Research on the Formation and the Color Development of Titanium-Chrome Spinels Containing Co<sup>2+</sup> and Ni<sup>2+</sup> Ions

Abstract

In previous papers, the author reported about the formation and the color development of titanium-tin single spinels, and titanium-aluminium single spinels containing Co2+ and Ni2+ ions. For the purpose of researching into the formation and the color development of titanium-chrome single spinels, the gradual substitution according to the following formula was carried out for each titanium spinel.Mg2+(Zn2+)+Ti4+_??_2Cr3+Thus, MgO-TiO2-Cr2O3, ZnO-TiO2-Cr2O3, CoO-MgO-TiO2-Cr2O3, CoO-ZnO-TiO2-Cr2O3, NiO-MgO-TiO2-Cr2O3, NiO-ZnO-TiO2-Cr2O3, CoO-NiO-MgO-TiO2-Cr2O3 and CoO-NiO-ZnO-TiO2-Cr2O3 systems were investigated. Each oxide mixture was calcined at 1350°C for 1 hour. Reflectance between 400-760mμ was recorded by a spectrophotometer to pursue the displacement of absorption, and to represent the results by C. I. E. color specification. X-ray analysis was also carried out to observe the spinel formation and to calculate the lattice constant. The results were summarized as follows.1. MgO-TiO2-Cr2O3 and ZnO-TiO2-Cr2O3 systems.Samples with the composition of (2-x)MgO⋅(1-x)TiO2⋅xCr2O3 and (2-x)ZoO⋅(1-x)TiO2⋅xCr2O3 were prepared to observe the displacement of the absorption of Cr3+ ions, and only single spinels were obtained. The lattice constant of these spinels changed linearly, and the absorption of Cr3+ ions shifted towards the violet region with increasing amount of Cr3+ ions.2. As shown in Table 1-6, single spinels were obtained except No. 37 (NiO⋅MgO⋅TiO2).3. CoO-MgO-TiO2-Cr2O3 system.Samples were prepared according to 0.2CoO⋅(1.8-x)MgO⋅(1-x)TiO2⋅xCr2O3, 0.5CoO⋅(1.5-x)MgO⋅(1-x)TiO2⋅xCr2O3 and CoO⋅(1-x)MgO⋅(1-x)TiO2⋅xCr2O3. As Co2+ ions have tetrahedral preference and Ti4+ and Cr3+ ions octahedral preference whereas Mg2+ ions have no preference, the cation distributions in these spinels are thought to be as follows. Co0.2Mg0.8[Mg(1-x)Ti(1-x)Cr2x]O4, Co0.5Mg0.5[Mg(1-x)Ti(1-x)Cr2x]O4, Co[Mg(1-x)Ti(1-x)Cr2x]⋅O4 (the bracket represents octahedral interstices). When x=0, clear hues ranging from greenish blue (0.2CoO⋅1.8MgO⋅TiO2) through bluish green (0.5CoO⋅1.5MgO⋅TiO2) to deep green (CoO⋅MgO⋅TiO2), resulting from the tetrahedral Co2+ ions, developed. When 0<x<1, green, and when x=1, bluish green, resulting from the tetrahedral Co2+ and octahedral Cr3+ ions, developed. In this system, the coordination number of Co2+ ions was continually 4, and the displacement of the absorption of tetrahedral Co2+ ions towards the violet region was observed distinctly, but that of Cr3+ ions was not observed, owing to the overlapping of the absorptions of Co2+ and