Title of Invention

A PROCESS FOR MANUFACTURE OF HIGHLY STABLE Y-AL2O3 MESOPOROUS STRUCTURE

Abstract

A highly stable ?-Al2O3 and in particular, to a highly stable mesoporous ?-Al2O3, stabilized by a small doping of R3+ cations where R is selected from Eu3-, La3-, Tb3- and Cr3+or other additive adapted to retain the mesoporous structure and porosity when exposed to elevated temperatures The highly stabilized ?-Al2O3 structure would be stable at high temperature having a mesoporous structure throughout such as about 1400 K and at the same time would be cost-effective to obtain The ?-Al2O3 also achieves a desired porosity of 40%, useful for gas sensors, catalysts, surface coating, phosphors and other applications Also disclosed is the process for simple and cost-effective manner of manufacture of such stabilized ?-Al2O3 in a mesoporous structure The method of manufacture of the ?-Al2O3 is environment friendly and require no additional reagent Importantly, the method of providing of ?-Al2O3 would require very small amount of doping to stabilize ?-Al2O3 phase over an extended range of temperature to 1400 K and involve simple and fewer steps.

Full Text

Field of the invention: The present invention relates to a highly stabie ?-A2O3 and in particular, to a highly stable mesoporous ?-Al2O3, stabilized by a small doping of R3+ cations where R is selected from Eu3 +, La3+, Tb3 + and Cr3 + or other additive adapted to retain the mesoporous structure and porosity when exposed to elevated temperatures Also disclosed is the process for simple and cost-effective manner of manufacture of such stabilized ?-A2O3 in a mesoporous structure Background Art The ?-Al2O3 is an important polymorph of alumima It has been an indispensable industrial material in the form of various filters (for gas separation, solid separation, bacteria elimination, dust elimination, etc ), catalyst carriers, acoustic materials, insulating materials, gas sensors, thin film coatings, high-temperature gas-separation and reactors This is extensively used as catalytic supports for automotive gas exhaust catalysts in internal combustion engines The activity depends on its small size and large surface area It is used as catalysts to effectively reduce nitrogen oxides and oxidize the carbon monoxide and hydrocarbons contained in gas exhaust This becomes unstable when exposed to temperatures above 1100 K, which often arise for a significant period as a result of fuel detonation in an engine A mesoporous ?-Al2O3 of stable microslructure and properties is very much demanded in these applications Several methods such as sol-gel chemistry, sonohydrolysis of alkoxide precursor, hydrothermal process, and Al-metal hydrolysis have been used to synthesize 7-A12O3 in controlled size at a nanometer scale In most of these methods, ?-Al2O3 forms at temperature between 400 and 1000 K At higher temperatures, it transformations to other polymorphs with a-Al2O3 as the equilibrium phase As such the above methods could not provide a mesoporous ?-Al2O3 This metastable phase exists in small crystallites of size under 10 nm It requires a strict control of a homogeneous micro structure at this scale and that is not so easy especially with the sol-gel method, which 2 involves a heterogeneous reaction at relatively high temperature to ensure a complete decomposition of precursor with a complete elimination of byproduct impurities US 20020192150 discloses preparation of stable ?-Al2O3 involving doping with a suitable additive such as rare-earth (R) oxide to delay the undesirable phase transformation and prevent grain growth at elevated temperatures Other dopants include oxides of barium, cerium, zirconium, phosphorus, or silicon Commercial doping of ?-Al2O3 involves the use of ?-Al2O3. It is the most effective to support ?-Al2O3 structure to as high temperature as 1273 K In all such prior art methods a rather large amount of stabilizer of 3 to 5 mol % is used to achieve a sufficient degree of ?-Al2O, stabilization R2O3 are expensive and add significantly to the cost of the final product Hence, a need remains for a low cost manufacturing of stabilized ?