Preparation And Properties Of Low Thermal Expansion Ca_1-x?Sr,Ba?_xZr₄?PO₄?₆ Ceramics

General materials have the properties of thermal expansion and contraction.Thermal expansion and shrinkage characteristics can lead to device fatigue,performance degradation,fracture and exfliation.Therefore,NZP materials with low thermal expansion properties and designable thermal expansion coefficient have become hot topics.This article prepares low-thermal-expansion ceramics to improve the life of high-temperature components used in aerospace missile engines with large temperature variations.The low-expansion ceramics of Ca_1-x?Sr,Ba?_xZr₄?PO₄?₆ were prepared by coprecipitation method.Samples were characterized by TG-DSC,XRD,normal temperature Raman spectroscopy,scanning electron microscopy analysis,coefficient of thermal expansion test.Single-phase Ca_1-x?Sr,Ba?_xZr₄?PO₄?₆ powder synthetized by co-precipitate was calcined at 900^oC.A phase was formed by solid solution and the space group was consistent after Sr²⁺/Ba²⁺doping.The Ca_1-x?Sr,Ba?_x Zr₄?PO₄?₆ powder has no phase change during sintering.The relative density,microstructure and bending strength analysis indicated that the optimal sintering temperatures of Ca_1-x-x Sr_xZr₄?PO₄?₆,Ca_l-xBa_xZr₄?PO₄?₆ and Ca_1-x-y-x-y Sr_xBa_yZr₄?PO₄?₆ ceramics are1400?1450?1450^oC.The coefficient of thermal expansion has a large relationship with its chemical composition of Ca_1-x?Sr,Ba?_xZr₄?PO₄?₆.As the content of Sr²⁺and Ba²⁺increases,the cell parameters change causes a change in coefficient of thermal expansion.In Ca_1-xSr_xZr₄?PO₄?₆,x increased from 0.4 to 0.5,and the coefficient of thermal expansion showed a decreasing trend.When x increases from 0.5 to 0.6,the coefficient of thermal expansion increases with x.In Ca_l-x-x Ba_xZr₄?PO₄?₆,When x increased from 0.1 to 0.2,the coefficient of thermal expansion showed a decreasing trend.When x increased from 0.2 to 0.3,the coefficient of thermal expansion increased with x.In Ca_1-x-ySr_xBa_yZr₄?PO₄?₆,when x increased from 0.1 to 0.2,the coefficient of thermal expansion showed a decreasing trend,when x increases from 0.2 to 0.4,the coefficient of thermal expansion increased with x.The thermal expansion curve shows that the hysteresis loop was affected by the chemical composition.Changing the sintering temperature had no significant effect on the coefficient of thermal expansion in Ca_1-x?Sr,Ba?_xZr₄?PO₄?₆,but the hysteresis loop on the thermal expansion curve increases significantly with the increase of the sintering temperature.The coefficient of thermal expansion in Ca_1-x-x Sr_xZr₄?PO₄?₆ was greatly affected by the sintering aid of MgO.When MgO was added,the coefficient of thermal expansion increased significantly due to the second phase generated during sintering.The addition of sintering aid of 8wt%ZrP₂O₇ produced a large amount of pores in Ca_0.5Sr_0.5Zr₄?PO₄?₆.The pores provided a site for the expansion of each grain,and the grain expansion was digested and absorbed by the pores.Therefore,the coefficient of thermal expansion showed a decrease,and at the same time,the strength decreased.