FIELD OF INVENTION:
The present invention relates to a method for the synthesis of lithium
zirconate powders having nanostructure in the agglomerated particles.
More specifically, the present invention deals with the synthesis of
nanostructured lithium zirconate powders by liquid petroleum gas (LPG)
fired spray pyrolysis system in a continuous mode. The invention is
further related to utilize advantage of solution combustion technique
using defined aqueous-based precursors and also by adopting desired
experimental parameters in the LPG-fired spray pyrolysis system.
BACKGROUND OF THE INVENTION:
Lithium zirconate (Li2ZrO3) is reported to efficiently adsorb carbon
dioxide gas at above ambient temperatures (300° - 600°C) indicating a
prospective material for effective elimination of CO2 from post
combustion gas streams in IGCC systems. The CO2 adsorption for this
material is reported to be highest at a temperature around 400°C
associated with high thermal stability at this temperature as well and
thus has attracted considerable interest in recent years to synthesize this
material in different crystalline phases with variable physical properties
that enhances CO2 adsorption characteristics at higher temperatures.

Lithium zirconate is also well-known in the nuclear industry due to its
properties, such as high tritium release rate, thermal stability, low
thermal expansion and good compatibility with structural materials e.g.
beryllium etc. and finds applications in thermonuclear fusion reactors as
a tritium breeder material and also as an advanced blanket material in
the fission reactions. Other applications of lithium zirconate include the
framework in molten carbonate fuel cell electrolyte plates, as dual ion
conducting membranes, zirconia based refractories, enamels and as an
additive in titanate dielectric bodies to obtain capacitors with special
electrical properties.
Several methods have been reported to synthesize the material using
varieties of raw materials and precursors and are listed below.
Lithium Zirconate Synthesis by Solid-State method
J-I Ida et al. [1] synthesized lithium zirconate nanopowders by solid-state
method with lithium carbonate and zirconium oxide as starting
materials. In this method, Li2CO3 and ZrO2 (1:1) was weighed, ground
and intimately mixed in an agate mortar with a suitable amount of
acetone or ethanol. The mixtures were calcined at various set

temperatures in the range of 500°C - 1400°C. XRD analysis showed the
mixture started forming monoclinic lithium zirconate at 500°C and
completed at 1200°C and as the temperature was increased the
impurities of monoclinic zirconium oxide started decreasing.
Lithium Zirconate Synthesis by Sol-Gel method
B.N. Nair et al [2] processed lithium zirconate mixing ZrO2 sol and
suitable lithium salt in which the zirconia sol was prepared using
isopropyl alcohol, zirconium propoxide, water and 1M. SEM analysis of
the samples showed particle size in the range of 200 - 400 nanometer
having tetragonal structure of lithium zirconate at 700°C and monoclinic
lithium zirconate at 900°C respectively.
Lithium Zirconate Synthesis using various Liquid Precursors
E.O. Fernandez et al. [3] synthesized nanocrystalline lithium zirconate
using zirconyl nitrate (ZrO(NO3)2XH2O) and lithium acetate
(CH3COOLi.2H2O) solutions. An appropriate amount of each chemical
was dissolved in deionized water to form a complex solution and the
solution was spray-dried with an input temperature of 423 K with a
pump rate of 2 mL/min, in which the obtained solid product was further
decomposed at three different temperatures of 673 K, 873 K and 1073 K
in air respectively.

The sample at 1073 K indicated the formation of monoclinic lithium
zirconate, whereas the samples at 673 K and 873 K did not indicate any
peaks of lithium zirconate formation with particles of size between 1 and
2 µm.
Lithium Zirconate Synthesis by Low Temperature Liquid Phase Co -
Precipitation method
Kwang Bok Yi and Dag 0irstein Eriksen [4] prepared Lithium zirconate
by low temperature liquid phase co-precipitation method using zirconium
oxynitrate and lithium nitrate as the raw materials in which the mixed
oxide was precipitated by the dropwise addition of aqueous ammonia.
The precipitate was filtered and the filtered cake was dried overnight in
air at 150°C followed by calcination at 500°C for 2 hours. XRD analysis
of the sample showed the peaks due to tetragonal lithium zirconate with
a particle size of 40 nm.
Lithium Zirconate Nanopowder by Electrostatic Spraying
Y-H Lee et al [5] prepared lithium zirconate nanopowder by electrostatic
spraying a pre-heated solution containing lithium nitrate and zirconyl