-Al2O3 US 20020043734 discloses a method of producing an alumina porous material using a mixed powder of alumina powder and aluminum hydroxide Al(OH)3 at different percentages as the starting material comprising the steps of heating the mixed powder to decompose the aluminum hydroxide and further heat treating it within a temperature range of 1,000 to 1,600 °C and to the alumina porous material produced by the above-mentioned method with a porosity exceeding 40 volume % and its specific surface area of 8 to 40 m2 /g and further to a filter and catalyst carrier that are obtained using this alumina porous material Objects of the Invention It is thus the basic object of the present invention to provide a highly stabilized ?-Al2O3 structure which would be stable at high temperature such as about 1400 K and at the same time would be cost-effective to obtain Another object of the present invention is to provide a method of manufacture of ?-Al2O3 which would be environment friendly and require no additional reagent Yet further object is directed to provide a method of manufacture of ?-Al2O3 having a mesoporous structure throughout the temperature range to upto about 1400 K 3 Yet another object is to provide a method of manufacture of ?-Al2O3 which would be convenient and simple to stabilize ?-Al2O3 phase Yet further object is to provide a method of providing of ?-Al2O3 which would require very small amount of doping to stabilize ?-Al2O3 phase over an extended range of temperature to 1400 K and involve simple and fewer steps Yet further object is directed to a method of manufacture of ?-Al2O3 which would have desired porosity of 40%, useful for gas sensors, catalysts, surface coating, phosphors and other applications Yet further aspect of the invention is directed to a method of manufacture of ?-Al2O3 having porous structure, which would be retained until about 1400K Summary of the Invention Thus according to a basic aspect of the present invention there is provided an highly stable ?-Al2O3 mesoporous structure comprising a reactive doped R3+ cation in ?-Al2O3 in a mesoporous structure wherein said R3+ cation is selected from Eu3+, La3+, Tb3+, Cr3+ or other suitable additives The highly stable ?-Al2BO3 mesoporous structure as above can preferably comprise 1) 0 2 to 1 5 mol% doping of said R3+ cation preferably selected from Eu3+, La3+, Tb3+, Cr3+ The mesoporous structure can have a large porosity of 35 to 40 preferably 40% and is adapted to be stable in the temperature range of upto 1400°K In the highly stable ?-Al2O3 mesoporous structure as above the R2O3 occurs in nanoparticles in hexagonal crystal structure dispersed in amorphous A12O3 The average crystal size is in the range of 4 to 8 preferably 6 5 nm by the widths in the different peaks In accordance with another aspect of the present invention there is provided a process for the manufacture of stabilized ?-Al2O3comprising providing hydrogenated mesoporous AlO(OH) a H2O powder , 4 adding to said mesoporous AlO(OH) a H2O a source of R3+ cations , drying the thus dispersed R3+ cation soaked AlO(OH) a H2O to obtain stable ?-Al2O3 doped with said R3+ cation In the above process said AIO(OH) a H2O dispersed R3+ cation is dried in the temperature range of 400 to 500 preferably 450°K The starting materials used comprise aqueous solution of RCl3 6H2O /(NH4)2Cr2O7 and a mesoporous AlO(OH) a H2O powder The said mesoporous AlO(OH) a H2O is obtained by hydrolyzing of pure Al-metal in cold water vapour The aqueous solution of RCl3 6H2O or (NH4)2Cr2O7 solution is used in 0 04 to 0 40 M or 0 2 to 1 0 M concentration In accordance with a preferred aspect the process of the invention comprise a) providing an aqueous R3+ solution , b) soaking R3+ cations in divided groups in mesoporous by reacting (a) above with a hydrogenated mesoporous AlO(OH) a H2O powder, c) washing the resultant distilled water to remove the chloride ions and other byproduct impurities , and d) heating and drying it at 400 to 500 preferably 450° K and obtaining there from the finely divided loose powder of highly stable a-Al2O3 of nanoparticles with R2O3 additives In accordance with another aspect after said step of drying the R2O3 dispersed amorphous A12O3 is heated to 650 to 800 °K preferably 700°K followed by reconstructive nucleation and growth for a period of 1 to 2 preferably 2 h of heating at 850 to 1100 preferably 900°K to provide the stabilized ?