differential thermal analysis, differential scanning calorimetry, thermogravimetric analysis

1. THERMAL ANALYTICAL
TECHNIQUE
BINDU KSHTRIYA

2. CONTENTS
THERMAL ANALYSIS TECHNIQUES.
DIFERENTIAL SCANNING
CALORIMETRY .
THERMOGRAVIMETRIC ANALYSIS
DIFFERENTIAL THERMAL ANALYSIS
APPLICATIONS

3. Thermal Analysis …
A group of analytical techniques
Each technique defines a material property
DSC
Differential Scanning Calorimetry
Heat Flow
TGA
Thermogravimetric Analysis
Mass
TG/DTA
Differential
Thermal Analysis
Temperature
difference
TMA
Thermomechanical Analysis
Dimension

4. Calorimetric principle
Ti is the initial temperature(before reaction )
Tf is the final temperature(after reaction)
If;
Ti <Tf, rxn is exothermic
Ti> Tf, rxn is endothermic
Heat flow is calculated as Q=M.Cp.T

5. 5
DIFFERENTIAL SCANNING
CALORIMETRY
It is a thermal technique in which the difference
in the amount of heat required to increases or
decreased the temperature of a sample and
reference are measured as a function of
temperature.
DIFFERENTIAL-measure difference in heat flow
from sample & reference.
SCANNING –scan over a range of temperature.
CALORIMETER-used to measure heat or heat
flow.

6. PRINCIPLE
Metal
1
Metal
2
Metal
1
Metal
2
Sample Empty
Sample
Temperatur
e
Reference
Temperatur
e
Temperature
Difference =
Heat Flow
ISOTHERMAL
PROCESS

7. 7
Principle of the thermal analysis :
Heating of the sample and the inert reference
material at a constant heating rate
Record of the furnace,
sample and inert
reference material
temperatures
Difference between
sample and inert
reference material
temperatures

8. BASIC DSC APPARATUS
A DSC apparatus is built around :
- a differential detector
- a signal amplifier
- a furnace
- a temperature controller
- a gas control device
- a data acquisition device
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10. COMPONENTS
PURGE GAS
TYPICAL PURGE GASES ARE AIR/NITROGEN
HELIUM MAY BE USEFUL FOR VOLATILE
COMPONENTS
CAN BE CARRIED OUT UNDER HIGH
PRESSURE

11. CRUCIBLE
ALUMINUM - INEXPENSIVE,LOW TEMP.
COPPER-FOR POLYMERS
ALUMINA-FOR HIGHER TEMP

12. Mathematical expression of the
calorimetric signal
Expression of the heat flux from the reference
side
Expression of the heat flux from the sample
side
12

13. HEAT FLUX FROM REFERENCE ( dq /dt )r = Cr dT/dt
(1)
HEAT FLUX FROM SAMPLE (dq/dt)s = CsdT/dt+dh/dt
(2)
Differential heat flux (1-2)
dq/dt=Cs dT/dt+dh/dt-Cr dT/dt
Also ,dq/dt=Ts-Tr/R(thermal equivalent of ohm law)
on derivatising the above equation
Rd2q/dt2=-dTs/dt+dTr/dt
Final calorimetric equation=
dq/dt=(Cs-Cr)b+dh/dt-CsRd2q/dt2
Where b =scanning rate(dT/dt)
CsRd2q/dt2 = thermal lag

14. 14
Heat Flux Plate DSC
Power
compensated
DSC

15. Power Compensated DSC
sample holder
• Al or Pt pans
sensors
• Pt resistance thermocouples
• separate sensors and heaters for the sample and reference
furnace
• separate blocks for sample and reference cells
temperature controller
• differential thermal power is supplied to the heaters to maintain the temperature of
the sample and reference at the program value
15

16. 16
HEAT COMPENSATED DSC
sample holder
• sample and reference are connected by
a low-resistance heat flow path
• Al or Pt pans placed on constantan disc
sensors
• chromel®-constantan area thermocouples
(differential heat flow)

17. furnace
one block for both sample and reference
cells
temperature controller
the temperature difference between the
sample and reference is converted to
heat flow in & out of the sample and is
recorded against time or temperature.

