Density–Porosity–Property Relationships in Zirconia-, Spinel-, and Silicon Carbide-Modified AZS Refractory Ceramics

Abstract

Alumina–zirconia–silica (AZS) refractories are widely used in high-temperature industrial applications because of their excellent thermal stability, corrosion resistance, and mechanical strength. This study investigated the effects of zirconia, spinel, and silicon carbide additions on the physical and mechanical properties of AZS refractory ceramics. Four compositions comprising Standard AZS (Batch A), Zr-rich AZS (Batch B), Spinel AZS (Batch C), and SiC AZS (Batch D) were developed and evaluated in terms of bulk density, relative density, apparent porosity, water absorption, elastic modulus, compressive strength, hardness, and flexural strength. The results showed that zirconia enrichment significantly improved densification and mechanical performance. Batch B exhibited the highest bulk density (3.78 g/cm³), relative density (0.900), elastic modulus (197.1 GPa), compressive strength (189.9 MPa), hardness (10.18 GPa), and flexural strength (96.4 MPa), while also recording the lowest apparent porosity (5.5%) and water absorption (1.45%). Conversely, Batch D showed the lowest density and mechanical properties and the highest porosity and water absorption. Correlation analysis revealed strong inverse relationships between porosity and density, stiffness, strength, hardness, and flexural strength, confirming that densification and porosity control are critical determinants of refractory performance. The overall performance ranking was Batch B > Batch A > Batch C > Batch D, indicating that zirconia enrichment is an effective approach for enhancing the structural integrity, durability, and service performance of AZS refractory ceramics in demanding high-temperature environments.