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Maybe regular use is enough to keep it clean, so it didn't need to be aggressively cleaned. I Googled the conductivity issue, and the first site that popped up had this. Apparently, the oxide coating on bulk aluminum doesn't prevent contact, although bulk aluminum oxide is an insulator. Again, not as bad as it sounds, as the oxide coating is self-limiting, unlike brass or steel."Alain CelzardUniversity of LorraineAluminium is a highly reducing metal, and because of this, it spontaneously oxidises in air. Fortunately, the alumina barrier which is formed is almost totally impervious, so oxidation is nearly completely stopped. Fortunately, otherwise aluminium would burn spontaneously in air. Moreover, Al powder is pyrophoric, i.e. can be very dangerous when exposed abruptly to air. But bulk Al is just covered by a very thin Al2O3 layer, and this is the reason why pure Al is never shiny. Alumina is an electronic insulator, but becomes ionic conductor at high temperature. Because it is very thin over its metal, alumina doesn't prevent electric conduction, but just add a contact resistance. Conduction takes place throughout alumina by tunnelling effect."
Bulk aluminum melts, but doesn't burn. Powdered aluminum is extremely flammable, and is used in solid-fuel rocket motors. The solid boosters for the space shuttle burned a mixture of powdered aluminum and oxidizer.From Wikipedia:"The rocket propellant mixture in each solid rocket motor consisted of ammonium perchlorate (oxidizer, 69.6% by weight), atomized aluminum powder (fuel, 16%), iron oxide (catalyst, 0.4%), PBAN (binder, also acts as fuel, 12.04%), and an epoxy curing agent (1.96%).[8][9] This propellant is commonly referred to as Ammonium Perchlorate Composite Propellant, or simply APCP. This mixture gave the solid rocket motors a specific impulse of 242 seconds (2.37 km/s) at sea level or 268 seconds (2.63 km/s) in a vacuum. "And, from https://cameochemicals.noaa.gov/chemical/14008 Aluminum Powder, Uncoated""Air & Water ReactionsHighly flammable. Produces flammable gases and heat on contact with water. May ignite on contact with water or moist air.Fire HazardExcerpt from ERG Guide 138 [Substances - Water-Reactive (Emitting Flammable Gases)]:Produce flammable gases on contact with water. May ignite on contact with water or moist air. Some react vigorously or explosively on contact with water. May be ignited by heat, sparks or flames. May re-ignite after fire is extinguished. Some are transported in highly flammable liquids. Runoff may create fire or explosion hazard. (ERG, 2016)Reactivity ProfileALUMINUM POWDER, UNCOATED is a reducing agent. Reacts very exothermically when mixed with metal oxides and ignited or heated (thermite process)." Then lists a bunch of other stuff it also reacts with. Like iron, and unlike copper, aluminum is NEVER found as a metal in nature. The only "pure" iron found on Earth is meteorites, and even those will have an oxide crust. Powdered iron will also burn, but it isn't nearly as reactive as aluminum.
Jbub: Interesting. I wonder what its purpose is? It can't be fuel, because, as an oxide, it's already "burned". Some type of catalyst, maybe? Or is it "oxidized coarsely powdered" aluminum, and the oxide coating stabilizes the unoxidized portion inside the particles? That would make sense, as it would make the product safer to handle, and when ignited, the aluminum particles would still burn.
Having nothing to do with flammable aluminum powder or vintage N-scale, just want to say that that I really like WM3793's Cumberland station on his small, developing layout. Is that kit or scratchbuilt? It's really nicely done. Rick
Aluminum would burn spontaneously in air? That sounds really strange. I know that Wikipedia is often not highly regarded as a reference, but I looked anyway. https://en.wikipedia.org/wiki/Aluminium Funny, it specifically shows: " It is nonmagnetic and does not easily ignite."It's the Internet - oh, what to believe?
I made a dozen sets of wired joiners tonight!
Or starting something you can't finish.Doug
The trick is not to finish too soon...
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Topic: Something Vintage This Way Comes... (Read 13305 times)
