A PROCESS OF PRODUCING NANOSTRUCTURED HYDRATED ALUMINA
AND PRODUCTS THEREOF
FIELD OF INVENTION
The present invention relates to a process of producing nanostructured hydrated
alumina either in powder form or in the form of suspension/sol. More
specifically, the present invention deals with a chemical process for the synthesis
of nanostructured hydrated alumina, either in the form of powder or in the form
of suspension/sol, in which the powder possesses ~ 30-100 nanometer sized
primary particles in the 0.5 - 10 micron sized of its counter
agglomerates/aggregates having specific surface area in the range of 80 - 170
m2/gm and further preparation of a stable suspension / sol thereof with sol
loading of 5 - 70 volume %.
BACKGROUND OF THE INVENTION WITH PRIOR ART DIFFICULTIES
Aluminium usually forms two types of hydroxides - tri-hydroxide and mono-
hydroxide. Some of those hydroxides are well-characterized crystalline
compounds, while the others are rather amorphous compounds. The most
common tri-hydroxides are gibbsite, bayerite and nordstrandite and more
common mono-oxide hydroxide forms are boehmite and diaspore. The above
hydrated aluminas often loosely called aluminum trihydrate, popularly known as
ATH. Besides the above hydroxides, the material also has several other
synonyms like, hydrated alumina, alumina hydrate. ATH is a versatile material

that has been catering a wide range of across many interdisciplinary areas,
starting metallurgical to ceramic processing industries. It is used as filler in FRLS
(fire retardant low smoke) in electrical/electronic cable industries, as catalyst
supports and absorbents in chemical industries, as functional additives in
polymers, paints, various polymer composites, automotive and in pharmaceutical
industries.
ATH is commercially available as a coarse-grained material, however
the several advantages in nanometer dimensions, nano-structured ATH is
bringing new interests in several applications. Nano ATH could significantly
reduce the filler load in a given composition, thus making the body more light as
compared to the same body in which coarse ATH has been incorporated.
Besides its lightweightness, it also significantly improves thermal stability,
mechanical strength, electrical properties, FRLS, environmental stability like UV
resistance, hydrophobicity, resistance to chemical attacks in high pollution areas.
Nano sized ATH also known to improve arc-track resistance in plastics for
electrical applications. As filler in fine printing papers, it increases opacity and
brightness, and in paper coatings, it imparts brightness, gloss and high ink
receptivity. Finer grained or nano ATH could be better reinforcing pigment in
adhesives, where it improves cold flow properties and cohesion besides the
stabilization in pH. Finer ATH also improves the surface properties those
exploited in polishing applications, cleansing agent, mould wash and separating
agent. Finer or nano ATH with high purity finds new applications in
pharmaceuticals, high purity chemical manufacturing and in paint industries.

Aluminium hydroxides produced from the Bayer process are generally yellowish
in color and relatively coarse in size. Different methods for synthesizing finer
ATH have been tried either by grinding the Bayer precipitates followed by the
size classification or by direct precipitation of a finer-sized ATH from Bayer liquor.
Various authors Csige et al, Sleppy et al, have worked on the development of
finer grade hydrates by grinding coarse ATH powders, but achieving finer-sized
(<2 micron) particles by such a method is highly energy intensive and hence did
not draw much attention. Therefore, attempts were made for direct precipitation
for finer-sized particles. Baksa et al. produced several fine hydrates in the air jet
mill by precipitation in the presence of a modifier namely, aluminium sulfate.
According to the authors, a lower precipitation temperature and a lower
pregnant liquor concentration are advantageous, and the addition of at least
1.0% AI2(SO4)3 is required as AI2O3. They also studied the production of 0.5
micron of ATH particles by decomposing gallium-aluminium alloy with NaOH and
or H2O. Satapathy and Pattanaik produced aluminum trihydrate of 4 micron in
size by a two-stage precipitation process using a liquor having alumina/caustic
ratio of 1 with the corresponding soda content of 0.28% and seed of 10 - 15
micron in size thereby. Martinswerk, Germany have been producing SGA (special
grade alumina) since 1970 and is a supplier of one micron precipitated ATH all
over the world. Interestingly, Shibue et al. found that the size of primary
particles is not affected significantly by the mechanical stirring and the size of the
particle decreases with an increase in the tank size. However, the authors found
that the particle size distribution is sharper in the batch than in continuous
precipitation.

