Title of Invention	A PROCESS FOR THE MANUFACTURE OF OPEN-CELL POROUS CERAMICS HAVING IMPROVED POROSITY AND MECHANICAL STRENGTH
Abstract	In the process of the present invention open-cell porous ceramics have been prepared based on bio-material pore forming substrate such as Luffa Cylindrica, Luffa Aculangula, member of Cucurbitaceae family. This substrate has network of cylindrical shaped ligaments which are capable of forming hollow structure of round cross section, having inherent mechanical strength more than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The above said natural biomaterial substrate having network of cylindrical shaped ligaments capable of providing round cross section open cell porous structure is coated with a ceramic slurry followed by a series of thermal operations to obtain an open-cell porous ceramic structure having increased inherent mechanical strength as a result of round cross section pores than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The said open-cell porous ceramic structure having round cross section pores when coupled with ceramic materials which are hard, wear resistant, thermal shock resistant, thermally and chemically stable and/or provided with additional strengthening materials such as different fibres results in an open-cell porous ceramic structure having not only increased porosity but also increased mechanical strength.

Title of Invention

A PROCESS FOR THE MANUFACTURE OF OPEN-CELL POROUS CERAMICS HAVING IMPROVED POROSITY AND MECHANICAL STRENGTH

Abstract

In the process of the present invention open-cell porous ceramics have been prepared based on bio-material pore forming substrate such as Luffa Cylindrica, Luffa Aculangula, member of Cucurbitaceae family. This substrate has network of cylindrical shaped ligaments which are capable of forming hollow structure of round cross section, having inherent mechanical strength more than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The above said natural biomaterial substrate having network of cylindrical shaped ligaments capable of providing round cross section open cell porous structure is coated with a ceramic slurry followed by a series of thermal operations to obtain an open-cell porous ceramic structure having increased inherent mechanical strength as a result of round cross section pores than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The said open-cell porous ceramic structure having round cross section pores when coupled with ceramic materials which are hard, wear resistant, thermal shock resistant, thermally and chemically stable and/or provided with additional strengthening materials such as different fibres results in an open-cell porous ceramic structure having not only increased porosity but also increased mechanical strength.

