Title of Invention	A PROCESS FOR THE PREPARATION OF A ZIRCONIA NANOPOWDER
Abstract	A process for the preparation of a Zirconta nanopowder comprising the steps of providing a 5 to 20 mol % of an aqueous solution of a zirconium salt, adding thereto a 5 to 20 mol % of an aqueous solution of an aluminium salt with stirring, followed by addition of ammonia solution with stirring for up to 30 minutes to obtain a gel which is dried to obtain an amorphous ceremic gel, the get being subjected to further heat treatment to obtain the zirconiananopowder.

Title of Invention

A PROCESS FOR THE PREPARATION OF A ZIRCONIA NANOPOWDER

Abstract

A process for the preparation of a Zirconta nanopowder comprising the steps of providing a 5 to 20 mol % of an aqueous solution of a zirconium salt, adding thereto a 5 to 20 mol % of an aqueous solution of an aluminium salt with stirring, followed by addition of ammonia solution with stirring for up to 30 minutes to obtain a gel which is dried to obtain an amorphous ceremic gel, the get being subjected to further heat treatment to obtain the zirconiananopowder.

Full Text	FIELD OF THE INVENTION This invention relates to a process for producing a transparent stabilized amorphous ceramic gel. BACKGROUND OF THE INVENTION zircania ZrO exists in three monoclinic (m), tetragonal (t) and 2 o cubic (c) polymorphism m-ZrO transforms to t-phsse at 1170 C and 2 o then to c-phsse at 2370 C, The high temperature c-phase, which has potential applications are oxygen sensors, solid fuel cells and even several devices is difficult to retain at room temperature because the transformation is reversible. Efforts have been made to stsbilise it by addition of a small amount of MgO, CaO, Y0 Si N or AiN, The additive controls a refined micro- 2 3 3 4 structure at a nanometer scale. The common methods of preparation include vapour phase reactions, co-precipitation process, hydro-thermal process, slkaxide or gel processes, mechanical attrition and combustion methods. None of these methods is- successful in producing a single phase c-ZrO compound- This high energy phase exists in extremely small crystallites of size belotu 30nm in support of their high surface energy. It requires a strict control of a homogeneous micro-structure at this scale and that; is not feasible so easily in these methods which involve s heterogeneous reaction at a relatively hicih temperature to ensure 3 complete decomposition of the pr&tzur&&r and to ensure a complete el imination of byproduct impurities. OBJECTS OF THE INVENTION An object of this invention is to propose 3 process for producing a transparent staba 1ised amorphous ceramic gel . Another object of this invention is to propose a process for producing a transparent stabilised ceramic gel which uses commercially available raw materials. Sti11 another object of this invention is to propose a proces for producing a transparent stabilised ceramic gel which involves fewer steps than the processes of the known art - Yet another object of this invention is, to propose a process for producing a transparent stabilised ceramic gel which is a highly pure c~ZrO powder. 2 Further objects and advantages of this invention wi11 be more apparent from the ensuing description. BRIEF DESCRIPTION OF THE INVENTION According to this invention is provided a process for the preparation of a transparent amorphous ceramic gel comprising the steps of providing an aqueous solution of a zirconium salt, adding thereto an aqueous solution of an aluminium ©alt with stirring, followed by addition of ammonia solution with stirring to obtain 3 gel which is dried to obtain the amorphous ceramic Q&l* In this invention, a transparent amorphous ceramic gel is deve- 4+ . 3+ loped by hydrolysing Zr cations with 5- 10 moltt Al additive in - 3- ~ an aqueous solution, Al additive supports gelation of hydro-4 + lyzed Zr in a polymeric network structure - Thermal decompo- o sition and annealing of gel at 350-850 C results in recrystalli- 3+ zation of a single phase finely divided loose nanopowder in Al istabi lised c-ZrO . It occurs via a refined mi c restructure in an 2 amorphous ceramic precursor of decomposed gel at as low tempera- o ture as 200 C by a self-control led process. The obtained sample o is stable as such to a temperature as high as 850 C, A transparent gel is formed by a simple reaction of three reactants (i) ZrGCl -6H 0" NH OH in a 2 2 3 2 4 aqueous solution at room temperature. Aqueous solutions of ZrDCl 6H 0 and A1C1 .6M 0 are obtained by dissolving in 2 2 3 2 distilled water in a molar concentration. The two solutions are 4+ 4+ mixed together in a predetermined Zr /Al ratio by stirring with a magnetic starrer for 30 mins. at room temperature NH OH is added in steps through an aqueous solution to induce their hydrolysis in a controlled manner while stirring with magnetic 4+ 4+-stirrer. A hydrolysis reaction of Zr and Al cations occurs with NH OH instantaneously and results in a white co-precipitate 4 in formation of their hydroxides. At intermediate stage of the reaction, the precipitates are not thermodynamically stable in an equilibrium configuration with solution. As a result, the precipitate dissolves in the solution after a certain period of the reaction. Viscosity of the solution goes on increasing as a function of time unti1 a clear transparent homogenized precursor mass appears. It takes 10-30 mins. to 4 -. get a clear transparent solution at an average value of its pH ~ 2.0 as per its concentration, A pH -2 value could foe maintained at a controlled and limited NH OH content just near comple-tion 4 of the hydrolysis reaction. The obtained viscous precursor mass is allowed to slowly evaporate the excess water at room temperature. When dried, it appears in a transparent sol id metalloceramic gel within a month or so depending on its composition- This is possible due to the AIO(OH) additive as will be apparent from the ensuing examples. 