Title of Invention

A PROCESS FOR THE PREPARATION OF ULTRA PURE, POROUS ALUMINA POWDER AND AN APPARATUS THEREFOR

Abstract

This invention relates to a process for the preparation of ultra pure, porous alumina powder comprising the steps of cleaning and refining a aluminium metal surface, followed by washing the refined surface, subjecting the washed surface to a treatment with aqueous Hg+2 solution followed by washing to remove excess Hg+2 ions, to obtain the nascent aluminium surface, and subjecting the same to treatment with cooled water vapour to obtain the alumina powder.

Full Text

- 1A - FIELD OF THE INVENTION This invention relates to a process for obtaining refined, ultra pure, porous alumina powder and an apparatus therefor. This invention further relates to a process for obtaining refined, ultra pure, porous alumina powder from the activated hydrolysis of wssste Al-metsl in water vapour. BACKGROUND OF THE INVENTION Alumina or sapphire (A1 O) is an important industrial product. 2 3 Incorporation of metals, metal oxides, or other materials in pores in a porous Al2O3 offers new Al2O3 ceramics and products. They display many unique properties and have a great deal of attention owing to potential applications in high performance catalysts, sensors, separation membranes, microelectronic circuits, phosphors, surface coating and hot gas fi11ers. In industries, a pure as well as derived Al2O3 ceramics in fine powders are produced from Al3+ salts through a vehicle of sol-gel or other precursor methods. A precursor or activator additive (organic chemical) used in these methods generates slot of tonic gases during processing and thermal decomposition of precursor mixture with Al3+ cations to have the final ceramic powder- It adds, unwanted impurities in final product. OBJECTS OF THE INVENTION An object of this invention is to propose a process and apparatus for obtaining refined, porous alumina powder which is ultra pure. A further object of this invention is to propose a process and 1 apparatus for obtaining refined, porous alumina, powder which is simple. Further objects and advantages of this invention will be apparent from the ensuing description. BRIEF DESCRIPTION OF THE INVENTION Thus according to this invention is provided a process for the preparation of ultra pure porous alueina powder comprising the steps of cleaning and refining a aluminnium metal surface, followed by washing the refined surface, subjecting the washed surface to a treatment with aqueous solution of a Hg+2 salt such as herein described followed by washing to remove excess Hg+2 ions, to obtain the nascent aluminium surface, and subjecting the same to treatment with cooled water vapour at 20 to 300C, to obtain alumina fibres followed by heating at 300 to a 400 C, to obtain alumina powder. In accordance with this invention,a process is developed to refine an ultra pure AL2O3 powder(porous) from waste Al-metal in A1—industries or workshops-It involves its activated hydro1ys is in flowing cooled H2O vapour at room temperature Otherwise, a thin surface passivation layer develops and stops the reaction. A set—up is designed to conduct a nondisrupted hydrolysis with freshly created nascent metal surfaces by a chemical treatment and mechanical deformation.It helps to refine a pure Al2O3 and to recover it leaving behind 2 3 byproduct impurities in base metal. A nondisrupted hydrolysis of Al-metal in cooleod H2O vapour is tested with specimens of (i) a pure metal (99%), (ii) an alloy. 