Heating coil material degradation and potential health effects

[TigoleBitties]

Hey All,

I took some time to do a little research today about common materials used in heating coils and potential health concerns. I'm still digging for more info but was not encouraged by this article I came across today.

Quick summary, it investigates how two popular alloys, kanthal and nichrome can degrade when heated via passing currents through them in typical coils. They examine both dry coil heating and coils immersed in liquids.

Here's an excerpt:

With dry heating, chromium composition in the Kanthal wire in contact configuration decreased from 19.72–21.03% to 13.47–15.53% after one heating cycle and to 5.76–8.54% after 50 burn cycles across the three gauges (Figure 4). After 150 heating cycles, the final chromium composition was 4.55%, 2.54%, and 1.86% for 30, 32, and 34-gauge wire, respectively. The iron composition decreased from 59.59–66.62% to 33.52–43.17% after 1 heating cycle and to 14.85–23.50% after 50 heating cycles. After 150 heating cycles, the metal content for nickel was 23.50%, 14.85%, and 22.15% for the three gauges, respectively (Figure 4). The total loss of metal in a contact configuration was between 15.27–19.17% for chromium and 52.48–58.26% for iron.

What surprised me is not only the amount of degradation over time but the fact that the coils still degrade appreciably even when kept at "low temps" around 300C when immersed in liquids during electrification.

Wanted to share this and get opinions.

 

[Canna Chameleon]

Seems like a study of those coils in liquid nicotine at higher temps than we use for dry herb doesn’t really equate.

Find a study about testing the material at 200c in normal air mix, then ask me again.

 

[TigoleBitties]

Seems like a study of those coils in liquid nicotine at higher temps than we use for dry herb doesn’t really equate.

From what I read the liquids tested weren't liquid nicotine but vegetable glycerin and propylene glycol so I'm not sure you read the paper. The thing that bothered me is that for the test in these liquids (wet media), the coil temps are right around 200C and the degradations still occur. Of course, as the coils are cooled by the surrounding liquid in this case, the current passing through them is likely substantially higher to maintain 200C so this is hard to compare dry coils heated to lower temps.

In the convection heaters we typically see, the coils must be significantly higher temp than 200C to create hot air at 200C at some distance from the heater. It's not an encouraging result from my perspective.

figure

 

[Canna Chameleon]

From what I read the liquids tested weren't liquid nicotine but vegetable glycerin and propylene glycol so I'm not sure you read the paper. The thing that bothered me is that for the test in these liquids (wet media), the coil temps are right around 200C and the degradations still occur. Of course, as the coils are cooled by the surrounding liquid in this case, the current passing through them is likely substantially higher to maintain 200C so this is hard to compare dry coils heated to lower temps.

In the convection heaters we typically see, the coils must be significantly higher temp than 200C to create hot air at 200C at some distance from the heater. It's not an encouraging result from my perspective.

figure

I’m not sure you know what I meant by liquid nicotine.

E-liquid is made up from just a few different ingredients: Propylene Glycol (PG), Vegetable Glycerin (VG), water, flavourings and nicotine. E-liquids typically feature both PG and VG, with one of the two often more dominant than the other.

link

In the convection heaters we typically see, the coils must be significantly higher temp than 200C to create hot air at 200C at some distance from the heater

the distance from the coil to the load in any of those vapes you mention is a few centimeters. I’m not convinced you have even a close comparison.

However I’m happy to take all your kanthal coiled vapes off your hands to dispose of them properly.

 

[TigoleBitties]

I’m not sure you know what I meant by liquid nicotine.

E-liquid is made up from just a few different ingredients: Propylene Glycol (PG), Vegetable Glycerin (VG), water, flavourings and nicotine. E-liquids typically feature both PG and VG, with one of the two often more dominant than the other.

link

Ok, guess that explains why the study used that.

the distance from the coil to the load in any of those vapes you mention is a few centimeters. I’m not convinced you have even a close comparison.

I'm not saying I'm convinced by this one study either but I'm considering the evidence. Not sure what evidence there is to the contrary that the comparison isn't close. My Prrl Neo has a typical kanthal coil that glows for a convection heat source a small distance from the herb.

