Differential Thermal Analysis (DTA)
A technique in which the temperature difference between a substance and a reference
material is measured as a function of temperature whilst the substance and reference
material are subjected to the same controlled temperature programme.
Chapter 5 - 5
The record is the differential thermal or DTA curve; the temperature difference (?T) should
be plotted on the ordinate with endothermic reactions downwards and temperature or time
on the abscissa increasing from left to right.
The term quantitative differential thermal analysis (quantitative DTA) covers those uses of
DTA where the equipment is designed to produce quantitative results in terms of energy
and/or any other physical parameter.
Sample
The sample is the material investigated, whether diluted or undiluted.
Reference Material
The reference material is a known substance, usually inactive thermally over the
temperature range of interest.
Specimens
The specimens are the sample and reference material.
Sample Holder
The sample holder is the container or support for the sample.
Reference Holder
The reference holder is the container or support for the reference material.
Specimen-holder Assembly
The specimen-holder assembly is the complete assembly in which the specimens are
housed. Where the heating or cooling source is incorporated in one unit with the containers
or supports for the sample and reference material, this would be regarded as part of the
specimen-holder assembly.
Block
Chapter 5 - 6
A block is a type of specimen-holder assembly in which a relatively large mass of material
is in intimate contact with the specimens or specimen holders.
Record
The record is the differential thermal or DTA curve shown in Fig. 5.2. The temperature
difference ( ?T) should be plotted on the ordinate with endothermic reactions downwards
and temperature or time on the abscissa increasing from left to right. It must be
remembered that although the ordinate is conventionally labelled ?T, the output from the
?T thermocouple will, in most instances, vary with temperature and the measurement
recorded is normally the e.m.f. output, E - i.e., the conversion factor, b, in the equation ?T
= bE is not constant since b = f(T). A similar situation occurs with other sensor systems.
All definitions refer to a single peak such as that shown in Fig. 5.2. Multiple peak
systems, showing shoulders or more than one maximum or minimum, can be considered to
result from superposition of single peaks.
Base Line
The base line (AB and DE, Fig. 5.2) corresponds to the portion or portions of the DTA
curve for which ?T is approximately zero.
Peak
A peak (BCD, Fig. 5.2) is that portion of the DTA curve which departs from and
subsequently returns to the base line.
Endothermic Peak
An endothermic peak, or endotherm, is a peak where the temperature of the sample falls
below that of the reference material, i.e., ?T is negative.
Exothermic Peak
An exothermic peak, or exotherm, is a peak where the temperature of the sample rises
above that of the reference material, i.e., ?T is positive.
Peak Width
Peak width (B ,D ,Fig. 5.2) is the time or temperature interval between the points of
departure from and return to the base line. There are several ways of interpolating the base
Chapter 5 - 7
line, and that given in Fig. 5.2 is only an example. Location of points B and D (Fig. 5.2)
depends on the method of interpolation of the base line.
Peak Height
Peak height (CF, Fig. 5.2) is the distance, vertical to the time or temperature axis, between
the interpolated base line and the peak tip (C, Fig. 5.2). There are several ways of
interpolating the base line, and that given in Fig. 5.2 is only an example. Location of
points B and D (Fig. 5.2) depends on the method of interpolation of the base line.
Peak Area
Peak area (BCDB, Fig. 5.2) is the area enclosed between the peak and the interpolated base
line.
Extrapolated Onset
The extrapolated onset (G, Fig 5.2) is the point of intersection of the tangent drawn at the
point of greatest slope on the leading edge of the peak (BC, Fig. 5.2) with the extrapolated
base line (BG, Fig. 5.2).
Differential Scanning Calorimetry (DSC)
A technique in which the difference in energy inputs into a substance and a reference
material is measured as a function of temperature whilst the substance and reference
Fig. 5.2 Formalized DTA Curve