Abstract
Geopolymers are inorganic materials that form long-range, covalently bonded, networks; they are materials similar to ceramics, whose components are mainly aluminium and silicates. Any inorganic source of silica and alumina, dissolved in the alkaline solution, acts as a precursor of geopolymers. The type of clays most commonly used in the synthesis of geopolymers is based on kaolinite. The present work concerns the modification of the geopolymer at the chemical and nanostructural level, through the design and development of hybrid coating sol-gel formulations to improve characteristics such as mechanical strength, chemical inertness, heat resistance and porosity for possible use in the restoration and conservation of cultural heritage. The methods of functionalization of the geopolymers here shown are: (i) the treatment of the geopolymeric surface, post-drying, through the application of the sol-gel directly on the monolith, for a modification of the surface properties; (ii) the pretreatment of the geopolymeric mixture, through the addition of the alkoxysilane which can induce a homogeneous consolidation of the molecular structure, implementing the properties of the entire monolith. The employed alkoxysilanes differ according to the length of the hydrocarbon chain and the presence of halogen atoms. Hydrophobicity tests were performed on these formulations.
Highlights
The term "geopolymer" describes a wide variety of natural or synthetic composite materials showing a polymeric structure [1,2,3]
The alkoxysilane agents may be chosen for the implementation of specific properties of the geopolymer materials that allow the production of various types of coatings, such as protective coating, reflective or antireflective coatings, refractory linings, coatings with controlled porosity; all these properties may result determining in the restoration of cultural heritage [26,27]
3.1 Sol-gel synthesis and geopolymer functionalization As shown before [29,30,31,32,33,34,35] for similar functional silica based coatings, the employed sol–gel mixtures were made from Tetraethyl orthosilicate (TEOS) and (3-Aminopropyl) triethoxysilane (APTES) precursors undergoing hydrolysis–condensation reactions in several steps in combination with two alkoxysilanes, namely (3,3,3-trifluoro-propyl) trimethoxy silane (F3) and 1H,1H-2H,2Hperfluorooctyl triethoxy silane (F13), employed individually
Summary
The term "geopolymer" describes a wide variety of natural or synthetic composite materials showing a polymeric structure [1,2,3]. They are materials similar to ceramics, whose components are mainly. Geopolymers have many advantages over traditional organic polymers, deriving their main characteristics from the starting mineral components and improving their chemical-physical and mechanical properties [14,15,16,17,18,19,20,21]. The alkoxysilane agents may be chosen for the implementation of specific properties of the geopolymer materials that allow the production of various types of coatings, such as protective coating, reflective or antireflective coatings, refractory linings, coatings with controlled porosity; all these properties may result determining in the restoration of cultural heritage [26,27]
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