I've read that such a glow means temps around 1000C which I think fits the dry air temps in this study unless my numbers are wrong.

However I’m happy to take all your kanthal coiled vapes off your hands to dispose of them properly.

Hey, I love my vapes as much as the next FCer so there's no hyperbole here. Trying to have a solid discussion based on the facts as I understand them.

 

[Canna Chameleon]

Trying to have a solid discussion based on the facts as I understand them.

Always willing to have data and fact based discussion. I just think your study isn’t the best to use.

This one is much better but still doesn’t allow the conclusions to be drawn.

However, it is difficult to conclude that nanoparticles produced from e-cigarette coils can cause severe toxic effects because of limited information.

Not sure what evidence there is to the contrary that the comparison isn't close.

The results of this study need to be viewed in the presence of several limitations. Particles were generated using a modified e-cigarette system, under controlled conditions. The air supplied to the system was filtered and dehumidified. Since humidity affects the oxidation rate of the metal, e-cigarette use under normal operating conditions may exhibit a different particle generation rate.


I‘d say that’s evidence that the rate of oxidation in your example isn’t valid for our use cause because of the liquid testing.

 

[TigoleBitties]

Always willing to have data and fact based discussion. I just think your study isn’t the best to use.

This one is much better but still doesn’t allow the conclusions to be drawn.

However, it is difficult to conclude that nanoparticles produced from e-cigarette coils can cause severe toxic effects because of limited information.

Thanks, I'm gonna give it a read.

Always willing to have data and fact based discussion. I just think your study isn’t the best to use.

This one is much better but still doesn’t allow the conclusions to be drawn.

However, it is difficult to conclude that nanoparticles produced from e-cigarette coils can cause severe toxic effects because of limited information.



The results of this study need to be viewed in the presence of several limitations. Particles were generated using a modified e-cigarette system, under controlled conditions. The air supplied to the system was filtered and dehumidified. Since humidity affects the oxidation rate of the metal, e-cigarette use under normal operating conditions may exhibit a different particle generation rate.


I‘d say that’s evidence that the rate of oxidation in your example isn’t valid for our use cause because of the liquid testing.

The testing of electrified coils immersed in liquids was shown to leach metals into the liquid in the study I originally posted but we as dry herb vapers maybe don't care so much about this use case.

However, the evidence in both papers shows that dry (kanthal, nichrome) coils shed undesirable metal particles at glowing temps which is often the case in our convection dry herb vapes.

From your paper:

Nanoparticles generated from e-cigarette coils may exert adverse health effects on individuals who inhale aerosols from the e-cigarettes. These nanoparticles are able to penetrate into the interstitial space and elicit an inflammatory response (Oberdörster et al. 1994; Srinivas et al. 2012). Nanoparticles also translocate from the lungs to the lymphatic system, where they accumulate in the tracheobronchial lymph nodes (Srinivas et al. 2012; Takenaka et al. 1986), and the circulatory system (Takenaka et al. 1986; Miller et al. 2013), where they accumulate at the site of atherosclerotic plaque build-up (Miller et al. 2013). However, it is difficult to conclude that nanoparticles produced from e-cigarette coils can cause severe toxic effects because of limited information. To consider the potential toxicity of metallic nanoparticles in humans, more detailed information such as mass based dose, chemical form, solubility, and surface area of particles should be analyzed. After characterization of nanoparticles, further research is needed to assess the effects of inhaled nanoparticles from e-cigarettes on the respiratory and cardiovascular systems of e-cigarette users and others who may be exposed to e-cigarette emissions.

I interpret this as - yes these metal particles are created and we know they aren't great but there's no smoking gun as of yet they'll harm you without more study. Doesn't make me feel too reassured in combination with what my paper also concludes.

I'm starting to feel a bias towards ceramic heaters or ceramic coated coils as a hedge against the downsides of high temp coils for dry herb vaping.