T.Tran et al. studied the effect of 3,4 Dihydroxy Benzoic Acid (3,4 DHBA), an
organic acid on the precipitation of ATH particles. In another study/ the same
group MJ. Kim et al. studied the precipitation of radial ATH particles with an aim
to investigate the various factors affecting the synthesis. Precise control of
supersaturating condition and temperature as a function of time is reported to be
important in producing such ATH particles with desirable shape and size.
J.K.Pradhan et al studied the various factors affecting the quality of ATH
precipitates. The effect of a number of parameters such as precipitation
temperature, amount of seed, seed surface area, precipitation time, soda content
of pregnant liquor, modifier additives, etc. on the precipitation of ATH were
studied to achieve the required fineness. S Roy et al reported the synthesis of
nano-porous hydrated alumina with a pore diameter of 3 - 7 nanometer using
aluminum nitrate as the precursor and sodium/potassium hydroxide as
precipitating agent under defined experimental conditions.
Packed bed reactors have also been used for synthesis of ATH. J. Chen et al.
developed a route for synthesizing so-called nano-fibrillar ATH by carbonation in
a rotating packed bed at room temperature. Pseudoboehmite fibers of 1-10 nm
in diameter and 50-300 nm in length are obtained. Z. Peng-yuan et al worked
on the preparation of ultrafine ATH via a new method combined with high gravity
reaction and thermal hydrolysis. Z. Peng-yuan et al prepared nano-ATH by the
RPB method, in which industrial ATH was used as raw materials for the

preparation of sodium aiuminate which was precipitated by carbonation and ATK
of below 50 nm was prepared.
Liu Ji-bo et ai. studied the effect of ultrasound frequency on the precipitation
process of supersaturated sodium aiuminate solution. Ultrasonic treatment at 16
kHz can enhance the decomposition rate of sodium aiuminate solutions that
effects the particle morphology and particle size distribution of ATH precipitate
by this method. S. P. McGrath et al. studied the sonochemical processing of
bauxite using Resonant Sonics. The device Resonant Sonics addresses all of
these issues such as ability to significantly increase the rate of alumina
precipitation, the ability to increase thermal efficiency and relatively high yield,
either directly or indirectly.
The Principle of Biomimetic Mineralization (BMS) has also been used in synthesis
of ATH. Yaacob I.I. et. al. reported using unilamellar vesicles as reactors for the
aqueous phase precipitation of nanometer sized ATH particles. ATH particles thus
obtained were of nanometer-sized with nearly spherical morphology. Tadafumi
Adschtri et al. studied hydrothermal synthesis of AIO(OH) using a flow type
apparatus over the range of temperature from S23 to 673 K at 30 MPa. Nano-
sized crystals were formed at supercritical condition.
Chemical methods or techniques for synthesizing nanostructured ATH in powder
form or in the form of suspension / sol using sodium aiuminate precursor with

sulphuric aeid as a precipitating agent following a precipitation technique under
defined experimental conditions has not been disclosed so far. It was in this
context, this invention was made. The invention provides the precursors to be
used, reaction conditions and experimental parameters to be followed for the
synthesis of nanostructured hydrated alumina (ATH) in powder form or in the
form of suspension / sol with typical characteristics of primary particle size with
counter agglomerate or aggregate size and specific surface area of the material.
OBJECTIVES OF THE IHVENTION
The main objective of the invention is to provide a precipitation technique for
synthesizing nanostructured hydrated alumina both in the form of powder
and in the form of suspension/sol, using sodium aluminate as precursor and
sulphuric acid as precipitating agent under defined experimental conditions
like pH range at which the precipitation reaction to be carried out,
concentration range of the precursor and precipitating agent, parameters
involved for filtering, washing and drying of the precipitates and procedures
for producing suspension/sol using the washed precipitates.
Another objective of the Invention Is to synthesize nanostructured hydrated
alumina powder and its suspension/sol in a cost-effective manner with
primary particles in the range of ~ 30 - 100 nanometer in its counter
agglomerate /aggregate size in the range of 0.5 - 10 microns having specific

