FIELD OF THE INVENTION:
The present invention relates to a continuous process for bulk synthesis of
nanostructured yttria stabilized zirconia [YSZ] powders in a continuous mode
using well defined precursors. More specifically, the present invention deals with
the disclosure of process parameters and precursor composition/s for carrying
out a controlled decomposition of the precursor droplets in a reactor attached
with a LPG- fired spray pyrolysis system thereby yielding nanostructured YSZ
powders as a decomposed solid product in a continuous mode.
BACKGROUND OF THE INVENTION:
Chemically pure zirconium dioxide [ZrO2] undergoes volume change at higher
temperature region that limits its application. In order to overcome this volume
change, zirconia is normally stabilized in cubic crystalline modification by using
various additives like calcium oxide, magnesium oxide and yttrium oxides [yttria].
Yttria stabilized zirconia is termed as "yttria stabilized zirconia' [YSZ] and is
widely termed as 'thermal barrier coatings '[TBCs] and numerous other industrial
purposes. For TBC applications, stabilized YSZ material [normally zirconia in
combination with 8 mol % yttria] is used since it has got low thermal conductivity
at elevated temperatures, which effectively reduces the operating temperature
and hence increases the durability of the underlying components. Attempts have
been made to improve the capability of TBCs and hence the YSZ material

characteristics that can survive hundreds of thermal cycles and can be operated
in harsher environments.
With the evolution of nanoscience and nanotechnology, several research reports
are available focusing laboratory-scale synthesis for YSZ material in
nanostructures, though there are hardly any report available addressing the bulk
synthesis of the material.
Conventionally, YSZ powders are normally prepared by solid state route by
mixing equivalent amounts of yttria and zirconia raw materials which are then
heat treated [calcined] at elevated temperatures. In other conventional methods,
YSZ powders are prepared by fusing yttria and zirconia powders at high
temperature and then by crushing the fused YSZ material into required size
fractions. Conventional YSZ powders having micron-sized crystallites are
available commercially from one or more sources. However, synthesis of YSZ
powders is still a subject of interest, particularly those dealing with
nanostructures particles. In this context, there are more examples of research
reports than patents.
United States Patent 6,869,550 describes a pre-alloyed yttria stabilized zirconia
powder suitable for use in thermal barrier applications that is prepared by alloying
zirconia and yttria. The derived powder is then spray-dried to produce an
agglomerated powder having an average particle size suitable for use in spray
coating applications for producing a porous thermal barrier coating having

substantially decreased thermal conductivity when compared to conventional TB
coatings, such those produced using plasma-densified powders.
United States Patent Number 5,958,361 describes a flame spray pyrolysis
process for the preparation of ultrafine metal oxide or mixed metal oxide ceramic
particles in general, having mean particle sizes in the range of 2 - 500 nm by
aerosolizing a ceramic precursor solution a ceramic precursor solution
comprising one or more glycolato poly metal looxanes in a volatile organic
solvent or volatile flammable organic solvent mixture, in an amount of from 1
weight percent to 30 weight percent of said ceramic precursor solution.
United States Patent Number 6,162, 530 describes a chemical method that is
scalable to large volume production comprising spray atomization of a reactant
solution into a precursor solution to form a nanostructured metal oxides and
hydroxide precipitate and thereafter sonication followed by heat treatment or vice
versa to derive the ceramics.
United States Patent Number No. 7,252, 767 describes a chemical method for
producing hydrous zirconium and hafnium oxide materials with desirable
properties, e.g., porosity, particle size, surface area, resistance to moisture
content etc. for various applications.
United States Patent Number 3,634,113 describes the synthesis of a zirconia
composition with a cubic crystal structure that is stabilized by an additive which is
a mixture of rare earth oxides.
There are many examples of scientific publications in various journals describing

