Wikipedia:Reference desk/Archives/Science/2021 June 20

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June 20

Are swimmers at risk of CTE?

Am watching the Olympic trials and swimming jumping into the pool headfirst, albeit leading with their arms, can't be good when repeated, can it? Aren't they repeated low-impact collisions? Imagine Reason (talk) 01:08, 20 June 2021 (UTC)

Each time someone plunks a baseball cap on their noggin, it is also a low-impact collision. That's why the smart guys you see on TV keep their eggheads bare.  --Lambiam 08:00, 20 June 2021 (UTC)

A Google search seems to indicate that it isn't a known problem; numerous sites give results similar to this:

Common ways swimmers get concussions are: *Hitting the head [on the floor of the pool] when diving *Running into wall during backstroke *Running into another swimmer *Slipping on the deck *During dryland training. A Complete Guide to Swimming Concussions by Dr. G. John Mullen. Alansplodge (talk) 11:42, 20 June 2021 (UTC)

Alansplodge's bracketed "on the floor of the pool" may not be a completely justified interpretation, since in the section immediately following that list, Mullen mentions "hitting the head or body on the diving board" (my emphasis) as a "common concussion scenario". In that section, he also mentions "even entering the water incorrectly" as a possible cause of concussions, suggesting that Imagine Reason's idea about the perils of jumping into the pool headfirst may have some basis, at least for swimmers who don't know how to do it properly. Deor (talk) 17:02, 21 June 2021 (UTC)

One should hope, though, that swimmers qualifying to compete in the Olympic Team Trials have progressed to the stage where they know how to avoid "entering the water incorrectly".  --Lambiam 00:23, 22 June 2021 (UTC)

Why do carbon fibers cause galvanic corrosion when in direct contact with aluminium?

It is apparently a fact that:

"The carbon fibers can cause galvanic corrosion when CRP parts are attached to aluminum."

And from another source:

"The carbon fibers in CFRPs cause this material to become electrically conductive. The carbon fibers are electrically conductive and electrochemically very noble."

And from this:

"Carbon composites are severely incompatible with aluminum galvanically so you can't have carbon and aluminum touching"

What is actually happening? Carbon is not exactly a metal and doesn't react with oxygen or much else at this temperature (hence the use in electrodes for electrolysis (e.g., salt water to chlorine and hydrogen, aluminium smelting, and even salt containing hydrogen fluoride (OK, possibly hyperbolic, but still not much should be happening chemically at room temperature with carbon, in any of its forms))).

What is the nobler "metal" in this case (nobler than aluminium)? The resin? And the carbon fibers acting like an electrolyte (perhaps together with salt water)?

What is actually going on, in detail?

--Mortense (talk) 23:20, 20 June 2021 (UTC)

The citation in the current WP article is to an article about Boeing that has absolutely no comment about this specific type of corrosion. The corrosionpedia article you quote is a much better source which explains the topic better than I can and I'm going to alter the citation to use that. I think that the role of the carbon fibre is just to act as a conductor, it doesn't get altered as a result: the other component is oxygen dissolved in water or seawater, which the fibre helps to link with. Mike Turnbull (talk) 11:45, 21 June 2021 (UTC)