Historical materials deteriorate due to external factors and aging processes. We preserve them through conservation interventions, including consolidation. Consolidants should be compatible with the material, penetrate deeply, function across a wide temperature range, avoid whitening the surface, and establish cohesion without altering the material's appearance. For carbonate surfaces, commercial consolidants based on Ca(OH)₂ nanoparticles (Nanorestore®, shorter NR and CaLoSiL®, shorter CS) are used, reacting with CO₂ to form CaCO₃. Consolidation is also achieved with an aqueous solution of calcium acetoacetate (shorter CFW) which reacts with water to produce CO₂ and acetone that evaporate, leaving solid CaCO₃. Since the conversion of CFW releases CO₂, studying the synergistic effects of mixing CFW and Ca(OH)₂ makes sense, as CO₂ accelerates carbonation and a pH increase from Ca(OH)₂ promotes the transformation of CaCO₃ into the thermodynamically most stable calcite. The main objectives of the master's thesis were: (i) to examine, for individual consolidant systems (CFW, NR, CS), as well as mixtures of CFW with NR and CS, the time-dependent effects (7 and 28 days) of relative humidity (33% and 93% RH) on the reaction rate of the reactants at a constant elevated temperature (40°C) in an air atmosphere, the transformation of the resulting amorphous CaCO₃ into its crystalline forms, and the morphology and size of the resulting crystallites, (ii) to study the interactions and possible synergistic effects of mixing consolidants, (iii) to determine the effectiveness of consolidation and the penetration depth of consolidants into gypsum substrates by applying different numbers of consolidant layers and combining the application order of the consolidants. The main analytical methods used were FTIR, XRD, SEM, DRMS, and indicator method. The standalone CFW system converts to amorphous CaCO₃ at 33% RH and to vaterite at 93% RH. In the independent NR system, predominant vaterite formation is observed regardless of humidity levels. The independent CS system results in recrystallization into vaterite and aragonite at both humidity levels, while a high proportion of the most stable calcite is only present in CS exposed to 93% RH for 28 days. Mixture systems exhibited a synergistic effect compared to the standalone CFW system at both 33% and 93% RH, as mixing accelerates its conversion. When exposed to the given conditions, the independent NR and CS sample systems generally exhibit a significantly higher degree of crystallinity compared to the mixtures, with the only exception being the CFW and NR mixture exposed to 93% RH.The consolidation effectiveness was studied on gypsum substrates by combining ten different consolidant systems. The best effect, due to the synergistic interaction, was shown by the mixture of CFW and Nanorestore® applied in 50 layers. Interaction after 28 days of exposure to 93% RH significantly improves not only surface consolidation but also mechanical consolidation properties to a depth of 10 mm.
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