Analysis of the Black Gunk on Atomizer Coils

[exogenesis]

The electrolysis thing was what I was thinking of,
and I think you have to use 'acid' flux to solder nichrome properly?
So the potential is certainly there.

How do you know your wire is ceramic coated, none of mine have been afaik.
The oxide layer is a plus I'd have thought (gives chemical resistance as well)
anyway the coil is 'disperse' enough that no loop touches another.

As long as the migrated tin (& other metals) stay in the crud,
and dont get into the vapour (unlikely?), then that's fine with me.

[kinabaloo]

The problem is not that the tin is being inhaled but that the solder joint gives out killing the atomizer; unless one wants to dismantle and resolder - no easy matter!

Yes, normally an acid flux.

Er, I said cermaic ! Oops, i meant of course enamel. Not quite the same but share quite a few letters

I have just remembered that some people have reported weak or intermittent functioning of their attys - these could also be explained by a deteriorating joint (but not a sudden snap).

If you think about it, the steel is also in contact with the fluid. Could be some complex electro-chemistry going on in there. Perhaps some 'sacrificial corosion'?

[exogenesis]

I guess they clean the residual acid flux well, after soldering,
but I would guess still there's probably some small amount of trapped
acid/salts left at the nichrome/solder interface?

About electrolysis thing, I think it's the wrong word really,
I was meaning it in this sense:
'bi-metal corrosion', probably aided by any remaining acid/salts (giving an 'electrolyte'),
but this is in a strictly local sense, (no applied voltage is actually required)
not electrolysis across a large distance like electro-plating in a bath of liquid.

Possibly this exacerbated to a degree by the current running through the
wire possibly creating local micro-voltages,

See these tables of 'galvanic corrosion risk' & 'galvanic series',
which show nickel & tin is one of the mixtures which has this risk,
(nichrome may be a lot more resistant)
Also there's some things in here I don't fully understand
e.g. the difference between 'active' nickel & 'passive' nickel in the last table.

Bi_Metallic Corrosion ( Galvanic Corrosion )

Also see wikipedia.
Galvanic corrosion - Wikipedia, the free encyclopedia

But all this is just a possibility not observation (except in a few cases maybe),
perhaps if some more people with 'unrecoverable' atomizers had a look at
where (/if) the wire snapped / blew-out we'd have more evidence either way.

Either way certainly more of the tin from the solder is ending up in the coil gunk than I
would have predicted (see first post),
whether it's enough to weaken the wire joint is another matter.



OK, enamel not ceramic,
what makes you think the wire is coated with this ?
I did a search of this site for enamel, and can't find any evidence.

[exogenesis]

In case anyone's interested,
it turns out the ??? unknown peak in the OP is just another sodium peak,
so no mystery after all.

[kinabaloo]

Exo - when two different metals are in contact there is a tiny voltage generated, and presumably when connected by electrolyte too. I don't think we ned to worry about residual acid flux for this possibility, the juice will do fine in this regard. Yes, galvanic corrosion would be an accurate desriptor.

Heat from the nichrome wire plays a big part too, maybe the biggest - as solder melting point is not that high and it is in contact with the at-times red-hot nichrome wire (a soldeing iron is roughly the same temp as the coil, although the heat capacity of the coil is far smaller). We know tin is leached out - and can call it substantial judging by the size of the peak generated by the analysis of the gunk and considering the volume of that gunk in relation to the volume of the solder blobs.

The mechanical snap from deposit buildup seems to cause most atomizer failures, but there are a few where the atomizer becomes very weak or works intermittently - for these cases deterioration of the solder through leaking tin by some electrochemical means is implicated.

"whether it's enough to weaken the wire joint is another matter." It must weaken it, but by how much is open to question, and surely will vary according to juice and other factors. I think it occasionaly causes problems and atomizer failure.

WRT the enamel - my 901s have enamel coated copper wires from the battery connector to the nichrome wire. The enamel is of no significance.

[Heed]

Are you guys familiar with "tin whiskers"?

Whisker (metallurgy) - Wikipedia, the free encyclopedia

Slashdot | Tin Whiskers — Fact Or Fiction?

Just wondering if it might be this phenomenon or something similar at work. If the whiskers are drawn to the coil they might become part of the carbon buildup mass which would account for the tin content in the analysis as well as a weakening of the solder joint.

[kinabaloo]

Heed - interesting; not heard of this phenomenon before. But the growth of these whiskers is much too slow i think (a few mm / year). Unless something about the atomizer conditions potentiates the process. One of the stated activators is thermal stress; interesting, that certainly exists at the solder joint. We will have to keep an eye out for evidence of this ...

There's certainly some interesting science in this 'hobby'

[Heed]

Hmm, I hadn't thought about the growth rate.

I did read heat can be a contributing factor, so I suppose it's possible it acts as a potentiator, but I don't know.

[kinabaloo]

It is possible that this phenomenon is involved. The environment of the atomizer has nearly every stressor.

It might be hard to detect the filaments as they could well be very fine, and be very short to before breaking off. A microscope should be able to detect them though.

[markule]

Disclaimer: I don't even own an e-cig yet. I'm doing lots of research before entering into what could become an expensive hobby (modding) as well as nicotine source. So, I only know what I've read. I was also, once upon a time, a chemist, but haven't done much with that since getting my master's in analytical chemistry. That said:

Since a major component of e-juice seems to be Propylene Glycol, and several reports indicate that the gunk is black, bubbly, plasticy looking stuff, my first thought is an oxidized polymer of propylene glycol. Feel free to look it up, polypropylene and/or polypropylene glycol (wikipedia even has an example of the polymerization reaction). If so, that black gunk could well be, essentially, burnt low density plastic. Given the wide range of variables for heat, oxygen, concentration in e-juice, ect, it's not surprising that different people are getting different results from cleaners, since they may well be making different formulations of the plastic. Bad news is, this stuff isn't very soluble in much of anything. Ether would likely work, if you could get it. Since there are other threads for it, I'll post some cleaning ideas based upon my chemistry experience there.

On a more general note, organic mixtures plus heat often result in mystery black gunk in the chemistry lab. Cleaning that stuff off glassware can be a real pain and over the years I've tossed lots of glassware when it became easier to replace than try to clean. Much the same applies here, I'd bet.