Title of Invention

A SPRAY PYROLYSIS PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED ALUMINA POWDER

Abstract

A spray pyrolysis process for the synthesis of nanostructured alumina powder comprising the steps of preparing a liquid precursor solution by dissolving together hydreted aluminium nitrate and amino acid (solid, glycine) in de-ionized/distilled water, maintaining the solution concentration in the range of 0.1 -1 Kg/Uter and "glycine - nitrate molar ratio in the range of 0.08 - 0.15; spraying off (variable pressure levels) the liquid precursor through a two- fluid pressure nozzle (with variable orifice diameter) as fine droplets into a pre-heated reaction chamber maintained at 100°- 480°C;dehydrating the precursor droplets in a dehydrating zone of the reaction chamber; decomposing the dehydrated precursor in a decomposition zone of the reactor to yield moisture free alumina powder in a powder formation zone of the reactor; collecting the coarse fraction of the alumina powder in a gravity container and finer fraction of the powder being segregated through a cyclone separator attached to the reactor and collecting same, which is known as porous, nanostructured amorphous alumina powders having tap density in the range of 0.04 - 0.08 g/cc; calcining the nanostructured alumina powder in the temperature range of 300° - 900°C resulting increase in specific surface area from 20 m2/g up to 80 m2/g associated with a phase transformation from amorphous to gamma phase of alumina and calcination beyond 900°C of the material transforms the gamma phase into alpha phase with the decrease in specific surface area of the nanostructured alumina powder.

