CHAPTER-3
EXPERIMENTAL-MATERIAL
PREPARATION AND
TECHNIQUES
Experimental
CHAPTER –III
3.0 EXPERIMENTAL-MATERIAL PREPARATION AND TECHNIQUES
The experimental part contains the synthesis of Barium Titanate powders
following the Wet-Chemical processes as follows.
 Sol-Gel Process
 Hydrothermal Synthesis
3.1 Synthesis of Barium Titanate using Sol-Gel process
3.1.1 Materials
Barium Hydroxide Octahydrate Ba(OH) 2 .8H 2 O –Merck –GR grade
Titanium tetrachloride – LOBA Chemie -LR grade
Isopropanol alcohol –Merck –GR grade
Sodium hydroxide – Merck –GR grade
All the chemical reagents were used without any prior purification.
3.1.2 Procedure
Synthesis of Barium Titanate powders was carried out in four necked round
bottom flask equipped with mechanical stirrer, water condenser, dropping funnel
and nitrogen inlet. The typical set up of the reaction is shown in the Figure 3.1
used during the complete synthesis of barium titanate. The powder was
synthesized using the barium precursors as Barium Hydroxide Octahydrate
Ba(OH) 2 .8H 2 O and titanium precursors as Titanium tetrachloride. The Isopropyl
alcohol was used as the reactive solvent and the medium for the reaction. The
aqueous solution of the sodium hydroxide was used as the alkaline mineralizer.
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During synthesis the aqueous solution of barium hydroxide octahydrate was
prepared by dissolving the weighed amount of solid in water. Simultaneously a
solution of titanium tetraisopropoxide was prepared in a four necked round
bottom flask as shown in Figure 3.1 by mixing the titanium tetrachloride to
isopropanol.
Figure 3.1 Typical set up of the reaction
The aqueous barium solution was added drop wise in the Ti-isopropoxide
solution under continuous stirring and nitrogen atmosphere. The pH of the
solution was maintained using the aqueous solution of caustic soda.
The
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temperature of the reaction increases from room temperature to elevated
temperature.
The synthesis of barium titanate ceramic powder was carried out using the
Barium hydroxide
Ba (OH) 2 .8H 2 O and titanium tetrachloride (TiCl 4 ). During
synthesis the ratio of the Ba/Ti has been varied and optimized for obtaining the
purified product. Several experiments were carried out varying the amounts of Ba
and Ti precursors. Thus the Ba/Ti ratio is maintained at 1.02 using, 31.5 g of Ba
(OH) 2 .8H 2 O and 11.0 ml of TiCl 4 .
During the synthesis to avoid any immature hydrolysis the alkoxides were
prepared using the Titanium tetrachloride and alcohol, alkoxide prepared is
reacted further with aqueous solution of barium hydroxide.
Titanium (IV) isopropoxide is prepared by diluting 11.0 ml (0.4 M) of Titanium (IV)
chloride into (80 ml amount of IPA) Isopropyl alcohol.
During the reaction aqueous solution of 0.2M barium hydroxide was prepared by
mixing 31.5 g of barium hydroxide octahydrate in the 390 ml of distilled water.
The weighed amount of sodium hydroxide was dissolved in 100 ml of water to
prepare 12 N alkaline solutions.
The addition time of barium solution during the reaction was also optimized. The
12N NaOH solution was added to maintain the pH of the reaction as pH= 8-9.
During the reaction the mixture is stirred continuously with high speed to avoid
any agglomeration and for preparing the homogenous solution. In order to
prevent the generation of barium carbonate (BaCO 3 ) the reaction is carried out
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under nitrogen atmosphere with continuous stirring. After complete addition of
reagents in the required amount the temperature of the reaction is increased
from 40 °C to 100 °C temperature. Thus during the course of work different
reaction parameters were studied. The reaction parameters such as reaction
time, reaction temperature were varied for the optimization of the reaction to
obtain pure and high yield. The optimization of the process parameters is
required to obtain the highest value of the dielectric constant. The reaction time
was varied from 10 minutes to 80 minutes. The reaction temperature is varied
from 40 ºC to 100 ºC. The prepared barium hydroxide solution is added in the
Titanium solution at constant rate at elevated temperature under nitrogen
atmosphere. After appropriate aging, BaTiO 3 suspension is filtered and washed
using soxhlet extractor for 24 hrs to remove the remaining sodium ions from the
filtered cake. This filtered cake is then kept in oven for overnight at 110 ⁰C. A
detailed flow chart of the synthesis process is presented in Figure 3.2.
