Inorganic pigments based on fluorite-type oxynitrides
- PDF / 334,812 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 100 Downloads / 209 Views
ia oxynitride rare-earth-doped pigments were prepared by ammonolysis of the zirconium rare-earth oxides, previously synthesized using the citrate complexation/ calcination route. Different coloration has been obtained, the intensity of which is a function of the nitrogen amount in the case of the oxynitrides; in the case of the oxides, both color and intensity depend on the doping amount of rare earth. The obtained phases, Zr(1−x)CexO2, Zr(1−x)RxO(2−x/2)䊐x/2, with R ⳱ Eu or Er and Zr(1−x)RxO(2−x/2−3/2y)Ny䊐x/2䊏y/2 (R ⳱ Ce, Eu, and Er), have been characterized by x-ray powder diffraction, scanning electron microscopy, and reflectance spectra data. These results show that the phases with minor rare-earth concentration adopt a baddeleyite-type structure, with a monoclinic symmetry, space group P21/c. By increasing the rare-earth doping, the obtained phases crystallize with the fluorite structure with tetragonal (P42/nmc) or cubic symmetry (Fm3¯m). On the other hand, the study of the magnetic properties of the oxides and oxynitrides indicate a paramagnetic behavior, and in the case of the cerium oxide, the nitridation process produces the reduction from Ce4+ to Ce3+. Diffuse reflectance data and CIE-LAB color coordinates suggest that these ceramics based on nitrogen containing zirconia are expected to be promising candidates as new ecological inorganic pigments.
I. INTRODUCTION
Inorganic pigments based on transition metal oxides are used in the coloration of different materials such as paints, plastics, ceramics, and glasses.1 Unfortunately, some of these classical pigments contain toxic metals such Cd, Pb, Co, and others, and for this reason, it is necessary to search for new environmentally friendly and economically viable materials to replace the mentioned toxic pigments.2,3 Zirconia is found in nature in small quantities as the mineral baddeleyite (m-ZrO2) and can also exist as tetragonal and cubic fluorite-like polymorphs, both stable at higher temperature but stabilized by doping down to room temperature.4 The vast majority of powder synthesis of zirconia-based solid solutions to date has been carried out using the conventional solid-state reaction routes, in which the constituent metal oxides are mechanically mixed, followed by firing at high temperature (1400–1600 °C) to allow interdiffusion of the cations. One aim of this work is therefore to verify the feasibility of a simple citric-acid-based technique for the lowtemperature synthesis of zirconia-based solid solutions in tetragonal and cubic forms.5 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0177 J. Mater. Res., Vol. 21, No. 6, Jun 2006
http://journals.cambridge.org
Downloaded: 18 Mar 2015
In recent years, a new class of ceramic materials zirconia containing nitrogen have been obtained via direct nitridation of ZrO2 at high temperatures in nitrogen atmosphere.6–9 The chemical composition of quaternary nitrogen containing zirconia materials prepared in this way can be described as Zr–M–O–N, where M ⳱ Ca
Data Loading...
