Flash rusting

The entire flash rusting discussion may be unnecessary. Igetoft [26] has pointed out that flash rusting requires not only water but also salt to be present. The fact that steel is wet does not necessarily mean that it will rust. 

Gauthier, C. et al., ACS Symposium Series 648, Film Formation in Water-Borne Coatings, Provder, T., Winnik, M.A., and Urban, M.W., Eds., American Chemical 

Nicholson, J., Waterborne Coatings Oil and Colour Chemists Association Monograph No. 2, Oil and Colour Chemists Association, London, 1985. 

Franks, R, Water, Royal Society of Chemistry, London, 1983. 

Forsgren, A. and Palmgren, S., Effect of Application Climate on Physical Properties of Three Waterborne Paints, Report 1997 3E, Swedish Corrosion Institute, Stockholm, 1997. 

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Substrates, Paints and Coatings. Both flash rusting and underfilm darkening studies exployed a white, pH 4.5, primer formulation (see Appendix), designated as Standard, based upon Haloflex 202, a chlorine-containing vinyl acrylic latex. A zinc phosphate free formulation, designated as Non-Standard, of pH6 was prepared by substitution of zinc phosphate for barytes. The comparison paints were a commercial butyl acrylate-methyl methacrylate water borne primer, formulated at pH 9, and a solvent based chlorinated rubber primer. 

Flash Rusting (Bulk Paint and "Wet" Film Studies). The moderate conductivity (50-100 ohm-cm) of the water borne paint formulations allowed both dc potentiodynamic and ac impedance studies of mild steel in the bulk paints to be measured. (Table I). AC impedance measurements at the potentiostatically controlled corrosion potentials indicated depressed semi-circles with a Warburg diffusion low frequency tail in the Nyquist plots (Figure 2). These measurements at 10, 30 and 60 minute exposure times, showed the presence of a reaction involving both charge transfer and mass transfer controlling processes. The charge transfer impedance 0 was readily obtained from extrapolation of the semi-circle to the real axis at low frequencies. The transfer impedance increased with exposure time in all cases. 

Table I shows that the corrosion rate in the Standard pH i(.5 paint was larger than that in the Non-Standard (zinc phosphate free) paint at pH 6, with all rates decreasing with time. The rates decreased with further increase of paint pH to 8. The increased tendency of flash rusting with increase of pH from 6 to 8 was, therefore, associated with lower substrate corrosion currents. Comparison between Non-Standard and Standard paint adjusted to pH 6 with NHj showed little difference in corrosion rates implying that pH was more influential than the presence of zinc phosphate at this pH. Adjustment of the Non-Standard paint with HjSO to an equivalent pH 4.5 of the Standard paint showed good agreement between corrosion rates. This result also indicated pH to be more influential than the presence or absence of zinc phosphate with regard to corrosion currents. The absence of flash rusting at pH 4.5 is therefore associated with higher corrosion currents.

It is therefore believed that at pH 6 and greater the corrosion process is localised and large local concentrations of ferrous iron are achieved. At pH 6 the oxidation to ferric iron is very rapid ( ) and precipitation of Fe(0H)j occurs to exhibit localised corrosion or "flash-rust" spots. At pH 5 and below a small but finite uniform dissolution of the iron substrate occurs. However, in this pH range the oxidation of the ferrous dissolution product to ferric ion is considerably slower, by almost 1000 times, and hence "flash rusting" is not observed. 

Flash rusting exhibited in neutral to alkaline water borne formulations appears to occur through a localised corrosion process probably Involving grit "activity" present from blasting, either directly or indirectly, in an electrochemical process. At such pH the rapid oxidation of ferrous to ferric ion produces... 

The spaces above the water level in the boiler and in the deaerator may experience flash rusting, but this should not be too serious over very short periods of time. If the boiler is to remain idle for more than a day or two, it should be... 

Formulation A is the base formulation. TEA is an optional additive that gives some reserve alkalinity and improved flash rust i nhi biti on. 

Corrosion inhibitors are used to prevent the formation of corrosion products when waterborne paints are applied to metallic substrates (flash rust). They include oxidiz-... 

Uses Corrosion inhibitor for in-can and flash rust control for water-based coatings... 

Uses Corrosion inhibitor for copper, high copper alloys, aluminum, steel, cobalt, and silver for use In aq. systems, metalworking fluids, metal cleaners, metallic pigments, flash rust Inhibitors, direct treatment, and cooling towers... 

