 2.0 cm/sec respectively. After drying it in ambient atmosphere for 20 hours the green flexible tape of about 500 micron thick and about 2.37 gm/cc green density was obtained. The green tape was then punched into circular pieces of 40 mm dia with a sharp edged die punch fitted in a ball press. The punched disc was fired in an oxidizing atmosphere at a temperature of 1350°C for 4 hours at the peak temperature under a load of 10 gm in an electrically heated
furnace hy healing ul a rate of (>oV per hour aller maintaining 'I hours ul H()()V and cooling at the rale of I()()°C pec hour to make the thin ceramic microfiltration membrane disc. The average shrinkage, bulk density and water absorption of the thin ceramic microfiltration membrane discs were found to be 6.5 %, 2.42 gm/cc and 15 wt% respectively. The casting slurry for support disc and guard ring was prepared using 70 gm of alumina powder of purity 98.2% of average particle si/e 3.2 micron in to an azeotropic solvent mixture of 42 cc methyl ethyl ketone and 21 cc of absolute alcohol containing 0.8 gm of phosphate ester as dispersant, 6 gm of polyvinyl butyral of molecular weight 72,000 as organic binder, a mixture of 6.4 gm polyethylene glycol of molecular weight 400 and 2.2 gm of benzyl butyl phthalate of molecular weight 312 as plasticizer, 0.7 gm cyclohexanone as homogenizer and a mixture of 0.9 gm of calcium fluoride, 0.5 gm of magnesium fluoride and 1.4 gm of aluminosilicate as inorganic binder, mixing to achieve a viscosity of 2200 cp and cast with a batch type tape casting machine following known technique. The dried cast tape was of average thickness of about 400 micron and average density 2.34 gm/cc. From the green tape, two pieces of support base of 55 mm dia and guard rings of outer diameter 55 mm and inner diameter 43 mm were punched, stacked and laminated under a load of 70 Kg. 19 numbers of perforations of
4 mm dia were punched in the central portion of support base leaving a distance of 2 mm between two perforations to prepare green perforated support base. Two punched guard rings were laminated and the laminated ring was subsequently fitted on to the periphery of the perforated support base and finally green perforated support base along with guard ring was fired at 1600°C under load of 25 gm following a schedule of heating at the rate of 30°C per hour maintaining 4 hours at 800°C and 1600°C each and cooling at a rate of 100°C per hour to make the perforated support base. The thin ceramic microfiltration membrane disc, prepared as above, was peripherally sealed within the annular space of the guard ring and perforated support base to make thin ceramic microfiltration membrane system. The filtration rate was found to be about 15 ml per minute using dry suction pump. The bacteriological test showed no colony growth in the filtrate compared to bacterial counts 20 to 50 per ml in control.
Example 2
60 gm of dry alumina powder of mean particle size d50 0.52 micron having purity of 96.5% alumina containing about 15% below 0.1 micron was taken in polyethylene bottle and 80 cc of azeotropic solvent mixture of methyl ethyl ketone and absolute alcohol containing 1 gm of phosphate ester as
dispersant was added to form a slurry. After mixing the slurry in a pot mill for 18 hours, the slurry was transferred to a measuring cylinder and allowed to settle for about 30 minutes and the supernatant suspension was decanted out into a polyethylene bottle. 0.09 gm of calcium fluoride, 0.06 gm of magnesium fluoride as inorganic binder and 0.6 gm of starch as burn out additive were added to the supernatant suspension to form a homogeneous mixture. Thereafter 8.5 gm of polyvinyl butyral as binder of molecular weight 1,00,000, a mixture of 9 gm polyethylene glycol of molecular weight 400 and 3.5 gm of benzyl butyl phthalate as plasticizer of molecular weight 312, 0.9 gm of cyclohexanone as homogenizer were added to the said mixture and thoroughly mixed for 20 hours when a casting slip of viscosity of 2000 cp was achieved. The casting slip was de-aired under vacuum for 1 minute and thereafter the vacuum was maintained for 15 minutes to remove entrapped air. This slip was cast on a smooth and clean glass plate with a laboratory batch type tape casting machine. The blade gap and speed were adjusted for 1.5 mm and 2.0 cm/sec respectively. After drying it in ambient atmosphere for 20 hours the green flexible tape of about 2.32 gm/cc green density was obtained. The green tape was then punched into circular pieces of 40 mm dia with a sharp edged die punch fitted in a ball press. The punched disc was fired in an oxidizing atmosphere at a temperature of
1300°C for 4 hours at the peak temperature under a load of 8 gm in an electrically heated furnace by heating at a rate of 30°C per hour after maintaining 2 hours at 800°C and cooling at the rate of 60°C per hour to make the thin ceramic microfiltration membrane disc. The average shrinkage, bulk density and thickness of the thin ceramic microfiltration membrane discs were found to be 13%, 2.35 gm/cc and 450 micron respectively.
The casting slurry for support disc and guard ring was prepared using 70 gm of alumina powder of purity 98.2% of average particle size 3.2 micron in to an azeotropic solvent mixture of 42 cc methyl ethyl ketone and 21 cc of absolute alcohol containing 0.8 gm of phosphate ester as dispersant, 6 gm of polyvinyl butyral of molecular weight 72,000 as organic binder, a mixture of 6.4 gm polyethylene glycol of molecular weight 400 and 2.2 gm of benzyl butyl phthalate of molecular weight 312 as plasticizer, 0.7 gm cyclohexanone as homogenizer and a mixture of 0.9 gm of calcium fluoride, 0.5 gm of magnesium fluoride and 1.4 gm of aluminosilicate as inorganic binder, mixing to achieve a viscosity of 2200 cp and cast with a batch type tape casting machine following known technique. The dried cast tape was of average thickness of about 400 micron and average density 2.34 gm/cc. From the green tape, two pieces of support base of 55 mm dia and guard