surfaee area in the range of 80 - 170 m2/g in the powder form and
preparation of suspension / sol using the washed precipitate having a so!
loading in the range of 5 - 70 volume %.
A still another objective of the invention is to define various process
parameters for producing the above hydrated alumina powder and its
suspension/sol in the said precipitation technique
A further objective of the present invention is to provide nanostructured
hydrated alumina powder and its suspension/sol that have applications in various
applications, e.g., ceramic coatings, so! processing, polymer composites,
additives, fillers, FRLS composite materials etc or in similar areas.
The objectives and the advantages of the present invention is realized and
attained to a particular materia! through the permutations and combinations of
the physical characters and chemical constituents of the derived nanostructured
hydrated alumina powders or suspensions/sols.
DESCRIPTION OF THE INVENTION
The following are the steps involved for producing nanostructured hydrated
alumina either in the form of powder or in the form of suspension/so!:
a) preparing an aqueous solution by dissolving solid sodium aluminate in

distilled/de-ionized water in a suitable container and obtaining a clear solution
of concentration in the range of 0.5 - 1.5 moles/liter by filtration, called as
precursor and transferring the precursor in a precipitating tank fitted with an
agitator/stirrer,
b) preparing a precipitating agent by diluting concentrated sulphuric acid
with distilled/de-ionized water in a suitable container and obtaining a
diluted sulphuric acid solution in the concentration range of 1.0 - 2.5
moles/liter, called as precipitating agent and adding slowly to the
precipitating tank containing the precursor, wherein both the precursor
and the precipitating agent are uniformly mixed by the agitator/stirrer,
c) carrying out the precipitation reaction between the precursor and the
precipitating agent until the pH of the of the mixed solution in the tank
reaches in the range of 5 ± 1 under equilibrium condition, to yield a
white gelatinous precipitate and the addition of the precipitating agent is
ceased,
d) filtering the precipitates using suitable filtration systems/ arrangements,
e) washing the filtered precipitates using distilied/deionized water several
times until the pH of the filtered liquid showed a pH equal to 7, so as to
remove unreacted or absorbed chemicals/substances with the precipitate
that may come either from the precursor or the precipitating agent,
0 drying the washed precipitates (for preparation of nanosfructured ATH
powder) using either a conventional oven or microwave oven at a
temperature in the range of 100 - 190°C that results dried precipitates,

g) pulverizing/milling the dried precipitates in a pot mill (nylon pot or
alumina-lined pots and alumina balls as the grinding media) for a period
of 1 - 5 hours so as to result the pulverized/milled powders and thereafter
sieving the resultant powders and thereafter collecting the sieved powders
and characterizing the derived nanostructured ATH powders,
h) preparing a suspension/sol (in case nanostructured suspension/sol) by
mixing uniformly the washed precipitate with distilled/deionized water or
any other solvent of choice, with the washed precipitate (sot) loading in
the range of 5 - 70 volume0/© in the distilled/de ionized water or any other
solvent/s of choice.
DEATILEO PESCRIFTOOH OF THE IMVEHTXOfl
A. Preparation of precursor and the precipitating agent/s:
The present invention has proposed the synthesis route for synthesizing
nanostructured hydrated alumina both in powder form and suspension/sol form,
by adopting a precipitation reaction technique. For the said purpose, solid
sodium aluminate is to be dissolved in de-ionized/distilled water maintaining the
solution concentration in the range of 0.5 - 1.5 moles/liter, which is termed as
"precursor'. The precipitating agent is to be prepared by diluting concentrated
sulphuric acid with de-ionized/distilled water in appropriate ratio depending on
the concentration of the sulphuric acid used, so as to make concentration of the
diluted acid in the range of i.O - 2.5 moies/iiter.