numerous methods for the laboratory-scale synthesis of yttria stabilized zirconia
[YSZ] powders. Journal of Power Sources, 170 [2007], 145 - 149 describes a
plasma spray synthesis of ultra-fine YSZ powder. Journal of Nanomaterials,
2006 [2006], Article ID 49283 describes the synthesis and characterization of
nanocrystalline YSZ powder by smoldering combustion synthesis. The journal,
Materials Chemistry and Physics, 71 [3] (2001), 235 - 241 describes the
synthesis of yttria stabilized cubic zirconia [YSZ] powders by a so-called
microwave-hydrothermal route. Journal of the European Society, 20 [9] (2000),
1289 - 1295 describes a combustion process for the synthesis and structural
characterization of nanocrystalline powders of pure zirconia and yttria stabilized
zirconia [YSZ]. Sensors and Actuators B: Chemical, 109 [1], 2005, 102 -106
describes a hydrothermal procedures for the synthesis of zirconia-doped
nanocrystalline powders that show important advantages from the
thermodynamic and kinetic point of view for the procedure. Journal of the
American Ceramic Society, 88 [5], 1133 - 1138, 2005 describes a method to
produce well-dispersed nanosized yttria tetragonally stabilized zirconia (Y - TZP)
powder in aqueous suspension. The y - TZP powder was produced by
precipitation from homogenous solution at 200°C under hydrothermal conditions.
A homogenous solution was created through the use of complexing agent, which
subsequently could be used in a dispersion scheme developed for the nanosized
Y- TZP powder.
Hence, there is continuing interest in developing unique processing method for

bulk synthesis of nanostructured yttria stabilized zirconia ceramic materials.
Accordingly, it is an object of this invention to disclose a continuous process and
process parameters with variables for bulk synthesis of nanostructures yttria
stabilized zirconia [YSZ] powder by liquid petroleum gas [LPG] fired spray
pyrolysis system.
It is another object of this invention to provide the chemical composition or
formulations of well-defined aqueous-based precursor/s for synthesizing YSZ
powders both in amorphous and cubic crystalline modifications respectively using
LPG fired spray pyrolysis system.
Other objects and novelty of the present invention shall become apparent from
the accompanying description and examples.
OBJECTS OF THE INVENTION:
An object of this invention is to propose a continuous process for bulk synthesis
of nanostructures yttria stabilized zirconia [YSZ] powders.
Another object of this invention is to propose chemical composition of well-
defined aqueous-based precursors for synthesizing YSZ powders both in
amorphous and cubic crystalline modifications.
Further object of this invention is to propose experimental variables and process
parameter in the LPG fired spray pyrolysis system so as to carry out both
dehydration and decomposition reaction of the precursor droplets effectively and

simultaneously in order to obtain nanostructured YSZ material in a continuous
mode.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a process for the bulk synthesis of
nanostructures yttria stabilized zirconia powder comprising;
preparing aqueous solution of yttrium nitrate,
preparing an aqueous-based precursor solution by dissolving zirconium oxy
nitrate hydrate, aqueous solution of yttrium nitrate and amino acetic acid in a
range of molar ratio of 1 : 0.53:0.20 - 1.0: 0.53: 0.35., subjecting the hot
precursor solution to the step of spray atomization and aerosolizing to form
amorphous nanostructured YSZ powder, fractionating the amorphous YSZ
powders into course and fine fractions separately, subjecting the amorphous YSZ
powders to the step of cleaning air pressure, heat treating the amorphous
nanostructured YSZ powders in air to produce cubic crystalline modification of
YSZ.
BRIEF DESCRIPTION OF THE ACCOMPANING DRAWING:
The invention will be explained in greater details with the help of the
accompanying drawings where:
FIG. 1 shows the size of the primary particles in the agglomerate of bulk YSZ
material in the transmission electron microscopy [TEM].

DETAILED DESCRIPTION OF THE INVENTION:
The present invention provides the process parameters and experimental
variables of the LPG - fired spray pyrolysis technique for synthesizing
nanostructured YSZ powders in a continuous mode using defined aqueous-
based precursor/s by permutations and combinations , which is actually a mixed
aqueous solution of i) yttrium nitrate, ii) amino acetic acid (Glycine) and iii)
zirconium oxynitrate in desired stoichiometry depending on the atomic ratio of
yttrium and zirconium in the targeted YSZ powder, though the most common
YSZ powder having a nominal molar percentage of 8 mol% of yttria is used in
this invention.
The disclosed process provides a formulation of the aqueous -based precursor
along with its concentration of the precursor in order to carry out both
dehydration and decomposition reaction of the precursor droplets effectively and
efficiently inside the reactor attached with the LPG-fired spray pyrolysis system
for synthesizing YSZ powders in a continuous mode.
Other objects, novel features, advantages and applications of the present
invention will be set forth in the description that follows further. The objectives
and the advantages of the present invention may be realized and attained by
deriving particular characteristics of YSZ powder by means of permutations and
combinations of the precursor composition/s and process parameters described
in the LPG- fired spray pyrolysis system.
As per the invention, an aqueous-based precursor solution in the form of fine

