Aluminum foil cooking water-cooling demonstration

Teaching anecdote. Aluminum foil melts above the temperature of a campfire, but water in the cooking food keeps it cool. Put a dry steel bolt in the foil and the foil will melt around it.

Yeah, why do you put it on the base there? Because of the good thermal conductivity. With your steel pots, if you're boiling water sometimes it can be damaged, so they put copper or aluminum on the bottom. Pure aluminum has excellent water corrosion resistance — the right aluminum alloys have excellent freshwater corrosion resistance. We build sewage treatment plants out of aluminum. They don't rust, if you pick the right alloys that don't have pitting or stress corrosion cracking problems, and there are plenty that don't. They tend to be lower strength, but you go down to Deer Island treatment facility, where they clean up across the harbor water — it's all lower-strength aluminum piping carrying dirty water, and it works. So aluminum actually has excellent corrosion resistance. And aluminum foil — a regular fire is just above the melting temperature of aluminum, but you don't melt the aluminum for cooking purposes because there's steam to cool it. You're cooking something with water. If you've been a Boy Scout, you've had a foil dinner, wrapped it in aluminum foil. If you put a steel bolt in there and put it in the fire, you'll probably melt your aluminum foil, because there's no steam to cool it. You can melt the foil in a hot fire, but you don't usually, because just a little bit of moisture in what you're cooking cools it.