Just arrived home to read Rich, Karl-Arne, then Rich again...
> On Jan 17, 2006, at 3:25 AM, Karl-Arne Markström wrote:
>
>> If I understand the physics correctly, the zirconium getter simply
>> dissolves and binds the
>> gas molecules in its own molecule structure.
>>
>> An interesting treatment of getters in general can be found in
>> http://www.thevalvepage.com/valvetek/getter/getter.htm
>>
>> Zirconium getters have their own section at about mid-page.
Thanks, Karl-Arne, that's a very interesting reference.
>>R. Measures wrote:
> Interesting indeed. Thanks, Karl Arne. So Nitrogen doesn't form a
> compound with Zr, the Zr acts as a N2-sponge?
>
It's hard to choose exactly the right words to describe what happens at
the metal surface. At the microscopic scale, the surface is very rough
and it might have internal pores like a sponge... but 'acts as a sponge'
isn't really the right image.
'Dissolved' isn't really right either, because the gas-metal
interactions take place almost exclusively with the atoms right on the
surface of the metal.
At the atomic scale, the metal surface has many 'unsatisfied' chemical
bonds, so gas atoms can attach to those. Oxygen tends to form strong
bonds with metals, while species like molecular nitrogen (N2) don't
have much chemical affinity with metals; but they can still be held by
weaker chemical forces.
Since the reaction doesn't involve all the metal atoms, it doesn't form
any distinctive chemical compound.
> Haveyou ever seen a Zr gettering wire wrapped around a a
> thoriated-tungsten filament? Have you ever observed that the leakage
> current of a 3-500Z that has long been in storage decreases after the
> filament has been lit for 100 or so hours?
>
The 3-500Z has its getter on the anode, so heating just the filament
isn't going to make much difference, is it?
73 from
Ian GM3SEK
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