Full Text	The present invention relates to a process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength. The open-cell porous ceramics are useful as media for heat transfer, catalytic reaction, or for filtering operation. Thus, industrially, present invention has an application in the development of burner element for radiative heat transfer in a gas burning furnace. The development may also be used, as catalyst support in petrochemical and related industries, as filters for control of gas and diesel engine emissions in automotive and related industries, or as separator of impurities from liquid metal in metallurgy and related industries. The above said uses call for open-cell porous ceramics wherein the open-cell porous structure is essential in conjunction with the ceramic structure being hard, wear resistant, thermal shock resistant, thermally and chemically stable. Researches for technological advancement in the above fields are oriented towards using this potential of ceramic materials. hi U.S. patent, "Method of preparation of ceramic foam", Yarwood; J. C.; Dore; J. E.; Preuss; R. K., U.S Pat. No. 4,075,303 Feb. 21, 1978, a process for forming a ceramic foam has been described and claimed wherein : 1. The maximum achieved porosity of the ceramic structure obtained by polymeric sponge method is reportedly not more than 87% for a pore size of 12 pores/linear cm. 2. The foam that forms from the foaming technique to develop the polymeric structure, have three sided ligament profile with concave side surfaces. Ceramic skeleton produced using this foam structure as a substrate have similar hollow spaces in the interior of their struts. hi the above said patent, the process steps are as under: 1. A slurry containing finely divided ceramic particles, water and additives is prepared. Ceramic particles may be one or combination of oxides, such as, Alumina, Zirconia, Magnesia, Chromia, Iron oxide, Titania, Silica; Silicon Carbide and minerals. 2. Selected polymeric sponge is immersed hi the ceramic slurry and allowed the slurry to infiltrate the open-cells of sponge through repeated compression/expansion steps. Eventually, an appropriate coating is formed on the polymeric walls when the excess slurry is squeezed out. 3. The infiltrated sponge is then passed through a series of thermal operation for drying, volatilization of organics and sintering to obtain a porous ceramic skeleton structure. In the above patent, they have obtained an improved coating and unproved physical properties of the said ceramic foam using polymeric sponge material. References may also be made to "Process for forming a ceramic foam", Hargus; P. M.; Mula; J. A. and Redden; M. K., U.S Pat. No. 4,886,011 Sept 12, 1989, "Molten aluminium resistant ceramic fiber composition", Bearden; J. M., U.S Pat. No. 4,857,489 Aug. 15, 1989 and "Technique for forming silicon carbide coated porous filters", Tungatt; P. D.; Tyler; D. E. and Cheskis; H. P., U.S Pat. No. 4,708,740 Nov. 24,1987. In all the above said references open-cell porous ceramic have been obtained using polymeric sponge material. The drawbacks of using such a polymeric sponge material for obtaining open cell porous materials are : 1. The maximum achieved porosity of the ceramic structure obtained by polymeric sponge method is reportedly not more than 87% for a pore size of 12 pores/linear cm. High porosity is mostly desirable for industrial applications. Apart from having increased efficiency, theoretically it favours increasing the permeability and decreasing the pressure drop at the same condition of number of pores per unit length. 2. The foam that forms from the foaming technique to develop the polymeric structure, have three sided ligament profile with concave side surfaces. Ceramic skeleton produced using this foam structure as a substrate have similar hollow spaces in the interior of their struts. As the supportability is sharply reduced at the points of hollow spaces, the mechanical strength falls and the particular shape of the hollow structure in these cases reduces the strength more reference of which may be made to Brown, D. D. and Green, D. J., Investigation of strut crack formation in open cell alumina ceramics, J. Am. Ceram. Soc. 77(1994) [6] 1467- 72. 3. In the prior art, since polymeric sponge has been used as a substrate, the cost of development of the polymeric structure is added upto the final cost of the ceramic product. In all the above said references, the use of polymeric sponge has resulted in a weak open cell porous ceramic structure. This drawback of a weak structure has been attempted to be overcome, as detailed in the above said references, by using the polymeric sponge as a substrate along with improved ceramic materials and/or by providing additional supportive materials such as different types of fibres. The main object of the present invention is to provide a process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength which obviates the drawbacks as detailed above. Another object of the present invention is to provide a process for the manufacture of open-cell porous ceramics having a hollow structure of round cross section. Yet another object of the present invention is to provide a process wherein the substrate material has network of cylindrical shaped ligaments. Still another object of the present invention is to provide a natural substrate as base material which is easily available, low cost thus making the process economically viable. In the process of the present invention open-cell porous ceramics have been prepared based on bio-material pore forming substrate such as Luffa Cylindrica, Luffa Aculangula, member of Cucurbitaceae family. This substrate has network of cylindrical shaped ligaments which are capable of forming hollow structure of round cross section, having inherent mechanical strength more than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The above said natural biomaterial substrate having network of cylindrical shaped ligaments capable of providing round cross section open cell porous structure is coated with a ceramic slurry followed by a series of thermal operations to obtain an open-cell porous ceramic structure having increased inherent mechanical strength as a result of round cross section pores than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The said open-cell porous ceramic structure having round cross section pores when coupled with ceramic materials which are hard, wear Vesistant, thermal shock resistant, thermally and chemically stable and/or provided with additional