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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.
Polymer Technology
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
Paints are specially formulated for specific purposes and locations. The following is a brief description of the most popular paint types: Oil paints: Oil paints consist of a suspension of pigments in a drying oil, such as linseed oil. The film is formed by a reaction involving atmospheric oxygen that polymerizes and crosslinks the drying oil. Catalysts may be added to promote the crosslinking reaction. Oil paints, once dried, are no longer soluble, although they can be removed through polymer degradation using the appropriate paint stripper.Oil varnishes: Varnish coatings consist of a polymer, either natural or synthetic, dissolved in a drying oil together with appropriate additives as catalysts to promote crosslinking with oxygen. When dried, they produce a clear, tough film. The drying oil is generally incorporated, along with the dissolved polymer, into the coating.Enamels: Classical enamel is an oil varnish with a pigment added. The added polymer is typically selected to provide a harder, glossier coating than the oil varnish mixture. Today, there are latex enamels that are similar to the oil enamels, except that no natural oil is present.Lacquers: Lacquers consist of polymer solutions to which pigments have been added. The film is formed through simple evaporation of the solvent, leaving the polymer film as the coating. These coatings are formed without subsequent crosslinking; thus, the surface exhibits poor resistance to some organic solvents.Latex paints: Latex paints today account for more than one-half of the commercial paint sold. They are characterized by quick drying (generally several minutes to several hours), little odor, and easy cleanup (with water). Latex paints are polymer latexes to which pigments have been added. The film is formed by coalescence of the polymer particles on the evaporation of the water. The polymer itself is not water soluble, though these paints are called waterborne coatings because the polymer emulsion is “carried” by water.
Experimental study of behaviour of circular footing on geogrid-reinforced sand
Published in Geomechanics and Geoengineering, 2022
Danny Useche-Infante, Gonzalo Aiassa Martinez, Pedro Arrúa, Marcelo Eberhardt
The model tests were conducted in a circular-steel tank of 600 mm internal diameter, 8 mm wall thickness and 450 mm height. In order to maintain the axisymmetric condition and minimising the out of plane displacement, the tank was built sufficiently rigid. The inner surface of the tank was made smooth by painting with an oil paint to reduce the boundary effects. A rigid rough circular-steel footing with diameter, B, of 100 mm and thickness of 15 mm, is placed over a geogrid-reinforced sand. A hydraulic jack with 50-ton capacity welded against a reaction frame was used to apply the load to the footing. The diameter of the foundation and size of the tank were chosen in such a way that the edge effect was minimum. The diameter of the tank was 6B and the height of the soil stratum 4.5B. According to Chummar (1972), the soil failure surface extends around of 2B on each side from the edge of the footing and its depth is about 1.1B from the base of the foundation. Therefore, in the tests carried out, it is guaranteed that the fault surface develops freely. Besides, the B/D50 ratio was 64.1, accordingly, the size of the soil particles has no significant influence on the results (see Kusakabe (1995)).
The Concept of Historical Aluminium-Pigmented Anticorrosive Armour Paints, for Sustainable Maintenance of Ferrous Heritage
Published in International Journal of Architectural Heritage, 2022
The paint binder employed could consist of mixtures of boiled linseed oils, linseed stand oils and refined tung oils (IVA 1935).14 Linseed stand oil was the most commonly used form. Stand oils have a substantially lower tendency to absorb and swell in water, a property that is beneficial for anticorrosive paints since this will decrease the fatigue of the paint layers (Laurell 1937). Results from IVA corrosion tests (1939–1947) conclude that quarter tung stand oil was superior compared to “boiled” linseed oil (Tengstrand 1948). From the 1920s, the industrial process of heat-treating linseed oils was gradually changed. The traditional high temperature-bodied linseed oil (i.e., heated close to the boiling point of 280° with the addition of metal oxide driers) was used parallel to a newer heating process of 130–150°C (in combination with liquid siccative and air-blowing), a procedure that resulted in polar and hydrophilic linseed oil (Karlsdotter Lyckman 2005; Andersson and Nylén 1957).15The high-temperature-boiled oils are also known as kettle-bodied or heat-bodied linseed oils, and long oil (resin-free) varnishes (Edwards 1936). This, in turn, resulted in reduced paint weathering resistance and linseed oils bodied by air blowing were therefore considered unsuitable as anticorrosive paint binders (Edwards 1927; Standeven 2011). The tung oil enhances the paint applicability and allows the paint film to dry faster and better, resulting in long-lasting elasticity and moisture resistance (IVA 1935, 1961; Vattenfall 1933). The tung oil also increases the paint’s tolerance of acidic or alkaline environments. The quarter tung stand oil could be diluted with raw linseed oil (IVA 1935; Laurell 1937). Gradually, paints with drying-oil binders received alkyd additions during the 1950s, and the linseed oil paint types were finally outcompeted by alkyds in the 1960s (IVA 1961).