Design of thermo-electric panels using basic chemicals.

1. INTERN REPORT
TOPIC :
SYNTHESIZING THERMOELECTRIC MATERIALS AND MAKING PANELS
NAME :
DEEPANSHU BHATIA
ENTRY NO. :
2012PH10837
PROFESSOR :
CHESTA RUTTANAPUN
GUIDE :
HAI RUDRADAWONG
INSTITUTE :
KING MONGKUT INSTITUTE OF TECHNOLOGY LADKRABANG , BANGKOK

2. PREFACE
This report documents the work done during the summer internship at
Thermoelectric LaboratoryofKing Mongkut Institute ofTechnology Ladkrabang
(KMITL), Bangkok, Thailand under the supervision of Prof. Chesta Ruttanpun.
The report first shall give an overview of the tasks completed during the period
of internship with technical details. Then the results obtained shall be discussed
and analyzed. Report shall also elaborate on the the future works which can be
persuaded as an advancement of the current work.
Deepanshu Bhatia
2012PH10837

3. ACKNOWLEDGEMENT
The internship opportunity I had with KMITL was a great chance for learning
by practical experiences. I am also grateful for having a chance to meet so many
wonderful people and professionals who led me though this internship period.
I am using this opportunity to express my deepest gratitude and special thanks
to Prof. Wichit Sirichote to guide me at their esteemed organization during the
training.
I express my deepest thanks to Prof. Chesta Ruttanpun and Hai Rudradawong
[Phd Student] for taking part in useful decision making & giving necessary
advices and guidance and arranging all facilities to make the project go
smoothly. I choosethis moment to acknowledge his contribution gratefully.
I will strive to use gained skills and knowledge in the best possible way, and I
will continue to work on their improvement, in order to attain desired career
objectives. Hope to continue cooperation with all of you in the future.
Sincerely,
Deepanshu Bhatia

4. ABSTRACT
The report presents the four tasks completed during summer internship at
KMITL which are listed below:
1) Synthesis of Thermoelectric Material from Solid state
reaction process.
2) Making Pellets from thermoelectric powder using Hydraulic press.
3) Making Thermo-electric panel of different sizes.
4) Testing of thermoelectric Panels.
All these Tasks have been completed successfully and the results obtained were
according to expectations with some minor errors.
Also during the evaluation of pellets it was found that the pellet’s finishing
depends not only on the quality of fine powder but also on the pressure applied
on it in hydraulic press and the time for which it is kept.
We had limited testing facilities. Panel could be heated only upto 200 C. Glue
used in the panels could only withstand up to 100C. Also we did not have the
required equippments to test for Seebeckcoefficient. So, we have a limited scope
to test the panels and sure we have exhausted the opportunities to maximum
extent.

5. INTRODUCTION
Thermoelectric substances :
Thermoelectric substances can be used to produce electric current from heat and
also cooling and heating from electric current.
When a conductive material is subjected to a thermal gradient, charge carriers
migrate along the gradient from hot to cold; this is the Seebeck effect. In the open-
circuit condition, charge carriers will accumulate in the cold region, resulting in the
formation of an electric potential difference.
The Seebeck effect describes how a temperature difference creates charge flow,
while the Peltier effect describes how an electrical current can create a heat flow.
Electrons transfer heat in two ways:
1) by diffusing heat through collisions with other electrons, or
2) by carrying internal kinetic energy during transport.
The former case is standard heat diffusion, while the latter is the
Peltier effect. Therefore, the Seebeck effect and the Peltier effect are the opposite of
one another.
The thermoelectric effect is the fact that a temperature gradient in a conducting
material results in heat flow , this results in the diffusion of charge carriers. The
flow of charge carriers betweenthe hot and coldregions in turn creates a voltage
difference.
Basic Physics Behind the experiment:

6. When an end of a thermoelectric material is heated up, electrons in the warmer side
of material have more energy. Since they are free to move, the excited electrons diffuse
toward the colder side of the thermocouple leaving holes behind.
The electric field develops by the movement of these electrons point towards the
colder side of the thermoelectric material which makes the cold side negative relative
to the warmer side. The electrons will keep moving toward the colder side until the
potential established by the charge separation counteracts the flow of electrons which
creates equilibrium.
S = [ V(Plate1) – V(Plate2) ]
---------------------------------------------------
[ T(Plate1) - T(Plate2) ]
Therefore, One can say that to obtain a high power output from thermoelectric
material , the potential difference obtained should be higher for minimum temperature
difference , i.e the Seebeck Coefficient of a material should be higher for good results.
Delafossite structure and its significance :
Delafossite is a copper iron oxide mineral with formula CuFeO2 . . It is member of the
delafossite mineral group with a general formula ABO2, a group characterized by a
sheet of linearly coordinated A cations stacked between edge-shared octahedral layers
(BO6). Delafossite along with other minerals of the ABO2 group has been recognized
for its electrical properties from insulation to metallic conduction.
By heating the given sample at the specified temperature for the given time we get
delafossite structure of the compound. Our compound is not CuFeO2, but it contains
substituted Cr in the delafossite CuFeO2 to see the effect of Cr content on the
thermoelectric properties.

7. METHODS AND PROCEDURES
FOLLOWED
Synthesis of thermoelectric Substances, fabrication and testing of Thermo-
electric panels
Part 1 :
Synthesis of thermoelectric Substances
We synthesised thermo-electric substances from chemicals. We mix the required
chemical compounds in the required proportion. Then we followed the following
procedures to get our thermoelectric material prepared in powdered form.
1. Ball milling :
After mixing the compounds we put the mixture in a container with milling
balls. The milling balls are of different sizes and help to mix the compound
and make a fine powder mixture. Put all the contents into a plastic container
along with the milling balls and ethanol and put the container for milling for
24 hours. Ethanol does not react chemically with the compounds, it just
provides a medium for the milling balls to mix the substance properly. After
24 hours the milling is over we get a solution of the mixture of fine powder
with ethanol.
2. Heating in heater:
After ball-milling we need to remove the ethanol. So, we put our compound in
a heater at about 90-100 C for 24 hours. The ethanol evaporates leaving
behind the properly mixed compounds. Till now it is mixed uniformly but not
in fine powdered form. We have to manually crush it by using mortar and
pestle to very fine powder before the next step. After, it gets converted to very

8. fine powder we move to the next step. We have to crush each sample for
about 1-2 hours to get very fine powder using two type of mortar and pestle.
3. Chemical reaction in oven :
Now comes the main transformation. This mixture is now heated at a specific
temperature under certain conditions to get the required delafossite structure.
We heat the sample at 1050 C for 20 hours in an electrical oven. The
temperature vs time graph programmed in the oven is as follows :
0
200
400
600
800
1000
1200
0 5 10 15 20 25 30
Y-Values

9. Heating Electric Oven:
The oven rose from room temperature to required set temperature 1050 C in
3 hours then it stays at that temperature for 20 hours and then we take out
the sample at this temperature to room temperature quickly to allow
quenching.
After cooling down the sample at room temperature we get a hardened solid
mass of the required thermoelectric substance. Now using the bigger mortar
and pestle crush it into smaller pieces and then more fine pieces, finer powder
and the very fine. It takes a lot of
time about 6-7 hours to crush it into final usable fine powder.

10. Mortar and pestle :
This final fine powder is our thermoelectric substance.
Part 2:
Making the pellet
Now, using the fine powder we can create thermoelectric pellets of different
shapes from cylindrical or cubical. We are considering only cylindrical ones.
We use iron moulds to make these pellets. Moulds look like this :

11. Using the moulds and applying a pressure of 9-12 *(10^6) Pascal, we get our pellets.
We use a hydraulic press for the purpose :

12. We make pellets of different sizes to compare their properties. Right now the pellet is
just compressed powder and it’s not very strong. We again repeat the heating in
oven step to make them strong. The pellets were sintered in furnance at 1050 C
under air atmosphere for 24h. After heat treatment the sample was rapidly quenched
at room temperature. Now these pellets are ready to use in our thermoelectric panel.
Pellets :
Part 3 :
Making the panel
To make the panel we have to keep the pellets in a grid pattern with a*b
pellets.
The base and head of panel are either made of ceramic thermally conducting
substance or metallic plates (zinc).
First we make a series connection between the pellets using copper plates.
These copper plates are joined with the pellets with conducting glue (Glue 1).