strengthening materials such as different fibres results in an open-cell porous ceramic structure having not only increased porosity but also increased mechanical strength. Accordingly, the present invention provides a process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength characterised by impregnating a skinned, deseeded and descaled ripe and dehydrated natural cellulosic bio-material in surface geometry of circular or rectangular shape of Cucurbitaceae family Luffa Cylindrica, Luffa Aculangula having network of cylindrical shaped ligaments with a ceramic slurry composition of iron oxide in the range of 0-10 wt%, alumina in the range of 0-70 wt%, titanica in the range of 0-10 wt%, silica in the range of 0-70 wt%, chromia in the range of 0-10 wt%, zirconia in the range of 0-30 wt% and water in the range of 5-45 wt%., removing excess slurry by conventional methods to obtain ceramic material coated cellulosic structure, drying the said ceramic material coated cellulosic structure at a temperature in the range of 60°C to 150°C for a period of 15 minutes to 6 hours, heating and sintering the said ceramic material coated cellulosic structure to obtain open-cell porous ceramic structure. In an embodiment of the present invention the cellulosic material used may be in surface geometry of any shape such as circular or rectangular. In another embodiment of the present invention the dimension of the cellulosic biomaterial used may be increased through artificial joining of the single units by methods such as stiching, applying commonly available organic adhesives. In still another embodiment of the present invention the ceramic slurry used may be such as capable of adhereing to the cellulosic material substrate consisting of a network of cylindrical shaped ligaments, withstanding thermal treatment and providing hard, wear resistant, thermal shock resistant, thermally and chemically stable properties. In an embodiment of the present invention the ceramic slurry used may be such as of composition : iron oxide in the range of 0-10 wt%, silica in the range of 0-70 wt%, chromia in the range of 0-10wt%, zirconia in the range of 0-30 wt% and water in the range of 5-45 wt%. In another embodiment of the present invention the ceramic material coated cellulosic structure may be dried at a temperature in the range of 60°C to 150°C for a period of 15 minutes to 6 hours. In yet another embodiment of the present invention the dried ceramic material coated cellulosic structure may be heat treated at a temperature in the range of 300 C to 800 C for a period in the range of 15 minutes to 6 hours. In still another embodiment of the present invention the dried and heat treated ceramic material coated cellulosic structure may be sintered at a temperature in the range of 1200 °C to 1600°C for a period in the range of 1 hour to 7 hours. On detailed methodology followed in the present invention, the stepwise procedure is, 1. Single or multiple units of a particular class of ripe, dehydrated, skinned, deseeded, descaled and without undesired parts of natural cellulosic bio-material such as Luffa Cylindrica, Luffa Aculangula, members of Cucurbitaceae family are provided to be used as substrate material in a ceramic slurry. 2. The said substrate is impregnated with a ceramic slurry capable of adhereing to the substrate, withstanding thermal treatment and providing hard, wear resistant, thermal shock resistant, thermally and chemically stable properties. 3. The substrate material as obtained by structural modification of natural bio- clementis impregnated into the ceramic slurry, followed by removal of excess slurry by conventional means, such as, pressing through wooden boards or rollers to get a skeleton structure of bio-element coated with ceramic material. This coated bio-element is thermally treated such as given below. a. The material is then dried at a temperature in the range between 60 °C to 150 °C for IS minutes to 6 hours. b. The volatiles are then driven off by heat treating at a temperature in the range between 300 °C to 800 °C for 15 minutes to 6 hours. c. The structure is then sintered at a temperature in the range between 1200 °C to 1600 °C for 1 hour to 7 hours. In the process of the present invention the novelty resides in the open cell porous ceramics having improved porosity and mechanical strength. The novel features of increased porosity, mechanical srength is achieved by the non obvious inventive step of providing a substrate having a network of cylindrical shaped ligaments which when impregnated with ceramic slurry and thermally treated results in an open-cell porous ceramic structure having improved porosity and mechanical strength. The network of cylindrical shaped ligaments of the natural bio-material as against the three-sided ligament profile with concave side surfaces of the artificial base material of the prior art results in open-cell porous ceramics having improved porosity and mechanical strength. The improved product has been obtained by the use of natural bio-material such as Luffa Cylindrica, Luffa Aculangula, all members of Cucurbitaceae family, as the base material for the development of an open-cell porous structure to obtain the following distinct characteristic advantages over the use of artificially developed base material such as polyurathane foam. Firstly, the unique shape and size of the presently used substrate material can lead to a uniquely developed ceramic structure appropriate for a number of applications such as porous burner element. Secondly, the ceramic network finally developed can give comparatively increased range of porosity, more importantly, towards the higher side under similar condition of cell size. Thirdly, the round cross section of the ligaments of bio-elements would influence to induce higher mechanical strength in the product than that obtained from using artificial base material which has three sided ligament structure of inward curvature. Fourthly, cost of production would be reduced as naturally available base material can be obtained much cheaply and easily in comparison to the base material obtained by chemical process development. The inventive step of the present invention of utilising the special structure of the naturally occuring bio-material such as Luffa Cylindrica, Luffa Aculangula of Cucurbitaceae family results in making ceramic product of desired pore orientation, number of pores per unit length, improved porosity and mechanical strength. The working of the process of the present invention is illustrated below in the following