Search

Abstract: A pink gahnite pigment, containing the chromophore ion Cr3+, has been synthesised under industrial conditions and characterised by X-ray powder diffraction (XRPD), electronic spectroscopy, electron paramagnetic resonance spectroscopy (EPR) and HF2EPR. The paramagnetic resonance techniques, in particular, have been applied to determine the incorporation of the chromophore in the spinel structure and to study its distribution. The pigment was found to be formed by aluminium borate and, mainly, gahnite (ZnAl2O4). The Cr3+ ion was revealed to be incorporated only in the octahedral site of this latter phase. The chromophore is subjected to a strong crystal field (Δ 0 =18800cm−1), which determines its colouring properties. A large zero field splitting interaction was observed in the X-band EPR spectra and interpreted by comparison with the high-frequency W-band spectra. The axial symmetry of the crystal field surrounding Cr3+ was ascertained by both the techniques. The observed spectroscopic features are due to the single ion properties of Cr3+ in a strong field, thus ruling out any possible clustering of the chromophore within the structure. [Copyright &y& Elsevier]

A new blue hercynite-based pigment, stable at the processing temperatures for the ceramic application, has been synthesized. It is constituted by corundum and Ti-bearing hercynite. In order to clarify the complex Fe distribution evidenced by Baldi et al. [Proc. CIMTEC 2002(2003)], a 57Fe Mo¨ssbauer and diffuse reflectance spectroscopy study has been undertaken. Fe was found to be distributed between corundum, as trivalent, and hercynite, both as Fe(II) and Fe(III). Moreover, Fe(II) occupies both tetrahedral and octahedral sites in the latter mineral, according to a temperature dependent disorder. UV–VIS investigation revealed the presence of a broad band in the blue region, the shape and position of which was found to be due to an intervalence charge transfer mechanism between Fe(II) and Ti(IV) in two edge-sharing octahedra of hercynite. [Copyright &y& Elsevier]

Nanocrystalline pigments for ceramic glazes have been obtained by mechanochemical insertion of Fe and Ti in an α-Al2O3 host matrix (Fe and Ti oxides were reduced by high energy milling with metallic Al with subsequent formation of additional Al2O3 by oxidation of Al(0)). The powders have been characterized by X-ray diffraction, laser granulometry and by surface area and porosity measurements. Sol-gel techniques have also been used in order to obtain pigments with pure Al2O3 and Cr or Fe/Ti-doped Al2O3. Pigments have been prepared using Al(III)-alkoxides or Al(III)-inorganic salts, obtaining products with different characteristics in the two cases. Pigments have been studied by X-ray diffraction, surface area and porosity measurements and by the analysis of electrochemical reactivity in aqueous suspensions. Coloring properties of pigments obtained by mechanomaking and by sol-gel techniques have been tested in ceramic glazes; their properties have also been analyzed by insertion in ceramic bodies for glazed gres (porcelain) technology. [ABSTRACT FROM AUTHOR]