Precipitation reaction is to be conducted using the aforesaid "precursor' and ths
precipitating agent under defined experimental parameters like, pH,
temperature, concentration of precursor, concentration of precipitating agent etc.
B. Conducting precipitation reaction:
Precipitation reaction is conducted in a precipitation tank that is fitted with i) a
magnetic stirrer/agitator for mixing the precipitating agent with the precursor, ii)
pH electrode for measuring pH of the solution and lii) thermometer for
measuring the temperature of the solution. A fixed volume of the precursor
with defined concentration is taken in a precipitation tank and then the
precipitating agent with defined concentration is added thereby slowly for
carrying out the precipitation reaction. Both the stirring speed in the magnetic
stirrer and the rate of addition of precipitating agent are maintained at a fixed
rate so that a uniform rate of mixing of the precursor and precipitating agent is
ensured. The rate of addition of the precipitating agent and speed of the stirrer
are to be adjusted such a way that the precipitating agent is almost
instantaneously spreads over the precursor solution and a large concentration
gradient thereby is avoided. Addition of the precipitating agent to the precursor
shows appearance of the precipitates, however addition is continued until the
desired pH level of the reaction medium in the range of 5 +, 1 is reached at
equilibrium condition. After thorough mixing between the precipitating agent
and the precursor at a parttcular pH with a fixed speed of the stirrer, a white
gelatinous precipitate yields.

The concentrations of both the precursor and precipitating agent may vary
widely in a large range. However, as a thumb rule, it has been observed that, as
the concentrations of the precursor increases, particle size of the precipitate
become coarse. The same is true for the precipitating agent as well.
C. Filtering and washing off the precipitates:
After the precipitation reaction is conducted under defined experimental
conditions, the entire suspension/mixture is subjected to filtration by which the
precipitates are to be separated out from the unreacted chemicals/species and
essentially are to be made free from those contaminants (both ionic and
molecular species or either) that would have originated either from the precursor
or the precipitating agent. The precipitates hence need to be thoroughly washed
with distiIled/de-ionized water until they are free from these unreacted chemicals
present in the reaction medium. For washing and filtration, a simple vacuum
filtration system or a rotating filter or a thickener filter press or any of those
available from commercial sources using appropriate filter cloth to be used
depending on the batch size of precipitates and other conveniences.
D. Drying of the precipitates:
The washed precipitates are obtained in the form of cakes, which were dried
either using an electrically-heated oven or microwave oven maintaining the

drying temperature in the range of 100°C - 190°C. The time duration for drying
and rate of drying may vary, depending on the batch size of the precipitates and
also the type of drying equipment used therein, however, importantly, the drying
process needs to be continued until the constancy in weight of the material is
attained at the particular drying temperature. After drying, volume of the
precipitates comes down significantly, (~ 90%).
E. PuhreriiatSon of the dried precipitates:
The dried precipitates are to be pulverized preferably by using nylon (or similar
inert material) bowl or even alumina-lined bowls and alumina balls as the
grinding media for a definite period of time depending on efficiency of the milling
apparatus used. However, in a normal condition, using a nylon bowl with
alumina balls, a period of 1 - 5 hours of milling is sufficient to get powders with
desired fineness of the dried cakes. After pulverization operation, the resultant
powders are sieved using 100 - 200 micron sieve that results free flowing
powder. The hard agglomerated mass those have not passed through the said
sieve is rejected. The capacity of the bowl depends on the quantity of the
powders to be pulverized.
F. Testing and characterisation of the dried precipitates:
The pulverized powders are characterized in terms of specific surface area in the

BET method and mierosfruefcires in the scanning electron microscope for
determining the size of primary particles as well as the size of the agglomerates
or aggregates. X -Ray Powder diffraction was used to analyze the phase and
crystallinity and thermogravimetry and differential thermal analysis (TGA-DTA)
analysis to determine the water of crystallization in the material obtained in the
powder form.
G. Preparation off Suspension/So!:
Suspensions/sols in a given solvent (water or other organic solvent) of the
washed precipitates with desired concentration in the range of sol loading of 5 =
70 volume % is prepared by mixing the washed precipitates and de-
ionized/distilled in appropriate ratio. The resultant suspensions/sols are used for
numerous purposes in the area of coating, e.g., coating applications including
generation of thin nanostruetured layer on supported substrate/s following
dip/spin coating technique/s, in-situ processing of the sol for making various
composites etc. The derived suspensions/sols give another opportunity to exploit
the material in different applications besides the same material in the powder-
form. Instead of water, other solvents, while preparing the suspension/sol could
also are used depending on the chemical compatibility between the solvent and
the precipitate.
Accompanying figure 1 represents a schematic diagram of the process of
producing of nanostruetured hydrated alumina.

Example 1:
Preparation of nanostructured hydrated alumina with specific surface area in the
range of 100 - 110 m2/g and a primary particles in the range of ~ 30 - 100
nanometers with counter agglomerate size in the range of ~ 0.5 - 8 micron and
drying of the precipitates by conventional electrical heating.
A stock solution is prepared by mixing 1 mole of sodium aluminate in 1 liter of
distilled /de-ionized water and the resulting solution is filtered to remove
impurities or other contaminants, wherein a clear solution is resulted which is
termed as precursor solution with concentration of 1 M. The precursor solution
of 1 in with a capacity of 20 liters is poured into the precipitation tank, which is
fitted with an agitator/stirrer. The precipitating agent was prepared by taking
sulfuric acid 98% (weight/volume), which is diluted appropriately to make
strength of 1.5 moles/liter using de -ionized/distilled water and then slowly added
to the precursor in the precipitation tank that is already under constant agitation.
As a result, pH of the mixed solution changes from originally at 10 to 5.0 +, 0.05
within a time period of 30 min., a white precipitate resulted. The addition of
precipitating agent is ceased till the pH of the medium reaches to the set level of
5 ± 0.05. The stirring was still continued for another 10 minutes and the entire
mixture was filtered using a vacuum filtration system. The filtered precipitate is
washed repeatedly with distilled/de-ionized water till the pH of filtrate reaches ~
7. Washed precipitates are dried in an electrical oven maintaining a temperature
of 110°C ± 10°C for several hours, till the dried precipitates showed constancy in

die weight at tins temperature and after this drying operation cakes are
obtained. The cakes are pulverized using a nylon pot with alumina grinding balls
for a period one hour in a ball mill machine that resulted free-flowing powder of
the material, which were sieved through 100 - 200 micron sieve and the sieved
powder was collected. All the measurements towards characterizations and
testing are carried out using sieved powders only. Specific surface area of the
said powder is found to be in the range of 100 -110 m2/g with primary particles
in the range of ~ 30 -100 nanometers with counter agglomerate/aggregate size
in the range of ~ 0.5 - 8 microns.
Example 2
Preparation af nanosfrueturad hydrated alumina with specific surface area in the
range of 130 - 140 m2/g and a primary particles in the range of - 30 - 100
nanometers with counter agglomerate size in the range of ~ 0.5 - 8 micron and
drying of the precipitates by microwave heating.
The precipitates obtained by following the same procedure as mentioned in
example 1, the washed precipitates are however, dried in microwave heating
maintaining a temperature of 110 ± 10°C. The resulted powders are found to
have more spherical primary particles in the range of ~ 30-100 nanometer in
the agglomerate range of ** 0.5 - 8 micron and the corresponding specific
surface area was in the range of 130 - 140 m2/g.

Example 3
Preparation of nanostructured hydrated alumina with specific surface area in the
range of 150 - 160 m2/g and a primary particles in the range of ~ 30 - 70
nanometers with counter agglomerate size in the range of ~ 0.5 - 5 micron with
the drying of the precipitates by conventional electrical heating.
A stock solution is prepared by mixing 0.5 mole of sodium aluminate in 1 liter of
distilled /de-ionized water and the resulting solution is filtered to remove
impurities or other contaminants, wherein a clear solution is resulted which is
termed as precursor solution with concentration of 0.5 M. The precursor solution
of 1 in with a capacity of 20 liters is poured into the precipitation tank, which is
fitted with an agitator/stirrer. The precipitating agent was prepared by taking
sulfuric acid 98% (weight/volume), which is diluted appropriately to make
strength of 1.0 moles/liter using de-ionized/distilled water and then slowly added
to the precursor in the precipitation tank that is already under constant agitation.
As a result, pH of the mixed solution changes from originally at 10 to 5.2 +. 0.05
within a time period of 30 mm., a white precipitate resulted. The addition of
precipitating agent is ceased till the pH of the medium reaches to (he set level of
5.2 ± 0.05. The stirring was still continued for another 10 minutes and the
entire mixture was filtered using a vacuum filtration system. The filtered
precipitate is washed repeatedly with distilled/de-ionized water till the pH of
filtrate reaches ~ 7. Washed precipitates are dried in an electrical oven
maintaining a temperature of 150°C ± 10°C for several hours, till the dried

