GB2055787A - Closed cellular hollow refractory spheres - Google Patents

Abstract

Closed cellular hollow refractory spheres useful for making refractory bricks and other light weight refractories are made by coating burnable core particles with a mixture of finely divided refractory material and a binder and then heating the coated core particles so as to remove the core and cause the refractory material to adhere together. The refractory material may include a catalyst.

Description

SPECIFICATION Novel closed cellular hollow refractory spheres and method of manufacturing such refractory spheres for use in light weight refractories and industrial catalysts This invention relates to novel closed cellular hollow refractory spheres and method of manufacturing such refractory spheres for use in light weight refractories and industrial catalysis.

More particularly this invention relates to closed cellular hollow refractory spheres, bubbles or beads and/or ceramic and catalytic aggregates material and method of manufacturing same for use in light weight refractories and industrial catalysis.

For brevity sake the expression "HOLLOW REFRACTORY SPHERES" wherever appearing throughout this specification is intended to mean and include "HOLLOW REFRACTORY AND CERAMIC AN D/OR CATALYTIC SPHERES, BUBBLES, BEADS OR AGGREGATES MATERIAL".

The typical process for manufacturing fused refractory grains by electrolytic fusion for use in refractory shapes has been known for quite some time, (References: POLUBOYARINOV D.N. & BALKEVICH V.L...

"HIGH ALUMINA REFRACTORIES FROM ELECTROMELTED CORONDUM".. Ogneupory 16(3)109-19 1951).

Refractories were and still are being manufactured using these grains. These fused refractories or refractory grains so manufactured offer certain disadvantages, that is to say, these grains pose problems in physical strength, thermal shock resistance and erosion resistance, and in the absence of better grains, these known types of refractory grains had come to be commonly used in dense refractories.

However, a comparatively new process for making sintered grains was also developed and was found to be better than the fusion process described in preceding paragraph and this sintered grain process gives some specific advantages over the fused refractory grains and a few of the advantages offered by the sintered grains refractories reside in the fact that these are having: i) a higher physical strength; ii) better thermal shock resistance; and iii) better erosion resistance.

Because of those advantages the trend during the last few years has been to replace dense fused grains with dense sintered grains. Atypical example of this is classical shift from dense fused alumina grains to dense sintered alumina grains for use in refractories.

For making hollow ceramic spheres only the fusion process was known and this too was restricted to the specific case of alumina and alumina- zirconia melts. (Reference: A.N. Gaodu; I.G. Subocher; M.M. Mirk'yan eta/Ogneupory, No. 9, 47-50 (1976)).

The principal object of the present invention is to offer sintered closed cellular hollow refractory spheres in which the disadvantages so far obtained in the refractory grains made by the electrolytic fusion process have been completely eliminated and the advantages of the sintered grains refractory shapes are incorporated fully and wherein the hollow ceramic spheres or closed cellular hollow refractory spheres of this invention cover a wide range of refractory oxides and catalytic materials thus creating a potential application for sintered/calcined hollow bodies in the fields of refractories and catalysis.

The closed cellular hollow refractory spheres or aggregates for making pre-formed bricks of various shapes and sizes and/or for making castables in conjunction with hydraulic binders for making monolithic refractory applications and/or for making plastic refractory bodies for use in light-weight refractories and/or loose fill insulation applications and/or for use in industrial catalysis are formed from refractory and catalytic material compositions containing for instance, Mullite, Magnesia, Zirconia, Zircon, Silicon Carbide, Alumina, Silica, Alumina, Silica, Alumina-silicate minerals, Chromite, Hydroxides and salts of Al, Si, Cu, Ni, Cr, Fe, Zn, Ti, Ag, Au, Co, Mo, Pt, Rh and similar minerals or combinations thereof and wherein air gap provided within each of said spheres leads to the product having a wide range of densities, wall thickness for wide range of light weight refractories and industrial catalysis applications.

In another embodiment of this invention the air gap provided within each of said refractory spheres provides thermal shock resistance and adequate physical strength.

In yet another embodiment of this invention each of the said hollow refractory spheres has a non-glassy rough surface texture which - when present in refractory bodies - increases its erosion resistance.

In still another embodiment of this invention each of said hollow refractory spheres is having a wide range of densities, wall thickness surface area and porosity for being put to wide range of light-weight refractories and industrial catalysis applications.