droplets is to be pyrolysed in a reactor attached with the LPG-fired [LPG = liquid
petroleum gas] spray pyrolysis system to form amorphous yttria stabilized
zirconia (YSZ) powders in a continuous mode, derived powders of which is
having nanostructure in the agglomerated particles [in the range of 10 -50
nanometer of primary particles ] and then the synthesized powders to be
collected in containers placed outside the reactor and subsequently heat
treatment of the derived amorphous YSZ material is to be carried out in a
furnace in air to obtain its cubic crystalline modification of YSZ.
The process describes the steps comprising: (1) preparing yttrium nitrate
aqueous solution by dissolving yttrium oxide powder in diluted nitric acid under
constant heating [temperature in the range of 80 ° - 100 ° C and stirring, (2)
preparing an aqueous-based precursor solution by dissolving the analytical
grades [AR grade > 99 wt % purity) chemicals, i.e., a) zirconium oxy nitrate
hydrate, b) amino acetic acid [Glycine] and c) aqueous solution of yttrium nitrate
(3) spray atomization and aerosolizing the hot precursor solution (precursor
solution temperature in the range of 50°- 80 °C) using compressed air (pressure
level of 8.0 kg/cm2 or more) as a counter fluid in a pre-heated stainless steel
(SS316 grade) reactor which is attached with the LPG-fired spray pyrolysis
system and to carry out a simultaneous dehydration and decomposition reaction
of the precursor droplets inside the reactor in the presence of hot air ( set
temperature of hot air in the range of 650°-750°C) to form dehydrated precursor

particles first and then amorphous nanostructured YSZ powder, (4) fractionating
the as-synthesized amorphous YSZ powders in ' coarse ' and 'fine ' fractions
by a cyclone separator and collecting the ' coarse' and ' fine ' fractions
separately in containers outside the reactor, (5) exhausting the decomposed
gases through a wet scrubber using 5 - 10 wt % commercial lime suspension
media prior which the decomposed gases had been passed through bag filters
that is periodically cleaned by air-pressure shocks and (6) heat treatment
(calcining) of the amorphous nanostructures YSZ powders in air in the
temperature range of 500°- 1000°C for obtaining cubic crystalline modification of
the YSZ that also has nanostructure in the micron-sized agglomerated particles
of the material.
The term "amorphous" as employed herein refers to YSZ material which has no
crystalline structure or a very poorly crystalline structure in the YSZ particles that
subsequently starts to transform to cubic crystalline modification under heat
treatment in air at a minimum temperature of 500°C in the range of 5000C - 1000°
C with the retention of nanostructure in the agglomerated particles of the
material.
As per the invented process, an aqueous-based precursor solution is prepared
by dissolving appropriate amounts of analytical grades (AR grade, > 99 w %
purity) zirconium oxy-nitrate hydrate, amino acetic acid and aqueous solution of
yttrium nitrate in de-ionized water by maintaining the solution concentration (total
solid load in the precursor) in the range of 100 - 250 gm/liter. The resultant

mixed solution is termed as 'precursor'.
The schematic diagram of a liquid petroleum gas (LPG) - fired spray pyrolysis
system which is in -house fabricated is explained elsewhere [Indian Patent
Application No. 216/Kol/2010 dt 05-03-2010] and could vary from case to case.
As freshly-formed amorphous YSZ particles inside the reactor of the spray
pyrolysis system would consist both ' coarse ' and ' fine ' particles , these are
further fractioned using a cyclone separator and collected separately as 'coarse'
and 'fine' fractions in containers outside the reactor. As the precursor droplets
falls vertically from the top to the down of the reactor, there is also a fall in
temperature of the particles and hence a minimum temperature of 1001) at the
collection point of the YSZ powders is maintained by the system so that the
powders are collected dry.
The resultant powders [finer fraction] are called amorphous YSZ that has the size
of the primary particles in the range of 10 - 50 nanometer in agglomerated
particles of YSZ ranging several microns and showed a tap density in the range
of 0.07 - 0.12 gm/cc. Amorphous structure of the said YSZ powder is confirmed
by x-ray powder diffraction pattern (XRD) analysis and its nanostructure in the
agglomerated particles by transmission electron microscopy (TEM) respectively.
Heat treatment (clacination) of the amorphous YSZ powder in presence of air