examples which should not be construed to limit the scope of the invention. Example -1 Skinned, deseeded and descaled single units of naturally obtained bio-element, Luffa Cylindrica, was provided to get one end hemispherically closed nearly cylindrical shape structure with dimention 10 cm length for cylindrical portion, 6 cm inside diameter and thickness 2 cm. A slurry containing chromia, water, clay material and alumina in the wt % ratio of 1:4:6.6:8.6 was prepared. The used clay material contains 48.9% silica, 34.51% alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia. The slurry was then mixed with 8% Polyvinyl alcohol, 15% Colloidal silica and 1% Bentonite as additives. The biostruture was then completely impregnated with the slurry. Excess portion of the slurry was then removed by putting the material under compression using suitable wooden boards while leaving the ceramic coated fibre-like web portion. The material was then put under three stages of thermal operation, i) 6 hours of drying at a temperature of 70 °C, ii) 5 hours of devolatilization operation at a temperature of 400 °C, and iii) 5 hours of sintering operation at a temperature of 1600 °C. The structural property of the finally obtained open-cell porous material is given below. Table I (Table Removed) Example - 2 Skinned, deseeded and descaled single units of naturally obtained bio-element, Luffa Cylindrica, was provided to get one end hemispherically closed nearly cylindrical shape structure with dimention of length 12 cm, inside diameter 7 cm and thickness 2 cm. A slurry containing iron oxide, water, clay material of composition 48.9% silica, 34.51% alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia and alumina in the ratio of 1:4.5:8.75:10.75 was prepared. The slurry was then mixed with 1.5% Montmarillonite, 8% Polyvinyl alcohol and 15% Colloidal silica as additives. The biostruture was then completely impregnated with the slurry. Excess portion of the slurry was then removed by putting the material under compression using suitable wooden boards while leaving the ceramic coated fibre-like web portion. The material was then put under three stages of thermal operation, for 5 hours of drying at a temperature of 90 °C, for 5 hours of devolatilization operation at a temperature of 400 °C, and for 6 hours of sintering operation at a temperature of 1600 °C. The structural property of the finally obtained open-cell porous material is given below. Table II (Table Removed) Example - 3 Skinned, deseeded and descaled single units of naturally obtained bio-element, Luffa Cylindrica, was provided to get one end hemispherically closed nearly cylindrical shape structure with dimention of length 9 cm, inside diameter 5 cm and thickness 1.5 cm. A slurry containing titania, water, clay material of composition 48.9% silica, 34.51% alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia and alumina in the ratio of 1:2.5:4.5:5.5 was prepared. The slurry was then mixed with 1.5% Bentonite, 8% Polyvinyl alcohol and 15% Colloidal silica as additives. The biostruture was then completely impregnated with the slurry. Excess portion of the slurry was then removed by putting the material under compression using suitable wooden boards while leaving the ceramic coated fibre-like web portion. The material was then put under three stages of thermal operation, for 5 hours of drying at a temperature of 80 °C, for 5 hours of devolatilization operation at a temperature of 400 °C, and for 5 hours of sintering operation at a temperature of 1600 The structural property of the finally obtained open-cell porous material is given below. Table III (Table Removed) Example - 4 Two cylindrical single units of deseeded, dsscaled, skinned, ripe and dehydrated Luffa Cylindrica were provided. The units were then coupled along the axis and joined together by sticking and applying adhesive. The joined structure was of the dimension of length 20 cm, inside diameter 6 cm and thickness 2 cm. A slurry containing chromia, water, clay material of composition 48.9% silica, 34.51% alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia and alumina in the ratio of 1:4:7:9 was prepared. The slurry was then mixed with 1.5% Bentonite, 8% Polyvinyl alcohol and 17% Colloidal silica as additives. The biostruture was then completely impregnated with the slurry. Excess portion of the slurry was then removed by putting the material under compression using suitable wooden boards while leaving the ceramic coated fibre-like web portion. The material was then put under three stages of thermal operation, for 6 hours of drying at a temperature of 80 °C, for 6 hours of devolatilization operation at a temperature of 400 °C, and for 6 hours of sintering operation at a temperature of 1625 °C. The structural property of the finally obtained open-cell porous material is given below. Table IV (Table Removed) From the above examples, we conclude that the process provides open-cell porous ceramics having improved porosity and mechanical strength. The main advantages of which are: 1. The unique shape and size of the presently used substrate material can lead to a uniquely developed ceramic structure appropriate for a number of applications such as porous burner element. 2. Maximum achieved porosity is 93% for a pore size across the fibre line of 8 pores/linear cm in comparison to 87% porosity for a pore size of 12pores/linear cm as reported so far. 3. The round cross section of the ligaments of bio-elements would result in a higher mechanical strength in the product than that obtained from using artificial base material which has three sided ligament structure of inward curvature. 4. The cost of production would be reduced as naturally available base material can be obtained much cheaply and easily, in comparison to the base material obtained by chemical process development. We Claim: 1. A process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength characterised by impregnating a skinned, deseeded and descaled ripe and dehydrated natural cellulosic bio-material in surface geometry of circular or rectangular shape of Cucurbitaceae family Luffa Cylindrica, Luffa Aculangula having network of cylindrical shaped ligaments with a ceramic slurry composition of iron oxide in the range of 0-10 wt%, alumina in the range of 0-70 wt%, titanica in the range of 0-10 wt%, silica in the range of 0-70 wt%, chromia in the range of 0-10 wt%, zirconia in the range of 0- 30 wt% and water in the range of 5-45 wt%., removing excess slurry by conventional methods to obtain ceramic material coated cellulosic structure, drying the said ceramic material coated cellulosic structure at a temperature in the range of 60°C to 150°C for a period of 15 minutes to 6 hours, heating and sintering the said ceramic material coated cellulosic structure to obtain open-cell porous ceramic structure. 