Full Text

FIELD OF THE INVENTION: This invention relates to a process for the continuous synthesis of porous nano- structured alumina powder. This invention further relates to a process for the continuous synthesis of hollow, porous nano-structured alumina powder, by wet chemical processing techniques, following a spray pyrolysls reaction using defined liquid precursors. BACKGROUND OF THE INVENTION: The alumina powders have applications In areas covering ceramics, metallurgy, polymers, composites, paints, precision polishing, additives, fillers etc. and in allied area. Aluminum oxide (alumina) is a ceramic material that finds diverse applications due to its extraordinary physical, chemical, mechanical properties. There are more than fifteen distinct crystallographic modifications of alumina. The alpha modification is its stable form and is widely used as a chief raw material for most engineering applications. The superior properties of alpha alumina and Its numerous compositions that can be achieved are high mechanical strength, wear resistance, corrosion resistance, capability to withstand high temperature and thermal stresses, high electrical insulation and improved dielectric properties. On the other hand, thermodynamic unstable forms of alumina are called transition alumina and are largely used as catalyst carriers (support), bi functional carriers (serves as support and also contribute to the catalytic performance), various kinds of fillers, modifiers (for modifying Theological properties), adsorbents, porous filters (membranes for separation) etc. either in monolith form or Its pelleted form. The physical properties like, particle size (both primary particle and agglomerate size), morphology, tap density, specific surface area etc of either form of alumina powders, whether stable or unstable, could be tailor-made besides maintaining the Tevet of chemical purity in the powder. Conventionally, thermal dehydration of aluminum hydroxides (depending on hydroxide modification i.e., bayrlte, gibbsite or boehmtte) produce different low temperature modifications e.g., chi, eta, rho, gamma (250°C - 900°C) and delta, kappa, theta alumina in the high temperature range (900°C - 1150°C). These Intermediate phases of alumina In the above two temperature ranges are many times collectively called as 'transition alumina' and industrial production of transition alumina by thermal dehydration of aluminum hydroxides is well known. As the free energy separations of those low temperature forms of alumina are close and thus synthesis conditions plays crucial role when a particular phase In purer form (free from other phases) is attempted to synthesize. As the alpha modification is the thermodynamic phase in the alumina system, ail the transition phases of alumina ultimately stabilize to alpha phase at higher temperatures. There are numerous examples of producing transition alumina using different wet chemical methods. Among the precipitation routes, precipitation of aluminum hydroxides as bohemlte using common sources of aluminum salts like nitrates and sulfates as the mother liquors and liquor ammonia as the precipitating agent is well evident. In this process, after the precipitation reaction is over, the precipitates are thoroughly washed in order to remove the adsorbed anionic or molecular species from the precipitates and then the precipitates are calcined in air at a given temperature for promoting first dehydration and then crystallization Into gamma alumina phase or other transition alumina phase/s. Among numerous wet chemical methods, MacKenzle, K.J.D., et at, investigated preparation of transition alumina by thermal dehydration of mechanically activated gibbsite, Gibbsite is also used by Mista, W, et al, for the preparation of transition alumina by flash calcination method, in a sol-gel process, attempts have been made by Varma H.K., et al, to spray dry the bohemite sols so as to avoid the agglomeration during the gelation step, The spray dried sols were then calcined for the preparation of gamma alumina powder, interestingly, spray pyrorysis of aluminum salts like aluminum sulfate is also evident for synthesizing gamma alumina powder. Suh, D.J. et al, investigated a fast sol-gel route to prepare high surface area gamma alumina powders via a precursor so-called alumina aerogels. Another technique for the preparation of gamma alumina powders by the hydrolysis of aluminum (rlisoproxide under (he of power ultrasound (100 W/cm2) in presence of formic acid or oxalic acid as peptizers, investigated by Ramesh S , et al, Synthesis of nanophase gamma alumina powder using electron beam heating to vaporize materials in inert or reactive environments has also been tried by Eastman J.A., et al. and named as electron beam evaporation method. The relationship between the imperfection structure of gamma alumina that is