1. THERMALANALYTICAL
METHODS OF ANALYSIS
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2. INTRODUCTION
 Scope of thermal methods
 Definition, general points
 Thermal methods of Analysis
 Various methods
 Applications of Thermal Analysis
 How it is applicable in analysis
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3. Scope of Thermal Methods
 Definition: Thermal analysis refers to the group of
methods in which some physical property of the sample
is continuously measured as a function of temperature,
whilst (at the same time) the sample is subjected to a
controlled temperature change.
 Generally,
Temperature – ability to transfer heat, or accept heat,
from other materials.
Thermometry – science of temperature measurements.
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4. METHODS OF THERMALANALYSIS
 Thermogravimetry (TG)
 Differential Thermal Analysis (DTA) and Differential
Scanning Calorimetry (DSC)
 Thermomechanical analysis
 Thermoacoustimetry Analysis
 Thermoptometry
 Electrothermal analysis
 Thermomagnetometry
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5.  Thermogravimetry (TG):– Is related to changes
in weight form, indicates whether the samples
is losing weight and how much.
 Differential Scanning Calorimetry (DSC) : -
Related to energy changes, indicates that
reaction is exothermic or endothermic (and is
often capable of measuring the heat change).
 Thermomechanical analysis:- Relates with
dimensional changes as a function of
temperature, useful in the study of metals,
alloys, polymers, ceramic, and glasses.
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6.  Thermoacoustimetry Analysis – characteristic
sound waves produced on heating.
 Thermoacoustimetry Analysis – characteristic
sound waves produced on heating.
 Thermoptometry – study if an optical
characteristic of a sample.
 Electrothermal analysis – electrical
conductivity. Mainly used in semi conductor,
polymer studies, also in purity determinations.
 Thermomagnetometry – variations in the
magnetic property of a material with
temperature.
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7. THERMAL METHODS OF ANALYSIS
 TG – technique in which the weight of sample
is measured. It is the function of temperature.
Ex. Reactant (solid) product (solid) + gas
Gas + reactant (solid) product (solid)
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9.  Derivative thermogravimetry (DTG): It
is the method of expressing the results of
TG by giving the first derivative curve as
a function of temperature or time.
 DTA: It is a technique in which difference
in temperature (∆T) between the sample
and an inert reference material is
measured as a function of temperature.
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10.  DSC: It is similar to DTA, but it differs
from DTA by measuring the energy that
has to be applied to maintain the constant
temperature.
 Evolved gas detection (EGD): It is the
method of detection of evolution of gas
from the sample.
 Evolved gas analysis (EGA): Here, the
volatile products, released by the sample
on decomposition, may be analyzed.
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11. MULTIPLE TECHNIQUES IN
THERMAL ANALYSIS
 It involves the combination of more than
one thermal method. The most common
combination is TG and DTA, ex;
simultaneous TG-DTA measurements of
kaolinite
 Most common combined techniques:
TG-DTG, TG-DTG-DTA, TG-EGD or
EGA
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13. APPLICATIONS
 Determination of thermal constant.
Ex. Specific heat, heat of conductivity, melting
and freezing points of pure metals.
 Phase changes and phase equilibrium.
Ex. Solid to liquid phase changes like melting
points or liquid to vapour changes like boiling
points.
 Structural changes
Ex. Solid-solid transitions where change in
crystals structure occurs, it may be endothermic
or exothermic.
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14.  Thermal stability.
Ex. Polymeric materials have been
widely studied
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15. THERMOGRAVIMETRY
INSTRUMENTATION AND TECHNIQUES
 The instrument used in thermogravimetry
(TG) is called thermobalance. It consist
of precision balance, a furnace, controlled
by a temperature programmer and a
recorder.
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16.  Points:
 It should provide continuous and accurate
record of sample weight as a function of
temperature (T).
 Capacity of modern thermobalance is probably
be of the order of the gram.
 It should operate a wide temperature range up
to 1000 Celsius or more.
 It is preferable if its upper limit is at least 100
celsius above the maximum working
temperature required by the operator.
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17.  It should ensure that the sample container is
always located within a uniform hot zone inside
the furnace.
 The temperature recorded on the TG curve
should ideally be the temperature of the sample
itself.
 Sample should not interact with furnace or any
other parts of the equipment.
 The balance should not be subject to radiation
or convection effects arising from the proximity
of the furnace.
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18.  Provision should be made for the safe and
efficient removal of volatiles from the furnace.
 It should be versatile i.e., should be easy to
operate and in multiple thermal studies
(simultaneous TG and DTA measurements,
great help).
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19. MAJOR COMPONENTS OF
THERMOBALANCE
BALANCE:
 Primary essentials are accuracy, sensitivity, and
reproducibility. A reasonable capacity is a high
degree of stability and a rapid responses are
also necessary. Two most common type of
balances used in thermal analysis are null point
balance and deflection balance.
