FORM 2
THE PATENTS ACT, 1970
COMPLETE SPECIFICATION
SECTION 10
" A process for manufacturing high purity partially / fully stabilised ultra fine zirconia powders by hydrothermal route "



The Associated Cement Companies' Limited An Indian Company having its Regd. Office at: * CEMENT HOUSE ' , 121 Maharshi Karve Road, Mumbai- 400,020, Maharashtra, India An Indian Company incorporated under Companies' Act.
The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:


This invention relates to " Process for manufacturing high purity partially / fully stabilized ultra fine zirconia powders by hydrothermal route ".
More particularly this invention relates to process for manufacturing high purity, partially / fully stabilized ultra fine zirconia powders without high temperature calcination by hydrothermal route by mixing herein stated flowable slurry of zircon and other raw materials by spray drying grinding/pulverising to desired particle size less than 0.1 micron for being directly used in the manufacture of high performance structural and electronic parts having desirable mechanical and electrical properties and wherein the degree of PSZ ( Partially Stabilized Zircon ) or FSZ ( Fully Stabilized Zircon) depends on the amount of additives homogeneously dispersed in the zirconia matrix to get better performance in the final products. The process herein described forms a subject matter for divisional patent divided out of Patent Appln. No. 176/B0M/96 of 29-3-1996.
Zirconia exists in three crystalline phases e.g. monoclinic, tetragonal and. cubic phases depending on the temperature at which it is calcined. The monoclinic phase exists at temperatures varying from room to 1170 deg. C, temperature. The tetragonal phase
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ture of 1170 deg. C., there is a reversible monocli-nic-tetragonal transformation which takes place together with large volume change leading to the micro cracks in the structure. Due to this reason, pure zirconia powder cannot be used in the manufacture of ceramic parts.
However, addition of suitable additive / stabiliser in pure zirconia powder suppresses the volume changes by keeping the high temperature tetragonal and cubic phases, metastable at room temperature. The additives, used for stabilization of said phases in ZrO are Y 0 , CaO, MgO, CeO and / or combinations thereof.
Prior art
Hydroxide route : In this method, the solution containing zirconium and appropriate amount of yttrium or cerium is treated. with ammonia to get the precipitate of zirconia and additive as hydroxides which are homogeneously mixed with an additive such as hydroxides; filtering and washing prior to oven drying and calcining, and finally grinding to desired sub-micron particle size yields powder of PSZ / FSZ.
The principal object of this invention therefore, is to produce high purity ultra fine PSZ/FSZ powder by
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ultra fine PSZ/FSZ zirconia powder by hydrothermal route for being used in high technique areas like structural parts, kiln furniture, oxygen gas sensors, solid oxide fuel cells, piezo-electric devices and the like high tech electronic applications.
Another object is to directly produce high purity fully stabilised ultra fine zirconia fine PSZ/FSZ powder by hydrothermai route without high temperature calcination and grinding steps leading to formation off highly reactive zirconia powder for being sintered at relatively lower temperature compared to the PSZ/FSZ powder produced by prior .art method.
Thus according to this process for making PSZ/FSZ powder directly without high temp, calcination by hydrothermai route comprises the steps of: preparing a slurry from crushed zirconia in a glass lined of stainless steel mixer and while stirring being continued adding herein stated precursor of CaO, MgO, CeCL , by 1-25 weight % on oxide basis in deminer-alised water taking weight ratio of solid to water as 1.0 : 1.0-10.0 and adjusting its pH in the range of 8.0 to 13.5 by addition of an alkali solution such as ammonia solution / NaOH depending on product specification laid down by end user; drying said slurry at temp, varying from 150-425 deg. C, under pressure
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range varying from 100-750 psi for 45 mins. to 4 hrs„; filtering out said slurry and washing said filtrate several times with demineralised water till all undis solved impurities being removed; oven or air drying said washed filtrate at temp, varying from 450 - 600 deg. C; crushing said dried agglomerates to desired particle size of 0.1 - 1 .0 micron to form PSZ powder

or converting said dried agglomerates into 15 - 60% flowable slurry by mixing demineralised waterfor being oven or spray dried at temp, varying from 150-300 deg. C.jto form FSZ powder having herein stated product analysis:
ZrCr, purity (including HfO +