-Al2O3 In accordance with yet another preferred aspect the process comprises a) providing the mesoporous AlO(OH) a H2O powder, b) adding aqueous EuCl3 solution 0 04 to 0 4 M concentration to the hydrogenated mesoporous AlO(OH) a H2O powder , c) drying the paste like product at 400 to 500 preferably 450°K , d) heating at temp range of 900 to 1100°K to provide in Eu3+ doped ?-Al2O3 a) 5 In the above process the volume/mass of the two reactive is selected to provide 0 2 to 1 5 mol% Eu2O3 in the final product with ?-Al2O3 drying the paste like specimen at 400 to 500 K in air after repeated washing in distilled water Eu3+ doped ?-Al2O3 provides thermal stability of 1400° K In accordance with yet further aspect the process comprises a) providing mesoporous AlO(OH) 2H2O powder , b) adding aqueous solution of RCI3 wherein R = La3+, Tb3+, any other rare earth cation to said hydrogenated powder , c) drying the paste like product at 400 to 500 preferably 450°K , d) heating at temp range of 900 to 1100°K to provide La3+, Tb3+, any other rare earth cation in doped ?-Al2O3 According to yet another preferred aspect the process comprises a) providing the mesoporous AlO(OH) a H2O powder, b) adding dropwise an aqueous solution of (NH4)2 Cr2O7 solution 0 2 to 1 0 M cover, c) drying the paste like product at 400 to 500 preferably 450°K , d) heating to a temp in the range of 800 to 1000°K to thereby provide the Cr3+ doped a-Al2O3 powder (mesoporous) It is thus possible by way of the invention to effectively stabilize ?-A2O3 using a small doping of 0 2 to 1 5 mol % of R2O3 (R = Eu3+, La3+, Tb3+ or Cr3+) The product has a large porosity, as much as 40%, in a specific mesoporous structure Importantly, the mesoporous structure protects the ?-Al2O3 phase The extended ?-Al2O3 stability extends to as high temperatures as 1400 K The process involves a selective chemical method, which is developed in this work with a reactive doping via a mesoporous AlO(OH) a H2O powder A pure ?-Al2O3 (mesoporous), after dehydrating AlO(OH) aH2O, stands up to 1250 K temperature The product is a finely divided loose powder suitable to fabricate components and devices Detailed Description of the Invention The starting reagents used are preferably commercial RC13 6H2O or (NH4)Cr2 of 99 9 % purity and a mesoporous AlO(OH) aH2O powder A freshly prepared AlO(OH) aH2O by hydrolysis of a pure Al-metal (99 9 %) in cold water vapour (as described in our copending Ind Patent Appln Nos 102/Cal/2001) was used It had - 90 % initial porosity An 6 aqueous RC13 6H2O or (NH4)2Cr2O7 solution in 004 to 040 M or 0 2 to 1 0 M concentration was used The final reaction and doping were carried as follows As shown schematically in scheme 1, the method of the present invention includes the steps of (a) providing an aqueous R3+ solution, (b) soaking R3+ cations in divided groups in mesopores by reacting (a) with a hydrogenated mesoporous AlO(OH) aH2O powder at room temperature, (c) washing the resultant in distilled water to remove the chloride ions and other byproduct impurities, and then (d) drying it at ~ 450 K in air A product of finely divided loose powder of highly stable ?-Al2O3 of nanoparticles with R2O3 additives after heating at 500 to 1000 K in air or vacuum was obtained Scheme 1: A schematic diagram in forming a stable ?-Al2O3 mesoporous by a reactive R3+ doping with a mesoporous AlO(OH) aH2O precursor power. On a dropwise addition of R3+ cations (in the aqueous solution) to a hydrogenated mesoporous AlO(OH) aH2O precursor, a coreduction reaction occured and converted RCl3 to R2O3 as per the reaction, 7 2RC13 + 6A1O(OH) aH2O ? R2O3 + 3A12O3 + 6 {aH2O + HCl} (1) The sample dried at 450K, was analyzed with X-ray diffraction, which revealed that the Eu2O3 occured in nanoparticles in R3c hexagonal crystal structure dispersed in an amorphous Al2O3 On heating, they dissolve in A12O3 in a complete amorphous structure at ~ 700 K A reconstructive nucleation and growth occurs and results in ?