rings of outer diameter 55 mm and inner diameter 43 mm were punched, stacked and laminated under a load of 70 Kg. 19 numbers of perforations of 4 mm dia were punched in the central portion of support base leaving a distance of 2 mm between two perforations to prepare green perforated support base. Two punched guard rings were laminated and the laminated ring was subsequently fitted on to the periphery of the perforated support base and finally green perforated support base along with guard ring was fired at 1600°C under load of 25 gm following a schedule of heating at the rate of 30°C per hour maintaining 4 hours at 800°C and 1600°C each and cooling at a rate of 100°C per hour to make the perforated support base. The thin ceramic microfiltration membrane disc, prepared as above, was peripherally sealed within the annular space of the guard ring and perforated support base to make thin ceramic microfiltration membrane system. The filtration rate was found to be about 150 litre per sq. metre per hour using a positive pressure of 0.6 Kg per sq. cm. The bacteriological test showed no colony growth in the filtrate compared to bacterial counts 105 to 10 per ml in control.
Example 3
140 gm of dry aluminium oxyhydroxide powder of mean particle size dso 1.60 micron having purity of 98% alumina containing about 5% below 0.1 micron was taken in polyethylene bottle and 140 cc of azeotropic solvent mixture of methyl ethyl ketone and absolute alcohol containing 2.3 gm of phosphate ester as dispersant was added to form a slurry. After mixing the slurry in a pot mill for 20 hours, the slurry was transferred to a measuring cylinder and allowed to settle for about 15 minutes and the supernatant suspension was decanted out into a polyethylene bottle. 0.3 gm of calcium fluoride, 0.8 gm of magnesium fluoride and 2.0 gm of aluminosilicate as inorganic binder and 0.7 gm of charcoal as burn out additive were added to the supernatant suspension to form a homogeneous mixture. Thereafter 35 gm of polyvinyl butyral as binder of molecular weight 72000, a mixture of 26 gm polyethylene glycol of molecular weight 400 and 9 gm of benzyl butyl phthalate as plasticizer of molecular weight 312, 3.5 gm of cyclohexanone as homogenizer were added to the said mixture and thoroughly mixed for 22 hours when a casting slip of viscosity of 1500 cp was achieved. The casting slip was de-aired under vacuum for 1 minute and thereafter the vacuum was maintained for 15 minutes to remove entrapped air. This slip was cast on a smooth and clean glass plate with a laboratory
batch type tape casting machine. The blade gap and speed were adjusted for 1.4 mm and 2.0 cm/sec respectively. After drying it in ambient atmosphere for 20 hours the green flexible tape of about 300 micron thick and about 1.80 gm/cc green density was obtained. The green tape was then punched into circular pieces of 40 mm dia with a sharp edged die punch fitted in a ball press. The punched disc was fired in an oxidizing atmosphere at a temperature of 1500°C for 2 hours at the peak temperature under a load of 10 gm in an electrically heated furnace by heating at a rate of 60°C per hour after maintaining 4 hours at 800°C and cooling at the rate of 150°C per hour to make the thin ceramic micro filtration membrane disc. The average porosity of thin ceramic micro filtration membrane discs was found to be 45%.
The casting slurry for support disc and guard ring was prepared using 70 gm of alumina powder of purity 98.2% of average particle size 3.2 micron in to an azeotropic solvent mixture of 42 cc methyl ethyl ketone and 21 cc of absolute alcohol containing 0.8 gm of phosphate ester as dispersant, 6 gm of polyvinyl butyral of molecular weight 72,000 as organic binder, a mixture of 6.4 gm polyethylene glycol of molecular weight 400 and 2.2 gm of benzyl butyl phthalate of molecular weight 312 as plasticizer, 0.7 gm cyclohexanone as homogenizer and a mixture of 0.9 gm of calcium fluoride,
0.5 gm of magnesium fluoride and 1.4 gm of aluminosilicate as inorganic binder, mixing to achieve a viscosity of 2200 cp and cast with a batch type tape casting machine following known technique. The dried cast tape was of average thickness of about 400 micron and average density 2.34 gm/cc. From the green tape, two pieces of support base of 55 mm dia and guard rings of outer diameter 55 mm and inner diameter 43 mm were punched, stacked and laminated under a load of 70 Kg. 19 numbers of perforations of 4 mm dia were punched in the central portion of support base leaving a distance of 2 mm between two perforations to prepare green perforated support base. Two punched guard rings were laminated and the laminated ring was subsequently fitted on to the periphery of the perforated support base and finally green perforated support base along with guard ring was fired at 1600°C under load of 25 gm following a schedule of heating at the rate of 30°C per hour maintaining 4 hours at 800°C and 1600°C each and cooling at a rate of 100°C per hour to make the perforated support base. The thin ceramic rnicrofiltration membrane disc, prepared as above, was peripherally sealed within the annular space of the guard ring and perforated support base to make thin ceramic microfiltration membrane system. The filtration rate was found to be about 200 litre per sq. metre per hour using
dry suction pump. The bacteriological test showed no colony growth in the filtrate compared to bacterial counts 270 to 300 per ml in control.
The main advantages are :
(1) Minimum thickness of porous membrane disc.
(2) Higher surface smoothness of disc.
(3) Strong guard ring and perforated support base for protection of
membrane disc.
(4) Very smooth (0.5 to 1 µm) and flat surface of guard ring for leak-
proof fitting.
(5) Control of crack or debonding and stickiness, flatness, surface
smoothness and homogeneity of greensheet as well as controlling
deformation of the greensheet after firing.