2. A process as claimed in claim 1, wherein the dried ceramic material coated cellulosic structure is heated at a temperature in the range of 300°C to 800°C for a period in the range of 15 minutes to 6 hours. 3. A process as claimed in claims 1-2, wherein the dried and heat treated ceramic material coated cellulosic structure is sintered at a temperature in the range of 1200 to 1600° C for a period in the range of 1 to 7 hours. 4. A process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength. The open-cell porous ceramics are useful as media for heat transfer, catalytic reaction, or for filtering operation. Thus, industrially, present invention has an application in the development of burner element for radiative heat transfer in a gas burning furnace. The development may also be used, as catalyst support in petrochemical and related industries, as filters for control of gas and diesel engine emissions in automotive and related industries, or as separator of impurities from liquid metal in metallurgy and related industries. The above said uses call for open-cell porous ceramics wherein the open-cell porous structure is essential in conjunction with the ceramic structure being hard, wear resistant, thermal shock resistant, thermally and chemically stable. Researches for technological advancement in the above fields are oriented towards using this potential of ceramic materials.
hi U.S. patent, "Method of preparation of ceramic foam", Yarwood; J. C.; Dore; J. E.; Preuss; R. K., U.S Pat. No. 4,075,303 Feb. 21, 1978, a process for forming a ceramic foam has been described and claimed wherein :
1. The maximum achieved porosity of the ceramic structure obtained by polymeric
sponge method is reportedly not more than 87% for a pore size of 12 pores/linear
cm.
2. The foam that forms from the foaming technique to develop the polymeric
structure, have three sided ligament profile with concave side surfaces. Ceramic
skeleton produced using this foam structure as a substrate have similar hollow
spaces in the interior of their struts.
hi the above said patent, the process steps are as under:
1. A slurry containing finely divided ceramic particles, water and additives is
prepared. Ceramic particles may be one or combination of oxides, such as,
Alumina, Zirconia, Magnesia, Chromia, Iron oxide, Titania, Silica; Silicon Carbide
and minerals.
2. Selected polymeric sponge is immersed hi the ceramic slurry and allowed the
slurry to infiltrate the open-cells of sponge through repeated
compression/expansion steps. Eventually, an appropriate coating is formed on the
polymeric walls when the excess slurry is squeezed out.
3. The infiltrated sponge is then passed through a series of thermal operation for drying, volatilization of organics and sintering to obtain a porous ceramic skeleton structure.
In the above patent, they have obtained an improved coating and unproved physical properties of the said ceramic foam using polymeric sponge material. References may also be made to "Process for forming a ceramic foam", Hargus; P. M.; Mula; J. A. and Redden; M. K., U.S Pat. No. 4,886,011 Sept 12, 1989, "Molten aluminium resistant ceramic fiber composition", Bearden; J. M., U.S Pat. No. 4,857,489 Aug. 15, 1989 and "Technique for forming silicon carbide coated porous filters", Tungatt; P. D.; Tyler; D. E. and Cheskis; H. P., U.S Pat. No. 4,708,740 Nov. 24,1987.
In all the above said references open-cell porous ceramic have been obtained using polymeric sponge material. The drawbacks of using such a polymeric sponge material for obtaining open cell porous materials are :
1. The maximum achieved porosity of the ceramic structure obtained by polymeric
sponge method is reportedly not more than 87% for a pore size of 12 pores/linear
cm. High porosity is mostly desirable for industrial applications. Apart from having
increased efficiency, theoretically it favours increasing the permeability and
decreasing the pressure drop at the same condition of number of pores per unit
length.
2. The foam that forms from the foaming technique to develop the polymeric
structure, have three sided ligament profile with concave side surfaces. Ceramic
skeleton produced using this foam structure as a substrate have similar hollow
spaces in the interior of their struts. As the supportability is sharply reduced at the
points of hollow spaces, the mechanical strength falls and the particular shape of
the hollow structure in these cases reduces the strength more reference of which
may be made to Brown, D. D. and Green, D. J., Investigation of strut crack
formation in open cell alumina ceramics, J. Am. Ceram. Soc. 77(1994) [6] 1467-
72.
3. In the prior art, since polymeric sponge has been used as a substrate, the cost of development of the polymeric structure is added upto the final cost of the ceramic product.
In all the above said references, the use of polymeric sponge has resulted in a weak open cell porous ceramic structure. This drawback of a weak structure has been attempted to be overcome, as detailed in the above said references, by using the polymeric sponge as a substrate along with improved ceramic materials and/or by providing additional supportive materials such as different types of fibres. The main object of the present invention is to provide a process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a process for the manufacture of open-cell porous ceramics having a hollow structure of round cross section. Yet another object of the present invention is to provide a process wherein the substrate material has network of cylindrical shaped ligaments. Still another object of the present invention is to provide a natural substrate as base material which is easily available, low cost thus making the process economically viable.
