Increasing ohm's on coils

[Alien Traveler]

Metal is tough, but not impervious to change, especially when subjected to high heat. As others mentioned, the coil metal breaks down over time.

Per Dr. Farsalinos (Dry-burning metal coils: is it a good thing?)

"Dry-burning the coils means heating them to temperatures well above 700oC (we have both measured temperatures under these conditions). This is expected to have significant effects on the structure of the metal and the bonds between metal atoms. This heat treatment in the present of oxygen will promote coil oxidation, change grain size of the metals/alloy, promote new bonds between metal atoms, etc. To this, we should add the continuous contact of the coil with liquid. The liquids may have corrosive properties on the metals, which could further affect the molecular structure and integrity of the metal. Finally, the vaper is inhaling the aerosol directly from the coil itself. All these factors may contribute to the presence of metals to the aerosol. Most materials that are used in e-cigarette products were not developed for this application. In this specific case, the resistance wires were develop and used as heating elements at high temperatures IF NO VECTOR can transport the metal / oxide particles to the human body. This not means that can be used in vaping in the same way."

I can't even imagine how much the coil has degraded with hundreds of dry fires.

FWIW, I tried cleaning nautilus bvcs (boiling, alcohol, etc.), and yeah, it was a little better than before cleaning, but not worth it to me. I've tried many times to dry fire and clean ss316 in rta's and it never tasted as sharp and fresh, or lasted as long as a new coil.

I can understand re-using a fancy, expensive coil, but it's not even worth considering for my simple round, spaced coils.

Dear Brewdawg1181, you have chosen the dumbest quote by Dr. Farsalinos.
Too bad when guys who have no knowledge in metallurgy try to comment on metals. You Dr. Farsalinos even does not know that metal does not have any "molecular structure" (they are crystals). Dr. Farsalinos may have some medical education, but he is complete nobody in materials.

 

[Alien Traveler]

Dry burning (as we do it) does not affect structure of coil materials (metals). It's just happens that temperature of dry burning is not high enough to get rid of all contamination. If our coils were made of platinum, we could heat them to very bright white temperature and remove everything and anything that stuck to them. We just cannot heat kanthal/nichrome coils to high enough temperature to clean them properly. And yes, I did a bit of "research" on it years ago.

 

[vaper1960]

I am not going to argue metalurgy (sp?) or molecular whatever (and yes, I'm into all that science) but wire is fairly cheap and coils are not hard to make (talking simple coils here) I don't think "dry-burning" degrades the coil much but (for me) it's an issue of my time and trouble vs saving a few bucks (actually cents) If I'm going to re-wick (which I also rinse everything with hot water and alcohol... ethanol) I will do about 2-3 dry-burns and then just replace the coil eventually. Besides all that, I wonder about the connection between the coil and the mounting screws... might be worth doing a new coil just for that (clean connection)
It is an impressive experiment... but not practical IMO. It's kinda like spark plugs in cars... yes, you can clean them (up to a point) but is it worth the trouble for all the work involved in removing/installing them?

 

[Brewdawg1181]

Dry burning (as we do it) does not affect structure of coil materials (metals). It's just happens that temperature of dry burning is not high enough to get rid of all contamination. If our coils were made of platinum, we could heat them to very bright white temperature and remove everything and anything that stuck to them. We just cannot heat kanthal/nichrome coils to high enough temperature to clean them properly. And yes, I did a bit of "research" on it years ago.

To be fair, in the article, Farsalinos says this: "To further explain my statement, I invited Pedro Carvalho a material sciences expert with good background on metal structure, composition and degradation." I guess it's unfortunate that he used the term molecular structure.

What you say is interesting, but raises questions. I'm no metallugist, but I do know that heat (at various levels) does change the structure of metals. Heat does cause enough change, obviously, to make ohms fluctuate (a structure change). Heat tempers steel (restructuring), and changes magnetism (restructuring). It only takes ~600F (reached with dry burn) to remove magnetism, so it's definitely changing. Vaping with liquid reaches 4-500F, and much higher firing without liquid. Annealing (restructuring the atoms) steel only requires to heat to a glowing point- which is exactly what we do when we dry fire. Part of the reason people dry fire & strum is to restructure the metal.