 

[XpeeN]

This one is much better

First, I commented about this paper at another thread:

About the paper, I wonder if they changed the coil after each experiment (or even for each case) or used same coil for a period of time (beside the 1st exp that they had to change to different ohms). My guts tells me they switched after at least each experiment, if not after each case, which leads to this point:
I doubt that the researchers did a burn-off before the experiment; that might change the results importance significantly and might make this paper irrelevant as everyone who installs a coil either do a burn-off or have 0 experience. You can also see in Fig 2(d) for example (and at other Figures there) that the number reduces as time goes by, which let me to thinking no burn-off was done at all and a fresh coil was installed each time.
If I'm correct, the question should be if a coil stays in good shape after a good burn off and right usage, or more precisely, when does the metal oxide layers that got formed get damaged? (as I said above, AFAWK with ss316L, the layers starts to get damaged around 500C, but if I recall correctly Kanthal A1 is even better in that regard and can be used above 500C without degradation, which can be enough for our usage, but it depends on the heater.)
As the quoted paper stated:

"One finding of interest was the steep decrease in the TNC over the course of the sampling period. This effect was consistent across the various operating conditions (power, resistance, and duty cycle). A possible explanation for this observation may be the formation of a metal oxide layer on the surface of the heating coil (Boggs 1971; Prescott and Graham 1992; Sauer et al. 1982; Sundberg et al. 2004). When Al alloys undergo oxidation, they develop layers of protective alumina on the surface (Sundberg et al. 2004; Boggs 1971). Any breach in this layer allows for oxygen to contact the metal underneath that layer, resulting in the formation of Fe oxide (Boggs 1971). As this layer is formed, further metal evaporation, and particle generation, would be decreased."

Seems like a study of those coils in liquid nicotine at higher temps than we use for dry herb doesn’t really equate.

Find a study about testing the material at 200c in normal air mix, then ask me again.

the distance from the coil to the load in any of those vapes you mention is a few centimeters

These things depending on your heater.As @TigoleBitties stated, I'm sure your impcognito's or my glow's coils reach well above 200C to vaporize at 200C, and there are vaporizers that relay on their heater to glow when vaporize. TM2 or splinterZ in the other hand? not as high (although I have no idea the actual temp they really reach). If we're talking about pure convection, it's also a question of surface area and the air's exposure time to the heater.
Didn't read the paper yet so I can't comment on that for now. I can just say, for the sake of discussion, that the general consensus is that things starts to go bad when the metal oxide layer, that get formed after a good burn-off, starting to get damaged (which happening at different temps with different materials). So manufactures and DIY people need to take that into account.

 

[Canna Chameleon]

First, I commented about this paper at another thread:








These things depending on your heater.As @TigoleBitties stated, I'm sure your impcognito's or my glow's coils reach well above 200C to vaporize at 200C, and there are vaporizers that relay on their heater to glow when vaporize. TM2 or splinterZ in the other hand? not as high (although I have no idea the actual temp they really reach). If we're talking about pure convection, it's also a question of surface area and the air's exposure time to the heater.
Didn't read the paper yet so I can't comment on that for now. I can just say, for the sake of discussion, that the general consensus is that things starts to go bad when the metal oxide layer, that get formed after a good burn-off, starting to get damaged (which happening at different temps with different materials). So manufactures and DIY people need to take that into account.

I remember seeing one time that @FearAndLawyering had thermal camera readings of the Cosmic X, which uses SS mesh.

Betting he can provide data on actual temps instead of us guessing


https://fuckcombustion.com/threads/cosmic-xtractor.51740/post-1628796

 

[FearAndLawyering]

I remember seeing one time that @FearAndLawyering had thermal camera readings of the Cosmic X, which uses SS mesh.

Betting he can provide data on actual temps instead of us guessing


https://fuckcombustion.com/threads/cosmic-xtractor.51740/post-1628796

I got curious and just checked. It’s a DIY thermal camera and not really calibrated but i have checked it on some reference temps and it’s fairly close.

Reading around 500f-550f with peaks to almost 600f, with TCR 110 set to 360f. Bounces around a bit because the regulation isn’t that tight. That’s without any inhaling though, i’m not sure how true-to-life it would be compared to a device being hit - IE i’m setting it to cruise and it’s building up temp in a way that wouldn’t happen in regular use.

 

[Canna Chameleon]

I got curious and just checked.

That’s what I love about this forum. All the people willing to help out testing…for science.

 

[XpeeN]

I remember seeing one time that @FearAndLawyering had thermal camera readings of the Cosmic X, which uses SS mesh.

