Stabilization of the gamma-Ce2S3 phase

The gamma -Ce2S3 phase is used as a safe red pigment for plastics. Therefor e its stabilization, at low temperatures (around 800 degreesC), has been pa rticularly studied during the last decade. This can be realized in differen t 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 concentr ation enhances the gamma -phase formation. However the gamma -phases so obt ained 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 t he gamma -phase. However during the thermal treatment under CS2, some phosp horus is lost from the solid phase resulting in a progressive transformatio n of the gamma -phase into the oc-one. The residual monazite (CePO4) does n ot much affect the red color of gamma -Ce2S3. The gamma -phase is also obta ined by using berate precursors and to a lesser extent by vanadate and arse niate 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 r eserved.