In another embodiment of this invention the said hollow refractory spheres become fluidisable thereby providing scope for use in fluid bed catalysis, combustion and other similar applications.

In yet another embodiment of this invention the closed cellular hollow refractory spheres work with any combination of refractory or catalytic oxides, hydroxides, carbides with or without other metal salt materials and can be operated and formed below the melting temperatures of the compositions.

The present invention provides a method of manufacturing hollow refractory spheres (as hereinbefore defined) which comprises coating burnable core particles (i.e. core particles which can be destroyed and substantially removed by heat) with a mixture of a finely divided refractory material and a binder (which may be either temporary or permanent), and then heating the coated core particles so obtained so as to burn or otherwise destroy and remove by heat the said core and cause the refractory material to adhere together, for example by sintering or by the action of a binder, so as to form the hollow refractory spheres.

The method of manufacturing closed cellular hollow ceramic or catalytic refractory spheres according to this invention preferably comprises of the following stages, wherein: i) in the first stage of the oxides, carbides or hydroxides with or without other metal salt materials as mentioned hereinbefore are taken in dry state, if necessary, with the solid component of the binder and are ground separately or together in a grinding mill to obtain a physical fineness below 100 microns and preferably below 40 microns;; ii) in the second stage of the binder comprising of a metal oxide, sol or combination of sols with metal salts or combinations of organic binder materials such as dextrin or acids is prepared in usual manner in such a way that the sol content varies from 0% to 100% of the binder and the metal salt content varies from 0% to 50% or more of the binder;; iii) in the third stage burnable core masses in spherical or granular form in the size range of 0.5 mm to 30 mm comprising of cork, carbon, wood starch, cellulosic materials, expanded cereals, expanded polypropylene, expanded polystyrene or similar expandable synthetic resins or combinations thereof are placed in a triturating spherodizing equipment for coating the core material by standard agglomeration technique with the binder of stage (ii) and the ground component of stage (i) and the process is continued as desired batchwise or continuously; (iv) in the fourth stage the addition of components of stage (i) and (ii) is continued and the growth of the spheres is controlled by ensuring dimensional control and/or density control in usual manner to obtain predetermined wall thickness varying from 0.1 mm to a few centimeters;; v) in the fifth stage the spheres of the fourth stage are cured and dried in a slow process at temperatures varying from 15"C to 300 Cthereby partially or totally destroying the burnable core material and thereby providing hollow air pockets or gaps within each of said spheres and which air pockets provide better thermal resistance and other claimed properties for said hollow refractory spheres; and vi) in the sixth stage the dried and cured hollow refractory spheres of stage (v) are further processed in a rotary or batch or tunnel kiln/activator at temperatures varying from 300to 1 8DOOC and above, and this operation is carried out mainly to obtain desjred catalytic or refractory properties and in that said processing of stage (vi) is preferably carried out at temperatures varying from 300"C to 1 0000C for catalytic hollow spheres and in that higher temperatures ranging from 800"C to 1 8000C is preferred for refractory applications and which operations are carried out and conducted under desired atmospheres such as oxidising, reducing or inert atmospheres in usual manner.

Following are the few examples which describe the method of carrying out and manufacturing the hollow refractory, ceramic and catalytic spheres or aggregates or castables according to this invention: Example 1 1. In the first stage 95 parts of calcined alumina ("INDAL-G" grade) and 5 parts of activated alumina ("ACO -AC-202 " grade) are ground together to obtain a specific surface area of 12000-13000 cm2/gm; 2. In the second stage the acid component of the binder is prepared by mixing 8 parts of commercial hydrochloric acid (30% strength) and 12 parts of water; 3.In the third stage the core masses of 3.5 parts in spherical form (1-3 mm dia) of expanded polystyrene such as "BASF" ("STYROPOR" or "THERMOCOLE") or expanded polystyrene or similar expandable resins are loade in a pan-nodulizer for coating the core material by standard agglomeration technique in usual manner and initially the acid component of binder of stage (2) is used to wet the surface of said core masses and the ground component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and in the process any agglomerates that are found are mechanically broken; 4. In the fourth stage the said addition of the components is continued till the bulk density of 0.65 Kgs/lit is obtained.The growth of spheres of stage (3) is controlled by ensuring density control in usual manner to attain and obtain pre-determined wall thickness; 5. In the fifth stage the spheres of the stage (4) are unloaded and then dried at room temperature varying from 20"C to 29"C for 24 hours in usual manner and this is followed by drying in a tray drier by gradually increasing the temperature to 1 500C and maintaining it for 4 hours thereby partially destroying the said burnable core material and providing hollow air gaps or pockets within each of said spheres and which provides better thermal insulation and thermal resistance properties for said hollow spheres; and 6. In the sixth stage the dried and cured hollow spheres of stage (5) are further processed in a rotary kiln at temperatures varying from 1650"C to 1700 C and thereafter the said hollow refractory spheres are collected at kiln discharge and are stored in drums after allowing them to cool down to room temperature.