1 - 3 - with 5-20% transition metals and carbons, and (iii) waste Al scrsps or plates from machine shops. A general observation of these experiments is that the impurities as such adversel inhibit hydrolysis of Al-metal. Irrespective of origin, the specimen invariably has a thin A12O3 surfaee layer. As such, it 2 3 strongly adheres to metal surface and does not allow it to hydrolyze. The oxide surface is refined and a refreshed metal surface is introduced by its chemical treatments and/or mechanical deformation. The specimen is thoroughly washed in distilled water with a mineral acid such as a 1-2% hydrochloric acid and then further treated with a mineral acid such as 0-1-0.2M hydrochloric acid for 10-20 mins., followed by washing in water again. It yields reasonably cleaned surfaces which still have part of oxide surface layers sufficient enough to prevent any hydrolysis reaction. Till this stage, it does not allow a visible reaction in H20 vapour. A further refined metal surface to allow H2O to react with Al atoms though it is obtained by treating with Hg2+ -cations. In this process, the specimen with refreshed surfaces is dipped in an aqueous Hg2+ solution at a concentration of 0.1-0.3M for 1—2 mins. Bnd then rinsed in water followed by oxalic acid to remove Hg+2 cations. The Hg2+ cations react with Al at nascent surface by getting reduced to HG metal, Hg2+ + 2 Al - 3 Hg + 2 Al , It forms a thin amalgam film with nascent Al surface. The amalgam induces residual surface oxide layer to pile off and segregate over it alongwith byproduct impurities, Those are removed along— with excess amalgam, if any, while wsshing in water. The nascent metal surfaces thus obtained are highly reactive to H2O molecules 2 and induce an activated self-induced hydrolysis as soon as put in cooled H2O vapour at room temperature. 2 H2O molecules at nascent Al surface decompose into OH and H+ ions. The OH anions conduct the hydrolysis by reacting with Al atoms at nascent Al surface, resulting in the hydrolyzed Al metal A1O(OH),HO product. The reaction can be expressed as 2 Nascent AlO(OH) absorbs H2O from the medium and converts to 2 AlO(OH),2H2O, Here, a nondisrupted continuous reaction over a 2 period of 2-5 mins. is necessary in order to refile a pure sample by leaving behind byproduct impurities in base metal. This is easily achieved in case the reaction is carried out with a pure Al metal. In this case, it proceeds so fast that the product grows as fibres perpendicular to reaction surface. Fibres of length 150-200 mm grow in 25-100 ?m diameters in cooled H2O vapour at 20-300C. - 5 - According to this invention is further provided an apparatus for the preparation of. obtaining refined, ultra fine, porous alumina powder. In accordance with this invention is further provided a special reaction chamber for an uninterrupted reaction with the help of a continuous flow of cooled H2O vapour in Al—metal having the usual impurities- A refreshed Al metal specimen with nascent surface is put in a box preferably made of glass with support at corners so that the surfaces are ,in direct contact of flowing H2O vapour. A 2 few holes of 2-3 mm diameter are made to allow H2O vapour to pass through the plate during the reaction. Another similar piste of Al or other material, with regular hoies of 2-3 mm diameter is placed parallel to the first plate at a distance of about 2 mm. Hyrolyzing Al metal in AlO(OH),2H20 at the first plate grows 2 through pores in the second plate as fibres. Pores support and col1imate their directional growth perpendiculsr to reaction surface as per H2O vapour flow. In this design, the product callects itself over the second plate. The product which grows effectively fast over a length through pores does not involve byproduct impurities by hydrolysis of other elements from surface in the first plate. Those are confined as residue to the first plate after the reaction and do not mix with the sample collected over the second plate• 5 The invention will now be explained in greater detail with the help of the accompanying drawing where Fig.1 shows the reaction chamber (i) comprising a bow (2), typically made of glass and the nascent Al metal surface (3) and the second piste (4) of Al or any other material, parallel to plate (3). The pistes are provided with holes (5) typically 2—3 mm in diameter and the two plates (3,4) are spaced at a distance about 2 mm. AlO(OH),2H2O 2 fibres grow through the holes. The chamber is also provided with a water vapour inlet (6) at the bottom thereof, and a water vapour outlet (7) at the top. The Al0(0H),2H2O forms as fibres 2 (8) through the pores-Expected impurities of