Claim :
1. A novel ceramic composition useful for making thin ceramic microfiltration
membranes and a process for making thin ceramic microfiltration
membranes thereof which comprises :
Ceramic Powder 60 to 85 wt%Charactersed by man partice
also in the range of 0.2 to 4 micro.Organic solvent
30 to 45 wt%
Dispersant 0.7 to 2.0 wt% of ceramic powder
Inorganic+Organic binder 5 to 30 wt% of ceramic powder
Additives 0.5 to 15 wt% of ceramic powder
Organic plasticizers 9 to 25 wt% of ceramic powder
Homogenizer 1 to 2.5 wt% of ceramic powder
2. A novel ceramic composition as claimed in claim 1 wherein the ceramic
powders used are stable oxides, oxyhydroxides and hydroxides of metals
and combination thereof.
3. A novel ceramic composition as claimed in claims 1 to 2 wherein Saide ceramic powder not reaction 85 have
with modal size dm-dso containing 30% of the fines dio below 0.1 micron and having a purity of at least 96%.
4. A novel ceramic composition as claimed in claims 1 to 3 wherein the
saisd organic solvents used are azeotropic mixture of methyl ethyl ketone-
absolute alcohol, trichloroethylene-absolute alcohol, toluene-methanol
5. A novel ceramic composition as claimed in claims 1 to 4 wherein the
said inorganic binders are halides, sulphates, borates and phosphates of
alkaline earth metals and aluminosilicates in the range of 0.1 to 5.0 wt%
of ceramic powder.
6. A novel ceramic composition as claimed in claims 1 to 5 wherein the
said organic binder used are polyvinyl butyral, polymethyl methacrylate,
polyvinyl alcohol of molecular weight in the range of 36000 to 1 ,00,000.
7. A novel ceramic compositon as claimed in claims 1 to 6 wherein the ratio
of organic to inorganic binders is in the range of 5 to 50.
8. A novel ceramic compositon as claimed in claims 1 to 7 wherein the
additives used are charcoal, starch, ultra high molecular weight
polyethylene in the range of 0.5 to 15 wt% of ceramic powder.
9. A novel ceramic composition as claimed in claims 1 to 8 wherein the
said dispersarits used are phosphate ester, menhaden fish oil, glycerol