The hollow refractory spheres so obtained by the method of Example 1 hereinbefore have the following characteristics: i) Bulk density: 0.7 - 0.8 Kgs/lit ii) Water absorption: 0.5 - 1.0 % iii) Chemical analysis: A12O3-99.1% Na2O - 0.3% SiO2 - 0.06% Fe2O3 - 0.04% Example 2 1. In the first stage 100 parts of a typical china clay is taken and ground in a ball mill to a surface area of 12000 to 13000 cm2/gm; 2. In the second stage the binder component is prepared by mixing 3 parts of dextrin (Corn Products "Yellow Dextrin") in 30 parts of water; 3.In the third stage 1.6 parts of expanded polystyrene beads such as ("BASF" STYROPOR or THERMOCOLE) with sizes from 1 to 5 mm are placed in a spherodizing equipment - pan noduliser - for coating the core material by standard agglomeration technique in usual manner and initially the binder of stage (2) is used to wet the surface of said beads forming core material and the powder component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and in that any agglomerates that are formed are mechanically broken; 4. In the fourth stage the said addition of the components is continued till the bulk density of 0.5 Kgs/lit is obtained. The growth of spheres of stage (3) is controlled by ensuring density control in usual manner to attain and obtain pre-determined wall thickness; 5.In the fifth stage the spheres of stage (4) are unloaded and then dried at room temperature varying from 20"C - 29"C for 24 hours in usual manner and this is followed by drying in a tray drier by gradually increasing the temperature to 150"C and maintaining it for 4 hours thereby partially destroying the said burnable core material of the spheres and providing hollow air pockets within said spheres and which provides better thermal insulation and thermal shock resistance properties for the said hollow refractory spheres; and 6.In the sixth stage the dried hollow refractory spheres of stage (5) are further processed in a batch kiln (shuttle type) at a temperature of 1 500"C for 3 hours and thereafter the said hollow spheres are unloaded and allowed to get cooled down to room temperature and then stored in drums.

The hollow refractory spheres so obtained by the method of Example 2 herein before have the following characteristics: i) Bulk Density: 0.63 - 0.7 Kgs/lit ii) Water absorption: 0% iii) C.C.S./sphere: 20 Kgs. approx.

Example 3 1. In the first stage 95 parts of silicon carbide (300 grit "GRINDWELL-NORTON" make) is mixed with 5 parts of calcined alumina ("INDAL- C"- grade) which is pre-ground to a surface area of 12000 - 13000 cm2/gms in a ball mill for 15 minutes.

2. In the second stage the binder is prepared by mixing 18 parts of water, 8 parts of commercial hydrochloric acid (30% strength) and 0.8 parts of "Dextrin" (Corn Products "Yellow-Dextrin"); 3. In the third stage 1.8 parts of expanded polystyrene ("BASF" STYROFOAM or THERMOCOLE) beads with sizes from 1 to 5 mm is placed in a spherodizing equipment - pan nodulizer - for coating the core material by standard agglomeration technique in usual manner and initially the binder of stage (2) is used to wet the surface of said polystyrene beads and the powder component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and any agglomerates that are formed are mechanically broken; 4.In the fourth stage addition of said components of stage (1) and (2) is continued till the bulk density of 0.75 to 0.77 Kgs/lit is obtained. The growth of spheres of stage (3) is controlled by ensuring density control in usual manner to attain and obtain predetermined wall thickness; 5. In the fifth stage the spheres of stage (4) are unloaded and dried at room temperature varying from 20"C to 29"C for 24 hours in usual manner and this is followed by drying in a tray drier by gradually increasing the temperature to 150"C and maintaining it for 4 hours thereby destroying the said burnable core material and providing hollow air gaps within the spheres and which air pockets provide better thermal insulation and thermal shock resistance properties to said hollow refractory spheres; and 6.In the sixth stage the dried hollow refractory spheres of stage (3) are further processed in a batch kiln (shuttle type) at a temperature of 1500 C for 3 hours and thereafter the said spheres are unloaded after cooling to room temperature and stored in drums.

The hollow refractory spheres so obtained by the method of Example 3 hereinbefore have the following characteristics: i) Bulk Density: 0.77 to 0.79 Kgs/lit )ii) Water Pick-up (shell): 7.2% iii) C.C.S. - : 25 to 40 Kgs/bubble or sphere iv) Individual sphere density (range) - 0.99 to 1.85 gms/c.c.

Example 4 1. In the first stage 90 parts of zircon powder ("ZIRFLOR" - Indian Rare Earth make "ZlRFLOR") is mixed with 10 parts of calcined alumina ("IN DAL-C" grade) which is ground to a specific surface area of 12000 13000 cm2/gm in a ball mill; 2. In the second stage the binder component is prepared by mixing 11 parts of hydrochloric acid (commercial 30% strength), 22 parts of water and 2 parts of "DEXTRIN" (Corn Products - 'Yellow-Dextrin'); 3. In the third stage 1.7 parts of expanded polystyrene beads "BASF" ('STYROFOAM' or 'THERMOCOLE') with size from 1 to 4 mm is placed in a spherodizing equipment - pan nodulizer - for coating the core material by standard agglomeration technique in usual manner as described in stage (3) of preceding examples and any agglomerates that are formed are mechanically broken in the process; 4.In the fourth stage the said addition of the components of stage (1) and stage (2) is continued till the bulk density of 0.85 kgs/lit is obtained. The growth of spheres of stage (3) is controlled by ensuring density control in usual manner to attain and obtain pre-determined wall thickness; 5.In the fifth stage the spheres of stage (4) are unloaded and dried at room temperature varying from 20"C to 29"C for 24 hours in usual manner and this is followed by drying in a tray drier by gradually increasing the temperature to 1 500C and maintaining it for 4 hours thereby partially destroying the said burnable core material and providing hollow pockets or air pockets within each of said hollow spheres and which provides better thermal insulation and thermal shock resistance properties to said hollow refractory spheres; 6.In the sixth stage the dried hollow spheres of stage (3) are further processed in a batch kiln (shuttle type) at a temperature of 1 500"C for 3 hours and thereafter the said hollow spheres are unloaded after allowing them to get cooled down to room temperature and then stored in drums.

The hollow refractory spheres obtained by the method of Example 4 hereinabove have the following characteristics: i) Bulk Density: 0.80 to 0.85 Kgs/lit ii) Water pick-up (shell): 10.8% iii) C.C.S. : 2.5 to 7.0 Kgs/sphere iv)lndividual sphere density (range): 1.3 to 2.2 gms/c.c.

Example 5 1. In the first stage 100 parts of active alumina ("ACC"-AC-701" grade) is ground in a ball mill for 1 to 2 hours; 2. In the second stage the binder component is prepared by mixing 0.2 parts of Acetic acid (glacial) and 65 parts of water; 3. In the third stage 3 parts of expanded polystyrene beads ("BASF" STYROFOAM or "THERMOCOLE") with sizes from 3 to 5 mm are placed in spherodizing equipment - pan nodulizer - for coating the core material by standard agglomeration technique in usual manner and initially then binder of stage (2) is used to wet the surface of said polystyrene beads and the powder component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and any agglomerates that are formed are mechanically destroyed or broken in the process; 4.In the fourth stage the said addition of the component is continued till the bulk density of 0.58 to 0.60 Kgs/lit is obtained. The growth of the spheres of stage (3) is controlled by ensuring density control in usual manner to obtain predetermined wall thickness; 5. In the fifth stage the spheres of stage (4) are unloaded and then dried at room temperature varying from 20"C to 29"C for 24 hours in usual manner and this is followed by drying in a tray drier by gradually increasing the temperature to 150"C and maintaining it for 5 hours thereby partially destroying the said burnable core material and providing hollow air pockets within each of said spheres and which provides low bulk densities for said hollow catalyst spheres; 6.In the sixth stage the dried hollow spheres of stage (5) are further processed in a batch activator at temperature of 550"C for 30 minutes and thereafter the said hollow catalyst spheres are unloaded after allowing them to get cooled down to room temperature and then stored in drums.

