Again, Tom, you don't show the whole tale. I wholley accept what Terman says
over this on the optimum temperature for a zirconium getter (1400 deg C) since
as you say, he's "peer reviewed" and his book has been used to teach in several
universities.. I said even though that it would start working at around 700 deg
C which this guys text says. Terman didn't give a minimum. Also, again you
didn't show the very last paragraph this guy said;
Quote;
"The chief disadvantage of zir-conium as a getter is that the optimum
temperature for the sorption of hydrogen is too low for the effec-tive cleanup
of oxygen, nitrogen and the oxides of carbon. If, there-fore, the
zirconium-coated part is to operate at a temperature much in excess of 300 C, a
supplementary lower temperature Zr getter or a getter of the barium or
barium-magnesium type should be added to absorb the hydrogen. Whether this
precaution is necessary or not depends upon the tube and the amount of water
vapor or pure hydrogen found within it".
Terman says they simply use two pieces of zirconium heated at two different
temperatures to do this. Also, the author of the webpage says; "700 C must be
considered minimum for activating the surface of the zirconium getter". Why the
question, it's in the text you pasted to the post? Under 700 deg C, it will not
soak up gasses like oxygen as it's not hot enough to activate it. Also, at that
temperature, it doesn't mean it works at its best like instant on, or works the
same no matter how much higher the temperature is. From experiments by Phillips
(see Termans Ref), it was determined to be if used as a getter, its optimum
temperature where it worked the best was 1400 deg C which is an anode that's
white hot. The lower the temperature, the less absorbsion it has. The sticker
is what zirconium does at over 300 deg C when it starts to liberate hydrogen
gas. How can an anode coated with zirconium running hot enough to absorb
oxygen, absorb hydrogen gas? There's a simple answer, i
t can't. I know for a fact there's no other components inside a 3-500Z like
another getter. Now if they had used tantalum, it starts to absorb oxygen, etc
at a lower temperature, and you don't have the hydrogen gas problem. The
problem is the extra cost it would make. If you would run a 3-500Z hot enough
to absorb, O2, and CO2, you'd ruin the glass to metal seals since they have a
maximum operating temperature.
>>Will said:
>>Althought Terman shows this same thing on page 315 of the
>>1st edition, 1943, here is a link to a website below about
>>getters;
>
>(1) http://www.thevalvepage.com/valvetek/getter/getter.htm
>
>>It's impossible to run one temperature on zirconium. It's
>>optimum temp according to Terman is 1400 deg C to absorb
>>oxygen, nitrogen, carbon dioxide, and carbon monoxide in
>> >vacuum power tubes.
>
>Will, I wonder if you aren't a little confused on this
>topic. You said above " It's impossible to run one
>temperature on zirconium. It's optimum temp according to
>Terman is 1400 deg C to absorb oxygen, nitrogen, carbon
>dioxide, and carbon monoxide in vacuum power tubes."
>
>You then sited a link.
>http://www.thevalvepage.com/valvetek/getter/getter.htm
>
>The very link you sited says this:
>
>"Zirconium
>Zirconium has valuable gettering characteristics and has
>come into wide use during the past decade. It forms very
>stable solid solutions (or compounds) with such gases as O,
>N, CO and CO2. Zirconium metal is cheaper than tantalum and
>requires somewhat lower operating temperatures. Zirconium is
>available either in solid metal form (sheets or wires) or it
>may be applied in the form of a powder to base metals
>(molybdenum) as described above. The proper outgassing
>temperature for zirconium lies between 1,000 and 1,700 C,
>which is attained by either direct or indirect heating of
>the zirconium metal or of the base metal to which zir-conium
>metal or zirconium powder has been applied. Wherever it is
>deemed inadvisable to heat the getter material to this
>temperature range, an outgassing temperature of 700 C must
>be considered minimum for activating the surface of the
>zirconium getter. While zirconium is effective as a getter
>from about 400 C on, it is most active at temperatures up to
>1,600 C if used, for example, on molybdenum and carbon
>anodes."
>
>The very text you referenced says "While zirconium is
>effective as a getter from about 400 C on, it is most active
>at temperatures up to 1,600 C if used,"
>
>It appears the text you referenced says "400deg C up is
>effective". Can you explain why that means it is useless
>below 1700 degrees C, when that isn't what they say? Can you
>also explain why Eimac was successful in using that very
>common gettering material, when you say it is impossible to
>use?
Can you provide us with some written proof that Eimac even done this? If they
did, it was very poor engineering practice in my opinion.
>
>Thanks,
>
>73 Tom
>
>
>
>
>
>
>
>
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Best,
Will
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