CoatingsPro Magazine

MAY 2016

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COATINGSPRO MAY 2016 21 the solvent moves in the direction in order to achieve equilibrium between the solutions on each side of the membranes. A l l organic f i lms act as semiper- meable membranes to some deg ree. In the case of blister ing on coatings, the ef fect occurs when molecu les of water f ind a contaminant on the sur face of the substrate. If the contaminant is something soluble, it tr ig gers osmosis. A solution for ms, concentrated at f irst but increasingly d i luting as more and more water molecu les are drag ged in. Eventua l ly a blister f u l l of the solution for ms, as ad hesion bonds brea k dow n. Te contaminant doesn't neces- sarily have to be ionic — only soluble — but if it is ionic, the solution formed by osmosis may initiate corrosion too. Ten gases may be evolved at the cathodes or anodes that occur naturally in the surface of the alloys, rapidly infating the blister. If the water molecules fnd nothing there, they just migrate back into the atmosphere, with little net efect except perhaps for occasionally knocking out the odd adhesion bond over time. T he pressure cooker test is usef u l to demonstrate osmot ic bl ister ing. T he test is used in some specif ica- t ions for arc hitect ura l coat ings. It is rea l ly an assessment of an appl i- cator's product ion process, in ter ms of t he pretreat ment and par t icu l arly t he f ina l r inse, by high l ight ing t he deg ree of sur face contaminat ion lef t under a f i lm. So, to answer your question: one can lead to the other. A: " T he contaminant does not have to be ionic — only soluble." W hile I'm not disputing this, I am wondering whether there are any cases of osmotic blistering that can be linked to non-ionizing compounds such as sugar. A: Osmosis works in the same way for any solvent/solute across a permeable membrane (i.e., fowing from diluted to concentrated). Solubility is more dependent on the fact that the solvent and solute need to have similar polarity for a solution to form. In a polar solvent like water, a solute could have dipoles but it would not necessar- ily follow that ions would be formed. A: If it can be demonstrated that blisters form without any corro- sion of an underlying metal substrate (and I suppose there are case studies of this) then it is not necessary for the contaminant to be ionic. Notes From the Blog when the going gets tough... we get tougher. Foot traffc, vehicle traffc, heat, cold, the relentless effects of weather... With these kinds of forces stacked against you, it's essential to have a coating that can rise to the challenge - one that you can have confdence in to remain strong and effective no matter how hard you use or abuse it. Wearcoat ® foor coatings defne durability. Easy to apply, easy to clean, non-slip and incredibly tough, Wearcoat ® will give you the edge you need to get the job done - safely and effciently. Call us today or check us out on the web. Our expert staff is ready to help with any coating needs you have... COATINGS FOR INDUSTRY, INC. Call us today – 215-723-0919 Fax 215-723-0911 www.coatingsforindustry.com COAT SG SERIES ANTI-SLIP COATINGS Serving the concrete fooring, structural steel, transportation and aerospace industries for over 35 years. Wr i te in Re ad e r In q u ir y #1

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