Appendix B
B–54 TA I
NSTRUMENTS
TGA 2950
again initiated, and so on until the final tempera-
ture is reached.
The stepwise heating technique can be easily
implemented by placing a ramp segment fol-
lowed by an isothermal segment into a “repeat to
final temperature” loop, and preceding the ramp
and isothermal segments with abort segments.
The abort segment preceding the ramp is setup
to terminate the ramp when the “%/minute” is
greater than a specified limit. The abort seg-
ment preceding the isothermal segment termi-
nates the holding period when the “%/minute” is
less than a second limit. An example of this
type of method is shown below.
1: Abort next seg if %/min > 0.5
2: Ramp 10
°
C/min to 700
°
C
3: Abort next seg if %/min < 0.05
4: Isothermal for 500 minutes
5: Repeat segment 1 til 700
°
C
The “%/min” limit for the isothermal segment is
selected to be equal to the baseline rate of
weight change encountered during the onset of
the transition of interest via a normal constant
heating rate scan of this material. (Be sure to
use the same ramp rate as that selected for
stepwise heating.) The “%/min” limit for the
ramp segment is selected to be about an order of
magnitude greater than that selected for the
isothermal segment (but not more than the
maximum rate of weight change encountered
during the transition of interest). The ramp final
temperature and the repeat final temperature are
set to the final experiment temperature. The
isothermal time is set to an arbitrary time, which
is sufficiently large such that the segment will
not terminate until the percent/minute limit has
been reached.
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