precipitates showed eonstaney in the weight at this temperature and after this
drying operation cakes are obtained. The cakes are pulverized using a nylon pot
with alumina grinding balls for a period one hour in a ball mill machine that
resulted free-flowing powder of the material, which were sieved through 100 -
200 micron sieve and the sieved powder was collected. All the measurements
towards characterizations and testing are carried out using sieved powders only.
Specific surface area of the said powder is found to be in the range of 150 -160
m2/g with primary particles in the range of ~ 30 - 70 nanometers with counter
agglomerate/aggregate size in the range of ~ 0.5 -10 microns.
Example 4
The precipitates obtained by keeping the procedure and other conditions same
as mentioned in example 3, but the washed precipitates are dried in microwave
heating maintaining a temperature of 150 ± 10°C. The resulted powders are
found to have regular spherical primary particles in the agglomerate in the range
of ~ 50 - 100 nanometer and the corresponding specific surface area was in the
range of 155 - 170 m2/g.
Example 5
Preparation of nanostructured hydrated alumina suspension/sol with i) 5
volume0/©, ii) 20 volume0/©, iii) 40 volume0/©, iv) 50 volume% and v) 70 volume%
Washed precipitates those obtained in the previous examples, gives an
opportunity to prepare various suspensions/sols with variable concentration/s by

mixing the washed preekiftate/B (by volume) and dfetifedAfe-taitized water (by
volume) in desired volume ratio that gives rise hydratad alumina suspension/sol.
The derived suspensions/sols are used in different applications, e.g., i)
generating nanostructured coated layer on substrates, H) evsttu incorporation of
the suspension/sol to another matrix/fehase etc., thus making composites with
different target properties of interest. A series of aqueous suspensions/sots of
the washed prectytata are prepared by increasing the precipitate concentration
by volume per 100 volume of deHonbedMistdled wafer, 04., i) 5 vot%, II) 20
vol*, Hi) 40 vor%, iv) 50 vol* and v) 70 vo»% are prepared. All the above
suspensions/sols are found to be stable at room temperature tor a period of at
least one week under ambient condtttons and no sedimentation was observed
which suggests the suspensions/sols have good shelNife.
The hvention as hereh narrated with exemplary embodiments should not be
read and construed in a restrictive manner as various modifications, alterations
and adaptations are possfete wfthin the scope and ambit of the Invention as
defined in the appended claims.

WE CLAIM:
1. A process of producing nanostructured hydrated alumina powder or
suspension / sol using defined precursor and precipitating agent/s under
defined experimental conditions, comprising the steps of.
(a) preparing an aqueous solution by dissolving appropriate amount of solid
sodium aluminate and de-ionized/distilled water in a suitable container (glass
or stainless steel or similar) maintaining a concentration in the range of 0 5 -
1.5 moles/liter, called as 'precursor',
(b) preparing the precipitating agent by dissolving concentrated sulphuric
acid in de-ionized/distilled water maintaining concentrations in the range 10-
2.5 moles/liter,
(c) carrying out precipitation reactions between the precursor and the
precipitating agent in a precipitation tank under constant stirring/ agitating in
the pH range of 5 ± 0.5, to result a white gelatinous precipitate,
(d) filtrating the solution containing the precipitate and washing the
precipitates with distilled/de-ionized water until the pH of filtrate becomes 7 to
free the precipitate from contaminants, using vacuum filtration system
/rotating filter/ thickener/filter press or any of these, depending on the batch
size,
(e) preparing a suspension/sol of any of the washed precipitate and mixing
the particular washed precipitate with de-ionized/distilled water in desired
ratio to result an aqueous suspension/sol with a sol loading in the range of 5 -
70 volume%
or alternatively drying the washed precipitates from step (d) using either
electrically-

