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Journal of the Chemical Society, Faraday Transactions


Journal of the Chemical Society, Faraday Transactions; was published from 1990 - 1998.  In 1999 it merged with a number of European chemical society physical Chemistry journals to become Physical Chemistry Chemical Physics.

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Paper

J. Chem. Soc., Faraday Trans., 1994, 90, 3335 - 3339, DOI: 10.1039/FT9949003335

Thermal behaviour and physico-chemical characterization of synthetic and natural iron hydroxyphosphates

Dominique Rouzies, Jean Varloud and Jean-Marc M. M. Millet

The thermal behaviour of five hydroxyphosphates, lipscombite [Fe3(PO4)2(OH)2], barbosalite [Fe3(PO4)2(OH)2], giniite [Fe5(PO4)4(OH)2· 2H2O], rockbridgeite Fe5(PO4)3(OH)5] and Fe4(PO4)3(OH)3, has been studied. Thermogravimetric analysis revealed the hydroxyphosphates to have distinct behaviours: some underwent dehydroxylation between 623 and 893 K like other phosphates [lipscombite, barbosalite, Fe4(PO4)3(OH)3], while rockbridgeite and giniite differed. Rockbridgeite, which appeared to contain only iron(III) ions, underwent a first partial dehydroxylation at only 438 K, while giniite totally dehydroxyated only at between 623 and 823 K. Comparison of the results obtained by thermogravimetric analysis with those obtained by other techniques, including chemical analysis, X-ray diffraction and Mössbauer spectroscopy, allowed us to propose the existence of a new solid solution for the giniite compound and to confirm that previously observed for rockbridgeite. The solid solution of the former corresponds to a variation in composition due to dehydroxylation–hydration : FeIII4+xFeII1–x(PO4)4(OH)2–x(2 +x)H2O with 0 < x < 1. The latter corresponds to a variation in the composition due to dehydroxylation–oxidation : FeIII4+xFeII1–x(PO4)3(OH)5–xOx with 0 < x < 1. In both cases, Mössbauer spectroscopy indicates that Fe2+ or Mn2+ substituents may be localized on the different crystallographic sites of the structures.