trioleate in the range of 0.7 to 2.0 wt% of ceramic powder.
10. A novel ceramic composition as claimed in claims 1 to 9 wherein the
organic plasticiers used are mixture of organic polyhydroxy compounds of
molecular weight 400 to 600 and organic phthalates of molecular weight 250 to 400 wherein the ratio of former to latter in the range of 0.8 to 4.
11. A novel ceramic composition as claimed in claims 1 to 10 wherein the
homogenizer used is cyclohexanone in the range of 1 to 2.5 wt% of

ceramic powder.
12. A process for making thin ceramic microfiltration memtranes using the
novel ceramic composition as claimed in claims 1 to 11, which comprises
dispersing ceramic powder in the organic solvent in presence of the
dispersant to form a slurry allowing the slurry to settle, decanting to
separate the supernatant suspension, mixing the supernatant suspension
with inorganic binder and additive to obtain a homogeneous mixture,
adding to the said mixture organic binder and plasticizers, followed by
thorough mixing to obtain a casting slip having viscosity in the range of
1000 to 3000 cp, de-airing the slurry, casting in the form of thin sheets by
known method and air drying to form a green flexible tape, cutting the
said tape into desired shape such as discs, firing in an oxidizing
atmosphere under a load to 7 to 50 gm at a temperature in the range of
1200° to 1500°C for 2 to 12 hours at the heating rate of 30° to 200°C per
hour after maintaining at 800°C for 2 to 4 hours and cooling at the rate of
60° to 300°C per hour to make the membrane disc.
13. A novel ceramic composition useful for making thin ceramic microfiltration
membranes and a process for making thin ceramic microfiltration
membranes thereof substantially as herein described with reference to
the examples.

Documents:

350-del-2001-abstract.pdf

350-del-2001-claims.pdf

350-del-2001-correspondence-others.pdf

350-del-2001-correspondence-po.pdf

350-del-2001-description (complete).pdf

350-del-2001-drawings.pdf

350-del-2001-form-1.pdf

350-del-2001-form-18.pdf

350-del-2001-form-2.pdf

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Patent Number

231671

Indian Patent Application Number

350/DEL/2001

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

07-Mar-2009

Date of Filing

27-Mar-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	DEBDAS CHATTOPADHYAY	CENTRAL GLASS AND CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032
2	NANDINI DAS	CENTRAL GLASS AND CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032
3	SIBDAS BANDYOPADHYAY	CENTRAL GLASS AND CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032
4	HIMADRI SEKHAR MAITI	CENTRAL GLASS AND CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032

PCT International Classification Number

C04B 38/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA