Stabilization treatment of cultural heritage artefacts: In situ monitoring of marine iron objects dechlorinated in alkali solution

•β-Fe2(OH)3Cl dissolve within few minutes when immersed in NaOH.•Fe(OH)2 and Fe3O4 form both in NaOH aerated and deaerated.•Chlorinated green rust forms during the dechorination in aerated solution.•Unwashed corrosion layers contain chlorine after drying.•Deaerated solution conduct to a more homogeneous layer mainly constituted of goethite.