formed by dehydration of boehmlte and the dehydration temperatures is established by Jlan-MIn H , by analyzing the integral width of X-ray reflections. Korean patent publication number 2000040938, in July 2000, describes a production process of gamma alumina powder that comprises several steps, starting from kaolinite, which is reacted with sulphuric acid prior heating it in the temperature range 800°C - 900°C and then the resultant solution Is filtered to remove impurities which is subsequently purified as hydrous aluminum sulphate by crystallization process and finally the crystals were heat treated m the temperature range 900°C - 1000°C to produce gamma alumina. Chiense patent publication number 1298915 in June 2001 describes the preparation of high- purity gamma alumina nanoparticles that emits blue tight, by the reaction with aluminum alkoxide solution and water vapor, following atomization, hydrolysis and further calcining the hydrofysed product at 600°C - 700°C. Japanese patent publication number 2000189744 in July 2000 describes the synthesis of both gamma-AIOGH and gamma alumina - described therein as humidity control materials, by heating aluminum hydroxide gels. Chinese patent publication number 1184078 in June 1998 describes the manufacture of gamma alumina powder from different solutions of aluminum salts like aluminum nitrate, aiuminum sulphate, aluminum chioride and sodium mefa-aluminate, to produce a gei by adjusting pH and then calcining the gel at a temperature in the range of 450°C - 700°C, Another Chinese patent publication (number 1164563) in November 1997 also describes the preparation of gamma alumina from different aluminum salts like aluminum sulphate, aluminum chloride or aluminum nitrate following precipitation reactions in different pH conditions and then filtering, drying and calcining the precipitates at different temperatures to produce gamma alumina. Russian patent publication number 2038304 in June 1995 describes the production of a low density gamma alumina by electro-erosion dispersion of aluminum in carbonated water and aging of aluminum hydroxide dispersion in ammonia solution. Japanese patent publication number 07267632 In October 1995 describes the manufacture of gamma alumina porous bodies by heating kaolin minerals and or alumina silica gels and then treating with alkalies or HF to elute amorphous silica and thus the formation of porous gamma alumina body. European patent publication number 518106 in December 1992 describes the manufacture and application of partially crystalline, transition-type aluminum oxides and gamma alumina by shock-calcination of fme-acicular boehmite. Chinese patent publication number 1062124 in June 1992 describes the preparation of gamma alumina from aluminum alkoxldes by hydrolysis and aging and then calcination of the aged-product. US laid-open patent application number 20010055558, in December, 2001 describes a gas phase method for obtaining transition alumina particles those suitable for polishing. These particles as described are either amorphous or transition alumina with gamma, delta or theta crystalline modifications with primary particle diameter of 5 to 100 nm. OBJECTS OF THE INVENTION: It is therefore an object of this invention to propose a process for the continuous synthesis of nanostructured alumina powder with hollow and nearly spherical morphology. It is further object of this invention to propose a process for the continuous synthesis of nanostructured alumina powder which produces alumina both in amorphous and crystalline forms with variable specific surface area and crystallinity. Another object of this invention is to propose a process for the continuous synthesis of nanostructured alumina powder which does not employ any conventional routes routes but rapid and cost-effective. These and other objects of the invention will be apparent from the ensuing description. DESCRIPTION OF THE ACCOMPANYING DRAWINGS: The invention will be explained in greater details with the help of the accompanying drawings where Fig.1 shows a schematic diagram of a spray pyroiysis machine Fig 2 shows the genera! morphology of the derived powders in the SEM. Fig 3 3hows the same in a magnified view. Fig 4 shows the morphology of an identified single particle that has net-shaped spherical morphology Fig 5 shows the morphology of a nearly spherical hollow particle. Fig 6 shows the nano-structure of the shell wall of the particles in the SEM, Fig 7 shows the X-ray diffraction patterns as a function of calcination temperature. Fig 8 shows the specific surface area profile in the BET as a function of calcination temperature. DETAILED DESCRIPTION OF THE INVENTION: Thus according to this invention is provided a process for the continuous synthesis of nanostructured alumina powder comprising mixing a solution of an aluminium salt and amino acid to form a precursor solution, spraying the precursor solution as fine droplets into a hot chamber to generate precursor dropfets and simultaneously with hot air, foliowed .by dehydration and decomposition of the precursor droplets to yield a-powder and calcination of the powder to yield nano-structured alumina powder. In accordance with this invention is disclosed a method for the production of porous, nanostructured alumina powders with hollow and nearly spherical morphology following a spray pyrorysis reaction technique using defined aqueous-based liquid precursor. Fig. 1 shows a schematic diagram of a spray pyrorysis machine which in.