Jon Singer on thu 19 oct 00
Emily Kiewel asks about this, mentioning that she...
>"...found at least 4 different melting
>points with differences ranging from 1042 C to 1640 C. Does anybody know
>the boiling point of manganese dioxide? It must be higher than the melting
>point, right?"
My copy of the CRC "Handbook of Chemistry and Physics" says that MnO2
(pyrolusite) decomposes by losing an oxygen at 535 celsius (995 Fahrenheit).
This means that it really doesn't _have_ any boiling point -- above
1,000 degrees
F, there is no such thing as MnO2. OTOH, most things have appreciable vapor
pressure even well below their melting points, and it is possible that MnO2 may
have appreciable vapor pressure well below its decomposition point; I
just don't
know.
[Emily, where were you looking when you found the four melting points??]
Also according to the Handbook:
Mn2O3, braunite, loses an oxygen at 1080 celsius, and Mn3O4, hausmannite,
melts at 1705 c. I think we won't get into Mn2O7 (a dark red oily substance
that explodes at 95 celsius...).
Unfortunately, the CRC Handbook doesn't list either a melting OR
boiling point for MnO (manganosite), which is probably what MnO2
becomes when it decomposes, so I'm still in the dark about this one.
Gavin or Monona (or anyone else), do you have a source for good info on this?
Sorry not to be more helpful --
jon
Ron Roy on thu 19 oct 00
It is worth noting that boiling points and melting points are not reliable
indicators to vaporization. Copper and Chrome both fume at our
temperatured - chrome in very refractory and yet it is fuming even at lower
temperatures.
RR
>have appreciable vapor pressure well below its decomposition point; I
>just don't
>know.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
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Emily & Kurt Kiewel on thu 19 oct 00
>[Emily, where were you looking when you found the four melting points??]
Let's see...Fournier's "Illustrated Dictionary of Practical Pottery",
Cooper & Royle's "Glazes for the Studio Potter", Peterson's "The Craft And
Art of Clay", and Lide's "Handbook of Chemistry and Physics" or the "CRC"
as you and my husband call it.
Basically I was getting the same complicated info that you and Tom B. are
giving me. Was hoping for something more definite. Sigh. Wish my mind
was better suited for chemistry!
The whole question started when some Chemistry Grad students were visiting
during a firing and suggested roasting marshmellows over my kiln. I
started talking about toxic gases and you know how scientists question
everything! They were sure the boiling point of manganese dioxide would be
way higher than the temps I was reaching (1260 C). This led to the search
that caused more questions!
Thanks both to you and to Tom B. for taking the time to reply.
Emily
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