Retention of Phosphate in Buried Ceramics: An Electron Microbeam Approach

Elevated concentrations of P 2 O 5 of 2–12 wt% absolute were observed in the matrices of a small group of ceramics with the electron microprobe. P 2 O 5 , CaO and FeO t are enriched towards the surfaces in some cases and elemental correlations suggest precipitation of a crystalline calcium phosphate with a stoichiometry close to CaO · P 2 O 5 . Scanning electron microscopy with X‐ray mapping showed P 2 O 5 to be dispersed in the ceramic matrix on a very fine scale, while X‐ray diffraction detected no crystalline phosphate. Parallels are drawn with the precipitation of phosphate in the surfaces of weathered glass. It is concluded that the amorphous phases produced on firing behave as chemically active substrates which facilitate the adsorption or precipitation of very fine grained calcium phosphate from the burial environment.