The hollow catalyst spheres so obtained by the method of Example 5 hereinabove have the following characteristics: Bulk Density: 0.46 Kegs'lit C.C.S./Sphere: 1 to 2 Kgs.

Pore Volume: 0.62 S.A. : 363 M2,gm Example 6 1. In the first stage 100 parts of catalyst powder prepared by reacting sodium aluminate with hydrochloric acid containing copper nitrate is taken; 2. In the second stage binder component is prepared by mixing 0.2 parts of acetic acid (glacial) with 80 parts of water; 3. In the third stage 2.3 parts of expanded polystyrene beads ("BASF" STYROFOR or THERMOCOLE) with sizes from 3 to 5 mm is placed in a spherodizing equipment - pan nodulizer - for coating the core material by standard agglomeration technique in usual manner and initially the binder of stage (2) is used to wet the surface of said beads and the powder component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and any agglomerates that are formed are mechanically broken; 4. In the fourth stage the said addition of the components is continued till the bulk density of 0.58 to 0.60 Kgs/lit is obtained. The growth of spheres of stage (3) is controlled by ensuring density control in usual manner to attain and obtain predetermined wall thickness; 5.In the fifth stage the spheres of stage 4 are unloaded and then dried at room temperature for 24 hours in usual manner and this is followed by drying in a tray drier by gradually increasing the temperature fo 150"C and maintaining it for 5 hours thereby partially destroying the said burnable core material and providing hollow air pockets within each of said spheres which provide low bulk density for the said hollow catalyst spheres; and 6. In the sixth stage the dried hollow spheres of stage (5) are further processed in a batch activator at a temperature of 550"C for 30 minutes and thereafter the said hollow catalyst spheres are unloaded after cooling to room temperature and stored in drums.

The hollow catalyst spheres so obtained by the method of Example 6 hereinabove have the following characteristics: Bulk Density: 0.31 Kgs/lit C.C.S./sphere: 1.8 Kgs/sphere Pore volume: 0.45 cc/gm S.A. : 340 m2/gm Example 7 1. In the first stage 90 parts of zircon powder ("Indian Rare Earth" 'ZIRCLOR') is mixed with 10 parts of calcined alumina ("INDAL-C" grade) which is preground to a specific surface area of 12000 - 13000 cm2/gm in a ball mill; 2. In the second stage the binder component is prepared by mixing 11 parts of hydrochloric acid (100% strength), 22 parts of water and 2 parts of "DEXTRIN" ("Corn Products" - YELLOW-DEXTRIN); 3.In the third stage 5.5 parts of cork granules (0.5 to 2.0 mm size) are placed in a spherodizing equipment - pan nodulizer - for coating the core material by standard agglomeration technique in usual manner and initially the binder of stage (2) is used to wet the surface of said cork granules and the powder component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and any agglomerates that are formed are mechanically broken; 4. In the fourth stage the addition of the components of stage (1) and (2) is continued till the density of 1.3 Kgs/lit is obtained. The growth of granules of stage (3) is controlled by ensuring density control in usual manner to obtain predetermined density control and wall thickness; 5.In the fifth stage the granules of stage (4) are unloaded and dried at room temperature varying from 20"-29"C for 24 hours in usual manner and this is followed by drying in an electric furnace by gradually increasing the temperature to 3500C and maintaining it for 4 hours thereby partially destroying the said burnable core material and providing hollow air pockets within each of said granules/spheres which provides better thermal insulation and thermal shock resistance for said hollow refractory granules/spheres; and 6. In the sixth stage the dried hollow refractory granules of stage (5) are further processed in a batch kiln (shuttle type) at a temperature of 1 500"C for 3 hours and thereafter the said hollow refractory granules/spheres are unloaded after cooling down to room temperature and stored in drums.

