Abstract
Marble and limestone have been extensively used as building materials in historical monuments. Environmental, physical, chemical and biological factors contribute to stone deterioration. The rehabilitation of stone damage and the delay of further deterioration is of utmost importance. Inorganic nanoparticles having chemical and crystallographic affinity with building materials is very important for the formation of protective coatings or overlayers. In the present work, we have tested the possibility of treating calcitic materials with suspensions of amorphous calcium carbonate (am-CaCO3, ACC) and amorphous silica (AmSiO2). Pentelic marble (PM) was selected as the test material to validate the efficiency of the nanoparticle suspension treatment towards dissolution in undersaturated solutions and slightly acidic pH (6.50). Suspensions of ACC and AnSiO2 nanoparticles were prepared by spontaneous precipitation from supersaturated solutions and by tetraethyl orthosilicate (TEOS) hydrolysis, respectively. The suspensions were quite stable (nine days for ACC and months for AmSiO2). ACC and Am SiO2 particles were deposited on the surface of powdered PM. The rates of dissolution of PM were measured in solutions undersaturated with respect to calcite at a constant pH of 6.50. For specimens treated with ACC and AmSiO2 suspensions, the measured dissolution rates were significantly lower. The extent of the rate of dissolution reduction was higher for AmSiO2 particles on PM. Moreover, application of the nanoparticles on the substrate during their precipitation was most efficient method.
Highlights
Marble and limestone are commonly used building materials for historical monuments, especially in the countries in the Mediterranean basin
Composites of amorphous calcium carbonate (ACC) and amorphous calcium oxalate (ACO) with alkoxysilane gels applied for the protection of monument building materials without silicates resulted in the increase of surface hydrophobicity and improved resistance to acid attack [12]
From the results shown so far, it may be concluded that the formation of ACC is feasible and that stable suspensions can be prepared in isopropyl alcohol
Summary
Marble and limestone are commonly used building materials for historical monuments, especially in the countries in the Mediterranean basin. Composites of amorphous calcium carbonate (ACC) and amorphous calcium oxalate (ACO) with alkoxysilane gels applied for the protection of monument building materials without silicates (marble, calcarenite, gypsum) resulted in the increase of surface hydrophobicity and improved resistance to acid attack [12]. CaCO3 and silica SiO2 nanoparticle suspensions were prepared from highly supersaturated solutions and from the hydrolysis of tetraortho silicate (Si(OC2 H5 )4 ,TEOS) in ethanolic solutions, respectively. Both solid particles in the respective suspensions have high crystallographic affinity for calcite. The further task of this work is the preparation of the composite material ACC–AmSiO2 , which we anticipate will be able to provide both consolidation and resistance to chemical dissolution of treated stone
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