5-20 mol% additive of Al cations effectively supports gela-tion in a stagle amorphous polymeric structure as per its >:~-ray diffraction. Several batches of the reactions are carried out by varying the A10 content in the final gel between 5 and 20 moIK, All of them result in a transparent solid gel or polymer. The gelation reaction occurs the best 25 C, or a preferably lower o temperature in the range of 5-10 C, with an average concentration of the precursor solution in the 0.2-0.5M range, o On heating at -200 C in air, a controlled thermal decomposition of metalloceramic gel occurs in a refined amorphous ceramic powder of decomposed gel. Latter is dispersed and boiled in water and then filtered in order to remove away residual byproduct impurities, especially Cl anions, if any {tested by adding an AgNO solution. The recovered powder recrystal1ised promptly into a further refined powder of Al stabilised c-ZrO at temperature 2 o as small as 350 C. It has an average size of crystallites as small as 5-10nm and that does not grow above 20nm until the o temperature is below 350 C. The invention will now be explained in greater detail with the help of the following non-1imiting examples. EXAMPLE 1 The proposed hydrolysis reaction is carried out by adding NH Oh 4 (dissolved in water in 0. 2M solution) to 0.5H ZrOC 1 8H 0 2 2 o solution in water at 25 C, or a preferably lower temperature in o the range of 5-10 C. NH OH is added in steps by stirring the 4 total solution with a magnetic stirrer. A white precipitate occurs in a hydrolysed ZKMOH) . xH 0 product. It was washed in 4 2 o distilled water, filtered, dried and then heated et 350 C to decompose into a desired c-ZrO nanopowder. It is not very 2 o stable. It converts to m-ZrO at 500 C 2 EXAMPLE 2 The above reaction is repeated by adding 0.5M A1C1 ,6H 0 (in 3 2 o water) to the 0.5M ZrOCl 8H 0 solution in water at 25 C. The volumes in the two solutions were taken such that the mixture contains 20 mol% of A1C1 .6H 0 and 80 mol% of ZrOCl 8H 0. A 3 2 2 2 white co-precipitate occurs in B hydrolysed product in A10 ZrO (OH) . xH 0 on adding the NH OH. Stirring for 10-30 mins. helps 4 2 4 to get a clear transparent solution at pH 2.0. It dries into a stable transparent gel at room temperature. On heating, it 3+ o converts into an Al stabi1ised c-ZrO nanopowder at 350-850 C- 2 A pure single phase ceramic powder is obtained in this invention. Furthermore, as no any other chemical additive has been used during the reaction, it yields a highly pure powder in a single c-ZrOjt polymorphic phase. Evidently, it is a very convenient and single method if compared with sol gel or other conventional methods in use to obtain similar ceramics. The final furnish c-ZrO product is obtained in a few steps. WE CLAIM: 1. A process for the preparation of a Zirconia nanopowder comprising the steps of providing a 5 to 20 mol % of an aqueous solution of a zirconium salt, adding thereto a 5 to 20 mol % of an aqueous solution of an aluminium salt with stirring, followed by addition of ammonia solution with stirring for upto 30 minutes to obtain a gel which is dried to obtain an amorphous ceramic gel, the gel being subjected to further heat treatment to obtain the zirconia nanopowder. 2. The process as claimed in claim 1 wherein said zirconium salt is zirconium oxychloride and the aluminium salt is aluminium chloride. 3. The process as claimed is claim 1 wherein the average concentration of the solution of the zirconium-aluminium salt is between 0.2and 0.5 M 4. The process as claimed in claim 1 wherein a 0.2M ammonia solution is added 5. The process as claimed in claim 1 wherein the zirconium and aluminium salt solutions are mixed at a tempeirature ia the range of 5-25°C, preferably 25°C. -8- 6. The process as claimed in claim 1 wherein after addition of ammonia, the reaction mixture is stirred for a period ranging from 10-30 mins at about pH 2. 7. The process as claimed in claim 1 wherein the ammonia solution is added stepwise with stirring. 8. The process as claimed in claim 1 wherein the drying time of the gel is dried at room temperature. 9. The process as claimed in claim 1 wherein the drying time of the gel is about 30 days. 10. The process as claimed in claim 1 wherein the thermal decomposition is carried out at a temperature in the range of 350-830°C. A process for the preparation of a Zirconta nanopowder comprising the steps of providing a 5 to 20 mol % of an aqueous solution of a zirconium salt, adding thereto a 5 to 20 mol % of an aqueous solution of an aluminium salt with stirring, followed by addition of ammonia solution with stirring for up to 30 minutes to obtain a gel which is dried to obtain an amorphous ceremic gel, the get being subjected to further heat treatment to obtain the zirconiananopowder.

