Effect of alumina nanofibers addition on the MgO-CaO compounds characteristics

Basic magnesia-doloma composites are refractory materials valued for their high melting point, excellent thermal stability, durability in alkaline environments, and suitability for quality steel manufacturing, as well as their wide availability. These properties make them attractive for a range of industrial applications. However, a major challenge is their susceptibility to hydration, which can weaken their structure and reduce performance over time. In this study, alumina nanofibers (AlNFs) with an average diameter of 360 nm were incorporated into the MgO-CaO ceramic matrix at concentrations up to 2.5 wt%. The composites were pressed at 100 MPa and sintered for 3 h at 1400 °C in air. The resulting materials were evaluated for their physical properties (hydration resistance, apparent porosity, and bulk density) and mechanical characteristics (cold crushing strength and Vickers microhardness). The phase composition, microstructure, and elemental distribution were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS). The results showed that AlNFs reinforcement improved densification, resulting in better physical and mechanical properties. The nanofibers also enhanced hydration resistance by preventing water penetration at grain boundaries and filling pores. The results show that the sample with 2 wt% was optimal. By increasing the AlNFs addition to 2 wt%, the intermediate phases CaAl₄O₇ and Ca₃Al₂O₆ enhanced the compressibility and properties of the composite through solid-state and melt-phase sintering mechanisms, respectively. When the AlNF addition was increased to 2.5 wt%, the slope of improvement in mechanical properties decreased due to excessive grain growth.