Metals corrosion-inhibiting pigments

Zinc yellow became an important corrosion-inhibiting pigment for aircraft during World War II. However, the war production rate of 11,000 t/yr has not since been reached. Now, 2inc yellow is widely used for corrosion inhibition on auto bodies, light metals, and steel, and in combination with red lead and ferric oxide for stmctural steel painting. 

Lead chromate pigments are mainly used as corrosion inhibitive pigments. These pigments are of low opacity and can be combined with higher opacity pigments for use in primers. Zinc chromate, also an anti-corrosion pigment, is used in metal pretreatments such as wash primer, which also promotes adhesion to aluminum and steel. 

Toxicology Toxic material TLV (as Pb) 0.15 mg/m of air Uses Corrosive inhibitive pigment for metal protective coatings, primers, and finishes industrial enamels requiring a high gloss heat stabilizer for PVC... 

It is applied using a fluidised bed process, generally in two coats. A precompounded blend of p.v.d.f., corrosion-inhibitive pigments and adhesive components is applied first, followed by a top coat of pure p.v.d.f. The primer coat protects the metal and the top coat protects the primer coat from attack by the chemicals. 

Structural adhesives are not usually applied directly to the prepared metal. Rather, a primer is applied first. The primers are usually of the same generic chemical composition as the adhesive being used over them (i.e., epoxy primer to epoxy adhesive). The primers may or may not contain a corrosion inhibiting pigment and may or may not have to be cured before application of the adhesive. EC-1593 is a 350 F (121 C) curing nitrile-phenolic primer while EC-3917 is a chromated epoxy-phenolic primer curing... 

Polymeric varieties of aluminium phosphates have found important applications in cements and in the bonding of refractories. The basis of phosphate bonding is the formation of polymers on dehydration, which may be poly or metaphosphates, or ultimately AIPO4 (5.135) (Chapter 12.10). The many applications of aluminium orthophosphates include dental cements, metal coatings, binders and adhesives and corrosion-inhibiting pigments (Chapter 12.8). 

Some pigments exert an inhibitive effect on the corrosion of metal. The mechanisms are complex and not always fully understood. Inhibitive pigments include red lead, zinc phosphate and zinc chromate. 

Inhibitive Pigment a pigment which retards or prevents the corrosion of metals by chemical and/or electrochemical means, as opposed to a purely barrier action. Red lead and zinc chromate are examples of inhibitive pigments as opposed to red iron oxide which has little or no inhibitive action. 

The most popular inorganic treatments are those with silica [4], phosphates [5], molybdate [6], and chromate [7], all of which serve mainly to reduce the chemical reactivity of the metallic pigments (Fig. 14.13). This includes corrosion inhibition of the pigment and inhibition of its often catalytic effect as well as a change in the physical surface characteristics, for example, where chargeability is important. 

Active pigments are anticorrosives with a chemical and/or electrochemical action. They are also described in the literature as inhibitive pigments. These pigments interact chemically, either directly or via intermediates with the metal substrate to reduce the rate of corrosion. Such intermediates can, for example, be formed by reaction with the resin system. 

As a rule, corrosion protection pigments possess several of the cited inhibition properties,. so that corrosion protection with a particular pigment is by a combination of different mechanisms. Optimum efficiency requires combination with a suitable binder. For example the utilization of a corrosion protection pigment which forms metal soaps only makes sense, if the binder is able to form soaps. 

Inhibisil [PPG]. TM for a non-toxic corrosion inhibiting silica pigment for metal finishes. 

Corrosion control by pigments relies on well-known principles of corrosion inhibition. Iron and steel exposed to air are quickly covered by an oxide film aqueous electrolytes tend to break down this film, and further oxidation of the metal surface ensues. The role of anodic corrosion inhibitors is to supplement or to aid in the repair of the surface oxide film. Basic pigments may form soaps, for example, with linseed oil autoxidation of these soaps may yield soluble inhibitors in the film. Some other pigments of limited solubility act directly as inhibitors. Active metal pigments supply electrons to the iron substrate and thus lower its potential and prevent metal dissolution. 

Chem. Descrip. Polymeric surfactant in methoxy propyl acetate Uses Pigment dispersant, film-former for solv.-based industrial paints, esp. baking enamels and high solids coatings, and automotive, maintenance, construction, machine, and furniture coatings has various binder props, such as adhesion on metal surfaces, corrosion inhibition, and film coherence Features Highly effective... 

Precaution Powerful oxidizer mixt. with boron burns violently if ignited Uses Rust-inhibitive pigment for paints corrosion inhibitor mfg. of chromium oxidizing agent depolarizer for batteries coating for light metal... 

Uses Corrosion inhibiting pigmentfor metal protective coatings and primers, high gloss industrial enamels pigment for traffic marking paints Manuf/Distrib. Am. Disps. D.N. Lukens Nichem... 

Uses Safety matches corrosion inhibitor in metal-joining compds. rust-inhibitive pigment for paints, ceramics, fuses, pyrotechnics, metal primers, ignition control devices, pipe jointing compds. 

Inhibitive Pigment a pigment which retards or prevents the corrosion of metals by chemical and/or electrochemical means, as opposed to a purely barrier action. Red lead and zinc chromate are examples of inhibitive pigments as opposed to red iron oxide which has little or no inhibitive action. Medium in paints or enamels. The continuous phase in which the pigment is dispersed thus in the liquid paint in the can it is synonymous with vehicle and in the dry film it is synonymous with binder (q.v.). Opacity (Hiding Power) ... 

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