Dehydroxylation and Rehydroxylation Mechanisms in Fired Clay Ceramic: A TG‐MS and DRIFTS Investigation

Abstract

Selected instrumental techniques [dilatometry, thermogravimetry – mass spectrometry (TG‐MS), and variable temperature – diffuse reflectance infrared Fourier transform spectroscopy (VT‐DRIFTS)] have been used to investigate the role of moisture in the rehydroxylation reaction which causes expansion and mass gain in fired clay ceramics. The temperature range over which adsorbed water molecules and structural hydroxyl groups are desorbed from fired clay ceramic as it is reheated, and the nature of the structural hydroxyls that are formed as the ceramic is cooled and then held under controlled conditions have been explored. The mass chromatogram for m/z = 18, supported by VT‐DRIFTS, showed that physisorbed water molecules were removed from the ceramic at about 105°C, whereas strongly bound molecules of water and structural hydroxyls were held to ≤500°C. Dilatometry revealed a marked contraction of the ceramic between 200°C and 330°C which corresponded to loss of strongly bound molecules of water. The VT‐DRIFTS also showed that the interaction of water molecules with the ceramic body following reheating occurred in two stages and confirmed the kinetic law previously derived from mass gain and moisture expansion in fired clay ceramics.

Physical and mineralogical properties of experimentally heated chaff-tempered mud bricks: Implications for reconstruction of environmental factors influencing the appearance of mud bricks in archaeological conflagration events

“…The effect of heat on the FTIR spectrum of clay minerals has been extensively explored (Farmer, 1974;Shoval et al, 1991Shoval et al, , 2011Berna et al, 2007;Savage et al, 2008;Clegg et al, 2012). It has been shown that reversible and irreversible structural changes with heat occur in clay minerals, producing significant spectral changes that allow identification of heating temperature.…”

RHX Dating of Archeological Ceramics Via a New Method to Determine Effective Lifetime Temperature

“…It causes a small increase in mass and appears to continue indefinitely. Wilson, Hall et al [1][2][3][4][5][6][7][8] established that the kinetics of this reaction depends on the quartic (fourth) root of the elapsed time (time) 1/4 ; and suggested that the RHX process may be used as an "internal clock" to establish the age of archeological ceramics; that is, the time elapsed since the ceramic pottery was fired. Figure 1 shows the notation and illustrates the RHX dating method.…”

Modeling Rehydration/Rehydroxylation Mass‐Gain Curves from Davenport Ceramics

“…1 In addition, Clegg et al demonstrated that the water lost from archeological samples during reheating was replaced after exposure to humid air. 2 The water vapor present in the atmosphere is sufficient to drive the rehydration/rehydroxylation process, which can be divided into the initial gain of physically bonded (i.e., adsorbed) water and the reaction of water with meta-clays in the sample. It is has been observed that both processes proceed concurrently at early times, thus comprising "Stage I" behavior.…”

“…(1)] as well as the time 1/n empirical model of rehydration/rehydroxylation mass gain [Eq. (2)]. The previous report by the authors examined the effects of temperature and humidity fluctuations.…”