1. Introduction
Zircon (ZrSiO4) pigments are commonly used in the ceramic
industry for glazes due to their high chemical stability and
superior resistance to the dissolution during firing in glazes.
These pigments are made by calcining a mixture of SiO2, ZrO2,
a dopant ion which produces the colour and a mineralizer.1
Turquosie blue zircon pigments containing vanadium, yellow
pigments containing praseodymium and pink pigments containing
iron are produced commercially. During the reaction, silica
is attacked by the mineralizer such as sodium floride (NaF) and
transported to the ZrO2 where ZrSiO4 is formed. The dopant
ion is trapped in the lattice during the formation process. Several
studies showed that the colouring ion must be present at
the time of ZrSiO4 formation.2–4 Recently, it was reported that
these pigments can also be prepared by non-conventional methods
such as aerosol hydrolysis,5 sol–gel6,7 and coprecipitation
routes8 at lower temperatures than solid-state methods.
Zircon pigments cannot be made from the mineral zircon
itself. There is thus the unusual circumstance that natural zircon
is processed to produce zirconium oxide, which is then
reconverted to zircon while making the colour.1 Since ZrO2 is
∗ Corresponding author. Tel.: +90 222 3213550x6371; fax: +90 222 3239501.
E-mail address: eozel@anadolu.edu.tr (E. Ozel).
obtained by complex and expensive purification process from
zircon sands, synthesis of a pigment by using zircon or intermediate
in the process of making ZrO2 might have a significant
economical advantage. Several numbers of patents have
claimed that intermediate products in the process of making
ZrO2 from zircon can be used to produce zircon pigments, which
has more regular and intense hue. Sodium silico-zirconate frit
(Na2O·SiO2·ZrO2) prepared from zircon sand by fusion with
alkali oxides such as Na2CO3 at about 1000 ◦C were mixed
with extra SiO2 to make up the correct molar proportioning and
calcined at 800–1000 ◦C together with a vanadium for blue and
iron compound for pink colour.9,10
In previous studies, zircon pigments were prepared from mineral
zircon, as the starting raw material. Zircon was decomposed
with waste KOH/NaOH mixtures and decomposed products
were used to produce pink–violet zircon pigments by adding iron
compounds11 and blue–green pigments by adding CrOOH and
PbCrO4.12 Naga et al.13 also reported that green zircon pigments
containing Cr2O3 were prepared with zircon sands dissociated
with fluoride salts.
In recent years, studies have focused on the synthesis
and characterisation of zircon pigments obtained from a nonconventional
mixture of precursors. Bondioli et al.14 reported
that it is possible to obtain a zircon hematite inclusion pigment
from the mixture containing FeOOH and Li2O–ZrO2–SiO2
glass that was prepared with lithium carbonate, zirconium