OK, I know about aluminum forming an oxide layer and thus protecting itself from serious corrosion. But is it really sapphire? And does anodized aluminum work that way?
This sounds like complete crap. If they could smear planes with mercury paste, why couldn’t they just strap bombs with altitude fuses on them? How about going in and killing pilots? The whole mercury paste thing sounds like James Bond.
What? No. The bulk of the metal is still bonded to itself and that provides the majority of the strength, tensile and otherwise.
Well, sapphire is an aluminum oxide but I don’t know if the surface of a piece of aluminum is chemically identical to sapphire. It’s like one of those logic questions, if all sapphires are aluminum oxide, are all aluminum oxides sapphires?
To be a sapphire aluminum oxide has to form the correct crystal matrix. Being distributed randomly all over doesn’t make it a sapphire.
That Mercury bit on airplanes sounds so stupid and a waste of time. This was probably the brain child of one person that did it once and bragged about it. By now it’s something that was common and done all the time.
I don’t know about commandos using mercury paste, but mercury is highly corrosive to aluminum, and evidently acts very quickly. There have been problems with using aluminum in heat exchangers that came into contact with gas streams having relatively low concentrations (several ppm) of mercury, and the result was holes in the heat exchanger. I have tried to find the cite on the accident, but to no avail.
I talked to an engineer who worked with/on Air Force planes.
He said they had to use special ink pens to mark the aluminum…if they used just regular graphite pencils that could cause serious problems long term.
As for mercury…IIRC…the problem is that aluminum is soluble in mercury…so mercury on an aluminum surface wouldnt just accelerate the aluminums oxidation…it would literally dissolve the aluminum in short order…again IIRC
So, I have no doubt that some mercury put in the RIGHT (critical place), of which there are plenty of on aircraft, could cause serious problems…at least in theory.
Now, whether that was actually done to any extent and was remotely effective I have no idea…
Never heard of the WW2 commando bit, and I likely would have, as military history is one of my hobbies and this is the kind of story that, if real, would be repeated over and over in any source covering commando operations. I doubt it simply because ordinary explosives would have been easier to procure, carry on the operation, and apply to the target (just slap on the plastique, stick in the fuse, and “light the blue touchpaper and retire to a safe distance”).
On a related note, the optimum practice when blowing up aircraft and other equipment en mass when you don’t have enough explosives or time to completely destroy all the aircraft is to find a critical part and then destroy the same part on all the aircraft /equipment. This way, undamaged parts from Plane A can’t be used to repair Plane B.
Wiki on aluminum oxide. Take a gander at the Natural Occurrence paragraph. Calling aluminum oxide sapphire is about like calling graphite diamond. Basically true, the structure of the latter is a lot more interesting (and expensive).
When I was stationed on Iceland, I toured the big aluminum smelter near Hafnarfjörður. One of the things the guide mentioned was that, thanks to the abrasive nature of alumina dust, wear and tear on the company’s internal combustion engines was a significant problem. The other thing he mentioned was that they imported their bauxite ore from Australia (Look at the big green dot in Oz on the Alumina Output map on the aluminum oxide article). He said that thanks to the abundant and cheap hydro power in Iceland, they could ship bauxite (impure alumina) all the way from Australia, smelt it into aluminum bars, and ship those all the way back to Australia to sell them at the mine cheaper than the Australians could make aluminum there. This was in 1976 so things may have changed since then, but Alcan would like to expand the smelter at Hafnarfjörður.
I would think sneaking in to spread mercury on aluminum plane parts is rather like putting salt on a bird’s tail to catch 'em.
I’ve heard of the mercury/aircraft thing (read it in an in-flight magazine of all places!) but never the WWII commando thing. The only scenario I can think of is they did it to some specific new model of German aircraft to make them think that there was a design flaw and hoped that they would ground them while looking for it.
and if you’re running a well-coordinated op, your friendly follow-up forces can bring a truck full of the right spare parts, opening up for a bit of salvage and reuse. (Returning captured ordnance to the rightful owners is always a popular idea.)
From what I’ve read, the French resistance did just that just before D-day - they smashed the same cylinder on dozens of steam locomotives, knowing that the invasion fleet brought along crates with brand-new cylinders of the same type.
A similar story is the additive that was designed to be put into automobile engines. It was a crumbley doughy substance that could be pushed into the gas tank. Once started, the engine would seize up after a few minutes, utterly destroyed. The idea is that the resistance (or commandos) would sneak into German motor pools and sabotage every vehicle they could. Why not use bombs you ask? For one, it took only a few pounds of this paste to destroy possibly hundreds of vehicles versus hundreds of punds of explosives. Second, setting fuses on every bomb and attaching it to a vehicle can take a lot longer then stuffing a few ounces of paste into a gas tank. Three, the Germans would not know that their vehicles were sabotaged until they tried to use them. This is a lot worse than knowing ahead of time that you’re, say, eight trucks short. Four, the saboteurs could get a lot further away before their deed was discovered. Sure, they could set long timers on bombs, but this left more time for service personnel to discover the bombs before detonation. Five, the saboteurs could wreak havok without hitting every single target. If one truck or tank suddenly goes kaput, the Germans would have to stop everything to inspect every other vehicle in the motor pool and possibly drain its gas tank. And that’s AFTER all the time spent to discover why the engines are seizing up.
I don’t know how much use the stuff got, but the key ingredient was ground up cashew shells and it was packaged in condoms.
A lot of these advantages for the engine-killing paste could be applied to the mercury paste.
Wouldn’t it tend to bead up and roll away from the desired area if used in liquid form? I’d imagine there must be something with which mercury could be simply mixed to form a semi-solid paste, alternatively, mercury amalgam of some kind could be used (perhaps even an amalgam of mercury and aluminium)
My memory was inaccurate since the item I’m thinking of was used in the oil system, not the gas tank. And it was an abrasive powder rather than a dough-like substance. Even so, my original points are still in effect.
In one of the WWII military books I own, Applegate’s** Kill or Get Killed** I think, there is a section on sabotage. The abrasive material in a condom is described as being corundum. The method for use was to drop it into the engine through the oil cap, not the gas tank. The heat and oil would degrade the condom after a while and the corundum would circulate with the oil and destroy the engine pretty shortly. It was actually considered desirable that the process took a little while, so that the vehicle would be disable on the road rather than at the parking yard where it might mmore quickly be diagnosed and repaired. As a bonus, disabled vehicles on the road can screw up whole convoys.
I’d just like to note that the quote in the OP doesn’t claim that the protective layer on aluminum metal is sapphire-- It claims that it’s chemically identical to sapphire. In short, it has the right chemistry, but the wrong crystallography.
And so we come full circle, because of course corundum is just another name for sapphire (the only distinction I can find is that it’s not called sapphire if it’s red, but it’s still corundum).