TA Instruments TGA 2950 - Constant Reaction Rate Scans

TA I NSTRUMENTS TGA 2950 B–63
Hi-Res
TM
Option
Constant Reaction
Rate Scans
In Figure B.15 we have overlaid the conven-
tional constant heating rate decompositions of
the bicarbonate mixture (curves c and e) with
constant reaction rate Hi-Res
TM
scans at differ-
ent resolution and sensitivity settings. Curve b
shows the Hi-Res
TM
scan run in an open sample
pan at resolution setting -4.0 and sensitivity
setting 1.0. For curve d (resolution -4.0) and
curve a (resolution -5.0) the sample was con-
tained in a hermetic aluminum DSC sample pan
with a 0.1mm pin hole in the top. All of the Hi-
Res
TM
scans were run at 5
o
C/min.
Comparing curve b to curves a and d, we can see
a significant improvement in resolution due to
the vapor pressure build up in the semi-hermetic
sample container. Because the sample pan was
open in curve b, there was no opportunity for a
vapor pressure/reaction rate equilibrium to occur
as the sample decomposed resulting in only
partial separation of the transitions. The pres-
sure buildup in the closed container (Curves a &
d) retarded the potassium bicarbonate decompo-
sition until the sodium bicarbonate decomposi-
tion had completed. As with dynamic rate mode
(Figure B.13), we see that higher resolution
setting (larger negative number) reduces transi-
tion temperature.