Prepartion Of Coated Ce2s3and Study Of Its Color Rendering

Ce2S3is a non-toxic red pigment with deep red color, high lightness, strongtinting strength, strong covering ability and good thermal stability. Ce2S3isinsoluble in water and alkali solution. Thermal stability temperature of Ce2S3is1500℃under inert gas and reducing atmosphere. Ce2S3has been used as redpigment in plastics industry. The thermal stability temperature of Ce2S3can beimproved via coating treatment. Ce2S3has been considered as a good alternativeto replace the traditional Cadmium, Chromium and other heavy metals toxic redpigment.In this paper, Ce2S3, TEOS and ammonia has been used as raw materialswhile PVP and CTAB has been used as additives. SiO2coated Ce2S3redpigment has been prepared via liquid phase method. The effect of the ceriumsilicon molar ratio, water silicon molar ratio, reaction temperature, reaction time,additives, coating times and surface treatment on the coloring properties andthermal stability has been discussed. Ce2S3and lead-free flux has been used asraw materials. Lead-free flux coated Ce2S3red pigment has been synthesized viasolid phase method. The effect of cerium flux mass ratio, reaction temperatureand cooling method on the coloring properties and thermal stability also hasbeen discussed in this paper.The cerium silicon molar ratio, water silicon molar ratio, reactiontemperature, reaction time, additives, coating times and surface treatment has astrong impact on the coloring properties and thermal stability of Ce2S3whensolid phase method was used to prepare SiO2coated Ce2S3. SiO2is notsufficient when the cerium silicon molar ratio is more than2:1because TEOS isinsufficient. When the cerium silicon molar ratio is less than2:1, TEOS isexcessive and SiO2easily agglomerate due to the high active surface.Hydrolysis of TEOS is not sufficient when water silicon molar ratio is less than30:1because water is not enough. The concentration of silicate will be dilutedand the silicon oxygen bond will be rehydrolyzed when water silicon molar ratio is more than30:1. When the reaction temperature is lower than40℃,collision speed among the particles is slow and the generation of dense SiO2coating layer is prevented. The generation speed of active silicon is very fastand disorganized aggregates forms when the reaction temperature is greater than40℃. The hydrolysis and condensation of TEOS is insufficient because of theshort reaction time, which is less than10h. When the time is greater than10h,part of silicon layer will be hydrolysized. SiO2is hard to be coated on Ce2S3without additives due to its low active surface. CTAB plays a role in bondingCe2S3and SiO2, CTAB using as additive. But the agglomerate of SiO2particlesalso increases. One SiO2protecting layer forms when the coating time is once.The coating layers increase with the coating time increasing. However, coatinglayer does not increase substantially when the coating reaches three times.Alkali corrosion treatment is not in favor of SiO2coating. The coating effect ofthe samples is better when the cerium silicon molar ratio is2:1, the water siliconmolar ratio is30:1, the reaction temperature is40℃, the reaction time is10h,adding PVP, the coating time is twice and no alikali corrosion treatment. In thiscase, several dense coating layers of amorphous SiO2form on the surface of thesamples. The UV-visible absorption spectrum peak shifts from529nm to536nmand the red value reduces from35.91to31.25, which still presents bright redcolor. The thermal stability temperature under oxidizing atmosphere increasesfrom350℃to500℃.The cerium flux mass ratio, reaction temperature and cooling method has astrong effect on the coloring properties and thermal stability of Ce2S3whenliqiud phase method was used to prepare lead-free flux coated Ce2S3. Lead-freeflux is insufficient when the cerium flux mass ratio is greater than1:1. Coatinglayer increases with lead-free flux increasing. However, coating layer does notincrease obviously when the cerium flux mass ratio less than1:1. Lead-free fluxdoes not melt completely when the reaction temperature is750℃. Lead-freeflux gradually melts completely with the reaction temperature increasing.However, burnt happens when reaction temperature continues rising after850℃.Part of lead-free flux exists on the surface in crystal form when using naturecooling method. The coating effect of the samples is best when the cerium fluxmass ratio is1:1, the reaction temperature is750℃and taking out directly into water. In this case, several dense coating layers of lead-free flux form on thesurface of the samples. The UV-visible absorption spectrum peak moves from529nm to539nm and the red value reduces from35.91to28.19, which stillpresents red color. The thermal stability temperature under oxidizingatmosphere increases from350℃to500℃.