Sciencemadness Discussion Board

Tungsten electrodes

elementcollector1 - 17-8-2012 at 12:35

Would these be useful as anodes? Tungsten resists attack by acids, alkali and oxygen, so... any thoughts?

Swede - 19-8-2012 at 18:33

No. Even normally unreactive elements like gold behave differently when part of an electrolytic setup. If your goal is (per)chlorates, tungsten will not work as an anode.

It is far more complicated than simply not dissolving. To put it simply, it has to not only hold together, it has to "make" the species of interest, and not just any old thing that conducts can do that.

If you want chlorates, your choices are pretty much hard graphite, platinum, lead dioxide, or best is MMO, mixed metal oxide-coated titanium. If you want perchlorates, you'll need Pt or PbO2. There are others that will work, but are exceptionally exotic and expensive.

The first question is always "what do you want to make with your anode?

elementcollector1 - 21-8-2012 at 11:09

Er... sodium hydroxide? And chlorine at the anode?
I was never really interested in chlorates...

I already tried gold as an anode, it failed miserably. (Luckily, it was plated.)
I thought tungsten might hold up somewhat better...

Swede - 25-8-2012 at 07:29

OK... 95% of the people who ask about anodes without being specific are looking for (per)chlorates.

As for your setup, I don't know the answer. Give it a try on a small scale.

elementcollector1 - 25-8-2012 at 14:27

Yeah, I'm different. XD
Might as well... Would have to break a few lightbulbs, though.

Dave Angel - 1-9-2012 at 02:48

Quote: Originally posted by elementcollector1  
Would have to break a few lightbulbs, though.

Assuming this isn't tongue in cheek, you're probably better off with tungsten TIG welder electrodes, though don't make the mistake I did and start cutting / grinding the red tipped (aka, Thoriated!) electrodes.

I've since discovered that one can buy Lanthanated (black tip) and Zirconated (white tip) electrodes - naturally occuring La having the lower ratio of radioactive isotopes (0.09%) so probably the best bet for modification.

Swede - 4-9-2012 at 10:29

There are pure W TIG electrodes available... I think they are used for Al welding. I think they are green tipped, but the package should clearly state what they are.

Dave Angel - 4-9-2012 at 12:48

I stand enlightened; indeed they are green tipped, and I will be using these in my spot welder mk II build - thanks Swede

elementcollector1 - 5-9-2012 at 18:43

Excellent! What are the dimensions of these rods, anyway? Is there a defined length for them?

Swede - 6-9-2012 at 10:30

TIG electrodes come in a variety of dimensions, but the normal diameters available at a typical welding shop are (at least in imperial units in the USA) 3/32" and 1/8", with some slight variations. Length will be from stub to 6" or so.

I'm sure there are larger and smaller available by special order, but they really don't come in jumbo sizes because such a welding machine would be thousands and thousands of amps to make use of a large diameter.

Dave, I've done a lot of experiments with both homemade and consumer-grade spot welders, mostly for sheet steel and titanium. I tried W as a contact, and it performed very poorly. A 1/8" rod goes nearly incandescent immediately, and atmospheric O2 then eats it alive. I've never found anything better than conical copper.

One option might be to bury a W electrode tip INSIDE a Cu carrier rod. The tip which carries the current needs to be of a significant cross section to handle the current without overheating. Although if you can find a piece of 8 to 12 mm W rod, and grind the tip conical, I'd bet it'll work OK.

Dave Angel - 6-9-2012 at 11:56

1.6, 2.4 and 3.2 mm seem to be common diameters in the UK, with lengths of 150 mm, so in line with your imperial measures. As you've indicated, the larger diameters are less readily available.

Anyway, thanks again for the advice Swede - I thought I'd seen a few of your post when did a cursory search for spot welders here. I noticed a similar incandescence with the W electrodes, though didn't find it to impact performance - the simple construction and operation probably did more in that regard, tbh!

On the next build then, I might RTFM of the hack-a-day and either use the MIG tips they recommended or get hold of some copper rod to modify in the manner you've suggested. For this latter idea, a decent contact might be achieved with a tap and die set to thread the W stubs and drilled out ends of the copper rod. Details probably a bit off-topic so I'll post in the appropriate thread and reference here when I get round to it.

watson.fawkes - 6-9-2012 at 17:12

Spot welders use low-resistance tips when the material being welded has adequate resistance to generate heat at the point of contact. For example, to weld mild steel sheet metal, you have three contacts: copper--steel--steel--copper. The two copper vs. steel points of contact have lower resistance that the steel vs. steel one, so the bulk of the heat is generated at the steel interface, which is what you want.

Refractory tips are used when you want to weld low-resistance metals like copper and silver. In that case the center junction has low resistance and you need to generate heat in another way. One way is to braze on disks of tungsten to copper tips. Heat is generated in the tungsten and flows into the point of contact between the materials to be welded.

Hybrid tips are used, for example, to spot-weld copper to steel. A copper electrode is used on the steel side and a refractory one is used on the copper side.

Since I'm on the subject, the reason that spot welders use just large copper rods, as a rule, is for energy efficiency. You want the resistance of the conductors from supply to point of contact to have as low a resistance as possible. In this way the bulk of the energy dissipation goes to the weld point.

platedish29 - 6-9-2012 at 17:45

If you planning to make a tungsten derivate from scrap, tungstan anodes could be useful for a especific chlorate set up wherein the metallic or diverse quality of compounds of W are consumed to one of high grade sources. Plus, anode demage would replenish the bath. Pick some of the powder and sinter. Apply 12V battery to maximum achievement of a substance elec. breakdown

Thik this would manifest as band-gap

Xanthippe - 11-9-2012 at 11:13

Just a thought. If you want to try platinum or iridium, use some discarded spark plugs. The outer steel shell can be ground off and the ceramic covers the steel portions of the center electrode. Look for plugs that have no built in resister.

elementcollector1 - 11-9-2012 at 13:24

That's an interesting thought, but sparkplugs are expensive and I know a place where I can get Pt wire, 1" for $7.

offset442 - 23-10-2012 at 18:43

As for a spot welder refractory tip a nice DIY tip might be a plasma cutter electrode, its a tungsten core with an iron doped copper wrapper . I get dozens of these from my cutter head, they are very cheap on eBay see pt 50/pt 30 ( shorter) touch consumables. These have a wide base that could be nested into a clamping device.