Syntheses Of Fe₂O₃/SiO₂ Red Ceramic Pigments Via Microemulsion Method

Silicon-iron-peach pigment is a natural ceramic material found in 1997,French.Due to its properties,such as high temperature stability and thermal stability,it was mainly used as colorant for ceramic body coloration.Recently,several preparation methods of synthesizing the red pigments have been reported,including solid-phase method and wet-chemical method?sol-gel method,co-precipatation with the aid of ultrasonic irradiation,microwave hydrothermal method,and so on?.However,there were many disadvantages,such as relative high synthesis temperature,poor coloration performance and complex preparing equipments,which limited its further application.In this paper,ethyl-silicate?TEOS?and ferric chloride?FeCl₃.6H₂O?were used as raw materials to prepare silicon-iron-peach pigment at low temperature via microemulsion method in an attempt to broaden the application areas of the as-prepared inclusion pigments.The water content can affect the reaction pool of the microemulsion,and then affect the synthesized Fe₂O₃/SiO₂ red pigments.So the aqueous solution with TEOS and pure TEOS wered employed as two different forms of introducing silicon source to prepare the Fe₂O₃/SiO₂silicon-iron-peach inclusion pigment.The effect of the phase transition of the precursor powders during the heat treatment,mass rati of SiO₂/Fe₂O₃,reactant concentration,the mass ratio of water and oil phases,mineralizer,calcination temperature and holding time on the synthesis of Fe₂O₃/SiO₂ red pigments had been discussed.DTA-TG,XRD,TEM,and color measurement were employed to characterize the as-prepared Fe₂O₃/SiO₂ red pigments.In the case of using TEOS aqueous solution to introduce the required Si resource,many factors were studied.The results showed that the prescursor obtained by microemulsion method was amorphous and calcined at different temperatures.With no any mineralizers,Fe₂O₃ crystallines were formed at first at low calcining temperature.When the calcine temperature increased to 1100?,transition from Fe₂O₃ crystalline to hematite??-Fe₂O₃?crystal phase.The Fe₂O₃/SiO₂ red pigment calcined at 1100?for 3h was of the greatest reddish hue of a*=29.06.TEM results revealed that hematite particles were wrapped by SiO₂ matrix.Well developed?-Fe₂O₃ hematite crystals and SiO₂cristobalite crystals were formed when the calcining temperature increased above1200?,which could improve the erosion-resistance of the red pigments.Prolonging the holding time at a certain temperature is good for the phase transition of Fe₂O₃ crystalline phase.Increasing SiO₂/Fe₂O₃ mass ratio could help to improve the efficiency of inclusion.On the contrary,lower SiO₂/Fe₂O₃ mass ratio would lead to a thicker wrapping layer.Consequently,a*value decreased.Fe₂O₃/SiO₂ red pigments with appropriate inclusion morphology could be obtained with SiO₂/Fe₂O₃ mass ratio of 85/15.Fe₂O₃/SiO₂ red pigments with good color performance were obtained when the mass ratio of water and oil phases was 20%.For the synthesized Fe₂O₃/SiO₂ red pigments,the mineralizers of NaF and CaF₂ could decrease the forming temperature of?-Fe₂O₃ hematite crystals and SiO₂ cristobalite crystals.And the effect of NaF is better than adding CaF₂.When NaF was added as mineralizer,well developed?-Fe₂O₃ hematite crystals and SiO₂ cristobalite crystals occurred in the products calcined at a lower temperature of 900?for 1h.Adding NaF not only decreased the crystalline forming temperature,and also improve the inclusion effective,which could improve the acid-resistance of the synthesized Fe₂O₃/SiO₂ red pigments.The similar results on the effect of calcine temperature,holding time and mineralizer were obtained when pure TEOS was used to introduce Si resource.SiO₂ and Fe₂O₃nanoparticles with different size,different morphology and different dispersity can be obtained through adjusting the calcination temperature when lacking of mineralizer.The Fe₂O₃/SiO₂ red pigments with the best reddish hue of a*=29.18 were obtained at the SiO₂/Fe₂O₃ mass ratio of 85/15.