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Thoriated tungsten electrodes

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David George 106/06/2022 08:37:41
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Hi I have just read in another post that Thoriated tungsten electrodes have a radioactive content. As an apprentice part of my roll was to keep these electrodes sharpened for three welders as well as making tea, winding rotary jigs as they welded items and grinding weld preps etc. I wondered what the levels of radioactive material there was and what problems it caused. In those days, early 1970s little use of protective equipment other than goggles, welding masks and gloves.

David

Kiwi Bloke06/06/2022 08:58:28
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Thorium decays by emitting alpha particles. These cause intense ionization, which will damage cellular DNA, but do not penetrate skin to a significant depth, unlike gamma rays, so just handling the electrodes is not risky. Inhalation of the dust liberated by grinding is different and is risky, because the lungs' lining isn't protected by relatively thick skin. It is regarded as a known problem, so precautions shpuld now be taken, but it can't be a high-probability risk, given the large number of people exposed to the dust, and the few cases of consequent lung cancer. These days, I think there is little need to use thoriated tungstens.

JA06/06/2022 09:01:53
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Thorium is radioactive. It emits low energy alpha (I think, from memory) particles that cannot penetrate the skin. However if the dust, from grinding etc, is breathed in then you have problems.

Magnesium alloyed with some Thorium was used in the aircraft industry. It produced a strong light alloy but was abandoned in the 1990's because of environmental problems during casting (what happened to the Thorium Oxide dust when the metal caught fire). The major Magnesium foundry in the UK was in south east London.

JA

The foundry had an open casting floor and if a fire had taken place with Magnesium/Thorium alloy  I believe all air conditioning units, where dust could gather, within a 5 mile radius would have had to be turned off and cleaned.

 

Edited By JA on 06/06/2022 09:09:05

Nick Clarke 306/06/2022 09:02:44
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This site from the epa EPA looks to be authoratative.

The Alpha particles will not get through your skin and the weak gamma rays will cause minor damage (they are energetic but so small that they go straight through damaging few cells) - of course it is a different story with huge doses of gamma rays and beta particles that are so massive they batter their way through causing damage as they go.

Another source is here **LINK** which notes the risk is negligible - however it does suggest beta particles are also involved as these are given out from elements in the decay chain, not thorium itself, hence the discrepancy compared to the epa information which only refers to thorium.

The Wikipedia page seems to give a lot of accurate information, but much is well buried.

old mart06/06/2022 18:11:47
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The thorium in the early jet engines was to help retain strength in the aluminium at higher temperatures near the combustion chambers. We have several examples of these engines at the museum, made by Napier in the 1950's. They are pretty well harmless as long as dust is not allowed to form from corrosion. One of the best corrosion and dust preventers is a liberal spraying of WD40 inside the engines, and keeping the exterior paint up to scratch. As I mentioned in the other thread, grinding dust is the danger, and even modern non thiorated electrodes will have the cobalt binder for the tungsten floating about to ingest if not ground carefully, preferably with a vacuum cleaner used. Cobalt is poisonous.

Martin King 206/06/2022 18:26:19
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JA, I worked at Stone Manganese Marine for part of my sandwich course at Uni, they used casting pits in the floor for large propellers etc. They were in Charlton SE London.

just before I got there they had a large fire in a huge bin of magnesium swarf, which proved nigh on impossible to put out. I dimly remember them talking about thorium problems then?

Cheers, Martin

Robert Atkinson 206/06/2022 19:59:33
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A couple of facts:
Old gas and paraffin lamp mantles contain significantly more Thorium than welding rods and once lit the ash is much easier to breathe in. There have been few issues with that.
Magnesium-Thorium alloy with up to 4% Thorium is specfically considered to NOT be radioactive material under UK radiation legislation. Thus it does not need any special handling or disposal. There is an odd exception, if it is being used for it's radioactive properties (e.g. as a test source) then you have to comply with the regulations.
Generally Thorum is not considered a significant hazard. Certainly no worse than Cadmium (plating, rechargable batteries) or many other engineering materials.

Robert G8RPI

Barry Smith 418/06/2022 11:26:10
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Sorry I had a little laugh as when I saw this post I was writing a report on exposure to thorium in a prospective uranium mine I agree very much with what others have said and have to admit to using my tig rods to test my gamma spectrometer and dose meters out, along with a bag of potassium chloride and some uranium glazed pottery.

From a health perspective I would be more concerned with the other elements in the rods than the small amount of Th and that includes both the tungsten and rare earth elements that are being used to replace Th. So good practice would be to minimise inhalation of dust whatever the source whilst welding., tig or otherwise.

What's seen safe now maywell be proved wrong in the future, as I know from working with asbestos and Mercury as an apprentice.

Barry

Hopper18/06/2022 11:38:13
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Yes those were the days -- when we resisted the change from asbestos to fibreglass lagging on the boilerhouse pipework because it was too itchy.

Nick Clarke 318/06/2022 11:53:55
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Posted by Barry Smith 4 on 18/06/2022 11:26:10:

What's seen safe now may well be proved wrong in the future, as I know from working with asbestos and Mercury as an apprentice.

Barry

When I was at school we played with little drops of mercury on the lab bench.

When I first trained as a science teacher we were told this was not a good idea as bits could get lost and it was very expensive. Also mercury vapour in discharge tubes was hazardous so extra care had to be taken when exhausting a glass vessel containing mercury with a vacuum pump to demonstrate the discharge through it.

