Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.735873
Title: Rehydroxylation dating
Author: Hare, Vincent John
ISNI:       0000 0004 6500 6008
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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Abstract:
This thesis is concerned with a better understanding of issues which currently limit the precision, accuracy and robustness of rehydroxylation (RHX) dating. MC simulations and analytical expressions show that age uncertainties of previous studies are underes- timates. The ratio of sample mass to balance resolution should be of the order of 10-6 or less for measurement precision under 1%. A combined measurement uncertainty of ~ 4 % should be possible, given well-designed experiments, appropriate samples, and a t1/N model with N = 4. Highly-fired materials have an age limit of ~ Ma, but low α and ymax preclude dating materials such as porcelain. There is little correlation between non-stabilisation of m2 and factors such as porosity, specific heat capacity or density. The strongest effect is that of sample dimension (thickness), which is found to cause long times to stage II mass gain following 105 °C heating - roughly proportional to the thickness squared, suggesting some long-lived contribution from Fickian diffusion. Another strong effect is acceleration of the rehydroxylation reaction upon cooling from high temperatures, which is also dependent on sample size. This causes long times to stage II, and inaccuracies in fitting αm. Sample dimensions therefore pose a fundamental challenge for rehydroxylation dating by gravimetric analysis. Evidence is presented for a long-lived weakly-bound (T1) water regime in certain materials. A new apparatus for high-precision mass measurements of multiple samples under controlled conditions was used to investigate differences between meta-clay minerals, and to evaluate the efficiency of different pretreatments on fired clays of known age (1.1a). RHX age determinations, corrected for ELT, range from 30.1 ± 0.3 a to 1.51 ± 0.04, and some clear differences ap- pear for different meta-clay minerals. FTIR spectra indicate that treatment with 0.5M HCl at 70 °C for 30 minutes causes rehydroxylation of clay minerals, but 0.1M HCl seems suitable. Organic removal by chloroform/methanol solvent extraction or H2O2 treatment avoids alteration of structural OH, but is not as effective as supercritical fluid extraction (SFE) in the case of lipids. The RHX age determination of a sample of Werra pottery (MAN07) was 169 ± 30 a, with an activation energy of 82.7 kJ mol-1 and at an ELT of 10.5 °C, which is not in agreement with the result obtained in previous studies. The relationship between the t1/4 model and diffusion mechanisms is briefly discussed, and a discussion of the issues is entertained. Goodness-of-fit statistics are highest for a model with long-lived T1 and T2 regimes, but this mass gain behaviour is identical to that expected from an accelerated t1/4 process and slow cooling. It is therefore not possible to exclude the possibility of a t1/4 regime.
Supervisor: Ramsey, Christopher Bronk Sponsor: John Fell OUP Research Fund
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.735873  DOI: Not available
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