Effect of micro/nano La₂O₃ addition on the sintering and properties of mullite synthesized

Abstract

The aim of this work is to prepare interlocking prismatic mullite from low‐cost associated rare‐earth kaolin. High‐performance mullite was synthesized by reaction sintering using calcined associated rare‐earth kaolin and α‐Al2O3 as raw materials and micro‐ and nano‐La2O3 as additives. The mineralogical, morphological, and chemical characteristics of calcined associated rare earth kaolin were analyzed, and the effects of the addition of micro‐ and nano‐La2O3 and sintering temperature on the phase transformation, sintering process, microstructure, and mechanical properties of mullite were studied. The results show that the associated rare earth elements Ce, Th, and Y in calcined kaolin are mainly light rare earth elements, which are mainly endowed in the interlayer structure of K‐bearing clay minerals. The addition of La2O3 can promote the growth of secondary mullite grains and accelerate the secondary mullitization process. The relative densities of mullite samples adding 4 wt.% micro/nano La2O3 and sintered at 1500°C for 4 h were 92.72% and 93.4%, and the micro Vickers hardnesses were 11.32 and 12.35 GPa, respectively. The mullite sample with 2 wt.% nano‐La2O3 had the most interlaced prismatic grains, resulting in the highest flexural strength of 157.8 MPa.