Pigments Ceramics

El objetivo de este trabajo consistió en aplicar del modelo de Kubelka Munk para la predicción de color en esmaltes utilizados en decoración de loza cerámica. El modelo relaciona los coeficientes de absorción y de dispersión de reflectancia difusa esperados para una mezcla de tres pigmentos cerámicos en el espectro visible con las respectivas concentraciones de la composición del esmalte, con lo cual es posible predecir un tono determinado. Se empleó la espectrofotometría visible con el fin de obtener los coeficientes de absorción y dispersión de los pigmentos elegidos sobre sustratos cerámicos para locería, y también para los espectros de reflectancia difusa de las mezclas elegidas para los esmaltes calcinados, los resultados obtenidos mostraron una buena predicción en algunas regiones del espectro visible, concluyéndose que el modelo podría utilizarse para el control de calidad de los productos fabricados en la industria cerámica.

Colors and pigments are not an issue of modern times. Ancient societies have used materials thousands of years ago, to produce color items and artifacts. Research conducted, has revealed various inorganic fossils and ma­terials, used by our ancestors for coloring. The interest of the scientific community on the subject is constantly high, originating from different scientific fields and disciplines. In this project we have experimented on pro­ducing a ceramic pigment, based on an ancient recipe for the production of the Egyptian lbue pigment/color. The objective of the research was to investigate whether the pigment produced, was appropriate to be used for the production of silk-screen printing ink by printing a fine printing of an artwork.

Grayish-blue coloured aluminaemolybdena was synthesized by high temperature reducing firing and experimented as ceramic pigment. Synchrotron light and conventional X-ray diffraction powder, ICP-OES and BET analyses proved that molybdenum spreads over alumina surface, without entering the corundum lattice, with a high superficial concentration (i.e. 27e99 Mo atoms nm À2 ) implying a prevailing octahedral coordination and a certain long-range order, eventually resulting in the formation of crystalline MoO 2 . XPS and DRS suggested the occurrence of different valences, Mo(VI) being predominant over Mo(V) and Mo(IV). The colouring mechanism is mainly due to electronic absorption of Mo(V) in the redeorange region of the visible spectrum, giving rise to a characteristic blue shade; the gray cast is caused by extensive light absorption by Mo(IV) crystal field transitions and particularly MoeO charge transfer. The colouring performance of Al 2 O 3 eMoO x in ceramic glazes and porcelain stoneware bodies for wall and floor tiles is excellent, being equivalent to the pigment coloration. Thermal stability in these matrices seems to be mostly affected by Na 2 O and MgO. However, the distinctly blue shade of these pigments is much less intense than that of the most performant ceramic colorants. At all events, aluminaemolybdena system develops a peculiar colour that cannot be reproduced unless utilising the most expensive blue and black cobalt-bearing ceramic pigments.

Grayish-blue coloured aluminaemolybdena was synthesized by high temperature reducing firing and experimented as ceramic pigment. Synchrotron light and conventional X-ray diffraction powder, ICP-OES and BET analyses proved that molybdenum spreads over alumina surface, without entering the corundum lattice, with a high superficial concentration (i.e. 27e99 Mo atoms nm À2 ) implying a prevailing octahedral coordination and a certain long-range order, eventually resulting in the formation of crystalline MoO 2 . XPS and DRS suggested the occurrence of different valences, Mo(VI) being predominant over Mo(V) and Mo(IV). The colouring mechanism is mainly due to electronic absorption of Mo(V) in the redeorange region of the visible spectrum, giving rise to a characteristic blue shade; the gray cast is caused by extensive light absorption by Mo(IV) crystal field transitions and particularly MoeO charge transfer. The colouring performance of Al 2 O 3 eMoO x in ceramic glazes and porcelain stoneware bodies for wall and floor tiles is excellent, being equivalent to the pigment coloration. Thermal stability in these matrices seems to be mostly affected by Na 2 O and MgO. However, the distinctly blue shade of these pigments is much less intense than that of the most performant ceramic colorants. At all events, aluminaemolybdena system develops a peculiar colour that cannot be reproduced unless utilising the most expensive blue and black cobalt-bearing ceramic pigments.