18. REFERENCE
MATERIALS
MATERIALS MELTING POINT(oC)
INDIUM 156.6
TIN 231.9
LEAD 327.5
ZINC 419.5
K2SO4 585.2
K2Cr2O7 670.03

19. DSC: Main Sources of
Errors
•Calibration
•Contamination
•Sample preparation – how sample is loaded into a pan
•Residual solvents and moisture.
•Thermal lag
•Heating/Cooling rates
•Sample mass
•Processing errors

20. MINIMISING ERRORS
PROPER CALIBERATION OF
INSTRUMENT
PROPER PLACING INSTRUMENT IN
THE LAB
AVOID EXCESSIVE HEATING RATE
PROPER GAS FLOW RATE
CONSTANT POWER SUPPLY

21. MAJOR
APPLICATIONS
1) ENTHALPY OF TRANSITION:-Hd=KA
2) GLASS TRANSITIONS(Tg)
3) POLYMER DEGRADATION STUDIES
4) LIQUID CRYSTALS
5) OXIDATIVE STABILITY
6) DRUG PURITY ANALYSIS

22. THERMOGRAVIMETRIC
ANALYSIS

23. A Thermogravimetric Analyzer (TGA)
measures the change in mass of a sample as
the sample is heated, cooled or held at a
constant (isothermal) temperature.
INTRODUCTION

25. TYPES OF
THERMOGRAVIMETRIC
ANALYSIS
Isothermal or static
Quasistatic thermo gravimetry
Dynamic thermogravimetry

26. Principle: In this technique the change in sample
weight is measured while the sample is heated at
a constant rate (or at constant temperature),
under air (oxidative) or nitrogen (inert)
atmosphere.
This technique is effective for quantitative
analysis of thermal reactions that are
accompanied by mass changes, such as
evaporation, decomposition, gas absorption,
desorption and dehydration.
INSTRUMENTATION

27. WORKING PRINCIPLE OF
BALANCE
27

28. Copyright@RGH 10 May 2014
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29. WORKING PRINCIPLE OF
BALANCE
Change in the sample mass causes a deflection of the beam.
The resulting imbalance in the photodiode current is amplified and fed
into coil E, which is situated between the poles of permanent magnet F.
The magnetic field generated by the current in the coil restores the
beam to its original position.
The amplified photodiode current is monitored and transformed into
mass or mass loss information by the data acquitting system.
In most cases mass vs temperature data can be either plotted in real
time or stored for further manipulation or display at a later time.
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30. The various components of modern thermo balance are
Recording balance
Sample holders
Furnace
Furnace temperature programmer or controller
Recorder
30

31. RECORDING BALANCE
It is the most important component of the
thermobalance.
Commercially available balance can provide
quantitative information about 1 mg-100 gm
mass.
31

32. There are two types of balance.
deflection type
null type
32

33. 2) Null-Point Balance
It is more commonly used. In this balance, a
sensor is employed to detect the deviation of
the beam from its null position.
A restoring force of either electrical or
mechanical weight loading is applied to the
beam to restore its null position from the
horizontal or vertical norm.
The restoring force is proportional to the
weight change and this force is recorded
directly or by transducer.
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34. 2) SAMPLE HOLDER
It is constructed from glass, quartz, alumina, stainless steel, platinum,
graphite etc.
In practice 4 types of sample holders have been used.
Shallow pans
Deep crucibles
Loosely covered crucibles
Retort cups
34

35. 3) THE FURNACE
The choice of furnace heating element and type of
furnace depends upon the temperature range being
studied.
Temperature Material
1100 0C Nichrome
1100-1500 0C Platinum or alloy of pt-rhodium
1100-1750 0C Pt-Rh in which (Rh-40)
>1750 0C tungsten or molybdenum
35

