Why are thermometers banned on flights? - Mercury rapidly destroys aluminum

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Why are thermometers banned on flights? - Mercury rapidly destroys aluminum

Planes are largely made from aluminum and, surprisingly, a very small amount of mercury can destroy a large amount of aluminum. Despite its apparently inert behavior, aluminium is actually a rather reactive metal which will combine violently with oxygen in air. However, this reaction quickly produces a thin, tough oxide layer which stops further attack. The process of anodising the aluminium thickens this layer to give better protection.

Mercury has the ability to disrupt this protective oxide layer, and the results can be spectacular. It can dissolve aluminium to form an amalgam which may break up the oxide layer from below--presumably the initial attack occurs through tiny faults in the oxide.

Many years ago a technician working for me spilled a few drops of mercury on his wooden bench, which had heavy aluminium angles screwed round the edges to protect it. Next morning large holes were eaten through the aluminium, the wood nearby was deeply charred, and large fragile towers of friable aluminium oxide had grown like strange corals.

Given the mobility of liquid mercury, the corrosive amalgam may form deep within the structure.

An aircraft in which mercury has been spilled must be put into quarantine until the amalgam makes its presence known. Ultimately, the aircraft is likely to be scrapped because the engineering textbooks state that the amalgam slowly spreads like wood rot to adjacent areas.

more on site ....

Someone who did try to transport mercury that spilled...

Air Niugini Mercury Spill

A man charged with carrying mercury aboard an Air Niugini aircraft from Port Moresby to Mt Hagen has been sent to jail for four years with hard labour for the offence.

On the 10th of July 2005 the accused carried a 1 litre container of mercury onto the aircraft and subsequently the container leaked inside the aircraft causing the aircraft to be grounded. Mercury is very corrosive and requires special handling before and during transportation on the aircraft. Air Niugini incurred considerable expense while the plane was taken out of service and a thorough examination of every nook and cranny was made.

By netchicken: posted on 30-8-2003

A small amount of mercury amalgamates itself into an aluminum I-beam and destroys it from within. Gallium scratched into the surface allows the mercury to penetrate the protective oxide layer that normally surrounds anything made of aluminum.

This is a time-lapse video, the action takes about two hours in real time. The powdery oxide is falling off, what you don't see is a significant pile of it building up underneath.

Here is another time lapse video, this time over only 30 minutes.

When a piece of aluminium is scratched under mercury, the fresh aluminium forms an amalgam. The aluminium in this then oxidises when exposed to air, forming white aluminium oxide. This process carries on until (in theory) all the aluminium has been used up.

Time lapse - recorded over 1/2 hour

mercury-aluminium.jpg - 12.28kb
By netchicken: posted on 30-1-2010

When iron rusts, it forms iron oxide—a reddish, powdery substance that quickly flakes off to expose fresh metal, which immediately begins to rust, and so on until your muffler falls off.

But when aluminum rusts, it forms aluminum oxide, an entirely different animal. In crystal form, aluminum oxide is called corundum, sapphire or ruby (depending on the color), and it is among the hardest substances known. If you wanted to design a strong, scratchproof coating to put on a metal, few things other than diamond would be better than aluminum oxide.

By rusting, aluminum is forming a protective coating that’s chemically identical to sapphire—transparent, impervious to air and many chemicals, and able to protect the surface from further rusting: As soon as a microscopically thin layer has formed, the rusting stops. (“Anodized” aluminum has been treated with acid and electricity to force it to grow an extra-thick layer of rust, because the more you have on the surface, the stronger and more scratch-resistant it is.)

This invisible barrier forms so quickly that aluminum seems, even in molten form, to be an inert metal. But this illusion can be shattered with aluminum’s archenemy, mercury.

Applied to aluminum’s surface, mercury will infiltrate the metal and disrupt its protective coating, allowing it to “rust” (in the more destructive sense) continuously by preventing a new layer of oxide from forming. The aluminum I-beam above rusted half away in a few hours, something that would have taken an iron beam years.

I’ve heard that during World War II, commandos were sent deep into German territory to smear mercury paste on aircraft to make them inexplicably fall apart. Whether the story is true or not, the sabotage would have worked. The few-micron-thick layer of aluminum oxide is the only thing holding an airplane together. Think about that the next time you’re flying. Or maybe it’s better if you don’t.

More ... http://www.popsci.com/scite...
By netchicken: posted on 30-1-2010

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