nitrate using distilled water and methanol. The sprayed powders were
placed on the Si-substrate and then heated upto a temperature of 900°C
for 30 min in a tubular furnace and the derived powders is reported to
have particle size between 50 - 80 nanometer in the SEM analysis.
Lithium Zirconate Synthesis by Impregnated Suspension Technique
Hernandez et al [6] synthesized mixtures of Li2ZrO3 and Na2ZrO3
through impregnated suspension technique, which consists of forming a
suspension of one of the solid precursors in an aqueous medium and
simultaneously incorporating an aqueous solution of other salt with
stirring and heating to bring the solution to complete evaporation and
finally the dried mixture is calcined to a specified synthesis temperature.
The calcined material showed particles in the range of 3 - 5 micron
forming agglomerates of about 10-15 microns.
L.Montanaro et al [7] prepared porous lithium zirconate for fusion
reactor blanket material using lithium acetate and zirconium propylate
raw materials. The material was prepared by dissolving lithium acetate
in water and by the addition of zirconium propylate to the solution. The

mixture was hydrolysed at 50°C under stirring with addition of acetic
acid to maintain required pH and the reaction was carried out for a
period of 3, 12 and 24 hours. The gels obtained after the reaction was
dried at 120°C and the dried gels were milled and calcined at different
temperatures of 400°C, 600°C, 900°C respectively. XRD results
showed the presence of cubic ZrO2 and lithium zirconate of samples
calcined at 400°C, whereas the tetragonal lithium zirconate phase
formed at temperature of 600°C, and monoclinic lithium zirconate at
900°C. The SEM images indicated particle size of 10 micron of heat
treated sample at 900°C and BET surface area of 50 - 60 m2 /g.
US Patent 4933155 [A] describes a method for producing a lithium
zirconate nanopowder by preparing a zirconium compound gel and an
aqueous solution of lithium salt, followed by dehydrating the mixture
with the addition of butanol and temporarily burning the mixture at
900°C to 1100°C for 1 - 6 hours, to produce lithium zirconate powder
finally by pulverization.
US Patent 20080226542 [B] describes an improved physical mixing
procedure for the preparation of lithium zirconate and doped lithium

zirconate powders by wet mixing the starting chemicals, i.e. zirconium
hydroxide and lithium carbonate in stoichiometric ratio and then
calcining the mixture at a temperature of at least 700°C to form the
material with a surface area of 0.49 m2 /g.
In a similar invention, US Patent 6271172[C] also reported a physical
mixing process using zirconia and lithium carbonate powders as the raw
materials and then calcining the mixed materials at higher temperatures
to obtain lithium zirconate powders.
UK Patent No 2227740[D] by Flipot and Brauns reported the synthesis of
lithium zirconate material by mixing lithium peroxide with excess
zirconia and excess lithium as well. The mixture is then heat treated at
900°C resulting a product that showed a fired density of 95% of the
theoretical.
There is a continuing interest in developing synthesis techniques and the
precursors for the production of nanostructured lithium zirconate
powders with different crystalline modifications and physical properties
that could be used for different applications.

Accordingly, it is an object of this invention to disclose a LPG-fired (liquid
petroleum gas) spray pyrolysis technique for the production of lithium
zirconate powders having nanostructure in the agglomerated particles in
a continuous mode.
It is another object of this invention to provide the chemical composition
of various aqueous-based precursors for synthesizing lithium zirconate
powders in amorphous, tetragonal and monoclinic modifications
respectively.
OBJECTS OF THE INVENTION:
An object of this invention is to propose a method for the synthesis of
lithium zirconate powders having nanostructure in the agglomerated
particles.
Further object of the present invention is to propose
formulations/compositions of aqueous-based precursors that are capable
of yielding nanostructured lithium zirconate powders at low
temperatures.

Still another object of the present invention is to propose experimental
conditions and process parameters in the LPG-fired spray pyrolysis
system so as to carry out the combustion reaction of the precursor
droplets effectively in order to obtain nanostructured lithium zirconate
material in a continuous mode.
Yet another object of the present invention is to define the heat treatment
conditions of the as-synthesized amorphous lithium zirconate powders so
as to obtain its tetragonal and monoclinic crystalline phases.
Further object of the present invention is to provide a LPG-fired spray
pyrolysis technique for synthesizing nanostructured lithium zirconate
powders, other than solid state route, sol-gel route, liquid phase co-
precipitation method, electrostatic spraying route, impregnated
suspension technique or by any improved physical mixing methods.
Still further object of the present invention is to synthesize
nanostructured lithium zirconate powder in a continuous mode using
various aqueous-based precursors by permutations and combinations,

which is actually an aqueous solution of lithium nitrate, Glycine or urea
and zirconium nitrate or zirconium oxynitrate with desired stoichiomtery
and defined ranges of concentration.
Still another object of the disclosed process is to provide a synthesis
technique for generating nanostructured lithium zirconate powder with
variable physical properties, e.g. crystalline modifications, crystallite size
in the agglomerated particles, specific surface area of the derived
powders that has great applications in high temperature adsorption of
carbon dioxide gas in IGCC, in nuclear industries as thermonuclear
fusion reaction and as an advanced blanket material etc.
BRIEF DESCRIPTION OF THE INVENTION;
According to this invention, a liquid petroleum gas (LPG)-fired spray
pyrolysis process is provided for the synthesis of nano-structured lithium
zirconate powders in amorphous, tetragonal and monoclinic crystalline
modifications using aqueous-based precursor/s in a continuous mode,
comprising the steps of :