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20. Null point
 As weight change occurs and balance beam
starts to deviate from its normal position a
sensor detects the deviation and triggers the
restoring force to bring the balance beam back
to the null position. The restoring force is
directly proportional to the weight change.
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21.  It consists of an electronic microbalance.
 It has a capacity of up to 1g, so samples up to 500
mg can placed if necessary.
 An electronic bridge circuit is maintained at a state
of constant electromagnetic balance.
 When the balance arm is deflected by the change in
sample weight an excess of current flows through
one of the pair of the photocells, the current
produced is proportional to the sample weight.
 Amplification is passed through the coil (F) thus the
balance is restored at its original position. This
current is further recorded of using a meter.
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22. Deflection
 Some systems depend simply on measuring
the deflection of the beam from the norm by
a suitable technique.
 Beam types (fulcrum is used to measure )
and cantilever type (here, the beam itself is
fixed at one end)
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23. Furnace
 Heart of the balance. It holds the sample container. This
ensures uniform heating of the sample over a wide range of
temperature. In this the wire is coiled by ceramic material
surrounded by an insulator, this is placed within the furnace
housing. This housing has a cooling facility and furnace is
connected to a programmer. Nichrome wire is usually used
for furnaces operating up to about 1000 Celsius. Platinum
and/or rhodium alloy is used for temperature up to about 1500
Celsius.
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24.  Temperatures can be measured by using
thermocouples like
 chromel/alumel (up to 1000c)
 platinum/metal alloys (1500c)
 requirements of thermocouples—
chemically inert at high temperatures,
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25. Programmer
 Directly linked to the furnace
 Maintains the control of throughout the process.
 It is brain of the thermobalance and directs the
operation,
 It contains temperature sensor directly in
contact with the furnace, sending information to
the programmer and thereby controlling the
electrical power sent to the furnace.
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26. Recorder
 It provides constant record of the sample as a
function of temperature.
 There are two types potentiometric recorder
 X-Y recorder: it plots rate directly against
temperature.
 X1-X2 or adjacent recorder: it provides
independent record of weight and temperature.
 Diagram: summary in block form of the various
components of a modern thermobalance
 Diagram: schematic diagram of balance and
furnace assembly.
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29. SOURCES OF ERROR IN
THERMOGRAVIMETRY
 Buoyancy effect of sample container
 Random fluctuation of balance
mechanism
 Electrostatic effect on balance mechanism
 Condensation on balance mechanism
 Measurement of weight by balance.
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30.  Turbulence effects from gas flow
 Induction effects from furnace
 Measurement of temperature by thermocouple
 Reaction between sample and container.
Errors from 2, 3, and 8 points can be avoided by
proper arrangement of the balance.
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31. Buoyancy effect of sample
container:
 Refers to the apparent gain in weight that
can occur when a crucible is heated. This
may be due to decreased buoyancy of
atmosphere at higher temperature and
increase convection effect and possible
effect heat from the furnace itself. In
modern balance this effect is very
minimum.
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32. Measurement of weight:
 The balance system may be calibrated for
recorded weight by adding known weights
to the container and noting the readings on
the chart.
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33. Furnace effects and turbulence
effects:
 The flow of gas over and around the
container in the furnace may cause
turbulence. The heat from the furnace may
cause convection effects.
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34. Temperature
 The actual temperature of the sample will
usually lag behind the temperature recorded
by the thermocouple. It may be caused due
to the finite time in which a weight change
is recorded, the heating rate, the gas flow,
the nature of the sample container and also
the characteristics of the sample.
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35. Reaction of the sample and
container:
 May cause changes in weight.
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36. INTERPRETATION OF TG
 We can consider that the TG curve directly
indicates the characteristic of that
compound.
 This is due to the sequence of
physicochemical events that occur under
particular conditions over the temperature
range
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37.  Ex:1. calcium carbonate
decomposes –single step(800oC–900o C)
forms calcium oxide (a stable solid) & gas
CO2
CaCO3 (s) CaO (s) + CO2 (g)
Mr (100) (56) (44)
 Ex: 2 another ex, ammoniun nitrate
NH4NO3 (g) 300 oC N2O (g) + 2H20 (g)
(two volatile prods)
Mr is 100 for CaCO3 & amm. nitrate leaves no
residue.
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39.  Ex: calcium oxalate monohydrate
(CaC2O4.H2O) is heated in air up to 1000 oC.
 We see a well separated three thermal
decompositions
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40. Step 1: hydrate water is lost:
CaC2O4. H2O (s) CaC2O4 (s) + H2O
Mr--146 18
W% - 12.3%
Step 2 : Anhydrous salt decomposes
CaC2O4 (s) CaCO3 (s) + CO (g)
Mr – 28
W% - 31.5%
Step 3: carbonate decomposes.
CaCO3 (s) CaO (s) + CO2 (g)
Mr -- 44
W% - 61.6%
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41. You will notice that these values calculated for
the three steps I, II & III correspond very
well to the positions of three plateaus
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