Subsequently the powder so synthesized is used for preparation of pellets for
characterizations. The electrical measurements were carried out on the pellet,
thus the pellets were prepared using the synthesized BaTiO 3 powder by applying
a load of five ton for one minutes.
The
prepared
pellets
were
than
sintered
before
characterization
and
measurement. The optimization of sintering time and temperature is required for
best possible results from the product. The sintering time is varied from 1 hrs to 3
hrs and sintering temperature was varied 1000 ⁰C to 1200 ⁰C.
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Figure 3.2 Flow chart for Sol-Gel process
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3.2 Synthesis of Barium Titanate using Hydrothermal process
3.2.1 Materials
Barium Hydroxide Octahydrate Ba(OH) 2 .8H 2 O –Merck –GR grade
Titanium tetraisopropoxide 97 % solution– Aldrich Chemicals -GR grade
Isopropanol alcohol –Merck –GR grade
Tetra methyl ammonium hydroxide (TMAH) Merck –GR grade
All the chemical reagents were used without any prior purification.
3.2.2 Procedure
The barium titanate powders were synthesized using the barium precursors as
barium hydroxide octahydrate Ba(OH) 2 .8H 2 O, Titanium isopropoxide as titanium
precursors (Ti(i-OPr) 4 , TITP. Isopropyl alcohol was used as the diluting solvent
for the reaction. The typical set up of the reaction is shown in the Figure 3.1
used during the complete synthesis of barium titanate. Tetra methyl ammonium
hydroxide (TMAH, Merck) is used as an alkaline mineralizer. During synthesis
the aqueous solution of barium hydroxide octahydrate was prepared by
dissolving the weighed amount of solid in water. Simultaneously titanium
tetraisopropoxide was diluted using isopropanol in a four necked round bottom
flask as shown in Figure 3.1.
The aqueous barium solution was added drop wise in the Ti-isopropoxide
solution under continuous stirring and nitrogen atmosphere. The pH of the
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solution was maintained by TMAH. The temperature of the reaction increases
from room temperature to elevated temperature.
During this experiment, 41.76 gm of barium hydroxide octahydrate was dissolved
in 390 ml of hot water in an air tight round bottom flask fitted with agitator in the
presence of nitrogen and at an atmospheric pressure under agitation. The solid
dissolution us carried out in the hot water under inert atmosphere to avoid the
unwanted formation of barium carbonate (BaCO 3 ). After complete dissolution the
concentrated solution is filtered through wattmann paper to remove the unwanted
impurities. Simultaneously diluted 40 ml of titanium tetraisoproxide by dissolving
in 100 ml isopropanol under agitation in different reaction vessel.
The diluted solution of TITP is dropped slowly into the clear solution of Barium
Hydroxide under vigorous stirring. The solution resulted in white colloidal sol after
addition of 10 ml of TMAH as weak base to neutralize the weak acid generated in
reaction.
The
required
amount
of
barium
hydroxide
Octahydrate
and
Titanium
isopropoxide is used during the synthesis for maintaining Ba/Ti ratio about one.
The reaction mixture is than transferred to the autoclave sealed vessel under
nitrogen atmosphere. The hydrothermal synthesis is carried out to study the
effect of high temperature and pressure on the particle size of the ceramic
powder. The effect of different reaction parameters were also studied during the
course of work.
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The sealed vessel is heated at varied temperature 130, 150, and 170 ºC varying
the reaction time as 1–3 hr. The resultant precipitate is then cooled to room
temperature and washed with water several times and finally dried at room
temperature. Yield of barium titanate powder was 85 – 90 %.
The samples synthesized varying the reaction time and temperature are used for
further characterization and studied the dielectric properties. Thus the particles
size obtained from the different reactions are correlated with the dielectric
properties by converting the powder in to pellet form. The particles were
compacted or consolidated into pellets by pressing hydrostatically with a force of
4816 kg/cm2 for about one minute. The effect of sintering during the course of the
studies was carried out. The sintering time was varied from 1000-1200 ⁰C
varying the sintering time from 1-1.5 hr. %. A detailed flow chart of the synthesis
process is presented in Figure 3.3.
