Replacing lead weights with US nickel coins

[Mobulai]

Most interesting 1st thread indeed — any idea if this would work for cupper plated steel (like EU cents)?
Or would galvanic reaction be bad?

An off topic aside, @Tanks A Lot how did you insert Latex style sub/superscript?

DaysUntil corroded

 

[pwoolf]

I didn’t see the UK on your list.

Is the 5pence coin not made from cupronickel ?

I think your idea is brilliant ! On future dive trips I will take a couple of these empty bags with me, visit a local bank for coins, and then at the end of the dive trip use the coins to give the dive guides an impressive looking tip

Fantastic! Yes, looking at UK coins the 5 pence coin *was* cupronickel pre 2011, but has since been replaced with a nickel plated steel coin. Unfortunately that will corrode.

But... looking more deeply, it seems the 20 pence coin and 50 pence coins are cupronickel. I missed that, thanks for bringing that to my attention. I've updated the calculator now to include these coins.

These are a bit higher value coins, so will make an even better dive tip--makes for happy dive operators!

 

[Eric Sedletzky]

I just use lead hard weights on a belt and they never seem to oxidize or change.
I think it’s a drop in the ocean compared to all the other problems the ocean faces.
Soft lead shot weights are a bigger problem, they trap water and lead oxide oozes out.

 

[pwoolf]

When we think of metals corroding, the intuitive assumption is that they will corrode faster in saltwater than freshwater. But this assumption is incorrect for lead.

Fantastic analysis--thank you! yes, the corrosion properties of lead do seem better than I had originally understood.

The thing that I'm still struggling with is that this corrosion rate suggests that lead has an extraordinarily low corrosion rate, at or below that of stainless. But that does not comport with my experience with uncoated lead weights and, say, my stainless steel regulator. The dive weight is bangled to all hell and has obvious corrosion marks, while the regulator looks like brand new.

I wonder, do these corrosion rates only tell half the story of a just a lead object in water. What about mechanical action?

A tour of Moh's hardness tells us:

Material	Harness
Lead	1.5
Lead chloride	1.5-2
Lead carbonate	3-3.5
Lead oxide	2
Antimony hardened lead	3.0
Cupronickel coin	3.5
cupronickel oxide	5-6
Stainless steel	5.5-6.2
Chrome oxide	8-8.5

Given this picture, an abraded, manipulated weight like lead will be constantly deforming. This means that the passivation layer will be constantly cracking and flaking off when, say the weight rubs against a belt, sack, or wet suit. This case would be much worse for shot, as it will behave as a ball mill.

Hardened lead is a better choice from a mechanical viewpoint, as the substrate will deform less. I'm not sure how antimony affects the passivation surface mechanics.

Coins are better in that the underlying cupronickel is as hard as the hardest passive surface on lead, and the passive surface is even harder.

Stainless is even better as it is hard and its passive layer is very hard, so there is very little deformation, so the passive layer stays intact.

What do you think about this?

 

[pwoolf]

Most interesting 1st thread indeed — any idea if this would work for cupper plated steel (like EU cents)?
Or would galvanic reaction be bad?

This would corrode more quickly than cupronickel. Would it work, yes. Would it be ideal, no. There will be galvanic corrosion of the steel core if (when) the copper coat is breached. That said, it depends on how long you want to use the coins and how well you treat them. If you were to use them for a few dives, rinse and dry them, I don't think you would have any problem spending them again . It is an easy test!

 

[pwoolf]

I just use lead hard weights on a belt and they never seem to oxidize or change.
I think it’s a drop in the ocean compared to all the other problems the ocean faces.
Soft lead shot weights are a bigger problem, they trap water and lead oxide oozes out.

Lead weights do oxidize in water, as evidenced by the more extreme surface area case of the shot weights you mentioned. The highest concentration of any lead will be near the weight (i.e. you, your gear, and your dive operator).

