Developments in Ceramic Materials Research

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S. Ardizzone, C. L. Bianchi, G. Cappelletti et al.
L* axis)with increasing the dopant content. The V-doped samples are all green (negative a*
values) with a shade which becomes darker the larger the dopant amount.
Figure 6. CIE L*a*b* parameters of 1200°C heated samples for the three guest ions, at variable metal/Zr
content.
V-Doped Pigments. Role of Mineralizers
Structural Aspects
In the case of vanadium doped pigments several attempts are reported in the literature to
stabilize the blue colour in the absence of mineralizers either by using the sol-gel process or
adopting high temperatures [33]. Only for very low vanadium loadings and high calcination
temperatures a light blue colour can be obtained. Otherwise when no mineralizers are added a
greenish, unsatisfying, colour of the pigment is invariably obtained, as shownin Figure 4 and
Figure 6.
Although it is generally acknowledged that the presence of a mineralizer, generally NaF,
is necessary in order to achieve a satisfying shade of colour, the specific function of the salt
has never been fully clarified. Eppler studied the role played by the mineralizer in the
structure formation of ZrSiO4 by means of the marker technique. He concluded that the
acceleration of the zircon crystallization, produced by NaF, takes place through the formation
of SiF4 which volatilizes thus favouring the transport of Si species into the zirconia phase
[1,12,13].
In the case of yellow Pr pigments, however, we have observed [17] that, besides the
possible effect provoked by the fluoride anion, the cationic partner of the salt played a