Design and synthesis of new materials for the protection, restoration, and conservation of carbonate stone artifacts of interest in the field of Cultural Heritage.

The conservation of carbonate stone materials, commonly found in historical architecture and sculpture, poses significant challenges due to their susceptibility to weathering and chemical degradation. This PhD research focuses on developing innovative inorganic treatments to improve the durability of calcareous substrates by forming insoluble and chemically compatible protective phases. Among the most studied consolidants, calcium oxalates, oxamates, and phosphates exhibit promising properties. Calcium oxalate treatments offer high selectivity in crystalline phase formation but suffer from limited penetration (<1–2 mm), while ammonium oxamates display higher solubility and slightly enhance penetration. Diammonium hydrogen phosphate (DAP) treatments, although less selective, achieve deeper penetration (up to 20 mm). Despite increasing interest in oxalate and oxamate derivatives, treatments based on organophosphorus derivatives remain less explored. To address this gap, novel organophosphate, phosphonate, and phosphinate compounds were synthesized with easily scalable methods. Additionally, three ammonium oxamate derivatives: ammonium thiooxamate, N–ethyloxamate, and N–2–picolyloxamate were studied. All compounds were characterised using FT–IR, ¹H, ¹³C, and ³¹P NMR, PXRD, elemental analysis, and where possible, single–crystal X–ray diffraction (SC–XRD) and 3D electron diffraction (3D–ED). Their reactivity with calcite was tested by reacting them with calcium carbonate powder, and the resulting phases were analysed via PXRD, FT–IR, and TGA. The most promising compounds were applied to three carbonate lithotypes white Carrara marble, Sardinian biomicrite limestone, and carbonate sandstone, selected for their historical relevance, petrographic diversity, and high calcite content. Application methods included immersion, brushing, and spraying, followed by artificial ageing protocols to simulate realistic degradation. Treatments were evaluated through a comprehensive suite of analytical techniques, including SEM, optical microscopy, thin–section petrography, GID–XRD, and various physical and mechanical tests. Most characterisations were performed in collaboration with the University of Barcelona and the Escola Politècnica Superior d’Edificació de Barcelona. Finally, the most effective treatments were validated in real–world conservation scenarios through partnerships with restoration institutions. This multidisciplinary approach enabled a thorough evaluation of the treatments and contributed to the advancement of sustainable and effective strategies for preserving carbonate stone heritage.