Title of Invention

A PROCESS OF MANUFACTURING HYDROUS ALUMINA NANOPOWDER

Abstract

A process of manufacturing hydrous alumina nanopowder: The present invention provides a process of manufacturing hydrous alumina nanopowder from aqueous metal salt solutions following a novel technique of in-situ precipitation-crystallization through a dispersion-emulsion intermediate stage. The process comprises the steps of preparing an aqueous solution of aluminium salt , dispersing the said aqueous solution as droplets into a mixture of solution of a water-immiscible organic solvent and a non-ionic surfactant to obtain a water -in-oil (w/o) type emulsion 'A' , refluxing the emulsion 'A' at a temperature in the range of 80° - 95°C for a period of 5 - 15 minutes , preparing separately another water-in-type ( w/o ) emulsion 'B' by dispersing concentrated ammonia solution and a water soluble Lewis base, into the mixture of solution consisting of the same organic solvent and surfactant as that of emulsion 'A' , refluxing the emulsion 'B' at a temperature in the range of 80° - 95°C for a period in the range of 5 - 10 min , adding emulsion 'B' to the emulsion 'A' at a temperature in the range of 80°-95°C , refluxing the resulting emulsion at a temperature in the range of 80° -95°C for 10 -20 min followed by cooling to obtain hydrous alumina particles suspended in the emulsion, adding the emulsion to an organic solvent and drying the particles to get the desired alumina nano powder.

Full Text

The present invention relates to a process of manufacturing hydrous alumina nano powder. This invention relates to a process for manufacturing hydrous alumina nanopowder from aqueous metal salt solutions. The hydrous alumina nanopowder are mainly used in the preparation of catalysts, colloidal dispersion, coatings on various substrates, membranes, alumina and alumina derived materials of desired porosity and mechanical strength and abrasive materials. The present day methods of preparing hydrous alumina nanopowders mainly consists of the solution phase reactions. Reference may be made to B. E. Yoldas in "J. Appl. Chem. Biotechnol. 23 (1973) p.p. 803-809" wherein aluminium secondary butoxide, AI(OC4H9n)3 and aluminium isopropoxide, A;(OC3H7n)3 were used as the starting materials. Hydrolysis was done by introducing the alkoxides in excess water under vigorous stirring. The water-alkoxide mole ratio was kept at around 200 moles water per mole of alkoxide to minimize the heat effect of the exothermic reaction. Cold water hydrolysis was carried out at 20°C and hot water hydrolysis was done at 80°C. The hydroxides were aged at room temperature in the mother liquor. Hot water hydrolysis produced boehmite powder of approximately 0.1µm long while the cold water hydrolysis produced large triangular and rectangular single crystals of bayerite. The main drawbacks of the above process are : (i) Uncontrolled nucleation and subsequent growth of the precipated particles in a bulk aqueous medium generates large particles. The use of alkoxides as the starting materials makes the process expensive. The alkoxides are hygroscopic and special precautions are needed during their handling. Reference may also be made to S. Music, D. Dragcevic and S. Popovic in "Mater. Letts. 41 (1999) 269 -274" wherein AI(NO3)3. 9H2O and 25% NH3 solution were used as the starting materials. To a 500 ml of 1M AI(NO3)3 solution, a proper amount of 25% NH3 aqueous solution was abruptly added and aluminium hydroxide was precipitated. The aqueous suspension of aluminium hydroxide of pH about 8.3-8.6 after strongly shaken by hand was transferred directly to a stainless autoclave, followed by heating at 150°C for 1-86 h. The washed precipitate was dried at 60°C for 24h. Tiny plate like cryatals of boehmite in the range of colloidal dimensions were obtained. The method suffers from the following disadvantages : (i) Crystallization temperature of boehmite is quite high, about 150°C. (ii) Use of an autoclave makes the process expensive and restricts the yield of the product. Reference may further be made to D. Mishra, S. Anand, R. K. Panda and R. P. Das in "Mater. Letts., 42 (2000) pp. 38-45 wherein boehmites were prepared hydrothermally from Al(NO3)3. 