carbon, chromium or other transition metals in commercial Al metal do not participate in formation of long Al(OH).2H20 fibres in continuous hydrolysis of Al metal 2 grow fast by leaving behind the impurities unreacted or reoxidised in the base metal specimen. As a result, the sample recovered from fibres over th second plate is free from impurities. A chemical analysis by optica1 absorption spectrum doss not show impurities of transition metal cations Mq+ to a ppm level. Also no signal appears in epr confirming the absence of paramagnetic M cations. A specimen obtained alongwith byproduct impurities by hydrolyzing a refreshed Al metal with nascent surface immersed in water as a whole has characteristic absorption in visible to UV region and an epr signal at g-value between 6.0 and 1.5 in Cr3+ and other Mq+ intpurities. A similar result is found from the hydrolysis in H2O vapour or in a humid air without using a separator of parallel plates to separate away the byproduct impurities. The invention will now be explained in greater detail with the help of the following non-1imiting examples. EXAMPLE 1 The proposed reaction process is carried out with a pure (99%) aluminium metal plate with freshly created nascent surfaces. A self-induced reaction occurs as soon as it is put in cooled watr vapour in the apparatus shown in Fig.1. It proceeds so fast that the product of AlO(OH). H2O grows as fibres perpendicular to the reaction surface. As long fibres as 130-200 mm grow in 25-100 ?m diameter in cooled H2O vapour at 20-300C. A refined Al2O3 powder, porosity 50% occurs after heating the fibres at 300-400 C. The recovered Al2O3 powder is porous and as pure as upto a ppm level. EXAMPLE 2 The reaction is repeated with aluminium alloys having 5-20 at % transition metal and carbon, A relatively slow hydrolysis reaction is noticed in cooled H2O vapour at 20-30 0C. A flowing H2O vapour is used to activate the reaction. A refined ?l2O3 powder (porosity ? 30%) free of carbon and other components of the master alloy appears after heating the recovered sample at 300-4000C in air. No hydrolysis has been observed in case the 7 - 8 - starting alloy has the carbon and other components larger than of 10 at %. EXAMPLE 3 The reaction is further tested with waste scraps or plates of aluminium metal from machine shops. Refreshed metal surfaces, are introduced by a chemical treatment and/or mechanical deformation. The specimen is washed in , 1-2% HC1 and then surface treated with 0.1-0.2M HgCl2 solution in water for 10-20 mins. followed by 2 washed in water to remove the adsorbed chemicals. It yields reactive surfaces to hydrolyse into AlO(OH).2H2O if immersed in cooled H2O vapour. A flowing H2O vapour is used at 2.0-300C. A refined Al2 O3 powder (porosity ? 40%) after heating the recovered 2 3 Q sample at 300-400 0C in air. The recovered Al2O3 is pure to ppm 2 3 level. As per x-ray diffraction, as received A1O(OH).H2O hydrolysis of 2 pure Al metal or with impurities in H2O vapour is amorphous. It 2 has crystalline structure in hydrolysis in water. An amorphous Al2O3 powder results on heating amorphous sample at 300 to 400 0C in air. It is porous with ? = 50 (80 to 90% before heating) porosity determined by difference in experimental and theoretical values of specific density. It absorbs as much N2 gas as 500 2 cm3 /g. ??does not drop below ? 40% until the temperature is above 1200 0C. Particles 5-20 nm diameter are distributed through pores of similar dimension. 