Stainless Steel mesh, Oxide discussion.

[junkman]

The first link is to Google search results for the phrase "oxidation of stainless steel at high temperature". If you're interested in the topic, spend some time reading thru the results. It's meant to show with some degree of confidence that the topic is well-researched and that none of the scholarly articles addressing this issue found hexavalent chromium in the oxide layer that develops on SS when oxidized at high temps.

The article by Guillamet et al. (1993) gives a detailed analysis of the oxides formed by oxidizing 304 and 316 SS at temperatures between 900-1100°C. Here's the abstract for those who cannot follow the link:

Stainless steels of type AISI 304 and 316 were heated in air (1-5-15 minutes at 900-
1000-1100C) and the oxide layers formed on the surface were analyzed by XRD, CEMS, SIMS
and FTIR. At these temperatures the main oxides are Cr2O3 and a spinel close to MnCr2O4
for polishing samples (with Fe2O3 for the chemically cleaned samples). The oxidation induces
a Cr and Mn depletion from the metallic substratum and a phase transformation gamma (f.c.c.) -> alpha
(b.c.c.) in a thin layer of the steels near the oxides - metal interface.​

For those who are not chemists, (Cr2O4)-2 is the chromite anion, a chromium(III) compound, which is extremely stable, not toxic, and widely found naturally in a class of oxide minerals in the spinel group.

I don't know - Looking at that Guillamet article, table 3 - what is the mention of Cr(VI)?

 

[zoiDman]

I would also like to know what happens to Chromium Alloys such at "Dry Burn" temperatures.

 

[junkman]

I would also like to know what happens to Chromium Alloys such at "Dry Burn" temperatures.

Well, the article quoted above was testing at temps that should exceed dry burn. My only issue is that there seems to be some contradiction to claim that Cr(VI) is not formed. The table I referenced mentions Cr(VI). I am not a doctor, metalurgist, chemist, etc, so I don't know what it means, but would like to have an explanation.

 

[Boden]

The first link is to Google search results for the phrase "oxidation of stainless steel at high temperature". If you're interested in the topic, spend some time reading thru the results. It's meant to show with some degree of confidence that the topic is well-researched and that none of the scholarly articles addressing this issue found hexavalent chromium in the oxide layer that develops on SS when oxidized at high temps.

The article by Guillamet et al. (1993) gives a detailed analysis of the oxides formed by oxidizing 304 and 316 SS at temperatures between 900-1100°C. Here's the abstract for those who cannot follow the link:

Stainless steels of type AISI 304 and 316 were heated in air (1-5-15 minutes at 900-
1000-1100C) and the oxide layers formed on the surface were analyzed by XRD, CEMS, SIMS
and FTIR. At these temperatures the main oxides are Cr2O3 and a spinel close to MnCr2O4
for polishing samples (with Fe2O3 for the chemically cleaned samples). The oxidation induces
a Cr and Mn depletion from the metallic substratum and a phase transformation gamma (f.c.c.) -> alpha
(b.c.c.) in a thin layer of the steels near the oxides - metal interface.​

For those who are not chemists, (Cr2O4)-2 is the chromite anion, a chromium(III) compound, which is extremely stable, not toxic, and widely found naturally in a class of oxide minerals in the spinel group.

The Oxide formation of SS has been well researched for SS heated in a neutral atmosphere. The Guillamet et al. study must have used a electric kiln to keep the metal at those temperatures in "air". Electric kilns have a neutral atmosphere and can be said to contain "air". If they were using a gas furnace the environment would not be "air" but the byproducts of combustion. The common way people are making wicks is using an Oxidizing flame. If you can find a study of oxides produced using an oxidizing flame that would help.

 

[zoiDman]

Well, the article quoted above was testing at temps that should exceed dry burn. My only issue is that there seems to be some contradiction to claim that Cr(VI) is not formed. The table I referenced mentions Cr(VI). I am not a doctor, metalurgist, chemist, etc, so I don't know what it means, but would like to have an explanation.

Yes... 1,100C would seem to include the Temperatures that are obtained during a Atomizer Coil Dry Burn.

The thing that I see that might be different between say a NiChrome Alloy and a SS Alloy is the amount of Iron.

The Upper Limit of Chromium and Nickel found in SS is 20% / 10% respectively. The rest is for the Most part Iron (> 60%) But some NiChrome Alloys, and other Coil Wire Alloys, contain No Iron.