-Al2O3 in 2 h of heating at 900 to 1100 K in air In 0 4 mol % Eu3+ Al2O3 sample, the lattice parameter is a - 0 7890 nm in comparison to the standard a = 0 7924 nm value in O7H -FD3M cubic crystal structure It had 40 % porosity as analyzed by N2 gas sorption Average crystallite size is determined to be 6 5 nm by the widths in the diffraction peaks In TEM micrograph, the particles and pores appear in 5-10 nm size in a mesoporous structure Beneficially, the Eu2O3, which dissolved in the amorphous A12O3 on heating at lower temperatures, does not recrystallize at such high temperatures That intimately adheres to the ? -Al2O3 recrystallized in nanoparticles in integral part of the modified surfaces or grain boundaries Similar results appear with other La3+, Tb3+ or Cr3+ additives as explored in this work As given in Table 1, all of them stabilize the?-Al2O3in nanoparticles over a wide range of temperature extending to as high value as 1400 K In no case, the crystallite size grows above 10 nm on heating the sample to this critical value of temperature The objects of the invention and its advantages are explained hereunder in greater detail in relating to non-limiting exemplary illustrations as per the following examples Example - 1 : This example was carried out with a pure AlO(OH) aH2O powder of a mesoporous structure It had derived by hydrolysis of a pure Al-metal (99 9 %) in cold water vapour as described above It had reactive hydrogen gas filled-up in pores by reaction with H2 gas, which generates during the synthesis On heating, it decomposed to a pure ?-Al2O3 power (mesoporous) The pores act as an efficient stabilizer so that the product retains its struture of ?-Al2O3 up to a temperature of 1250 K, with 40 % porosity and 8 0 nm controlled size 8 Otherwise, it grows to other polymorphs at much lower temperature ~ 900 K as per the microstructure The product is a finely divided loose nanopowder Example-2 : In this example, Eu3+ is doped in ?-Al2O3 in a solid solution It was done with a reactive doping through a mesoporous AlO(OH) aH2O powder According to it, a predetermined volume of aqueous EuCl3 solution (0 04 to 0 4 M concentration) was added dropwise to a hydrogenated mesoporous AJO(OH) aH2O powder at room temperature The volume or mass in two reactants was taken in a way that gave 0 2 to 15 mol % EU2O3 in the final product with ?-Al2O3 Stirring the mixture over a magnetic stirrer promoted a homogeneous reaction A paste like specimen formed which was dried at ~ 450 K in air after repeated washing in distilled water A nanopowder (mesoporous) resulted in Eu3+ doped ?-Al2O3 on heating at 900 to 1100 K in air or vacuum The Eu3+ additives promoted the ?-Al2O3 stability so that it exists up to an extended temperature of 1400 K A 2 h of heating at 1400 K retains 10 nm crystallite size and 30 % porosity Example-3 : The same procedure of Example -2 was extended to obtain stabilized ?-Al2O3 with other additives of R = La3+, Tb3+ or other rare-earth cations The reaction was carried out by a dropwise addition of an aqueous RCl3 solution (0 04 to 0 4 M concentration) to a hydrogenated mesoporous AlO(OH) aH2O powder A R3+ doped ?-Al2O3 powder (mesoporous) results in 2 h of heating at 900 to 1300 K in air by recovered precursor powder after washing and drying at 450 K in air It exists to a temperature of 1400 K with a maximum of 10 nm crystallite size and 30 % porosity Example-4 : The above procedure of Example -2 or 3 is extended to obtain a stabilized ?-Al2O3 with Cr2O3 additive, which is an economic material in comparison to those of rare-earth oxides used in these examples The reaction was carried out in a similar manner by a dropwise addition of an aqueous (NH4)2Cr2O7 solution (0 2 to 10 M concentration) to a hydrogenated mesoporous AlO(OH) aH2O powder A Cr3+ doped ?