E-cigarette chemistry and misinformation

[Templar1191]

Hello, My name is Templar. I want to start a thread talking about the chemistry and other scientific sides of e-cigarette usage. I want to cover general e-cigarette chemistry, focusing heavily on the chemical reactions that occur between and to e-juice and the metals atomizer coils are made from.

Atomizer coil metals:
Any kind of metal that has a current passed through it to produce heat, quickly and on-demand.
Stainless steel (~75% iron, 15% nickel, 7% chrome, 2-3% molybdenum) (SS), Nickel 200, kanthal(Iron/chrome/aluminum alloy), Nicrome(80% nickel, 20% chrome), and titanium. There has been a lot of information floating around about exposure to nickel and other metals by using coils made with these metals.

There would be one main method of exposure of metals from these coils. Unless you like to drink your fluid while your vaping, it is unlikely that swallowing Titanium or nickel compounds would be your exposure. How is it possible for you to get exposed to these metals?
Vaporization of the oxide layer on the metal when it heats up.

Passivation/oxidation layers
Most metals react with oxygen in their elemental (metallic) state. Nickel forms nickel oxide, titanium and aluminium oxides are some examples of protective oxidation or passivation on metals. Rust off steel or iron based alloys (what you see on red/orange rusty metals) is an extreme form of an oxidation layer. However, unlike Nickel, Titanium, aluminium, chrome, silver, the oxidation layer on ferrous metals is NOT protective. It does not adhere well to the metal and flakes off, causing erosion of iron/steel metals.

The basic reaction is any of the above metals, e.g. aluminium + oxygen(air) -> oxide layer
Oxides that form these oxide layers for these species are generally very stable. For example, aluminium metal melts at 1200F but aluminium oxide (the oxidation/passivation layer, or film) melts at 3600F. Aluminium oxide boils (readily turns to vapour) at about 5400F. These temperatures are HOT. Chrome is similar, it melts at 1900C, its oxide which is green, melts at 2450C, and boils at 4000C or about 7300F.
Do you see the pattern here? In order for a metal oxide to become a fine particle you can inhale, it needs to start getting close to its melting point (elemental metals dusts or particles will never be produced below 300-400C(750F) and react quickly with air to form oxides)

Titanium oxide, forms on titanium coils:
Melting point 1,843 °C (3,349 °F; 2,116 K)
Boiling point 2,972 °C (5,382 °F; 3,245 K)

Nickel, Titanium, aluminium, chrome, silver all form protective oxide layers that are formed after an initial oxidation/reaction period (when metal is first exposed to air). These thin, sub 1 micron thick oxide layers from common coil materials outlined above adhere strongly to the metal, stopping further oxidation. They themselves are highly unreactive.

Titanium/Nickel/Kanthal/Iron+chrome alloys and stainless steel all form these tough, unreactive and non-volatile oxide layers.

It is unlikely for coils to reach 300C during usage, let alone 600C required to get metals beginning to glow red, and thus reacting more with the oxygen.

I have engineering qualifications focusing on process and industrial engineering. I want to add more to this thread over the next 2 days so I can continue to fill in blacks for people getting scared about nickel exposure (quite bad if you ingest, absorb or inhale specific chrome compounds) and titanium, among others.

 

[retired1]

Moved to Wick and Wire from General E-Liquid Discussion

 

[Templar1191]

So, I am no longer as busy. Let me continue.

SHORT SUMMARY OF ABOVE POST: exposure to metal group compounds from a coil below 200C is highly unlikely due to non-volatility and passivating nature of protective oxide layers.
This goes for Chromium, nickel, titanium.
While chromium and nickel do have toxic compounds (NiCl2, Cr 3+,5+) they will not form from the incredibly mild (not acidic or basic; think acidity and bases and juice cooled!) conditions on a coil head with cotton wick. NOTE: while the vapour wont contain significant traces of toxic compounds, the wick juice may! Do not let it get in your mouth.

NOTE: excessive dry firing coils could result in more oxide layer generation, which may flake off into wick juice. Just take the same precaution as above.

NICOTINE as a catalyst
Nicotine does have some basicity. What do I mean by this? Sodium carbonate (washing power) is a less caustic and basic base than lye (sodium hydroxide).
Both basicity and acidity(think battery acid) can catalyze chemical reactions; they will occur at lower temperatures and more products will be formed than without the acid/base catalyst.

