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Re: Rubber toroids
---------- Forwarded message ----------
Date: Wed, 22 Oct 1997 10:39:28 -0400 (EDT)
From: Wes A Brzozowski <wesb-at-blue.spectra-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Rubber toroids
Sorry to get into this so late; I'm weeks behind in my e-mail at the
moment, and just got to the first message on this topic.
This topic came up about a year ago, and I posted a bunch of plating info,
as well as some possible serious safety problems, and some details on a
similar technique I'd been working on. I don't have the original post
handy, but since I post here fairly infrequently, it shouldn't be too
hard to find in the archives.
To summarize, I'd been forming small parts (just working small scale, to
get data on the process, before trying anything large like a toroid) out
of polystyrene. This stuff can be formed for individual parts without
injection molding by dissolving it and building it up, layer by layer.
I used a laquer that used a minimum of tolulene to actually dissolve it
(more like a thin putty, in that form) and then thinning that with
acetone, to make a quick drying laquer. Neither of these solvents are
good to use in poor ventilation or near flame or sparks, but they're not
all that frightening to coilers who can handle the risks associated with
electrocution, or poisoning from ozone or the nitrogen oxides produced by
our spark gaps. But you do have to know the materials well enough to be
able to manage the associated risks.
The laquer is made easily conductive by the addition of powdered graphite
(I've experimented with mixes of graphite and conductive lampblack, which
have radically different particle sizes, and thus load the laquer with a
higher percentage of conductive material) and had been trying to get a
process down to plate the conductive plastic with a good, solid, well
adhering plate. One of my old posts gave some plating formulations; if you
want good adhesion, just ordinary old copper sulfate solution will tend
to fall a little short. Commercial plating tends to use a mix of copper
sulfate and sulfuric acid in the plating bath. While the word "acid" tends
to frighten a lot of people off, it's once again a matter of knowing the
materials and managing the risks. Personally, I consider an operating coil
to be much more dangerous, but we readily manage those risks. When using
sulfuric acid, you do want things like safety glasses and old
clothes, though. (When you wash the clothes, you'll see how easy it is to
spatter droplets of the plating solution; every place a droplet hit your
clothing will be replaced by a small hole.) It may be possible to plate up
a coating in a non-acid solution that will adhere over time even though
it's suffering the localized hotspots of an electrical discharge, bit I'd
expect it to be some trick. Then again, people here have managed some
pretty neat tricks in the past. Might be worth a try, but remember that
adding a little H2SO4 may be a trick worth falling back on...
The original posts also contained some severe warnings about using nickel
plating for something like a toroid, but which some people are suggesting
now. The discharge from a toroid may vaporize small amounts of metal. While
copper can be ingested in small amounts (hey, we actually need it in trace
amounts; perhaps coiling can be healthy? ;-) nickel can do really nasty
things to you. Worse are some of the incredibly toxic organometallics it
can form. Given sufficient energy and ordinary atmospheric components,
nickel can form nickel-carbonyl, a toxin that makes the cyanides
everyone's been worrying about look like candy. The stuff is vaporized at
low temperatures, making the path to ingestion just ordinary breathing.
Now, I don't know for sure wether an electrical discharge to a nickel
surface will produce nickel-carbonyl, but I personally wouldn't try to
find out by experiment. The stuff is just too scary to me to think of
ingesting in any trace amounts, and I'm not particularly worried about
handling cyanide solutions (though I am particularly cautious when doing
so). In any case, it might be worthwhile to hold off on the nickel plating
until the toxicity issue is resolved.
One other item; the use of copper chloride as an electrolyte has been
mentioned, and while it seems that it should be able to deposit a layer
of copper just like copper sulfate can, I can also see some problems,
which may be the reason it's not used commercially. First, there's the
problem of using an acid-copper bath to improve adhesion. If we need
to add acid to get a decent plate for a surface that's punished the way a
toroid is, the addition of acid to a chloride solution will evolve
hydrochloric acid fumes, which are quite unpleasant to breathe. The
second is the fact that a class of chemicals called chlorates are produced
commercially by the electrolysis of chloride solutions. If any copper
chlorate is being produced in the process, you could be producing a very
unstable vat of liquid. I'm not sure how it acts in solution, but solid
copper chlorate has been known to explode without provocation. Now, I'm
not sure wether the intermediate steps needed to produce a chlorate
radical can happen in a copper solution, and I may be all wet on this last
item which is admittedly speculative, but it's a worthwhile question to
ask, in case it happens to be meaningful. I'd look for some good, solid
references before using this kind of plating bath. Perhaps they do exist,
and there's only the adhesion problem to worry about, which would be
great, but a reference or two would be really nice for this one...
Anyway, anyone interested in this subject might want to look for those old
postings from a year ago or thereabouts. I think there might be some
useful information there. In any case, I'm personally very interested in
seeing people work on this problem again, so keep tossing out those
ideas!~
Wes B.
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* wesb-at-spectra-dot-net * "It's a magical world, Hobbes ol' buddy... *
* * ..Let's go exploring." - Calvin *
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