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Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
If you want good material and also want to keep cost down a bit, Tungsten is in fact what you want. What the others didn't mention is that it comes in different alloys. There is Thoriated, Ceriated, Lanthanated, and others. For your particular application i would go with the Thoriated. It is found in welding supply houses and is a little more than half the price of pure tungsten. You can identify it by the red band painted on its end. Red will be 2% Thoriated. Ceriated will have an orange band. Lanthanated will have a black or blue band depending on the %of alloying. Alloyed tungstens are used for gas tungsten arc welding and can resist extreme temperatures that you will never see in a spark gap. Thats your best bet!
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
gbd, here is a photo of my disk that I have used with a 9000rpm angle grinder, now with a 1500 rpm synchronous motor. One thing I will state is that make sure you put it in some sort of enclosure so that if it does explode you don't get a flying electrode in the forehead. Some here might say that it is not safe, but I have tried it at short to long runs with no problems, with 4kW through it. Mark it out as carefully as possible, I attached it to the drillpress to make it perfectly circular (without electrodes of course), and bastard filed the edge. Crude, yes. Where there's a will there's a way. If we thought about the best way of doing things all the time as the only way to do them, then we's never get out of our armchairs.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
"make sure you put it in some sort of enclosure so that if it does explode you don't get a flying electrode in the forehead."
About 56 years ago a lesson was learned about centrifugal (fleeing a center) force and the strength of materials; The scar on my left index finger is still there and makes it easy to remember which hand is left.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
dr electrons wrote:
"For your particular application i would go with the Thoriated."
Not a good idea. Thoriated tungsten spark-gap electrodes will release micron sized particles of radioactive thorium oxide into the air around the spark gap. With thorium being an alpha emitter with a long half-life, you don't want particles lodged in your lungs for the rest of your life.
"It is found in welding supply houses and is a little more than half the price of pure tungsten." Not true. TIG welding electrodes are available in several different alloys; pure tungsten being the LEAST expensive. The following are the most commonly encountered alloys; all alloys except the thoriated alloy are acceptable for Tesla coil spark gaps.
Pure tungsten - color coded green 1% thoriated - color coded yellow 2% thoriated - color coded red 1% lanthanated - color coded black 1.5% lanthanated - color coded gold 1% zirconated - color coded white 2% ceriated - color coded gray
"Alloyed tungstens are used for gas tungsten arc welding and can resist extreme temperatures that you will never see in a spark gap."
Not true. Ionized plasma is ionized plasma. The current seen in spark gaps of medium or large sized Tesla copils is considerably higher than seen during normal TIG welding.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Herr Zapp wrote ...
Not a good idea. Thoriated tungsten spark-gap electrodes will release micron sized particles of radioactive thorium oxide into the air around the spark gap. With thorium being an alpha emitter with a long half-life, you don't want particles lodged in your lungs for the rest of your life.
A small footnote here: thoriated gas mantles, welding rods, valve filaments, &c become more radioactive as they age. Industrial thorium is extracted mainly from monazite sands, where Th-232 and Th-228 are in equilibrium. Thorium daughters are very largely removed during refining, but Ra-224, Ra-228, Pb-212 and Bi-212 start to build up again when refining is over, and are released into the atmosphere when gas mantles and welding rods are heated.
Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
Herr Zapp is right about the prices. I got mine plasma speaker electrodes as "the less expensive tungsten rod" in the shop. It's color coded GREEN. Its for aluminum welding, 1/8" dia.
No hazard stuff come out of this material when is used as a spark gap or plasma electrode? As I found it's 'only' 99,5 % pure..
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I've used 1/4" diameter pure tungsten rods for a static spark gap - great.
Don't use ferromagnetic materials as they heat up (eddy-currents, skin effect etc.)
I wouldn't use radioactive rods because I don't want any more toxins than I have already and why would I want to pre-ionise the gap in a sgtc? The sg will be more lossy I expect (longer gap).
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Herr Zapp wrote ...
dr electrons wrote:
"For your particular application i would go with the Thoriated."
Not a good idea. Thoriated tungsten spark-gap electrodes will release micron sized particles of radioactive thorium oxide into the air around the spark gap. With thorium being an alpha emitter with a long half-life, you don't want particles lodged in your lungs for the rest of your life.
"It is found in welding supply houses and is a little more than half the price of pure tungsten." Not true. TIG welding electrodes are available in several different alloys; pure tungsten being the LEAST expensive. The following are the most commonly encountered alloys; all but the thoriated alloy are acceptable for Tesla coil spark gaps.
Pure tungsten - color coded green 1% thoriated - color coded yellow 2% thoriated - color coded red 1% lanthanated - color coded black 1.5% lanthanated - color coded gold 1% zirconated - color coded white 2% ceriated - color coded gray
"Alloyed tungstens are used for gas tungsten arc welding and can resist extreme temperatures that you will never see in a spark gap."
Not true. Ionized plasma is ionized plasma. The current seen in spark gaps of medium or large sized Tesla copils is considerably higher than seen during normal TIG welding.
Regards, Herr Zapp
Whole! Whole lot of inaccurate info there zapp, however im not here to argue. I have been a U.S. Navy certified tig welder for 15 years. That would qualify me to know what i am talking about. By the way, do a little homework on what happens to the radioactive particles when tungsten is exposed to high temperatures. Get a hobby and stop trying to prove everybody wrong. If you MUST, ill get you a price list for tungsten electrodes. Pure is the most expensive due to the rarity of the metal. I will no longer participate in threads you are involved in. Sure sounded like you knew what you were talking about though. Google a little more next time, or read a welding book.
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
As previously suggested, I think I will aquire some 1/4 inch pure tungsten and use that for the flying electrode, and perhaps use the same for the stationary electrodes. also, I have revised my RSG design a little, its still the same helicopter style gap, but will have a hollow support on top that is attached just below the primary's base, and will house the top of the shaft, just to provide a bit more stability.
well, I think the question has been debated thoroughly and answered. thank you for your help everyone.
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Spark gap electrodes?
