1. Summer Training (2014) Report
On
“Characterization of 8 mole% yttria stabilized zirconia
obtained from different sources”
By
Khagesh Kumar Tanwar
Under the supervision of
Dr. Abhijit Das Sharma, Principal Scientist
Fuel Cell & Battery Division
CSIR-Central Glass & Ceramic Research Institute
Kolkata - 700032

2. Introduction: - Solid oxide fuel cell (SOFC) is a ceramic device that converts the chemical energy
of a fuel gas and an oxidant gas directly to electrical energy without combustion as an
intermediate step. Solid oxide fuel cells are a class of fuel cells characterized by the use of a
solid oxide material as the electrolyte. The main function of an electrolyte is to conduct ions
between anode and cathode. The conductivity through the electrolyte should be only because
of ions, electronic conductivity must be kept as low as possible to prevent losses from leakage
currents. From the last decades of research it has been observed that the stabilized zirconia is
most convenient in order to fulfill the desirable properties of the electrolyte. Stabilized zirconia
has been used almost exclusively as the electrolyte in SOFCs. ZrO2, in its pure form, exhibits
three well-defined polymorphs. At room temperature, ZrO2 has a monoclinic structure changes
to a tetragonal form above 11700
c and to a cubic fluorite structure above 23700
C. The
monoclinic/tetragonal transformation in ZrO2 is thermodynamically reversible but associated
with large volume change (3 to 5%) (Contraction on heating and expansion on cooling). The
cubic phase exists up to the melting point of 26800
C. However, the addition of certain aliovalent
oxides can stabilize the cubic fluorite structure of ZrO2 from room temperature to its melting
point. Stabilization of cubic polymorph of zirconia over wider range of temperatures is
accomplished by substitution of some of the Zr4+
ions (ionic radius of 0.82 A0
, too small for ideal
lattice of fluorite characteristic for tetragonal zirconia) in the crystal lattice with slightly larger
ions, e.g., those of Y3+
(ionic radius of 0.96 A0
). The common stabilizing oxides for ZrO2 are CaO,
Y2O3, MgO, Sc2O3 and certain rare-earth oxides. Yttria is added to stabilize the conductive cubic
fluorite phase, as well as to increase the concentration of oxygen vacancies, and thus increase
the ionic conductivity. The ionic conductivity of YSZ (yittria stabilized zirconia) increases for
yttria addition of up to about 8-9 mole% (fully stabilized zirconia) then decreases for higher
yttria content. Due to good mechanical, excellent chemical stability and adequate level of
oxygen-ion conductivity in both oxidizing and reducing environment, yttria stabilized zirconia
(ZrO2-8%Y2O3) is the most used electrolyte in SOFCs applications [1].
Density of an electrolyte is the most considerable factor in order to increase the oxygen-ion
conductivity of electrolyte and efficiency of the cell, low density leads to leakage of fuel through
the electrolyte and also reduce the ionic conductivity by providing more pore space. So the
electrolyte must be dense (or contain no connected porosity) to prevent gas cross leakage.
Density of YSZ also increases with increase in sintering temperature up to a certain value and
then start decreasing. During the process sintering particles comes closer to each other and
formation of grains takes place and also some pores get created at the intersections of grain
boundaries. The rate of grain growth will be high if the particles are in Nano range than the
particles in micro range. If the rate of grain growth is so high then pores may be created on the
grains (formation of grains takes place by leaving the pores behind) but they weaken the
electrolyte. The theoretical density of YSZ is 5.95 gm. /cc.

3. Research objectives
The main objectives of this research are:
1. Characterization of 8mole% YSZ (from ISRO, IRE and TOSOH) powder.
Optimization of pallets by sintering to achieve high density, suitable for use as an
electrolyte in SOFC.
2. To compare the results of 8 mole% YSZ powders obtained from separate suppliers.
3. To characterize the physical properties of sintered pallets.
Research plan:
Powder characterization:
1. Tap density measurement.
2. BET surface area measurement.
3. Phase study before sintering by using XRD.
4. Particle size distribution.
5. Thermogarvimetric analysis.
Bulk sample fabrication and characterization:
1. Compaction under different load.
2. Densification study as a function of temp and compaction load.
3. Measurement of porosity and volume shrinkage with the help of density.
4. Density measurement
 Measuring the green density by geometric volume measurement
(vernier calipers) method.
 Measuring the density after sintering using two methods; geometric
volume measurement (vernier calipers) method and Archimedes
method.
5. Dilatometric analysis.
 Thermal expansion co-efficient.
6. Microstructural study of the optimized sample.
 SEM(Scanning electron microscopy)

4. Theory and Experimental:
Tap density:-
It is a term used to describe the bulk density of a powder after consolidation prescribed in
terms of “tapping” the container of powder. The method of tapping is best described as “lifting
and dropping”. Tapped density is variously reported in units such as g/cc, lb. /cu. Ft [2].
Bulk density:
Bulk density of a powder simply expresses the amount, usually weight or mass, of powder in a
specified volume.
However, since powders are composed of particles and voids, the volume occupied by a given
number of particles depends on how closely they are packed. The packing of particles are
depends on their shape, cohesiveness, short range motion and external forces. Practically the
bulk density of a powder tends to increase the more it is subjected to tapping, vibration and
other mechanical action which cause particles to occupy the voids between larger voids.
Measurement of tapped density:-
The tapped density is obtained by mechanically tapping a graduated glass measuring cylinder
containing the sample until no further change in volume is observed. The cylinder can be
tapped manually or by mechanical device.
Manual tapping: - In this method the tapping (lowering and rising) of the cylinder is done by
hand. It can be done either a) without reference to the height traversed and arbitrary
acceleration in both upward and downward directions. In this process the hand remaining in
contact with the cylinder all the times, or b) by fixing the upward distance traveled and allowing
free-fall of the cylinder under gravity (drop box).
Carr’s index and hausner ratio:-
Carr’s index is also known as compressibility ratio. The inter particulate interactions that
influence the bulking properties of the powder are also the interactions that deals with flow
properties of powder. It is possible to gain information about the relative importance of these
interactions in a given powder by comparing the bulk and tapped densities, and such a
comparison can be used to index the ability of the powder to flow [2].