(a) preparation of one or more aqueous-based precursor solutions
(precursor) by dissolving the stoichiometric amounts of the starting raw
materials i) zirconium oxy nitrate hydrate or zirconium nitrate hydrate,
ii) urea or amino acetic acid (Glycine) and iii) lithium nitrate hydrate in
de-ionized/distilled water by maintaining an optimized 'Urea-Nitrate' or
'Glycine-Nitrate' molar ratio of 0.3 in the range of 0.15 - 0.45 therein in
the precursor and in all precursor compositions by permutations and
combinations having variable 'Urea-Nitrate' or 'Glycine-Nitrate' molar
ratio thereof;
(b) generating a stream of fine precursor droplets by spraying the hot
precursor solution having a solution temperature in the range of 50° -
80°C in a pre-heated reactor attached with the LPG-fired spray pyrolysis
system using compressed air having pressure of 8.0 kg/cm2 or more as
the counter fluid in a two-fluid nozzle gun.
(c ) mixing the precursor droplets and hot air (blow from outside having a
set temperature in the range of 650° - 750°C) inside the reactor and
carrying out a simultaneous dehydration and decomposition reaction to

yield dehydrated precursor particles first and then amorphous lithium
zirconate powders having nanostructure in the agglomerated particles
along with the decomposed gases in a continuous mode ;
(d) fractionating the bulk as-synthesized amorphous lithium zirconate
powders as 'coarse' and 'fine' fractions by a cyclone separator and
collecting the 'coarse' and 'fine' fractions separately in containers
outside the reactor.
(e) exhausting the decomposed gases through a wet scrubber using 3-5
wt% commercial lime solution/suspension as media prior which the
decomposed gases had been made to pass through a bag filter that is
periodically cleaned by air-pressure shocks, and
(f) heat treatment (calcining) of the nanostructured amorphous lithium
zirconate powders in air in the temperature range of 500° - 1100°C
having soaking period of about 1 hour at the set temperature for
obtaining both tetragonal and monoclinic crystalline modifications of
lithium zirconate that also has nanostructure in the agglomerated
particles.
DETAILED DESCRIPTION OF THE INVENTION;
One or more objects of the present invention are accomplished by the
provision of aqueous-based precursor/s which are to be spray pyrolysed
in a LPG-fired (LPG=liquid petroleum gas) spray pyrolysis system for the
production of amorphous lithium zirconate powders in a continuous
mode having nanostructure in the agglomerated particles (upto 100
nanometer crystallites) and also the tetragonal and monoclinic crystalline
modifications of lithium zirconate subsequently by heat treatment of the
amorphous material.
The process describes the steps comprising : (1) preparing an aqueous
precursor solution by dissolving the analytical grade (AR grade, >99 wt%
purity) chemicals, i.e., a) zirconium nitrate hydrate or zirconium oxy
nitrate hydrate, b) amino acetic acid (glycine) or urea and c ) lithium
nitrate in de-ionized water in desired proportions, (2) spray atomization
of the hot precursor solution (precursor solution temperature in the
range of 50° - 80°C) to form precursor droplets 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 in 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 lithium zirconate powder, (3) fractionating the
bulk lithium zirconate powders in 'course' and 'fine' fractions by a
cyclone separator and collecting the 'coarse' and 'fine' fractions
separately in containers outside the reactor, (4) exhausting the
decomposed gases through a wet scrubber using 3-5 wt% commercial
lime solution/suspension as media prior which the decomposed gases
had been made to pass through a bag filter that is periodically cleaned by
air-pressure shocks and (5) heat treatment (calcining) of the amorphous
lithium zirconate powders in air in the temperature range of 500 -
1100°C for obtaining tetragonal and monoclinic crystalline modifications
of the lithium zirconate that also has nanostructure in the agglomerated
particles.
The as-synthesized amorphous lithium zirconate powder is heat treated
at 400°C to eliminate the absorbed gases in the material that might have

been absorbed in the reactor during its formation and thereafter heat
treated in the temperature range of 500° - 900°C to develop its
tetragonal crystalline phase first at 500°C and then monoclinic phase at
900°C and is characterized by :
(a) a crystallite size up to about 100 nanometers in the agglomerated
particles of the material which is determined by the transmission
electron microscopy (TEM)
(b) a specific surface area in the range of 2 - 10 m2/g which is
determined by BET analysis, and
(c) formation of tetragonal crystalline modification of lithium
zirconate at a minimum temperature of 500°C from its as-
synthesized amorphous phase and subsequently to monoclinic
phase of the material at a minimum temperature of 900°C, as
determined by X-ray diffraction pattern (XRD) analysis.
In the practice of the invented process, various aqueous-based precursor
solutions are prepared by dissolving appropriate amounts of analytical
grades (AR grade, >99 wt% purity) zirconium oxy-nitrate hydrate or

