Re: RE: Polish the Gap

["John Philip Sanderson" <John.Sanderson-at-xxxxxxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Dear Mike, 

Thanks for the tip about cadmium oxide.  That is certainly something to 
be avoided.  

FWIW the silver contacts are soft and cut easily.  I guess a melting 
point experiment is the only way to be sure though.  (Unfortunately for 
me, 962 degrees Celsius is going to be a bit hard to obtain and measure 
accurately!  -But this is a university, I'll see what I can do...)

I checked out the surgical cutter last night... the spark-gaps look like 
tungsten carbide.  I have no idea of how much use that thing has seen, 
but the gaps appear clean; there is only a very light dusting of whitish 
oxide powder on them. 

John S.

> Original poster: "Mike Doyle" <mdoyle-at-CHERRYCORP-dot-com> 
> 
> John - 
> A word of caution,  in my experience switch contacts are not made 
> from pure
> silver unless they are to be used in a low current application. 
> Pure silver
> has to low of a melting point and would cause contact welds in a high
> current switch application. Generally something is added to the 
> silver such
> as cad oxide.
> Cadmuim is considered toxic and I would be concerned about its 
> release if it
> was used in a spark gap.
> 
> You could try scraping or cutting the contacts - pure silver is 
> very soft
> and can be cut or scraped easily but when mixed with cad oxide 
> becomes much
> harder.
> 
> Michael Doyle - Senior Lab Technician
> Cherry Electrical Products
> 11200 88th Ave, P.O. Box 581913
> Pleasant Prairie, WI  53158-0913
> Phone: (414) 942-6627
> Fax: (414) 942-6334
> EMAIL: mdoyle-at-cherrycorp-dot-com <mdoyle-at-cherrycorp-dot-com> 
> http://www.cherrycorp-dot-com/ <" 
> target="l">http://www.cherrycorp-dot-com/> 
> 
> 
>    -----Original Message-----
>    From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
>    Sent:	Wednesday, November 01, 2000 7:47 AM
>    To:	tesla-at-pupman-dot-com
>    Subject:	Re: Polish the Gap
> 
>    Original poster: "John Philip Sanderson"
> <John.Sanderson-at-eng.monash.edu.au> 
> 
> 
>    ----- Original Message -----
>    From: Tesla list <tesla-at-pupman-dot-com>
>    Date: Wednesday, November 1, 2000 1:34 am
>    Subject: Re: Polish the Gap
> 
>    > Original poster: "Albert Hassick" <uncadoc-at-juno-dot-com> 
> 
>    <snips>
> 
>    Dear Al, 
> 
>    Thanks very much for your detailed explanation of the static 
> gap.  I
> 
>    really like the idea of using cable lugs to mount the 
> electrode 
>    material. -A great basis from which to try all manner of 
> different 
>    electrodes, as you clearly have done.  Your comments about 
> tungsten 
>    carbide also agree with Marc Metlica's observations, that this is
> indeed 
>    a good SG electrode material.  Since I have so many of these 
> little 
>    silver "buttons" from contactors, (I am now reasonably certain 
> thatthey 
>    are solid silver), I will give them a go in a small series gap for
> my 
>    little 15/60 setup, replacing the carriage-bolt arrangement I
> currently 
>    use.  In the next incarnation of my 5kVA beast, I'll give 
> tunsgsten 
>    carbide a try.
> 
>    And since we're talking SG electrode materials, I guess I should
> also 
>    take a peek inside my old electrosurgical cutting machine (yet
> another 
>    interesting Tesla coil application) to see what sort of gap 
> materialwas 
>    used by the manufacturer.  Of course, power levels in that 
> thing are
> 
>    pretty low, but I think the spark-gaps would have been fairly
> robustly 
>    designed.  (I wouldn't expect any doctors to be opening it up 
> in the
> 
>    surgery to clean the gaps!)
> 
>    Cheers, 
> 
>    John.
>