Paints Metallic zinc

A cmcial development for zinc phosphate coatings came in 1943 when it was found that more uniform and finer crystals would develop if the surface was first treated with a titanium-containing solution of disodium phosphate (6). This method of crystal modification is a prime reason for the excellent paint (qv) adhesion seen on painted metal articles. 

Painting with aluminium-pigmented paint is considered in Chapter 14 because its properties are essentially those of a paint and not of a metallic coating in this respect aluminium paint differs from zinc-rich paint which can be formulated to provide galvanic properties similar to those of metallic zinc. 

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. 

Protecting a surface from corrosion by coating can be accomplished by a number of well-established processes which include paints, metal plating (with zinc or cadmium), diffusion, thermal spraying, and, more recently, vapor deposition processes. Of these physical vapor deposition (PVD) is used extensively in corrosion protection. Typical applications are ... 

Steel objects, when exposed to humid atmospheres or when immersed in electrolytes, corrode at a rapid rate. For example, abrasively polished, cold-rolled steel panels will show signs of rust within 15 minutes when immersed in dilute chloride solutions with pH in the range of 7-10. One of the methods used to control this rapid corrosion is to coat the metal with a polymeric formulation such as a paint. The role of the paint is to serve primarily as a barrier to environmental constituents such as water, oxygen, sulfur dioxide, and ions and secondarily as a reservoir for corrosion inhibitors. Some formulations contain very high concentrations of metallic zinc or metallic aluminum such that the coating provides galvanic protection as well as barrier protection, but such formulations are not discussed in this paper. 

The interfacial chemistry of corrosion-induced failure on galvanized steel has been investigated (2) adhesion of a polyurethane coating was not found to involve chemical transformations detectable by XPS, but exposure to Kesternich aging caused zinc diffusion into the coating. Similar results were obtained with an alkyd coating. Adhesion loss was proposed to be due to formation of a weak boundary layer of zinc soaps or water-soluble zinc corrosion products at the paint metal Interface. 

In order to obtain maximum corrosion protection for painted metal articles, the metal parts are pretreated with an inorganic conversion coating prior to the painting operation. These zinc or iron phosphate coatings greatly increase both paint adhesion and corrosion protection. Traditionally, a chromic acid post-treatment has been applied to these phosphatized metal surfaces to further enhance corrosion protection. 

A number of methods are used to reduce and prevent corrosion. The most common method is to paint iron materials so that the metals are protected from water and oxygen. Alloying iron with other metals is also a common means to reduce corrosion. Stainless steel is an alloy of iron, chromium, nickel, and several other metals. Iron may also be protected by coating it with another metal. Galvanizing refers to applying a coating of zinc to protect the underlying metal. Additionally, because it is a more active metal, zinc oxidizes rather than iron. 

Uses Zinc (Zn) is one of the most common elements in the Earth s crust. Metal zinc was first produced in India and China during the Middle Ages. Industrially important compounds of zinc are zinc chloride (ZnCl2), zinc oxide (ZnO), zinc stearate (Zn (Ci6H3502)2), and zinc sulfide (sphalerite, ZnS). It is found in air, soil, and water, and is present in all foods. Pure zinc is a bluish-white shiny metal. Zinc has many commercial uses, as coatings to prevent rust, in dry cell batteries, and mixed with other metals to make alloys like brass and bronze. Zinc combines with other elements to form zinc compounds. Zinc compounds are widely used in industry to make paint, rubber, dye, wood preservatives, and ointments.109-112... 

Zinc oxide is a very old technological material. Already in the Bronze Age it was produced as a byproduct of copper ore smelting and used for healing of wounds. Early in history it was also used for the production of brass (Cu-Zn alloy). This was the major application of ZnO for many centuries before metallic zinc replaced the oxide [149]. With the start of the industrial age in the middle of the nineteenth century, ZnO was used in white paints (chinese white), in rubber for the activation of the vulcanization process and in porcelain enamels. In the following a number of existing and emerging electronic applications of ZnO are briefly described. 

From a practical point of view, the attainment of the specified dry film thickness is important. In many cases, a minimum thickness must be achieved or protection will fail in a short period. This aspect demands skill in application and close inspection and control. For metallic zinc paints, the thickness would normally be of the order of 60-100/im, for anticorrosive pigmented paints, together with top coats, 100-200 //m, and for inert barrier types 150-300/im. For special environments or projects, these thicknesses may be varied but it should not be presumed that protection will always be improved or be more effective over a longer period of time by increasing the film thickness. 

Data on zinc and zinc products are available from the American Zinc Institute, Inc., of New York. Market development and promotion pamphlets relating to galvanized sheets, metallic zinc paint, and rolled zinc are available at no cost. Information on slab zinc production and shipments is collected monthly. Data on labor are also assembled, monthly, for the membership only. 

Polysilicate. [DuPont] Polysilicate binder for refractory, ceramic, metal, inorg. fiber, catalyst support, inorg. paint systems, zinc coatings findustrial applic. glass surface modifier. 

The built-in costs of corrosion of automobiles were identified as corrosion protection for steel body panels such as metallic zinc coatings, paint, adhesives and sealants, nonferrous metals, corrosion-resistant materials, rust-proofing heat exchanger components, mufflers, and tail pipe corrosion. The greatest impact on the cost of corrosion for automobiles was the adverse effect of corrosion on the cost of replacement of the automobile. Both the lO model and focused sector study showed that in both models the cost of replacement of the automobiles dominated the total cost and avoidable cost estimation. 

Other anode systems specially developed are sprayable conductive polymer coatings, metallized zinc coatings, and conductive paints. Typical primary anode for the conductive polymer or paints is platinized niobium wire attached to the concrete prior to application. Estimated cost is 76/m with a service life of five years. 

On the basis of the electrochemical nature of corrosion, it is clear that metallic zinc must be in direct contact with the electrolyte to protect bare steel regions. Paint or other coatings on top of the zinc coating will therefore eliminate or at best reduce the cathodic protection effect. 

Chem. Desaip. Zinc dust CAS 7440-66-6 EINECS/ELINCS 231-175-3 Uses Corrosion inhibitor, pigment in thin-film metal protective coatings, corrosion-resist, metal coatings, aerosol paints in lubricants, chemicals Features For use with either org. or inorg. binders Reguiatory ASTM Spec. D-520 Type I compliance Properties Superfine powd. 100 /. thru 325 mesh 4.5 p median particle size sp.gr. 7.0 dens. 58.4 Ib/solid gal 99.3% total zinc, 96.5% metallic zinc, 3.1 zinc oxide ZCA Zinc Dust 64L [Zinc Corp. of Am.]... 

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