FIELD OF THE INVENTION
This- invention relates; to a process for obtaining refined, ultra
pure, p o r a u s a 1umina p o w d e r and a n a p p a r a t u s t h e r e fo r .
This invention further relates to a process for obtaining
refined, ultra pure, puroue alumina powder- from the activated
hydrolysis of waste A1-metal in water- vapour.
BACKGROUND OF THE INVENTION
Alumina or sapphire (A3 0 ) is an important industrial product.
•~> '¦;¦
'Incorporation of metals, metal oxides, or other- materials in
pores in a porous Al 0 offers new Al O ceramics and products.
-J -;r ,-j ..,.
uL. *._¦ X. 1.^
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 fillers.
In industries, a pure as well as derived Al 0 ceramic1-- in fine
i-j -:»
X.. i.J
3 +
powders are produced from Al 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 toxic
gases during processing and thermal decomposition of precursor
3 +
mixture with Al cations to have the final ceramic powder. It
adds unwanted impi-iri ties in final product .
OBJECTS OF THE INVENTION
An object of this invention is to propose a process and apparatus
for obtaining rn r i 'W', porous alumina powder which is ultra pure.
i
A further object of this invention is to propose a process and
apparatus for obtaining refuieti, oorous aiumina powder which is
simple.
Further ODjects and advantages of ttus invention will he
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 alumina powder comprising
the steps of cleaning and relimiK) a aiuminnium metal
surface, followed by washing the refined surface, subjecting the
+2
washed surface to a treatment with auueous solution of a Hg
¦t
salt such as herein described followed by washing to remove
+2
excess Hg ions,to obtain the nascent aluminium surface, and
subjecting the same to treatment with cooled water vapour at 20
o
to 30 C, to obtain alumina fibres followed by heating at 300 to
o
400 C, to obtain alumina powder.
In accordance with this invention,a process is developed to
refine an ultra pure AL 4? powder from waste Al-metal
*~* T
X- -Ji
in Al-industnes or workshops.it involves its activated
hydrolysis in flowing cooled H O 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 Al O and to recover it leaving behind
2 3
byproduct impurities in base metal. A nondisrupted hydrolysis o
Al-fiietal in cool eod H O vapour is tested with specimens of (l)
a pure metal (99%), (j. l) an alloy
with !'i-2 *¦*'/, transition metals and carbons, and (iii) waste Al
scraps or plates from machine shops. A general observation of
these experiments is that the impurities ss such adversely
inhabit hydrolysis of Al-metal. Irrespective of origin, the
specimen invariably has a thin Al 0 surface layer. As such, it
2 3
strongly adheres to metal surface and does not a 1.1 ow it to
hydrolyze -
The oxide surface js refined arid 3 refreshed metal surf are is
i ntrar.iijc ed by its chernic a I treatments and/or methani c a.1 de f ur-
mrstinn. "The specimen is thoroughly washed in distilled water with
a mineral acid such as a 1--2K hydroch lo/fr ic acid and then further
treated with a mineral scid such as 0. 1—0.2M hydrochloric. acid
for 10-213 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
i n )¦! 0 v ap ou r .
A further- refined metal surface to allow H Oto react with Al
¦¦¦>
2 +
atoms though it is obtained by treating with Hg -cations. In
this process, the specimen with refreshed surfaces :i s dipped in
2+
an aqueous Hg solution al a concentration of 0 . .1--0 . J>M for 1—2
mins. and then rinsed in water followed by oxalic <::c ess amalgam, if any, while wp.tihing in wattr. The nascpc.t
metal surfaces thus obtained are highly reactive to H 0 ibdIbcuIps
and induce an activated ^elf-induced hydrolysis ars soon as- put in
cooled H G vapour- at room terapc-raturp,
'¦¦>
+
H 0 molecules at nascent A.l surf act? decompose into OH and H
.ions. The OH anions conduct the hydrolysis by reacting with A1
atoms at nascent Al surface, rciMlting in the hydrolyzed Al metal
A10''OH).H 0 product. The reiitcticin ran be expressed as

Nii5c rr11 A I G (0H ) absorh I¦¦( O f r-om t h t? modi uin £nd c:on vert«; to
AID (i')H )^H 0. Here, a nond i srup ted continuous reaction over a
period of 2-''< mins. is necesiF.ary in order to refile a pure sample
by leaving behind byproduct impurities in base metal. This is
easily achieved in case the re ac I. t. on is carried out with a pure
Al metal. In this case, it proceeds so fast that the product
grows as fibres perpendicular to react-ion surface. Fibres of
length 150--.20O mm grow in 2f.:i'-lO0 i_wn diameter's in cooled H 0
2
o
v a p o i -ir a t 2 0—3 0 C .
