Molybdate pigment

Figure 31. Flow diagram for the production of bismuth vanadate molybdate pigment a) Reaction vessel b) Filter c) Dryer d) Furnace treatment...

The most important chromate pigments include the lead chromate (chrome yellow) and lead molybdate pigments (molybdate orange and molybdate red) whose colors range from light lemon yellow to reds with a blue hue. Chrome yellow,... 

The colors of lead molybdate pigments vary from red with a yellow hue to red with a blue hue. Since chrome orange is no longer available (see Section 3.4.3), molybdate orange has become much more important. 

To give the lead molybdate pigments very good stability to fight, weathering, chemical attack, and temperature, the same methods are used as those for the stabilization of chrome yellow pigments (see Section 3.4.1) [3.134]-[3.142],... 

Phosphate-containing molybdate pigments are especially suitable for water-thin-nable or latex-based binders, because they improve adhesion to iron substrates. The other molybdate pigments are mainly used in solventborne binder systems. 

Unlike chromate ions in chromate pigments, the Mo04 ions in molybdate pigments are not chemically reduced in most coatings. Hence, they are ineffective for cathodic protection. Their protective action is assumed to be due to activity in the anodic region, similar to that of phosphate ions. As with the protective phosphate films, molybdate films are very resistant to chloride and sulfate [5.124], The duration... 

Property Zinc molybdate pigment Calcium zinc molybdate pigment Basic sodium zinc molybdate pigment Basic calcium zinc phosphomolybdate pigment... 

Inhibitive Primers. The traditional primers are red lead and linseed oil, alkyd resins and zinc potassium chromate, proprietary epoxy, alkyd, urethane and latex systems with modified phosphate, borate and molybdate pigments. Chromate-based pigments, although in use in aircraft coatings, automotive primers and coil coating primers, are subject to environmental concern on the toxicity of hexavalent chromium which is likely to result in their replacement by innocuous products. 

From a regulatory prespective, it is the trivalent character of its chromium content that distinguishes chrome titanium yellow from the hexavalent character of the chromium in lead chromate and lead molybdate pigments. 

Molybdate pigments are calcium or zinc salts precipitated onto an inert core such as calcium carbonate [47,96-98], They prevent corrosion by inhibiting the anodic corrosion reaction [47]. The protective layer of ferric molybdate, which these pigments form on the surface of the steel, is insoluble in neutral and basic solutions. 

Use of these pigments has been limited because of their expense. Zinc phosphate versions of the molybdate pigments have been introduced in order to lower costs and improve both adhesion to steel and film flexibility [23,47,96-98]. The molybdate pigment family includes ... 

Although molybdate pigments are considered nontoxic [103], they are not completely harmless. When cutting or welding molybdate-pigmented coatings, fumes of very low toxicity are produced. With proper ventilation, these fumes are not likely to prove hazardous [101]. The possible toxicity is about 10% to 20% that of chromium compounds [103,104]. 

Incorporation of the cerium molybdate pigment could favor dissociation of the cerium cation and the molybdate anion in concentrations high enough to inhibit the local cells of corrosion that appear. Although they mentioned this possibility, the authors did not provide results or indicate that the work was continuing. 

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