Re: construction materials

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Bert and all,
                 A query to all:

On 17 Aug 00, at 11:16, Tesla list wrote:

> Original poster: "Bert Hickman" <bert.hickman-at-aquila-dot-com> 
> 
> Tesla list wrote:
> > 
> > Original poster: "Bill Lemieux" <gomez-at-netherworld-dot-com>
> > 
> <SNIP>
> > > I've seen some nice tungsten
> > > electrodes, but aparently they are hard to machine, and quite expensive.
> > 
> > Check out your local dart shop.  If you have access to a machine shop, then
> > tungsten is no harder to machine than steel.  If you don't have access to a
> > machine shop, it doesn't matter does it?
> > 
> > > However, I was leaning more towards brass. Does this stand up well to TC
> > > abuse?
> > 
> <SNIP>
> 
> Great post, Bill. However, there may be a possible health risk in using
> darts, since the barrel of so-called "tungsten darts" are actually made
> from a tungsten-nickel alloy that contains typically 10-30% nickel. For
> a variety of reasons (machinability, brittleness, cast), no dart barrels
> are made from 100% tungsten. 
> 
> The possible health risks of using these are similar to concerns
> previously voiced on this list. Similar objections exist
> against using stainless steel alloys for high-power spark gap
> electrodes. Since some metal is likely to be vaporized or oxidized in
> operation, these byproducts may then be accidently inhaled. The Material
> Safety Data Sheet (MSDS) for nickel lists it as a possible
> cancer-causing agent (a carcinogen), and similar warnings apply to
> chromium. Nickel's green and black oxides(Ni II, Ni III) also have
> similar MSDS warnings, along with chromium oxide. If you do decide to
> use darts as electrodes, you may want to also use an exhaust fan to keep
> from accidently inhaling metal or oxide particles. 
> 
> On the other hand, pure tungsten is not listed as a carcinogen.
> However, thorium oxide (added to make 2% thoriated tungsten welding
> rods) adds an unnecessary degree of risk, since thorium oxide is also a
> known carcinogen. There are strict rules regarding machining thoriated
> tungsten, requiring the use of respirators, and the waste material must
> be disposed of as a low-yield radioactive material. The welding industry
> recognizes the risk and is actively looking for safer alternatives, such
> as other rare earth metals. Using thoriated tungsten adds no benefit
> when used in a high-power Tesla Coil spark gap, and it may actually
> reduce your gap's ability to quench versus using pure tungsten rod. For
> a variety of reasons, try use pure tungsten if at all possible in your
> rotaries...
> 
> Safe coilin' to you!
> 
> -- Bert --

Has anyone tried a test using tungsten, and then replaced the 
electrodes with tungsten carbide of the same size?  I am 
curious to know how they stack up alongside each other. I've 
been using tungsten carbide since it is readily available from 
a local toolmaker who will machine it and braze it to brass 
roeds for me. I have always had excellent results from it and 
it has a low rate of wear. I'm not interested in arguments 
about resistance because most of the dissipation is in the gap 
arc and the electrodes are negligibly short and effectively as 
wide as the spark wants it to be.

Regards,
Malcolm

 -- 
> Bert Hickman
> Stoneridge Engineering
> Email:    bert.hickman-at-aquila-dot-com
> Web Site: http://www.teslamania-dot-com
> 
> 
> 
>