GRIPPER SERIES HOT WATER LEAK TEST TANK INLINE SERIES WITH OPTIONAL PLC CONTROLLED CHANGEOVERS November 2015 Spray 25 different crystal plane orientations and the wavy lines represent grain boundaries between the two different crystal planes. Some crystal planes are more susceptible to corrosion than others and in certain instances grain boundaries contribute to or cause localized corrosion. There are two oval lines in Figure 2 around a water molecule and an electron—one above the top group and another under the first row of atoms below the grain boundary. The encircled water molecule-electron pairs illustrate water molecules removing electrons from surface atoms. An iron atom becomes an ion when two electrons are removed and an aluminum atom becomes an ion when three electrons are removed. The metal atoms under the metal ions become new surface atoms when the ions leave the bulk metal. Hence, corrosion continually creates new unstable surface atoms and thus penetrates through the package metal. Other molecules, such as oxygen, are also electrochemically active and able to cause metal or coated metal corrosion. Surfactants often enhance corrosion by making the metal surface more available to water molecules and other electrochemically-active formula ingredients. Surfactants could also promote the diffusion of water and other formula ingredients through coatings. Internal coatings are not perfect barriers between the package metal and your formula. However, a defect in the coating or a hole in a coating is not necessary for metal corrosion to occur under the coating, because water molecules and formula ingredients diffuse through coatings to the underlying metal surface. Whether or not corrosion occurs in this situation is determined by the chemical composition of the liquid diffusing through the coating. Interestingly, some molecules are weakly electrochemically active and prevent corrosion by attaching themselves to metal surfaces—referred to as adsorption. The molecules share the metal’s valence electrons instead of removing them with this type of situation. Thus, adsorption could control or prevent corrosion by blocking electron removal by other electrochemically active ingredients in your formula. Corrosion inhibition by absorption is only one of several corrosion inhibitor mechanisms. We would be happy to teach our Elements of Spray Package (Aerosol Container) Corrosion short course at your R&D facility. Want a specific topic discussed in of Corrosion Corner? Please send your suggestion/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 December. Spray AUTOMATED PLC CONTROLLED PRODUCT FILLING MEASURING CHAMBERS AUTOMATED PLC CONTROLLED PROPELLANT CHARGER MEASURING CHAMBERS Terco, Inc. 459 Camden Drive, Bloomingdale, IL 60108 U.S.A. | Tel: +1 630-894-8828 | www.terco.com sales@terco.com
Spray November 2015
To see the actual publication please follow the link above