F.
The zinc at this temperature attacks the iron and forms a series of
alloys ranging from pure zinc on the top to pure iron at the bottom of
the coating. Even if this cracks in part the iron is more or less
protected from corrosion so long as any zinc remains. Aluminum is used
similarly in the calorizing process for coating iron, copper or brass.
First a surface alloy is formed by heating the metal with aluminum
powder. Then the temperature is raised to a high degree so as to cause
the aluminum on the surface to diffuse into the metal and afterwards it
is again baked in contact with aluminum dust which puts upon it a
protective plating of the pure aluminum which does not oxidize.
[Illustration: PHOTOMICROGRAPHS SHOWING THE STRUCTURE OF STEEL MADE BY
PROFESSOR E.G. MARTIN OF PURDUE UNIVERSITY
1. Cold-worked steel showing ferrite and sorbite (enlarged 500 times)
2. Steel showing pearlite crystals (enlarged 500 times)
3. Structure characteristic of air-cooled steel (enlarged 50 times)
4. The triangular structure characteristic of cast steel showing ferrite
and pearlite (enlarged 50 times)]
[Illustration: Courtesy of E.
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