TA I
NSTRUMENTS
TGA 2950 B–7
Hi-Res
TM
Option
Using Hi-Res
TM
TGA
Background
TGA is particularly useful for observing the
thermal decomposition of compounds. When
individual thermal decompositions occur at well
separated temperatures, quantitative information
about sample composition can be obtained from
the percent weight change at each transition.
However, many TGA decomposition transitions
overlap or appear drawn out in temperature due
to the time-dependent nature of the reactions
taking place. This overlap substantially reduces
the ability to obtain an accurate measurement of
weight change and reaction temperature.
It has long been known that using very slow
heating rates will improve the separation of
some overlapping transitions and, thus, increase
the resolution of the TGA scan. Another
technique to increase resolution is to increase
furnace temperature until the onset of decompo-
sition and then hold temperature isothermally
until the decomposition is complete. After
which, the temperature is raised again until the
next decomposition begins, and so on until the
final temperature of interest is reached. A third
technique to increase resolution is controlling
the furnace temperature in such a way as to
maintain a preselected constant reaction rate (%/
minute). This results in slower or even negative
heating rates during a transition which gives the
reaction more time to reach completion before
the next transition is encountered.
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