The present demand for anti-stain ceramic materials was
addressed by coating porcelain stoneware tiles by mixtures of
nano-sized zirconium hydroxide and micronized glass frit. Upon
firing, the frit particles form a liquid phase, which can penetrate
the pore structure closing it. The so formed glassy matrix embeds
zirconium oxide or silicate, which are produced ‘‘in situ’’ by zirconium
hydroxide. As a result, the treated tiles become fully stain
resistant, reaching the top scale level for anti-stain properties.
Anti-stain behavior is also combined with enhanced mechanical
performances. The presence of zirconium hard materials confers
to tiles exalted mechanical properties without perceivable change
of the esthetical initial characteristics.
In the current study, nano- and microparticles were used as the
optimum candidates to fill the surface pores of porcelain stoneware
substrates. The use of nano-sized zirconia to produce hard
ceramic materials was previously tested leading to satisfactory
results with respect to mechanical properties. However, the treatment
procedure was unsustainable since two firing steps were
needed. Moreover, the stain resistance issue was not taken into
account.
The theoretical framework of the present study addresses the
gaps identified in previous work. The novel treatment methodology
described in this article consists of the combination of micronized
glass frit, which imparts anti-stain performances, with
nanoparticles of zirconium compounds, which ensure mechanical
resistance.
The extraordinarily low dimensions of zirconium hydroxide
synthesized with hydrolysis ratios lower than 1 led to a complete
transformation of zirconium hydroxide to zircon simply through
a typical industrial porcelain stoneware cycle with a maximum
temperature of 1215 C held for 10 min. This latter finding extends
the applicability of the developed treatment to a wide range of tile
finishes, including bright and dark colors. It is worthwhile to note
that the obtained coating is permanent with no need of costly and
time-consuming periodical treatments.
The modest cost and versatility of the developed procedure
makes it easily extendible on an industrial scale and to a large variety
of ceramic supports, ranging from porcelain stoneware to ‘‘cotto’’.
Therefore, innovative ceramic products can be produced