Coloration mechanism in silicate gels and gel-glasses containing iron |
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Authors: | M G Ferreira da silva J M Fernández Navarro |
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Institution: | (1) Departamento de Engenharia Cerâmica e do Vidro, Universidade de Aveiro, 3800 Aveiro, Portugal;(2) Instituto de Cerámica y Vidrio, C.S.I.C., Arganda del Rey, Madrid, España |
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Abstract: | The present investigation was carried out in order to study the incorporation of iron oxide in several samples with a general composition xFeO-(100-x)SiO2 (x between 0.1 and 9.5) and 5RnO-xFeO-(95-x)SiO2 (R=Li, Na or Ca) prepared by the sol-gel method. Samples were gelated and dried at 60°C and thermally treated between 200 and 1000°C in oxidizing and reducing atmospheres. The color change and structural evolution were studied by VIS and NIR spectrophotometry, TEM and X-ray diffraction.When the temperature increases, the color changes from yellow to brown-reddishness, going through a bright ruby-red, at the same time the absorption edge shifts to higher wavelengths and at elevated temperatures to smaller wavelengths newly. A part of iron oxide is incorporated into the glass network and the remaining as colloidal particles, producing a double mechanism of coloration by optical absorption and dispersion.In the samples heat-treated in oxidizing conditions all iron is present in the ferric state. When the heat-treatment is carried out in reducing conditions the presence of iron (II) was detected at temperatures of nearly 1000°C. |
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Keywords: | iron oxide colloidal particles color mechanism spectrophotometry |
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