In the process of the present invention open-cell porous ceramics have been prepared based on bio-material pore forming substrate such as Luffa Cylindrica, Luffa Aculangula, member of Cucurbitaceae family. This substrate has network of cylindrical shaped ligaments which are capable of forming hollow structure of round cross section, having inherent mechanical strength more than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The above said natural biomaterial substrate having network of cylindrical shaped ligaments capable of providing round cross section open cell porous structure is coated with a ceramic slurry followed by a series of thermal operations to obtain an open-cell porous ceramic structure having increased inherent mechanical strength as a result of round cross section pores than that obtained from the three sided ligament profile with concave side surfaces of polymeric sponge used in the prior art processes. The said open-cell porous ceramic structure having round cross section pores when coupled with ceramic materials which are hard, wear Vesistant, thermal shock resistant, thermally and chemically stable and/or provided
with additional strengthening materials such as different fibres results in an open-cell porous ceramic structure having not only increased porosity but also increased mechanical strength.
Accordingly, the present invention provides a process for the manufacture of open-cell porous ceramics having improved porosity and mechanical strength characterised by impregnating a skinned, deseeded and descaled ripe and dehydrated natural cellulosic bio-material in surface geometry of circular or rectangular shape of Cucurbitaceae family Luffa Cylindrica, Luffa Aculangula having network of cylindrical shaped ligaments with a ceramic slurry composition of iron oxide in the range of 0-10 wt%, alumina in the range of 0-70 wt%, titanica in the range of 0-10 wt%, silica in the range of 0-70 wt%, chromia in the range of 0-10 wt%, zirconia in the range of 0-30 wt% and water in the range of 5-45 wt%., removing excess slurry by conventional methods to obtain ceramic material coated cellulosic structure, drying the said ceramic material coated cellulosic structure at a temperature in the range of 60°C to 150°C for a period of 15 minutes to 6 hours, heating and sintering the said ceramic material coated cellulosic structure to obtain open-cell porous ceramic structure.
In an embodiment of the present invention the cellulosic material used may be in surface geometry of any shape such as circular or rectangular.
In another embodiment of the present invention the dimension of the cellulosic biomaterial used may be increased through artificial joining of the single units by methods such as stiching, applying commonly available organic adhesives.
In still another embodiment of the present invention the ceramic slurry used may be such as capable of adhereing to the cellulosic material substrate consisting of a network of cylindrical shaped ligaments, withstanding thermal treatment and providing hard, wear resistant, thermal shock resistant, thermally and chemically stable properties.
In an embodiment of the present invention the ceramic slurry used may be such as of composition : iron oxide in the range of 0-10 wt%, silica in the range of 0-70 wt%, chromia in the range of 0-10wt%, zirconia in the range of 0-30 wt% and water in the range of 5-45 wt%.
In another embodiment of the present invention the ceramic material coated cellulosic structure may be dried at a temperature in the range of 60°C to 150°C for a period of 15 minutes to 6 hours.
In yet another embodiment of the present invention the dried ceramic material coated cellulosic structure may be heat treated at a temperature in the range of 300 C to 800 C for a period in the range of 15 minutes to 6 hours.
In still another embodiment of the present invention the dried and heat treated ceramic material coated cellulosic structure may be sintered at a temperature in the range of 1200 °C to 1600°C for a period in the range of 1 hour to 7 hours. On detailed methodology followed in the present invention, the stepwise procedure is,
1. Single or multiple units of a particular class of ripe, dehydrated, skinned, deseeded,
descaled and without undesired parts of natural cellulosic bio-material such as
Luffa Cylindrica, Luffa Aculangula, members of Cucurbitaceae family are provided
to be used as substrate material in a ceramic slurry.
2. The said substrate is impregnated with a ceramic slurry capable of adhereing to the
substrate, withstanding thermal treatment and providing hard, wear resistant,
thermal shock resistant, thermally and chemically stable properties.
3. The substrate material as obtained by structural modification of natural bio-
clementis impregnated into the ceramic slurry, followed by removal of excess
slurry by conventional means, such as, pressing through wooden boards or rollers
to get a skeleton structure of bio-element coated with ceramic material. This coated
bio-element is thermally treated such as given below.
a. The material is then dried at a temperature in the range between 60 °C to 150 °C for
IS minutes to 6 hours.
b. The volatiles are then driven off by heat treating at a temperature in the range
between 300 °C to 800 °C for 15 minutes to 6 hours.
c. The structure is then sintered at a temperature in the range between 1200 °C to 1600
°C for 1 hour to 7 hours.
In the process of the present invention the novelty resides in the open cell porous ceramics having improved porosity and mechanical strength. The novel features of increased porosity, mechanical srength is achieved by the non obvious inventive step of providing a substrate having a network of cylindrical shaped ligaments which when impregnated with ceramic slurry and thermally treated results in an open-cell porous ceramic structure having improved porosity and mechanical strength. The network of cylindrical shaped ligaments of the natural bio-material as against the three-sided ligament profile with concave side surfaces of the artificial base material of the prior art results in open-cell porous ceramics having improved porosity and mechanical strength.
The improved product has been obtained by the use of natural bio-material such as Luffa Cylindrica, Luffa Aculangula, all members of Cucurbitaceae family, as the base material for the development of an open-cell porous structure to obtain the following distinct characteristic advantages over the use of artificially developed base material such as polyurathane foam. Firstly, the unique shape and size of the presently used substrate material can lead to a uniquely developed ceramic structure appropriate for a number of applications such as porous burner element. Secondly, the ceramic network finally developed can give comparatively increased range of porosity, more importantly, towards the higher side under similar condition of cell size. Thirdly, the round cross section of the ligaments of bio-elements would influence to induce higher mechanical strength in the product than that obtained from using artificial base material which has three sided ligament structure of inward curvature. Fourthly, cost of production would be reduced as naturally available base material can be obtained much cheaply and easily in comparison to the base material obtained by chemical process development. The inventive step of the present invention of utilising the special structure of the naturally occuring bio-material such as Luffa Cylindrica, Luffa Aculangula of Cucurbitaceae family results in making ceramic product of desired pore orientation, number of pores per unit length, improved porosity and mechanical strength.
