It include all the thermal methods widely used in large and small scale industries with detailed applications and examples for explanations. Medha Thakur (M.Sc Chemistry)

1. THERMAL
METHODS
Presented By: Medha Thakur
MSc (Chemistry)
S.N.D.T University

2. Contents
• Introduction
• Thermogravimetry
• Thermogram
• Apparatus
• Thermobalance
Property
• Applications
• Differential Thermal
Analysis (DTA)
• Differential Scanning
Calorimetry
• Instrumentation For
DTA & DSC
• Applications Of DTA &
DSC
• Thermometric Titration
• Instrumentation
• Theory
• Applications

3. INTRODUCTION
• Based upon the measurement of the dynamic
relationship between temperature and some
property of a system such as mass, heat of
reaction or volume.
• There are about 12 thermal methods,
however the most common are
Thermogravimetric, Differential thermal
methods, Differential scanning calorimetry
and Thermometric titrations.

4. THERMOGRAVIMETRY
• In a TGA, the mass of a sample is noted
continuously as its temperature increased
linearly from room temperature to as high
as 1200°c.
• A plot of Mass or weight loss or % weight
loss as a function of temp. is plotted.
• This plot is called as Thermogram (TG).
• A TG provides both qualitative and
quantitative information.

5. Thermogram
• A typical thermogram, for
CuSO4.5H2O is shown in the
fig.
• 1. The horizontal portions
(plateaus) indicates the
regions where there is no
weight loss.
• 2. the curved portions are
indicative of weight loss.

6. The fig. shows that CuSO4.5H2O has 3 distinct regions
of decomposition.
• sometimes a derivative thermogravimetric curve
(DTG) is obtained.

7. fig. 2). In this DTG curves, there is no weight change then
dw/dt = 0.
• Inflections such as B and C in the fig. imply the formation
of intermediate compounds,
• Inflection at B arises from the formation of CuSO4.3H2O.
• Inflection at C arises due to the formation of a golden
yellow basic sulphate composition 2CuO.SO3.

8. APPARATUS
Apparatus for a TGA is called a
thermobalance which includes
1. Sensitive analytical balance
2. A furnace
3. A furnace temperature
controller
4. A recorder that provides a
graph of sample mass as a
function of temperature.

9. Thermobalance Property
1. registering continuously the weight change of the sample
studied.
2. furnace reach the maximum desired temperature (approx.
1500°C).
3. The rate of heating should be linear and reproducible.
4. The sample holder should be in hot zone of the furnace
and it should be of uniform temperature.
5. capable of carrying out accurate isothermal studies.
6. The balance mechanism should be protected from the
furnace and from the effect of corrosive gases.
7. A balance sensitively suitable for studying all sample
weights.
8. The furnace should be capable of heating and cooling
rapidly so that several TGAs can be carried out.

10. APPLICATION
1. The determination of purity and thermal stability of
both primary and secondary standards. Some of the
primary standards are Na2CO3, Na – tetraborate,
KHPhthalate, etc. Many of these absorb water when
exposed to moist atmosphere.
• TG shows the extent of absorption and hence the
most suitable drying temperature for a given
primary standard.
2. The most imp application of TGA is the study of
drying temperature of gravimetric precipitation.

11. 3. Direct application to analytical
problems:- TG may be used to
determine composition of binary or
ternary mixtures.
A simple e.g. is given by the automatic
determination of mixture of Ca, Ba, and
Sr as their carbonates.

12. • A further e.g. is the
automatic determination of
a mixture of Ca and Mg as
their oxalates.
• Ca-oxalates monohydrate
has the following three
distinct regions of
decomposition.
• In comparison with this Mg-
oxalate dehydrate has only
two decomposition stages.

13. • 4. The determination of composition of complex
materials and mixtures:- Complex material like clays
and spoils can be studied by TGA.
• 5. study of polymers :- Thermogram provides
information about decomposition mechanism for
various polymeric preparations. In addition, the
decomposition patterns are characteristic for each
kind of polymer and in some cases can be used for
identification purposes.

14. • Fig. below shows decomposition patterns for 5
polymers obtained by thermogravity.