9H2O and urea. The required amounts of aluminium nitrate, urea and distilled water were transformed into a closed reactor under pressure. In all the experiments, the mole ratio of urea to alumina was kept at 2. The contents were then heated to different temperatures (160°, 180°, 200° or 220°C) and maintained at that temperature for the required period. The stirring rate was kept constant at 300 rpm. The products were cooled to room temperature, filter and washed with distilled water. Crystallization of boehmite occurred above 160°C. The method has the following drawbacks : (i) Boehmite crystallized at a considerably high temperature, i.e. above 160°C and under pressure, (ii) Use of an autoclave makes the process expensive and restricts the yield of the product. Reference may also be made Y.-S. Byoun, C.-S. Oh and S.-C. Choi in Cerm. Trans, 51, (1995), edited by H. Hausner, G. L. Messing and S. Hirano (American Ceramic Society, Westerville, OH) pp. 21-25, wherein agglomerate-free nano-size a-A12O3 powder was perpared following a w/o (water-in-oil) type microemulsion. Microemulsions were prepared with sodium di-octyl sulphosuccinate (AOT), n-heptane and water. The microemulsion and a solution of aluminium sec-butoxide were mixed. After hydrolysis, solvent was removed by centrifugation, and the product was dried at 100°C to synthesize alumina powder. The powders were prepared by the hydrolysis at a water/alkoxide molar ratios of ~2 and water/ surfactant molar ratios of-10 and 50. Calcination of the precursor powder from 400° to 1000°C produces a-Al2O3 at 1000°C. The a-A12O3 was formed via transition of boehmite. The powder dried at 100°C was nano-sized and agglomerate free. The powder calcined at 600°C was also ultrafine. The method suffers from the following drawbacks : (i) The use of alkoxides makes the process expensive. (ii) The alkoxides are hygroscopic and special precautions are needed during their handling, (iii) The synthesized particles are contaminated with the cation impurities present in the surfactant molecules. The main object of the present invention is to provide a process of manufacturing hydrous alumina nanopowders which obviates the drawbacks of the hitherto known processes. Another object of the present invention is to provide a process for the manufacture of the hydrous alumina nanopowders at a low temperature, thus making the process energy efficient. Yet another object of the present invention is to provide a process for manufacturing nanopowders of varying particle size and size distribution. Still another object of the present invention is to provide a process of manufacturing hydrous alumina nanopowders which is very simple and cost-effective. Another object of the present invention is to provide a process which uses precursor chemicals which are easy to handle and safe. Another object of the present invention is to provide a process which directly produces end product of minimum agglomeration and does not require any post-processing steps like high energy ball-milling screening, thus avoiding possibility of contamination and thus results in further cost saving. The present invention relates to a process of manufacturing hydrous alumina nanopowder from aqueous metal salt solutions following a novel technique of in-situ precipitation-crystallization through a dispersion-emulsion intermediate stage. The novelty of the present invention primarily resides in providing a process of obtaining hydrous alumina nanopowder which is economical, environment friendly, energy efficient, high yielding and time saving which makes the process suitable for industrial manufacture. The hydrous alumina nanopowder are mainly used in the preparation of catalysts, colloidal dispersion, coatings on various substrates, membranes, alumina and alumina derived materials of desired porosity and mechanical strength and abrasive materials. Accordingly, the present invention provides a process of manufacturing hydrous alumina nanopowder characterized in that (i) preparing an aqueous solution of aluminium salt selected from aluminium nitrate nonahydrate [AI(NO3)3. 9H2O], aluminium chloride hexahydrate (AICI3. 6H2O) wherein AI3+ concentration is in the range of 0.025-2M, filtering, (ii) dispersing under constant stirring the said aqueous solution of step (i) as droplets into a mixture of solution of a water-immiscible organic solvent and a non-ionic surfactant of hydrophilic-lipophilic balance (HLB) value in the range 4-15, wherein the proportion of water-immiscible organic solvent and a non-ionic surfactant is in the range of 1:2 - 1:5 (v/v) , (iii) obtaining a water -in-oil (w/o) type emulsion 'A' from step (ii), stirring the said emulsion 'A' for a period of 5 - 15 minutes, refluxing the emulsion 'A' at a temperature for 80° - 95°C for a period of 5 - 15 min under stirring, (iv) preparing separately another water-in-type ( w/o ) emulsion 'B' by dispersing concentrated ammonia solution (25%, GR) and a water soluble Lewis