Rehydroxylation [RHX]: Some scientific comments and issues Christopher Hall
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Transcript of Rehydroxylation [RHX]: Some scientific comments and issues Christopher Hall
Rehydroxylation [RHX]:
Some scientific comments and issues
Christopher Hall
University of EdinburghSchool of Engineering
Centre for Materials Science & Engineering
UoE/National Museums Scotland Research Laboratory for Conservation Science
Moisture dynamics in buildings andmasonry structures
Hall, Hamilton, Viles et al 2010
Delta-Min Marie Curie Network
Mechanisms of Mineral Replacement Reactions 2009-2012
Penn floor tileSt Bride’s ChurchFleet StreetLondon UK
Museum of London WFG62
Assigned date AD 1350-1390
Penn floor tileSt Bride’s ChurchFleet StreetLondon UK
Museum of London WFG62
Assigned date AD 1350-1390
Normalised stage 2 slope ln(α/α25) plotted against 103 /T K-1, where α25 is theinterpolated slope at 25 °C, for three fired clay brick and tile samples. Red: Romanopus spicatum clay paving brick, London; blue: ‘Westminster’ clay tile, MertonPriory; green: clay brick, King Charles II Court, Greenwich
Arrhenius plot: effect of temperature on rehydroxylation mass gain rate.
Samian ware:X-ray diffraction
Stackhouse, Coveney et al.
Stage I
Stage II
Variation of the fractional mass gain (Δm/mo) with the fourth root of time (time)1/4 of kaolin samples fired at different temperatures [Hesham Mesbah]
Open questions
Why (time)1/4?
A Putnis Rev Mineralogy Geochem 2009
Pseudomorphic replacement of calcite and aragonite byHydroxyapatite
Normal diffusion
(time)1/2
Lizana and Ambjörnsson Phys Rev Lett 2008 v100 20601
Lizana and Ambjörnsson Phys Rev Lett 2008 v100 20601
Open questions
Why (time)1/4?
… and, if single-file diffusion, on what structure?
Open questions
Why (time)1/4?
… and, if single-file diffusion, on what structure?
Why rehydroxylation when firing has proceeded to 1050 °C?
Does accurately describe the entire process on 1000 year time scales?
Some conclusions
Incontrovertible evidence that the RHX process occurs more or less universally in all fired clay ceramics
Strong evidence that the (time)1/4 clock is valid
Data acquisition for a single sample is still laborious
Major validation studies needed
Mechanistic and materials fundamentals not fullyunderstood
AcknowledgementsMoira Wilson, Margaret Carter, Ceren Ince, Bill Hoff, Hesham Mesbah (Manchester)
Andrea Hamilton (Edinburgh)