Stepwise Isothermal Scans - TA Instruments TGA 2950 Operator's Manual

Stepwise
Isothermal Scans
TA I TGA 2950
NSTRUMENTS
In Figures B.16 and B.17 we see the result of
stepwise isothermal scans of the bicarbonate
mixture using a conventional 1
and the abort segment. The following method
was used for the scan in Figure B.16:
1: Abort next seg if %/min > 0.15
2: Ramp 1 ° C/min to 300
3: Abort next seg if %/min < 0.015
4: Isothermal for 500 minutes
5: Repeat segment 1 til 300
Although this method gives apparently excellent
separation results, the quantitative value of the
weight loss plateau between the two bicarbonate
decompositions is in question because there is
no inflection point in the plateau and the rate of
weight loss immediately increases after the
isothermal segment is aborted. This indicates
that the two decompositions are still overlapped
and that holding for a longer isothermal time
period during the first transition would have
resulted in a lower weight loss plateau between
transitions.
In Figure B.17 the same stepwise isothermal
method is repeated with the %/minute limits for
the abort segments set to smaller values (0.05%/
minute for the ramp abort and 0.005%/minute
for the isothermal abort). The following method
was used for the scan in Figure B.17:
1: Abort next seg if %/min > 0.05
2: Ramp 1 ° C/min to 300
3: Abort next seg if %/min < 0.005
4: Isothermal for 500 minutes
5: Repeat segment 1 til 300
TM
Hi-Res Option
° C/minute ramp
° C
° C
° C
° C
B–65