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Figure 3.3 Flow chart for Hydrothermal process
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3.3 Preparation of Pellets
The powder synthesized using wet chemical process was used further for
preparation of pellet by applying pressure of 4816 kg/cm2 for about one minute.
The effect of sintering was studied on the prepared pellets by varying the
sintering time and temperature. The conducting silver paste was applied on both
the surfaces of sintered pellets for measurement purpose. These silver pasted
sintered pellets were used measuring dielectric properties.
The microstructure of the sintered barium titanate is characterized by Scanning
Electron Microscopy on polished and thermally etched samples. Energy
Dispersive Spectroscopy (EDS) analysis is also conducted on the samples using
INCA X-Sight, Model 7583, Oxford make EDS attachment on the SEM. The
crystallite size is measured using line-broadening of X-ray diffraction signature
from the alloys. X-ray Diffraction work is performed on a Bruker AXS D8 Advance
X-Ray diffractometer using Ni filtered Cu-K α radiation. Normal XRD scans with
step resolution of 0.02° with time step of 0.5 sec is used. To ensure stability of
the measurements with respect to change in resolution in angular coordinates
and time, measurements are repeated with angular step size (in 2θ) of 0.05° with
time step of 2 sec. The Cu - K α2 diffraction signal is removed by a standard
stripping procedure to obtain the correct lattice parameters and grain size. The
relative dielectric constant (ε r ) and the dielectric loss (tanδ) are measured at
room temperature using Genrad 1658, RLC Digibridge. All measurements are
made at 50 Hz, by applying 1 V potential difference across the test capacitor.
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The dielectric measurements for each sample synthesized varying the reaction
time and temperature of the materials is listed in Chapter V Results and
discussion. Thus, on detail studies and optimizing the reaction parameters the
best synthesized materials was used further for dopant studies and polymer
ceramic composite studies.
3.4 Doping of Barium Titanate with Rare Earth Elements
The barium titanate powder synthesized using optimized hydrothermal process is
further used for studying the effect of rare earth elements Lanthanum and
Magnesium as Dopants for the ceramic powder.
3.4.1 Materials
Hydrothermally synthesized BaTiO 3 powder
Lanthanum chloride - Merck GR grade
Magnesium chloride - Merck GR grade
3.4.2 Procedure
Barium Titanate powder was doped with the rare earth elements using the wet
chemical process. During the process hydrothermally synthesized barium titanate
is used for the dopant studies. The ceramic rare earth dopants were added to
Barium Titanate using the chemical route synthesis, to study the doping effect on
Barium Titanate for improving its dielectric properties.
The Barium Titanate was synthesized via hydrothermal process as mentioned
above. The solution of Lanthanum chloride LaCl 3 was prepared by dissolving a
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required amount of LaCl 3 in distilled water. The resultant solution was added
drop wise in the main solution of Barium Titanate under continuous stirring. The
whole solution was fitted in the autoclave under the inert atmosphere. The
reaction was continued at optimized reaction temperature and time for 150°C and
2 hr. The temperature and the pressure of the reaction have to be maintained
during the course of the reaction. The material was cooled to room temperature,
filtered washed and dried. Different sets of reactions were carried out varying the
concentration from 0.1 to 1 wt % with respect to Barium Titanate. The resulting
powder was used further for different characterization studies including its
dielectric properties.
Similarly, the effect of magnesium doping (MgCl 2 .2H 2 O) with Barium Titanate
was also studied using hydrothermal process by varying concentration from 0.1
to 1 wt% and studying its dielectric properties. The Magnesium chloride was
dissolved in water and was added to the reaction mixture of barium titanate
solution dropwise and allowed the reaction to continued for 2 hours at 150 ºC.
The materials was filtered, washed and dried.
The doped powders were dried and were used for further characterization and
studied the dielectric properties.
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3.5 Surface Modification of Barium Titanate
The hydrothermally synthesized barium titanate powder using the optimized
reaction process having highest dielectric constant is used for preparation of
polymer ceramic nanocomposites. The surface modification of powder was
required to increase the compatibility of the powder with polymer matrix.