When I actually started to teach I asked the lab techs in my first school for a mercury trough, a specially shaped porcelain dish that you filled with mercury and inverted a 1m sealed tube of mercury with your finger over the end and supported in a stand to make a Torricelli barometer.

'Is that to demonstrate or a class set of 15?' was the reply from the techs.

Can you imagine 30 year 11 pupils each pair with a 1m tube of mercury plus a dishful as well waving it about and then asking them to stick their fingers in more of the metal? And if their fingers were not on tight (and 1m of mercury weighs!) it would be all over the floor.

I said a demonstration please and later the head of department and I quietly binned all but a couple of the mercury troughs in case some future teacher had the wrong idea. And how much had stocking that much mercury cost in the first place?

Edited By Nick Clarke 3 on 18/06/2022 11:58:49

Martin Kyte18/06/2022 13:51:53
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Back in the day when Laurence Bragg was in charge of the Royal Institution there was a visit from Marie Curie who brought a present of a flask of Radium in solution (of what I don't know). The stuff was proported to glow in the dark so Bragg, who lived in the flat on the site wandered down to the workshop to see if this was true and how bright it was. Being in dressing gown and slippers he unfortunately dropped the flask which broke and soaked into the floor. Some years later during a Lab refurbishment high levels of radioactivity were found around a particular bench which resulted in a large section of the floor being removed and disposed of.

Tales from the past are numerous and somewhat cringe making now the implications are better known.

The old Cavendish Lab in Cambridge had wooden block flooring which when walked on in certain areas caused small bubbles of Mercury to be squeezed up out of the cracks from all the spills over the years.

I'm told by a very reliable source that our lab once had an X-Ray technician who was in the habit of lining up the beam by eye. Literally, by looking down the beam untill he could feel the tingle!! as he made the adjustments.

On balance I'm glad I work now rather than then.

regards Martin

Edited By Martin Kyte on 18/06/2022 13:52:19

Edited By Martin Kyte on 18/06/2022 13:53:03

Edited By Martin Kyte on 18/06/2022 13:53:50

Martin Kyte18/06/2022 14:00:05
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Getting back to the Mercury question when things are banned or restricted it's helpfull to find out why. For example leaded solder being phased is driven by a desire to restrict the amount of lead going into landfill from consumer electronics rather than any particular hazard during use. Similarly Mercury in it's metalic elemental form is relatively safe. However it's not something that is good to have in the environment especially rivers and oceans where it gets into the food chain. Massively restricting the use of Mercury is really the only way of ensuring that more of the stuff doesn't end up in the environment.

regards Martin

Robert Atkinson 218/06/2022 14:14:34
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As a private individual you now need a Explosives Precursors & Poisons (EPP) licence to possses Mercury. This applies even if you already had it. There are exaemptions for when it is part of something else e.g. fluorescent lamps.

Mercury is of course both a EP and a P.

Robert G8RPI.

pgk pgk18/06/2022 14:40:32
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Posted by Martin Kyte on 18/06/2022 13:51:53:

I'm told by a very reliable source that our lab once had an X-Ray technician who was in the habit of lining up the beam by eye. Literally, by looking down the beam untill he could feel the tingle!! as he made the adjustments.

On balance I'm glad I work now rather than then.

regards Martin

And I recall a very aged (well he looked very old) leathery skinned and white haired part-time x-ray tech coming to check my machine in the 70's, First he took a couple of exposures with his arm under the beam to assess the ionization by how his arm hairs lifted. Unsatisfied, he then stared into the tube to assess the cathode heater while running his hands over the high-tension leads looking or losses of insulation...

pgk

JA18/06/2022 15:06:18
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In the early 1960 Mercury got into the food chain very seriously in Japan. It, no longer as a pure element, ended up in Dolphins (at the top of the food chain), a highly prized food. A large number of human consumers of Dolphin meat got very badly poisoned

I remember in about 1973 Mercury started to be taken very seriously. I worked as a very junior member of staff in the mechanical engineering labs at Hatfield Polytechnique. In the fluids dynamics labs we recovered a considerable amount from under the floor boards. It came from broken manometers. Also it was common practice to label each tube on a manometer bank with masking tape. Eventually the labels had to be removed so out came the bottle of Xylene.

Thinking back to sixth form at school, it as common practice to dip an old penny in Aquaregia, wash off the acid and then put it in mercury. The result was a nice shiny silver penny which you tried to use as a half crown. Having no success it remained in ones pocket and, after few days, was an ordinary shiny penny. So what happened to the Mercury (not a question).

JA

Mark Rand18/06/2022 19:44:04
1314 forum posts
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In the early '80s we had 400kg of mercury in the stores, but we had stopped using manometers for flowmeter and condenser vacuum measurements in steam turbine performance testing.

I proposed to our management that we should sell the mercury, since it was valuable, but we had no further use for more than about 20kg of it. I was informed by a very unimpressed departmental manager that the company as a whole would get the benefit and that neither the department or our small section would see anything from it, other than the hassle of the sale. So it was not allowed.

A decade later, a large sum of money had to be paid out to dispose of 400kg of toxic waste!

Samsaranda18/06/2022 20:10:13
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In the 60’s I was in the Air Force and a stone bottle containing mercury, part of a freight consignment, got smashed in the freight bay of one of our Brittania aircraft. The mercury very quickly found its way out through the aircraft lower pressure skin, there were a serious of holes where it swiftly made an amalgam, dissolving the alloy of the aircraft skin. The underside of the aircraft required an amount of repairs to remove the damage caused. Mercury can cause a lot of problems. Dave W

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