PermeateFree said:
I see a lot good and a lot of bad in this invention.
“Unsinkable metal” stays afloat even with holes punched in it
Superhydrophobic materials, which are excellent at repelling water, can be extremely useful for a whole range of reasons, both obvious and not-so-obvious. They can prevent ice from building up on surfaces, make electronics waterproof, make ships more efficient or keep people from peeing in public. Now engineers have found a quirky new use for superhydrophobic materials – making “unsinkable” metals that stay floating even when punctured.
The end result is virtually unsinkable, the team says. After being weighed down for two months, the structures jumped back to the surface as soon as the load was removed. Even damaging the surfaces didn’t make them sink – the team drilled six holes in them measuring 3 mm, and one measuring 6 mm, and the structures stayed afloat. Apparently, enough air remains trapped in other parts of the structure.
https://newatlas.com/materials/unsinkable-metal-superhydrophobic/
I have a very soft spot for superhydrophilic glass. With a drop contact angle of zero degrees, water runs off instantly, perfect for car windows.
Superhydrophobic glass also exists. But I don’t like it. Water drops sit on it until they evaporate, and as they evaporate they ruin the hydrophobicity.
Now I know a little about hydrophobic and hydrophilic metals. In a nutshell, pure metals are always strongly hydrophobic. With a pure surface, you could probably easily float any piece of metal on water. Take a compass for instance, a pure piece of magnetised iron can be used as a magnetic compass by floating it on water. A child’s science experiment used to be to float a magnetised sewing needle on water, without a cork.
But then corrosion rears its ugly head. The presence of oxygen, water and metal in close proximity speeds up corrosion. And as corrosion progresses, the contact angle rapidly drops. Take aluminium for instance, or zinc, or steel. In a time of order 3 hours the surface will change from superhydrophobic to slightly hydrophilic. Over a further 3 days the drop contact angle keeps dropping so that within a week it’s become superhydrophilic.
So that are looking for ways not to make the surface superhydrophobic, that’s easy, but to stop corrosion.
Gold has little corrosion. Gold foil will float easily on water. Perhaps forever if it stays moist, but not through a number of wetting-drying cycles.
Now we turn to the link in the OP. “They built structures made up of two treated aluminium surfaces facing each other, connected by a small central pole. The distance between the two plates was carefully chosen to trap the maximum amount of air, like a waterproof compartment in the middle. The end result is virtually unsinkable, the team says. After being weighed down for two months, the structures jumped back to the surface as soon as the load was removed.”
Trapped air is good, but the air does slowly diffuse out of the gap. The process is identical to the capture of atmospheric carbon dioxide by water. The bigger the pressure difference between air and water, ie. the greater the depth of submergence, the faster the loss of air.
As part of my work for CSIRO I developed an equation for the exact inverse of this process. Given a crevice filled with water, and the application was a crevice between two aluminium parts, calculate the rate at which the gap dries out by the diffusion of water vapour through the crevice. The same equation may apply in this case. (Or may not, depending on the aluminium surface preparation).
In summary, the longer the time and the greater the depth of submergence, the better the chance of sinking. Also, if it’s sunk once then it will probably never float again, even if completely dried out.
If you want an unsinkable material – used a closed foam.