2026-08-28T05:05:54Zhttps://riubu.ubu.es/oai/request

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

00925njm 22002777a 4500 dc Urbaneja Miguel, Álvaro author Torija López, Alba author Carrancho Alonso, Ángel author Iriarte Avilés, Eneko author González Moreno, Sara author González Martín, José Manuel author Trigo López, Miriam author Vallejos Calzada, Saúl author 2026-05-29 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. 2238-7854 https://hdl.handle.net/10259/11978 10.1016/j.jmrt.2026.05.175 Iron-oxide phase equilibria Redox-controlled thermal processing Process–structure–property relationship Magnetite–hematite transformation Atmosphere-controlled heat treatment Functional optical materials Atmosphere-controlled thermal processing enables tunable optical properties via iron-oxide phase engineering in natural silicate materials