base, into an organic solution consisting of the same organic solvent and surfactant as that of emulsion 'A' wherein the proportion of ammonia and Lewis base is in the range of 1 : 2 - 1: 5 (v/v), (v) refluxing the emulsion'B' at a temperature for 80° - 95°C for a period of 5 - 10 minutes under stirring, (vi) adding emulsion 'B' to the emulsion 'A' at a temperature for 80°-95°C under stirring , (vii) maintaining the pH of the resulting emulsion in the range of 6- 8.5 and refluxing the resulting emulsion at a temperature for 80° -95°C for 10 - 20 minutes followed by cooling to ambient temperature to obtain hydrous alumina particles suspended in the emulsion, (viii) adding the emulsion obtained from step vii to an organic solvent selected from acetone, ethyl alcohol and drying the particles at a temperature for 80° - 110°C to get the desired alumina nano powder. In an embodiment of the present invention the HLB value may be maintained in the range of 4 - 15 by mixing water immiscible organic solvent such as cyclohexane, n-hexane, n-heptane, xylene, benzene with a non-ionic surfactant such as sorbitan monooleate, sorbitan monopalmitate, sorbitan monolaurate, polyethoxyethylene sorbitan monooleate, polyethoxyetylene sorbitan monoostearate with a concentration in the range of 1 - 5 vol% with respect to the volume of the water immiscible organic solvent under stirring. The process of the present invention comprises the following under stirring. 1. An aluminium metal salt solution was prepared by dissolving aluminium nitrate nonahydrate, AI(NO3)3.9H2O, aluminium chloride hexahydrate, AICI3.6H2O in water with AI3+ concentration in the range of 0.025 - 2 M, and the solution was filtered. 2. The aqueous aluminium salt solution was dispersed as droples into a solution having hydrophilic - lipophilic balance (HLB) value in the range of 4 - 15, and prepared by mixing water immiscible organic solvent such as cyclohexane, n-hexane, n-heptane, xylene, benzene with a non-ionc surfactant such as sorbitan monooleate, sorbitan monopalmitate, sorbitan monolaurate, polyethoxyetylene sorbitan monooleate, polyethoxyetylene sorbitan monoostearate with a concentration in the range of 1 - 5 vol % with respect to the volume of the water immiscible organic solvent under stirring to obtain a w/o type emulsion 'A'. 3. The volume ratio of the aqueous aluminium salt solution to the organic solution of surfactant was kept in a proportion in the range of 1:2 -1:5 (v/v). 4. The emulsion 'A' was refluxed at a temperature in the range of 80° - 95°C for a period in the range of 5 -15 min under stirring. 5. Another w/o type emulsion 'B' was prepared separately by dispersing concentrated ammonia solution (25wt%, G.R.) into an organic solution consisting of the same organic solvent and surfactant as that of emulsion 'A' as in '2' above. 6. The volume ratio of the concentrated ammonia solution to the organic solution of surfactant was kept in a proportion in the range of 1:2 -1:5 (v/v). 7. The emulsion 'B' was refluxed at a temperature in the range of 80° - 95°C for a period in the range of 5 -10 min under stirring. 8. The emulsion 'B' was added to the emulsion 'A' kept at a tmperature in the range of 80° - 95 °C under stirring. The pH of the resulting emulsion was maintained in the range of 6-8.5. 9. The resulting emulsion was refluxed at a temperature in the range of 80 - 95 *C for 10-20 min. followed by cooling to ambient temperature to obtain precipitated hydrous alumina nanopowders which remained suspended in the emulsion system. 10. The resulting emulsion, with the particles in the suspension, was then added to an organic solvent such as acetone, ethyl alcohol under stirring for a period in the range of 5-20 mins when flocculation of the particles occurred. 11. The volume ratio of the emulsion, containing the suspended particles, to the organic solvent such as acetone, ethyl alcohol was kept in the range of 1:1 to 1:3. 12. The flocculated particles were separated by centrifugation and washed with organic solvents, such as acetone, ethyl alcohol. 