zirconium nitrate hydrate, glycine or urea and lithium nitrate in de-
ionized water in desired molar ratios.
The schematic diagram of a liquid petroleum gas (LPG)-fired spray
pyrolysis system which is in-house fabricated is described in Indian
Patent Application No. 569/KOL/2009 dated 30th April, 2009.
Appropriate amounts of zirconium oxy nitrate hydrate or zirconium
nitrate hydrate (solid), glycine or urea (solid) and lithium nitrate (solid)
are dissolved together in de-ionized/distilled water by maintaining the
solution concentration (solid load) in the range of 100 - 300 gm/liter.
The resultant solution is termed as 'precursor'.
In general, the production process starts with spray atomizing the hot
precursor solution using compressed air (pressure = 8.0 kg/cm2 or
more) as a counter fluid in a two-fluid nozzle gun attached with the LPG-
fired spray pyrolysis system, thereby generating 'fine droplets' of the
precursor. Other gases like pure oxygen, enriched oxygen etc can also be
used as the counter fluid instead of air here. The process of generating

fine droplets from its liquid precursor is often popularly called as 'spray
atomization', though there is no actual atomization. The fineness of the
precursor droplets depends both on the diameter of the orifice of the
nozzle through which it is sprayed off and also on the pressure level of
the compressed air used in the two-fluid gun. The process is described
in Indian Patent Application No. 569/KOL/2009 dated 30th April, 2009.
As the precursor droplets enter into the pre-heated reactor through the
spray gun and get mixed with the hot air, the droplets start falling
downwards in the reactor and in the process, a simultaneous
dehydration and decomposition reaction of the droplets occur. The
dehydration step which occurs first, yields dehydrated precursor
particles, which then undergoes a decomposition reaction to form
amorphous lithium zirconate particles along with the release of
decomposed gases. The decomposed gases are removed by passing the
gases through a bag filter and subsequently through a wet scrubber
which uses commercial a lime solution/suspension (3-5 w%).
As the freshly-formed lithium zirconate particles would consist both
'coarse' and 'fine' particles, these are 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 it is important to maintain a minimum temperature
of 100°C at the collection point, which keeps the powders dry.
The finer fraction of the collected powders are called amorphous lithium
zirconate that has crystallites upto 100 nanometer in the agglomerated
particles and showed a tap density in the range of 0.07 - 1.02 gm/cc.
The amorphous lithium zirconate powders upon heating in air at a
minimum temperature of 500°C produces tetragonal phase and then
produces monoclinic phase at 900°C as confirmed by x-ray powder
diffraction pattern (XRD) analysis.
Several precursor compositions can be prepared by permutations and
combinations by taking the starting raw materials, i.e., i) zirconium
oxynitrate hydrate or zirconium nitrate hydrate, ii) amino acetic acid
(Glycine) or urea and iii) lithium nitrate hydrate in desired molar ratio so

as to maintain the desired ratio of either i) Glycine-Nitrate or ii) Urea-
Nitrate ratio in the precursor solutions in order to carry out the
pyrolysis reaction of the precursor droplets efficiently using the LPG-fired
spray pyrolysis system.
The concentration of the precursor (solid load) under a fixed precursor
feed rate has an influence on the yield of the powder. Higher the
concentration of the precursor, higher is the yield and vice versa.
However at higher concentration of the precursor, the derived lithium
zirconate particles become coarser as compared to a lower concentration
through the crystalline phase does not change in any case. On the other
hand, the yield of the lithium zirconate powders under a given
concentration of the precursor is also decreased by increasing the
precursor feed rate and vice versa.
The invention will now be explained in greater details with the help of the
following non-limiting examples. Fig. 1 shows the nano-crystallites of the
tetragonal lithium zirconate powders obtained at 600°C in the
Transmission Electron Microscopy (TEM) as an example.

