Preparation And Study Of The Na⁺ Ion-doped γ-Ce₂S₃ Bright Red Pigment Coated With Mullite

Red tonal connotation is rich,profound,has always been regarded as a symbol of all good things such as festival,peace and progress.At present,inorganic red pigments mostly contain cadmium,lead,mercury and other heavy metal elements which are extremely harmful to human body,and their application scope is increasingly restricted by relevant laws and regulations.Therefore,it is urgent to develop non-toxic red pigments substitutes.γ-Ce₂S₃is a new type of red inorganic pigment,which is characterized by environmental protection,non-toxic,bright red color,strong absorption of ultraviolet light,color stability,becoming the best alternative for red pigments containing toxic heavy metals.However,the traditionalγ-Ce₂S₃synthesis method has a high synthesis temperature,and the pureγ-Ce₂S₃is easy to be oxidized,and becomes Ce O₂at 350℃in air atmosphere.Therefore,the aim of this study is to reduce the synthesis temperature ofγ-Ce₂S₃,while improving the antioxidant capacity ofγ-Ce₂S₃,and enable it to expand the application of new fields.The main research contents are as follows:1)Ce（NO₃）₃·6H₂O as cerium source,Na NO₃as Na⁺source,TEOS as silicon source,Al（NO₃）₃·9H₂O as aluminum source,ethanol and water as co-solvent,urea as alkali source,mullite coated Na⁺ion-dopedγ-Ce₂S₃（asγ-[Na]-Ce₂S₃@mullite）was synthesized by sol-gel method combined with sulfuration-heating process.The synthetic conditions of mullite,the effects of different pre-firing temperatures on the morphology of precursor and chromaticity value of the coating pigments were systematic studied,and the thermal stability of the coating pigments was also analyzed.The results show that short rod-like and spheroidal mullite crystals can be synthesized at 1 300℃for 3 h with n _Al:n _Si=3.2:2,the best chromaticity value of the coated pigment can be obtained when the pre-firing temperature is 400℃:L*=36.24,a*=41.86,b*=36.26,and the best pigment sample still has good chromaticity value when it kept at 800℃for 10 min in air atmosphere:L*=29.84,a*=20.83,b*=18.17.This study indicates that the thermal stability ofγ-Ce₂S₃can be improved from 350℃to 800℃by sol-gel method ofγ-[Na]-Ce₂S₃@mullite.2)In order to reduce the particle size ofγ-[Na]-Ce₂S₃@mullite,citric acid was added as complexing agent and template agent on the basis of the previous experiment,and the particle size of the synthetic coating-pigment was reduced by controlling the morphology of the precursor.The influence of pre-firing temperature,n（CA）:n（Urea）on the shape and appearance of the precursor,as well as the particle size and chroma ofγ-Ce₂S₃@mullite pigment was systematically studied,and the temperature stability ofγ-Ce₂S₃@mullite pigment was analyzed.The results showed that when the temperature was 500℃,n（Urea）:n（CA）=0.5,the specific surface area of209.45 m~2/g,pore volume of 0.2633 cm~3/g,and pore size of 6.34 nm could be obtained.The average particle size of the synthesizedγ-Ce₂S₃@mullite is 6.46μm,and the chromaticity value L*=37.84,a*=38.36,b*=37.42.The chromaticity value ofγ-Ce₂S₃@mullite is still good after calcination at 800℃for 10 min in air atmosphere（L*=25.26,a*=30.25,b*=28.26）.It is proved that the addition of citric acid can effectively reduce the particle size ofγ-[Na]-Ce₂S₃@mullite without affecting other properties.3)In order to explore the practical value ofγ-[Na]-Ce₂S₃@mullite,γ-[Na]-Ce₂S₃@mullite was added into the flux,and the application effect ofγ-[Na]-Ce₂S₃@mullite in the flux was investigated.The effects of addition amount ofγ-[Na]-Ce₂S₃@mullite,sintering temperature and holding time on the color development of the sample and the color development effect ofγ-[Na]-Ce₂S₃@mullite in different fluxes were systematically studied.The results show that when the amount of pigment is 5%and the sintering temperature is 560℃for 5 min,the samples have the best color L*=44.13,a*=20.52,b*=23.25.Meanwhile,the alkali metals and alkali earth metals in the flux have a negative effect on the color ofγ-[Na]-Ce₂S₃@mullite.