2026-08-28T05:05:49Zhttps://riubu.ubu.es/oai/request

oai:riubu.ubu.es:10259/119782026-08-28T00:05:21Zcom_10259_4313com_10259_5086com_10259_2604col_10259_4314

Atmosphere-controlled thermal processing enables tunable optical properties via iron-oxide phase engineering in natural silicate materials Urbaneja Miguel, Álvaro Torija López, Alba Carrancho Alonso, Ángel Iriarte Avilés, Eneko González Moreno, Sara González Martín, José Manuel Trigo López, Miriam Vallejos Calzada, Saúl Iron-oxide phase equilibria Redox-controlled thermal processing Process–structure–property relationship Magnetite–hematite transformation Atmosphere-controlled heat treatment Functional optical materials Ciencia de materiales Mineralogía Materials science Mineralogy Controlled-atmosphere thermal processing was investigated as a method to engineer iron-oxide phase assemblages in iron-bearing silicate materials. Natural sandstone was heated between 200 and 1000 °C under air, N2 and CO2 atmospheres to evaluate how oxygen partial pressure governs redox transformations and the resulting macroscopic optical behaviour. The treatments produced a wide and reproducible range of optical responses from a single starting material. Colour evolution, quantified in the CIELAB space, correlates with bulk mineral transformations. Oxidizing conditions stabilize hematite-dominated assemblages and generate red hues, whereas reduced-oxygen atmospheres promote magnetite formation and progressive darkening. Rock-magnetic measurements identify atmosphere-dependent phase assemblages, including a high-coercivity iron oxide under strongly oxidizing conditions. The magnetic response mirrors the optical evolution, indicating that colour development originates from internal phase transformations. Compressive strength remained within the same order of magnitude as the untreated material across the studied conditions, indicating no catastrophic mechanical degradation. These results show that oxygen availability acts as a key processing variable controlling iron-oxide stability and optical response. The study establishes a process-based approach for tuning optical properties in mineral materials through atmosphere-controlled thermal processing without chemical additives. Unlike previous studies focused on temperature-driven effects or isolated observations, this work demonstrates a reproducible process-based approach to tune optical properties in natural silicate materials through controlled atmosphere engineering. We gratefully acknowledge the financial support provided by all funders. Authors S. Vallejos and Á. Carrancho received Grant PID2023-147301OB-I00 and Grant PID2024-159094NB-I00, respectively, funded by MICIU/AEI/10.13039/501100011033 and FEDER. The financial support provided by Fondo Europeo de Desarrollo Regional-European Regional Development Fund (FEDER, ERDF) and Regional Government of Castilla y León -Consejería de Educación, Junta de Castilla y León- (BU025P23 and BU037P23) is gratefully acknowledged. This work was supported by the Regional Government of Castilla y León (Junta de Castilla y León) and by the Ministry of Science and Innovation MICIN and the European Union NextGenerationEU PRTR. Author Saul Vallejos received grant BG22/00086 funded by Spanish Ministerio de Universidades. 2026-08-27T11:52:34Z 2026-08-27T11:52:34Z 2026-05-29 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion 2238-7854 https://hdl.handle.net/10259/11978 10.1016/j.jmrt.2026.05.175 eng Journal of Materials Research and Technology. 2026, V. 42, p. 10750-10759 https://doi.org/10.1016/j.jmrt.2026.05.175 Atribución 4.0 Internacional http://creativecommons.org/licenses/by/4.0/ info:eu-repo/semantics/openAccess application/pdf Elsevier https://riubu.ubu.es/bitstream/10259/11978/4/Urbaneja-jmrt_2026.pdf.jpg Hispana TEXT http://creativecommons.org/licenses/by/4.0/ RIUBU. Repositorio Institucional de la Universidad de Burgos https://hdl.handle.net/10259/11978