According to this invention i <* further prov.i. tied an a p p a r a t u s for
the preparation of obtaining refined, ultra fine, porous alumina
powdo r.
In aircordsnce with tf"i j. •=¦ invention i s further provided a special
reaction chamber for .jn uninterniptpfj rpaction with the help of a
'..ont i rmoLm flow of fooled H D vapour in A l-metal having the u&ual
impurities. A refreshed A] metal sppr: imen with nascent surface is
put in a box preferably marie of glass with support at corners so
that the surf ar i?b are in direct c: of 11 a c:: t of flowing H 0 vapour. A
few holes of ?~7. mm diameter are made to allow H U vapour to pass
->
through the plate during the reaction. Another similar1 plate of
A I or othr msteii ,il , with regular HdIpb of 2-3 mm diameter i e"
placed parallel to the first plate at a distance of about 2 mm.
Hyro't yriug Al metal in AUKOHJ^H 0 at the first plate grows
through pores in thp second plate as fibres, Pores'- support and
collimate their directional growth perpendicular to reaction
':ii-urf t-c. e as per H G vapour flow. In this def-ign, the product
collects itself over the second plate. The product which grows
eff e (." t i v e 1 y f a s t over" a 1 ¦¦? n g t h t h r o i1 q h p o r e s d o pe; not involve
byproduct impurities by hydrolysis, of other element?; from surface
i 11 tii e f i rst p .1 a t e - Those ar p con fined as r es i due to the f i r st
plate after the reaction and do not mi;: with the sample collected
o v e r t h e s e c on d p I a t r .
.... h ...
The invention will now be e>ip 1 ained in greater detail with the
help of the- accompanying drawing where* Fig.l shows the reaction
chamber <1^ comprising a box (2), typically made of glass and the
iiasrt'iil Al met.;.;! vui-fart (?•>) and the second piste (4) of Al or
any o t h e r mat e r i a 1 , p a r all e 1. to p 1 a t e ¦: .3 ) . f I1i e p 1 a t es are
provided with h r.j 1 e s (5) typ i c & 1 1 y 2-3 mm in diameter snd the two
plates <3,4> are spanerf at a distance about 2 mm, AlO(P.H>. (A l-f 0
fibres grow through the holes. The chamber is also provided with
a Wciter- vapour .inlet (6) at the bottom thereof, and a water
vapour outlet <7) at the top. The AID (OH) .^H 0 forms as fibres
(. B ) t h r on g h t h e p o r e s „
Expected impurities of carbon, chromium or other transition
metals in commercial Al metal do not participate in formation of
long Ain(DH).o(H 0 fibres in continuous hydrolysis of A] metal
grow fast by leaving behind the impurities unrescted or
reoxidised in the base metal specimen. As a result, the sample
recovered from fibres- over th second plnte is free from
impurities. A chemical analysis by optical absorption spectrum
q +
does not show impurities of transition metal cations M to a ppm
level. Also no signal appear?; in epr ronf i rmi ng the absence of
q +
parautayn e t i c. M c a t ion;:i.
A specimen obtained alongwnth bypi^otluct impurities by hyctrol y z i ng
a refreshed Al metal with nascent surface immersed in water- as a
ujhole hti.;!!::- charge ter-i ;?t ic absorption in visible to UV region and
3+
an epr signal at g--value between 6.0 and t .'5 in Cr and other
q +
M i fnpi.ii' i t i es. A similar result- is found from the hydro lysis;; in
H 0 vapour or in a humid air without- using a separator of
.ti.
psral lei piste?; to separate aw By tht* byproduct impuri tieSi
Thf? invention will now be e>:p 1 a i ried in greater detail with the
h e 1 f.j of the f o.1 1 ohii i¦)g rtorp¦¦¦¦ 1 i m i t :i ng examp 1 e s.
EXAMPLE .1
The proposed reaction proces-?, i & csrried out with & pure . H G cjrnws as fibres perpendicular to the
reaction 5m-fac:e. As long fibres as 150---200 mm grow in 25-100 jum
o
diameter in cooled H O vapour at 20—30 C. A refined A! 0 powder,
2 7* 3
n
porosity "' 5.0V, occurs after heating the fibres at 300-400 C. The
recovered Al D powder is porous and as pure as upto a ppm level.
