Paints, zinc dust

In order to produce ready-for-use zinc dust paint, zinc dust is slowly added to the binder in a ratio of 4-4.5 1 while stirring. Binder additives (e.g., antisettling agents such as bentonite, pyrogenic silica) and zinc dust additives (e.g., extenders such as mica, talc, kaolin, or colored components such as chromium(III) oxide, titanium dioxide) can be used to adjust the application behavior and properties of the paints. 

Chem. Descrip. Zinc dust CAS 7440-66-6 EINECS/ELINCS 231-175-3 Uses Rust inhibitor pigment, weather resist, aid in metal protective paints, zinc-dust primers, finish coats Features Premium grade high purity... 

Uses Rust inhibitor pigment, weather resist, aid in metal protective paints, zinc-dust primers, finish coats... 

Because of its resistance to corrosion, zinc may be used to coat iron. This may be done by dipping the iron into molten zinc or by spraying zinc on the iron articles, for example iron sheets. This is known as galvanising. Smaller iron articles may be coated by heating with zinc dust, a process known as sherardising, or suspensions of zinc may be used in paints. 

Zinc oxide or zinc white is used in paints, but more preferable, because of its better covering power, is lithopone (a mixture of zinc sulphide and barium sulphate). Both paints have the advantage over white lead that they do not blacken in air (due to hydrogen sulphide). Zinc dust and also zinc chromate are constituents of... 

The most significant chemical property of zinc is its high reduction potential. Zinc, which is above iron in the electromotive series, displaces iron ions from solution and prevents dissolution of the iron. For this reason, zinc is used extensively in coating steel, eg, by galvanizing and in zinc dust paints, and as a sacrificial anode in protecting pipelines, ship hulls, etc. 

Oleo-resinous binder with zinc dust and graphite pigments Generally called zinc dust graphite paint, this relatively cheap material can resist temperatures in the range of 200-300°C. However, regular maintenance repainting will be required. 

Characteristics of coating Hot-dip galvanising A/etai spraying Plating Sherardising Zinc dust painting... 

Etch primers are widely used. They are mostly based on polyvinyl butyral and contain chromates and phosphoric acid. They are said to act both as primers and as etching solutions because it is believed that the chromates and phosphoric acid form an inorganic him, which provides adhesion, while oxidised polyvinyl butyral provides an organic him. For direct application to new galvanised steel, the best known primers are based on calcium orthoplumbate pigment and metallic lead, but these are now less used for environmental reasons. Zinc-dust paints and zinc-phosphate pigmented paints are also used, but the trend is to use pretreatments to assure good adhesion. 

While a non-phosphated topcoat/adhesive interface provided an excellent, moisture resistant, occlusive seal even under the most severe cycle testing, phosphated ZM adherends did not prove to be as durable in comparison (Figure 11). The reason for this lies in the fact that phosphate coverage on Zincrometal is incomplete. Partially crystalline phosphates are non-uniformly interspersed on randomly exposed zinc dust spheres at the surface. Consequently, the moisture resistance normally provided at the adhesive/topcoat interface was reduced due to the incomplete sealing between the topcoat/ adhesive surfaces. This became apparent as most of the failures examined after aging in these environments were concentrated at the adhesive/phosphate/paint interface. Results obtained on these samples were similar to those obtained for phosphated CRS joints, indicating that the locus of failure occurred at phosphate crystal sites. Note, however, that the durability of these joints was still considered to be very good in comparison to other metallic oxide/ adhesive interfaces. 

Iron phosphide anticorrosive pigments are recommended by manufacturers as replacement materials for zinc dust to reduce the price of zinc-rich paints [5.103]. For toxicological data, see Section 5.2.14. 

Zinc is frequently applied to the surface of iron or steel by other methods. In the Schoop process, molten zinc is sprayed onto the surface by a blast of air in a manner similar to that used in spraying paint. In addition to metals, objects made of wood, leather, paper, and the like may be coated with zinc by this process. In the process of sherardizing, iron is covered with a thin layer of zinc dust at temperatures of 700 to 800°C. Under these conditions, zinc penetrates the surface of the iron to a considerable extent. 

While the correct loading level of zinc dust in primers is still a matter of debate, these primers normally have a zinc dust content of more than 80% in the dry paint film [5.53, 5.105]. The requirements of test methods for zinc dust pigments suitable for use in protective coatings are specified in ISO 3549 - Zinc dust pigments for paints - Specifications and test methods [5.106]. 

ISO 3549, Zinc dust pigments for paints - Specifications and test methods. International Organization for Standardization, Geneve, Switzerland, 1995... 

Silicic acid esters, Si(OR)4, are produced by the reaction of SiCl4 with the appropriate alcohols. The most important representative of this group is tetraethoxysilane (tetraethyl orthosilicate) Si(OC2H5)4, which is used directly, or after hydrolysis to ethylpolysilicates, as a binder for ceramic pastes, for inorganic zinc dust paints (corrosion protection), for the surface treatment of glass and for the modification of silicates. Silicic acid esters are further used for rendering polymer surfaces scratch-resistant. 

The use of the optimum pigment concentration, which can vary consideration, is equally important. Thus zinc salts of nitro-isophthalic acid are used at a concentration of ca. 0.5% by weight in paints, whereas ca. 90% is necessary in the case of zinc-dust pigments, to guarantee the zinc-iron contact necessary for cathodic protection. 

Figure 8. Zinc dust paints based on an epoxy ester after a 168-h salt spray test in accordance with DIN 50 021 and ASTM B 117-64 left, control paint right, paint containing 2% Aerosil R 972 related to zinc dust mass.

Suprapal . [BASF AG] Styrene copolymers for roadmaiking paints, gravure and flexographic inks, paper coatings, zinc dust [ximers. 

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