3.5.1 Materials
Hydrothermally synthesized Barium titanate
3-Glycidoxypropyl (trimethoxy) silane –Aldrich
Acetic acid-Merck
3.5.2 Procedure
Hydrothermally prepared nano Barium Titanate was organically modified using
3-Glycidoxypropyl (trimethoxy) silane. The different aqueous solutions of 0.1, 0.3
and 0.5 wt% of silane (with respect to Barium Titanate) were prepared. During
addition of silane to the acidified water, the system was stirred for about 15 min
before it hydrolyzed and formed a clear and homogeneous solution. The weighed
amount of powder was mixed with the aqueous silane solution. The silane was
applied on ceramic nanoparticles as diluted in order to improve processability
and to increase filler wetting and dispersion. Aqueous solution was prepared,
adjusting the pH of the water to 3.5 with acetic acid and then introducing the
silane. The fillers were mixed with the silane for several minutes without
additional solvent. After applying the silane, the powder of BaTiO 3 was dried at
110 °C to avoid condensation of silanol groups at the surface. Silane treated
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Barium Titanate was crushed in motor pastel. The crushed powder was sieved
and it was used to prepare nanocomposites.
3.6 Preparation of Polymer-Ceramic composites
3.6.1 Materials
Silane modified Barium titanate
Epoxy- Diglycidyl ether of Bisphenol-A (DEGBA) Kuver Chemicals
Poly (vinylidene fluoride) (PVDF) - Aldrich Chemicals
Polyvinylbutyral (PVB) - National Chemicals
Di-n-octyl phthalate-SULAB chemicals
Dimethyl formamide (DMF)– LR grade
3.6.2 Procedure
Hydrothermally synthesized Barium Titanate using optimized process was used
for preparation of polymer ceramic nanocomposites. Glycidoxytrimethoxy silane
was applied onto ceramic particles as diluted aqueous solutions of 0.1, 0.3 and
0.5 wt% (with respect to Barium Titanate) of silane in order to improve
processability and increase filler wet-out and dispersion. Aqueous solution was
prepared, adjusting the pH of the water to 3.5 with acetic acid and then
introducing the silane. After the silane was added to the acidified water, the
system was stirred for about 15 min before it hydrolyzed and formed a clear and
homogeneous solution. The fillers were mixed with the silane for several minutes
without additional solvent. After applying the silane, the BaTiO 3 was dried at 110
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°C to avoid condensation of silanol groups at the surface. The detection of small
quantities of silane in the products after the silanization process was achieved by
Fourier Transform Infrared Spectrometry (FTIR).
3.6.2.1 Epoxy-Ceramic Composite
Weighed amount of silane modified Barium Titanate powder and epoxy resin
were mixed efficiently using mechanical stirrer for 5 min at speed of 1000 RPM.
The mixture was stirred and a weighed amount of commercially available curing
agent was added in the reaction mixture and stirred for five more seconds. The
whole reaction mixture was subsequently poured in the mould. The material was
cured at room temperature for two hours followed by post curing at 60 °C for one
hour. The composite so prepared was released out of mould. The different
composites were prepared by varying the percentage of barium titanate loading
from 60 to 90 wt%. The composites were evaluated for the dielectric properties.
3.6.2.2 PVDF-Ceramic Composite
The granule of PVDF was dissolved in Dimethyl formamide (DMF). The silane
modified hydrothermally synthesized barium titanate powder was mixed in parts
under continuous stirring.
The calculated amount of di-n-octyl phthalate was
added and mixed well and allowed to cure at room temperature. The different
composites were prepared by varying the percentage of barium titanate loading
from 60 to 90 wt%. The composites were evaluated for the dielectric properties.
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3.6.2.3 PVB-Ceramic Composite
The powder of PVB was dissolved in Dimethyl formamide (DMF). The silane
modified hydrothermally synthesized barium titanate powder was mixed in parts
under continuous stirring.
The calculated amount of di-n-octyl phthalate was
added and mixed well and allowed to cure at room temperature. The different
composites were prepared by varying the percentage of barium titanate loading
from 60 to 90 wt%. The composites were evaluated for the dielectric properties.
All these above mentioned samples, powders, modified BT powder, doped BT
powder and polymer composites were characterized using different analytical
techniques. These samples were also tested for dielectric measurements.
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