This document provides an introduction to thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). It discusses key concepts like how TGA measures weight changes as a function of temperature, allowing one to determine characteristics of thermal decomposition reactions. Examples are given of TGA curves for silver nitrate and cupric nitrate hemipentahydrate to illustrate how different materials may experience one or multiple steps of weight loss at different temperatures. The document also briefly introduces DTA as measuring the temperature difference between a sample and reference as they are heated.
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Syllabus
Unit-I : Thermal methods of Analysis:
Introduction of different thermal methods,
Thermogravimetry TG and DTG, Static thermogravimetry,
quasistatic Thermogravimetry and dynamic
thermogravimetry, Instrumentation, Factors affecting
thermograms, Applications of thermogravimetry,
Differential thermal analysis (DTA), DTA curves, Factors
affecting DTA curves, instrumentation, applications of
DTA. Simple numerical problems.
Differential Scanning Colorimetry(DSC): Introduction,
Instrumentation, DSC-curves, factors affecting DSC curves
and applications. Thermometric Titrations; Introduction,
apparatus, theory and applications.
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Thermogravimetry (TG)
Thermo analytical methods may be defined as those
techniques in which changes in physical and/or
chemical properties of a substance are measured as a
function temperature. The property studied can be the
weight or the enthalpy change in a system
Thermogravimetry (TG) is a technique in which a
change in the weight of substance is recorded as a
function of temperature.
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Differential Thermal Analysis (DTA)
Differential Thermal Analysis (DTA) is a method
for recording the difference in temperature
between a substance and an inert reference
material as a function of temperature.
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THERMOGRAVIMETRY (TG)
In a thermogravimetric analysis (TGA) the weight
of a sample is continuously recorded as a function
of temperature. The result is expressed in the form
of a thermogram, which is a plot of weight versus
temperature.
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The curve exhibits two plateaus (AB and CD) and
one inflection (BC). The region AB in which the
weight remains constant is the region in which
AgNO3 is stable. At 473°C the following reaction
takes place.
AgNO3(s) — Ag(s) + NO2(g) +1/2 O2 (g)
Due to the loss of NO2 and O2,the weight
decreases from B to C. In the region CD i.e. at
temperatures above 608°C, metallic silver alone
can exist and there is no further change in the
weight. From the thermogram we infer that
AgNO3 is stable up to 473°C.
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It is possible that there can be more than one step in
which weight losses can occur. The thermogram (Fig.
1.2) of cupric nitrate hemipentahydrate [Cu(NO3)2
2.5H2O] illustrates this point.
Fig. 1.2 TGA of cupric nitrate hemipentahydrate
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In contrast to the thermogram of silver nitrate
which exhibits only one region of weight loss, the
thermogram of cupric nitrate hemipentahydrate
exhibits two region of weight loss. One between
100-150°C and another between 200-280°C. The
two steps correspond to the following reactions:
Cu(NO3)2 .2.5H2O(s) — Cu(NO3)2(s) + 2.5H2O(g)
Cu(NO3)2(s) — CuO(s) + NO2(g) +3/2 O2 (g)
The copper oxide thus formed is stable up to
950°C.
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In Next lecture We will Start With
Instrumentation for Thermogravimetry
Factors Affecting TGA