The hollow refractory granules/spheres so obtained by the method of Example 7 hereinabove have the following characteristics: Bulk Density: 1.68 Kgs/lit Water pick-up: 16.35% (cold Crashing Strength) C.C.S./Granule/sphere: 5 to 7 Kgs Example 8 1. In the first stage 95 parts of silicon carbide (300 grit - "GRINDWELL-NORTON" make) is mixed with 5 parts of calcined alumina ("lndal-C" grade) which is preground to a specific surface area of 12000 - 13000 cm2/gms in a ball mill; 2. In the second stage the binder is prepared by mixing 18 parts of water, 8 parts of commercial hydrochloric acid (30% strength) and 0.2 parts of "DEXTRIN" ('Corn Products' - "Yellow-Dextrin"); 3.In the third stage 5 parts of cork granules (0.5 to 2.0 mm size) are placed in a spherodizing equipment pan-nodulizer - for coating the core material by standard agglomeration technique in usual manner and initially the binder of stage (2) is used to wet the surface of said core granules and the powder of component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and any agglomerates that are formed are mechanically broken; 4. In the fourth stage the said addition of the components of stage (1) and stage (2) is continued till the bulk density of 0.9 Kgs/lit is obtained. The growth of granules of stage (3) is controlled by ensuring density control in usual manner to attain and obtain predetermined wall thickness; 5.In the fifth stage the granules of stage (4) are unloaded and dried at room temperature varying from 20"-29"C for 24 hours in usual manner and this is followed by drying in an electric furnace by gradually increasing the temperature to 350"C and maintaining it for 4 hours thereby partially destroying the said burnable core material and providing hollow air gaps within said granules which provide better thermal insulation and thermal shock resistance for said hollow refractory granules; and 6. In the sixth stage the dried hollow refractory granules/spheres of stage (5) are further processed in a batch kiln (shuttle type) at a temperature of 1500 C for 3 hours and thereafter the said hollow refractory granules are unloaded after allowing them to get cooled down to room temperature and then stored in drums.

The hollow refractory granules obtained by the method of Example 6 hereinabove have the following characteristics: Bulk Density: 1.55 Kgs/lit Water pick-up: 7.25% C.C.S./granule/sphere: 10 to 15 Kgs.

Example 9 1. In the first stage 100 parts of calcined alumina ("INDAL-C" grade) is grond ground in a ball mill to a specific surface area of 12000 - 13000 cm2/gm; 2. In the second stage the binder component is prepared by mixing 4 parts of "DEXTRIN" ("Corn Products YELLOW-DEXTRIN); 20 parts of hydrochloric acid (30% strength) and 25 parts of water; 3. In the third stage 31 parts of ground charcoal (wood charcoal) is placed in a spherodising equipment pan nodulizer- and nodulise to 1-5 mm size using 15 parts of 1.25 S.Pg. sulphite lye ("Lignin Research" INDOLIGA-B) solution.These spheres are dried at room temperature varying from 20"C-290C for 24 hours in usual manner and are again placed in a spherodizing equipment - pan nodulizer - for coating the core material by standard agglomeration technique in usual manner and initially the binder of stage (2) is used to wet the surface of said charcoal spheres and the powder component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and any agglomerates that are formed are mechanically broken; 4. In the fourth stage the acid addition of the components is continued till the bulk of 1.3 Kgs/lit is obtained. The growth of spheres of stage (3) is controlled by ensuring density control in usual manner to attain and obtain predetermined wall thickness; 5.In the fifth stage the granules/spheres of stage (4) are unloaded and then dried at room temperature varying from 20"C-29"C for 24 hours in usual manner and this is followed by drying in an electric furnace by gradually increasing the temperature to 1 000"C and maintaining it for 4 hours thereby destroying the said burnable core materials of each of said granules/spheres and providing hollow air pockets within said granules/spheres which provides better thermal insulation and thermal shock resistance properties for said hollow refractory granules/spheres; and 6.In the sixth stage the dried hollow refractory granules/spheres of stage 5 are further processed in a batch kiln (shuttle type) at a temperature of 1580"C for 3 hours and thereafter the said hollow refractory granules/spheres are unloaded after cooling to room temperature and then stored in drums.

The hollow refractory granules/spheres so obtained by the method of Example 9 hereinabove have the following characteristics: Bulk Density: 1.4 Kgs/lit Water pick-up: 8.25% C.C.S./granule/sphere: 7 to 8 Kgs.

Example 70 1. In the first stage 95 parts of silicon carbide (300 grit "GRINDWELL-NORTON" make) is mixed with 5 parts of calcined alumina ("INDAL-C" grade) which is preground to a specific surface area of 12000-13000 cm2/gms in a ball mill for 15 minutes.