5. The compressibility index and hausner ratio are measures of the products ability to settle, and
permit an assessment of the relative importance of inter particulate interactions. In a free-
flowing powder these interaction are less significant and the bulk densities will be closer in
value. For poorly flowing materials, these are greater inter particulate interactions and a
greater difference between the densities will be observed.
The Carr’s compressibility index is the percentage change in powder bulk volume upon tapping
volume.
Carr’s Index = (v0 – vf)*100/v0
Hausner ratio is the fractional change in volume from “loose” to “tapped”.
Hausner ratio = v0 /vf
V0 = unsettled apparent volume (bulk volume).
V f = final tapped volume.
BET surface area measurement
The Brunauer-Emmett-Teller (BET) method is the most widely used procedure for the
determination of the surface area of solid material and involves the use the BET equation.
{1/W(P0/P - 1)} = {1/Wm C} + {(C – 1)(P/P0)/Wm C} ---(1)
In which W is the weight of gas adsorbed at a relative P/P0 and Wm is the weight of adsorbate
constituting a monolayer of surface coverage. The term C, the BET C constant, is related to the
energy of adsorption in the first adsorbed layer and consequently its value is in an indication of
the magnitude of the adsorbent/adsorbate interaction.
Multiple BET method
The BET equation (1) requires a linear plot of {1/W(P0/P - 1)} Vs P/P0 which for more solids,
using nitrogen as the adsorbate, is restricted to a limited region of the adsorption isotherm,
usually in the P/P0 range of 0.05 to 0.35. This linear region shifted to lower relative pressure for
micro porous materials.
The standard multipoint BET procedure requires a minimum of three points in the appropriate
relative pressure range. The weight of the monolayer of adsorbate Wm can be obtained from
the slop S and intercept I of the BET plot from equation (1)

6. S = (C – 1)/Wm C ---(2)
I = 1/ Wm C ---(3)
Thus, the weight of a monolayer Wm can be obtained by combining equation (2) and (3)
Wm = 1/(S+i) ---(4)
The second step in the application of the BET method is the calculation of the surface area. This
requires knowledge of the molecular cross-sectional area Acs of the adsorbate molecule. The
total surface area St of the sample can be expressed as:
St = (Wm* N* Acs)/M ----(5)
Where N is Avogadro’s number (6.023*1023
molecule/mole) and M is the molecular weight of
the adsorbate. Nitrogen is the most widely used gas for surface area determination since it
exhibits intermediate values for the C constant (50 - 250) on most solid surfaces, precluding
either localized adsorption or behavior as a two dimensional gas. Since it has been stabilized
that C constant influences the value of the cross-sectional area of n adsorbate, the acceptable
range of C constant for nitrogen makes it possible to calculate its cross-sectional area from its
bulk liquid properties. For the hexagonal closed-packed nitrogen monolayer at 77k, the cross-
section area Acs for nitrogen is 16.2 A0
.
The specific surface area S of solid can be calculated from the total surface area St and the
sample weight W, according to the equation (6)
S = St/W ---(6)
The specific surface area is increased as the particle size becomes small. The specific surface
area also increased if the particle has pores.
The average particle size can be determined from BET specific area by assuming the all particles
spherical in shape and density equal to theoretical density (5.95 gm. / cc).
d = 6/(ABET *ρ)
d= average particle diameter.
ρ = theoretical density (5.95 gm. / cc).
ABET = BET surface area of particles.

7. X-ray Diffraction:
X-ray diffraction (XRD) is an analytical technique looking at X-ray scattering from crystalline
materials. Each material produces a unique X-ray "fingerprint" of X-ray intensity versus
scattering angle that is characteristic of its crystalline atomic structure. Qualitative analysis is
possible by comparing the XRD pattern of an unknown material to a library of known patterns.
X-ray crystallography is a tool for identifying the atomic and molecular structure of a crystal, in
which the crystalline atoms cause a beam of incident x-ray to diffract into many specific
directions. By measuring the angles and intensities of the beams, a crystallographer can
produce a three- dimensional picture of the density of electron within the crystal. From this
electron density, the mean position of the atoms in the crystal can be determined, as well as
their chemical bonds, their disorder and various other information.
Since many materials can form crystal – such as salts, metals, minerals, semiconductor, as well
as various inorganic, organic and biological molecules. X-ray crystallography has been
fundamental in the development of many scientific fields.
An electron in an alternating electromagnetic field will oscillate with the same frequency as the
field. When an x-ray beam hits an atom, the electrons around the atom start to oscillate with
the same frequency as the incoming beam. In almost all directions we will have destructive
interference, that is, the combining waves are out of phase and there is no resultant energy
leaving the solid sample. However the atoms in a crystal are arranged in a regular pattern, and
in a very few directions we will have constructive interference. The waves will be in phase and
there will be well defined x-ray beams leaving the sample at various directions. Hence, a
diffracted beam may be described as a beam composed of a large number of scattered rays
mutually reinforcing one another. This model is complex to handle mathematically, and in day
to day work we talk about x-ray reflections from a series of parallel planes inside the crystal.
The orientation and inter planar spacing of these planes are defined by the three integers h, k
and l called indices. A given set of planes with indices h, k and l cut the a-axis of the unit cell in h
sections, the b axis in k sections and the c axis in l sections. A zero indicates that the planes are
parallel to the corresponding axis. E.g. the 2, 2, 0 planes cut the a– and the b– axes in half, but
are parallel to the c– axis.
Directions in which we have constructive interference is determined by Bragg’s law:
2dsinθ = nλ
Here d is the spacing between diffracting planes, θ is incident angle, n is any integer, and λ is
the wavelength of the beam.

