Stabilization of the γ-Ce2S3 phase

The gamma -Ce2S3 phase is used as a safe red pigment for plastics. Therefore its stabilization, at low temperatures (around 800 degreesC), has been particularly studied during the last decade. This can be realized in different ways: (1) the presence of alkali metals leading to A(0.5)Ce(2.5)S(4) (A = Li, Na and K). (7) The presence of an important carbon or silicon concentration enhances the gamma -phase formation. However the gamma -phases so obtained are dark or brown due to the presence of traces of these two elements. (3) The use of phosphate precursors (or phosphate dopant) also leads to the gamma -phase. However during the thermal treatment under CS2, some phosphorus is lost from the solid phase resulting in a progressive transformation of the gamma -phase into the oc-one. The residual monazite (CePO4) does not much affect the red color of gamma -Ce2S3. The gamma -phase is also obtained by using berate precursors and to a lesser extent by vanadate and arseniate precursors or by treating some ceria associated with SiO2. (4) gamma -Ce2S3, as a major phase, is also obtained by treating some specific ceria under CS, and its color is red. (C) 2001 Elsevier Science B.V. All rights reserved.