Evaluation of the Effect of Fe₂O₃ as a Sintering Additive on Densification, Microstructure, and Thermal Stability of Al₂O₃

Abstract

This study investigates the fabrication of alumina-based (Al₂O₃) ceramics using pressureless sintering, employing hematite (Fe₂O₃) as a sintering aid. Fe₂O₃ powders were synthesized via combustion and incorporated into Al₂O₃ concentrations of 0.5, 1.0, and 2.0 wt.%. The samples were sintered at 1400 °C and characterized by X-ray diffraction (XRD) with Rietveld refinement, thermogravimetric analysis (TG/DTG), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and density measurements using the Archimedes method. The results demonstrated that the addition of Fe₂O₃ increased the densification of Al₂O₃ ceramics, with the highest densification (~85%) observed in samples containing 1.0 and 2.0 wt.% Fe₂O₃. XRD analysis identified only the corundum phase of Al₂O₃, suggesting that Fe₂O₃ was incorporated without forming secondary phases. However, Rietveld refinement calculations revealed distortions in the unit cell volume, which contributed to lowering the melting temperature of Al₂O₃, thereby facilitating sintering. SEM images showed that Fe₂O₃ acted as a grain growth inhibitor, resulting in finer microstructures with smaller grains. EDX mapping indicated that Fe ions preferentially accumulated in regions with higher pore concentrations. Thermal analysis demonstrated improved thermal stability in Fe₂O₃-containing samples. Overall, the study confirms that Fe₂O₃ serves as an effective sintering aid, enhancing densification and thermal stability while refining the microstructure of Al₂O₃ ceramics. These findings contribute to the development of optimized ceramic materials for high-performance applications.

Keywords

Al₂O₃ / Fe₂O₃ / Sintering aid / Microstructure / XRD / TGA

Acknowledgments

The authors thank the Brazilian agencies CNPq, CAPES, and FAPERJ for supporting this investigation. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. The authors thank the Brazilian Navy Research Institute (IPqM) researchers for performing the thermal analyses. Pedro Henrique Poubel Mendonça da Silveira and Marcelo Henrique Prado da Silva thank the Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for their support—grant numbers E-26/200.338/2024 and 200.339/2024.

Author Contributions

Conceptualization, P.H.P.M.d.S. and A.V.G.; Methodology, P.H.P.M.d.S. and A.V.G.; Software, P.H.P.M.d.S.; A.E.E.; J.L.d.S.; Validation, M.H.P.d.S. and A.V.G.; Formal Analysis, P.H.P.M.d.S.; Investigation, P.H.P.M.d.S. and N.V.L.S.; Resources, M.H.P.d.S.; Data Curation, A.E.E.; Writing—Original Draft Preparation, P.H.P.M.d.S. and N.V.L.S.; Writing—Review & Editing, J.L.d.S.; Visualization, A.V.G. and M.H.P.d.S.; Supervision, M.H.P.d.S.; Project Administration, M.H.P.d.S.; Funding Acquisition, A.V.G.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data supporting findings of this study are available upon reasonable request.

Funding

This research was funded by the Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ), grant numbers E-26/200.338/2024 and E-26/200.339/2024.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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