Results and Discussion
3.1. The influence of mixing procedure
(Run1)
For each of NBS28 and SWy-1, three conditions were compared (Fig. 2):
the samples enveloped with PTFE in silver capsules (Fig. 2(a), (b)) show
a CO peak with half the peak height of the reference gas peak. The small
peaks around 170–180 s between the reference gas and CO peaks are the
peaks of atmospheric N2 remaining in the silver capsule.
Comparing the CO gas generation from non-silicates (NBS18, IAEA-601, and
-602) and silicates (NBS28 and SWy-1), the latter showed peaks with
lower intensity and tailing on the right side, suggesting that thermal
decomposition did not occur instantaneously. The tailed peaks took
40–50 min to return to background levels, resulting in a measurement
time of approximately 60 min per sample. Next, whether using Ni/C
instead of graphite would improve the reactivity was tested (Fig. 2(c),
(d)). The shape of the CO peaks became sharper, and the peak height
increased distinctly, especially in SWy-1. Furthermore, the
homogenization of Ni/C and PTFE with the sample before weighing and
encapsulation resulted in sharper and higher peaks (Fig. 2(e), (f)). The
peak height was close to that of non-silicate minerals. This is
considered to be due to the closer distance between the sample and the F
and C sources, in addition to the homogenization process, which crushed
the grains of NBS28 (several hundred micrometers in diameter) into finer
grains. However, the tailings of the peaks were still not completely
resolved. It took 40–50 min to return to the background level. It is
possible that some oxygen was retained in the residue and then gradually
released, even though the majority of the samples broke down. The CO
peak area, which is directly proportional to the oxygen output, and the
isotope ratio could not be calculated since the peaks’ long tailings
made it impossible to establish their end positions.