at different set temperature show that the amorphous structure slowly transform
to its cubic crystalline modification from 500 ° C onwards with a soaking time of
(~1 hour) at the set temperature.
The solid load of the precursor solution under a fixed precursor feed rate in the
spray atomizer has an influence on the yield of the powder. A higher solid load of
the precursor solution gives higher yield of the YSZ powder and vise versa.
However, at higher solid load of the precursor solution, the derived YSZ particles
become coarse as compare to that of a lower one. On the other hand, the yield of
the YSZ powders under a given solid load of the precursor solution is also
increased by increasing the precursor feed rate in the spray atomizer and vice
versa.
Several precursor compositions can be prepared by permutations and
combinations by taking the starting raw materials, i) zirconium oxynitrate hydrate,
ii) amino acetic acid (Glycine) and iii) aqueous solution of yttrium nitrate in
desired molar ratio so as to maintain a specific level of molar ratio of "Oxynitrate-
Nitrate-Glycine "in the defined range in the precursor solution/s for carrying out
the pyrolysis reaction of the precursor droplets effectively and efficiently inside
the reactor in the LPG- fired spray pyrolysis system.
EXAMPLE 1:
This example illustrates the production of nanostructered amorphous yttria

stabilized zirconia (YSZ) powders in a continuous mode having primary particles
in the range of 10 - 30 nanometer in the agglomerated particles of the material in
accordance with the present invention.
The YSZ precursor solution in this example is prepared by dissolving the
chemicals, I.e., i) zirconium oxy nitrate hydrate (solid) , ii) aqueous solution of
yttrium nitrate (liquid) and iii) amino acetic acid (solid) (Glycine) in distilled
/deionized water. All the above chemicals have a purity of > 99 weight %.
Aqueous solution of yttrium nitrate was prepared by mixing yttrium oxide in
diluted nitric acid under constant stirring and heating the resultant suspension by
maintaining the medium temperature in the range of 80°- 100°C.
The amount of yttrium nitrate solution to be used for preparing the precursor
would depend on the stoichiometry of yttria: Zirconia molar ratio (8 mol% of
yttria) in the YSZ composition and hence on the concentration of yttrium ion in
the so-derived yttrium nitrate solution which was measured by standard
procedure before using the solution.
The solid load of the YSZ precursor solution (concentration) was maintained in
the range of 150 - 155 g/liter.
The resultant precursor solution is spray atomized/ aerosolized by using
compressed air as a counter fluid having pressure level about 8.5 kg/ cm2 and
maintaining the solution temperature in the range of 60° - 80°C with a precursor
feed rate in the range of 08 -10 liters/hour in a continuous mode. Spray
Atomizing /aerosolizing of the precursor particles though can be varied into

different sizes by varying the nozzle orifice diameter, is kept at 0.1 mm. By spray
atomization, the precursor droplets are split into finer droplets or particle mists or
aerosols that is allowed to pas through the preheated reactor (stainless steel
grade: SS316 material having ID of about 1 meter and height of about 05 meters)
from the top to downward bias, attached in the LPG-fired spray pyrolysis system,
wherein the precursor droplets get mixed with the hot air blown inside the reactor
from outside sources that had a set of temperature of about 750 ° C in the
system.
A schematic diagram of the in-house fabricated LPG-fired spray pyrolysis system
is furnished in the Indian Patent Application No. 216/ Kol/2010 dt 05-03-2010,
though the technical features and design of such a system could vary from case
to case.


Weight corresponding yttrium is 13.74 g.
The precursor droplets after spray atomization are made to travel the reactor
from the top to the bottom of the reactor. During the course of travel, the droplets
are made to undergo a dehydration reaction first with the formation of dried or
dehydrated particles and then undergo a decomposition resulting YSZ particles.
The resultant powders would contain both 'coarse' and 'fine 'fractions and are
fractioned by a cyclone separator into 'coarse ' and 'fine' fractions of the
material and were made to be collected separately in containers outside the
reactor. The coarse fraction is rejected.
Finer fraction of the derived powder is nanostructures amorphous YSZ that
showed a tap density of ~ 0.07 g/cc and a specific surface area in the range of
6-7 m2/g in the BET analysis. The material also showed amorphous structure in
the XRD [X -ray powder diffraction] analysis and Figure 2 shows the size of