EXAMPLE 1:
This example illustrates the production of nanostructured amorphous
lithium zirconate powders having upto 100 nanometer crystallites in the
agglomerated particles of the material in accordance with the present
invention.
The precursor in this example is prepared by dissolving the chemicals,
i.e. i) zirconium oxy nitrate hydrate (solid), ii) lithium nitrate (solid) and
iii) urea (solid) in de-ionized water maintaining an optimized molar ratio
of 1:2:1.2 respectively that in turn makes 'Urea-Nitrate' molar ratio of
0.3 in the resultant precursor solution. All the above chemicals are
analytical grade (AR) in which the purity is maintained > 99 weight%
and are taken in weight proportions as per the Table 1' by maintaining
the desired molar ratio of the chemicals and dissolved together in ~ 3
liters of de-ionized water i.e. by maintaining a total solid content of ~
140 gm per liter of the solution, which is termed as 'precursor'.
Fine droplets of the resultant precursor is generated by spraying the
precursor solution (maintaining a solution temperature of about 80°C)

with a feed rate about 10 liters/hour and by using compressed air having
pressure level about 8.5 kg/cm2 consistently as a counter fluid in a two-
fluid nozzle (nozzle orifice diameter, about 0.1 mm) gun attached with the
OPG-fired spray pyrolysis system (SPS). Precursor droplets are allowed
to pass in the pre-heated stainless steel (SS316 grade) reactor of the SPS,
wherein the precursor droplets get mixed with the hot air that had a set
temperature of about 750°C in the system.
A schematic diagram of the LPG-fired spray pyrolysis system is furnished
in the Indian Patent Application No. 569/KOL/2009 dated 30th April,
2009, though the technical features and design of such a system could
vary from case to case.
As the precursor droplets start moving from the top to the downwards of
the reactor following a simultaneous dehydration and decomposition
reaction of the precursor droplets occur, resulting amorphous lithium
zirconate particles at the end of the reactor. The resultant amorphous
lithium zirconate powders contain both 'coarse' and 'fine' fractions,
which are fractionated by a cyclone separator into 'coarse' and fine'
fractions of the material and were collected separately in containers
outside the reactors. The coarse fraction is rejected.
Finer fraction of the derived powder is amorphous lithium zirconate that
showed a tap density of ~0.08 g/cc and a specific surface area of 8
m2/g in the BET analysis. The material also showed tetragonal
crystalline structure in the XRD analysis when heated at a minimum
temperature of 500°C and Figure 1 shows the crystallite size upto 100
nanometer in the agglomerated particles of the derived powders in the
transmission electron microscopy (TEM). XRD data further confirmed
that the tetragonal crystalline modification remained stable upto
temperature of 800°C and then slowly transformed into monoclinic
crystalline modification of lithium zirconate while heating the material in

air at a minimum temperature of 900°C with a soaking period of one
hour at each set temperature of calcination. As the temperature was
raised from 800°C, the tetragonal structure of lithium zirconate started
getting converted into monoclinic phase, which completed at 900°C and
hence both the tetragonal and monoclinic structure co-existed in variable
proportions in the temperature range of 800° - 900°C during the heating
process.
It is also 'Table 1' only describes the concentration level of the precursor
solution so as to maintain an optimized "Urea-Nitrate" molar ratio of
0.3. However by varying the amount of area in the precursor
composition, several independent precursor solution could be prepared
by permutations and combinations by maintaining the "Urea-Nitrate"
molar ratio in the range of 0.15 - 0.45. However, as the "Urea-Nitrate"
ratio in the precursor solution is lowered in the said range to that of the
optimized level of 0.3, there is a tendency to incomplete the
decomposition of metal nitrates in the precursor resulting the presence of
un-burnt zirconium oxynitrate and or lithium nitrate in the amorphous

lithium zirconate powder as impurities in the course of spray pyrolysis
reaction. On the other hand, higher "Urea-Nitrate" ratio in the
precursor to that of 0.3 level showed the presence of higher amount of
carbonaceous materials probably arising out of incomplete
decomposition of urea in the precursor in the course of spray pyrolysis
reaction. However, irrespective of the "Urea-Nitrate" ratio of the
precursor, the powder yielded after the spray pyrolysis reaction, upon
heat treatment produces tetragonal phase of lithium zirconate first and
then monoclinic phase in the temperature range of 500° - 900°C.
It is further reported in this example, though the precursor concentration
(solid load) is chosen at 140 gm/litre, the solid load could be varied in
the range of 100 - 300 gm/liter at a given "Urea-Nitrate" molar ratio of
the precursor and by permutations and combinations, several precursors
could be prepared by varying the solid load of the precursor and
pyrolysed. However, when the concentration of the precursor is lowered,
the particles generated during the course of spray pyrolysis reaction
become finer as compared to a precursor with higher amount of solid
load. The crystallite size of the resultant powders comes down by

