In-situ synthesis of mullite-SiCw composite ceramics in Li2O-Al2O3-SiO2 ternary system for solar heat transmission pipeline

Abstract

Nano-SiC whiskers (nano-SiCw) were in-situ synthesized in Li2O-Al2O3-SiO2 ternary system for preparing highly densified mullite-SiCw composite ceramics used for solar heat transmission pipeline. Mechanisms on the in-situ synthesis of nano-SiCw in the ternary system were investigated and the impact of nano-SiCw on the performances of the composites had been studied. Results showed that the growth processes of nano-SiC whiskers in Li2O-Al2O3-SiO2 ternary system were dominated by liquid-solid (LS) mechanism and the Li2CO3 additive could improve the SiCw yield through increasing the content of liquid phase and lowering the liquid viscosity. Sample BS3 (with 2.22 wt% Li2CO3 additive) sintered at 1440 °C obtained the highest SiC content of 47.9%. Nano-SiC whiskers with a diameter of 20–30 nm were interlocking with rod-like mullite crystals to improve the mechanical properties of the composites, and sample BS1 sintered at 1420 °C showed the highest bending strength of 115.4 MPa. The in-situ synthesized SiCw also shew significant effects on improving the thermophysical properties of the composites and sample BS1 exhibited a 3.6 times higher thermal conductivity than that of blank sample B1 without the introduction of nano-SiCw.