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Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
dr electrons -
You stated: ''Whole! Whole lot of inaccurate info there, zapp ...."
Perhaps you could provide some SPECIFIC information from reliable sources to refute my "inaccurate info"?
Even the most cursory examination of any welding supply price list will show that pure tungsten is the LEAST expensive of the various TIG electrode alloys. Perhaps you misread your electrode price chart, accidentally comparing different diameters or quantities. As for any other "inaccuracies" in my post, by all means provide reliable data to show me wrong, rather than just making unsupported accusations.
I think the focus of this forum should be to share technically accurate, peer-reviewed, independently veriafiable data, and not baseless opinions, "tribal knowledge" or outright misinformation.
Incidentally, here's a link to some information on the potential dangers of working with thoriated tungsten welding electrodes, and current efforts to curtail their use due to risk of inhaling micronized particles of radioactive thorium oxide:
These recommendations were developed by the AWS (American Welding Institute), the TWI (British Welding Institute,) the HSE (British Health and Safety Executive), the DVI (German Welding Society), and the Bavarian Department for Development and Environmental Issues.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I don't know about welding, but pure tungsten is probably the best for a Tesla coil spark gap.
The alloys in TIG welding electrodes are to improve electron emission, which makes a better welding arc and allows the electrode to run cooler, but in a Tesla coil you want the arc to stop as soon as possible. You don't want the emission: it'll only encourage power arcing.
The AWS have a fact sheet on thoriated tungsten:
I heard that ceriated is preferred now, because it's not radioactive.
Brass bolts work fine too, but make sure they really are brass. The last ones I got were brass-coated steel, and the heads burnt off them after a few minutes of runtime. (Steel has very poor thermal conductivity.)
I've also heard of people using worn-out tungsten carbide cutters as electrodes, but I don't know how well that works.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Herr Zapp wrote ...
dr electrons -
You stated: ''Whole! Whole lot of inaccurate info there, zapp ...."
Perhaps you could provide some SPECIFIC information from reliable sources to refute my "inaccurate info"?
Even the most cursory examination of any welding supply price list will show that pure tungsten is the LEAST expensive of the various TIG electrode alloys. Perhaps you misread your electrode price chart, accidentally comparing different diameters or quantities. As for any other "inaccuracies" in my post, by all means provide reliable data to show me wrong, rather than just making unsupported accusations.
I think the focus of this forum should be to share technically accurate, peer-reviewed, independently veriafiable data, and not baseless opinions, "tribal knowledge" or outright misinformation.
Incidentally, here's a link to some information on the potential dangers of working with thoriated tungsten welding electrodes, and current efforts to curtail their use due to risk of inhaling micronized particles of radioactive thorium oxide:
These recommendations were developed by the AWS (American Welding Institute), the TWI (British Welding Institute,) the HSE (British Health and Safety Executive), the DVI (German Welding Society), and the Bavarian Department for Development and Environmental Issues.
Herr Zapp
I really dont feel like feeding your superiority complex. By "pure" (by the way, not the kindergarden understanding of pure) 100% tungsten, not 98.9. If you didnt learn everything you know from google you would know that radioactive elements are very heavy, hence, not airborne like you enjoy throwing around. So unless you plan on making shish kabobs with welding electrodes, there is no problem. Msds and the other crap you are reading on the net is pure (100%) B.S. If you want "specific" info ask someone else who graduated from M.I.T. I am simply sick of you not contributing to threads and just quoting someone elses information and calling it your own. Go back to school or stifle it. Ill say nothing else.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
dr electrons -
Like I said, this is an open forum, and by posting you are soliciting responses to whatever you write. If the content of your post is controversial or wildly inaccurate, it will likely trigger a reply from someone. If you're not able to accept feedback and respond appropriately (like providing additional data to support your position), then participating in on-line forums may not be something you want to continue to do.
Regarding gbd's original question, the bottom line is that almost any non-toxic, non-flammable, non-reactive metal can be used as the electrodes in a Tesla coil spark gap. Some metals will erode more quickly than others, but given the typically low duty cycle of amateur-built coils, the electrode erosion rate may be completely acceptable. Steel and brass bolts, steel and brass acorn nuts, tungsten rod, copper pipe, tungsten carbide drill blanks, copper/tungsten EDM electrode material, zinc rod, and copper rod stock have all been successfully used as electrode materials.
In the last few years, more and more medical professionals have expressed concern about the inhalation of low-levels of radioactive materials, like radon gas, and thorium oxide from TIG welding electrodes. Since "pure" tungsten TIG electrodes cost less than thoriated tungsten, theoretically provide better quenching, and are free of any risk from thorium oxide inhalation, they are a better choice than thoriated material for spark gap electrodes.
These are hard, cold, independently verifiable facts, not opinions.
As for sub-micron sized radioactive particle falling out of the sky like lead marbles "because they're heavy", please explain that theory to the tens of thousands of people who were exposed to the sub-micron sized radioactive dust from the Chernobyl reactor accident as it slowly drifted three-quarters of the way around the earth.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, the AWS position as stated in that sheet, is that the main risk is from dust produced when preparing the electrode tip with a grinder. You don't get clouds of radioactive stuff coming off it when you weld.
Dr. Electrons, what proof do you have that welding with thoriated tungsten isn't bad for your health? "I've been doing it for years, I'm fine, and I don't know anyone else who has got sick from it either"?
That's not proof. I have friends who smoke, and none of them has got lung cancer yet. So please quit beating on Herr Zapp.
