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 use of aluminum in the construction of your ashtray as you've described will not result in the ingestion/inhalation of any form of aluminum in any significant way.  

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.  

Although your question was about potential safety issues, I will make one comment regarding your discussion of the design. You suggested that heat transfer into the aluminum might play a role in extinguishing the cigarette, which is not the case. So long as there is sufficient oxygen available for the combustion, the cigarette will continue to burn.