8. The two parallel incident rays 1 and 2 make an angle (THETA) with these planes. A reflected
beam of maximum intensity will result if the waves represented by 1’ and 2’ are in phase. The
difference in path length between 1 to 1’and 2 to 2’ must then be an integral number of
wavelengths, (LAMBDA). We can express this relationship mathematically in Bragg’s law. The
process of reflection is described here in terms of incident and reflected (or diffracted) rays,
each making an angle THETA with a fixed crystal plane. Reflections occurs from planes set at
angle THETA with respect to the incident beam and generates a reflected beam at an angle 2-
THETA from the incident beam. The possible d-spacing defined by the indices h, k, l are
determined by the shape of the unit cell.
Rewriting Bragg’s law we get:
Sin θ = λ/2d
Therefore the possible 2-THETA values where we can have reflections are determined by the
unit cell dimensions. However, the intensities of the reflections are determined by the
distribution of the electrons in the unit cell. The highest electron density is found around
atoms. Therefore, the intensities depend on what kind of atoms we have and where in the unit
cell they are located. Planes going through areas with high electron density will reflect strongly,
planes with low electron density will give weak intensities.
In x-ray diffraction measurement, a crystal is mounted on a goniometer and gradually rotated
while being bombarded with x-ray, producing a diffraction pattern of regularly spaced spots
known as reflections. The two-dimensional images taken at different rotation are converted
into three-dimensional model of the density of electron within the crystal using the
mathematical method of Fourier transforms, combined with chemical data known for sample.

9. Particle size distribution:-
The particle-size distribution (PSD) of a powder, or granular material, or particles dispersed
in fluid, is a list of values or a mathematical function that defines the relative amount, typically
by mass, of particles present according to size. PSD is also known as grain size distribution. The
PSD of a material can be important in understanding its physical and chemical properties. It
affects the strength and load-bearing properties of rocks and soils. It affects the reactivity of
solids participating in chemical reactions, and needs to be tightly controlled in many industrial
products such as the manufacture of printer toner, cosmetics, and pharmaceutical products.
Particle size influences many properties of particulate materials and is a valuable indicator of
quality and performance. This is true for powders, suspensions, emulsions, and aerosols. The
size and shape of powders influences flow and compaction properties. Larger, more spherical
particles will typically flow more easily than smaller or high aspect ratio particles. Smaller
particles dissolve more quickly and lead to higher suspension viscosities than larger ones.
Smaller droplet sizes and higher surface charge (zeta potential) will typically improve
suspension and emulsion stability. Particle size growth may be monitored during operations
such as granulation or crystallization. The size and shape distribution of the particles impacts
powder behavior during die filling, compaction, and sintering, and therefore influences the
physical properties of the parts created.
A spherical particle can be described using a single number—the diameter— because every
dimension is identical. But in case of non-spherical particles it can be described using multiple
length and width measures. These descriptions provide greater accuracy, but also greater
complexity. Thus, many techniques make the useful and convenient assumption that every
particle is a sphere. The reported value is typically an equivalent spherical diameter. This is
essentially taking the physical measured value (i.e. scattered light, settling rate) and
determining the size of the sphere that could produce the data. Although this approach is
simplistic and not perfectly accurate, the shapes of particles generated by most industrial
processes are such that the spherical assumption does not cause serious problems. Problems
can arise, however, if the individual particles have a very large aspect ratio, such as fibers or
needles. Shape factor causes disagreements when particles are measured with different
particle size analyzers. Each measurement technique detects size through the use of its own
physical principle. For example, a sieve will tend to emphasize the second smallest dimension
because of the way particles must orient themselves to pass through the mesh opening. A
sedimentometer measures the rate of fall of the particle through a viscous medium, with the
other particles and/or the container walls tending to slow their movement. Flaky or plate-like
particles will orient to maximize drag while sedimenting, shifting the reported particle size in
the smaller direction. A light scattering device will average the various dimensions as the
particles flow randomly through the light beam, producing a distribution of sizes from the
smallest to the largest dimensions. The only techniques that can describe particle size using
multiple values are microscopy or automated image analysis. It’s always not essential to choose
the automated image analyzing method because it depends on situation. So here we measure
the particle size by dynamic light scattering (DLS) method [4].

10. Dynamic Light Scattering (DLS) can measure suspensions and emulsions from 1nm to 1µm.
Both the lower and upper limits are sample dependent. The lower limit is influenced by
concentration and how strongly the particles scatter light. A low concentration sample of
weakly scattering particles near 1nm can be extremely difficult or at least difficult to reproduce.
The upper size limit is determined mainly by the density of the particles. DLS algorithms are
based on all particle movement coming from Brownian motion. Motion due to settling is not
interpreted correctly by DLS systems. In addition, particles settled on the bottom of the sample
cuvette cannot be inspected by the laser light source. Particles with a high density will settle
more quickly than low density particles. The upper limit of DLS may be 8µm for emulsion
samples where the two phases have similar density. The upper limit of uranium particles may
be as small as 300nm. The upper limit of particles with a density of 1.7 may be around 1µm.
Using DLS does not require any knowledge of the sample RI (it would be required to convert
from intensity to volume distribution), or concentration. What is required is viscosity, especially
for higher concentration samples. More sophisticated DLS systems can also measure other
sample characteristics including zeta potential, molecular weight, and second virial coefficient.
Generating this additional information may require a greater skill set of the operator.
Particle size can be determined by measuring the random changes in the intensity of light
scattered from a suspension or solution. Small particles in suspension undergo random thermal
motion known as Brownian motion. This random motion is measured to calculate particle size
using the process described below.
Light from the laser light source illuminates the sample in the cell. The scattered light signal is
collected with one of two detectors, either at a 90 degree (right angle) or 173 degree (back
angle) scattering angle. The obtained optical signal shows random changes due to the randomly
changing relative position of the particles.
Fig: - Autocorrelation function from DLS for a sample where all the particles are the same size.
The signal can be interpreted using an autocorrelation function. Incoming data is processed in
real time with a digital signal processing device known as a correlator and the autocorrelation
function, shown in figure as a function of delay time, τ, is extracted. The autocorrelation
function from dynamic light scattering in Figure shows a sample where all of the particles are
the same size, the baseline subtracted autocorrelation function, C, is simply an exponential
decay of the following form:

11. C = exp(-2Γτ)
Γ is readily derived from experimental data by a curve fit. The diffusion coefficient is obtained
from the relation Γ=Dt*q2
where q is the scattering vector, given by q=(4πn/λ)sin(θ/2). The
refractive index of the liquid is n. The wavelength of the laser light is λ, and scattering angle, θ.
Inserting Dt into the Stokes-Einstein equation then solves for particle size Dh is the final step.
Dh = KB T/3πηDt
Where:
Dh = the hydrodynamic diameter
Dt = the translational diffusion coefficient
KB = Boltzmann’s constant
T = temperature
η = dynamic viscosity
Thermogravimetric analysis and Differential thermal analysis (TG-DTA): -
Substance subjected to thermal treatment may undergo physical or chemical changes such as
magnetic properties, dimension, weight, crystalline transition and mechanical properties which
can be measured by different -2 techniques. To measure the change in weight with the function
of temperature we use the TGA-DTA technique. Thermogravimetric analysis (TGA) is a
technique to determine changes in sample weight in relation to changes in sample
temperature. In this test a sample is suspended on a highly sensitive balance over a precisely
controlled furnace. Different components decompose by different characteristic temperatures.
So in this technique it is possible to identify the component by knowing the decomposition
graph (weight changes Vs time).
Differential thermal analysis (DTA) in this technique the heat flow to the sample and reference
is the same. As the sample and the reference are heated identically, phase changes and other
thermal processes occurring in the sample will cause a difference in temperature between the
sample and reference. DTA measures this temperature difference. DTA involves heating or
cooling a test sample and an inert reference under identical conditions, while recording any
temperature difference between the sample and reference. Changes in the sample which lead
to the absorption or evolution of heat can be detected relative to the inert reference. DTA
curve can be used as a fingerprint for identification purposes [5].

12. Bulk sample fabrication and characterization:-
Bulk sample fabrication by compaction:
Compaction:
Compaction is one of the most important stages in sinter-forming route. It gives the powder an
initial shape and provides necessary strength for handling of further processes. It depends on
an external source of pressure for deforming the powders into a relatively high density mass,
also providing shape and dimensional control to the powder. The pressure determines the
densities of the components. With sufficiently high green density, it is possible to produce high
density with small grain size at relatively low sintering temperature [6].
Sample preparation:
Pallets were prepared using 8YSZ powder and 2% PVB was used as binder. Ethyl methyl ketone
was used to mix the powder and binder. The homogeneous mixture was then kept under IR
lamp to dry it. Now 1.5 gm. of powder was taken to prepare each pallet, pressed it under
different loads (2tons and 4tons) for 1.5 minutes in a die of 15mm diameter. Twenty pallets
were prepared for each powder (ten pallets under each 2T and 4T loads).
Densification study as a function of temp and compaction load:
Sintering:
Sintering is the process of forming a solid mass of material by heat without melting it to the
point of liquefaction. Sintering happens naturally in mineral deposits or as a manufacturing
process used with metals, ceramics, plastics, and other materials. The atoms in the materials
diffuse across the boundaries of the particles, fusing the particles together and creating one
solid piece. Because the sintering temperature does not have to reach the melting point of the
material, sintering is often chosen as the shaping process for materials with extremely high
melting points such as tungsten and molybdenum. An example of sintering can be observed
when ice cubes in a glass of water adhere to each other [6].
Stages of sintering:
The entire process of sintering can be categorized into three stages:
Stage 1: The particle contacts are transformed to sintered contacts or necks. Powder particles
remain detached. At the plane of contact grain boundaries can be created between two
contiguous particles.
Stage 2: I t‘s the intermediate stage where single particles resume loosing their identity when
the x: a ratio goes over a certain value after strong neck growth. Pores form a consistent

13. network and grain growth occurs, that result in the formation of a new micro structure. This
stage witnesses the most of the shrinkages.
Stage 3: At the point when the apparent density becomes 90 to 95% of the theoretical density,
the relative proportion of the closed pore spaces increase very rapidly and the isolated pores
turn into spheroidised. If cannot diffused, gas stay enclosed in the porosity and further
densification becomes impossible as the gas pressure reaches equilibrium with the pressure
due to surface tension, For fine grained micro structures, some additional low densification can
occur when gases trapped is easy to diffuse in the solid matrix or pores are empty [6].
Effect of sintering on pore structure:
The sintering rate is governed by the geometry of the grain boundary and the pore during
intermediate stage. At the onset of the intermediate stage, the pore geometry is extremely
convoluted and the pores are situated at grain boundary intersections. As sintering continues,
the pore geometry comes close to a cylindrical shape in which densification happens by
decreasing of the pore radius. For the period of sintering, the interaction between pores and
grain boundaries can have three forms as follows:
• Pore scan slow down grain growth.
• Pores can be dragged by the moving grain boundaries at the time of any grain growth.
• Grain boundaries can disintegrate from the pores, leaving pores isolated in the grain interior.
Most materials show moderate to high grain growth rates at the temperatures typical of
sintering; any differences in initial grain sizes produce forces on the grain boundaries that cause
grain growth. When the temperature is increased, the rate of grain boundary motion also
increases. The reason of Breaking away of the boundaries from the pores occurs is that the
pores are slower moving than the grain boundaries. When tension is created by a moving grain
boundary, pores can move by volume or surface diffusion or even by evaporation-condensation
across the pore. However, this requires close control of the heating rate, using a process
termed rate-controlled sintering [6].
Densification:
During densification process, the lower mobility of the pores coupled to the diminishing pinning
force allows breakaway. Separation of the pores from the boundaries confines the potential
final density. Therefore, it is important to minimize breakaway by careful processing control. A
combination of large pore size and grain size spearheads towards breakaway during grain
growth. In the ideal case, the large pores are immobile in the early stages of sintering and are
pinned against, the grain boundaries to maintain a small grain size. During the later stages of
sintering, the pores become fewer in number and diminish in size due to shrinkage. Even
though the grains are relatively large, the pores are sufficiently mobile to migrate with the
boundaries. Densification depends on the rate of pore shrinkage while this situation persists
and high grain boundary diffusivity is helpful. During the process, as the pore size decreases,
there is less inhibition to grain growth and pore mobility is a greater concern. For the pores to
remain on the moving grain boundaries, it is essential to increase their mobility, for instance, by