13. After this connection the pellets are connected in series such that when the
whole system is placed between temperature gradients the thermoelectric
currents of all the pellets add up. The connection made with this glue have to
be kept in open at room temperature for 2-3 days. After that it was kept for 1
day in heater at 100 C.
Connecting the pellets in series using copper plates and copper wires :
After making the pellets in series this whole grid like system has to be joined
to the ceramic or metallic plates. The glue (Glue 2) used is thermally
conducting and electrically insulating. In case of metallic plate panel we have
to be very careful because any error in insulating glue can lead to short
circuiting the whole panel with zinc plates on top and bottom, hence
hampering the performance. To ensure that the glue is properly applied it has
to be dried one day in room temperature and subsequent day in oven at 100
C. After these procedures ensure that all connections are properly made and
no connection is short circuited by any of glue thermally or electrically.
Panel (with ceramic base ) :

14. Panel (with metallic base ) :

16. Part 4 :
Testing the panel
To test the panel we apply a finite temperature gradient and measure the
series current of the panel.
We first measure the resistance of the panel at room temperature. Then apply
an external resistance equivalent to this in our circuit. Add an ammeter in
series, voltmeter in parallel and then gradually increase the temperature
gradient and observe the change in current.
The colder junction is maintained by keeping ice on it and hotter one by using
heater.
This way we get the readings and plot the graph for various panel of different
grid configurations, different thermoelectric substance, different heights of
pellets and get our conclusions.

17. Observations and Results:
From the above process we prepared Two different kind of thermoelectric substance
1) Cu Fe 0.75 Cr 0.25 O 2 (Sample 1)
2) Cu Fe 0.9 Al 0.1 O 2 (sample 2)
And from these two substances we prepared total 6 Modules
3 From sample 1 and 3 from Sample Two as Follows
*here parameter used to compare the size of pellet is weight (in grams) of pellet
because the height is directly proportional to wt., as other conditions like pressure,
temp. were identical during its manufacturing.
From Sample 1:
Module No. Pellet’s weight (in
gm of sub. filled )
Type of Plates used
Sam1 Mod a 4gm Ceramic
Sam1 Mod b 4gm Metallic
Sam1 Mod c 5gm Ceramic
From Sample 2:
Module No. Pellet’s weight (in gm of
sub. filled )
Type of Plates used
Sam2 Mod a 2gm Metallic
Sam2 Mod b 3gm Metallic
Sam2 Mod c 6gm ceramic
For testing the module’s performance, we prepared a following setup by applying a
temp gradient on the opposite sides of modules we measured the output current as a
function of temperature Gradient.
Case 1: Sam1 Mod a
Bottom Surface
Temp
Top Surface Temp
(in C)
Temp gradient Current Output
( in uA)

18. ( in C)
21.5 13 8.5 21
30 17 13 32
42.4 21.3 21.1 50
56 24.8 31.2 58
69 30.6 38.4 65.3
83 28.5 54.5 76.9
93 31 62 86.7
Case 2: Sam1 Mod b
BottomSurface
Temp
( in C)
Top Surface
Temp
(in C)
Temp gradient Current
Output
( in uA)
70 30 40 58
80 35 45 72
115 28 87 163
130 45 90 191
150 50 100 203
Case 3: Sam1 Mod c
Bottom Surface
Temp
( in C)
Top Surface
Temp
(in C)
Temp gradient Current Output
( in uA)
46 13 33 110
55 18 37 120
56 18.4 37.6 123
71.6 22 49.6 172
84.4 32 52.4 192.2
103.3 34 69.4 246
125 50 75 279
135 55 80 300
Case4: Sam2 Mod a
Bottom Surface Temp
( in C )
Top Surface Temp
(in C)
Temp gradient Current Output
( in uA)
45 20 25 11
60 27 33 12
77 32 45 15