15. • Fig. illustrates how a
thermogram is used for
quantitative analysis of a
polymeric material.
• The sample is polyethylene
that has been formulated
with fine carbon black
particles to inhibit
degradation from exposure to
sunlight.
• This analysis would be
difficult by most other
analytical methods.

16. DTA – DIFFERENTIAL
THERMAL ANALYSIS
• It is a technique in which temperature difference
(ΔT) between the sample and an inert reference
material is measured as a function of
temperature while the sample and reference are
subjected to controlled temperature programme,
thus the heat absorbed or emitted by a chemical
sample is observed.
• inert reference compound such as alumina, SiC
or glass beads which are continuously increased
at a constant rate under various atmosphere.

17. DSC – DIFFERENTIAL
SCANNING CALORIMETRY
• In DSC also the sample and reference substance are
subjected to a continuously increasing temperature.
here however, heat is added to the sample or to the
reference as necessary to maintain the two at
identical temperature.
• the added heat, which is recorded compensates for
that lose or gained as a consequence of endothermic
or exothermic reaction occurring in the sample.
• The plot of ΔT vs time or temperature is called
differential thermogram.

18. DTA of
Calcium
Oxalate
Monohydrate
• thermogram obtained by
heating Ca-oxalates
monohydrates in a
flowing stream of air.
Two minima
Endothermic
Process
Single
maxima
Exothermic
Process

19. Sources of differential
thermogram peaks:
• Endothermic reaction : If sample absorbs some amount of heat
during phase transition then reaction is said to be endothermic.
• In endothermic reaction more energy is needed to maintain
zero temperature difference between sample and reference.
• E.g. fusion, vaporization, sublimation, absorption, desorption.
• Exothermic reaction : If sample related some amount of heat
during phase transition, then reaction is said to be exothermic.
In exothermic reaction, less energy needed to maintain zero
temp difference between sample & reference.
• E.g. Crystallization, degradation, polymerization.

20. INSTRUMENTATION
for DTA and DSC:
• The basic instrument of DTA and DSC :-
• In DTA, both S&R container are heated by same device temp sensors.
• In DSC, the S & R are provided with heaters. These are so close to the
sample and reference vessel as possible
DTA DSC

21. APPLICATIONS
1. Inorganic Substances
• Studies involving the thermal behavior of inorganic
compounds such as silicates, ferrites, dehydration,
oxidation, reduction, adsorption, degradation and solid state
reaction.
• Also includes study of phase transitions.
• e.g. This is a Differential thermogram for pure Sulphur.

22. 2. Organic Compounds
• The DT (Differential Thermal) method provides a
simple and accurate way of determining the
melting, boiling and decomposition points of
organic compound.
• The data is more consistent and reproducible than
those obtained with oil bath or capillary tube.
• fig. shows thermogram for benzoic acid.
First Peak Melting Point
Second Peak Boiling Point

23. 3. Polymers
• DT methods have been widely applied to the study and
characterization of polymeric materials.
1. fig. shows thermogram of a physical mixture of 7
commercial polymers. Each peak corresponds to the
characteristic M.P. of one of the components. PTFE has an
additional low temperature peak which arises from a
crystalline transition.
• Thus DTA can be used for qualitative analysis of polymer
mixtures.

24. 2. Fig. below is an idealized DT obtained by heating a polymer
over a sufficient temperature range to cause its ultimate
decomposition. The initial decrease in T is due to the glass
transition (Tg), a phenomenon observed initially when many
polymers are heated.
• The maxima's are the result of exothermic processes of
cystallisation and oxidation and the minima is due to melting.
• The final negative change in T results from the endothermic
decomposition of the polymer to produce a variety of products.

25. APPLICATIONS OF DSC
1. The DSC curve for an amorphous sample of polyethylene
terephthalate (PET) is shown below. Its similar in appearance
to DTA plots.
• Two plots arises from microcrystal formation and meting. A glass
transition is also evident, but no oxidation peak is found in the
DSC curve because the experiment was carried out in an
atmosphere of nitrogen.