14. increasing surface diffusivity. Rapid grain growth should be avoided as in variably the
densification rate is low.
Ceramic materials that show a high sensitivity to residual porosity could be improved in
properties by the understanding of the mechanisms by which the breakaway event can be
avoided. The dominant factor in the rate of densification is the effect of temperature among
other factors including grain size, density, and time. In case bulk diffusion is in active at the end
of the initial stage of sintering, there will be no densification. However, pore growth and
possibly grain growth might be active. Pore rounding takes place simultaneously with
densification. When the pores spheroidise in to a closed structure, approximately 8% porosity,
the final stage of sintering occurs. Most materials are sintered to densities over 92% of
theoretical and send into the final stage. During intermediate stage sintering, Surface transport
is active. It helps to smooth the pore structure and allow pore migration with grain boundaries
during grain growth. However, surface transport does not contribute to densification or
shrinkage. The specific sintering events depend on the micro structure (grain size, pore size, and
pore spacing). Besides, since the micro structure is continually changing, the influence of
temperature can be quite prominent. A high diffusivity and a small grain size [72] enhance the
densification rate. Grain growth is slowed down by pores, dispersoids, and second phase
inclusions. So these can be used to improve densification. Final stage sintering is a process
where spherical pores shrink by a diffusion mechanism and thus it’s as low one. Should the
pores have a trapped gas, then solubility of the gas in the matrix will influence the rate of pore
elimination. Because of this, it is preferable to sinter in vacuum or to use an atmosphere that is
soluble in the sintering material. When a gas is sealed in the pores, internal gas pressure
controls the densification rate. If the closed pores are mobile enough to stay coupled to the
grain structure, then shrinkage will go on further to the final stage. A homogeneous grain size
and sintering in a vacuum helps densification in the final stage in most materials, the
distributions in particle size and packing create a pore size distribution. The longer the sintering
times the lesser is the number of pores. Besides, pore size coarsens in that case while the total
porosity may even increase. Differences in pore curvature will result in the growth of the larger
pores at the expense of the smaller, less stable pores. This process is well-known as Ostwald
ripening. To attain 100% density by sintering, it requires precise manipulation of the initial
powder micro structure and heating cycle, because several factors can inhibit final pore
elimination [6].
Porosity: -
Porosity or void fraction is a measure of the void (i.e., "empty") spaces in a material, and is a
fraction of the volume of voids over the total volume, between 0 and 1, or as a
percentage between 0 and 100%. There are many ways to test porosity in a substance or part,
such as industrial CT scanning. The term porosity is used in multiple fields
including pharmaceutics, ceramics, metallurgy, materials, manufacturing, earth sciences, soil
mechanics and engineering. Porosity also can be measured by density by the formula given
below.
Porosity = {1 – (Dexp. /Dtheo.)} * 100

15. In case of an electrolyte porosity should be very low because it may decrease the oxygen-ion
conductivity of electrolyte and efficiency of the cell, high porosity leads to leakage of fuel
through the electrolyte and also reduce the ionic conductivity by providing more pore space.
Archimedes density: -
Archimedes principle indicate that the upward buoyant force that is exerted on a body
immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that
the body displaces.
The weight of the displaced fluid is directly proportional to the volume of the displaced fluid (if
the surrounding fluid is of uniform density). The weight of the object in the fluid is reduced,
because of the force acting on it, which is called up thrust. In simple term, the principle states
that the buoyant force of an object is equal to the weight of fluid multiplied by the submerged
volume times the gravitational constant g.
For fully submerged object, Archimedes principle can be reformulated as follows:
Apparent immerged weight = weight of object – wt. of displaced fluid
(Density of object)/(density of fluid) = (weight of sample)/ (weight of
placed fluid)
 (Density of object)/ (Density of fluid) = (weight of object)/ (wt. of object – apparent
immerged wt.)
 Do/Df = Wo/(Wo - Wa)
 Do = (1- Wo/Wa)* Df
Do = density of object
Df = density of fluid (0.86 gm. /cc for xylene)
Wo = weight of object
Wa = apparent immersed weight
Thermal expansion coefficient: -Thermal expansion is the tendency of matter to change
in volume in response to a change in temperature, through heat transfer. When a substance is
heated, its particles begin moving more and thus usually maintain a greater average separation.
Materials which contract with increasing temperature are unusual; this effect is limited in size,
and only occurs within limited temperature ranges. The degree of expansion divided by the
change in temperature is called the material's coefficient of thermal expansion and generally
varies with temperature. Specifically, it measures the fractional change in size per degree
change in temperature at a constant pressure. Several types of coefficients have been

