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Coating Protection
Published in Karan Sotoodeh, Coating Application for Piping, Valves and Actuators in Offshore Oil and Gas Industry, 2023
Titanium dioxide (TiO2) is a widely used pigment type that is inorganic and white in color. Many types of pigment contain zinc. The main effect of zinc is galvanic protection, which is explained in more detail later in this chapter. Zinc, as a sacrificial metal, forms an anode and is corroded in favor of the metal surface in contact with it. Thus, the metal surface in contact with the zinc in the paint is protected. The effect of zinc on surface protection is called “cathodic protection” or “galvanic effect.” Corrosion inhibition is generally associated with inorganic pigments, such as zinc oxide, zinc chromate and red lead. It is interesting to know that some types of coating could be pigment and/or solvent-free, but all types of coating contain binder or resin. When a coating is applied on a surface, the solvent evaporates during the curing process and only the resin (binder) and pigments are left on the substrate.
Characterization of the Cr(VI)/Cr(III) Ratio in Aerosols
Published in Jacques Buffle, Herman P. van Leeuwen, Environmental Particles, 2019
Rob F.M.J. Cleven, Jan L.M. deBoer, Anton van der Meulen
Under environmental conditions chromium in compounds exists in the trivalent Cr(III) or the hexavalent Cr(VI) state. Cr(III) is an essential trace element for mammals, including man, whereas it is presumed that Cr(VI) compounds are genotoxic and potentially carcinogenic in humans.1 Evidence exists for the carcinogenicity of calcium chromate, strontium chromate, and zinc chromate. In the diet, chromium is predominantly present as Cr(III). Cr(VI) present in the diet will be converted partially to Cr(III) due to intragastric reduction. There is sufficient evidence, based on animal studies, that exposure to Cr(VI) compounds by inhalation will result in an increased risk for carcinogenic effects.2 The unit risk for Cr(VI) is 40.10−3.1 This means that in a hypothetical population of 1000, in which all individuals are exposed continuously from birth throughout their lifetimes to a concentration of 1 μg.m−3 of hexavalent chromium in the air they breathe, 40 additional cases of cancer are expected to occur. Assuming an acceptable risk of one extra case of cancer per million persons exposed lifetime, this risk corresponds with an airborne concentration of 0.025 ng Cr(VI).m−3. Many people will be exposed to unacceptable chromium levels, if all airborne chromium would be in the hexavalent state, as concentrations of total Cr in ambient air amount to some ng.m−3. Thus, there exists a need for speciation techniques to measure airborne Cr(VI).
Colorants, Pigments, and Dyes
Published in Mihai V. Putz, New Frontiers in Nanochemistry, 2020
Functional pigments are the ones that are used to modify the application characteristics, appearance or film properties of coatings. Corrosion inhibiting pigments take place in this class. Complex zinc chromate pigments, strontium chromate, barium phosphosilicates, barium borosilicates, red lead and zinc phosphates are used in primers to inhibit corrosion of steel by passivation of anodic area. In contrast to other pigments, they must be somewhat soluble in water to function.
Long-term corrosion resistance of zinc-rich paint using functionalised multi-layer graphene-tripolyphosphate: in situ creation of zinc phosphate as corrosion inhibitor
Published in Corrosion Engineering, Science and Technology, 2019
Mona Ehsanjoo, Somayeh Mohammadi, Naz Chaibakhsh
Phosphate compounds such as zinc phosphates are important traditional and good alternatives for the replacement of zinc chromate for active corrosion inhibition of metals [30,31]. The anti-corrosion behaviour of phosphate compounds is related to the formation of an adhesive and sparingly soluble phosphate salts film on the steel substrate which can also polarise cathodic areas [32].