13. The washed particles were dried at a temperature in the range of 80°-110°C. The novelty of the present invention primarily resides in providing a process of obtaining hydrous alumina nanopowders which is economicl, environment friendly, energy efficient, high yielding and time saving which makes the process suitable for industrial manufacture and the non-obvious inventive steps lies (i) in the dispersion of the aqueous aluminium salt solution as microdroplets into a solution of non-aqueous, water-immiscible organic solvent and non-ionic surfactant of hydrophilic-lipophilic balance (HLB) value in the range 4 - 15 to obtain an water-in oil (w/o) type emulsion and (ii) carrying out the homogenous precipitation reaction inside the dispersed aqueous microdroplets, known as the microreactors, using a water soluble Lewis base in the form of dispersed aqueous microdroplets in another w/o type emulsion prepared as in (i) above, thus avoiding the formation of areas of high local concentration of A13+ ions typically developed during direct mixing of the two solutions thereby leading to uncontrolled nucleation and subsequent formation of agglomerated particles with a broad size distribution. The surfactant added to the system reduces the interfacial tension between the aqueous droplets and the water immiscible organic solvents and prevents the coalescence of the aqueous droplets by steric hindrance after absorbing on their surfaces. The stabilized aqueous microdroplets produce nanopowders with minimum of agglomeration and avoids grinding and milling operations, prevents dust hazards and possibility of contamination. By judicious selection of surfactants of different HLB values and process parameters, hydrous alumina nanopowders with desired size and size distribution are prepared. The following examples are given by way of illustration and should not be construed to limit the scope of the present invention. Example 1 18.76 gm of A1(NO3)3. 9H20 was dissolved in 100 mL of deionized water to make A1(NO3)3 solution of concentration of about 0.5M (water phase), In another container (conical flask), 78.4 mLof cyclohexane, a water immiscible organic solvent was taken. To this solvent, 1.6 mL, of sorbitan monooleate (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain an "oil phase". 25 mL of the aluminium nitrate solution (water phase) was added to the "oil phase" containing sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a w/o type emulsion "A" was formed. The volume ratio of the water phase : organic phase in the emulsion was 1:4. Stirring was continued for 10 min. In another container (conical flask), 78.4 mL of cyclohexane was taken. To this solvent 1.6 ML of sorbitan monooleate (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain another "oil phase". To this solution 20 mL of concentrated ammonia solution (25 wt%, GR) was added under stirring magnetically with a speed of 150 rpm when another w/o type emulsion 'B' was formed. The volume ratio of the water phase : organic phase in the emulsion 'B' was 1:4. Stirring was continued for 10 min. Both the emulsions 'A' and 'B' were refluxed seperately at 90°±1°C under stirring for 10 min. The emulsion 'B' was then added to the emulsion 'A' kept under stirring at 90°±1°C and the resulting emulsion of pH 8.2 was then refluxed at 90°+1°C for 15 min followed by cooling to the ambient temperature. The precipitated hydrous alumina nanopowders remained suspended in the emulsion. The entire emulsion was poured into acetone followed by stirring with a speed of 150 rpm for 15 min. Hydrous alumina nanopowders were flocculated. The volume ratio of the acetone : emulsion was 3:1. The flocculated particles were separated by centrifugation at 6000 rpm for 10 min and again dispersed in acetone under stirring. The process was repeated three times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for1h to obtain dried nanopowders. The powder exhibited mean particle size of 10.6 nm. The X-ray diffraction (XRD) indicated the formation of boehmite particles. Yield of the powder was 93%. Example 2 18.76 gm of A1(NO3)3- 9H2O was dissolved in 100 mL of deionized water to make A1(NO3)3 solution of concentration of about 0.5M (water phase). In another container (conical flask), 78.4 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 1.6 mL of sorbitan monooleate (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain an "oil phase". 25 mL of the aluminium nitrate solution (water phase) was added to the "oil phase" containing sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a w/o type emulsion "A" was formed. The volume ratio of the water phase : organic phase in the emulsion was 1:4. Stirring was continued for 10 min. In another container (conical flask), 78.4 mL of cyclohexane was taken. To this solvent 1.6 mL of sorbitan monooleate (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain another "oil phase". To this solution 20 rnL of concentrated ammonia solution (25 wt%, GR) was added under stirring magnetically with a speed of 150 rpm when another w/o type emulsion 'B' was formed. The volume ratio of the water phase : organic phase