Thermoanalytical Techniques - Thermal Analysis of Construction Materials - page 2

2.0 CLASSICAL TECHNIQUES

Ever since the invention of DSC, there has been much confusion
over the difference between DTA and DSC. The exact ICTA definition of
DTA is a method that monitors the temperature difference existing between
a sample and a reference material as a function of time and/or temperature
assuming that both sample and reference are subjected to the same environ-
ment at a selected heating or cooling rate. [1][2] The plot of

T as a function
of temperature is termed a DTA curve and endothermic transitions are
plotted downward on the y -axis, while temperature (or time) is plotted on
the x -axis. DSC, on the other hand, has been defined as a technique that
records the energy (in the form of heat) required to yield a zero temperature
difference between a substance and a reference, as a function of either
temperature or time at a predetermined heating and/or cooling rate, once
again assuming that both the sample and the reference material are in the
same environment. [1][2] The plot obtained is known as a DSC curve and
shows the amount of heat applied as a function of temperature or time. As
can be seen from the above definitions, the two techniques are similar, but
not the same. The two yield the same thermodynamic data such as enthalpy,
entropy, Gibbs' free energy, and specific heat, as well as kinetic data. It is
only the method by which the information is obtained that differentiates the
two techniques. A brief history on the development and a comparison of the
two techniques are given.*

∆

2.1 Differential Thermal Analysis and Differential

Scanning Calorimetry

A little over a hundred years ago, two papers were published by Le
Châtelier dealing with the measurement of temperature in clays; the first
entitled On the Action of Heat on Clays and the second On the Constitution
of Clays . [20][21] The experiment described in these papers was not a truly
differential one since the difference in temperature between the clay and
reference material was not measured. The apparatus consisted of a Pt-Pt/
10%-Rh thermocouple embedded in a clay sample, which in turn was
packed into a 5 mm diameter Pt crucible. The crucible was then placed in

*For a more detailed history, comparison, and theoretical description, consult the refer-
ences listed in Refs. 3-19.