The mechanism for the colour change of iron chromium black pigments in glazes through transmission electron microscopy techniques

Black iron–chromium (Fe–Cr) bearing oxide pigments are generally utilised as effective colourants in a wide variety of applications. However, in the case of their use within ZnO-containing glazes, they yield an undesirable brown colour instead of expected black colour. In order to understand the col...

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Bibliographic Details
Published in:Dyes and pigments 2011-11, Vol.91 (2), p.126-133
Main Authors: Yurdakul, Hilmi, Turan, Servet, Ozel, Emel
Format: Article
Language:English
Subjects:
Color
Colour
Electron energy loss spectroscopy (EELS)
Electron microscopy
Energy dispersive X-ray spectroscopy (EDXS)
Fe–Cr black pigment
Focused ion beam (FIB)
Glaze
Glazes
Iron
Mathematical analysis
Oxides
Pigments
Transmission electron microscopy
Transmission electron microscopy (TEM)
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Summary:Black iron–chromium (Fe–Cr) bearing oxide pigments are generally utilised as effective colourants in a wide variety of applications. However, in the case of their use within ZnO-containing glazes, they yield an undesirable brown colour instead of expected black colour. In order to understand the colour change in this system, we report the use of focused ion beam (FIB) sample preparation technique followed by the use of analytical transmission electron microscopy (TEM) characterisation techniques. According to the results, the formation of a reaction layer between the pigment and glaze was identified with an average composition of Zn 0.48Fe 0.79Cr 1.32O 4. Additionally, the valance of Fe was determined as 3+ in the pigment grain, whereas 2+ in the reaction layer and the glaze, respectively. Therefore, it was concluded that the colour change is occurring as result of the valence variation of Fe, the formation of Zn 0.48Fe 0.79Cr 1.32O 4 compound and the outward diffusion of Fe into the glaze. ► Fe–Cr black pigments lead to an undesirable brown colour in the case of introducing Zn-based glazes. ► Novel microscopy techniques – Focused Ion Beam (FIB) and Analytical TEM – were used to clarify this issue. ► A reaction layer formation composed of multi-grains between the pigment and glaze was identified with an average composition of Zn 0.48Fe 0.79Cr 1.32O 4 (atomic %). ► The outward diffusion of Fe into the glaze was observed. ► The valance of Fe ion was 3+ in pigment whilst 2+ in reaction layer and glaze.
ISSN:0143-7208
1873-3743
DOI:10.1016/j.dyepig.2011.03.014