in the emulsion 'B' was 1:4. Stirring was continued for 10 min. Both the emulsions 'A' and 'B' were refluxed separately at 90°±1°C under stirring for 10 min. The emulsion 'B' was then added to the emulsion 'A' kept under stirring at 90°+1°C and the resulting emulsion of pH 6.0 was then refluxed at 90°±1°C for 15 min followed by cooling to the ambient temperature. The precipitated hydrous alumina nanopowders remained suspended in the emulsion. The entire emulsion was poured into acetone followed by stirring with a speed of 150 rpm for 15 min. Hydrous alumina nanopowders were flocculated. The volume ratio of the acetone : emulsion was 3:1. The flocculated particles were seperated by centrifugation at 6000 rpm for 10 min and again dispersed in acetone under stirring. The process was repeated three times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for 1h to obtain dried nanopowders. The powder exhibited mean particle size of 10.9 nm. The X-ray diffraction (XRD) indicated the formation of bayerite particles. Yield of the powder was 92%. Example 3 1.876 gm of Al(NO3)s. 9H20 was dissolved in 100 mL of deionized water to make Al(NO3)s solution of concentration of about 0.05M (water phase). In another container (conical flask), 78.4 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 1.6 rnL of polyoxyethylene sorbitan monooleate (HLB value 15) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain an "oil phase". 25 mL of the aluminium nitrate solution (water phase) was added to the "oil phase" containing polyoxyethylene sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a w/o type emulsion "A" was formed. The volume ratio of the water phase : organic phase in the emulsion was 1:4. Stirring was continued for 10 min. In another container (conical flask), 78.4 mL of cyclohexane was taken. To this solvent 1.6 mL of polyoxyethylene sorbitan monooleate (HLB value 15) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain another "oil phase". To this solution 20 mL of concentrated ammonia solution (25 wt%, GR) was added under stirring magnetically with a speed of 150 rpm when another w/o type emulsion 'B' was formed. The volume ratio of the water phase : organic phase in the emulsion 'B' was 1:4. Stirring was continued for 10 min. Both the emulsions 'A' and 'B' were refluxed separately at 90°+1°C under stirring for 10 min. The emulsion 'B' was then added to the emulsion 'A' kept under stirring at 90°±1°C and the resulting emulsion of pH 8.3 was then refluxed at 90°±1°C for 15 min followed by cooling to the ambient temperature. The precipitated hydrous alumina nanopowders remained suspended in the emulsion. The entire emulsion was poured into acetone followed by stirring with a speed of 150 rpm for 15 min. Hydrous alumina nanopowders were flocculated. The volume ratio of the acetone: emulsion was 3:1. The flocculated particles were seperated by centrifugation at 6000 rpm for 10 min and again dispersed in acetone under stirring. The process was repeated three times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain dried nanopowders. The powder exhibited mean particle size of 12.1 nm. The X-ray diffraction (XRD) indicated the formation of boehmite particles. Yield of the powder was 93%. Example 4 1.876 gm of A1(NO3)3. 9H2O was dissolved in 100 mL of deionized water to make Al(NO3)s solution of concentration of about 0.05M (water phase). In another container (conical flask), 78.4 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 1.6 mL of sorbitan monooleate (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain an "oil phase". 25 mL of the aluminium nitrate solution (water phase) was added to the "oil phase" containing sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a w/o type emulsion "A" was formed. The volume ratio of the water phase : organic phase in the emulsion was 1:4. Stirring was continued for 10 min. In another container (conical flask), 78.4 mL of cyclohexane was taken. To this solvent 1.6 mL of sorbitan monooleate (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 min to obtain another "oil phase". To this solution 20 mL of concentrated ammonia solution (25 wt%, GR) was added under stirring magnetically with a speed of 150 rpm when another w/o type emulsion 'B' was formed. The volume ratio of the water phase : organic phase in the emulsion 'B' was 1:4. Stirring was continued for 10 min. Both the emulsions 'A' and 'B' were refluxed separately at 80°±1°C under stirring for 10 min. The emulsion 'B' was then added to the emulsion 'A' kept under stirring at 80°±1°C and the resulting emulsion of pH 7.8 was then