Nicotine base, nicotine oil are in the freebase form in juice. Tobacco contains nicotine in salt form for the most part. Without getting too technical; nicotine oil vaporizes much better than nicotine salt (think liquid vs crystalline solid). However, as the pKa of nicotine is about 3.15, water is about 10 and battery acid is about -8. Its a special log scale so battery acid is hundreds of times more catalytic to reactions(acid/basicity scale), and water at pKa 10 has no basic or acidic catalytic ability.
Nicotine is unlikely to catalyze bad reactions on the coil.

Pyrolysis and decomposition of e-juice: Juice + heat + air (oxygen) = crap
It is a known fact that wicks foul up. Fouling of wicks/coils is due to pyrolysis, reaction or decomposition of ingrediants in the juice. Pyrolysis and decomposition is bad for ecigs; its like the smoke you get off wood when it gets really hot.

Juice gets hot, pyrolyses and reacts a tiny amount (if it was bad your coils would look like the inside of a chimney!) to form gunk. It is more likely when:

1. Bad juice: the juice contains cheap, (probably bad) additives and flavours that react at the higher temperatures with other compounds to form "polymers". Imagine a molecule of nicotine and a molecule of flavouring reacting together. Think of this as similar to soot in a fire place... but nowhere near as bad!
2. Coil temp: hotter coils mean more Juice + heat + air reactions. Simple. More clouds = more gunk. Try to get around this by building larger coils; this way you get more area to vaporize the fluid to make up for a lower coil temp. Drawing in a drag for a longer period will give thinner clouds, but the lower temperature reduces fouling of the coils. I have tested this myself with sub ohm coils (UWELL crown, Aspire atlantis). Regardless of the fluid, coils stay good for longer (better flavour and less colouring (gunk) of the juce in the tank) when used at lower powers/wattages, but thinner clouds and longer hits.
3. Wicks: how wet??: try to keep coils as wet as possible without leaking/drinking the juice while inhaling. Keeping the coil wet and the cotton saturated will supply more juice to cool the coil as it boils. Water in a jug wont reach over ~100C; it limits the temperature of the kettle by boiling off. Similar effect with e-juice, but boiling point is 180C for PG and 290C for VG (pure) at atmospheric pressure.
4. VG OR PG??: VG is sweeter, gives thicker clouds, but boils 100C higher than PG. This means: more reactions, more gunk, more bad stuff in the vapour. Pg has a lower boiling point and less reactions. But the sweetness and cloud thickness is an ok trade for people

I have asthma, so I am very acutely tuned to how these vapours effect my lungs. I have noticed that since I started moving to lung instead of mouth hits the irritation of the lungs has increased, likely due to warmer and more vapour. Try to get regular exercise to keep the lungs working well. 15-20 minutes a day. Honestly, its nothing, do it on an exercycle in front of a YT video; go for a run, play some sport. If your lungs are tigher than they used to be, of you're getting lots of mucus and coughs, back off on the clouds.

More soon.

 

[Templar1191]

So I had a big post I had written out here that got deleted when somebody turned my computer off at the wall.

Propylene glycol performs its role as a more volatile and lower boiling point liquid to "dilute" glycerine with. Glycerine MUST be distilled under vacuum in industrial settings to separate it, eg during soap manufacture. If glycerin boils at 290C, it will decompose and degrade, significantly. This is in the form of bulk liquid; so the high surface area of a coil and high air flow will increase this decomposition and also result in oxidation as well.

Propylene glycol boils at ~190C, about 100C lower than glycerin. This will lower the boiling point of the e-juice depending on composition. Furthermore, the boiling of the PG will help volatilize the glycerin and other flavours. Think of it as a carrying agent, to help "carry" vapours of the e-juice.

Boiling high VG or pure VG juice during vaporization means high temperatures. Decomposition and oxidation of glycerin means formaldehyde, acetaldehyde, acrolein etc. All the nasty stuff.

Remember, some flavouring agents will decompose with the glycerin at high temperatures. It is not just the glycerine decomposing and oxidizing that will cause problems.

Try to aim for at least 20% PG fluids. Basically. For clouds, the trade off will be thinner vapour with higher PG but a lower BP and thus lower coil temperature.
I have had some experience with different coil materials now.

Coil length: having longer single wire coils is recommended. This increases the effective heating area for vaporization. More coil area = lower temperatures.