2 .3
EXAMPIE 2
The reaction is repeated with aluminium alloys having 5—2(3 at V.
transition metal and carbon, A relatively slow hydrolysis
o
reaction is noticed in cooled H (."J vapour at 20--30 C. A flowing
H 0 vapour is used to activate the reaction. A refined Al 0
j- .p. O
powder (porosity "" 305O free of carbon and other components of
the master alloy appears after- ties ting the recovered sample st
o
300—400 C in air. No hydrolysis has; been observed in case the
.... s ....
starting alloy has the carbon and other rompDnents larger than of
1.0 at '/,.
EXAMPLE 3
The reaction is further tes-ted 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 l-2'/f HC1 and then surface treated with
0.1—0.2M HljCI solution in water- for 10-20 mine. followed by
washed in water to remove the adsorbed chemicals. It yields
reactive surfaces to hydrolyse into AIO •¦¦>
refined Al 0 powder (porosity "* 40%) after heating the recovered
c:>
samp-ie at 300—400 C in air. The recovered Al 0 is pure to ppm
2 3
level.
As per x-ray diffraction, as received A1G
pure Al metal or with impurities in H O vapour is amorphous. It
haEj crystalline structure in hydrolysis in water. An amorphous
o
Al G powder results on heating amorphous sample at 300 to 400 C
*? --T
in air. It is porous with 4p ":: 50 (80 to <:^0V. before heating)
porosity determined by difference in experimental and theoretical
values of specific: density. It absorbs as much N gas as S0ii
2
cm /c:j . fc does not drop he low ^ 40*/i until the temperature is above
o
1200 C. Particles 5—20 nm diameter- are distributed through pore;-:
of similar dimension.
..... 9 .....
the method of obtaining pure Al D powder by se.1 pctive hydrolysis
of Al metal in cooled H O vapour, explored here is much more
convenient snd 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 Al O . Thift :t => not
2 3
possible by other method!:; as such. It has many advantages and
b e n (¦> f i t s that csn mskp .it a success in producing a specially pure
and porous Al 0 powder useful to fabricate a variety of
nanr'COi!ipnpite& for ptructuriil optical and ether applications of
catalysts, gas sensors, and surface coating. Doping of pores by
transition metal or rare-earth cations generate new materials for
op) t i <:. s I and e .1 ec t ran i c d e v i c es „

WE CLAIM:
1- A process for the preparation of ultra Dure 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
+2
solution of a Hg salt such as herein described followed by
+2
washing to remove excess Hg ions, to obtain the nascent
aluminium surface, and subjecting the same to treatment with
o
cooled water vapour at 20 to 30 C to obtain alumina fibres
o
followed by heating at 300 to 400 C, 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 claimed in claim 1 wherein the step of
refining comprises washing with a 0.1—0.2M mineral acid for 10-20
trims.
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 comprises washing with water.
6. The process as claimed in claim 1 wherein 0.1—0.3H solution
+2
of a Hg compound is used.
7. The process as claimed in claim 1 wherein the aluminium
+2
surface is treated with Hg cations for 1—2 mins.
+2
S. The process as claimed in claim 1 wherein the Hg cation
treated aluminium surface is washed with water and oxalic acid
+2
solutions to remove excess Hg cations.
9. ft process for the preparation of ultra pure porous alumina
powder substantially as herein described.

.10. A resction chamber for the preparation o-f ultra pure porous
s.l urn in ; ,
.:in alumin i um metal turfsct in a parallel relationship to ta:iri
aluminium metal r>urfai:e, both the aluminium metal surface and the
second metal Eurfisce beincj provided with holes;.-,
a water vapour inlet and a water vapour outlet.
1.1. "fhe chamber as claimed in claim 10 which is prefei^ably made
0 f g 1 a s s .
1.',?. The chamber as claimed in claim 10 writ? re in said aluminium
surface and second metiil surface are in the form of sheets.
13. The? chamber as; claimed in claim 10 wherein said aluminium
metal surface is provided with supports.
1 4. The chamber1 ar» (..1 aimed in claim 10 wherein said second metal
plate is made of aluminium or any other metal.
15. The chamber as c 1 aimed in claim 10 wherein the surfaces are
provided with holes of 2.....3 mm diameter-.
1.6. The chamber as claimed :i n claim 10 wherein the sheets are
placed at a distance of about '2 mm from each other.
17. The chamber as claimed in claim 10 wherein the water' vapour
inlel; is provided at the bottom of the chamber.
IB, The chamber as claimed in claim 10 wherein the water vapour
outlet is provided at the top of the chamber.
1.9. A reaction chamber for the preparation of ultra pure porous
alumina powder subst ant i al ly 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
+2
with aqueous Hg solution followed by washing to remove excess
+2
Hg ions, to obtain the nascent aluminium surface, and
subjecting the same to treatment with cooled water vapour to
ontain the alumina powder.