-house fabricated. The technical features and design of such a machine could vary from case to case.. The precursor solution is fed through the feed inlet (1) provided with valve Vi and the compressed air through air inlet (2) provided with valve V provided with valve of a two fluid nozzle gun (3) attached with the spray pyrolysis machine and furnished with a deblocking pin (4). Hydrated aluminum nitrate (solid) and aminoacetic acid (solid, glycine) are dissolved together in de-ionized/distilied water by maintaining the solution concentration in the range of 0.1 - 1 kg/liter and 'glycine - nitrate' molar ratio in the range 0.08 - 0.15. The resultant solution/s is then termed as 'liquid precursor'. In general, the production process starts with spraying off the liquid precursor along with air/compressed air using a two-fluid nozzle gun (3) (diameter of the nozzle orifice and also number of cavities of the spray gun may vary) attached with the spray pyrolysis machine, thereby generating Tine droplets' of the liquid precursor. Other gases like pure oxygen, enriched oxygen etc can also be used as the counter fluid here. The process of generating fine droplets from its liquid precursor is often popularly called as atomization process, though there is no actual atomization, The fineness of the precursor droplets depends both on the diameter of the orifice of the nozzle through which it is sprayed and also on the pressure level of the compressed air used in the two- fluid gun (3). The resultant fine droplets are then allowed to pass in the pre- heated reaction chamber (5) of the spray pyrolysis machine wherein the precursor droplets come in contact with hot air (H), which was made to blow in from outside by a blower (7) and passes through electricalry heated coils or gas heating system (6), attached with the spray pyrolysis machine. The temperature of the reaction chamber is maintained by controlling the temperature of the hot air and also the blower speed The design of the reaction chamber (5) as well as the temperature profile in various reaction zone/s therein may vary from case to case. In principle, the dehydration reaction of the precursor droplets occurs in the dehydration zone (8) of the reaction chamber and this step requires maximum energy (endothermic reaction) as compared to the resi of the steps in the course of synthesis. So, the hottest zone (or maximum heat flow region) in a given temperature profile of 100° - 480°C in the reactor need to kept for dehydration step for the yield of dehydrated precursors under a given feed rate efficiently. When the feed rate is increased, a counter amount of heat supply is to be maintained so as to maintain the minimum temperature required dehydrating the increased flow of precursor droplets effectively and efficiently in this zone (8), On the other hand, if the heat flow is not counter balanced with the increased flow of the precursor in the dehydrating zone (8), liquid precursor will escape in the succeeding reaction zone i,e, the decomposition zone (9) resulting in incomplete dehydration. The next step of chemical reaction is the decomposition reaction of the freshly-formed dehydrated precursors, which takes place in the decomposition zone (9). Although this is an exothermic reaction, it requires a minimum temperature of 250°C so as to carry out the decomposition reaction completely under a given feed rate of precursor droplets. As in the previous zone, in this zone too, when the feed rate is increased, a counter amount of heat supply is to be maintained so as to maintain the minimum temperature in this zone (9) as well. The last step is the formation of said alumina powders from the decomposed precursors In the powder formation zone (10). This powder needs to be made free from the decomposed gases and moisture prior to segregating them by a cyclone separator (11) attached with the spray pyrolysls machine with respect to Its coarse to finer fraction In this zone, maintenance of a minimum temperature of 100°C is essential, since the powders are susceptible to absorb moisture and other gases due to Its hollow and porous morphology. A low temperature ( zone could result in accumulation of moisture and other gases with the said alumina