Využití zinksilikátových nátěrů při restaurování povrchu železných kovů / The use of zinc-silicate coatings in restoration of a surface of iron metal

The introduction summarizes the issues of corrosion protection of corroded structures and structural items from iron metals mechanically cleaned to St2/St3 [1] grade, which from various reasons cannot be shot blasted before coating. The paper discusses the negative impact of soluble salts (mostly chlorides) cumulated in rust on formation of osmotic blisters and the service- life of protective coats, regardless of whether they formed on a corroded surface before coating or as a result of gaseous acidic atmosphere elements (SO₂) penetration through the applied coats, which further acts as a source of formation of soluble ferrous sulphate in a form of sulphate nests. Further on, the paper refers to the earlier published utilisation of the sol gel technique for preparation of pre-hydrolysed ethylsilicate used for stabilisation of amorphous rust, avoidance of propagation of sulphate nests and making of zinc silicate coats. Condensation tests performed without any corrosion stimulators [2] and in a neutral saline mist [3], both lasting 1440 hours, proved a generally very good protective effect and high resistance to osmotic blisters for a model organically modified zinc-silicate coat (hereinafter as OMZSC) with a high content of metallic zinc on a strongly corroded unalloyed structure steel. Further on, the study describes the reasons of this behaviour given by a character of the silica sol-based inorganic binder that differs from the organic coat binders. In the end, the paper mentions the possibility of using the organically modified zinc-silicate coating systems (the base layer with a high content of metallic zinc + the top layer with the required pigmentation and reduced content of metallic zinc) to restore the original appearance of forged and cast iron structure components of historical artefacts, and it presents examples of practical applications.