lowering the solid load of the precursor 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 the 'Example 1' is followed exactly in similar manner
in this example, except that the chemical, 'urea' in the precursor
composition was replaced with 'amino acetic acid (Glycine)' in which the
molar ratio of the chemicals, zirconium oxynitrate hydrate, lithium
nitrate and Glycine was kept at 1:2:1.2 in order to make an optimized
"Glycine-Nitrate" molar ratio of 0.3, in order to carry out the spray
pyrolysis reaction of the resultant precursor droplets in an efficient
manner which is free of un-decomposed precursor material/s in the
derived amorphous lithium zirconate powders at the end of the pyrolysis
reaction in the reactor.
Table 2 describes the precursor composition in this example in weight
ratio in which and the final precursor concentration was made at 125 gm
of solid load per liter of the solution. 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 amorphous lithium
zirconate that showed a tap density of 0.07 g/cc and a specific surface
area of 10 m2/g. The material upon heating in air at a minimum
temperature of 500°C produces its tetragonal modification and finally
transforms to monoclinic phase at a minimum temperature of 900°C.
It is also reported in this example, similar to the Example 1 that the
precursor composition stated in the Table 2' only describes the
concentration level of the precursor solution so as to maintain an

optimized "Glycine-Nitrate" molar ratio of 0.3. However, by varying the
amount of glycine in the precursor composition, several independent
precursor solution could be prepared by permutations and combinations
by maintaining the "Glycine-Nitrate" ratio in the range of 0.15 - 0.45.
However, as the "Glycine-Nitrate" ratio in the precursor solution is
lowered in the said range to that of the optimized level of 0.3, there is a
tendency to incomplete the decomposition of metal nitrates in the
precursor resulting the presence of un-burnt zirconium oxynitrate and or
lithium nitrate in the amorphous lithium zirconate powder as impurities
in the course of spray pyrolysis reaction. On the other hand, higher
"Glycine-Nitrate" ratio in the precursor to that of 0.3 level showed the
presence of higher amount of carbonaceous materials probably arising
out of incomplete decomposition of glycine in the precursor in the course
of spray pyrolysis reaction. However, irrespective of the "Glycine-
Nitrate" ratio of the precursor, the powder yielded after the spray
pyrolysis reaction upon heat treatment produces tetragonal phase of
lithium zirconate first and then monoclinic phase in the temperature
range of 500° - 900°C.

It is further reported in this example, though the precursor concentration
(solid load) is chosen at 125 gm/ litre, the solid load could be varied in
the range of 100 - 300 gm/liter at a given "Glycine-Nitrate" molar ratio
of the precursor and by permutations and combinations, several
precursors could be prepared by varying the solid load of the precursor
and pyrolysed. However, when the concentration of the precursor is
lowered, the particles generated during the course of spray pyrolysis
reaction become finer as compared to a precursor with higher amount of
solid load. The crystallite size of the resultant powders comes down by
lowering the solid load of the precursor 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 3 :
The procedure of the 'Example 1' is followed exactly in similar manner
in this example, except that the chemical, 'Zirconium oxynitrate hydrate
is replaced with zirconium nitrate' in the precursor composition in which
the molar ratio of the chemicals, zirconium nitrate hydrate, lithium
nitrate and urea was kept at 1:2:1.8 in order to make an optimized

"Urea-Nitrate" molar ratio of 0.3, in order to carry out the spray
pyrolysis reaction of the resultant precursor droplets in an efficient
manner which is free of un-decomposed precursor material/s in the
derived amorphous lithium zirconate powders at the end of the pyrolysis
reaction in the reactor.
Table 3 describes the precursor composition in this example in weight
ratio in which and the final precursor concentration was made at 130 gm
of solid load per liter of the solution. 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 amorphous lithium
zirconate that showed a tap density of 1.02 g/cc and a specific surface
area of 4 m2/g. The material upon heating in air at a minimum
temperature of 500°C produces its tetragonal modification and finally
transforms to monoclinic phase at a minimum temperature of 900°C.
It is also reported in this example, similar to the Example 1 that the
precursor composition stated in the Table 3' only describes the
concentration level of the precursor solution so as to maintain an
optimized "Urea-Nitrate" molar ratio of 0.3. However, by varying the
amount of urea in the precursor composition, several independent
precursor solution could be prepared by permutations and combinations
by maintaining the "Glycine-Nitrate" molar ratio in the range of 0.15 -
0.45. However, as the "Urea-Nitrate" ratio in the precursor solution is
lowered in the said range to that of the optimized level of 0.3, there is a
tendency to incomplete the decomposition of metal nitrates in the
precursor resulting the presence of un-burnt zirconium nitrate and/or
lithium nitrate in the amorphous lithium zirconate powder as impurities
in the course of spray pyrolysis reaction. On the other hand, higher
"Urea-Nitrate" ratio in the precursor to that of 0.3 level showed the
presence of higher amount of carbonaceous materials probably arising

