molybdenum and fuming nitric acid

Hi,
We are working with moly furnace components at the moment. We were under the assumption that moly was unaffected by strong acids, yet, when we immersed our pure moly sample in fuming nitric acid, it rapidly developed a loose dark red deposit. Given that we are immersing the components in 1600 deg C Calcium fluoride, we want to avoid nasty suprises, like the moly is impure in some way.
I would be very grateful for any comments on just what we have seen. Is it a moly oxide of some kind ? Moly Trioxide of course is clear/white.
Thanks for any help.
Steve Taylor

Steve Taylor wrote:
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no idea... maybe the people from sci.chem could help you here.

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Steve:
Bruce Craig's "Handbook of Corrosion Data" (ASM International 1989) says on page 378 that: "molybdenum is rapidly attacked by oxidizing agents such as nitric acid".
L. L. Shreir's "Corrosion" (2nd ed., Butterworths,1976), says that (P 5.15): "Molybdenum exhibits good reisistance to hydrochloric, hydrofluoric, phosphoric, and sulfuric acids....It is rapidly attacked by oxidizing acids such as nitric acid, and by reducing acids containing oxidizers such as HNO3, FeCl3, etc."
Similar information can be turned up via a Google search too of course.
Why are you using nitric acid?
Pittsburgh Pete
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Pittsburgh Pete wrote:
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Pete,
Thanks for that - The acid was being used to see if my material was pure - I am not a chemist, I am the engineer who designed the apparatus. It was my supposedly expert customer who suggested nitric as a kind of assay, since he didn't believe the metal was pure.
Steve