This specimen was ruined when the protective hydrogen atmosphere was accidentally shut off.
The 500X photomicrograph at left shows grain boundary oxidation near the surface.
The etchant for both was Murakami's.
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Molybdenum is used for extremely high temperature furnace
heating elements because of its creep resistance, but it is completely
unable to resist oxidation in air. Molybdenum oxide is volatile
at high temperatures and simply evaporates as fast as it forms. This specimen was ruined when the protective hydrogen atmosphere was accidentally shut off. The 500X photomicrograph at left shows grain boundary oxidation near the surface. |
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The second photomicrograph, this time at 1000X, illustrates
the unaffected interior of the heating element. The etchant for both was Murakami's. |
| Specimen 7 is a complex brazed joint between Kovar and OFHC
copper. |