Differential Thermal Analysis of
Mixed Organic Materials
LOUIS HEMPHILL, Associate Professor
Sanitary Engineering Department
University of Missouri
Columbia, Missouri
The problems of waste disposal and water pollution control have stimulated
interest in the revision of established analytical methods and fostered the development of new methods. Recent developments in analytical chemistry instrumental methods have shown that physical methods of analysis are sometimes able
to measure selected constitutents below the sensitivity limit of wet chemistry
methods. Instrumental analysis has demonstrated that often a chemical species
can be determined qualitatively and/or quantitatively by measuring specific energy absorption or emission. A large portion of the analytical problems in sanitary engineering are centered about determining the nature and concentration of
heterogeneous organic waste materials. Analysis of organic waste materials,
qualitatively and quantitatively, by differential thermal analysis has shown that
this analytical method may be useful for sanitary engineering application.
It is the purpose of this paper to 1) describe the basic theory and features of
differential thermal analysis and 2) present results of a laboratory study designed
to evaluate differential thermal analysis for sanitary engineering application.
BASIC THEORY AND FEATURES OF DIFFERENTIAL THERMAL ANALYSIS
Differential thermal analysis (DTA) differs from conventional methods of
thermal analysis in that temperature changes accompanying thermal energy reactions are measured rather than changes in dimensions or mass. Two major thermal reactions, exothermic and endothermic, may occur during heating or cooling
of a material. Differential thermal analysis is the process of measuring and recording exothermic or endothermic reactions. In practice, a sample material
and a thermally stable standard material are heated or exposed to the same temperature environment. During the heating period the sample material may undergo a series or sequence of thermal reactions such as melting, boiling, combusr
tion or isothermal phase changes. In each of these reactions, energy is absorbed
or emitted by the sample material. The thermal energy changes accompanying
each reaction are reflected in the differential temperature generated by the sample and standard.   An idealized DTA reaction peak is shown in Figure 1.
The three basic or elemental components of the DTA system are a controlled
heat source, sample holder and a differential temperature measuring-recording
device. The type and construction of each of these units is often variable depending upon specific application.
Several investigators have stated the general requirements of the heat source
and have described this portion of the apparatus as being the most important (1).
The heating rate available for conventional DTA furnaces is limited by the power
supply and materials of construction.
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