-Al2O3 powder 9 (mesoporous) resulted in 2h of heating at 800 to 1000 K in air by the precursor powder after washing and drying at 450 K in air It exists to a temperature of 1300 K with a maximum of 10 nm crystallite size and 35 % porosity The preferred optimal contents of the various R2O3 additives were further identified as given in Table 1 The EU2O3 or Tb2O3 is found to be the most effective in stabilizing ?-Al2O3 over an extended range of temperatures Table 1 : Modified thermal stability of ?-Al2O3 with additives through different routes Sample Additive Method Critical Nature Reference (mol %) Temperatur e A12O3 - Dccompositio 900 K Bulk Oxides and Hydroxides n of of Aluminum, ALCOA non porous Labs Pennsylvania, boehmite USA, 1987 La3+ A12O3 0 1 - Coprecipitatio 1300K Nonporous USPatcnt20020192150 03 n (2002) La3+ A12O3 10-5 0 ?-Al2O3 1000 K Nonporous Appl Catal 7(1983)211 impregnated with La(NO3)3 A12O3 - A1-Hydro lysis 1250 K Mesoporou Present invention Cr3+ A12O3 05- Reactive 1300 K Mesoporou Present invention 1 5 doping s Eu3+ A12O3 02-15 Reactive 1400 K Mesoporou Present invention doping s Tb3+ A12O3 02-1 5 Reactive 1400 K Mesoporou Present invention doping s La3+ A12O3 02-15 Reactive 1300K Mesoporou Present invention doping s As apparent from the table, the stabilized ?-Al2O3 are far superior to those obtained following other known methods of ?-Al2O3 stabilization Moreover, the method of the invention gave mesoporous structure, which further stabilize this phase with the intergranular additives Importantly, only 0 2 to 15 mol % of the additives is sufficient enough to meet the maximum stability 10 Furthermore, the additives of R2O3, with R = Eu3+, La3+, Tb3+ or Cr3+, used in the present method do not segregate in an independent phase on heating the sample to the critical value of temperature As a result, the improved stability in a solid solution of the product with ?-Al2O3 is achieved It provides for new optical properties with strong photoluminescence in the visible and ultraviolet regions of the electromagnetic spectrum with new applications of optical materials Obviously, the invention serves as a very simple and economic method for processing of stabilized ?-Al2O3in a mesoporous structure with a simple reaction in water The method is further adapted to incorporate several other additives either to promote ?-A2O3 phase in an extended thermal stability or to induce new properties II WE CLAIM : 1. A process for the manufacture of stabilized ?-Al2O3 comprising: providing hydrogenated mesoporous AIO (OH).aH2O powder; adding to said hydrogenated mesoporous AIO(OH).aH2O powder, aqueous solution of at least one of RCI3 6H2O wherein R is selected from Eu3+, La3+ and Tb3+ and (NH4)2CR2O7; drying the thus dispersed soaked AIO (OH).aH2O to obtain therefrom the stable ?-AI2O3 doped atleast one of Eu3+, La3+, Tb3+ and Cr3+. 2. A process as claimed in claim 1 wherein said aqueous source of R3+ cation is added dropwise on said hydrogenated mesoporous AIO (OH).aH2O. 3 A process as claimed in anyone of claims 1 or 2 wherein said AIO (OH).aH2O dispersed R3+ cation is dried in the temperature range of 400 to 500 preferably 450°K. 4. A process as claimed in anyone of claims 1 to 3 wherein the stabilized ?-Al2O3obtained comprise small doping of 0 2 to 1.5 mol% of R2O3 wherein R=Eu3+, La3+, Tb3+ or Cr3+, large porosity of 35% to 40% preferably 40% in a mesoporous structure and thermal stability of upto 1400°K 5. A process as claimed in anyone of claims 1 to 4 wherein said mesoporous AIO(OH).a H2O IS obtained by hydrolyzing of pure Al-metal in cold water vapour. 6. A process as claimed in anyone of claims 1 to 5 wherein aqueous solution of RCI3.6H2O or (NH4)2Cr2O7 solution is used in 0 04 to 0.40 M or 0.2 to 1.0 M concentration. 7 A process as claimed in anyone of claims 1 to 6 comprising a) providing an aqueous R3+ solution ; b) soaking R3+ cations in divided groups in mesoporous by reacting (a) above with a hydrogenated mesoporous AIO(OH) a H2O powder; c) washing the resultant distilled water to remove the chloride ions and other byproduct impurities ; and a) 12- d) heating and drying it at 400 to 500 preferably 450° K and obtaining therefrom the finely divided loose powder of highly stable ?