primary particles in the range of 10 - 30 nanometers in the micron-sized
agglomerated particles of the derived powders in the transmission electron
microscopy [TEM]. The amorphous YSZ material starts crystallizing into cubic
structure while heating the material in air at a minimum temperature of 500°C.
This example further describes that the precursor composition stated in the
'Table 1' only demonstrates a specific composition of the precursor solution
with specific level of "Oxy-nitrate: Nitrate: Glycine" molar ratio of 1.0: 0.53:
0.27 in the precursor. However, by varying the amount of glycine in the
precursor composition in the Table 1 having specific moles with any value in
the range of 0.2 -0.35 in the above ratio, several independent precursor
solution can be prepared by permutations and combinations and by
maintaining a fixed "Oxy-nitrate: Nitrate" molar ratio therein. However, as the
counter molar ratio of glycine in the above precursor solution approaches to
lower limit of 0.2, there is a tendency to incomplete the decomposition of
metal nitrates and oxy-nitrates in the precursor resulting the presence of un-
burnt zirconium oxy nitrate and yttrium nitrate in the amorphous YSZ powder
as impurities in the course of decomposition of the precursor droplets. On the
other hand, when the glycine amount in the precursor composition is raised to
the upper limit in the above range, i.e., 0.35, the YSZ powder would still yield,
however with impurities of carbonaceous materials probably arising out of
incomplete decomposition of glycine in the precursor in the course of

decomposition reaction of the precursor droplets. However, irrespective of the
glycine content in the precursor solution in the above range, the YSZ powder
yielded after the decomposition reaction, heat treatment procedure of the
decomposed product/s at the end, produces cubic crystalline modification of
YSZ beyond a temperature of about 5000C.
It is further reported in this example, though the precursor concentration (solid
load) is chosen in the range of 150 - 155 gm/liter, the solid load could be
varied in the range of 100 - 250 gm/liter by choosing a specific level of "Oxy-
nitrate: Nitrate: Glycine "molar ratio of the precursor solution and by
permutations and combinations, several precursors could be prepared by
varying the solid load of the precursor solution and pyrolysed under a given
condition of spray pyrolysising parameters. However, when the solid load of
the precursor solution is lowered, the particles generated during the course of
spray pyrolysis reaction becomes finer as compare to a precursor with
higher amount of solid load. The size of the primary particles in the resultant
powders comes down to the value stated in this example by lowering the
solid load of the precursor solution and at the same time , the specific
surface area of the derived powders goes up by lowering the solid load of the
precursor and vice versa.

EXAMPLE 2:
The procedure of Example 1 is followed in this example, except that the amount
of glycine in the precursor composition was reduced was reduced to13.10 gm
that makes a counter "Oxy-Nitrate: Nitrate: Glycine "molar ratio of 1.0: 0.53: 0.24
as per the Table 2 and the final solid load in the precursor solution was made in
the range of 100 - 105 gm/liter. The subsequent procedures for carrying out
spray pyrolysis reaction of the precursor droplets and all its variables followed by
subsequent heat treatment of the derived powders remain the same to that of
Example 1.
The finer fraction of the derived powder yields amorphous YSZ material that
showed a tap density of 0.06 g/cc and a specific surface area in the range of 7- 8
m2 /g with not much difference in the size of the primary particles to that of the
example 1. The amorphous YSZ material starts crystallizing into cubic structure
while heating the material in air at a temperature beyond 500 ° C.


EXAMPLE 3:
The procedure of the Example 1 is followed in this example, except that the
amount of glycine in the precursor composition was increased to 16.50 gm
having a counter "Oxy-nitrate: Nitrate: Glycine "molar ratio of "1.0: 0.53: 0.31
"as per the Table 3 and the final solid load in the precursor solution was
made in the range of 180 -185 gm/liter. The subsequent procedures for
carrying out spray pyrolysis reaction of the precursor droplets and subsequent
heat treatment of the derived powders remain the same to that of Example 1.
The finer fraction of the derived powder yields a nanostructured YSZ material
that showed a tap density of 0.09 g/cc and a specific surface area in the
range of 5 - 6 m2/g. The size of the primary particles could be found in the
range of 10-50 nanometers. The amorphous YSZ material starts crystallizing
into cubic structure while heating the material in air at a temperature beyond
500 ° C.