So let me ask, in simple terms: For 316L, for instance- if it's not changing, why is it no longer shiny after use & dry burn? I'm truly not trying to argue here, because I don't know enough about it. But I do know what I wrote above is true. So please explain the nuances I'm missing that make it possible that we're not changing the metal by dry firing, or even simply repeatedly firing in a 4-500F range? Are you saying metals never change, even with application of heat or contact with liquids?

 

[DaveP]

I gave up dry burning long ago. In just a little more time over dry burning, I can remove and replace the coil. With Rayon and SS316L I don't even get that yucky taste of a new coil like I did with Kanthal and Cotton (yes, I know the wicking is interchangeable between coil types).

 

[Frenchfry1942]

I just came to the realization that I have four identical tanks running and a flavor assigned to each. I guess that seems boring, but I have done what I think works for me and that is okay. Each tank and coil only experience one eJuice flavor.

Being a simple Kanthal builder who wraps for the same resistance, re-burning the coil, and scrubbing it with a small 2" wire brush (6" handle in the painter's section at Lowe's), the flavors stay pretty good.

Having favorite flavors and assigning a specific tank for each flavor works.

 

[Alien Traveler]

To be fair, in the article, Farsalinos says this: "To further explain my statement, I invited Pedro Carvalho a material sciences expert with good background on metal structure, composition and degradation." I guess it's unfortunate that he used the term molecular structure.

If Pedro Carvalho did not pay attention to "molecular structure", he is no material sciences expert. Sorry.

...
So let me ask, in simple terms: For 316L, for instance- if it's not changing, why is it no longer shiny after use & dry burn? I'm truly not trying to argue here, because I don't know enough about it. But I do know what I wrote above is true. So please explain the nuances I'm missing that make it possible that we're not changing the metal by dry firing, or even simply repeatedly firing in a 4-500F range? Are you saying metals never change, even with application of heat or contact with liquids?

There are some changes in austenitic SS after prolonged heating, like in grain size, . But it does not influence it's properties as a heating element. 316L is rated in heat resistance at about 1700F (900C), which is close to typical temperature of dry burning. Dark color after dry burning is due not to metal properties, but to contamination - cindered ashes of flavors, cotton and such. May be even of VG and PG (I am not sure).
A few years ago I took a look at a kanthal coil after dry burning; if you are interested it's here: Coil under electron microscope

 

[MacTechVpr]

Agree with @Alien Traveler that apparent surface differences with use are most likely attributable to accretion on wire surfaces of juice. Perhaps other sediments. A uniformly strain formed contact coil will retain its original (electrically) pre-oxidized appearance for up to 6 weeks depending on power applied and use. That's when I target changing them to make best use of their performance. However, I've had them yield acceptably well out to 6 months or more with disciplined low-power dry burn to limit surface accumulation. Keeping the wick clean, e.g. with timely replacement or dry burning if synth, helps a great deal.

So, no, I can't see any metal scaling as speculatively suggested as being a problem…unless the wire is physically abused. That merely damages the surface creating capture points for accretion much like a scratched Teflon pan. The layers of useful and quite thin oxidation as with Kanthal are extremely useful for the durability and efficient functionality of an element. So I'd say baby your winds and clean or dry burn faithfully.

Good luck.

 

[Brewdawg1181]

If Pedro Carvalho did not pay attention to "molecular structure", he is no material sciences expert. Sorry.

There are some changes in austenitic SS after prolonged heating, like in grain size, . But it does not influence it's properties as a heating element. 316L is rated in heat resistance at about 1700F (900C), which is close to typical temperature of dry burning. Dark color after dry burning is due not to metal properties, but to contamination - cindered ashes of flavors, cotton and such. May be even of VG and PG (I am not sure).
A few years ago I took a look at a kanthal coil after dry burning; if you are interested it's here: Coil under electron microscope

Just to be clear, even though it doesn't matter, but bothers you- Farsalinos wrote the article, after consulting with Carvalho. That could be Farsalino's mistake, but that's just a nit. The article doesn't really drive my decision not to dry fire.

None of this really matters to me anyway, since I treat coils as one-use disposable. But arcane information does interest me sometimes. The microscopic images are interesting, but don't really address long term metal degradation, having only observed 20 days and 3 dry fires.

