Murgia, Simone, Aragoni, M. Carla, Carcangiu, Gianfranco, Coles, Simon J., Columbu, Stefano, Ennas, Guido, Lippolis, Vito, Meloni, Paola, Navarro Ezquerra, Antonia, Orton, James B., Pintus, Anna, Podda, Enrico, Rainer, Daniel N., Gimeno Torrente, Domingo and Arca, Massimiliano (2025) Protecting white Carrara marble with organophosphorus salts: a case study of ammonium hydrogen phenylphosphonate. Materials Advances. (doi:10.1039/d5ma01116g).
Abstract
Ammonium hydrogen phenylphosphonate (1) was investigated as a novel agent for the protection and consolidation of carbonate stone substrates. Compound 1 quantitatively reacted with calcium carbonate to give calcium phenylphosphonate dihydrate (2), which was characterized by spectroscopic and microanalytical means and whose structure was solved using 3D electron diffraction. Compound 1 was applied to artificially weathered Statuario white Carrara marble mock-ups through immersion, brushing, and spraying techniques, and its effect on structural, hygric, and mechanical properties was evaluated by means of a comprehensive set of techniques, including X-ray diffraction, ultrasonic velocity measurements, colorimetry, porosimetry, and contact angle measurements. While the application of well-known diammonium hydrogen phosphate (DAP) on carbonate stones results in the deposition of non-stoichiometric hydroxyapatite (HAP), the treatment with compound 1 results in the formation of a thin, homogeneous coating of stoichiometric compound 2 that enhances cohesion, reduces porosity, and improves mechanical resistance, restoring the marble properties to near-pristine conditions. The treatment induces only minimal chromatic changes, making it a promising solution for the conservation of stone cultural heritage.
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