Investigation On The In-Situ Synthesis And Mechanical Properties Of Lanthanum Zirconate And Zirconia For Plutonium Curing

Pyrochlore structural Ln2Zr2O7 has good chemical stability, high anti-radiation ability, the ability of curing variety of actinides. Which is considered as the ideal base of curing actinides, for example, [La1-xPux]2Zr2O7(x=0-1) has be reported. Based on the toughening principle of second phase particles, the nano-nano composite powders of La2Zr2O7 and 4YSZ were synthesized by using the in-situ method. Dense ceramics were prepared from the spark plasma sintering(SPS). The influence of 4YSZ content on the fracture toughness of La2Zr2O7 curing matrix was studied. The main content and conclusion are as follows:The phase structure and distribution of the nano-nano composite powders of La2Zr2O7 and 4YSZ from the in-situ reaction were studied. XRD and Raman results indicate that the reaction products of the xLaO1.5-(1-x) ZrO2(0<x<0.5) binary system is composed of La2Zr2O7 and Zr O2 phases, where the ZrO2 phase has a phase transition from monoclinic(m) to the tetragonal(t) phase with increasing the x value. When x=0.24, the critical size of t-ZrO2 is about 38 nm. TEM observation showed that the interfaces between the two-phase have coherent properties; SEM image showed that the ZrO2 particles were distributed at the grain boundaries of La2Zr2O7 particles. In the ternary system of(1-0.54x)ZrO2-(1-x)LaO1.5-0.04xYO1.5(0<x<1), YO1.5 is doped into ZrO2 phase for the formation of t-4YSZ.The microstructure and fracture toughness of La2Zr2O7-4YSZ composite base materials from the SPS process were studied. The XRD analysis showed that no phase transition and other products were examined in the samples of La2Zr2O7-x mol% 4YSZ(0≤x≤50) prepared from SPS sintering under the condition of 1450 oC, 40 MPa, 5min. All the samples have a relative density > 96%. SEM observation shows the particle sizes of La2Zr2O7 and 4YSZ phase are in the range of 0.5-1.3μm and 0.19-0.57μm, respectively and decrease with increasing x value. Vickers indentation test showed that the hardness(HV) of the samples were 8-12 GPa, which increased with the content of 4YSZ(x). The fracture toughness(KIC) of the samples is between 0.9-1.8MPa?m1/2, which has a variation trend same with hardness. The surface crack in the composites observed by SEM, the results indicated that the toughening improvement by 4YSZ addition can be attributed to crack deflection and crack bridging.