CORROSION PREVENTION By Kent Hugus, EAA 15280 P. O. Box 1394, Brunswick, Ga.

(Reprinted from T-18 Newsletter No. 16)

M a metal caused by the interaction of its surfaces with other substances in its environment.

ETAL CORROSION D E F I N E D : The disintegration of

Metals vary in susceptibility to corrosion. The least active metals are termed "cathodic." An example is gold which has a solution potential of 0.0 in the electrochemical series. Very active metals are termed "anodic", such as magnesium which leads the solution potential parade with —1.66 volts. (2024 aluminum and steel stand —.68 and —.67, respectively). Why solution potential ratings? Because corrosion is generally believed to be an electrochemical activity. When metals are immersed in an electrolyte such as dirty water, the difference in potential creates an electron flow from anodic to cathodic material. The metal particles on the anodic metal are transformed into ions which combine with non-metallic ions in the electrolyte and form corrosion products. These products are usually brittle, scaly and weak. A corrosion spot on a single metal may result from a casual electrolyte. The drop of electrolyte may vary in strength throughout its mass, creating a differential in potential from one area to another. Likewise, the metal itself may vary in its composition with more alloying elements in one area than another and you again have a potential differential. What can be done about it? 1. Keep it clean.

Dust is condensation nuclei for

moisture and moisture is an electrolyte. Keep your metals covered. A plastic drop cloth is fine provided it is propped up to allow some air circulation. Fingerprints may last

LETTERS . . . (Continued from page 3) Dear Paul: I want to thank you for the article on the homebuilt accidents. You will recall that I wrote you recently on this subject. Let's have more of this, os for those of us who

forever if allowed to "set up." Work should be wiped with solvent after handling to remove prints. I use alcohol. Steel wool and crocus cloth both leave corrosive residue so don't use them on aluminum. Substitute good quality wet or dry No. 400 paper and aluminum wool. Mild

corrosion may be removed with any of the good aluminum polishes available or with non-chlorinated "Bon-Ami." 2. Follow the drawings. The use of zinc-chromate

for faying (contacting) surfaces and closed assemblies such as rod ends serves as an insulation. It also supplies a constant supply of chromate ions, the "good guys" in the corrosion battle. The anodizing called out for certain parts provides an oxide film which inhibits corrosion. 3. Protect your workmanship.

B.

Wash primer

C. Zinc-chromate D. Lacquer or enamel. If you are located in a corrosive atmosphere, it may be well to invest in an Alodine 1200 kit for treatment of heavier bare parts. This is a two-part treatment which uses an acid cleaner followed with a protective film. To use the kit, a plastic bucket, nylon bristle brush, rubber gloves and plenty of water are required. This is a brief statement of a very wide field. An excellent manual is available on the subject. Ask for Issue 49 of the Lockheed Service Digest from Lockheed Aircraft Corp. in Burbank, Calif. 91503. ®

try things on our own someone else's mistakes can be terrifically beneficial. It is with o great deal of foreboding that I

read the comment

Protective finish for

aluminum should comprise the following, in order, from inner to outer layer: A. Chemical film such as Alodine

in your

latest

issue of

SPORT AVIATION that the FAA has asked you to help rewrite the regulations on homebuilts. The Federal government never made a regulation that didn't stifle the public more.

The reason that homebuilts have gained such popularity is because of the freedom they enjoy now. In spite of your good intentions you are going to suggest regulations that will hurt us.

Del Yettow 527 N. State St. St. Joseph, Mich. 49085 Dear Paul and Gang: Just read the April issue of SPORT AVIA-

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TION and in particular the "Education Through Error." It is appalling that so many fine people have perished in aircraft due to aerobatics. The aircraft of Mr. Pitts and Mr. D'Apuzzo and others are not to blame as the

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SPORT AVIATION

this. The point

I am trying to make is that

and spins is a much safer pilot, but training should be with an instructor. C. L. "Bud" McHolland

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