According to one embodiment the zirconia source includes ZrO2 itself or hydrated ZrO2 sulphate or nitrate or chloride salt of zirconium, zirconium

carbonate, zirconium acetate and/or combina- ... ...
tions therof depending on the specification stipulated
by end user.
In another embodiment, the additive source comprises additive oxide such as Y 0 / MgO / CaO / CeO, sulphate or nitrate or chloride salt of additives, hydrated oxide or hydroxide of respective additives, carbonate or acetate of additives or combinations thereof and wherein said stabilizer added to the zirconia precursor being 1-25 Wt. % on solid basis.
In another embodiment the pressure is maintained between 200-750 psi and the temperature of the hydro-thermal treatment route is maintained between 150 -425 deg. C.,
In still another embodiment the hydrothermal
reaction is kept within 8.0 - 13.5 pH with the help of alkali such as carbamide, hydroxide of sodium / potassium / ammonia or combination thereof.
The following working examples show the process of manufacturing high purity partially or fully stabilised ultra fine zirconia powders by hydrothermal route :
EXAMPLE - 1
a) mixing 54 parts of zirconium oxychloride with 1 part of Yttrium chloride in 300 parts of demin-
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eralised water in a stirred glass reactor to form a
solution and adding to said solution 50 parts of 25% ammonia solution to get a pH of around 10.0;
b) subjecting the product of step (a) to hydro-thermal treatment under optimised stirring condition at temp, varying from 150-190 deg. C. under corresponding pressure varying from 300-350 psi for 1-2 hrs;
c) filtering the product of step (b) through a centrifuge or like filtering medium followed by several washings of the precipitate of step (b) with demineralised water before spray drying at 200 deg. C, to directly obtain final yttrium partially stabilised ZrO-2. having following product analysis:
Zr02. purity (including HfO ).. 99.2% mi n.