WE CLAIM:
1. A continuous process for the bulk synthesis of nanostructured 8 mol %
yttria stabilized zirconia ( YSZ) powder or YSZ powders having yttria
outside 8 mol%
comprising
preparing aqueous solution of yttrium nitrate,
prepare an aqueous-based precursor solution by dissolving zirconium oxy
nitrate hydrate, aqueous solution of yttrium nitrate and amino acetic acid
in a range of molar ratio of 1 : 0.53 : 0.20 - 1.0 : 0.53 : 0.35.
subjecting the hot precursor solution to form aerosols or fine droplets by
spray atomization or aerosolizing the precursor
subjecting the derived aerosols to undergo a controlled dehydration cum
decomposition reaction inside a reactor to form amorphous YSZ powders
fractionating the amorphous YSZ powders into coarse and fine fractions
separately,
subjecting the amorphous YSZ powder to the step of cleaning using
air pressure steps ,
heat treating the amorphous YSZ nanostructured powders in air to
produce cubic crystalline modification of YSZ.
2. The process as claimed in Claim1, wherein the said yttrium nitrate is
prepared by dissolving yttrium oxide powder in diluted nitric acid under
constant stirring and heating at a temperature range of 80° C to 100°C.

3. The process as claimed in claim 1, wherein the "precursor' is prepared
by the dissolving zirconium oxy nitrate hydrate, yttrium nitrate and
aminoacetic acid [ Glycine] in de-ionized or distilled water with an
optimized molar ratio of "0.70 : 0.12 : 0.19" having a counter" Oxy-nitrate
: Nitrate : Glycine" molar ratio of 1.0 : 0.53 : 0.27 in the precursor solution
in the range of 1.0 : 0.53 : 0.20 - " 1.0 : 0.53 : 0.35 " therein and all
precursors thereof by permutations and combinations by varying the
Glycine" amount in the precursor in the defined range of
"Oxy-nitrate: Nitrate: Glycine "molar ratio.
4. The process as claimed in claim 1, wherein the step of aerosolizing the
hot precursor is carried out in the temperature range of 50°- 80° C in a
pre-heated reactor attached with LPG-fired spray pyrolysis system using
compressed air having pressure of 8.0 kg/cm2 or more as the counter fluid
using a two-fluid nozzle gun.
5. The process as claimed in claim 1 wherein the precursor droplets and hot
air [blown from outside having a set temperature in the range of 650 ° C
- 750 ° C] get mixed inside a reactor for carrying out a simultaneous
dehydration and decomposition reaction of the precursor droplets to yield

dehydrated precursor particles first and then amorphous yttria stabilized
zirconia (YSZ) powers having nanostructure in the agglomerated particles
along with the decomposed gases in a continuous mode.
6.The process as claimed in claim 1, wherein the said amorphous YSZ
powders are heated in air at any set temperature in the range of 500 - 1000°
C having soaking time of about 1 hour at the set temperature
for obtaining stabilized cubic crystalline modification that also has nano
structure in the agglomerated particles.
7.A process as claimed in claim 6, the specific surface area of the derived
nanostructured YSZ powders vary in the range of 5 - 9 m2/g and increases
by reducing either the i) feed rate of the precursor for spray atomizing/
aerosolizing or ii) concentration (solid load) of the precursor Is.
8. A process as claimed in claim 7, the specific surface area of the derived
nanostructures YSZ powders increases within its range by increasing the
i) temperature of the hot precursor during atomization/aerosolizing
process and, or ii) set temperate of the hot air blown inside the reactor in
the LPG- fired spray pyrolysis system.

9. A process as claimed in claim 8, the minimum temperature of the
amorphous YSZ powders in the power collection containers for both
coarse and fine fraction powders need to be 100°C.

According to this invention, there is provided a process for the bulk
synthesis of nanostructures yttria stabilized zirconia powder by LPG-fired
spray pyrolysis system with the steps comprising;
preparing an aqueous -based precursor solution by dissolving zirconium
oxy nitrate hydrate, aqueous solution of yttrium nitrate and amino acetic
acid in a range of molar ratio of "1 : 0.53:0.20" - "1.0: 0.53: 0.35"., spray
atomization or aerosolizing the so-derived precursor solution in hot
condition (50°- 80°C) to form fine droplets or aerosols of the precursor in a
pre-heated reactor attached with the LPG-fired spray pyrolysis system,
carrying out a simultaneous dehydration and decomposition reaction of the
aerosols in the said reactor to form amorphous nanostructured YSZ
powder,
fractionating the amorphous YSZ powders into coarse and fine fractions
separately,
,heat treating the amorphous nanostructured YSZ powders in air to
produce cubic crystalline modification of YSZ.