heated oven or microwave oven maintaining a temperature in the range of
100°C - 190°C, until the constancy in weight of the dried precipitate resulted at
this temperature, pulverizing/mining the dried precipitates in nylon pots or
alumina- lined pots using alumina balls as grinding media for a period of 1 - 5
hours to result the pulverized/milled powders, sieving off the pulverized/milled
powders using 100 - 200 micron sieve, collecting the sieved powder and
characterizing the sieved powders in terms of specific surface area by BET,
crystalinity by X-ray powder diffraction, primary particle size and
agglomerate/aggregate size by scanning electron microscopy, thermogravimetry
analysis and differential thermal analysis (TGA-DTA) for analyzing water of
crystallization.
2. A process of producing nanostructured hydrated alumina as claimed in
claim 1 wherein the 'precursor' sodium aluminate is analytical grade/s
(chemical purity >98 wt%) and the precipitating agent is sulphuric acid with
concentrations in the range 1.0 - 2 5 moles/ liter and the resultant sieved
powder is nanostructured hydrated alumina which has primary particles in the
range of - 30 - 100 nanometer with corresponding agglomerates/aggregates of
0.5 - 10 micron with specific surface area in the range of 80 -170 m2/gm and
the derived suspension/sol with a sol loading in the range of 5 - 70 volume %
by mixing the washed precipitate arid de-ionized /distilled water or any other
solvent of choice in desired volume ratio, are nanostructured hydrated alumina
suspension/ sol.
3. A process according to claim 1, wherein a precipitation reaction is
conducted at room temperature in the precipitation tank with magnetic
stirrer/agitator, pH electrode far measuring pH of the mixed
solution/suspension, a thermometer for measuring the temperature of the
solution in the tank.

4. A process as claimed in the preceding claims, wherein as the
concentration of the precursor and the precipitating agent increase, the
resultant particle size (both primary particles and agglomerate/aggregate) of
the precipitates become coarser.
5. A process as claimed in the preceding claims, wherein the precipitates
start appearing by the addition of the precipitating agent to the precursor and
the volume of the precipitates increases until the pH of the suspension/mixed
solution reaches to 5.0 ± 0.5 at equilibrium condition.
6. A process as claimed hi the preceding claims, wherein the washed
precipitates are dried in an electrically-heated oven or in a microwave oven and
upon drying the volume of the precipitates decreased up to 90% and hard mass
results.
7. A process as claimed in the preceding claims, wherein the pulverized
powders characterized in terms of specific surface area and primary particle
size in the agglomerate/aggregate of the powder.
8. A process as claimed in the preceding claims, wherein the suspension
/sol of the washed precipitate with a sol loading in the range of 5 - 70 volume%
are used for different purposes of coating, ceramic & polymer processing
applications.

ABSTRACT
This invention relates to a process for producing nanostructured hydrated
alumina either in the form of powder or in the form of suspension/sot which are
obtained by synthesizing hydrated alumina following a precipitation reaction
between aqueous solution of sodium aluminate (precursor) and sulphuric acid
(precipitating agent) under defined experimental conditions. Gelatinous
precipitates start appearing when the precipitating agent is added to the
precursor solution and the addition of the precipitating agent is continued until
the pH of the resultant suspension reached at a value in the range of 5 + 1
under equilibrium condition. The resultant precipitates are filtered and then
washed several times with de-ionized/distilled water so as to make the
precipitate free from the un-reacted chemicals that comes either from the
precursor or the precipitating agent in the reaction medium. The washed
precipitates are dried in the range of 100 - 190°C. The resultant dried powders
are called nanostructured hydrated alumina. The powder has a primary particle
size in the range of ~ 30 - 100 nanometer. Nanostructured ATH
suspensions/sols with variable amounts of sol loading are made by mixing the
washed precipitate with de-ionized water in the desired ratio of the two
components. The suspensions/sols with a sol loading in the range of 5 - 70
volume % are stable (no sedimentation) at ambient conditions and the derived
suspensions/sols are used in various applications in the area of coatings and
processing of ceramic/polymeric materials.