On Monday 06 July 2020 00:43:30 Chris Albertson wrote: > On Sun, Jul 5, 2020 at 3:33 AM andy pugh <[email protected]> wrote: > > You say this a lot, but I have never heard anyone else say it. What > > is your source? > > THis might be a "Chemistry 101" question. It should be easy enough to > figure out except that I last studied this stuff in the last 1970s > > We all know that burning carbon produces a lot of heat. The chemical > equation is > C + O2 --> CO2 -394 kJ / mole > > The corresponding equation of aluminum is > 4Al + 3O2 --> 2Al2O3 -1676 kJ/mole > Aluminum produces more heat per mole than carbon and also more heat > per gram than carbon. It would make good fuel except for combustion > stops once the oxide layer is formed. > > Next, I looked up the specific heat of aluminum. It is very close to > 1.0 kJ / (Kg K). So it only takes 1 Joule to heat one gram of > aluminum one degree K. > > So there is plenty of energy and the metal is also easy to heat. But > what we don't know is the fraction of aluminum that is oxidized. You > could figure this out if you had a good enough scale and could collect > all the chips. We could see how much mass the chips gained from the > added oxygen.
Difficult to do since the chips would have to be collected in an inert atmosphere, weighed, then exposed to normal air for perhaps 1 second, then weighed again. 99% of the weight gain would be in the first millisecond of normal air exposure. As would the temp gain. One rapidly runs into the real world while trying to imagine the lab lashup to measure that. And I don't think excedrin can fix that headache :) Long term alox vs weight story: I bought an Ohaus 505 powder scale in the early '60's to weigh powder for reloading my own ammo with, for a wildcat cartridge called the 30-06 Ackley-Improved, and which I have subsequently burned up/used up 4 barrels shooting at about 5k round per barrel. This scale has an aluminum pan that is stamped but was not given a protective coating. Its a very good scale, accurate to about .05 gr. No trouble at all seeing a single ball of H414 powder hitting the pan But the gradual buildup of the oxide on this pan has caused it to gain around .25 gr in the past nearly 60 years, and has required me to hit its edge with a file to remove enough weight to restore its zero balance point with the balance beam dead level. Not even cleaning it with a green scotchbrite pad will restore that balance, I must file away a teeny bit of alu. So the effect is there, but hard to measure without the right tools, and an O-Haus powder scale is about as good as you can get that is still affordable. IIRC it was close to a 90 dollar bill in 1963 or 1964. To put that in scale, custom dies were still $16.50 from RCBS, and my original 20+ lb's of cast iron framed Herters O frame press cost $14.95. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
