Analysis of the Structure and Durability of Refractory Castables Impregnated with Sodium Silicate Glass

Abstract

This study examines the impact of the impregnation of fireclay-based conventional (CC) and medium-cement castables (MCCs) with liquid sodium silicate glass under vacuum conditions. The goal is to assess how this treatment affects the physical and mechanical properties and durability (alkali and thermal shock resistance) of these castables used in biomass combustion boilers, where they are exposed to temperatures up to 1100 °C. The research work employs standard test methods to evaluate the physical and mechanical properties. Additionally, advanced techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and specific tests for alkali resistance and thermal shock resistance are used. The research findings suggest that impregnation with sodium silicate glass under vacuum significantly enhances the alkali resistance of both CC and MCCs. This improvement is primarily due to the reduction in porosity and the increase in density. SEM images reveal that the impregnated samples are coated with a glassy layer and the pores are partially filled with sodium silicate. Tests for alkali resistance demonstrate the formation of a protective glassy layer (with a thickness of 0.9–1.5 mm) on the castable surfaces, thereby reducing the further penetration of alkali into deeper layers of the samples. However, it is important to mention that the impregnated refractory castables have reduced resistance to thermal shock cycles.