a) mixing 10 parts of hydrated zirconia with
1 part of magnesium nitrate in 50 parts of deminera-1ised water in a stirred glass reactor to form a slurry in which 1.25 parts of NaOH is added to get its pH to around 13.00;
b) subjecting the slurry of step (a) to hydro-thermal treatment under constant stirring at 180-200 deg. C, temp, under corresponding pressure of 400 psi. for 3 hrs.;
c) filtering the product of step (b) through a centrifuge or like filtering device followed by washing with hot demineralised water till unwanted cation and; anions such as nitrate, soda and the like impurities are removed;
; d) converting the washed cake of step (c) to
20,% aqueous slurry with addition of demineral i sed
water before spray drying at 170-180 deg. C, to
directly obtain final magnesia partially stabilised
ZrO having the following product analysis: ZrO purity (including HfO +
stabilizer oxide) 96.2% min.
MgO 3.0% mi n.
Y 0 3.40% min.
SiO 0.02% max.
Fe 0 0 . 04% max.
Na 0 , 0.07% max.
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Al 0 0.05% max.
TiO . . ... 0.60% max.
Cr 0 , MnO, NiO 0.01% max.
Average crystal particles size: 0.5 micron
Crystal structure monoclinic /tetragonal
EXAMPLE - 3
a) mixing 23 parts of hydrated zirconia with 1 part of yttrium nitrate in 100 parts of demineralised water in a stirred glass reactor to form a slurry in which 2.5 parts of NaOH is added to get the pH of around 13.2 ;
b) subjecting the product of step (a) to hydro-thermal treatment under constant stirring condition at 140-150 deg. C, temp, under corresponding pressure of 500-525 psi for 1-2 hrs.,
c) filtering the product of step (b) through a centrifuge or like filtering device followed by repeated washings with hot demineralised water till unwanted cations and anions such as nitrate, soda and the like impurities are removed;
d) air or oven drying the product of step (c) at temp, varying from 200-250 deg. C, to obtain final yttrium partially stabilised ZrO having the following product characteristics:
ZrO purity (including HfO +
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stabilizer oxide) .... 99.2% min.
Y 0 5.3% min.
SiO 0.01% max.
Fe 0 0.03% max.
Na 0 0.08% max.
Al 0 0.01% max.
TiO 0.45% max.
Cr 0 , MnO, NiO 0.01% max.
Average crystal particle size: 0.7 micron
EXAMPLE - 4
a) , mixing 8.5 parts of hydrated zirconia with 1
part of yttrium nitrate in 37 parts of demineralised
water in a stirred glass reactor to form a slurry in
which 1 part NaOH is added to get the pH around 13.0;
b) subjecting the slurry of step (a) to hydro
's
thermal treatment under constant stirring at temp, of 180-200 deg. C, under 300-400 psi pressure for 45 minutes to 1 hour;
c) filtering the product of step (b) through a centrifuge or like filtering means followed by repeated washings with hot demineralised water till unwanted cations and anions such as nitrate, soda and the like are removed;
d) converting the washed cake of step (c) into aqueous slurry with addition of 20% demineralised
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water before spray drying at 170-180 deg. C, temp, to
obtain final yttrium fully stabilised ZrO having
following product analysis:
ZrO purity (including HfO ) ... 86.00 % min.
Y 0 13.30 % mi n.
SiO 0.02 % max.
Fe 0 0.01 % max.
Na 0 0.07 % max.
Al 0 0.03 % max.
TiO 0.45 % max.
Cr 0 , MnO, NiO ,0.01 % max.
Average crystal particle size 0.30 micron
While we have described and illustrated a particular embodiment of our present invention we so not wish to limit ourselves to the e exact form shown which is intended to illustrate the process rather than to limit it. It is to be expressly understood that the process is susceptible of such changes and modifications which may be made by any person well versed in the art and any such changes or modifications so made therein by such skilled person shall define no material changes from the process herein described and illustrated by accompanying typical examples.
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define no material changes from the process herein described and illustrated by accompanying typical examples.
WE CLAIM :
1. A process for manufacturing PSZ/FSZ powder directly without high temperature calcination by hydrothermal route comprises the steps of: preparing a slurry from crushed zirconia in a glass lined of stainless steel mixer and while stirring being continued adding herein stated precursor of Y2O3, CaO, MgO, CeO2 , by 1-25 weight % on oxide basis in deminer-alised water taking weight ratio of solid to water as 1.0 : 1.0-10.0 and adjusting its pH in the range of 8.0 to 13.5 by addition of an alkali solution such as ammonia solution / NaOH depending on product specification laid down by end user; drying said slurry at temp, varying from 150-425 deg. C, under pressure range varying from 100-750 psi for 45 mins.to 4 hrs.; filtering out said slurry and washing said filtrate several times with demineralised water till all undissolved impurities being removed; oven or air drying said washed filtrate at temp, varying from 450 - 600 deg. C; crushing said dried agglomerates to desired particle size of 0.1 - 1 .0 micron to form PSZ powder
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or converting said dried agglomerates into 15 - 60% flowable slurry by mixing demineralised waterfor being oven or spray dried at temp, varying from 150-300 deg. C to form FSZ powder having herein stated product analysis:
ZrO2 purity (including HfO +
stabiliser oxide) ..84.0 % - 99.2 % min
MgO . ... 0 . 0 % to 3 . 0 % min
Y^. 0^ ... 0 . 0 % to 8.8% max
CaO ..3.4 % to 13.0 % ""
CeO^ 0.0 % to 15.4 % ""
SiC>2. 0.01% to 0.02 % ""
Fe203 0.01% to 0.04 % ""
Na203 0.01% to 0.08 % ""
AI2O3 0.05% to 0.04 % ""
TiOo. 0.04 % to 0.60 % ""
Cr2C3, MnO, NiO 0.0 % to 0.06 % ""
Average crystal particles size: 0.3-0.7 micron
2. A process as claimed in Claim 1 wherein the PSZ/FSZ powder wherein said zirconia precursor being mixed under stirring condition with precursor of Y2O3, MgO, CaO, CeO 1-25 Wt. % on oxide basis for 45 mins. to 4 hrs.in demineralized water by maintaining a ratio of solid : demineralized water in the range of 1.0 ; 5.0 to 10.0 and adjusting
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the slurry between 8 - 13.5 pH with addition of alkali .
3. A process as claimed in Claims 1 and 2 wherein the desired purity for PSZ/FSZ the stirred slurry being obtained by filtering and washing several times with demineralized water till undissolved impurities being removed to achieve desired purity.
4. A process as claimed in Claim 1 and 2 wherein said washed product of claim 3 being air or oven dried at temp, varying from 500 - 600 deg. C. before crushing /pulverising the agglomerates in a ball mill and spray drying it at temp, varying from 150-300 deg. C, to obtain a particle size of 0.1 to 0.7 microns.
5. A process as claimed in Claims 1 to 2 wherein 15-70% of the product of claim 3 being pulverised and converted into aqueous slurry by mixing demineralized water before being oven or spray dried at temp, varying from 450-600 deg. C. to obtain PSZ/FSZ powder of average particle size varying from 0.1 to 0.7 mi crons.
6. A process as claimed in claim 1 wherein the alkali source for adjustment of pH of the slurry / solution containing precursor of zirconia and
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additive includes such as carbamide, hydroxide of sodium / potassium / ammonia alone or desired combination thereof depending on the specification stipulated by end user.
7. A process for manufacturing high purity partially / fully stabilised ultra fine zirconia powders by hydrothermal route substantially as herein described and in the herein stated accompanying examples.
Dated this 7th day of March 2000
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ABSTRACT
A process for making PSZ/FSZ powder by
hydrothermal route and depending on process conditions
comprises the steps of: preparing a slurry by mixing
herein stated precursors of Y 0 / MgO / CaO / CeO by
1-25 Weight % on oxide basis, with zirconia in demin-
eralised water taking the weight ratio of solid :
water as 1.0 :1.0 - 10.0 and adjusting its pH in the
range of 8.00 to 13.5 depending on process conditions
by addition of alkali; drying said slurry at temp,
varying from 150-425 deg. C, under pressure range
varying from 100-750 psi for 8-10 hrs.; filtering out
said slurry and washing said filtrate several times
with demineralised water till all undissolved impuri
ties are removed; drying said washed filtrate by air /
oven drying at temp, varying from 450 - 600 deg. C.j
crushing the dried agglomerates to desired particles
size of 0.1 - 1 .0 micron or converting said dried
agglomerates into 15 - 60% flowable slurry by mixing
demi neral i sed water and spray drying at tamp. varying
from 25-300 deg. C. to obtain PSZ/FSZ powder having
herein stated product analysis.
00000
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