title: Occupancy of the sodalite cages in the blue ultramarine pigments.
abstract: A quantitative EPR study of blue ultramarine pigments has been performed in order to determine the concentration of the S(3)(-) chromophore. Copper sulfate CuSO(4) x 5H(2)O has been used as a standard, while a ruby crystal was used as an inner standard to take into account the changes of the quality factor of the cavity. These experiments show that, in the most-colored pigments, less than half of the sodalite cages are occupied by a S(3)(-) radical. In other experiments, it has been shown that the blue ultramarine pigments can be significantly modified by heating under a dynamic vacuum. The concentrations of S(3)(-) and S(2)(-), as deduced from EPR and Raman experiments, are increased after this type of treatment. These changes imply that sulfur species are transformed into S(3)(-) or S(2)(-) during this treatment. It is discussed that these sulfur species could be S(2)(-).
authors.affiliation: Laboratoire de Spectrochimie Infrarouge et Raman (UMR 8516 CNRS), 13 rue de Toul, 59046 Lille Cedex, France.
authors.forename: N
authors.initials: N
authors.lastname: Gobeltz-Hautecoeur
authors.forename: A
authors.initials: A
authors.lastname: Demortier
authors.forename: B
authors.initials: B
authors.lastname: Lede
authors.forename: J P
authors.initials: JP
authors.lastname: Lelieur
authors.forename: C
authors.initials: C
authors.lastname: Duhayon