Full Text

FIELD OF THE INVENTION
This invention relates to a process for producing a transparent
stabilized amorphous ceramic gel.
BACKGROUND OF THE INVENTION
zircania ZrO exists in three monoclinic (m), tetragonal (t) and 2
o cubic (c) polymorphism m-ZrO transforms to t-phsse at 1170 C and
2 o then to c-phsse at 2370 C, The high temperature c-phase, which
has potential applications are oxygen sensors, solid fuel cells and even several devices is difficult to retain at room temperature because the transformation is reversible. Efforts have been made to stsbilise it by addition of a small amount of MgO, CaO,
Y0 Si N or AiN, The additive controls a refined micro-
2 3 3 4 structure at a nanometer scale. The common methods of preparation
include vapour phase reactions, co-precipitation process, hydro-thermal process, slkaxide or gel processes, mechanical attrition and combustion methods.
None of these methods is- successful in producing a single phase c-ZrO compound- This high energy phase exists in extremely small crystallites of size belotu 30nm in support of their high surface energy. It requires a strict control of a homogeneous micro-structure at this scale and that; is not feasible so easily in these methods which involve s heterogeneous reaction at a relatively hicih temperature to ensure 3 complete decomposition of the pr&tzur&&r and to ensure a complete el imination of byproduct impurities.

OBJECTS OF THE INVENTION
An object of this invention is to propose 3 process for producing
a transparent staba 1ised amorphous ceramic gel .
Another object of this invention is to propose a process for producing a transparent stabilised ceramic gel which uses commercially available raw materials.
Sti11 another object of this invention is to propose a proces for producing a transparent stabilised ceramic gel which involves fewer steps than the processes of the known art -
Yet another object of this invention is, to propose a process for producing a transparent stabilised ceramic gel which is a highly
pure c~ZrO powder.
2
Further objects and advantages of this invention wi11 be more apparent from the ensuing description.
BRIEF DESCRIPTION OF THE INVENTION
According to this invention is provided a process for the preparation of a transparent amorphous ceramic gel comprising the steps of
providing an aqueous solution of a zirconium salt, adding thereto an aqueous solution of an aluminium ©alt with stirring, followed by addition of ammonia solution with stirring to obtain 3 gel which is dried to obtain the amorphous ceramic Q&l*
In this invention, a transparent amorphous ceramic gel is deve-
4+ . 3+
loped by hydrolysing Zr cations with 5- 10 moltt Al additive in

