Non-Metallic Coatings for Corrosion Protection

CORROSION of metals, for the purpose of this talk, may be divided into two general classes, namely, atmospheric and chemical. Atmospheric corrosion is caused by the natural agents -water, air, salt, and temperature -as well as by the agents arising from industrial operations which pollute the atmosphere. Chemical corrosion affects metals in refineries and chemical plants where severe conditions exist due to .acids, alkalies, salts, solvents, gases, ?steam, etc. A special condition is encountered on road equipment and motor vehicles due to the large amounts of corrosive salts which are used on our roads in the winter. Exposure to corrosive conditions such as those referred to above causes metal to be destroyed and, therefore, it has to be protected. The non-metallic or organic coatings used to protect the metal are themselves destroyed ultimately by these same conditions. Since all types of organic coatings do not have the same kind and degree of resistance to degradation, a particular kind of -coating must be used for a particular set of conditions in order to obtain the maximum benefit. In ?addition to the above mentioned agents, organic coatings are degraded ?by sun-light, which is probably the severest single factor in the breakdown of organic coatings exposed outdoors. We can divide organic coatings, in a general way, into the following classes: (1) Conventional coatings, and (2) Special coatings.