classification and chemical descript

classification and chemical description of the complex inorganic
color pigments in the fourth edition. CPMA describes the industrial
ceramic pigment by a code such as CPMA 1-01-4 for vanadium
doped zirconia [10]. The commercial yellow ceramic pigments
included into the CPMA classification are the vanadium doped
zirconia (CPMA 1-01-4), the Naples yellow of lead antimonate
pyrochlore (CPMA 10-14-4), the yellows based on doped rutile or
cassiterite (CPMA 11-15-4 for Ni,Sb–TiO2, CPMA 11-16-4 for Ni,
Nb–TiO2, CPMA 11-52-4 for Ni,W–TiO2 and CPMA 11-22-4 for
V–SnO2) and the yellow of praseodymium in zircon (Pr-zircon,
CPMA 14-43-4) [11].
The bismuth vanadate BiVO4 with fergusonite structure is
also used as yellow pigment in plastic and ceramic industries.
This structure can be considered derived from fluorite CaF2
lattice substituting Ca by both A and B cations in 1:1 atomic
ratio, A occupies a very deformed dodecahedral environment
and B is in tetrahedral coordination [12,13]. It can be
synthesised by solid state route, but more glossy colours are
obtained using hydrothermal and coprecipitation routes; depend-
ing of the synthesis conditions zircon or powellite phases
crystallize. DTA–TG and XRD analysis indicate that first zircon
crystallizes and transforms with the thermal treatment into a
fergusonite phase which stabilizes in the cooling. The quality of
the colour depends of the microstructure developed by the
thermal treatment [14]. The stabilization by solid state reaction
has made many patents that try to do it by alkaline or earth
alkaline cations doping bismuth or substituting vanadium by
molybdenum or tungsten. Using alkaline or earth alkaline
dopants the monoclinic form of fergusonite or β-fergusonite
[15] is stabilized. Gotić et al. [16] have obtained the pigment by
solid state reaction at 700 1C which is integrated by compact
and irregular particles which relative high size (around 15 μm)
with brown–yellow colourations. By hydrothermal or copreci-
pitation routes fine and regular particles of 0.3–1.2 μm are
obtained which produce lemon-yellow pigments.
From the sequence of pressure-driven phase transitions above
described for ABX4 compounds [1] (I41/amd (zircon)-I41/a
(scheelite)-I2/a (fergusonite)), it can be observed that the
extremes (zircon and fergusonite) produce some known stable
ceramic pigments but as far we are concerned, there is not any
known ceramic pigment based in scheelite. Only recently and
related to powellite, isostructural with scheelite, ceramic pigments
with the general formula Pr2À xCaxMo2O9À δ (x between 0 and 1)
have been obtained [17] which develop colorations from yellow to
green with easily application in plastics and in low reactive ceramic
glazes. The performance of pigments enamelled in a lead free
double firing ceramic glaze produces light yellow colours not
better than b*¼ 19. Using NH4Cl, NaF and Na2SiF6 as flux agents
in the (Pr2À xCax)Mo2O9 x¼ 0.1 composition with the same molar
addition of halogens (0.84 mol per formula weight), a structural
effect of fluoride ion is observed but the yellow colour on
enamelled samples does not improve. Finally, using an ammonia
coprecipitation method in the x¼ 0.6 sample, more regular and
higher crystal size crystallization are produced. The microstructure
obtained from CO method gives more intense yellow coloured
powders and improve their resistance against glaze, producing
significantly best yellow colours than ceramic samples [18].