Preparation of La_2(Ce_xZr_(1-x))_2O_7 Nano-porous Powders Via Citric Acid Derived Sol-gel Processing

摘要

La_2(Ce_xZr_(1-x))_2O_7 powders were synthesized by the Pechini routine with citric acid as a chelating agent. TG-DTA, XRD and SEM were used to characterize as-prepared powders. Experimental results show that the crystalline structures of La_2(Ce_xZr_(1-x))_2O_7 transform to cubic fluorite phase with Ce substitution for Zr from x=0.1 to 1.0, no longer keeps the cubic pyrochlorite structure of La_2Zr_2O_7. La_2(Ce_xZr_(1-x))_2O_7 powders present nano-porous low-density microstructurally, and successively lump-like, fluff-like and cotton-like morphologically with the increase of citric acid addition, this typical nano-porous microstructure results from a pore-crating mechanism initiated by self-propagation reactions between citric acids and nitrates. It is shown that the thermal conductivity k of powder compacts decreases sharply down from 1/10 to 1/32 of that of its single crystal bulk, as compact porosity increases from 60% to 95%. Therefore thermal barrier coatings (TBCs) of La_2(Ce_xZr_(1-x))_2O_7 with such nano-porous structures by an appropriate processing may work with quite a high insulative performance and very promising for TBC applications of high-efficiency and large propulsion engines.