16. developed: volumetric, area, and linear, which is used depending on the particular application
and which dimensions are considered important. For solids, one might only be concerned with
the change along a length, or over some area. The volumetric thermal expansion coefficient is
the most basic thermal expansion coefficient. In general, substances expand or contract when
their temperature changes, with expansion or contraction occurring in all directions.
Substances that expand at the same rate in every direction are called isotropic. For isotropic
materials, the area and linear coefficients may be calculated from the volumetric coefficient.
Materials generally change their size when subjected to a temperature change while the
pressure is held constant. In the special case of solids materials, the pressure does not
appreciably affect the size of an object, and so, for solids, it's usually not necessary to specify
that the pressure be held constant.
Common engineering solids usually have coefficients of thermal expansion that do not vary
significantly over the range of temperatures where they are designed to be used, so where
extremely high accuracy is not required, practical calculations can be based on a constant,
average, value of the coefficient of expansion [8].
Linear thermal expansion:
To a first approximation, the change in length measurements of an object ("linear dimension"
as opposed to, e.g., volumetric dimension) due to thermal expansion is related to temperature
change by a "linear expansion coefficient". It is the fractional change in length per degree of
temperature change. Assuming negligible effect of pressure, we may write:
Where is a particular length measurement and is the rate of change of that linear
dimension per unit change in temperature.
The change in the linear dimension can be estimated to be:
This equation works well as long as the linear-expansion coefficient does not change much over
the change in temperature . If it does, the equation must be integrated [8].
SEM (Scanning electron microscopy): -
A scanning electron microscope (SEM) is a type of electron microscope that produces images of
a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in
the sample, producing various signals that can be detected and that contain information about

17. the sample's surface topography and composition. The electron beam is generally scanned in a
raster scan pattern, and the beam's position is combined with the detected signal to produce
an image. SEM can achieve resolution better than 1 nanometer. Specimens can be observed in
high vacuum, in low vacuum, (in environmental SEM) in wet conditions and at a wide range of
cryogenic or elevated temperatures. The most common mode of detection is by secondary
electrons emitted by atoms excited by the electron beam. The number of secondary electrons
is a function of the angle between the surface and the beam. On a flat surface, the plume of
secondary electrons is mostly contained by the sample, but on a tilted surface, the plume is
partially exposed and more electrons are emitted. By scanning the sample and detecting the
secondary electrons, an image displaying the tilt of the surface is created.
The types of signals produced by a SEM include secondary electrons (SE), back-scattered
electrons (BSE), characteristic X-rays, light (cathodoluminescence) (CL), specimen current and
transmitted electrons. Secondary electron detectors are standard equipment in all SEMs, but it
is rare that a single machine would have detectors for all possible signals. The signals result
from interactions of the electron beam with atoms at or near the surface of the sample. In the
most common or standard detection mode, secondary electron imaging or SEI, the SEM can
produce very high-resolution images of a sample surface, revealing details less than 1 nm in
size. Due to the very narrow electron beam, SEM micrographs have a large depth of field
yielding a characteristic three-dimensional appearance useful for understanding the surface
structure of a sample. This is exemplified by the micrograph of pollen shown above. A wide
range of magnifications is possible, from about 10 times (about equivalent to that of a
powerful hand-lens) to more than 500,000 times, about 250 times the magnification limit of the
best light microscopes.
Fig: - Schematic of a SEM.

18. RESULTS AND DISCUSSIONS: -
Tap density:
From the table below compressibility index (Carr’s index) and Hausner ratio can be used to
estimate the flow characteristic of the powder [3].
Compressibility index Flow character Hausner ratio
1-10 Excellent 1.00-1.11
11-15 Good 1.12-1.18
16-20 Fair 1.19-1.25
21-25 Passable 1.26-1.34
26-31 Poor 1.35-1.45
32-37 Very poor 1.46-1.59
>32 Very, very poor >1.60
Reference: – Carr RL. Evaluating flow properties of solids. Chem Eng 1965; 72: 163-168.
Powder name Tap density Carr’s index (%) Hausner ratio Flow character
Tosoh 1.341 23.86 1.31 passable
IRE 1.651 32.78 1.49 Very poor
ISRO 1.163 31.62 1.46 Very poor
It was observed that the tap density was the maximum for IRE powder and minimum for ISRO
powder, the ISRO powder has large surface area then other two. Flow character for Tosoh was
passable and very- very poor for both IRE and ISRO powder.
BET surface area measurement: BET specific surface area was maximum for ISRO powder
(185.903 m2
/ gm.), minimum for TOSOH (13.424 m2
/ gm.) and for IRE it was 30.407 m2
/ gm. It
is also possible to determine average particle size from specific area by assuming the all
particles spherical in shape and density equal to theoretical density (5.95 gm. / cc).
d = 6/(ABET *ρ)
d= average particle diameter.
ρ = theoretical density (5.95 gm. / cc).
ABET = BET surface area of particles.
The average particle size of the powders was calculated by using formula given above.
It was 79.95 nm for TOSOH powder, 35.05 nm for IRE and 5.09 nm for ISRO powder.

19. BET Surface area plot for TOSOH Powder: -
BET Surface area for plot IRE powder: -

20. BET Surface area plot for ISRO powder: -
X – Ray Diffraction (XRD): -
XRD plot for TOSOH: -

21. -
XRD plot for IRE: -
XRD plot for ISRO: -

22. XRD plot for ISRO after sintering at 10500
C: -

23. Particle size distribution: - The 0.002 gm. of powder was added to 40 ml water to make
dispersion solution and calculated the particle size distribution by laser diffraction technique
using instrument SZ-100 HORIBA.
The particle size was also calculated by BET surface area using formula give below:
d = 6/(ABET *ρ)
d= average particle diameter.
ρ = theoretical density (5.95 gm. / cc).
ABET = BET surface area of particles.
The value of particle size distribution and d50 are as follows:
Powder name Avg. particle size(by using
BET surface area) (nm)
Avg. particle size(by using
SZ-100 HORIBA) (nm)
d50 (nm) d90 (nm)
TOSOH 79.95 80 82.33 151.57
IRE 35.05 133 134.16 171.25
ISRO 5.09 25 24.29 82.33
The particle size measured using two different method was almost same for TOSOH powder but
different for IRE and ISRO. The particle size of both two powders was small there may be quick
agglomeration of particles.
Particle size distribution plot for TOSOH powder: -

24. 0 50 100 150 200 250
0
2
4
6
8
10
diameter(nm)
frequency
0 50 100 150 200 250
0
20
40
60
80
100
diamerter (nm)
undersize
Particle size distribution plot for IRE powder: -

25. 0 50 100 150 200 250
-2
0
2
4
6
8
10
12
14
16
18
diameter(nm)
ferequency(%)
0 50 100 150 200 250
0
20
40
60
80
100
diameter(nm)
undersize
Particle size distribution plot for ISRO powder: -

26. 0 50 100 150 200 250
-1
0
1
2
3
4
5
6
7
diameter(nm)
frequency
0 50 100 150 200 250
0
20
40
60
80
100
diameter(nm)
undersize
TG-DTA: - The weight loss on increasing temperature was calculated by STA 449 F3 NETZSCH. It
was observed from the graph the weight loss for ISRO powder was maximum (24.43%),
minimum for TOSOH (1.29%) and for IRE powder it was 6.48%.

