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Ramped Pyroxidation/ Combustion

Ramped pyroxidation/combustion involves heating samples incrementally in the absence/presence of oxidation and trapping fractions of the CO2 gas that is produced as part of the associated thermal decomposition of sample material. This allows specific components with different thermal degradation temperatures to be targeted for radiocarbon dating or stable isotope analysis.

For example, bulk samples from various systems are comprised of multiple carbon components, integrating labile (readily degraded) and recalcitrant carbon.

Sample types such as DOC, POC, lake/river/wetland bulk sediment, bulk soil or bulk peat are all suitable for Ramped Pyroxidation (RP) or Ramped Combustion (RC). RP and RC are valuable tools that uses the thermal stability of organic carbon (OC) to isolate components from a bulk sample (Williams et al., 2014; Rosenheim et al. 2013; 2012).

Ramped pyroxidation/combustion incrementally heats bulk samples in the absence of oxygen to precipitate the breakdown of OC fractions according to their degradation temperature. RC also heats samples under a ramped temperature cycle but in the presence of O2, which reduces the risk of charring in the process. Both methods produce a CO2 spectra (after oxidation at 850˚C). The CO2 can be collected over selected temperature steps for radiocarbon and stable isotopic analysis.

Thus we can characterise compositional diagenetic characteristics of a comprehensive range of organic samples, significantly enhancing the analysis of bulk soil/peat/aquatic sediment, DOC and POC for chronology and carbon source attribution.

An example CO2 spectrum produced during a Ramped Pyroxidation Run

The RP Facility at the 14CHRONO Centre, Queen’s University Belfast.

The system can be set upfor Ramped Pyroxidation or Ramped Combustion, depending on sample type. The samples are transferred directly to a Hydrogen Graphitisation line.

14CHRONO is also investigating other applications of ramped pyroxidation/combustion, such as a possible solution to dating contaminated samples.

The RP/RC method has been successfully applied to the dating of lime mortar samples where results suggest that CO2 fractions only associated with the setting of the lime binder were isolated. This has potentially provided a refined and improved chronology of the sites in question. Further work is ongoing to investigate the benefits of this method relative to other methods, such as sequential dissolution.

The RP/RC method was also applied to dating a wooden bowl from a museum collection that had been treated with preservatives, developing a new technique for radiocarbon dating of organic artefacts that are contaminated by museum conservation processes. This technique could provide a new avenue for the investigation of museum or archaeological collections previously considered too difficult to date.

 

For queries or details regarding ramped pyroxidation / combustion at 14CHRONO (currently research only)

Please contact Dr Gerard Barrett

EMAIL g.barrett@qub.ac.uk

PHONE +44 (0)28 9097 5105

References:

Keaveney, EM, Barrett, GT, Allen, K, Reimer, PJ (2021). A new ramped pyroxidation/combustion facility at 14CHRONO, Belfast: setup description and initial results. Radiocarbon 63(4): 1273–1286.

Barrett, GT, Keaveney, E, Lindroos, A, Donnelly, C, Daugbjerg, T.S., Ringbom, Å, Olsen, J, Reimer, PJ (2021). Ramped pyroxidation: A new approach for radiocarbon dating of lime mortars. Journal of Archaeological Science 129: 105366.

Barrett, GT, Keaveney, E, Reimer, PJ, O’Neill-Munro, N, Barrett, MT, Mullarkey, P, Seaver, M (2021). Ramped pyroxidation radiocarbon dating of a preservative contaminated early medieval wooden bowl. Journal of Cultural Heritage 50:150-162.

Rosenheim, BE, Galy, V (2012) Direct measurement of riverine particulate organic carbon age structure. Geophysical Research Letters 39(19).

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