Aluminium, heat and biological safety

I'm currently working on a really simple project, an ashtray that can stop cigarette combustion.

I planned to put an aluminium block into my ashtray, with some kind of curves or holes in it, in order for the cigarette to fit in, then stop combusting by lack of $\ce{O2}$, and maybe by heat transfer, as the cigarette tip and the aluminium will be in contact.

I choose aluminium, because I've got some, because it seems quite inert to me, and because it's not too hard to work with. But I can't solve the safety estimation for this material.

Here is some information I found around :

• A cigarette tip being around $\pu{900^oC}$
• Aluminium point of boiling at $\pu{2519^oC}$
• Aluminium toxicity seems still debated, but aluminium is more or less eatable, i.e. used as pigment in food (E173)

Of course, aluminium won't burn, but I'm afraid that heating it may produce a layer of aluminium oxide, which may scatter on the cigarette tip, or get combined with ash components.

So, how can we estimate the safety of this material under these condition?

• The cigarette tip will not vaporize or react with the aluminum in any significant way. Also, aluminum does form an oxide layer pretty much immediately on contact with air under standard conditions, no elevated temperatures required. This stable oxide layer is really what the cigarette tip comes in contact with. – airhuff May 18 '17 at 22:34
• Also, to be honest, I think the biggest safety concern is caused by the cigarette itself. Aluminum oxide is a relatively inert material, which is why chemists had a real hard time converting it to aluminum in the early days. Also, unlike iron oxide, the aluminum oxide layer does not shed off from the aluminum surface quite easily. Which is why aluminum oxide coatings are popular. – CoffeeIsLife May 19 '17 at 2:19

All aluminum that has been exposed to air is covered in a chemically and physically stable oxide. This aluminum oxide has an even lower vapor pressure than aluminum metal, such that the tip of the cigarette will actually be more than $\pu{2000^oC}$ below it's boiling point. By physically stable, I mean that aluminum oxide adheres strongly to the bulk aluminum and will not flake off as in the case of many other metal oxides.