Spectral reflectance curves of glazed tiles coloured with pigments
prepared with decomposed products or pure oxides calcined
at different temperatures are given in Fig. 3. As expected,
there was no absorption in glaze containing pigment prepared
with decomposed product,washed withwater and has no colour.
In contrast, the absorption is above 500 nm and the wavelength
of absorption is centred in yellow–red region in the glaze containing
pigments prepared with decomposed product washed
with H2SO4 solution. Reflectance curves or colour properties of
pigments prepared with decomposed product and pigment made
from pure oxides are very similar.
The L*a*b* values of coloured porcelainized tiles containing
pigments are given in Table 3. It is clear that the intense blue
colours were obtained in porcelainized tiles containing 5 wt.%
pigment. Although colour intensity is less than pigments prepared
with pure oxide, decomposed zircon as a raw material can
safely be used to produce pigments and reduced the pigment
production cost if higher amount of pigment is used in a final
product.
The XRD patterns of V-containing blue pigments produced
from decomposed zircon with excess SiO2, NH4VO3 and mineralizer
mixture and calcined at different temperatures are shown
in Fig. 4. Decomposed zircon products of Na2ZrSiO5 and
Na2ZrO3 react with excess SiO2 and crystallise as zircon at
the calcination temperatures. Small amount of an intermediate
compound, Na2ZrSiO11 were also observed at 900 ◦C while this
phase completely disappeared at 1000 and 1100 ◦C. Although