Radiocarbon ages and thermal stability
measurements can be used to estimate the stability of
soil organic carbon (OC). Soil OC is a complex
reservoir that contains a range of compounds with
different sources, reactivities, and residence times.
This heterogeneity can shift bulk radiocarbon values
and impact assessment of OC stability and turnover in
soils. Four soil horizons (Oa, Bhs, Bs, Bg) were
sampled from highly weathered 350 ka Pololu basaltic
volcanics on the Island of Hawaii and analyzed by
Ramped PyrOX (RPO) in both the pyrolysis (PY) and
oxidation (OX) modes to separate a complex mixture
of OC into thermally defined fractions. Fractions were
characterized for carbon stable isotope and radiocarbon
composition. PY and OX modes yielded similar
results. Bulk radiocarbon measurements were modern
in the Oa horizon (Fm = 1.013) and got progressively
older with depth: the Bg horizon had an Fm value of
0.73. Activation energy distributions (p(E)) calculated
using the ‘rampedpyrox’ model yielded consistent
mean E values of 140 kJ mol-1 below the Oa horizon.
The ‘rampedpyrox’ model outputs showed a mostly
bimodal distribution in the p(E) below the Oa, with a
primary peak at 135 kJ mol-1 and a secondary peak at
148 kJ mol-1, while the Oa was dominated by a
single, higher E peak at 157 kJ mol-1. We suggest
that mineral-carbon interaction, either through mineral
surface-OC or metal-OC interactions, is the stabilization
mechanism contributing to the observed mean
E of 140 kJ mol-1 below the Oa horizon. In the Oa
horizon, within individual RPO analyses, radiocarbon
ages in the individual thermal fractions were indistinguishable
(p[0.1). The flat age distributions indicate
there is no relationship between age and thermal
stability (E) in the upper horizon ([25 cm). Deeper in
the soil profile higher lEf values were associated with
older radiocarbon ages, with slopes progressively
steepening with depth. In the deepest (Bg) horizon,
there was the largest, yet modest change in Fm of 0.06
(626 radiocarbon years), indicating that older OC is
slightly more thermally stable.
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Kinetics of thermal dewaxing of injection‐molded silicon carbide
Powder injection molding is a near‐net shape, high‐speed fabrication process that has been studied only lightly with silicon carbide (SiC) as the powder. The addition of nanoparticles to the monomodal powder to form a bimodal powder increases the solid fraction in the feedstock but may also adversely affect other properties. In this paper, the kinetic properties of thermally dewaxed SiC mono‐ and bimodal feedstocks by three models were compared to solvent‐dewaxed SiC and thermally dewaxed powder metal from other studies. The activation energy
- NSF-PAR ID:
- 10460692
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal of Ceramic Engineering & Science
- Volume:
- 1
- Issue:
- 2
- ISSN:
- 2578-3270
- Page Range / eLocation ID:
- p. 85-91
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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