-Al2O3 nanoparticles with R2O3 additives. 8. A process as claimed in claim 7 wherein after said step of drying the R2O3 dispersed amorphous AI2O3 is heated to 650 to 800 °K preferably 700°K followed by reconstructive nucleation and growth for a period of 1 to 2 preferably 2 h of heating at 850 to 1100 preferably 900°K to provide the stabilized ?-Al2O3 9. A process as claimed in anyone of claims 1 to 8 comprising a) providing the said mesoporous AIO(OH) a H2O powder; b) adding aqueous EuCI3 solution 0.04 to 0.4 M concentration to the hydrogenated mesoporous AD(OH) a H2O powder; c) drying the paste like product at 400 to 500 preferably 450°K, d) heating at temp range of 900 to 1100°K to provide in Eu3+ doped y-AI2O3 10. A process as claimed in claim 9 wherein the volume/mass of the two reactives is selected to provide 0.2 to 1.5 mol% Eu2O3 in the final product with ?-Al2O3 drying the paste like specimen at 400 to 500 K in air after repeated washing in distilled water; Eu3+ doped ?-Al2O3 provides thermal stability of 1400° K. 11. A process as claimed in anyone of claims 1 to 8 comprising : a) providing said mesoporous AIO(OH). aH2O powder; b) adding aqueous solution of said RCI3 wherein R = La3+, Tb3+, any other rare earth cation to said hydrogenated powder; c) drying the paste like product at 400 to 500 preferably 450°K; d) heating at temp, range of 900 to 1100°K to provide La34, Tb3+, any other rare earth cation in doped ?-Al2O3 12. A process as claimed in anyone of claims 1 to 8 comprising . a) providing the said mesoporous AD(OH),a H2O powder; b) adding dropwise an aqueous solution of said (NH4)2 Cr2O7 solution 02 to 1 0 M cover: c) drying the paste like product at 400 to 500 preferably 450°K; d) heating to a temp, in the range of 800 to 1000°K to thereby provide the Cr3+ doped ? AI2O3 powder (mesoporous) a) 13 13. A process of manufacture of stabilized ?-Al2O3 substantially as herein described and illustrated with reference to the accompanying examples. A highly stable ?-Al2O3 and in particular, to a highly stable mesoporous ?-Al2O3, stabilized by a small doping of R3+ cations where R is selected from Eu3-, La3-, Tb3- and Cr3+or other additive adapted to retain the mesoporous structure and porosity when exposed to elevated temperatures The highly stabilized ?-Al2O3 structure would be stable at high temperature having a mesoporous structure throughout such as about 1400 K and at the same time would be cost-effective to obtain The ?-Al2O3 also achieves a desired porosity of 40%, useful for gas sensors, catalysts, surface coating, phosphors and other applications Also disclosed is the process for simple and cost-effective manner of manufacture of such stabilized ?-Al2O3 in a mesoporous structure The method of manufacture of the ?-Al2O3 is environment friendly and require no additional reagent Importantly, the method of providing of ?-Al2O3 would require very small amount of doping to stabilize ?-Al2O3 phase over an extended range of temperature to 1400 K and involve simple and fewer steps.

Documents:

00244-kol-2003 abstract.pdf

00244-kol-2003 claims.pdf

00244-kol-2003 correspondence-1.1.pdf

00244-kol-2003 correspondence-1.2.pdf

00244-kol-2003 correspondence.pdf

00244-kol-2003 description (complete).pdf

00244-kol-2003 form-1.pdf

00244-kol-2003 form-19.pdf

00244-kol-2003 form-2.pdf

00244-kol-2003 form-3.pdf

00244-kol-2003 p.a.pdf

244-KOL-2003-FORM-27.pdf

244-kol-2003-granted-abstract.pdf

244-kol-2003-granted-claims.pdf

244-kol-2003-granted-correspondence.pdf

244-kol-2003-granted-description (complete).pdf

244-kol-2003-granted-examination report.pdf

244-kol-2003-granted-form 1.pdf

244-kol-2003-granted-form 18.pdf

244-kol-2003-granted-form 2.pdf

244-kol-2003-granted-form 3.pdf

244-kol-2003-granted-letter patent.pdf

244-kol-2003-granted-pa.pdf

244-kol-2003-granted-reply to examination report.pdf

244-kol-2003-granted-specification.pdf