powders resulting the powders heavier. So, as the chemical reaction proceeds starting dehydration, to decomposition and finally the generation of the moisture-free dry powders at the end, there is a fall in temperature in the reaction chamber in the above sequence of reaction. This gives the technical guideline to design the reactor suitably along with the direction of the heat flow and thus the maintenance of temperature In different reaction zones therein. The temperature profile in each reaction zone in the chamber was measured by inserting appropriate thermocouples (12a-d) that was built-in in the spray pyrohysis machine during its fabrication. The coarse powders (13) produced in the reaction chamber (5) are collected by gravity container (14) which may be made of borosiiicate glass. The finer fraction of the powders (15) are segregated by a cyclone separator (11) attached with the spray pyrolysis machine and collected separately in container/s (16) outside the reaction chamber (5) and the decomposed gases are sent out through gas outlet (17) water-immersed porcelain beads (18) in the water injection cum exhaust chamber (19), Water circulation in the exhaust chamber (19) is maintained by water entering in through the inlet (20) and exiting through outlet (21). The yield of finer fraction is always more than its counter coarse fraction irrespective of feed rate and concentration of the precursor and hence the finer fraction Is considered for al! analysis and further applications. However, when the diameter of the nozzle orifice of the spray gun is relatively big coupled with low air pressure level in the counter fluid, the size of precursor droplet increases for which the yield of coarse fraction will be higher. The resultant powders (finer fraction) are caiied porous, nanostructured alumina powders that showed a tap density in the range of 0.04 - 0.08 g/cc, amorphous structure in the XRD and hollow and nearly spherical morphology In the SEM respectively. The size of these hollow-sphere particles depends on the.droplet size of the precursor feed (with a given precursor concentration) that has been, generated by a two-fluid spray gun In the spray pyrolysis machine using air/compressed air as the counter fluid. Thus, the droplet size of the precursor is depended both on the i) diameter of the orifice and if) air pressure in the two-fluid spray gun in spray pyrolysis machine. Lower diameter of the orifice coupled with higher air pressure increases the fineness of the droplet see and vice versa, The as-derived powders when heat-treated (calcination) In presence of air at different temperature/s in the range of 300o - 10000C with a definite period of soaking time at the calcination temperature, the specific surface area and the crystalinity into gamma alumina phase of the powders increases as a function of calcination temperature. The specific surface area of the derived powders however decreases beyond a calcination temperature of 1000°C by converting the powder into alpha alumina phase. The feed concentration of the precursor (under a given feed rate) has an Influence on the yield of the powder. As a thumb rule, higher the concentration of the precursor, higher is the yield, though the powders derived using higher concentration of the precursor shows higher tap density and relatively low specific surface area. Higher concentration of the precursor also tends to increase the coarse fraction of the powders. Morphology of the powders in the SEM as well as the amorphous nature in the XRD does not however change with the change in concentration of the precursor. As mentioned before, feed concentration is fixed \n the range of 0.1 - 1.0 kg/liter. Any higher concentration of 1.0 kg/liter makes the dissolution of the two reactants i.e., aluminum nitrate and glycine difficult at ambient temperature in the range of 20° - 35°C. On the other hand, any concentration lower than 0.1 kg/liter of the precursor reduces the yield of the powder. Hence, an optimum range of precursor concentration as mentioned in the above was preferred. Yield of the powders under a given concentration of the precursor is also dependant on the feed rate. As a thumb rule, higher the feed rate, higher would be the yield. However, as the feed rate increases, enough heat supply into the reaction chamber need to be maintained in order to ensure a counter water evaporation rate from the precursor. This is to avoid the generation of uivdecomposed precursor mass in the reaction chamber, which would otherwise result in hard solid or semi-solid lumps in stead of yielding the said powder. It is for this that it i$ important to maintain proper heat supply in the reaction chamber with the maintenance of reaction temperature/s in different stages, which is good enough for conducting complete reaction. Any higher temperature than its specified levels