27. Green density:
Green densities of discs were calculated by simple geometric method. Thickness (t) and
diameter was measured using a vernier callipers to an accuracy of 0.01 mm. Mass was
measured using a precision balance to an accuracy of 0 .0001 gm. The sample density, i.e. the
mass /volume, was then determined where the disc volume was calculated from the formula
πr2
*t. pallets were prepared under two different pressure 4T (tons) and 2T (tons). The observed
green density was maximum 2.873 gm. /cc for Tosoh powder, lowest 2.148 gm. /cc for ISRO
under compaction pressure of 2T. Green density under 4 tons compaction pressure was
observed 3.004 gm. /cc for Tosoh, 2.816 gm. /cc for IRE and 2.247 gm./cc for ISRO powder.
Observations (compaction pressure 2 tons):-
S.NO. NAME OF POWDER AVG. GREEN
DENSITY (gm. /cc)
1. TOSOH 2.873
2. IRE 2.679
3. ISRO 2.148

28. Observations (compaction pressure 4 tons):-
S.NO
.
NAME OF POWDER GREEN DENSITY
1. TOSOH 3.004
2. IRE 2.816
3. ISRE 2.247
Geometric sintered density: - Densities of sintered pallets were calculated by simple geometric
method. Thickness (t) and diameter was measured using a vernier callipers to an accuracy of
0.01 mm. Mass was measured using a precision balance to an accuracy of 0 .0001 gm. The
sample density, i.e. the mass /volume, was then determined where the pallets volume was
calculated from the formula πr2
*t. pallets were prepared under two different pressure 4T (tons)
and 2T (tons). Observed geometric sintered density were maximum 5.595 gm. /cc for Tosoh
powder, minimum 3.760 gm. /cc for IRE and 4.005 gm. /cc for ISRO when the compaction
pressure was 2T and sintering temp. 14500
C. When compaction pressure was 4 tons and
sintering temperature 15500
C the geometric sintered density was observed maximum, 4.659
gm. /cc for Tosoh, 4.144 gm. /cc for IRE and 4.677 gm. /cc for ISRO powder.
The highest density was measured 5.682gm. /cc when the compaction pressure was 4T and
sintering temp.14500
C.
Observations: -
Temp.(0
C) Tosoh(2T) Tosoh(4T) IRE(2T) IRE(4T) ISRO(2T) ISRO(4T)
1050 2.893 3.012 2.945 3.098 3.463 3.497
1150 3.288 3.385 3.181 3.386 3.740 3.893
1250 4.406 3.953 3.338 3.550 3.942 4.083
1350 4.649 5.248 3.500 3.727 4.005 4.236
1450 5.595 5.682 3.760 4.037 4.359 4.489
1550 - 4.659 - 4.144 - 4.677

29. Archimedes density: - Densities of sintered pallets also were calculated by Archimedes density
method. The pallets was immerged in xylene and kept in vacuum for 6hrs and calculated
apparent immerged weight and weight of pallet. The weight was measured using a precision
balance to an accuracy of 0 .0001 gm.
The maximum Archimedes density was 98.31% of the theoretical density for TOSOH when the
pallets were compacted under 4T pressure and sintered at 14500
C.
Temp.(0
C) Tosoh(2T) Tosoh(4T) IRE(2T) IRE(4T) ISRO(2T) ISRO(4T)
1050 2.978 3.093 2.994 3.190 3.418 3.565
1150 3.340 3.493 3.254 3.458 3.762 3.984
1250 4.426 4.518 3.392 3.566 4.024 4.192
1350 4.990 5.526 3.512 3.790 4.096 4.379
1450 5.851 5.850 3.866 4.086 4.455 4.589
1550 - 5.598 - 4.294 - 4.708
Plot between Archimedes Density and Temperature:
1000 1100 1200 1300 1400 1500
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Temp. (
0
C)
TOSOH(2T)
IRE(2T)
ISRO(2T)
ARCHIMEDESDENSITY
Plot: - Archimedes Density Vs temperature when pallets were compacted under 2T pressure.

30. 1000 1100 1200 1300 1400 1500 1600
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Temp. (
0
C)
TOSOH(4T)
IRE(4T)
ISRO(4T)
ARCHIMEDESDENSITY
Plot: - Archimedes Density Vs temperature when pallets were compacted under 4T pressure.
Volume shrinkage: - The volume shrinkage was calculated on basis of green volume of pallets.
The maximum shrinkage was 64.81% observed in ISRO pallets.
Temp.(0
C) Volume shrinkage (%)
Tosoh(2T) Tosoh(4T) IRE(2T) IRE(4T) ISRO(2T) ISRO(4T)
1050 4.01 3.97 16.94 18.54 56.15 53.82
1150 15.46 15.58 24.04 24.78 58.80 58.40
1250 36.09 35.34 28.05 28.54 60.96 60.66
1350 40.73 45.31 31.30 31.22 61.74 61.76
1450 50.31 49.49 35.78 36.85 64.66 63.99
1550 - 46.83 - 38.37 - 64.81
Plot between volume shrinkage (%) and temperature: -
1000 1100 1200 1300 1400 1500
0
10
20
30
40
50
60
70
Temp. (
0
C)
TOSOH(2T)
IRE(2T)
ISRO(2T)
VOL
M
SHRINKAGE(%)
Plot: - volume shrinkage Vs temperature when pallets were compacted under 2T pressure.