out of incomplete decomposition of urea in the precursor in the course of
spray pyrolysis reaction. However, irrespective of the "Urea-Nitrate"
ratio of the precursor, the powder yielded after the spray pyrolysis
reaction, upon heat treatment produces tetragonal phase of lithium
zirconate first and then monoclinic phase in the temperature range of
500° - 900°C.
It is further reported in this example, though the precursor concentration
(solid load) is chosen at 130 gm/litre, the solid load could be varied in
the range of 100 - 300 gm/liter at a given "Urea-Nitrate" molar ratio of
the precursor and by permutations and combinations, several precursors
could be prepared by varying the solid load of the precursor and
pyrolysed. However, when the concentration of the precursor is lowered,
the particles generated during the course of spray pyrolysis reaction
become finer as compared to a precursor with higher amount of solid
load. The crystallite size of the resultant powders comes down by
lowering the solid load of the precursor 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 4 :
The procedure of the 'Example 3' is followed exactly in similar manner in
this example, except that the chemical 'urea' in the precursor
composition was replaced with 'amino acetic acid (Glycine)' in which the
molar ratio of the chemicals, zirconium nitrate hydrate, lithium nitrate
and Glycine was kept at 1:2:1.8 in order to make an optimized "Glycine-
Nitrate" molar ratio of 0.3, in order to carry out the spray pyrolysis
reaction of the resultant precursor droplets in an efficient manner which
is free of un-decomposed precursor material/s in the derived amorphous
lithium zirconate powders at the end of the pyrolysis reaction in the
reactor.
Table 4 describes the precursor composition in this example in weight
ratio in which and the final precursor concentration was made at 120 gm
of solid load per liter of the solution. 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 amorphous lithium
zirconate that showed a tap density of 0.09 g/cc and a specific surface
area of 6 m2/g. The material upon heating in air at a minimum
temperature of 500°C produces its tetragonal modification and finally
transforms to monoclinic phase at a minimum temperature of 900°C.
It is also reported in this example, similar to the Example 1 that the
precursor composition stated in the Table 4' only describes the
concentration level of the precursor solution so as to maintain an
optimized "Glycine-Nitrate" molar ratio of 0.3. However by varying the
amount of glycine in the precursor composition, several independent
precursor solution could be prepared by permutations and combinations
by maintaining the "Glycine-Nitrate" molar ratio in the range of 0.15 -

0.45. However, as the "Glycine-Nitrate" ratio in the precursor solution
is lowered in the said range to that of the optimized level of 0.3, there is a
tendency to incomplete the decomposition of metal nitrates in the
precursor resulting the presence of un-burnt zirconium nitrate and/or
lithium nitrate in the amorphous lithium zirconate powder as impurities
in the course of spray pyrolysis reaction. On the other hand, higher
"Glycine-Nitrate" ratio in the precursor to that of 0.3 level showed the
presence of higher amount of carbonaceous materials probably arising
out of incomplete decomposition of glycine in the precursor in the course
of spray pyrolysis reaction. However, irrespective "Glycine-Nitrate" ratio
of the precursor, the powder yielded after the spray pyrolysis reaction,
upon heat treatment produces tetragonal phase of lithium zirconate first
and then monoclinic phase in the temperature range of 500° - 900°C.
It is further reported in this example, though the precursor concentration
(solid load) is chosen at 145 gm/litre, the solid load could be varied in
the range of 100 - 300 gm/liter at a given "Glycine-Nitrate" molar ratio
of the precursor and by permutations and combinations, several
precursors could be prepared by varying the solid load of the precursor

and pyrolysed. However, when the concentration of the precursor is
lowered, the particles generated during the course of spray pyrolysis
reaction become finer as compared to a precursor with higher amount of
solid load. The crystallite size of the resultant powders comes down by
lowering the solid load of the precursor 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.

WE CLAIM ;
1. A liquid petroleum gas (LPG)-fired spray pyrolysis process for the
synthesis of nano-structured lithium zirconate powders in amorphous,
tetragonal and monoclinic crystalline modifications using aqueous-based
precursor/s in a continuous mode, comprising the steps of :
(a) preparation of one or more aqueous-based precursor solutions
(precursor) by dissolving the stoichiometric amounts of the starting raw
materials i) zirconium oxy nitrate hydrate or zirconium nitrate hydrate,
ii) urea or amino acetic acid (Glycine) and iii) lithium nitrate hydrate in
de-ionized/distilled water by maintaining an optimized 'Urea-Nitrate' or
'Glycine-Nitrate' molar ratio of 0.3 in the range of 0.15 - 0.45 therein in
the precursor and in all precursor compositions by permutations and
combinations having variable 'Urea-Nitrate' or 'Glycine-Nitrate' molar
ratio thereof;
(b) generating a stream of fine precursor droplets by spraying the hot
precursor solution having a solution temperature in the range of 50° -
80°C in a pre-heated reactor attached with the LPG-fired spray pyrolysis