- 3- ~
an aqueous solution, Al additive supports gelation of hydro-4 +
lyzed Zr in a polymeric network structure - Thermal decompo-
o
sition and annealing of gel at 350-850 C results in recrystalli-
3+ zation of a single phase finely divided loose nanopowder in Al
istabi lised c-ZrO . It occurs via a refined mi c restructure in an
2 amorphous ceramic precursor of decomposed gel at as low tempera-
o ture as 200 C by a self-control led process. The obtained sample
o is stable as such to a temperature as high as 850 C,
A transparent gel is formed by a simple reaction of three
reactants (i) ZrGCl -6H 0" NH OH in a
2 2 3 2 4
aqueous solution at room temperature. Aqueous solutions of
ZrDCl 6H 0 and A1C1 .6M 0 are obtained by dissolving in
2 2 3 2
distilled water in a molar concentration. The two solutions are
4+ 4+ mixed together in a predetermined Zr /Al ratio by stirring
with a magnetic starrer for 30 mins. at room temperature NH OH is added in steps through an aqueous solution to induce their
hydrolysis in a controlled manner while stirring with magnetic
4+ 4+-stirrer. A hydrolysis reaction of Zr and Al cations occurs
with NH OH instantaneously and results in a white co-precipitate
4 in formation of their hydroxides.
At intermediate stage of the reaction, the precipitates are not thermodynamically stable in an equilibrium configuration with solution. As a result, the precipitate dissolves in the solution after a certain period of the reaction. Viscosity of the solution goes on increasing as a function of time unti1 a clear transparent homogenized precursor mass appears. It takes 10-30 mins. to

4 -.
get a clear transparent solution at an average value of its pH ~
2.0 as per its concentration, A pH -2 value could foe maintained
at a controlled and limited NH OH content just near comple-tion
4 of the hydrolysis reaction.
The obtained viscous precursor mass is allowed to slowly evaporate the excess water at room temperature. When dried, it appears in a transparent sol id metalloceramic gel within a month or so depending on its composition- This is possible due to the AIO(OH) additive as will be apparent from the ensuing examples. 5-20 mol% additive of Al cations effectively supports gela-tion in a stagle amorphous polymeric structure as per its >:~-ray diffraction. Several batches of the reactions are carried out by varying the A10 content in the final gel between 5 and 20 moIK, All of them result in a transparent solid gel or polymer.
The gelation reaction occurs the best 25 C, or a preferably lower
o
temperature in the range of 5-10 C, with an average concentration of the precursor solution in the 0.2-0.5M range,
o On heating at -200 C in air, a controlled thermal decomposition
of metalloceramic gel occurs in a refined amorphous ceramic powder of decomposed gel. Latter is dispersed and boiled in water and then filtered in order to remove away residual byproduct impurities, especially Cl anions, if any {tested by adding an AgNO solution. The recovered powder recrystal1ised promptly into
a further refined powder of Al stabilised c-ZrO at temperature
2 o as small as 350 C. It has an average size of crystallites as
small as 5-10nm and that does not grow above 20nm until the
o temperature is below 350 C.

The invention will now be explained in greater detail with the help of the following non-1imiting examples.
EXAMPLE 1
The proposed hydrolysis reaction is carried out by adding NH Oh
4 (dissolved in water in 0. 2M solution) to 0.5H ZrOC 1 8H 0
2 2 o solution in water at 25 C, or a preferably lower temperature in
o the range of 5-10 C. NH OH is added in steps by stirring the
4 total solution with a magnetic stirrer. A white precipitate
occurs in a hydrolysed ZKMOH) . xH 0 product. It was washed in
4 2
o distilled water, filtered, dried and then heated et 350 C to
decompose into a desired c-ZrO nanopowder. It is not very
2
o stable. It converts to m-ZrO at 500 C
2
EXAMPLE 2
The above reaction is repeated by adding 0.5M A1C1 ,6H 0 (in
3 2
o water) to the 0.5M ZrOCl 8H 0 solution in water at 25 C. The
volumes in the two solutions were taken such that the mixture
contains 20 mol% of A1C1 .6H 0 and 80 mol% of ZrOCl 8H 0. A
3 2 2 2
white co-precipitate occurs in B hydrolysed product in A10 ZrO (OH) . xH 0 on adding the NH OH. Stirring for 10-30 mins. helps
4 2 4
to get a clear transparent solution at pH 2.0. It dries into a
stable transparent gel at room temperature. On heating, it
3+ o
converts into an Al stabi1ised c-ZrO nanopowder at 350-850 C-
2 A pure single phase ceramic powder is obtained in this invention.
Furthermore, as no any other chemical additive has been used during the reaction, it yields a highly pure powder in a single c-ZrOjt polymorphic phase. Evidently, it is a very convenient and