in the reaction zones in the chamber improves the production rate and the yield The anionic ratio of the precursor i.e., 'glycine - nitrate' molar ratio is one of the important aspect of the process which is normally kept in the range of 0.08 - 0.15. A ratio below 0.08 would not be able to convert the precursor into decomposed product effectively and efficiently at the minimum specified temperature of decomposition. Whereas, a ratio above 0.15 will cause carbon or carbonaceous product impurities in the decomposed product i.e., alumina. The scientific principle involved In the decomposition reaction here is a kind of thermally-induced redox reaction between the anions present in the precursors i.e., glycine and nitrate in this case, in which nitrate acts as an oxidant and glycine as a reductant. The anionic molar ratio in the precursor beyond 0.15, the resultant decomposed product needs to be calcined separately at a higher temperature in order to make the powder free from un-decomposed carbon or carbonaceous matters. The invention will now be explained in greater details with the help of the following non-limiting examples. Example 1: Aluminum nitrate nano hydrate (solid) and aminoacetic acid (glycine, solid) were dissolved together in de-ionized water by maintaining a concentration of 1 kg/liter and 'glycine-nltrate' molar ratio of 0 1 and thus an aqueous solution was prepared, which is termed as liquid precursor', The liquid precursor (feed rate of 4.0 liters/hour) was sprayed off along with compressed air (pressure level of 3.5 kg/cm2) using a two-fluid nozzle (nozzle orifice diameter 0.5 mm) gun attached with the spray pyrolysis machine, thereby generated fine 'precursor droplets'. A schematic diagram of the spray pyrolysis machine is furnished in the Diagram 1, though the technical features and design of such a machine could vary from case to case. The resultant precursor dropiets were then aiiowed io get mixed with hot air in a pre-heated reaction chamber of the spray pyrolysis machine in which the temperature of dehydration zone, decomposition zone and the bottom zone were kept at around 450°C, 250°C and tfO°C respectively with a variation of temperature in each zone within +/- 10°C, The precursor dropiets when came in contact with hot air that was blown in from outside the reaction chamber slowly moves from one reaction zone (higher temperature) to another (lower temperature) vertically down in the reaction chamber following dehydration to decomposition reaction and finally the formation of moisture-free porous alumina powders at the end. The coarse powder was collected through gravity in a borosiilcate glass outside the reaction chamber. A cyclone separator that Is attached with the spray pyrolysis machine fractionated the finer fraction of the powders and were collected separately in glass containers outside the reaction chamber. Finer fraction of the derived powder showed a tap density of ~ 0.04 g/cc and also showed amorphous structure in the XRD Figure 2 shows the general morphology of the derived powders in the SEWT, whereas Figure 3 shows the same in a magnified view. Figure 4 shows the morphology of an identified single particle that has net-shaped spherical morphology, whereas Figure 5 shows the morphology of a nearly spherical hollow particle, Figure 6 shows the nano- structure of the shell wall of the particles in the SEM. Figure 7 and Figure 8 show how the crystallinity into gamma alumina phase and specific surface area of the powders of the powders changes a function of temperature Example 2. Aluminum nitrate nano hydrate (solid) and glycine (solid) were dissolved together in de-ionized water at a concentration of 0.7 kg/liter and by maintaining 'glycine- nitrate* molar ratio at 0.15 and thus an aqueous solution was prepared, which Is termed as 'liquid precursor'. The liquid precursor was sprayed off (feed rate of 5.0 liters/hour) along with compressed air (pressure level of 4.0 kg/cm2) using a two-fluid nozzle (nozzle orifice diameter 0.5 mm) gun attached with the spray pyrofysis machine, thereby generated fine 'precursor droplets'. The resultant precursor droplets were then allowed to get mixed with hot air in a pre-heated reaction chamber of the spray pyrolysis machine in which the temperature of dehydration zone, decomposition zone and the bottom zone were kept at around 470°C, 280UC and 120°C respectively with a variation of temperature in each zone within +/- 10°C. The precursor droplets when came in contact with hot air that was blown In from outside the reaction chamber slowly moves from one reaction zone (higher temperature) to another (lower temperature zone) vertically down to the reaction chamber following dehydration, decomposition reaction and finally, the formation of moisture-free alumina powders at the end. The coarse powder was collected through gravity in a