I agree that the ocean faces a ton of challenges, many of which we have zero power to change. BUT, the good news is that replacing lead in our dive kit IS something we can do now. Coins made from marine-grade alloys like cupronickel are similarly priced to lead, last longer, and eliminate heavy metal exposure completely. Unlike other ocean challenges, this is one we can solve immediately at little to no extra cost.

 

[pwoolf]

@pwoolf that figure of 0.56 mm/yr is for distilled/de-ionized water that will leach ions from commercial lead and break it down faster. the next sentence is that the corrosion is reduced when higher chloride ion concentrations are present (aka salt water). From those rates, usage during dives isn't a concern as long as you don't lose the weights.

You are right, the corrosion picture for lead is more complicated than I originally thought. I just posted a discussion above about the relative hardness and effects of mechanical abrasion on lead, as that plays a role too.

As for things being okay assuming one doesn't lose the weight, the environmental risk is definitely less if the weight spends 99% of the time above water! The challenge here is that dive weights, by design, are ballast and intended to be dropped in an emergency. Given that their design intent includes a path to be dropped, then it seems worth considering the bottom of the sea as a potential endpoint.

 

[OMyMyOHellYes]

No one is arguing that ingesting lead is something you want to do. Pretty much everything on the face of this planet is "poison". There's the nasty hydroxic acid (dihydrogen monoxide or DHMO) as an example. It's everywhere in the environment and you likely experience exposure and even ingestion every day! Some folks occasionally find themselves totally immersed in the stuff!

Even oxygen is corrosive and toxic.

It is the concentration and amount of exposure over long lengths of time that would be of concern.

Even poison things occasionally have good uses, in the right place at the right time (see also water and oxygen).

Blanket hysteria of "OMG! Pb! Eeeek!" is over the top dramatics. If you work with a lot of it every day, yeah, it may be a concern. (I once worked at an indoor range and had a colleague that also smelted and cast lead bullets on a commercial basis. He had annual checks of lead concentration in his blood. Never crossed into a problematic concentration.) Slight, occasional contact? Just not so much of a problem.

If loading up the pockets with coin tickles one's fancy, then good on 'em. Carry on. But for the vast, vast large overwhelming likely almost total majority of folks walking around, or swimming under, Pb is just not a material threat or concern.

 

[pwoolf]

No one is arguing that ingesting lead is something you want to do. Pretty much everything on the face of this planet is "poison". There's the nasty dihydrogen monoxide (DHMO) aka hydric acid as an example. It's everywhere in the environment and you likely experience exposure and even ingestion every day! Some folks occasionally find themselves totally immersed in the stuff!

Even oxygen is corrosive and toxic.

It is the concentration and amount of exposure over time long lengths of time that would be of concern.

Even poison things occasionally have good uses, in the right place at the right time (see also water and oxygen).

Blanket hysteria of "OMG! Pb! Eeeek!" is over the top dramatics. If you work with a lot of it every day, yeah, it may be a concern. (I once worked at an indoor range and had a colleague that also smelted and cast lead bullets on a commercial basis. He had annual checks of lead concentration in his blood. Never crossed into a problematic concentration.) Slight, occasional contact? Just not so much of a problem.

If loading up the pockets with coin tickles one's fancy, then good on 'em. Carry on. But for the vast, vast large overwhelming likely almost total majority of folks walking around, or swimming under, Pb is just not a material threat or concern.

You raise good points about dose and exposure. However, the science on lead is quite clear - unlike water or oxygen, there is no known safe level of lead exposure. The CDC, WHO, and EPA all emphasize this, particularly because lead bioaccumulates over time.

For divers, the risk isn't theoretical. Regular handling of lead weights leads to hand-to-mouth transfer and equipment contamination. Dive operators who handle hundreds of weights daily face even higher exposure risks.

Since we have alternatives like cupronickel coins that work just as well, why accept any unnecessary lead exposure? It's not about hysteria - it's about making simple, practical choices that eliminate risks when we can.

 

[crofrog]

Why not use gold, or tungsten.