Chem. Descrip. Ammonium benzoate CAS 1863-63-4 EINECS/ELINCS 217-468-9 Uses Rust inhibitor for aq. industrial coatings, latex emulsion primers, waterborne lacquers, water-reducible alkyds and epoxies Features Flash rust inhibitor cost-effective Properties Off-wh. cryst. sp.gr. 1.76 dens. 10.48 Ih/gal bulking value 0.095 gal/lb m.p.198C Use Level 0.1-0.5%... 

Uses Corrosion/rust inhibitor in water-based protective coatings inhibits flash rust and In-can rusting stabilizes metal substrates for water blasting... 

Chem. Descrip. Diethanolamine-free alkanolamine alkanoate Uses Corrosion inhibitor for aq. systems, metalworking and lubricant industries resist, against flash rusting in cleaning and metalworking applies, and in latex paint coatings... 

Chem. Descrip. Barium sulfonate in mineral spirits Uses Rust/corrosion inhibitor for prevention of flash rusting and staining in latex coatings increases corrosion resist, of alkyd and alkyd/melamine coatings... 

Uses Rust/corrosion inhibitor for prevention of flash rusting in latex coatings rust and corrosion inhibitor for solv.-based coatings Properties Dens. 7.7 Ib/gal flash pt. (Seta) 108 F 2.1% metal UseLevei 0.25-3.0%... 

Chem. Descrip. Blend of contact and vol. water sol. conosion inhibitors Uses Corrosion inhibitor that prevents flash rusting in direct to metal applies, in PVA, acrylic, and water-based systems Properties Sp.gr. 1.08 dens. 9.0 0.1 Ib/gal vise. 5-10 mPa-s pH 9.5 ... 

Features Flash rust/in-can corrosion inhibitor provides belter dried film corrosion resist. 

Uses Rust/corrosion inhibitor for water-based paints/coatings, water-based industrial primers, water-reducible alkyds Features Flash rust/in-can corrosion inhibitor nitrite-free provides belter dried film corrosion protection than water-sol. salts Properties Yel. clear liq. disp. in water sol. in glycol ether, insol. in min. spirits sp.gr. 1.06 dens. 1040 kg/m bulk dens. 8.83 Ib/gal vise. 200 mPa s max. flash pt. > 52 C pH 8.0-10.0 anionic Use Level 0.1 -0.6% (on total formulation wt.)... 

Uses Corrosion inhibitor for waterborne coatings on ferrous surfe., e.g., metal primers, flat or gloss disp. paints, polyacrylics, polyvinyl acetates, PS acrylics and terpolymers, waterborne alkyds, aq. stoving enamels temporary rust inhibitor for metal surfs. in-can corrosion inhibitor, esp. under acid conditions Features Fights flash rusting... 

Chem. Descrip. Barium alkylarylsulfonate in propyiene giycoi n-butyi ether Uses Corrosion inhibitor for ferrous metais used in gioss waterborne iatex coatings prevents flash rusting of waterborne iatex coatings Features No ozone-depieting substances Properties Dk. brn. iiq. soi. or misc. in min. spirits, n-butanoi, xyiene, MiBK, toiuene insoi. in water, acetone, ethyiene giycoi sp.gr. 1.00 dens. 8.20 ib/gai vise. 150 cps VOC 492 g/i 50% act. by wt. 44% act. by voi. Use Levei 1 -5%... 

Emulsion systems for anticorrosive coatings are usually copolymers of vinylidene chloride, vinyl chloride, and an alkyl acrylate or methacrylate. Relatively small amormts of surfactant and colloid are used in order to minimize water sensitivity in the dried coating. Flash rusting inhibitors such as ammonium chromate/dichromate or alkali metal nitrate/nitrites may also be added. 

On ferrous substrates, flash rusting may be a problem and penetration into porous substrates is poorer than with solvent-borne coatings, which can lead to premature failiu e especially on a chalky surface. 

Limitations Limited penetrating power (water emulsion) because of water surface tension may flash rust as a primer over bare steel not suitable for immersion service or strong chemical environments. Soluble in ketones, esters, aliphatic chlorinated hydrocarbons, and aromatic hydrocarbons. 

Silicones, water based aqueous R R N N May flash rust as a primer on... 

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