Naval diver thermal protection using magnesium alloy

Navy Port Hueneme diving school developed magnesium-graphite/SiC composites that corroded faster than they could be metallographically polished (Latanision's work). Navy weaponized the corrosion: (1) divers crack-open packets to generate H₂ for salvage lift balloons; (2) divers pierce packets in cold water for exothermic warmth.

Two structural applications. The US Navy out in Port Hueneme, California, where they have a diving school, developed about thirty or forty years ago — people around 1980, 70s and 80s, were very interested in these ceramic-metal composites, the aluminum-silicon-carbide composites I mentioned. The Navy was trying to make lightweight magnesium composites with silicon carbide or graphite. Professor Latanision, who worked on corrosion here, was working on some of these things. He found that if he tried to polish them to make a metallographic sample, they would corrode faster than he could polish. They had to polish in oil rather than water, because you've got graphite and magnesium, the two far ends of the galvanic series. It corroded so fast.

Two applications of the same magnesium-carbon composite: salvage (generates hydrogen on contact with seawater, lifts objects via plastic-bag flotation) and diver thermal protection (corrosion heat warms diver in cold water). Demonstrates "magnesium corrodes really well" point.

The Navy loves it. Panama City is where Navy divers do things, and they have a little research lab. A number of years ago they developed a magnesium-carbon composite. They take carbon powders and magnesium powders and press them together, and you can stick this in seawater. If you try to polish it in the laboratory and you use a water-based polish slurry, it would corrode faster than the new propulsion — so they use oil-based polishing. But if you stick it in seawater, one use they found was salvage. You put it in a little plastic bag. The diver takes it down beneath the surface, gets a big plastic part, puts it over whatever he wants to lift, connects it, puts the little plastic-coated piece of magnesium-carbon alloy underneath, breaks the bag, seawater comes in, and he generates a hydrogen bubble that floats the thing to the surface. That's how fast it corrodes — you can generate your own hydrogen underwater. So you don't have to carry big tanks of gas that are lighter than water; you can carry a little thing and the water will produce your own gas.

Port Hueneme (~1980) graphite-magnesium composite developed for two diver applications — a hydrogen-generating lifting bag for underwater salvage, and a heat-generating belt-pack to keep divers warm in cold water. Used to motivate the magnitude of the galvanic potential between the most-noble and least-noble entries on the series.

Anybody been to Port Hueneme? Port Hueneme, about thirty-five years ago, decided to get into the metal matrix composite business. They were making graphite-magnesium composites — very lightweight. Graphite's lightweight, magnesium's lightweight. These are interesting because if you're making a sample and trying to polish it to look at the microstructure, if you polished it in water it would be corroding in the polishing machine faster than you could polish it. Because you've got the biggest voltage difference between those two.