refluxed at 80°±1°C for 15 min followed by cooling to the ambient temperature. The precipitated hydrous alumina nanopowders remained suspended in the emulsion. The entire emulsion was poured into acetone followed by stirring with a speed of 150 rpm for 15 min. Hydrous alumina nanopowders were flocculated. The volume ratio of the acetone : emulsion was 3:1. The flocculated particles were seperated by centrifugation at 6000 rpm for 10 min and again dispersed in acetone under stirring. The process was repeated three times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for 1h to obtain dried nanopowders. The powder exhibited mean particle size of 14.6 nm. The X-ray diffraction (XRD) indicated the formation of bayerite particles. Yield of the powder was 91%. The main advantages of the present invention are: (i) The process for the manufacture of hydrous alumina nanopowders does not require any sophisticated instruments like spray dryer, spray pyrolyser. (ii) The process requires low temperature (80°-90°C) of crystallization, thus the process is energy efficient, (iii) It is a tailor-made process, as the particle size and size distribution can be varied according to the necessity by changing the process parameters, (iv) The process is simple and cost-effective. (v) It uses aqueous metal salt solution and water soluble Lewis base which are not health-hazard and does not create any atmospheric pollution during heat-treatment of nanopowders, thus the process is environment friendly. (vi) The process uses raw materials which can be handled without any specific precautions. (vii) The process of the present invention directly produces nanometre-sized crystalline powders with the desired size and size distribution as well as with minimum agglomeration and does not require any post-processing steps like high energy ball-milling, screening, thus avoiding possibility of contamination and eliminating dust hazards during handling. We Claim: 1. A process of manufacturing hydrous alumina nanopowder characterized in that (i) preparing an aqueous solution of aluminium salt selected from aluminium nitrate nonahydrate [AI(NO3)3. 9H2O], aluminium chloride hexahydrate (AICI3. 6H2O ), wherein AI3+ concentration is in the range of 0.025-2M, filtering, (ii) dispersing under constant stirring the said aqueous solution of step (i) as droplets into a mixture of solution of a water-immiscible organic solvent and a non-ionic surfactant of hydrophilic-lipophilic balance (HLB) value in the range 4 -15, wherein the proportion of water-immiscible organic solvent and a non-ionic surfactant is in the range of 1:2 - 1:5 (v/v) , (iii) obtaining a water -in-oil (w/o) type emulsion 'A' from step (ii), stirring the said emulsion 'A' for a period of 5 -15 minutes , refluxing the emulsion 'A' at a temperature for 80° - 95°C for a period of 5 - 15 min under stirring, (iv) preparing separately another water-in-type (w/o ) emulsion 'B' by dispersing concentrated ammonia solution (25%, GR) and a water soluble Lewis base, into an organic solution consisting of the same organic solvent and surfactant as that of emulsion 'A' wherein the proportion of ammonia and Lewis base is in the range of 1 : 2 - 1: 5 (v/v), (v) refluxing the emulsion 'B' at a temperature for 80° - 95°C for a period for 5-10 minutes under stirring, (vi) adding emulsion 'B' to the emulsion 'A' at a temperature in the range of 80°-95°C under stirring , (vii) maintaining the pH of the resulting emulsion in the range of 6- 8.5 and refluxing the resulting emulsion at a temperature for 80° -95°C for 10 - 20 minutes followed by cooling to ambient temperature to obtain hydrous alumina particles suspended in the emulsion, (viii) adding the emulsion obtained from step vii to an organic solvent selected from acetone, ethyl alcohol and drying the particles at a temperature for 80° -110°C to get the desired alumina nano powder. 2. A process as claimed in claim 1 wherein the HLB value of the ionic surfactant is maintained in the range of 4 - 15 by mixing water immiscible organic solvent selected from cyclohexane, n-hexane, n-heptane, xylene, benzene with a non- ionic surfactant such as sorbitan monooleate, sorbitan monopalmitate, sorbitan monolaurate, polyethoxyetylene sorbitan monooleate, polyethoxyetylene sorbitan monoostearate with a concentration in the range of 1 - 5 vol. % with respect to the volume of the water immiscible organic solvent under stirring. 3. A process of manufacturing hydrous alumina nanopowder substantially as herein described with reference to the examples.

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