Clapton Surface area: claptons have much higher surface area than single wire coils. This is a double edged sword. On the one hand, the thinner wound wire will act as a heat sink to evenly distribute heat from the core current carrying wire, to provide more even heating and increase coil area. More area and even heating means, in theory, lower temperature wire, and less decomposition of glycerin etc. In practice, claptons provide great flavour and vapour production, but the increased surface area will clog easier than single wire coils with decomposition of juice ingredients.

I have personally switched over entirely to claptons. The catalytic activity of kanthal and SS316 of my coils should not be significant. Dark fluids, or fluids which darken quickly in sunlight, will clog up the coil more readily. If they are cleaned somewhat regularly and the cotton replaced, the issues should be minimal.

Titanium
So titanium was an interesting coil material. Basically, I concluded it could be dry fired to ensure even heating, but this should be done outside to avoid any vapours. The oxide that formed on the surface after dry firing flaked off in large mm size chunks, and I think that should be brushed off and washed prior to using the coil.

I heated some Ti metal up to 1300C using a bunsen flame. It did not combust, even when heated to yellow hot. When I was dry firing it, when it started to move into white hot, it would stay hot for longer even after current had stopped. I assume this was a battle between oxide formation killing the oxidation reaction between Ti and the Ti achieving high enough temperature to being burning/oxidizing in the air.

Flavour did not seem remarkable over stainless steel, and I found that even firing of titanium was harder than with SS316. I have since swapped out my Ti coils for SS ones.

Nickel
I received some Ni200 wire but I have not tried it out yet. The reason I haven't is because of several things.
- Nickel oxide vapours and juice contamination. Even thought they are very non-reactive and excellent passivating oxides, I dont want to be dealing with their vapours while dry firing. A small amount of the nickel oxide will be dissolving in the fluid, especially if the fluid has a very tart flavour, and I dont want to risk getting nickel contaminated fluid in my mouth (presence of weakly acidic flavourants)
ALL soluble forms of nickel are toxic(Nickel ions)
- User reviews have not been glowing for nickel. If there is much benefit over the very inert SS316 or Ti coils, it will probably be discounted from the use of a compound that is toxic to the human body when absorbed.
- Nickel will have more catalytic properties than Ti or SS316 at 200-300C, catalysing more reactions. Nickel is a very catalytically active metal, and finds use in hydrogenations, dehyrogenations, and various other chemical reactions occuring at 250-700C in industry.
- I have moved over entirely to home made SS316 claptons and some kanthal clapton wire I have received and flavour is much better all round (though I personally prefer the SS316 clapton coils at the current time).

Kanthal
I bought some kanthal wound core clapton from geekvape. Was very economical. I have not been as pleased with flavour on the SS316 clapton I have. However, the kathal clapton has much much higher surface area (tighter wound, thinner wire around the spiral wound core).

Kanthal actually has a similar composition to SS316.
kanthal: 20-30% chrome, 4-7% Aluminum, balance iron
SS316: 17% chrome, 14% nickel, 3% molybdenum, balance steel and other minor harmless additives

In the scheme of things, the only thing that should be worrying about kanthal is the aluminium.

Chromium

Unlike nickel, chromium is only highly toxic and carcinogenic in either hexavalent form, or in high concentrations (egCr 3+). Cr(VI) or Cr 6+ or hexavalent chromium is a highly oxidized form of chrome that takes a yellow/orange colour. It is a strong oxidizer (see sodium dichromate, sodium chromate) but will not form under coil operating conditions 200-300C.

States of chrome 3+, 2+ 1+ and 0(metal) are much safer, and the body actually requires small amounts of chrome for enzymes and other biological uses. These forms of chrome are much better dealt with by the body as they naturally occur. There are various biological checks which reduce the amount of these 4 types of chrome entering the body.

Cr 3+ is the most common form of chromium and will likely be on of the oxidation states of the chrome oxide or protective layer on your chrome alloy coil wire. It is highly insoluble in water. This means that not only is it a strong passivating layer to prevent further oxidation of the coil material during operation, but it will also not practically dissolve in the e-juice.

To compare:
Acute toxicity of hexavalent chromium : 50-150 micro grams per kg (how much chrome would you need to swallow in one go to die 50% of the time per KG of body weight)
Acute toxicity of Cr 3+ : 1500-3300 micrograms per kg.

