Origin of color in aerosol-derived vanadium-doped zirconia pigments
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Origin of color in aerosol-derived vanadium-doped zirconia pigments P. Tartaj and C. J. Serna Instituto de Ciencia de Materiales de Madrid, C. S. I. C., Cantoblanco, 28049 Madrid, Spain
J. Soria Instituto de Cat´alisis y Petroleoqu´ımica, C. S. I. C., Campus Universitario de Cantoblanco, 28049 Madrid, Spain
M. Oca˜na Instituto de Ciencia de Materiales de Sevilla, C. S. I. C.-UNSE, Am´erico Vespucio s/n, 48092-Sevilla, Spain (Received 23 December 1996; accepted 27 May 1997)
The preparation of vanadium-zirconia yellow pigments from amorphous spherical V–ZrO2 particles obtained by the hydrolysis of liquid aerosols consisting of a mixture of vanadium (V) oxychloride and zirconium n-propoxide is reported. The composition of the amorphous precursors (VyZr ratio) and the heating temperature were systematically varied to determine their influence on the optical properties of the pigments. The origin of the yellow color of the pigments was found to be mainly due to the presence of V2 O5 in the outer layers of the zirconia grains. A small fraction (,15%) of the total vanadium content was found as vanadium (IV) forming a solid solution with the monoclinic zirconia lattice.
I. INTRODUCTION
Zirconium vanadium yellow baddeleyite is an inorganic pigment mainly used for coloring glazes. Whereas several papers have been published on this pigment, controversy still exists on the origin of the yellow color. Thus, it was first suggested that this color was due to minute V2 O5 particles coating ZrO2 grains.1–4 More recently, the yellow color has been attributed to V 14 forming a solid solution with the ZrO2 lattice.5 Since the first appearance of V–ZrO2 pigments in the color industry, they have been mostly prepared by the traditional method involving the mixing by grinding of ZrO2 and NH4 VO3 (or V2 O5 ), followed by the calcination of the mixture at high temperature (1250 ±C) and a further grinding process to reduce and homogenize particle size.1 In the last years, it has been shown that the hydrolysis of liquid aerosols is an interesting method for the preparation of single6 and multicomponent7–10 ceramic metal oxide powders, since it yields particles of uniform shape (spherical), the size of which can be controlled by the characteristics of the aerosol generator. This method has also been recently applied to prepare vanadium-zircon pigments.11 The main advantages that it presents over the conventional method are its simplicity (it eliminates grinding) and continuous character which makes it appropriate for industrial purposes. In this paper, we report a procedure for the preparation of V–ZrO2 pigments, based on the hydrolysis of aerosols consisting of droplets of a mixture of zirconium n-propoxide and vanadium oxychloride, with the proper VyZr ratio. This method produces amorphous powders, J. Mater. Res., Vol. 13, No. 2, Feb 1998
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which have to be further thermally treated to develop the crystalline phases and color. The composi
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