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

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-Al 2 O 3 as raw materials and micro- and nano-La 2 O 3 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-La 2 O 3 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 La 2 O 3 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 La 2 O 3 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-La 2 O 3 had the most interlaced prismatic grains, resulting in the highest flexural strength of 157.8 MPa.