A more corrosion resistant grain Figure 3: Different crystal planes (grains), grain boundaries and inclusions. Want a specific topic discussed in Corrosion Corner? Please send any suggestions/questions/comments to rustdr@pairodocspro.com or visit www.pairodocspro.com. Back articles of Corrosion Corner are available from Spray. Thanks for your interest and I’ll see you in September. SPRAY August 2015 Spray 75 • The chemical composition of the boundary between two different types of grains is typically different from the chemical composition of the grains • The boundary between different grains is not always metallic; the boundary could be a mixture of metallic and non-metallic compounds, or non-metallic compounds • Inclusions are also found in Figure 3: the white particles inside grains • Iron carbide compounds are also present in the grains— agglomerates of darker areas and spots The material defects shown in Figure 3 can contribute to or cause spray package corrosion. Aluminum and steel both have one or more of the types of material defects shown in Figure 3. The chemical composition of your formula determines whether or not the material defects in Figure 3 contribute to or cause spray package metal corrosion. The current state of corrosion science on how and why corrosion initiates is not advanced enough to model and predict when corrosion will occur. Hence, corrosion testing is essential for reducing the risk that a given type of formula will contribute to or cause corrosion of the type of spray package chosen for your formula. We would be happy to teach our Elements of Spray Package (Aerosol Container) Corrosion short course at your R&D facility. Grain boundary Iron carbide Inclusion A less corrosion resistant grain
Spray August 2015
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