2. in the second stage the binder is prepared by mixing 18 parts of water, 8 parts of hydrochloric acid (30% strength) and 3 parts of "DEXTRIN" (Corn Products "Yellow Dextrin"); 3. In the third stage 31 parts of ground charcoal (wood charcoal) is placed in a spherodizing equipment pan nodulizer - and noduliseto 1-3 mm size using 15 parts of 1.25 S.Pg. sulphite lye ("Lignin Research" Indoliga-B) solution.These granules are dried at room temperature varying from 20"C-29"C for 24 hours in usual manner and are again placed in a spherodising equipment - pan nodulizer - for coating the core material by standard agglomeration technique in usual manner and initially the binder of stage (2) is used to wet the surface of said charcoal granules and the powder component of stage (1) is sprinkled and the operation is continued by simultaneous addition of the components of stage (1) and stage (2) and any agglomerates that are formed are mechanicaly broken; 4. In the fourth stage the said addition of the components of stage (1) and stage (2) is continued till the bulk density of 1.0 Kg/lit is obtained. The growth of granules of stage (3) is controlled by ensuring density control in usual manner to attain and obtain predetermined wall thickness; 5. In the fifth stage the granules of stage (4) are unloaded and then dried at room temperature varying from 20"C to 29"C for 24 hours in usual manner and this is followed by drying in an electric furnace by gradually increasing the temperature to 1 0000C and maintaining it for 4 hours thereby destroying said burnable core material of said granules and providing hollow air pockets in each of said granules and which air pockets provide better thermal resistance and thermal shock resistance properties for the said hollow refractory granules/spheres; and 6.In the sixth stage the dried hollow refractory granules/spheres are further processed in a batch kiln (shuttle type) at a temperature of 1500 C for 3 hours and thereafter the said hollow refractory granules/spheres are unloaded after allowing them to get cooled down to room temperature and stored in drums.

The hollow refractory granules/spheres so manufactured by the method of Example 10 hereinabove have the following characteristics: Bulk Density: 0.67 Kgs/lit Water pick-up: 30% C.C.S./granule/sphere: 25 to 35 Kgs.

While we have described and shown a particular embodiment of our present invention, we do not wish to limit ourselves to the exact form shown since the particular embodiment shown by way of various examples described herein are intended to illustrate the invention rather than to limit it. It is to be understood that the invention is not confined to the disclosure being susceptible of such changes and modifications which shall define no material departure from the salient features of the invention as expressed in the appended claims and illustrated by way of examples.

Claims (22)

1. The closed cellular hollow ceramic and catalytic refractory spheres, bubbles or beads or aggregates for making pre-formed bricks of various shapes and sizes and/or for making castables in conjunction with hydraulic binders for making monolithic refractory applications and/or for making plastic refractory bodies for use in light weight refractories and/or loose fill insulation applications industrial catalysis are formed from refractory catalytic compositions containing for instance, Mullite, Magnesia, Zirconda, silicon carbide, alumina, silica, alumina-silicate minerals, chromite, hydroxides and salts of Al, Si, Cu, Nu, Cr, Fe, Zn, Ti, Ag, Au, Co, Mo, Pt, Rh and similar minerals or combinations thereof and wherein air entrapped within each of said hollow refractory spheres, bubbles, beads or granules is having a wide range of densities, wall thickness for a wide range of light weight refractories and industrial catalysis applications.

2. Closed cellular hollow refractory and catalytic spheres, claimed in Claim 1 wherein the air gap within each of said sphere, bubble or bead provides thermal shock resistance and thermal insulation and adequate physical strength.

3. Closed cellular hollow refractory and catalytic spheres, as claimed in Claim 1 and 2 wherein the non-glossy rough surface texture on each of said sphere, bubble or bead increased erosion resistance when present in refractory bodies.

4. Closed cellular hollow refractory and catalytic spheres as claimed in Claims 1 to 3 wherein the same are used for making castables in conjunction with hydraulic binders for manufacturing monolithic refractory bodies and in making plastic refractory bodies.

5. Closed cellular hollow refractory and catalytic spheres as claimed in Claims 1 to 4 wherein each of said hollow sphere, bubbles or beads is having a wide range of densities, wall thickness surface area and porosity for being put to wide range of light weight refractories and industrial catalysis applications including fluid bed catalysis and fluid bed combustion systems.

6. Closed cellular hollow refractory and catalytic spheres as claimed in Claims 1 to 5 wherein each of said spheres, bubbles or beads are used for making pre-formed refractory bricks of various sizes, shapes and dimensions.

7. Closed cellular hollow ceramic refractory spheres, bubbles or beads as claimed in Claims 1 to 6 work with any combination of refractory/catalyst oxides, hydroxides, carbides with or without other metal salts materials.

