Effect of Si/Al ratio on in-situ synthesis of Al2O3–β-Sialon composite ceramics for solar thermal storage by aluminothermic and silicothermic nitridation

Abstract

In-situ Al2O3–β-Sialon composite thermal storage ceramics were one-step synthesized by aluminothermic and silicothermic reduction nitridation method, using solid waste coal-series kaolin, Al powder and Si powder as raw materials and firing at 1600 °C in N2 atmosphere. The effects of Si/Al ratio and firing temperature on the phase composition, structure and properties of fired samples were researched by XRD, SEM, DSC-TG, etc. The results show that increasing Si/Al ratio and firing temperature can improve the properties by increasing the content of β-Sialon. However, with the increasing Si/Al ratio, the deviations between actual and designed contents of β-Sialon increase due to Si volatilization, and the properties cannot be further improved when Si content is larger than 16.3 wt%. The fired samples with Si metal and Al metal mass ratio = 64.9% obtained optimal properties: water absorption 8.4%, bulk density 2.58 g·cm−3, room temperature bending strength 82.7 MPa, high-temperature bending strength 81.1 MPa, thermal expansion coefficient (room temperature-1000 °C) 5.06 × 10−6·°C−1, thermal conductivity (at room temperature) 7.77 W·(m·K)−1, specific heat capacity (at room temperature) 0.7 J·(g·K)−1, which mean that it is a good candidate for the thermal storage material.