I don't know what role the Iron plays in all this. If any.

 

[junkman]

The Oxide formation of SS has been well researched for SS heated in a neutral atmosphere. The Guillamet et al. study must have used a electric kiln to keep the metal at those temperatures in "air". Electric kilns have a neutral atmosphere and can be said to contain "air". If they were using a gas furnace the environment would not be "air" but the byproducts of combustion. The common way people are making wicks is using an Oxidizing flame. If you can find a study of oxides produced using an oxidizing flame that would help.

Boden,

What do you make of table 3 in the Guillamet study?

 

[Boden]

I don't know - Looking at that Guillamet article, table 3 - what is the mention of Cr(VI)?

Good eyes junkman, I'm not sure what that annotation means.

Edit: After reading the paper (and a bit of research on the tests performed) I would say they were only looking at Total Chromium Oxide and the side band tests reveled the Oxide state which seems to be inconsequential to the authors.

Edit2:
Figured it out (looked at the key ) a) polished (3 µm grad diamond paste ; b) chemically cleaned using HCl/Nitric acid.

They were looking for what Oxides were formed dependent on surface preparation. The polished SS Oxidized to Cr(III)+Cr(VI) (proportions unknown) while the chemically cleaned surface only showed Cr (III).

 

[junkman]

View attachment 180643

Good eyes junkman, I'm not sure what that annotation means.

Edit: After reading the paper (and a bit of research on the tests performed) I would say they were only looking at Total Chromium Oxide and the side band tests reveled the Oxide state which seems to be inconsequential to the authors.

Edit2:
Figured it out (looked at the key ) a) polished (3 µm grad diamond paste ; b) chemically cleaned using HCl/Nitric acid.

They were looking for what Oxides were formed dependent on surface preparation. The polished SS Oxidized to Cr(III)+Cr(VI) (proportions unknown) while the chemically cleaned surface only showed Cr (III).

Interestingly, the higher temp doesn't show Cr(VI) for either polished or etched?

While I am encouraged a bit by this paper, I still don't feel confident in saying the Cr(VI) isn't formed.

It seems like it should be information that is available, but I guess our use case is just not something that has been studied?

 

[junkman]

Yes... 1,100C would seem to include the Temperatures that are obtained during a Atomizer Coil Dry Burn.

The thing that I see that might be different between say a NiChrome Alloy and a SS Alloy is the amount of Iron.

The Upper Limit of Chromium and Nickel found in SS is 20% / 10% respectively. The rest is for the Most part Iron (> 60%) But some NiChrome Alloys, and other Coil Wire Alloys, contain No Iron.

I don't know what role the Iron plays in all this. If any.

I thought coil questions were answered somewhere in this thread. Something about forming an aluminum oxide coating that was fairly robust and not dangerous?

 

[zoiDman]

I thought coil questions were answered somewhere in this thread. Something about forming an aluminum oxide coating that was fairly robust and not dangerous?

I believe the reference to Aluminum Oxides were for "Kanthal" wire.

But many Attys / Cartos / Clearos use Plain Old "NiChrome 80" which contains No Aluminum.


MatWeb - The Online Materials Information Resource (NiChrome 80)

http://www.matweb.com/search/DataSheet.aspx?MatGUID=81a977d47d6b4b6d963b0f07c417e474(Kanthal A)

BTW - I believe that Most, if not All Kanthal Resistance Wire contain Large percentages of Iron.

Once again, I am unsure of how this May or May Not play a role in the Formation of Bad Chromium Oxides.

 

[Boden]

I believe the reference to Aluminum Oxides were for "Kanthal" wire.

But many Attys / Cartos / Clearos use Plain Old "NiChrome 80" which contains No Aluminum.


MatWeb - The Online Materials Information Resource (NiChrome 80)

MatWeb - The Online Materials Information Resource(Kanthal A)

BTW - I believe that Most, if not All Kanthal Resistance Wire contain Large percentages of Iron.

Once again, I am unsure of how this May or May Not play a role in the Formation of Bad Chromium Oxides.

Let's figure out if it is being formed on the mesh first. It has a vastly larger surface area so the amounts would be much larger if they are there.

 

[zoiDman]

Let's figure out if it is being formed on the mesh first. It has a vastly larger surface area so the amounts would be much larger if they are there.