borosllicaie glass outside the reaction chamber, A cyclone separator that is attached with the spray pyrolysis machine fractionated the finer fraction of the powders and were collected separately in glass containers outside the reaction chamber. Finer fraction of the derived powder showed a tap density of 0.45 g/cc and also showed amorphous structure in the XRD. The morphology of the finer fraction of the derived powders showed similar to that in the example 1. The specific surface area and crystallinity into gamma alumina phase of the powders also showed similar trends to that of the Example 1. Example 3: Aluminum nitrate nano hydrate (solid) and glycine (solid) were dissolved together in de-ionized water at a concentration of 0,3 kg/liter and by maintaining 'glyeine- nitrafe' moiar ratio at 0,12 and thus an aqueous solution was prepared, which is termed as 'liquid precursor'. The liquid precursor was sprayed off (feed rate of 6.0 liter/hour) along with compressed air (pressure ievei of 4 kg/cm2) using a two- fluid nozzle (nozzle orifice diameter 0.7 mm) gun attached with the spray pyrolysis machine, thereby generated fine 'precursor droplets'. The resultant precursor droplets were then allowed to get mixed with hot air In a pre-heated reaction chamber of the spray pyrolysis machine in which the temperature of dehydration zone, decomposition zone and the bottom zone were kept at around 480°C, 260°C and 120°C respectively with a variation of temperature in each zone within +/- 10°C. The precursor droplets when came in contact with hot air that was blown in from outside the reaction chamber slowly moves from one temperature to another temperature zone vertically in the reaction chamber following dehydration, decomposition reaction and finally, the formation of the powders at the end. The coarse powder was collected through gravity in a borosilicate glass outside the reaction chamber. A cyclone separator that is attached with the spray pyrorysis machine fractionated the finer fraction of the powders and were collected separately in glass containers outside the reaction chamber. Finer fraction of the derived powder showed a tap density of 0.05 g/cc and also showed amorphous structure in the XRD. SEM micrographs of the powders showed marginally bigger size of the hollow spheres. The specific surface area and crystaiiinity into gamma aiumma phase of the powders showed similar trend to that of the example 1. Example 4: The porous alumina powders derived in the 'Example 1' were subjected to heat treatment at different set temperatures In the range of 300° - 1000°C In air with a fixed soaking time of one hour at the calcination temperature The heating rate was fixed at 1°/min to that of the set temperature. The crysfalinrty and specific surface area of resultant calcined powders were examined by X-ray powder diffraction (Cu-Ka radiation) and BET (liquid nitrogen as absorbing media) methods. Figure 7 shows how the gamma alumina phase develops as a function calcination temperature of the powders Figure 8 explains the increase in specific surface area as a function of calcination temperature. Morphology of the powders however remains similar as a function of calcination temperature, though some particles strated to become flaky-type towards the higher calcination temperatures (beyond 800°C). The increase in specific surface area as a function of temperature is believed to be because of phase transition into gamma alumina phase. The powder when calcined beyond a temperature of 10000C was converted into alpha alumina phase and specific surface area of the powder decreased as well 1. A spray pyrolysis process for tht synthesis of nanostructurtd alumina powder comprising the steps of preparing a liquid precursor solution by dissolving together hydrated aluminum nitrate and amino acid (solid, glycine) in dt-kxiatd/distilltd water, maintaining the solution concentration in the range of 0.1 - 1 Kg/Liter and "glycine - nitrate molar ratio in the range of 0.08 - 0.15; spraying off (variable pressure levels) the liquid precursor through a two-fluid pressure nozzle (with variable orifice diameter) » fine droplets into a pre-heated reaction chamber maintained at 100° - 480°C; dehydrating the precursor droplets in a dehydrating zone of the reaction chamber; decomposing the dehydrated precursor in a decomposition zone of the reactor to yield moisture free alumina powder in a powder formation zone of the reactor; collecting the coarse fraction of the alumina powder in a gravity container and finer fraction of the powder being segregated through a cyclone separator attached to the reactor and collecting same, which is known as porous, nanostructurtd amorphous alumina powders having tap density in the range of 0.04 - 0.08 g/ cc; calcining tht nanostructurtd alumina powder in the temperature range of 300° - 900°C resulting increase in specific surface area from 20 m2/g up to 80 m2/g associated with a phase transformation from amorphous to gamma phase of alumina and calcination beyond 900°C of the material transforms the gamma phase into alpha phase with the decrease in specific surface area of the nanostructured alumina powder. 