Note I changed the subject heading to reflect the present topic:
OK, what I am learning is that other electrode types might be
prefered due to increased longevity, as per my original concern
and now voiced by others.
From the Merck Index: Specific melting/boiling properties of
Al are mp 660 C, bp 2327 C.
The boiling point is presumably @ 1 atm and, like water, with
reduced pressure (i.e., 10e-7 Torr) this drops a great deal. Al
normally never goes to vapor, but I suspect this is exactly what
one accomplishes by using the vacuum chamber. Perhaps herein is
the problem as well. For instance, is the rate of vaporization a
matter for concern and does tungsten heat up more quickly than
nichrome or kanthal?
Dominic-Luc Webb
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On Mon, 8 Dec 2003, Hans Summers wrote:
Nichrome is also used in every day household toasters! The average household
toaster holds two slices of bread. From my reading, it contains about 5m of
nichrome wire and the power consumption is about 1 KW (UK mains 240V ac).
Note that these ratings are applicable in air. I do not know how this is
likely to change in a vaccuum.
I suspect the problem with Tungsten might be oxidation. H P Friedrichs has
used tungsten light bulb filaments in homemade triodes etc. See his book
Instruments of Amplification
. He found the lifetime
was only of the order of 15 minutes, when he removed the tungsten wire from
a light bulb and reused it in his valves. This was extended to a matter of
hours when he retained the entire lightbulb assembly i.e. did not handle the
tungsten wire.
Personally I would like to have a go at making some valves (lack of time at
the moment) and am wondering if nichrome would be suitable rather than
tungsten, and be much more convenient and easy to obtain.
Hans
-----Original Message-----
From: gjnelson@... [mailto:gjnelson@...]
Sent: 08 December 2003 14:39
To: VacuumX@...
Cc: dominic-Luc Webb
Subject: Re: [VacuumX] Digest Number 81
According to telescope making volume 3, the filament materials in
order of merit are tungsten, tantalum, molybdenum and columbium.
Nichrome may also work as Nickel is a possible material. Nichrome may
be more easily available if you work in an industry that uses
furnaces as it is used for furnace elements .
Electrical pass throughs can also be constructed by drilling a hole
and then making sure that contact does not touch the sides and use a
neoprene or similar insulating material to insulate. Also from
telescope making vol3.
Geoff
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There is 1 message in this issue.
Topics in this digest:
1. aluminizing chamber electrodes queery
From: Dominic-Luc Webb <dlwebb@...>
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Message: 1
Date: Mon, 8 Dec 2003 12:38:11 +0100 (MET)
From: Dominic-Luc Webb <dlwebb@...>
Subject: aluminizing chamber electrodes queery
This is my first post to this list. Let's see if it works.
I have a vacuum chamber, which pulls needed vacuum for aluminizing, so
I am now at stage of needing to get electrodes into the stainless
steel chamber. James Learch already offered some ideas, and I was
hoping to see if there were others as well. I would be happy to know
of specific electrodes used and how they were inserted into the
chamber.
Along same line, anyone know if Tungsten is really required? Can I now
instead use something like Kanthal wire or perhaps a car cigarette
lighter heating element, etc? This seems more convenient.
I'll now wait and see if this gets distributed to the members.
Dominic-Luc Webb
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