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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.
Oxidation and Corrosion
Published in Alan Cottrell, An Introduction to Metallurgy, 2019
The most familiar method of applying a protective coat is, of course, by painting. Oil paints consist of pigments suspended in linseed oil to which is added a thinner (white spirit or turpentine) and a drier (a metal linoleate or naphthenate). The main pigments used are red lead, zinc oxide and chromate, iron oxide and powdered aluminium. Paint films are electronic insulators and so the cathodic reaction cannot occur except at the metal surface. This reaction is not inhibited, however, because the film is usually porous and allows oxygen and water to migrate through it fairly readily. The effectiveness of a paint depends upon the high resistance it provides in the electrolytic path between anodic and cathodic areas of the metal and also, when certain pigments are present, on the anodic inhibition it can provide. Slightly soluble chromates in the paint can slowly dissolve out when water is present and passivate the underlying metal surface. Red lead reacts with linseed oil to form soaps which then break down into lead salts of various fatty acids (e.g. azelaic, suberic, pelargonic acids) which are good anodic inhibitors.
Spray Drying for Production of Food Colors from Natural Sources
Published in M. Selvamuthukumaran, Handbook on Spray Drying Applications for Food Industries, 2019
Mehmet Koç, Feyza Elmas, Ulaş Baysan, Hilal Şahin Nadeem, Figen Kaymak Ertekin
Minerals are generally defined as crystalline or geologically occurring elements or chemical compounds. Minerals have been used for a long time as natural colorants in the food and cosmetics industries. Minerals provide various color tones depending on their chemical composition and/or their physical structure. Many minerals contain metallic cations, which contain d orbital electrons. Metallic cations in minerals usually absorb and reflect visible light (Mason 2013). For example, viridian, which is a chromium oxide mineral, is a green pigment used as a colorant. Furthermore, viridian is exempt from certification in cosmetics because of being obtained from natural sources (Martins et al. 2016). The Cinnabar, Ochre, lead, a nd Realgar are some examples of red pigments, which originate from the source of minerals. Cinnabar, expresses as common bright scarlet to a brick-red form of mercury sulfide (HgS) and serves directly as dyeing pigment. Red ochre is a natural pigment that contains anhydrous and hydrated iron oxide (Fe2O3nH2O). Red ochre has several hues, which range from yellow to deep orange or brown. Red lead (Pb3O4 or 2[PbO][PbO2]) is a bright red or orange crystalline or amorphous pigment. Realgar (a-As4S4) is an arsenic sulfide mineral, which is also a mineral of arsenic. It is thought that these pigments are not safe and usage in the food industry is very limited because of this.
First Analytical Study on Second-Century Wall Paintings from Ulpia Traiana Sarmizegetusa: Insights on the Materials and Painting Technique
Published in International Journal of Architectural Heritage, 2020
Ioana Maria Cortea, Luminița Ghervase, Ovidiu Țentea, Anca Constantina Pârău, Roxana Rădvan
The hypothesis that a red lead pigment had been used, was confirmed via the XRD analysis, which showed the presence of minium along with several degradation by-products—such as massicot, plattnerite, galena, plumbous sulfite, and anglesite (Table 4). As shown in previous studies (Aze et al. 2008), red lead alterations during natural ageing can lead to a complex mixture of alteration products that vary depending on the environmental factors, initial pigment properties, or pictorial technique.