Dehydroxylation
Definition
The loss of structural hydroxyl groups from clay minerals (principally kaolinite) between about 450 and 600 °C during firing; an irreversible reaction that converts crystalline clay to an amorphous phase, recorded in XRD as the disappearance of the kaolinite peaks.
- Mineral affected
- Kaolinite (clay)
- Temperature range
- About 450 to 600 degrees C
- Detection method
- XRD, disappearance of kaolinite peaks
- Reversibility
- Irreversible
Common questions
Why does dehydroxylation matter for dating or sourcing fired ceramics?+
Because it is irreversible, the mineral change it leaves behind confirms a sample was fired above roughly 450 to 600 degrees C, letting analysts distinguish deliberately fired ceramic from unfired or low-fired clay in provenance and authenticity questions.
How is dehydroxylation identified in a laboratory sample?+
X-ray diffraction shows the characteristic kaolinite peaks have vanished and been replaced by an amorphous pattern, which is the standard signature analysts look for.
Related terms
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- The combination of clay matrix and included particles (temper, natural inclusions, and voids) that makes up a fired ceramic; the raw material...
- Grog
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- Mullite
- An aluminosilicate phase (3Al2O3·2SiO2) that nucleates in fired clay above roughly 980 °C, coinciding with the characteristic exothermic reaction of the kaolinite-to-mullite...
- Provenance
- The documented origin of a media file: the device that captured it, the time and location of capture, the chain of custody...
- Temper
- Material deliberately added to clay before forming to reduce drying shrinkage and firing cracking; common temper types include sand, grog (crushed old...