Effect of the impregnation with liquid glass on the properties of refractory castable

Abstract

In this study, the impact of liquid glass (sodium silicate) impregnation under vacuum on the physical, mechanical properties, and alkali resistance of fireclay-based conventional castable (CC) and medium cement refractory castable (MCC), which are using in boilers for biomass combustion, was analysed. In research standard test methods for physical and mechanical properties (EN ISO 1927-6), as well as scanning electron microscope (SEM), testing methods for alkali resistance (ASTM C 454–83) and thermal shock resistance by evaluating changes in ultrasound pulse velocity were used. The results of the investigation have shown that the alkali resistance of CC as well as MCC can be improved by impregnation with liquid sodium silicate glass under vacuum. Impregnated refractory castables have lower porosity (7–9%), higher cold crushing strength (up to 18%). The structure of impregnated samples is denser compared with that of nonimpregnated refractory castables. The SEM images showed that the impregnated samples pores are partially filled with the sodium silicate. Alkali resistance tests showed that a glassy protective layer (width approximately 1 mm) formed on the surfaces of refractory castables, thus reducing further penetration of alkali (potassium) into deeper layers of the samples. However, impregnated refractory castables are less resistant to thermal shock cycles.