Developments in Ceramic Materials Research

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S. Ardizzone, C. L. Bianchi, G. Cappelletti et al.
Table 1. XPS atomic ratios of V-doped pigments calcined at 800 and 1000°C
with different mineralizers
sample cation/Zr V/Zr Si/Zr
V0.1800 - 0.20 0.7
V0.11000 - 0.30 1.0
V0.1LiF.800 0.9 0.20 1.2
V0.1LiF.1000 0.7 0.60 1.2
V0.1NaF.800 0.6 0.08 1.0
V0.1NaF.1000 0.7 0.09 1.2
V0.1KF.800 0.5 0.09 0.9
V0.1KF.1000 0.4 0.10 0.9
V0.1LiCl.800 0.9 0.20 1.1
V0.1LiCl.1000 1.6 0.30 1.0
V0.1NaCl.800 0.6 0.06 0.7
V0.1NaCl.1000 0.6 0.08 1.0
V0.1KCl.800 0.7 0.20 0.9
V0.1KCl.1000 0.5 0.10 1.1
The B.E. of Zr varies between 181.7 and 182.7 eV. These values pertain to Zr(IV) species
in zirconium oxides [36]. The BE of the Si 2p peak range between 102.9 and 101.0 eV.
Literature data report 103.2 eV for SiO2 and 101.3 and 102.3 eV are reported for different
silicates [36]. In the case of the present samples, not composed by pure zircon, the silicon
peak may contain more than one component as the result of both silica and silicate species.
Optical Characterization
Figure 10 reports UV-Vis diffuse reflectance spectra acquired on samples calcined at
800°C containing the same V/Zr molar ratio (0.1) but different mineralizers. All the spectra
show a similar shape in the considered region, except for the case of the samples obtained in
the presence of KF and KCl. These powders have a zircon content scarce or null, and present
a yellow colour, consequently they do not reflect light at low wavelengths. For all the other
samples the zircon content is high and the colour vary from green (in the absence of
mineralizer) to blue (sample obtained in the presence of NaF) while for the other pigments
lighter shades of blue can be appreciated. The spectra are compared to the reference one
obtained on the sample without mineralizer which is characterized by a green colour. The
sample without mineralizer shows a minimum of reflectance at about 400 nm [35] due to V 5+
not present in the blue samples. All the samples show: i) a signal at 640 nm [22] attributed to
dodecahedral and tetrahedral V 4+ coordination; ii) a signal at 780 nm [5] due to a shoulderforbidden
transition of V 4+ . Unfortunately the signal attributed in the literature to
dodecahedral V 4+ (300 nm) [37] is not detectable in our spectra because of the instrumental
measurement range.
The presence in the sample without mineralizer of V 5+ is responsible for its green colour
since pentavalent V compounds are yellow.