Primers, general corrosion inhibiting

Fig. 8 shows a primer formulated with a corrosion-inhibiting pigment such as a chromate. As discussed previously, some permeability to moisture is necessary for these pigments to dissolve and be transported to the interface where passivation of the substrate can occur. Optimum performance is generally found at PVC/CPVC Just below 1 [71]. 

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. 

The presence of NTMP resulted in a four-fold increase in bond durability of adherends etched in FPL over that of untreated adherends. Durability can also be improved by the incorporation in a primer of a corrosion-inhibitor such as strontium chromate. Corrosion inhibiting primers are generally used with bonded components in U.S. Air Force aircraft (24). 

The laminates consist of alternate layers aluminium (0.2-0.5 mm thick], which has been anodised and then primed with Cytec-Fiberite s BR-127 corrosion-inhibiting primer, bonded together with fibre-rich, epoxy-based adhesive-prepregs (about 0.125 mm thick]. The reinforcing fibre is usually unidirectional in nature, although woven fabric is occasionally used. Generally two or three sheets of adhesive separate each sheet of aluminium this can be in the 0° direction or laid up in a cross-plied orientation. 

A well known metal adhesion application is in washed primers. Application information is available. Additional information is provided in the general references and Refs. 37 and 38. The Navy has long recognized the need to pretreat a metal surface prior to painting to inhibit corrosion and promote adhesion and specifies wash primers in MIL-F-15328C and MIL-C-8514B. 

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