Betting he can provide data on actual temps instead of us guessing


https://fuckcombustion.com/threads/cosmic-xtractor.51740/post-1628796

I got curious and just checked. It’s a DIY thermal camera and not really calibrated but i have checked it on some reference temps and it’s fairly close.

Reading around 500f-550f with peaks to almost 600f, with TCR 110 set to 360f. Bounces around a bit because the regulation isn’t that tight. That’s without any inhaling though, i’m not sure how true-to-life it would be compared to a device being hit - IE i’m setting it to cruise and it’s building up temp in a way that wouldn’t happen in regular use.

That's a great resource! Thanks both u and FearAndLawyering. This forum never cease to surprise me , great information as always and ents discussing together. That's what it's all about

Yeah ~500f was around what I was expected from the splinter z\cx heater. so yeah heaters with much smaller surface area for air exposure will obviously go hotter to compensate, which is our problem really (again didn't read the first paper yet so idk about nano-particles generation at around 200C so I ignore it for now).

That’s without any inhaling though, i’m not sure how true-to-life it would be compared to a device being hit - IE i’m setting it to cruise and it’s building up temp in a way that wouldn’t happen in regular use.

I'm talking out of my ass here but is it possible that the (glass) shell get hot as well after a while and helping heating the air too, while the heater maintaining the temp using TC?

 

[FearAndLawyering]

I'm talking out of my ass here but is it possible that the (glass) shell get hot as well after a while and helping heating the air too, while the heater maintaining the temp using TC?

Some, but you don’t really want this to happen. the glass getting warm will weaken the epoxy holding it in. i’m pretty sure that’s what causes the glass to just fall out in some units. The whole selling point of these on demand 510s is they heat quickly, you hit quickly, they cool down, not keeping a lot of residual heat IMO.

You’d need to do the math to figure out what the goal resistance/temp for the TCR settings to get a better idea of the intended working range and not the heat soaked values

 

[XpeeN]

OK I just read your 1st comment again and I didn't get it right at first, I guess I should stop commenting at mornings

. Now it makes better sense to me

 

[Hippie Dickie]

did they mention which nichrome formula, either nichrome 60 or nichrome 80?

i started my design with nichrome 60 wire and had degradation - the wire turned from silver to bronze-ish which i took to be corrosion, i.e. material loss. when i switched to nichrome 80 wire, and now ribbon, that never happens. although i did have a nichrome 80 ribbon fracture at a tight bend - fabricating mistake - which in light of the OP info is probably break down of the ribbon - losing material from repeated heating and cooling cycles. my other units have never experienced this, even after 1000s of cycle.

temperature: my ribbon coil is temperature controlled and never goes over 420°F in normal operation - i allow a max of 500°F, but above 420°F is harsh and less desirable. even changa does okay at 420°F.

the ribbon coil is isolated from the air path.

 

[TigoleBitties]

did they mention which nichrome formula, either nichrome 60 or nichrome 80?

i started my design with nichrome 60 wire and had degradation - the wire turned from silver to bronze-ish which i took to be corrosion, i.e. material loss. when i switched to nichrome 80 wire, and now ribbon, that never happens. although i did have a nichrome 80 ribbon fracture at a tight bend - fabricating mistake - which in light of the OP info is probably break down of the ribbon - losing material from repeated heating and cooling cycles. my other units have never experienced this, even after 1000s of cycle.

temperature: my ribbon coil is temperature controlled and never goes over 420°F in normal operation - i allow a max of 500°F, but above 420°F is harsh and less desirable. even changa does okay at 420°F.

the ribbon coil is isolated from the air path.

From the article I posted, I found this reference to the makeup of the nichrome:

"For nickel, the metal content dropped from 51.50–54.30% to 21.03–37.41% after 1 heat and to 9.16–14.41% after 50 heats."

I've read that the number in nichrome 60 or 80 represents the percentage of Nickel present so it looks like they were using nichrome 60 wire. To my understanding, this composition is a bit less durable than nichrome 80 but only slightly.

 

[Hippie Dickie]

thanks for that. well, the durability is more than slight in my use case. i will check more carefully next time i take my cube apart.