Progettazione e sintesi di nuovi materiali per la protezione, il ripristino e la conservazione di manufatti lapidei carbonatici

In recent times, the historical and architectural heritage has been subject to increasing degradation processes, largely due to outdoor air pollution, in addition to physical and biological factors. This research aims at evaluating the effectiveness and compatibility of new consolidating treatments of inorganic composition applied to distinct carbonate lithologies, such as marble and biomicrite limestones. The new compounds belong to the general classes of monoesters and functionalized monoamides of ammonium oxalate, with general formulas ROC(O)COONH4 and RNHC(O)COONH4, respectively (R = alkyl or aryl substituent). These salts were synthesized, purified, and fully characterized by elemental microanalysis, melting point determination, and spectroscopic methods (FT-IR, NMR). A few of the synthesized salts or their derivatives were characterized by single crystal X-ray diffraction. Full characterization of treated and untreated authentic stone samples was carried out by means of SEM, powder XRD, synchrotron tts-microXRD measurements, mercury intrusion porosimetry, determination of water transport properties, and pull-off tests. Furthermore, the experimental measurements were accompanied by DFT computational studies, aimed at understanding the stability of oxalate and oxamate salts in water solution as well as the nature of the interaction between the anions and the lattice of carbonate stone substrates. While the ammonium salts of oxalate monoesters, prone to spontaneous hydrolysis in aqueous solutions, are a potential source for calcium oxalate treatments, more effective than ammonium oxalate due to their larger solubility, ammonium oxamates represent a novel class of compounds alternative to ammonium oxalate. In conclusion, this thesis represents a comprehensive investigation that demonstrates that the salts of both oxalate monoesters and functionalized monoamides can be successfully adopted as novel precursors for the conservative treatments of carbonate stones.