Rehydroxylation of fired clays: Is the time to the quarter (TTTQ) model correct?

Fired-clay ceramics gain mass with time as a result of rehydroxylation (RHX) of the dehydroxylated structures of clay minerals. The mass gain is usually described using the time to the quarter (TTTQ) model, which is fundamental to the archeometric dating technique called RHX dating. In RHX dating practice, experimental mass gain fits can be improved by adding a time-offset correction (t(0)), apparently corresponding to changes in diffusional parameters. Using theoretical mass gain data generated by diffusional, geometric contraction, and reaction-order kinetic models, we showed that TTTQ model can successfully fit data produced by any deceleratory kinetic model, especially if the t o is applied. The quality of the fits and linearity of Arrhenius plots of theoretical data likely would cause misidentification of the reaction model in favor of TTTQ model in RHX dating practice. The model misidentification results in incorrect values of activation energy (E-a) despite ideal mass gain fits and linearity of Arrhenius plots. In this paper we question the validity of t(0) and propose a calculation of correct E-a from any RHX mass gain data using a model-independent approach.

Automated summary

This paper discusses the mass gain of fired-clay ceramics due to rehydroxylation over time, highlighting the limitations of the TTTQ model and proposing a method for calculating the correct activation energy.