2. The process as claimed in claim 1 wherein the aluminium salt is aluminium nitrate hydrate and the amino acid is glycine. 3. The process is claimed in claim 1 wherein the morphology and the physical nature of the alumina powder are best described as hollow spheres or distorted hollow spherical particles those embedded with nano-sized primary particles with significant porosity in the intra-partkte structure as observed in the Scanning Electron Microscopy (SEM). 4. A pyrolysis system for the synthesis of nanostnxtured alumina powder comprising a two fluid pressure nozzle gun (3) in communication with a pre-heated reaction chamber at 100 - 480°C, said reaction chamber provided with means (6,7) for supplying hot air, said reaction chamber defining a dehydration zone (8), a decomposition zone(9) for formation of the powder material, in a powder formation zone (10), the reaction chamber further provided with a gravity container (14) at the bottom portion thereof, for collection of coarse particles (13) of the powder material, said reaction chamber being in flow-communication with a cyclone separator (11) for separating fine particles (15) of the powder material in container (16), said cyclone separator comprises an outlet connection (17) for allowing the exhaust gas to be transported to an injection-cum-exhaust chamber for final expulsion of the decomposed gases therethrough. 5. The spray pyrolysis system as claimed in claim 4 wherein the said two-fluid pressure nozzle gun is provided with a feed inlet fitted with vafve means V1, and an air inlet fitted with valve means V2, along wirth a de- blocking pin (4). 6. The system as claimed in claim 5, wherein the temperatures in the three zones of the reaction chamber are monitored by means of thermocouples (12a, 12b, 12c and 12d) and the reaction chamber is provided with a disperses 7. The system as claimed in claim 6, wherein said means for supplying hot air (H) comprises an air blower (7) and with electrically heated coil/s or a gas heating means (6). 8. The system as claimed in claim 7, the size of nanostructured alumina particles and hence the size of the hollow spheres in the particle is controlled by controlling the size of the precursor droplets by varying either or both the inlet pressure and diameter of the nozzle orifice in the aforesaid two-fluid pressure nozzle gun. A spray pyrolysis process for the synthesis of nanostructured alumina powder comprising the steps of preparing a liquid precursor solution by dissolving together hydreted aluminium nitrate and amino acid (solid, glycine) in de-ionized/distilled water, maintaining the solution concentration in the range of 0.1 -1 Kg/Uter and "glycine - nitrate molar ratio in the range of 0.08 - 0.15; spraying off (variable pressure levels) the liquid precursor through a two- fluid pressure nozzle (with variable orifice diameter) as fine droplets into a pre-heated reaction chamber maintained at 100°- 480°C;dehydrating the precursor droplets in a dehydrating zone of the reaction chamber; decomposing the dehydrated precursor in a decomposition zone of the reactor to yield moisture free alumina powder in a powder formation zone of the reactor; collecting the coarse fraction of the alumina powder in a gravity container and finer fraction of the powder being segregated through a cyclone separator attached to the reactor and collecting same, which is known as porous, nanostructured amorphous alumina powders having tap density in the range of 0.04 - 0.08 g/cc; calcining the nanostructured alumina powder in the temperature range of 300° - 900°C resulting increase in specific surface area from 20 m2/g up to 80 m2/g associated with a phase transformation from amorphous to gamma phase of alumina and calcination beyond 900°C of the material transforms the gamma phase into alpha phase with the decrease in specific surface area of the nanostructured alumina powder.

Documents:

173-KOL-2005-(27-04-2012)-CORRESPONDENCE.pdf

173-KOL-2005-(27-04-2012)-OTHERS.pdf

173-KOL-2005-CORRESPONDENCE-1.3.pdf

173-KOL-2005-CORRESPONDENCE.1.1.pdf

173-KOL-2005-CORRESPONDENCE.pdf

173-KOL-2005-EXAMINATION REPORT.pdf

173-KOL-2005-FORM 18.pdf

173-KOL-2005-FORM 3.pdf

173-KOL-2005-FORM 5.pdf

173-KOL-2005-GPA.pdf

173-KOL-2005-GRANTED-ABSTRACT-1.1.pdf

173-KOL-2005-GRANTED-CLAIMS-1.1.pdf

173-KOL-2005-GRANTED-DESCRIPTION (COMPLETE)-1.1.pdf

173-KOL-2005-GRANTED-DRAWINGS-1.1.pdf

173-KOL-2005-GRANTED-FORM 1-1.1.pdf

173-KOL-2005-GRANTED-FORM 2-1.1.pdf

173-KOL-2005-GRANTED-SPECIFICATION-1.1.pdf

173-KOL-2005-REPLY TO EXAMINATION REPORT.pdf