In summary: Cr 3+ oxides on the coil arent volatile at 200-300C, arent potent toxins or carcinogens, are encountered naturally in water and food, are required by the body in trace amounts (30 micro grams per day for a man), are not absorbed readily due to their insolubility, and are all round fairly safe.

Exotic coil materials:
I am very interested in trying certain noble metals and other highly non reactive metals for coils. I have some ideas, but I wont post about them until theyre working. I am looking for metals which are:
- Non toxic or good biocompatability
- Form oxide layers that are protective, inert, non-volatile and not a dust hazard (like titanium dioxide)
- High melting points, good mechanical properties, not brittle
- Not catalytically active
- Workable resistances/conductivity (silver, gold, copper and aluminium have very low resistances, but are)
- Can be dry fired for adequate cleaning

 

[Rickajho]

Boiling high VG or pure VG juice during vaporization means high temperatures. Decomposition and oxidation of glycerin means formaldehyde, acetaldehyde, acrolein etc. All the nasty stuff.

What are the implications then for us people who are allergic to PG and in order to vape at all must avoid PG as much as possible, or eliminate it completely?

In so many words, what are the safest techniques to vape high VG/100 VG for those who have little choice in the matter?

 

[Templar1191]

An allergy to PG is really the strangest thing ever. Same with allergies some people have to metals. Chrome, nickel metals can produce allergies... very strange. I was under the impression it needs to be an irritating chemical or strange protein that causes allergies (pollen, formaldehyde, pollen, fur) but I guess not.

So back onto the issue of PG allergy... I'm sorry to hear that you have this.

The best thing to do would be try to keep your wicks and coils clean. Replace your wicks and clean coils more frequently than you would otherwise.

Impurities produced during vaping with either be emitted into the vapour as vapours themselves, or be absorbed back onto the wick. Formation of residues and darkening of the coil metal indicates that impurities will be accumulating there as well.

I would also encourage people to use TC coils (SS316 recommended) and see how much vapour they can get off the coils at as low a temperature as possible. Make sure the coils heat evenly. This is very important. A coil that doesnt heat evenly will produce hot spots which will affect the precision of your TC settings. A coil that heats uniformly, evenly, will result in a much more precise temperature control..

Therefore, for those who cannot use PG, I would suggest going for longer coils. If longer coils arent a possibility, use more coils. The TF RTA tank by smok has the option of 4 coils, but they are quite small. The resistance of the TF RTA tank I have is 0.16ohm so each coil should be about 0.64 ohms (kanthal claptons pre-installed). More coils for the same amount of vapour production as a single coil means either shorter operation time or less vapour production demand from each coil.

The idea of longer or more numerous coils is increasing coil surface area in contact with wick and fluid. With a higher surface area, you can get more vapour with a lower temperature. This is limited though, if you get nothing off a VG ejuice at 200C, increasing the amount of coil surface area at 200C with a pure VG juice may not make a significant improvement to vaporisation.

However, if you run one coil at 250C and get good vapour, maybe you can run a coil twice as long which heats to 230C and gets similar vapour production. That 20C difference is important here, and would likely result in less impurities.

That is all I can currently advise... cloud chasing with pure VG is not something I would want to partake in personally. Until research is conducted regarding cloud chasing setups I would be cautious. You can still get good hits without reducing visibility in your room to <30cm

BTW do you guys think I should start up a vape shop focusing on big clouds?

 

[Rickajho]

FWIW: PG allergy is far from unknown in the medical field. Ask any Allergist - allergic reaction to PG is not a rare thing in their field as it is present in many products. It can be especially dangerous in concentrated exposures as the carrier in anesthesia drugs, having the potential to result in months of debilitating nerve damage and extremity weakness and numbness. When I mentioned my reaction to using an 80 PG liquid within four days of vaping: chronic nausea that escalated to vomiting, transient intense outbursts of itching on hands, arms, and legs, ultimately leading to significant difficulty breathing and pondering a trip to the emergency room - my Allergist just headed for the computer and printed out case studies regarding PG allergy.

 

[Hitmetwice]

Allergies are not something I have fortunately. They must be a real pain to live with. Especially for those that are allergic to many things.

PG really is very inert and GRAS
unless of course one is allergic.

Propylene Glycol (PG) Safety

EDIT...Great idea for a thread BTW. Thoroughly enjoying the read. Cheers OP.