Let me beat on him a bit instead... He mentioned zinc rod, and I'd be more worried using that in a spark gap. It's common knowledge that zinc fumes are bad for your health. Stay away from galvanized bolts and so on.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Steve -
I didn't suggest that zinc was necessarily a good material choice for spark gap electrodes, I only included it in a list of materials that HAD been used successfully in the past.
This does bring up an interesting point about zinc electrodes. There is a lot of turn-of-the-century information on spark gaps (quenched and rotary) used in the early spark-gap radio transmitters, and curiously, many of these systems used zinc electrodes, despite its low melting point and presumable high erosion rate. These early radio guys did a tremendous amount of experimentation with every component in their transmitters, and I find it strange that zinc seems to have been widely used as spark-gap electrode material.
Is it possible that zinc's low melting point generated a particularly low resistance when the gap was conducting, due to an abundance of metal ions in the plasma? And that a high electrode erosion rate was accepted as a worthwhile tradeoff for lower losses in the spark gap?
I haven't seen any recent data from anyone who conducted controlled experiments comparing zinc vs tungsten or copper electrode performance in spark-gap Tesla coils. Jeff Behary (electrotherapymuseum.com) has done a lot of work replicating early spark gap designs, but I couldn't find evidence that he experimented with zinc electrodes.
Does anyone out there have any additional data on the use of zinc electrodes in spark gaps?
(I agree fully with the cautions about inhaling zinc fumes. I cringe to think about all the times I tried to weld and braze galvanized material when I was much younger and a lot more ignorant, cussing at the white vapor rising from the workpiece .......)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
An old book in my collection describes a lightning arrester made of multiple spark gaps between metal cylinders, and discusses the problem of quenching the gap.
"To assist in the suppression of these sparks... the cylinders are made of an alloy of zinc called a non-arcing metal. This alloy has the following properties. Firstly, the vapour formed by the arc is a poor conductor, so that there is little tendency for the arc to be maintained. Secondly, a film of non-arcing oxide is formed by the discharge."
("The Transmission and Distribution of Electrical Energy", H. Cotton, English Universities Press, 2nd ed., 1951)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Steve McConner wrote ...
An old book in my collection describes a lightning arrester made of multiple spark gaps between metal cylinders, and discusses the problem of quenching the gap.
"To assist in the suppression of these sparks... the cylinders are made of an alloy of zinc called a non-arcing metal. This alloy has the following properties. Firstly, the vapour formed by the arc is a poor conductor, so that there is little tendency for the arc to be maintained. Secondly, a film of non-arcing oxide is formed by the discharge."
("The Transmission and Distribution of Electrical Energy", H. Cotton, English Universities Press, 2nd ed., 1951)
So, maybe zinc electrodes quenched better?
I'm surprised that there isn't more interest in using low work function electrodes, such a f-block lanthanides, among Tesla enthusiasts. Cerium has a low work function of 3.0eV and its oxide is cheap and easy to get. A lower work function makes for a faster streamer rise time, and thus a sheerer wave front for a juicy dv/dt.
I've found a patent utilising this concept: Combustion initiators employing reduced work function stainless steel electrodes United States Patent 5898257
Abstract
The electron emitting cathode of an initiator (spark plug or ignitor) comprises a small button of high temperature, preferably austenitic, stainless steel powder welded to a support conductor. The stainless steel powder has distributed through it a dopant powder consisting of a minor portion of a highly stable oxide of an element having a low work function. The dopant powder has a much smaller mesh size than the stainless steel powder (1/5or less). Rare earth lanthanides are preferred that have a low work function, preferably under 3.0 eV and are not radioactive. Cerium, in the form of CeO2 is most preferred. The compositions of the low work function stainless steel electrodes and methods of making the same are disclosed.
The full text can be accessed free here:
I'm not a TC person, so there may be good reasons for not using electrodes of this type in Tesla work, but I shall certainly get round to trying it in triggered gaps when needs be.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Steve, PM -
Here is some additional information on the use of "non-arcing metals" in lightning arrestor spark gaps (connected across the AC powerline), from the Journal of the Franklin Institute (1895):
" ......... while experimenting with this system, I discovered that if the electrodes of a lightning arrester were made of zinc, the short-circuiting arc, which had heretofore threatened the life of the lightning arrester, absolutely failed to be maintained. In other words, zinc proved to be what is now known as one of the "non-arcing" metals. Subsequent investigation disclosed the fact that there were four other metals which exhibited similar characteristics, namely, bismuth, antimony, cadmium and mercury.
The discovery of the non-arcing metals at once solved the problem of a lightning arrester adapted to the requirements of alternating current circuits, and which would meet the conditions already enumerated."
The paper can be found at:
Also written relative to "non-arcing" metals used in spark-gap lightning arresters (Morey and Oehne, 1908), including a hypothesis as to "why" zinc electrodes provide bettter quenching than aluminum, copper, etc:
"In his experiments Wurts (Alexander J. Wurts) discovered that when brass electrodes were used on alternating current some compositions of brass acted differently from others. Upon investigation he found that brass containing much zinc was the best. He explained it in this manner: Zinc and antimony supply the arc stream with oxide of metal, which chokes the arc with vapors of high resistance. Other metals, such as copper, aluminum, bronze, etc., furnish the arc stream with pure vapors of the metal itself, which offer comparatively no resistance to the passage of a current. Cadmium, bismuth, magnesium, and mercury were found to have this non-arcing property. The vapors of these metals are also unidirectional, —that is, they have a tendency to prevent a reverse of current. The non-arcing property is also very largely due to this. The arrester constructed of non-arcing metal best suited the alternating current and the gaps must be small--1/32 or 1/64 of an inch, in order to hold the vapor between electrodes."
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Spark gap electrodes?
