Study on the Formation and the Color Development of Titanium-Tin Spinels Containing Co²⁺ and Ni²⁺ Ions

Abstract

For the purpose of researching the formation and the color development of titanium-tin single spinels, the gradual substitution of Sn⁴⁺ ion for Ti⁴⁺ ion in titanium spinels was carried out. Thus CoO-MgO-TiO₂-SnO₂, CoO-ZnO-TiO₂-SnO₂, NiO-MgO-TiO₂-SnO₂, NiO-ZnO-TiO₂-SnO₂, CoO-NiO-MgO-TiO₂-SnO₂ and CoO-NiO-ZnO-TiO₂-SnO₂ systems were investigated.
Each oxide mixture was calcined at 1350°C for 1 hour. The reflectance between 400-760mμ was recorded by self-recording spectrophotometer to pursue the displacement of absorption and to represent the result by C. I. E. color specification. X-ray analysis was also carried out to observe the spinel formation and to calculate the lattice constant of spinels. The results were summarized as follows.
1. Each smple was composed of single spinel and not mixture of spinels.
2. CoO-MgO-TiO₂-SnO₂ system.
In this system, samples were prepared according to 0.2CoO⋅1.8MgO⋅(1-x)TiO₂⋅xSnO₂, 0.5CoO⋅1.5MgO⋅(1-x)TiO₂⋅xSnO₂ and CoO⋅MgO⋅(1-x)TiO₂⋅xSnO₂. When x=0, brilliant hues ranging from greenish blue to green developed, giving deep absorption characteristic of tetrahedral Co²⁺ ions at about 550-680mμ. With increasing the amount of Sn⁴⁺ ions, this absorption shifted towards the violet region, owing to the contraction of tetrahedral interstices in spite of the expansion of the lattice. At the same time, the interaction between Co²⁺-Ti⁴⁺ ions being feeble, the absorption about 400-500mμ became shallow remarkably.
Therefore color changed bluish, and when x=1, clear hue so-called cerulean blue developed.
3. CoO-ZnO-TiO₂-SnO₂ system.
There was a typical difference in color between CoO-MgO-TiO₂ and CoO-ZnO-TiO₂ and between CoO-MgO-SnO₂ and CoO-ZnO-SnO₂ system. Samples of CoO-ZnO-TiO₂ system were brown, while in xCoO⋅(2-x)ZnO⋅TiO₂ dark green developed only in the range of x>1. On the other hand, samples of CoO-ZnO-SnO₂ system were greyish green. Zn²⁺ ions having gtrong tetrahedral preference, small amount, of Co²⁺ ions occupied tetrahedral interstices in these spinels. The influence of Zn²⁺ ions being more intense in titanium spinels than in tin spinels, the main absorption band of tetrahedral Co²⁺ ions appeared more distinctly in the latter. Samples of CoO-ZnO-TiO₂-SnO₂ system did not show clear hue.
4. NiO-MgO-TiO₂-SnO₂ system.
Although nickel titanate, 2NiO⋅TiO₂, and nickel stannate, 2NiO⋅SnO₂, did not exist, it was possible to substitute about 10% of the Mg²⁺ ions in 2MgO⋅TiO₂ and 2MgO⋅SnO₂ by Ni²⁺ ions at 1350°C. NiO⋅MgO⋅TiO₂ and NiO⋅MgO⋅SnO₂ did not form the single spinel owing to the lack of cations having tetrahedral preference. In this system samples were prepared acccording to 0.2NiO⋅1.8MgO⋅(1-x)TiO₂⋅xSnO₂, and light green resulting from the octahedral Ni²⁺ ions developed in all ones.
5. NiO-ZnO-TiO₂-SnO₂ system.
It was possible to substitute 50% of the Zn²⁺ ions in 2ZnO⋅TiO₂ and 2ZnO⋅SnO₂ by Ni²⁺ ions. In this system samples with the composition of NiO⋅ZnO⋅(1-x)TiO₂⋅xSnO₂ were prepared, and the