|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
apparatus for obtaining refined, porous alumina, powder which is
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.
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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
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
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.
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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•
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
(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.
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
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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
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
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.
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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-
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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
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.
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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
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.
|Indian Patent Application Number||102/CAL/2001|
|PG Journal Number||7/2007|
|Date of Filing||22-Feb-2001|
|Name of Patentee||INDIAN INSTITUTE OF TECHNOLOGY|
|Applicant Address||AN INDIAN INSTITUTE OF KHARAGPUR 721302,|
|PCT International Classification Number||B 22 F 9/16;|
|PCT International Application Number||N/A|
|PCT International Filing date|