Hacker News Reader

Comment by Physkal | Hacker News Reader

Why would the aluminum stock not be useful after 10 years, oxidation?

It might be in specific forms ready to be processed - eg. blocks of specific dimensions or weights.

After 10 years outside, it's probably covered in dust and grime, and gotten an oxide layer. It probably isn't immediately sellable to a car factory...

But it could be reprocessed very inexpensively and become sellable. The loss of value would probably be well under 1%.

People saying "it's so old, it's basically scrap" either don't know what they're talking about, or they're deliberately deceiving - and being market traders, I suspect the latter in the hopes of pushing market prices higher.

> and gotten an oxide layer

Aluminium has an oxide layer the second it comes into contact with air.

It keeps increasing (exponentially slower, thus with a finite total depth) even without any other chemical.

Anyway, out on the world there are many chemicals that can make it deeper, can peel it from the metal so another layer forms, or can mix with it and make it less insulating. I would be surprised if loses are as low as 1% as people point on this thread, but shouldn't be very large either.

Oxidation is technically a fire, albeit very slow

Fire is a type (fast) of oxidation. That doesn’t mean that oxidation is a type of fire.

really? citation?

"Fire is the rapid oxidation of a material" https://en.wikipedia.org/wiki/Fire

You might want to include the end of that sentence: "...in the exothermic chemical process of combustion, releasing heat, light, and various reaction products."

This confirms the, imo, common-sense position that no, oxidation is not just a slow fire. A fire is a specific type of oxidation process that involves the production of significant light and heat. In other words, it is only true that oxidation is a slow fire if one adopts a definition of fire that is significantly different from its ordinary usage.

A fire releases the "heat, light and various reaction products" that it does because of the speed of oxidation. It's obvious even from the snippet I posted that slow oxidation is not actually a fire.

Yes, but aluminum oxidizes rapidly yet this oxidation process does not produce significant heat and light. So in this context, the independent heat/light requirement makes a difference!

Mill aluminium under inert gas into a powder and then release the pure unoxidized powder into the air.

My money is on some fireworks occurring.

Oxidation of aluminum does produce heat and light (the reaction is exothermic). It’s just a very small and fast fire.

It does as a powder.

thank you

Fire is a phenomena whereby a fuel is combined with an oxidizer to make a new product in a manner that releases heat (ie: an exothermic redox reaction).

Rusting of metals fits that bill since heat is in fact released (just a super tiny amount and rather slowly), so it's _technically fire_ - although fire more commonly implies the rapid release of copious amounts of energy as part of the process.

thanks

Acids can make that much thicker. Acids that exist in the environment in small amounts...

Like sulfur / sulfuric acid from all the coal we're burning.

I have a 1983 Honda and the aluminum shines like a mirror. It didn’t always. When I got it the metal looked dull and weather possible damaged. It is amazing what buffing it can do. From garbage to mirror finish. Very satisfying to watch aluminum being polished. The aluminum did loses some of the outer layer that had oxidizes but looks brand new once cleaned up. Looks new and has the structural integrity to be used in aircraft is not the same but for the purposes of a motorcycle cover it is just fine. There are many other applications for aluminum that structural integrity is not if concern like heat sinks. The LED light I am building uses aluminum extrusion as heat sink.

Old Airstream trailers (1950s-1990s at least) can be buffed to a mirror-like finish.

Oddly, new Airstreams seem to come pre-oxidized. Not sure if this is a design choice, or if they don't use aluminum any more.

It's for manufacturability, not design... Airstreams are now a premium brand, and it's quite expensive to develop and maintain a mirror polish. Someone buying a $150k polished trailer expects it to be completely unblemished.

You can still polish it yourself, it only takes about 80 hours of manual labor...

That makes sense. Like a popcorn ceiling.

Also any road damage or wear will be much more visible on a polished surface, which is not a premium look.

I thought earlier-era Airstreams were buffed and clearcoated before initial sale. My only evidence is vintage photos, and the fact that some owners "restore" the mirror finish.

Mirror finished anything on the road seems like a really bad hazard.

Well you will see big rigs with the polished tanks on the road already. They are typically cylindrical and even the back end is bubbled out so you do get some shine it’s not like a direct beam of light hitting your eyes.

There are no flat or concave surfaces, so any reflections are diffused out. Ends up not being an issue at all.

Aluminum is very oxidation resistant once the initial thin oxide layer forms. I doubt that is the issue.

I would guess the reason is similar and would be weathering/erosion due to being outside and pelted with sand/rain/etc.

Yeah I was going to say, repeated rain (which is slightly acidic) and the like will keep pelting it. I mean the lifetime can probably be extended if they store it inside a building, but that's a lot of building space.

Aluminum "scrap" is still very useful and valuable.

Reply on news.ycombinator.com