single method if compared with sol gel or other conventional methods in use to obtain similar ceramics. The final furnish c-ZrO product is obtained in a few steps.

WE CLAIM:
1. A process for the preparation of a Zirconia nanopowder comprising the steps of providing a 5 to 20 mol % of an aqueous solution of a zirconium salt, adding thereto a 5 to 20 mol % of an aqueous solution of an aluminium salt with stirring, followed by addition of ammonia solution with stirring for upto 30 minutes to obtain a gel which is dried to obtain an amorphous ceramic gel, the gel being subjected to further heat treatment to obtain the zirconia nanopowder.
2. The process as claimed in claim 1 wherein said zirconium salt is zirconium oxychloride and the aluminium salt is aluminium chloride.
3. The process as claimed is claim 1 wherein the average concentration of the
solution of the zirconium-aluminium salt is between 0.2and 0.5 M
4. The process as claimed in claim 1 wherein a 0.2M ammonia solution is added
5. The process as claimed in claim 1 wherein the zirconium and aluminium salt
solutions are mixed at a tempeirature ia the range of 5-25°C, preferably 25°C.

-8-
6. The process as claimed in claim 1 wherein after addition of ammonia, the reaction
mixture is stirred for a period ranging from 10-30 mins at about pH 2.
7. The process as claimed in claim 1 wherein the ammonia solution is added
stepwise with stirring.
8. The process as claimed in claim 1 wherein the drying time of the gel is dried at
room temperature.
9. The process as claimed in claim 1 wherein the drying time of the gel is about 30
days.
10. The process as claimed in claim 1 wherein the thermal decomposition is carried
out at a temperature in the range of 350-830°C.
A process for the preparation of a Zirconta nanopowder comprising the steps of providing a 5 to 20 mol % of an aqueous solution of a zirconium salt, adding thereto a 5 to 20 mol % of an aqueous solution of an aluminium salt with stirring, followed by addition of ammonia solution with stirring for up to 30 minutes to obtain a gel which is dried to obtain an amorphous ceremic gel, the get being subjected to further heat treatment to obtain the zirconiananopowder.

Documents:

00709-cal-2000-abstract.pdf

00709-cal-2000-claims.pdf

00709-cal-2000-correspondence.pdf

00709-cal-2000-description(complete).pdf

00709-cal-2000-description(provisional).pdf

00709-cal-2000-form-1.pdf

00709-cal-2000-form-18.pdf

00709-cal-2000-form-2.pdf

00709-cal-2000-form-3.pdf

00709-cal-2000-form-5.pdf

00709-cal-2000-g.p.a.pdf

00709-cal-2000-letters patent.pdf

709-CAL-2000-FORM 15.pdf

709-cal-2000-granted-abstract.pdf

709-cal-2000-granted-claims.pdf

709-cal-2000-granted-description (complete).pdf

709-cal-2000-granted-form 2.pdf

709-cal-2000-granted-specification.pdf

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Patent Number

200204

Indian Patent Application Number

709/CAL/2000

PG Journal Number

15/2007

Publication Date

13-Apr-2007

Grant Date

13-Apr-2007

Date of Filing

22-Dec-2000

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY

Applicant Address

AN INDIAN INSTITUTE OF KHARAGPUR, WEST BENGAL, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	RAM S	AN INDIAN NATIONAL OF MATERIALS SCIENCE CENTRE, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR 721 302

PCT International Classification Number

C04B 35/48

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA