Thermal treatment effects on the microstructure and flexural performance of handmade α-Al₂O₃ crucibles

Abstract

Alumina crucibles are widely used ceramic components in materials science and engineering owing to their high thermal stability and suitability for processes such as melting and solid-state synthesis. This study reports the structural, morphological, and mechanical characterization of locally handmade alumina crucibles sourced from a commercial supplier in Bogotá, Colombia, evaluated after three distinct thermal histories: as-received at room temperature (AT), high-temperature exposure at 1350 °C for 12 hours (HT), and cold treatment by liquid nitrogen immersion at -196 °C (CT). X-ray diffraction identified alpha-Al₂O₃ (corundum) as the dominant crystalline phase in all conditions, with minor SiO₂ and Al₂SiO₅-related secondary signals. No phase transformations were detected after any treatment, confirming the material’s high structural and chemical stability. Fracture surface analysis revealed that HT samples exhibited the largest projected pore area (8.12 ± 1.67 µm²) compared with AT (6.51 ± 1.60 µm²) and CT (5.38 ± 1.22 µm²), accompanied by a distributed network of grain-scale microcracks. Mechanical testing indicated that HT crucibles reached the highest apparent bending modulus (331.78 GPa) and load-bearing capacity, surpassing AT (238.87 GPa) and CT (106.17 GPa), which was attributed to a microcrack toughening mechanism, whereas CT displayed a more brittle response. The mechanical behavior was governed primarily by defect architecture rather than compositional changes, and the crucibles demonstrated performance levels compatible with the moderate temperature melting of non-ferrous metals.