The Preparation And Property Of La_1-xSr_MnO₃Ceramic Absorbing Coating

Perovskite lanthanum strontium manganate materials (LSMO) rendersemiconductor behavior in high temperature and show stable physical and chemicalcharacteristics. Therefore, their application in frequency selective surfaces (FSSs) mayresults in the wideband radar absorbers working in high temperature. The LSMOcoating was prepared by screen printing technique and then was characterized by X raydiffraction, scanning electron microscopy, universal electronic testing machine, DC fourprobe tester equipment etc. The procedure of coating preparation was optimized, and theconductive mechanism was understood by resistivity-temperature characteristic. Basedon the surface resistant in high temperature, the FSS was designed to achieve thewideband absorbing property. Finally, the temperature-dependent of the absorbingproperty was studied experimentally. It is found that our proposed LSMO coating hashigh potential application in the high temperature. The main research contents andconclusions are as follows:1. Coating preparation program was designed after analyzing the whole screenprinting process. LSMO powder was synthesized by high temperature solid-statemethod, sintering at1200℃for6h. Terpineol was used as organic solvent in slurry,while ethyl cellulose (EC) as thickening agent. Slurry was mixed with the LSMOpowder and the solvent adding EC in the weight ratio of1:1. Coatings was obtained bysintering the slurry printed on Al2O3substrate.2. The effect of procedure on the phase structure, morphology adhesion andelectrical properties was investigated. When the weight fraction of EC is5%,6%, theslurry is suitable for screen printing with the viscosity of104mPa·s. La1-xSrxMnO3coatings (x=0.1,0.2,0.3,0.4) sintered at1100℃for4h are proved with a structure ofsingle phase, whereas for the coating prepared at the tempareture of1200℃or1300℃，Al2O3in the substrate spreads into the coating surface. We can observecomplex peaks from XRD result, and lower conductivity from four-point probes.Adding silica white as glass phase as well as powder unreacted, is good for coating andadhesion enhancement, while shows lower conductivity. Finally, coatings withoptimized comprehensive performance can be prepared at1200℃for4h，with silicawhite fraction of1%, unreacted powder fraction of33%.3. Based on the single phase coating (La0.7Sr0.3MnO3) the conductive mechanismwas revealed by resistivity-temperature characteristic. It shows that high temperatureconductivity conforms to the small polaron conduction model. A FSS radar absorberwas fabricated with designed parameters and the effect of temperature on the propertywas evaluated. The results show that coating absorbing properties have slight changes when the temperature varied between200℃and1000℃,which are basically consistentwith the design result. However, test result shows relatively poor absorbingperformance when the temperature is lower than200℃.