8 - 9 - The method of obtaining pure Al2O3 powder by selective hydrolysis of Al metal in cooled H2O vapour, explored here is much more 2 convenient and simple to conduct in a single step as compared to conventional hydrolysis with an electrochemical cell or sol—gel method. It yields an ultra pure refined Al2O3 . This is not possible by other methods as such. It has many advantages and benefits that can make it a success in producing a specially pure and porous Al2O3 powder useful to fabricate a variety of nanocomposites for structural optical and other applications of catalysts, gas sensors, and surface coating. Doping of pores by transition metal or rare-earth cations generate new materials, for optical and electronic devices- - 10 - 1. A process for the preparation of ultra pure porous alumina Rowder comprising the stepts of cleaning and refining a aluminium metal surface, followed by washing the refined surface, subjectinig the washed surface to a treatment with aqueous solution of a Hg+2 salt such as herein described followed by washing to remove excess Hg+2 ions, to obtain the nascent aluminium surface,and subjecting the same to treatment With coaled water vapour at 20 to 30 0C to obtain alumina fibres followed by heating at 300 to 400 0C, to obtain alumina poWder. 2. The process as claimed in claim 1 wherein the step of cleaning comprises washing with a 1—2% mineral acid solution. 3. The process as elaiated in claim 1 wherein the step of refining comprises washing with a 0.1-0.2M mineral acid for 10—20 mins. 4. The process as claimed in claims 2,3 wherein said mineral acid is hydrochloric acid. 5. The process as claimed in claim 1 wherein the step of washing the refined surface compnises wasing with water. 6. The process as claimed in claim 1 Wherein 0.1—0.3M solution of a Hg+2 compound is used. 7. The process as claimed in claim 1 wherein the aluminium surface is treated with Hg+2 cations for 1-2 mnins. 8. The process as clsissed in claim 1 wherein the Hg+2 cation treated aluminium surface is washed with Mater and oxalic acid solutions to remove excess Hg+2 cations. 9. A process for the pregsaration of ultra pure porous alumina powder substantialiy as herein described. - 11 - 10. A reaction chamber for the preparation of ultra pure porous alumina powder comprising a box, an aluminium metal surface in a parallel relationship to said aluminium metal surface, both the aluminium metal surface and the second metal surface being provided with holes, a water vapour inlet and a water vapour outlet* 11. The chamber as claimed in claim 10 which is preferably made of glass. 12. The chamber as claimed in claim 10 wherein said aluminium surface and second metal surface are in the form of sheets. 13. The chamber as claimed in claim 10 wherein said aluminium metal surface is provided with supports. 14. The chamber as claimed in claim 10 wherein said second metal plate is made of aluminium or any other metal. 15 The chamber as claimed in claim 10 wherein the surfaces are provided with holes of 2—3 mm diameter. 16. The chamber as claimed in claim 10 wherein the sheets are placed at a distance of about 2 mm from each other, 1.7. The chamber as claimed in claim 10 wherein the water vapour inlet is provided at the bottom of the chamber, IS. The chamber as claimed in claim 10 wherein the water vapour outlet is provided at the top of the chamber, 19. A reaction chamber for the preparation of ultra pure porous alumina powder substantially as herein described. This invention relates to a process for the preparation of ultra pure, porous alumina powder comprising the steps of cleaning and refining a aluminium metal surface, followed by washing the refined surface, subjecting the washed surface to a treatment with aqueous Hg+2 solution followed by washing to remove excess Hg+2 ions, to obtain the nascent aluminium surface, and subjecting the same to treatment with cooled water vapour to obtain the alumina powder.

Documents:

00102-cal-2001-abstract.pdf

00102-cal-2001-claims.pdf

00102-cal-2001-correspondence.pdf

00102-cal-2001-description(complete).pdf

00102-cal-2001-description(provisional).pdf

00102-cal-2001-drawings.pdf

00102-cal-2001-form-1.pdf

00102-cal-2001-form-18.pdf

00102-cal-2001-form-2-1.pdf

00102-cal-2001-form-2.pdf

00102-cal-2001-form-3.pdf

00102-cal-2001-form-5.pdf

00102-cal-2001-g.p.a.pdf

00102-cal-2001-letters patent.pdf

102-CAL-2001-FORM 15.pdf

102-CAL-2001-FORM 27.pdf

102-cal-2001-granted-abstract.pdf

102-cal-2001-granted-claims.pdf

102-cal-2001-granted-description (complete).pdf

102-cal-2001-granted-drawings.pdf

102-cal-2001-granted-form 2.pdf

102-cal-2001-granted-specification.pdf