Sains Malaysiana, 2018;47:581-587.

Abstract

Ceramic colour pigments based on the malayaite structure was synthesized by sol-gel with an aim to obtain homogeneous
powder systems. The formulation was Ca(Sn1-xCrx
)SiO5
where x = 0, 0.02 and 0.05. Thermogravimetric analysis and
infrared spectroscopy suggested suitable calcination temperatures to be > 1000°C. Formation of malayaite phase was
found to be very difficult; high calcination temperatures up to 1400°C was required which was typical for this particular
phase. Nevertheless, small amounts of impurities were still present and were found to be both wollastonite (CaSiO3
) and
cassiterite (SnO2
). The oxidation state of chromium was found to be mainly 4+. The obtained pigment particles were
in the range of 1-5 micron with a high degree of agglomeration due to sintering. UV-vis spectra demonstrated broad
absorbance peak in the 550-600 nm range which could be attributed to both Cr(III) and Cr(IV). The colour parameters in
the CIELab system showed a red tone (more positive a* values whereas b* remained relatively constant) when chromium
was doped into the malayaite host. Preliminary interaction testing with a low-fire glaze displayed an even improvement
in the a* parameter (getting more red tone). Microscopic studies showed a certain degree of chromium diffusion out
of the pigment powders toward the glaze matrix. These results have demonstrated a great potential for this refractory
colour pigments to be possibly utilized in other kinds of glazes as well.