19. Case 5: Sam 2 Mod c
Bottom Surface
Temp
( in C)
Top Surface Temp
(in C)
Temp gradient Current Output
( in uA)
35.5 13.5 22 95.7
47.5 20.5 27 114.8
60 30.4 29.6 160
70 34 36 180
68 30.2 37.8 212
73 32 41 241
105 42 63 280
108 40 68 323
124 50 74 345
131 40 91 382
# Note: Out of all modules two Modules (Sam 2 Mod 1, Sam 2 Mod 2) were defective
as we can see from the readings that the output current is very low and not increasing
with increase in gradient and also the Internal Resistance is not as per the expectation
there might be some short circuiting in the module.
Conclusion:
From the above results one can conclude that the Current output of modules increases
with increase in Temp. Gradient, i.e Temp gradient is providing an electromotive force
implicitly.
Other conclusion which can be drawn from the results is that the two modules named
as Sam2 Mod a, Sam 2 Mod b were defective, may be the conducting glue
(electrically) had made a contact between the top and bottom plates or maybe there
was an electrical contact between the metallic plates and the pellets due to which the
total internal resistance was too low and the whole module was short circuited.
The thermally conducting glue used to connect pellets with the plates was not a good
choice to be used in our modules because as we reached at temp. around 130 C the
thermally conducting glue( Fiber Adhesive) started to break. Due to which we had
to limit ourselves to Max limit of 130-150 C, and got the Maximum Current readings
till this Temp range only.
Also max. Current for a module was more in case of module where large pellet (larger
in length) of same material were used.

20. We got the Max current for module named as Sam 2 Mod c of 382 uA ( i.e for Sample
2) , that too at Temp gradient of 91 C , but if we had some better Thermally conducting
glue that can with stand in Temp range of 400-500 C than , we would have got a far
better readings.
Scope of Improvement in Future:
We tried a very new concept of using a Metallic plates instead of Ceramic Plates in the
Modules and as result we got enhanced values of Max . current (almost Twice)
through the Metallic Plates Modules than from the Ceramic plates module.
We also tried to decrease the heat conduction between top and Bottom plates (as it
degrades the Temp gradient produced by heating one side) by replacing the copper
plates used to connect the pellets in series by copper wires, but unfortunately due
to some manufacturing errors the circuit got short circuited and we were not able to
take the real readings of modules and we didn’t have enough time in the end to make
that type of module again but I think is proper care is taken while joining the pellets
with copper wires instead of copper plates , the heat conduction can between two
plates can be reduced upto an extent and we can get high temp gradient by heating
upto a small range of Temp.
Sources Of Error:
 During the preparation of pellets the powder was kept in a ceramic dish for days
wrapped in Al Foil, due to which after some time moisture got into it and when
we made pellets from that moisturized powder they we not as good in finishing
as the one made by dry powder.
 Also some times the pressure applied to Dies kept in Hydraulic Press to make
Pellets was not same in each case some time it dropped to half of its actual
value which might have brought non uniformity in pellets.

21.  While preparing modules and joining pellets with copper plates and electrically
conducting glue there were instances when electrical glue spread over the pellet
to get is short circuited.
 While applying thermally conducting Glue sometimes there were direct
contacts made between top and bottom plates by the overflow of glue.
 And there are manual error also while measuring the readings like contacts are
not made proper while connecting external circuits.
# If these all errorsarehandled properlyandthe new methodswe tried like using metallic
plates and copper wires and using a high temp. resistant glues, we can reach to a whole
new level of Thermoelectricity in Future.
REFERENCES :
Wikipedia : Thermoelectric substances
Research paper on Thermoelectric properties of Sn+2 –
Substituted CuFeO2 Delafossite-Oxide (Advanced Materials
Research Vol. 802(2013) pp 17-21 ,
doi:10.4028/www.scientific.net/AMR.802.17)