36. 4) TEMPERATURE
MEASURMENT
The most common method is thermocouple.
For 1100 0C: chromel or alumel thermocouples made up of
alloys of Pt and rhodium.
For higher temperature: tungsten or rhenium thermocouple.
The position of temperature measuring device relative to the
sample is very important.
36

37. 5)RECORDER
Two types:
1. Time-base potentiometric strip chart
2. X-Y recorders.
In some instruments, light-beam-galvanometer photographic paper recorders or one
recorder with two or more pens are used.
One can check the heating rate of the furnace for linearity.
In x-y recorders we get curves having plot of weights against temperature.
In most cases normal mode of recording data for Thermogravimetry is the weight
change vs temperature or time.
But % mass change vs time or temperature is more suitable.
37

38. FACTORS AFFECTING
TG CURVE
Instrumental
Heating rate
Effect of furnace atmosphere
Sample holder
Characteristic s of the sample
Weight of sample
Sample particle size
Compactness of sample
Previous history of the sample
38

39. DIFFERENTIAL THERMAL
ANALYSIS

40. What is DTA ?
A technique in which the temperature
difference between a substance and a
reference(Al2o3) material is measured
as a function of temperature while the
substance and reference are
subjected to a controlled temperature
program

41. Thermogram
A differential thermogram
consists of a record of the
difference in sample and
reference temperature(∆T)
plotted as a function of
time t, sample
temperature(Ts), reference
temperature(Tr) or furnace
temperature(Tf).

42. Instrumentation
A differential thermal analyzer is composed
of five basic components, namely :
1}Furnace
2}Sample holder
3}temperature controller and recorder
4}thermocouple
5}Cooling device

43. 1} Furnace
Tubular furnace is most commonly used because it
possess the desired characteristic for good
temperature regulation and programming.
Dimension of the furnace is depends upon the length
of the uniform temperature zone desired.
The choice of resistance material is depends on the
maximum temperature of the operation and gaseous
environment.
Grooved muffled cores preferred.

44. 2} Sample holder
Should having low cost, ease of fabrication and inertness towards
the sample.
Metallic material: nickel, stainless steel, platinum
Non-metallic material: glass, vitreous silica or sintered alumina.
Most commonly the shape of holder is cylindrical.
The nature of physical constant between the sample,
thermocouple junction and the specimen holder affect the DTA
signals. So to maintain it, a sample holder with dimples in which
thermocouple junctions are inserted (thermocouple wells) are
used.

45. 3} Temperature controller and
recorder
A] Temperature Controller
In order to control temperature, the three basic elements are
required. sensor, control element and heater
.
The control element governs the rate of heat-input required to
match the heat loss from the system.
The location of sensor with respect to the heater and mode of heat
transfer measure the time elapsed between sensing and variation
in heat input.

46. B] Temperature programming
It transmits a certain time-based instruction to the control unit.
By this device one can achieve linearity in the rate of heating or
cooling it is driven in a non-linear fashion using a special cam-
drive.
Heating rates of 10-20 o C / mints are employed.
C] Recorder
The signals obtained from the sensors can be recorded in which
the signal trace is produced on paper or film, by ink, heating
stylus, electric writing or optical beam.

47. 4} Thermocouple
Thermocouples are the temperature sensors.
It is made up from chromel and alumel wires are
used to measure and control temperature up to
1100 0C in air.
For above 1100 0C one should use thermocouple
made from pure platinum & platinum-rhodium alloy
wires.

48. Applications:
Thermal Stability
Material characterization
Compositional analysis
Used to analyze filler content in polymers; carbon black in oils; ash and carbon in
coals.
Kinetic Studies
Corrosion studies
Automatic Thermogravimetric Analysis
Evaluation of gravimetric precipitates
Evaluation of suitable standards
Testing of purity of samples
Curie point determination

49. THANK YOU
BINDU KSHTRIYA