8. Closed cellular hollow refractory and catalytic spheres, bubbles or beads as claimed in Claims 1 to 7 wherein said ceramic or catalytic aggregates can be operated and formed below the melting temperature of the compositions.

9. A method of manufacturing hollow refractory spheres (as herein before defined) which comprises coating burnable core particles (i.e. core particles which can be destroyed and substantially removed by heat) with a mixture of a finely divided refractory material and a binder (which may be either temporary or permanent), and then heating the coated core particles so obtained so as to burn or otherwise destroy and remove by heat the said core and cause the refractory material to adhere together, for example by sintering or by the action of a binder, so as to form the hollow refractory spheres.

10. A method of manufacturing closed cellular hollow ceramic catalytic/refractory spheres or bubbles, beads or granules as claimed in Claims 1 to 8 comprises of following stages, wherein: i) in the first stage the oxides, carbides, hydroxides mentioned herein before are taken in dry state and if necessary with solid component of the binder are ground separately or together in a grinding mill or ball mill to obtain a physical fineness below 100 microns and preferably below 40 microns; ii) in the second stage the binder compising of metal oxide sol or combination of sols with metal salts or combinations of organic binder materials such as dextrin or acids is prepared in usual manner in such a way that the sol content varies from 0% to 100% of the binder and the metal salt content varies from 0% to 50% or more of the binder:: iii) in the third stage burnable core masses in spherical or granular form in the size range of 0.5 mm to 30 mm comprising of cork, carbon, wood, starch, cellulosic materials, expanded cereals, expanded polypropylene, expanded polystyrene or similar expandable synthetic resins or combinations thereof are placed in a spherodising equipment for coating the core material by standard agglomeration technique with the binder of stage (ii) and the ground component of stage (i) and this process is continued as desired batchwise or continuously; iv) in the fourth state the process of simultaneous feeding of the components of stage (i) and stage (ii) is continued and the growth of the spheres, bubbles or beads is controlled by ensuring dimensional control and/or density control in usual manner to obtain predetermined wall thickness varying from 0.1 mm to a few centimeters;; v) in the fifth stage the spheres of the fourth stage are cured and dried in a slow process at temperatures varying from 15"C to 300"C thereby partially or totally destroying the burnable core material and thereby providing hollow pockets within the spheres, bubbles or beads in which air is entrapped and which provides better thermal resistance and thermal shock resistance;; vi) in the sixth stage the dried and cured hollow spheres, bubbles or beads of the fifth stage are further pcoessed in a rotary kiln or batch/tun nel kiln/activator at temperatures varying from 300"C to 1 8000C and above, and this operation is mainly conducted and carried out to obtain desired catalytic or refractory properties and in that said processing of stage (vi) is preferably carried out at temperatures varying from 300"C to 1000"C for catalytic hollow spheres, bubbles or beads or aggregates and in that higher temperatures ranging from 800"C to 1800"C is preferred for refractory applications and which operations are carried out and conducted under desired atmospheres such as oxidising, reducing and inert atmospheres in usual manner;

11. A method of manufacturing hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 1 herein.

12. A method of manufacturing hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 2 herein.

13. A method of manufacturing hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 3 herein.

14. A method of manufacturing hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from refractory compositions as claimed in Claim 10 and substantially as described in Example 4 herein.

15. A method of manufacturing hollow catalytic spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 5 herein.

16. A method of manufacturing hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 5 herein.

17. A method of manufacturing hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 7 herein.

18. A method of manufacturing hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 8 herein.

19. A method of manufacturing hollow ceramic refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 10 and substantially as described in Example 9 herein.

20. A method of manufacturing closed cellular hollow ceramic refractory spheres, bubbles, beads or aggregates prepared from compositions as claimed in Claim 11 and substantially as described in Example 10 herein.

21. Closed cellular hollow ceramic catalytic/refractory spheres, bubbles, beads or aggregates prepared from compositions for use in light weight refractories and industrial catalysis applications as claimed in Claims 1 to Sand substantially as herein described by way of Examples 1 to 10 herein.

22. Closed cellular hollow ceramic and catalytic refractory spheres, bubbles, beads or aggregates prepared from refractory/catalytic/ceramic compositions for use in light weight refractories and industrial catalysis applications whenever prepared in accordance with method as claimed in Claims 9 to 20 above and substantially as described and illustrated by way of Examples 1 to 20 herein.