Analysis of the Black Gunk on Atomizer Coils

[kinabaloo]

A significant downside with a pure piezo approach is that the mist it creates will feel cool as opposed to warm. Perhpas the liquid can be warmed first but that warmth will be gone i suspect before the mist reaches the mouth. The reason for going with heating coils / vapor rather than piezo / mist might well have been because it better simulates smoking / is more pleasant, rather than cost as people have tended to assume.

ps : the tin might be coming from a tin coat on the nichrome wire. http://www.eng-tips.com/viewthread.cfm?qid=5078&page=2

 

[breakfastchef]

Maybe I am off base, but it seems to me that anything we can do to ...... the build up of carbon on the heating element is our best choice to increase the longevity of atomizers. A quick rinse in warm water each and turning the atomizer upside down to drain overnight is the easiest, preventative measure I can think of.

I had my first atomizer fry this week. When I took it apart, the material inside the heating coil was black and brittle. I cannot imagine anything reviving wicking material once it has reached that point. This particular atomizer was only dripped using a variety of smoking juices.

 

[exogenesis]

Just as a matter of interest,

I forgot that I had evaporated the some of the same e-liquid on piece of metal sheet,
and analysed that as well.

Analysis showed a far 'cleaner' makeup compared to the 'burnt' coil gunk (not too surprising),
particularly NO metals, not even calcium,
but still quite a bit of silicon (from additives or plant extract material ?)

SUMMARY  
       % by atoms % by weight
Carbon    81       75
Oxygen    16       19
Metals     [SIZE=3][COLOR=red]0      0[/COLOR][/SIZE]
Silicon    2        5
Nitrogen   1        1

So some (most?) of the metals in the coil deposit must be coming from the coil itself,
especially the tin (from the solder blobs ?).

The sodium. calcium and potassium could be left behind during evaporation/concentration of the liquid,
I estimate a factor of 2000 or so in these tests,
but also maybe some from the atomizer coil as well.

 

[kinabaloo]

This is an analysis of the dry residue of your e-juice? Slowly evaporated, right. Or the evaporated liquid?

Why don't the sodium, potassium and calcium show up? Because the analysis is of the liquid after evaporation? Before and after would be nice (eek - more work)

What is the 2000 factor?

We need cleaner juices! Say NO to dry residue !!

 

[exogenesis]

The analysis directly above is for quickly evaporated, but not burnt e-liquid,
i.e. the clean residue after evaporation.
(not the re-condensed vapour we were PMing about).

I guess the metals don't show cos it needs a 2000x concentration
to get a detectable amount of them,
or they are not present in the liquid itself, but come from the coil.
Probably a bit of both.

2000 is my very approx. estimate of 2ml e-liquid converted to 1 cubic mm of coil gunk,
i.e. the residue left after vaping 2ml on a hot coil.

Actually I though that showed the liquid it to be very 'clean',
if you dont burn it,
or contaminate it via a hot wire with solder blobs.

 

[kinabaloo]

Exogenesis - The carbon and oxygen are showing as with inorganic bonds?

Likely, the dry residue is mostly flavourings.

At present the flavorings used in juices, including those bought from vendors i imagine, are the flavourings made for food where dry residue is not an issue. If juices were made with flavorings with no dry residue, we would have far less of a problem with atomizers getting deposits and the need to clean them / replace them so often.

 

[exogenesis]

Mostly organic bonds it seems.

Maybe thats true about most of the residue coming from flavours,
perhaps later I'll try this again several times with:

1 pure VG
2 pure PG
3 'flavourless' e-liquid probably TW's
4,5,6... loranne flavours straight from the bottle, or perhaps 1 in 3 with PG,
(I've got some non-oil, 'non-sugar' ones I don't like much)
then ditto, but sugar containing ones
then ditto, but oil containing ones

Trouble is it takes at least 2days to get 10 ml of liquid through the 'autosmoker',
in order not too have it flooding, or running dry too long.

 

[kinabaloo]

Atomiser death - new theory

We all know that atomizers eventually die and it was long believed, reasonably enough, to be that the fine nichrome wire broke after the repeated stresses of expension and contraction, plus getting thinner as it slowly gets thinner with age.

Sun created a new theory about the final death - through examining many deceased atomizers he noticed that the nichrome wire had been disconnected at the the solder joint; his theory being that as the deposit on the coil grew bigger, it eventually pulled out the wire from the joint.

I think this may play a small part sometimes, but is not the main reason.

A well-soldered joint could not be pulled apart. Unless ... the joint had become weakened.

I believe the solder joint is weakened chemically (perhaps aided by heat) by the juice/vapor. In particular, tin is leached from the solder joint making it much softer and the join looser. Eventually, the electrical connection is lost (and the nichrome wire might even remove its leg from the joint to take up a more comfortable position (i.e. not necessarily with any great force exerted by the deposit growing in size).

The evidence for this - and also the inspiration, though it took a day for the implications to become apparent to me - was discovered by Exogenesis in his analysis of atomizer coil deposits (http://www.e-cigarette-forum.com/fo...12335-analysis-black-gunk-atomizer-coils.html). The results showed an unusual amount of the element tin within the deposit.

A possible solution is for silver solder to be used for connecting the nichrome wire heater coil.

It remains uncertain what part of the juice causes the leaching of tin and by what reaction or other effect.

Exogenesis - yes, that's a lot of work! Could you use smaller samples for analysis or is 2 days worth the minimum can work with?

 

[exogenesis]

Good theory, certainly a lot of things can happen at a joint
between two different metals, chemically speaking.

The solder blobs are so large in comparison to the thin nichrome
that if anything I'd hazzard that the wire itself would weaken at the joint.

I like to get a close as possible to real vaping on the auto-vaper,
so getting a reasonable encrustation of gunk is the aim.
Actually the OP was a little light on 'crust depth', so I'll probably
run analysis again when more liquid has been used on this coil.

(assuming the wire etc last that long)

 

[kinabaloo]

Although i have found reference to tin, among others, sometimes being used to thinly coat nichrome wire, i doubt it is used on our nichrome because it would likely lower the resistance too much. Instead, it is coated by enamel (at least the ones i have are, 901s). The reason for a coating presumably because nichrome otherwise gains a thin oxide layer though since that would be protective, like with annodised aluminium, i'm not sure why this is sometimes done. In the case of the enamel it is just for electrical insulation, for winding overlapping coils and such.

I have not found mention of a tiny amount of tin being part of the nichrome alloy as yet, but it's a possibility. Solder, of course is a much softer alloy so more likely the source.

I am looking into what might attack solder joints - acids might, even VG/PG might have some effect, perhaps on the flux. Any thoughts?

Thinking about it, the maufacturers probably avoided lead based solder and used the Tin-copper-silver variety. So an alternative solder to avoid this problem might need consideration of another alloy.

Exogenesis, perhaps as you alluded, the juice sets up an electrochemical reaction at the join between the wire and the solder. Something like: tiny electrical current because two metals in contact causing an electolysis in which the tin goes into solution.

 

[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.