And the heat resistance rating is kind of meaningless, really. For example, tungsten is used in incandescent light bulbs because of a melting point of >6000F. But they don't last forever. A light bulb rating is only the point at which 50% of a test sample is anticipated to fail. In fact, over time, particles of the tungsten leave the filament and deposit on the inside of the bulb, and enough tungsten eventually leaving the filament to the point that it fails. And that happens in a vacuum, with no liquid to affect the metal. Ratings for other products don't mean that there's no effect at all up to that point.

Anyway, thanks for the images. They look pretty cool.

 

[Rossum]

IYears ago someone here (@Rossum ?) took pictures of coils with an electron microscope. You could see all the damage. Tiny flakes of metal coming off the surface of the wire and so forth.

Nope, wasn't me.

I do have a fuzzy recollection of having seen those pics though.

They didn't bother me enough not to dry-burn my Kanthal though, nor did Dr. F's ramblings.

 

[Rossum]

I'm rebuilding every 8 ml or so (NET)

Needing to do that was one of the reasons I gave up on Boba's Bounty way back when; I loved the stuff, but it wasn't worth the hassle.

My ADV mod runs straight unflavored (65% VG). I go through 3-4 ml a day in that mod. The last time I re-wicked it was on January 11th (I keep a log).

 

[MacTechVpr]

@Alien Traveler was kind enough to re-post his pic's link — Coil under electron microscope — just a bit earlier.

Nice to see ya @Rossum take some time to break away from the reluctant resistance.

Good luck.

 

[Alien Traveler]

I rewick my coils 3 times. When a coil has been used for a while the metal degrades. After you dry burn it and give it a brushing it won't come up shiny any more. And you can feel the roughness of the metal with your finger. From my observations they seemed to be healthy enough after 3 changes, but more than that they started to get dodgy. That's with 28g wire at low power. I suspect high power would mess them up faster. Or maybe thicker wire lasts longer.

Years ago someone here (@Rossum ?) took pictures of coils with an electron microscope. You could see all the damage. Tiny flakes of metal coming off the surface of the wire and so forth.

They were not flakes of metal, but sintherized remnants of organic goo from half-burnt juice after it was dry burnt.

 

[englishmick]

They were not flakes of metal, but sintherized remnants of organic goo from half-burnt juice after it was dry burnt.

Thanks for the info. I remembered the pictures but I guess I forgot the words that went with them. To be honest I wouldn't have known whether I was looking at a string of iron atoms or a strand of hair. The pictures were cool though.

 

[AvaOrchid]

Well I don't really get the "mess up" part. It's just metal. Of course it won't be so shiny anymore due to the residue.

......What have I gotten myself into.... NEED NEW COILS!

The appearance of the coil isn't all that important however since we are using this to vaporize liquid into our lungs if the coils metal is degrading to the point where it's its pitting and it's got a lot of flakes coming off of it it would be better to change it out. I use a lot of different toppers so it's very rare that I use a product for more than a week. And I take the cotton out and clean the coil before I put my stuff away. So even though I'm changing out the cotton a lot I don't really think that my coil itself is degrading much because I'm not using it solidly so it's not uncommon for me to use the same coil that has been in a device for 3 months but that does not mean I've been using that coil for 3 months. Out of that three months I probably at most used the coil for 14 days and I believe that my relatively low wattage I'm probably not degrading that coil to the point where it's flaking off. It would take an extremely small Fleck of particulate metal to actually aerosolize and be able to carry through vaporized liquid however because coils are cheap there's not a great reason to use a coil past when it starts to degrade. And since we all don't have electron microscopes to examine our coils you kind of have to just judge it based on how much use you've gotten. I feel like 3 months of actual use would probably be the the longest that I would be willing to use a coil but in reality I usually get bored and want to rebuild it before then. Of course that's just my opinion based on just a very little a few anecdotal stories and a little bit of advanced photography I guess from other sites. I'm just pointing out that the problem isn't really what it looks like the problem is you don't want to use a coil that is degrading to a point where it could possibly become particulate matter so I don't know if that actually happens and there's been a lot of false information about that sort of thing or more logical and more likely threat would actually be a piece of your coil coming apart and causing a hard short