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- Pre-ignition weighing
- Igniting samples
- Post-ignition weighing
Advice on LOI Procedures (from Exp. 366 Methods, from Exp 393/Jeff Ryan)
Shipboard sample preparation and LOI determination procedures described in Murray (2000) and updated in recent IODP Proceedingsvolumes (e.g., Reagan et al. [2015] for Expedition 352) are appropriate for a range of sediment and rock compositions, but some care must be taken with unusual sample matrixes. As an example, attempting sample ignitions on carbonate-rich materials can lead to spurious results and issues with contamination if quartz crucibles are used for sample ignitions because carbonates will react with quartz upon heating to both devitrify and decompose the crucible. Alumina ceramic crucibles may be better for carbonates but risk contamination for Al and potentially other elements due to spallation over time. Putting sediment in quartz crucibles ruins the crucibles and the LOI (consulted with Jeff Ryan on this Exp 393)
Maximum ignition temperatures of 1000°C and higher are appropriate for ultramafic and some mafic igneous materials but may result in sample sintering and/or sticking to some Si- or Ca-rich materials. Ignition temperatures of <850°C are inadequate to decompose carbonate minerals in sediment samples, even if samples are held at temperature for several hours. In general, igniting samples to at least 900°C as a maximum temperature is advisable to decompose all volatile-bearing phases and obtain reliable measures of LOI.
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Figure 32. Reference weights. A: Weights. B: Tweezers.
Weighing Crucibles
** When preparing for LOI make sure samples high in carbonates or sediment samples go in CERAMIC crucibles instead of QUARTZ.***
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The quartz crucibles have three sections: an outer (or large) crucible, an inner (or small) crucible, and a lid (Figure 33). If alumina ceramic crucibles are needed, as for carbonate rich samples or sediment samples, replace the inner quartz crucible with the ceramic crucible.
Figure 33. Crucible components. A: Outer (large) crucible. B: Inner (small) crucible. C: Lid.
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