The working of the process of the present invention is illustrated below in the following examples which should not be construed to limit the scope of the invention.
Example -1
Skinned, deseeded and descaled single units of naturally obtained bio-element, Luffa Cylindrica, was provided to get one end hemispherically closed nearly cylindrical shape structure with dimention 10 cm length for cylindrical portion, 6 cm inside diameter and thickness 2 cm.
A slurry containing chromia, water, clay material and alumina in the wt % ratio of 1:4:6.6:8.6 was prepared. The used clay material contains 48.9% silica, 34.51% alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia. The slurry was then mixed with 8% Polyvinyl alcohol, 15% Colloidal silica and 1% Bentonite as additives.
The biostruture was then completely impregnated with the slurry. Excess portion of the slurry was then removed by putting the material under compression using suitable wooden boards while leaving the ceramic coated fibre-like web portion.
The material was then put under three stages of thermal operation, i) 6 hours of drying at a temperature of 70 °C, ii) 5 hours of devolatilization operation at a temperature of 400 °C, and iii) 5 hours of sintering operation at a temperature of 1600 °C.
The structural property of the finally obtained open-cell porous material is given below.
Table I
(Table Removed)
Example - 2
Skinned, deseeded and descaled single units of naturally obtained bio-element, Luffa Cylindrica, was provided to get one end hemispherically closed nearly cylindrical shape structure with dimention of length 12 cm, inside diameter 7 cm and thickness 2 cm.
A slurry containing iron oxide, water, clay material of composition 48.9% silica, 34.51% alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia and alumina in the ratio of 1:4.5:8.75:10.75 was prepared. The slurry was then mixed with 1.5% Montmarillonite, 8% Polyvinyl alcohol and 15% Colloidal silica as additives.
The biostruture was then completely impregnated with the slurry. Excess portion of the slurry was then removed by putting the material under compression using suitable wooden boards while leaving the ceramic coated fibre-like web portion.
The material was then put under three stages of thermal operation, for 5 hours of
drying at a temperature of 90 °C, for 5 hours of devolatilization operation at a
temperature of 400 °C, and for 6 hours of sintering operation at a temperature of 1600
°C.
The structural property of the finally obtained open-cell porous material is given
below.
Table II
(Table Removed)
Example - 3
Skinned, deseeded and descaled single units of naturally obtained bio-element, Luffa
Cylindrica, was provided to get one end hemispherically closed nearly cylindrical
shape structure with dimention of length 9 cm, inside diameter 5 cm and thickness 1.5
cm.
A slurry containing titania, water, clay material of composition 48.9% silica, 34.51%
alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia
and alumina in the ratio of 1:2.5:4.5:5.5 was prepared. The slurry was then mixed with
1.5% Bentonite, 8% Polyvinyl alcohol and 15% Colloidal silica as additives.
The biostruture was then completely impregnated with the slurry. Excess portion of
the slurry was then removed by putting the material under compression using suitable
wooden boards while leaving the ceramic coated fibre-like web portion.
The material was then put under three stages of thermal operation, for 5 hours of drying at a temperature of 80 °C, for 5 hours of devolatilization operation at a temperature of 400 °C, and for 5 hours of sintering operation at a temperature of 1600
The structural property of the finally obtained open-cell porous material is given
below.
Table III
(Table Removed)
Example - 4
Two cylindrical single units of deseeded, dsscaled, skinned, ripe and dehydrated Luffa Cylindrica were provided. The units were then coupled along the axis and joined together by sticking and applying adhesive. The joined structure was of the dimension of length 20 cm, inside diameter 6 cm and thickness 2 cm.
A slurry containing chromia, water, clay material of composition 48.9% silica, 34.51% alumina, 1.71% ferric oxide, 0.5% titania, 0.67% calcium oxide and 0.2% magnasia and alumina in the ratio of 1:4:7:9 was prepared. The slurry was then mixed with 1.5% Bentonite, 8% Polyvinyl alcohol and 17% Colloidal silica as additives. The biostruture was then completely impregnated with the slurry. Excess portion of the slurry was then removed by putting the material under compression using suitable wooden boards while leaving the ceramic coated fibre-like web portion. The material was then put under three stages of thermal operation, for 6 hours of drying at a temperature of 80 °C, for 6 hours of devolatilization operation at a temperature of 400 °C, and for 6 hours of sintering operation at a temperature of 1625 °C.
The structural property of the finally obtained open-cell porous material is given below.
Table IV
(Table Removed)
From the above examples, we conclude that the process provides open-cell porous ceramics having improved porosity and mechanical strength. The main advantages of which are:
1. The unique shape and size of the presently used substrate material can lead to a
uniquely developed ceramic structure appropriate for a number of applications such
as porous burner element.
2. Maximum achieved porosity is 93% for a pore size across the fibre line of 8
pores/linear cm in comparison to 87% porosity for a pore size of 12pores/linear cm
as reported so far.
3. The round cross section of the ligaments of bio-elements would result in a higher
mechanical strength in the product than that obtained from using artificial base
material which has three sided ligament structure of inward curvature.
4. The cost of production would be reduced as naturally available base material can be
obtained much cheaply and easily, in comparison to the base material obtained by
chemical process development.