31. 1000 1100 1200 1300 1400 1500 1600
0
10
20
30
40
50
60
70
TOSOH(4T)
IRE(4T)
ISRO(4T)
VOL
M
SHRINKAGE(%)
Plot: - volume shrinkage Vs temperature when pallets were compacted under 4T pressure.
Porosity: - The porosity was calculated on the basis of theoretical density of 8%YSZ (5.95 gm.
/cc). Minimum porosity was 1.672%, observed in TOSOH pallets when it was compacted under
4T and sintered at 14500
C.
Temp.(0
C) Porosity (%)
Tosoh(2T) Tosoh(4T) IRE(2T) IRE(4T) ISRO(2T) ISRO(4T)
1050 49.949 48.008 49.669 46.377 42.546 40.084
1150 43.857 41.294 45.302 41.882 36.773 33.042
1250 25.613 24.066 42.991 40.058 32.370 29.538
1350 16.134 7.126 40.966 36.294 31.159 26.403
1450 1.655 1.672 35.025 31.327 25.117 22.874
1550 - 5.907 - 27.831 - 20.865

32. Graph plot between porosity (%) and temperature: -
1000 1100 1200 1300 1400 1500
0
10
20
30
40
50
Temp. (
0
C)
TOSOH(2T)
IRE(2T)
ISRO(2T)
POROSITY(%)
Plot: - Porosity (%) Vs temperature when pallets were compacted under 2T pressure.
1000 1100 1200 1300 1400 1500 1600
0
10
20
30
40
50
Temp. (
0
C)
TOSOH(4T)
IRE(4T)
ISRO(4T)
POROSITY(%)
Plot: - Porosity (%) Vs temperature when pallets were compacted under 4T pressure.

33. SEM (scanning electron microscopy):
It can be observed form the SEM images that the TOSOH is denser than rest two. The pores
should be at the grain boundaries but some smaller pores are on the grains it means the grain
growth was so high and hence the grain formation took place leaving the pores behind. These
pores are not through the pallets so they do not affect the conductivity much more but they
weaken the electrolyte and reduce the life of cell. The large and small pores are also there at
the intersection of the grain boundaries these pores are through the pallets. Through these
pores there may be leakage of fuel gases on working condition and hence decreases the
efficiency. In case of electrolyte small grains are more essential than larger ones but due to
presence of small grains the length of grain boundary would by more that are not convenient
for electrolyte so large and small both grains should be there. In case of three of the powders
both of grains are present.
TOSOH: -

34. IRE: -
ISRO: -

35. Acknowledgement:
I am grateful to Mr. Kamal Das Gupta, Director, CGCRI for his kind permission to allow me to
carry out this Summer Training at this institute. It’s my pleasure to acknowledge Dr. R.N. Basu,
chief scientist and HOD, Fuel Cell and Battery Division (CGCRI) and my supervisor Dr. Abhijit Das
Sharma, principal scientist, Fuel Cell and Battery division (CGCRI) to give me an opportunity to
work at this institute during my Summer internship 2014 under their guidance and for their
invaluable advice, encouragement, support and trust throughout my internship. I am
particularly grateful to my supervisor Dr. Abhijit Das Sharma for providing me indepth
knowledge based on electrolyte. I am very much thankful to Dr. R.N. Basu and Dr. A. Das
Sharma for their humanitarian support. I also express my gratitude to Mr. J. Mukhopadhyay for
their guidance and valuable interactions throughout my internship.
I would like to express my deepest appreciation to Dr. P Sujata Devi, Principal scientist, Nano
structured material Division and Dr. Vamsi Krishna Balla, senior principal scientist and HOD,
Bioceramics and Coating Division for proving me their Particle size distribution and SEM
laboratory and additional learning opportunity during my stay at CGCRI.
I am also thankful to the host of technical staff members of FCBD Smt. Nabanita chakrabarti,
Mr. Satyen, Mr. Sudip and Mr. Goutam for their constant technical support and company.
I have made friends at CGCRI during my tenure and wish everyone best of luck for their
research journey. In particular, I wish to thank Mr. Quazi Arif Islam (Tanmay), Md. I Gazi and
Mr. Mohan for their company and help when I needed.
I like to thank for unwavering support, guide, believe and hope throughout my educational
career from my family members, especially my father and beloved mother.
(Mr. Khagesh Tanwar)

36. References: -
1. Science and technology of ceramic fuel cells by N.Q. MINH and T. TAKAHASHI.
2. http://en.wikipedia.org/wiki/User:Softwarestorage/Tapped_density
3. (1)carr RL. Evaluating flow properties of solids. Chem Eng 1965; 72: 163- 168
4. http://www.horiba.com/scientific/products
5. http://www.netzsch.com
6. http://doras.dcu.ie/17363/1/muhammad_hasanuzzaman_20120704095920.pdf
7. https://mail-
attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=e2afd5b696&view
=att&th=14715d4f96467beb&attid=0.5&disp=safe&realattid=f_hxd5t66t4&zw&sa
duie=AG9B_P_n1YLR87zyBB-
n8_pPYVV9&sadet=1404820734861&sads=TPd9LBYT54irFx1zdEZ5aIw6SHA
8. http://www.horiba.com/fileadmin/uploads/Scientific/eMag/PSA/Guidebook/pdf/
PSA_Guidebook.pdf
9. https://mail-
attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=e2afd5b696&view
=att&th=14715d4f96467beb&attid=0.3&disp=safe&realattid=f_hxd5t66k2&zw&sa
duie=AG9B_P_n1YLR87zyBB-
n8_pPYVV9&sadet=1404820727809&sads=oj35yh_0AwMyDzvINt1BbrxCUVI