26. • 2. DSC experiment are usually performed in the temperature
scan mode, but isothermal experiment are occasionally
encountered. Fig. is an illustration of the use of DSC to
monitor the isothermal crystallization of polythene.
• The area under the exothermic peak in this experiment can
be used to estimate the degree of crystallization that has
occurred at this temperature.
• it is possible to completely characterize the crystallization
behavior of the material.

27. 3. DSC methods have found widespread use in the
pharmaceutical industry fro testing the purity of
drug samples. An e.g. is shown in figure in which
DSC curves are used to determine the purity of
phenacetin preparation. Generally curves of this
type provide purity data with relative uncertainties
of 10+%.

28. THERMOMETRIC TITRATION
• These involves the measurement of temperature of a
system as a function of time or of volume of titrant
added.
• A plot of temperature against volume of titrant or time
is made. The end point of the titration is obtained from
this plot.
• A thermometric titration depends upon the heat of the
reaction or enthalpy. The heat of a reaction is given by
the equation
• ΔH = ΔG + T ΔS
• Hence thermometric titration may be feasible even
when ΔG is small.

29. The Titration of Boric acid
• is a classic e.g. of thermometric titration. The
potentiometric titration of Boric acid with NaOH does
not offer a clear end point. Since ΔG is very small
whereas the thermometric titration of Boric acid under
the same condition gives a clearly marked end point
because TΔS and hence ΔH is large.
• The change in temperature ΔT of a thermometric
titration. depends on ΔH and is given by the relation
• ΔT = - n ΔH/k
• where n= no. of moles of reactant and
k is the heat capacity of the system.
• since ΔH and k are constant, ΔT is proportional to the
no. of moles of the analyte. By knowing ΔT, n the
number of moles of reactant can be calculated.

30. INSTRUMENTATION
• a) Reagent delivery system: TH reagent is delivered by a
syringe which is powered by a motor. It is delivered at a constant
rate of a few μl/min.
• b) Titration Vessel: thermally insulated to prevent heat loss or
grain. Efficient stirring must be provided. The titration must be
completed in less than 5 minutes in order to avoid excess heat to
the surrounding.
• c) Temperature measurements: Thermistors are generally
employed as temperature sensors. There is a change in the
resistance of a thermistor even with slight change of temperature.
The changes in resistance appear as voltage difference across a
bridge circuit, the difference is then recorded on a mV recorder.

31. INSTRUMENTATION

32. THEORY
A typical thermometric titration curve is made up of 3 parts. The
region A to B gives the temperature of the system before addition of
reagent.
• At point B, reagent addition is began at a controlled rate.
• Point C corresponds to the end point of the titration.
• Beyond C, a straight line is obtained. Its slope may be positive or
negative depending on whether the dilution process is exothermic
or endothermic.
• By extrapolating the part C, ΔT can be calculated and hence
numbers of moles of reactant (titrand) determined.

33. APPLICATIONS
• 1. Acid-base titrations:
• Titration involving S.A. and S.B. have been carried out, but a
more significant application is the titration of W.A. with S.B.
e.g. Boric acid with NaOH. Mixtures of acids (S and W) can be
titrated and the resulting thermogram has 2 inflections.
• 2. Precipitation Titrations: When a slightly soluble (or
insoluble) compound MX is formed heat is either evolved or
absorbed according to eqn
• M+(aq) + X-(aq) → MX(s) ± ΔH
• If ΔH is sufficiently large than the reaction may be followed by
thermometric titration. e.g. of precipitation is determination of
halides with Ag and Hg ions, estimation of Ca, Ba, Sr, with
oxalate ions.

34. • 3. Redox Titrations:
• The titration of permanganate with Fe[II] and with oxalic acid
can be carried out.
• 4. Complexometric Titrations:
• A mixture of Ca and Mg can be easily titrated with EDTA
thermometrically, the curve obtained shows exothermic section
AB and endothermic section BC.
• The complexation reaction between Ca and EDTA is
exothermic whereas complexation between Mg and EDTA is
endothermic. From the plot, concentration of Mg and Ca can
be easily determined.