Investigation On The Preparation And Surface Modification Of Ion-doped γ-Ce₂S₃ Red Pigment

Red has been respected by the Chinese nation,because of its unique charm.Red pigments in the pigments area have a pivotal position.Currently,the most widely used traditional inorganic red pigment is CdSe_1-xS_x.The CdSe_1-xS_x coated with zirconium silicate has been used as the ceramic red pigment.However,CdSe_1-xS_x contains cadmium,which is harmful to human health and the environment.With the continuous improvement of people’s health awareness and environmental awareness,the use of CdSe_1-xS_x red pigment has been increasingly restricted.Therefore,a kind of new red pigment has high-performance and environmentally non-toxic characteristic is needed to meet the market demand.Red pigment ofγ-Ce₂S₃ has advantages for bright red color,environmentally non-toxic and resistance to ultraviolet radiation.It is supposed to be a preferred candidate to replace CdSe_1-xS_x red pigment.It has been widely used in coating,printing and plastic industry.However,theγ-Ce₂S₃ prepared by conventional synthesize method has a weaker temperature stability,only 350℃.It is easily adsorbed moisture spontaneous decomposition and release toxic H₂S gas,when it is exposed to moisture for a long time at normal temperature.This greatly limits its application areas.In view of demand for pigments industry and the disadvantages ofγ-Ce₂S₃mentioned above.In this dissertation,the preparation,doping and surface modification for theγ-Ce₂S₃ red pigment are intense research.The mainly research contents are as following:The heterogeneous precipitation method was employed to prepare the ZnO adheringγ-Ce₂S₃ by using commerciallyγ-Ce₂S₃ as the raw material,six hydrated zinc nitrate（Zn（NO₃）₂·6H₂O）as zinc source,anhydrous sodium carbonate（Na₂CO₃）as precipitant,and mixture of alcohol and water as reaction medium.It was studied that the H₂S releasing after adherence of ZnO on the surface of pigment during heating process.The results show that a layer of ZnO could be uniformly adhered to the surface of theγ-Ce₂S₃particles and the pigment could still keep the brilliant red by using mixture of ethanol and water as reaction medium,simultaneous dropping form of precipitated ions and 0.3ml/min dropping rate,0.2 molar ratio of ZnO andγ-Ce₂S₃,and heat-treatment at 300℃for 30 min.The chroma of L*,a*and b*is 34.17,33.10 and 22.80,respectively.It has an obviously the inhibitory effects on releasing H₂S after adhered ZnO on the surface ofγ-Ce₂S₃ and the amount of H₂S releasing is reduced from 4.21mg/m³ to 0 after heating at350℃for 10 min.The precipitation method was employed to prepare the oxalate precursor of the ion-dopedγ-Ce₂S₃ red pigment doped with La³⁺,Eu²⁺,Ca²⁺and Ca²⁺&Eu²⁺,La³⁺&Eu²⁺,Ca²⁺&La³⁺.CeCl₃·7H₂O,Eu₂O₃,CaCl₂·2H₂O,LaCl₃ and C₂H₂O₄·2H₂O was used as cerium source,europium source,calcium source,lanthanum source and precipitant respectively.The doped oxalate salt was prepared by coprecipitation,which by high-temperature calcination to obtain doped cerium oxide precursor.Doped cerium oxide precursor was vulcanized by Ar as the carrier gas and CS₂ as the sulfur source.The effect of dopants on the synthesis temperature,the color renderings and the temperature stability ofγ-Ce₂S₃ was studied.The results show that Ca²⁺and Eu²⁺dopants can significantly reduce the synthesis temperature ofγ-Ce₂S₃.A pureγ-Ce₂S₃ phase at 900℃by 0.08 of the Ca²⁺/Ce³⁺or 0.03 of the Eu²⁺/Ce³⁺doping ratio can be obtained.La³⁺doping does not play a significant role in reducing the synthesis temperature ofγ-Ce₂S₃.Theα-Ce₂S₃ phase is still present in the sample of the same vulcanized conditions,the crystal phase of the vulcanized product has a more complicated tendency when the La³⁺doping amount is 0.08.The Ca²⁺doping can lead the intrinsic absorption edge of the dopedγ-Ce₂S₃ blue shift and the color of the sulfide product shifts to orange red with the increase of the Ca²⁺doping amount.The doping ions enter the lattice ofγ-Ce₂S₃ in the form of Eu²⁺,When the Eu doping.Eu²⁺has the 4f electrons which can entry into the lattice ofγ-Ce₂S₃ introduces new electron transitions of 4f→5d.This will cause the intrinsic absorption edge of the sample to become wider.The color of the sample is eggplant and it can not be adjusted back to red by composite doping.The temperature stability ofγ-Ce₂S₃ can significantly improve by ion doping,and the degree of raise for the composite doping is better than that of the single ion doping.Theγ-Ce₂S₃ pigment F-treatment with a certain concentration NH₄F solution by NH₄F as the fluoride source.It was studied that the influence and influence mechanism ofγ-Ce₂S₃ red pigment F-treatment for the color renderings and the particle size improvement.The effect of different F-treatment conditions such as NH₄F solution concentration,pH,and solution medium on the effect of F-treatment was also studied.The results show that the color rendering of pigment and reduce the particle size of pigments can significantly improve by F-treatment.The redness value a*of the pigments can be increased more than 10,the particle size distribution of the pigment is narrowed,and the average particle size is reduced from 35.00μm to 29.37μm after the pigment F-treatment for 2 h in 75 g/L NH₄F solution.The concentration and pH value of the NH₄F solution have a significant effect on the F-treatment effect.The F-treatment effect is better when the higher of the concentration and the lower of the pH value for NH₄F solution.The media type of NH₄F solution can affect the effect of F-treatment too.When using ethanol&water as the medium the CeF₃ particles on the pigment surface is finer and more evenly distributed in comparison with when using water as the medium.The ionization and hydrolyzation of NH₄F is influenced by ethanol,and it will affect the content of CeF₃ on the surface of the pigment.Those will deterioration of the F-treatment effect.