We Claim:
1. A process for the manufacture of open-cell porous ceramics having improved
porosity and mechanical strength characterised by impregnating a skinned,
deseeded and descaled ripe and dehydrated natural cellulosic bio-material in
surface geometry of circular or rectangular shape of Cucurbitaceae family Luffa
Cylindrica, Luffa Aculangula having network of cylindrical shaped ligaments
with a ceramic slurry composition of iron oxide in the range of 0-10 wt%,
alumina in the range of 0-70 wt%, titanica in the range of 0-10 wt%, silica in the
range of 0-70 wt%, chromia in the range of 0-10 wt%, zirconia in the range of 0-
30 wt% and water in the range of 5-45 wt%., removing excess slurry by
conventional methods to obtain ceramic material coated cellulosic structure,
drying the said ceramic material coated cellulosic structure at a temperature in
the range of 60°C to 150°C for a period of 15 minutes to 6 hours, heating and
sintering the said ceramic material coated cellulosic structure to obtain open-cell
porous ceramic structure.
2. A process as claimed in claim 1, wherein the dried ceramic material coated
cellulosic structure is heated at a temperature in the range of 300°C to 800°C for a
period in the range of 15 minutes to 6 hours.
3. A process as claimed in claims 1-2, wherein the dried and heat treated ceramic
material coated cellulosic structure is sintered at a temperature in the range of
1200 to 1600° C for a period in the range of 1 to 7 hours.
4. A process for the manufacture of open-cell porous ceramics having improved
porosity and mechanical strength substantially as herein described with reference
to the examples.

Documents:

1090-del-2001-abstract.pdf

1090-del-2001-claims.pdf

1090-del-2001-correspondence-others.pdf

1090-del-2001-correspondence-po.pdf

1090-del-2001-description (complete).pdf

1090-del-2001-form-1.pdf

1090-del-2001-form-18.pdf

1090-del-2001-form-2.pdf

1090-del-2001-form-3.pdf

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Patent Number

220518

Indian Patent Application Number

1090/DEL/2001

PG Journal Number

31/2008

Publication Date

01-Aug-2008

Grant Date

29-May-2008

Date of Filing

30-Oct-2001

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

Inventors:

#	Inventor's Name	Inventor's Address
1	SOMESWAR DATTA
2	MITHILES CHAKRAVARTY
3	TARUN KUMAR KAYAL

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