Study On La And Y Series Perovskites And Their Infrared Functional Coatings

The infrared emissivity is an important physical property of materials,and its value has a great influence on the behavior of infrared radiation(thermal radiation)of objects.The infrared radiation of an object is mainly determined by the infrared emissivity of its surface layer,in order to change the radiation characteristics of a material,coatings with special infrared emissivity are employed to realize the infrared feature of material in certain occasions.Infrared functional coatings are mainly divided into high infrared emissivity coatings and low infrared emissivity coatings.The high infrared emissivity coating mainly used in two fields.Firstly,high infrared emissivity coating applied on the outermost layer of the spacecraft TPS(thermal protection system),which can accelerate the heat dissipation of spacecraft by its high emissivity,namely reducing the temperature of structural components.Secondly,high infrared emissivity coating applied on the inner wall of furnace,which can improve the radiation performance of refractory the utilization rate of input heat energy,thus achieve the energy saving purpose.The low infrared emissivity coating can reduce the intensity of infrared signal radiated by the material,therefore decrease the probability of the object being identified or captured by infrared detection equipment(infrared imager,infrared guidance missile).The low infrared emissivity coating can improve the survivability of the target object by infrared stealth.Perovskite ceramics are a kind of materials which with the same crystal structure(ABO3).The perovskite materials have a series of excellent physical and chemical properties,and some properties can be regulated by using different elements or doping.In recent years,some works have been devoted to the study of infrared properties of perovskite ceramics.These studies suggest that the infrared emissivity of perovskite can be regulated by A or B elements,which indcate that the perovskite materials is a potential material for preparing infrared functional coatings.With this in mind,the LaBO3 and YBO3 perovskite were selected as research materials in this paper.Firstly,we use Y2O3,La2O3,Cr2O3 and Mn3O4 oxides as raw materials synthesized YCrxMn1-xO3 and LaCrxMn1-xO3(x=0,0.25,0.5,0.75,1)perovskite ceramic powders by high temperature solid state reaction method.The results show that the infrared emissivity of LaBO3 powders(600℃,3-5μm)is higher than that of YBO3 powders under the same conditions.In addition,when the A-site element is constant,the B-site element has the same effect on the infrared emissivity of the two series powders.The infrared emissivity increases with the increase of Mn content in the B-site.Meanwhile,the LaMnO3 whin the highest emissivity(0.922)and the YCrO3 with the lowest emissivity(0.751)in the test conditions of 600℃ and 3-5μm.LaMnO3 powder was used as the main material for preparing a high infrared functional coating.The LaMnO3-phosphate inorganic coating was prepared by slurry method using the self-made phosphate(high temperature resistant)as the binder and LaMnO3 as fillers.The coating shows high infrared emissivity at 600℃,the value of emissivity is 0.94 at 3-5μm and 0.93 at 8-14μm.When the coating is coated on the surface of metal blocks,the heating rate of the coated sample is obviously lower than that of the sample without coating under the same heating condition.The steady-state temperature of Ti65 alloy and 316L stainless steel can be reduced by 72℃ and 45℃respectively.When the coating is coated on the inner wall of a refractory cavity,the heating rate is higher than that of the cavity without coating under the same heating condition,which shows the coating has a certain energy-saving effect.In the simulation experiment of this paper,the energy-saving efficiency of the coating can reach 13.2%.YCrO3,with the lowest emissivity,is used as the main material for preparing low infrared emissivity coating in this paper.In order to reduce the emissivity of YCrO3 at high temperature,we used metal Ag and YCrO3 to prepare an Ag-YCrO3 composite powder.Firstly,using Ag powder and YCrO3 powder as raw materials,a spherical Ag-YCrO3 composite powder(YCrO3 embedded Ag)was prepared by ball milling.The Ag-YCrO3 composite coating with low infrared emissivity at high temperature was prepared by cold spraying technique on the surface of superalloy,the emissivity of coating is ε(600℃,3-5μm)=0.665 and ε(900℃,3-5μm)=0.376.The coating shows excellent resistance to the salt spray-thermal exposure cycle(900℃),meanwhile after 20 cycles of salt spray-thermal exposure the binding force of the coating is increased and the emissivity of the coating is further reduced.The above results show that the Ag-YCrO3 composite coating can achieve effective infrared stealth function.