system using compressed air having pressure of 8.0 kg/cm2 or more as
the counter fluid in a two-fluid nozzle gun ;
(c ) mixing the precursor droplets and hot air (blow from outside having a
set temperature in the range of 650° - 750°C) inside the reactor and
carrying out a simultaneous dehydration and decomposition reaction to
yield dehydrated precursor particles first and then amorphous lithium
zirconate powders having nanostructure in the agglomerated particles
along with the decomposed gases in a continuous mode ;
(d) fractionating the bulk as-synthesized amorphous lithium zirconate
powders as 'coarse' and 'fine' fractions by a cyclone separator and
collecting the 'coarse' and 'fine' fractions separately in containers
outside the reactor ;
(e) exhausting the decomposed gases through a wet scrubber using 3-5
wt% commercial lime solution/suspension as media prior which the
decomposed gases had been made to pass through a bag filter that is
periodically cleaned by air-pressure shocks ; and
(f) heat treatment (calcining) of the nanostructured amorphous lithium
zirconate powders in air in the temperature range of 500° - 1100°C
having soaking period of about 1 hour at the set temperature for

obtaining both tetragonal and monoclinic crystalline modifications of
lithium zirconate that also has nanostructure in the agglomerated
particles.
2. A process as claimed in claim 1, wherein the 'precursor' is prepared
by the dissolving zirconium oxy nitrate hydrate, lithium nitrate hydrate
and urea in de-ionized or distilled water with an optimized molar ratio of
1:2:1.2 having a counter "Urea-Nitrate" molar ratio of 0.3 and all
precursors thereof by permutations and combinations by varying the
"Urea-Nitrate" molar ratio in the range of 0.15 - 045.
3. A process as claimed in claim 2, wherein another 'precursor' could
alternatively be made by the dissolving zirconium oxy nitrate hydrate,
lithium nitrate hydrate and amino acetic acid (Glycine) in de-ionized or
distilled water with an optimized molar ratio of 1:2:1.2 having a counter
"Glycine-Nitrate" molar ratio of 0.3 and all precursors thereof by
permutations and combinations by varying the "Urea-Nitrate" molar
ratio in the range of 0.15 - 0.45.

4. A process as claimed in claims 2 and 3, wherein other sets of
'precursors' could also be prepared either by dissolving i) zirconium
nitrate hydrate, lithium nitrate hydrate and urea or ii) zirconium
nitrate hydrate, lithium nitrate hydrate and amino acetic acid (Glycine)
in de-ionized or distilled water having an optimized molar ratio of 1:2:1.8
of the raw materials in the sequence with a counter "Urea-Nitrate" or
"Glycine-Nitrate" optimized molar ratio of 0.3 and all precursors thereof
by permutations and combinations by varying the "Urea-Nitrate" or
"Glycine-Nitrate" molar ratio in the range of 0.15 - 0.45.
5. A process as claimed in claims 2, 3 and 4, the as-synthesized powder
prepared by using any of the precursors is an amorphous lithium
zirconate having up to 100 nanometer crystallites in the agglomerated
particles that produces tetragonal lithium zirconate at a minimum
temperature of 500°C and the monoclinic modification of lithium
zirconate at a minimum temperature of 900°C in air in the course of heat
treatment of the amorphous material in the temperature range of 500 -
1100°C with a soaking time of about 1 hour at the set temperature.

6. A process as claimed in claim 5, the specific surface area of the
derived nanostructured lithium zirconate powders vary in the range of 2
- 10 m2/g and increases by reducing either the i) feed rate or ii)
precursor concentration (solid load) of the precursor/s in all types of
precursors, claimed in claim 2, claim 3 and claim 4 respectively and
alternatively either by increasing the i) temperature of the hot precursor
during atomization process or ii) set temperature of the hot air blown
inside the reactor in the LPG-fired spray pyrolysis system.
7. A process as claimed in claim 6, the minimum temperature of the
powders in the power collection containers both for coarse and fine
fraction powders need to be 100°C.
8. A process as claimed in claim 7, the hot air is generated by the
combustion of liquid petroleum gas (LPG) and the entire system design
of the LPG-fired spray pyrolysis system and parameters set therein might
vary from case to case.

A method for the synthesis of nanostructured lithium zirconate powder
in a continuous mode using LPG-fired (LPG = liquid petroleum gas) spray
pyrolysis technique is disclosed. As per the disclosed invention,
amorphous lithium zirconate having nanostructure in the agglomerated
particles is obtained as a decomposed solid product following a
combustion reaction of aqueous-based liquid precursor droplets under
defined experimental conditions in the LPG-fired spray pyrolysis system.
The amorphous lithium zirconate is further heat treated to obtain its
tetragonal crystalline phase at a minimum temperature of 500°C and
thereafter at a minimum temperature of 900°C to obtain its monoclinic
phase. Transmission electron microscopy (TEM) of lithium zirconate
powders both in amorphous and crystalline modifications show the
primary particle size in the range of 20 - 100 nanometer.