Formation and Color of the Solid Solutions in (Co, Mg, Zn)₂SiO₄ System

Abstract

This study was concerned with the formation and color of the olivine type and the phenacite type solid solutions in (Co, Mg, Zn)₂SiO₄ system. Specimens were prepared by calcining the mixtures of each oxide of cobalt, zinc and silicon, and basic oxide of magnesium at 1300°C for 3h. Formation range of the olivine type and the phenacite type solid solutions in (Co, Mg, Zn)₂SiO₄ system were examined by X-ray analysis, and the lattice parameters of each solid solution were calculated. The color was discussed by measuring the spectral reflectance, and the stability of specimens in glazes (colored glaze test) was observed. The results were summarized as follows.
1) The incorporation of Zn₂SiO₄ into Mg₂SiO₄ or Co₂SiO₄ was ca. 15mol%.
2) The incorporation of Co₂SiO₄ into Zn₂SiO₄ was ca. 45mol%, but that of Mg₂SiO₄ into Zn₂SiO₄ was ca. 35mol%.
3) Equal amounts of Mg²⁺ occupied M1 and M2 sites respectively in olivine. In the case of incorporation of Co₂SiO₄ into Mg₂SiO₄, a large portion of Co²⁺ occupied M1 site, and therefore, the deviation from Vegard's law was observed in olivine type solid solutions in (Co, Mg, Zn)2SiO4 system.
4) Purple or pink developed in olivine type solid solutions in (Co, Mg, Zn)₂SiO₄ system, resulting from the octahedral Co²⁺. On the other hand, blue developed in the phenacite type solid solutions in (Co, Mg, Zn)₂SiO₄ system owing to the tetrahedral Co²⁺.
5) The phenecite type solid solutions in (Co, Mg, Zn)2SiO4 system were stable in zinc-mat glaze, and development of blue or violet was observed.
6) The olivine type and the phenacite type solid solutions in (Co, Mg, Zn)₂SiO₄ system decomposed in lime-zinc glaze and lime glaze, but in these solid solutions cobalt ions were maintained only as the divalent state, and therefore, blue or violet developed.