I think Both are good areas of Research. SS Mesh Oxidation is a Hot Topic right Now for RBA Users.

But EVERYONE uses a Atomizer Coil of some material.

A shame that someone like Janty or Kanger doesn’t have some data on studies they have Already Been Done.

Oh well, I guess that is what the FDA sees as their role.

 

[Boden]

Interestingly, the higher temp doesn't show Cr(VI) for either polished or etched?

While I am encouraged a bit by this paper, I still don't feel confident in saying the Cr(VI) isn't formed.

I noticed that as well in the high temp test. It is possible that It is vaporized in the specific test they did or that the "*Cr2O3 on the tops of layer" was the only thing they cared about. It's not really clear.

I found this: Breakdown and Evolution of the Protective Oxide Scales of AISI 304 and AISI 316 Stainless Steels under High-Temperature Oxidation

It shows that Cr (III) vaporizes at above 1000C.(no mention of Cr (VI) But they were using a synthetic air substation so It could mean anything. Plus, on the Guillamet article the Cr (III) is still there above 1000C. Edit: this would explane it "The sample reaches the breakdown state after almost 2 h of oxidation."

It seems like it should be information that is available, but I guess our use case is just not something that has been studied?

That's my guess, I can find no other use for flame treated heavily oxidized SS.

 

[DrMA]

Nice find, Boden. I'll keep looking as well. But you must admit that there is a lot of evidence for Cr(III) and none so far for Cr(VI). I'd say the weight of evidence tends to support the use of SS wicks as safe.

 

[StaircaseWit]

Many are no longer flame-treating SS mesh for coiling purposes (see the myriad "unoxidized mesh" threads) and simply pulsing the coil on the mesh to achieve oxidation between coil and mesh (or more precisely on the mesh only where the coil is in contact), so even the "flame treatment" part of testing has some variables.

I wonder what temperatures are achieved in the stainless mesh during dry-burn? I know there are a lot of variables (wattage, coil temperature, duration, etc.) but does anyone have a rough estimate? Are we achieving the same mesh glow with common dry-burn techniques?

 

[Kurt]

Just thought i would throw something out there... Why doesnt someone go get their urine or blood tested for chromium? If we're vaping it at high enough levels for it to hurt us it would be detected in those tests. It stays in your sytem for 120 days at high levels. Small amounts of chromium is fine and is actually something the body needs to break down certain sugars, yes even chromium(IV).

That would be Cr(III) not Cr(VI), which has a laundry list of problems it causes, including cancer and metal poisoning. Cr(III) is fine. Cr(VI) is not.

 

[Kurt]

Well, I had all that completely backwards.

So all we need is one of you smart guys to invent a polymer - glass alloy.
It would be flexible enough to make a mesh that could be rolled up,
and strong enough to be heat resistant and totally inert to all acids and solvents.

Maybe that is what is in Raidy's secret atomizer.

Ok, snap to it.

What about very-high temp resistant silicone?

 

[Kurt]

Many are no longer flame-treating SS mesh for coiling purposes (see the myriad "unoxidized mesh" threads) and simply pulsing the coil on the mesh to achieve oxidation between coil and mesh (or more precisely on the mesh only where the coil is in contact), so even the "flame treatment" part of testing has some variables.

I wonder what temperatures are achieved in the stainless mesh during dry-burn? I know there are a lot of variables (wattage, coil temperature, duration, etc.) but does anyone have a rough estimate? Are we achieving the same mesh glow with common dry-burn techniques?

the question would be what are the electrolysis products of the coil wire with the SS wick? The oxidation that occurs is not likely to be from hi temp, but electrolysis. Like the white powder that forms on sparkplugs.

 

[Kurt]

And this is just a guess, but I would doubt the Cr is oxidizing to Cr(VI) in an electrolysis. Cr(VI) probably needs more extreme conditions than simple electrolysis. And I would agree that the Guillamet paper implies no Cr(VI), but it is not entirely clear from the tables. I think what Boden is doing with getting the tests run is the smartest thing.

I am not a metal chemist, so until I learn more myself, I will be of only limited help here. But it is heartening to see the concern and hopefully how to resolve this issue!

 

[Kurt]

Someone just informed me that their torch that they use for oxidation goes up to 2500 C. That is very hot. Not saying, given we don't have Boden's results yet, that it is too hot, but it is far hotter than the study cited.