A different kind of pest

Roamy here. I usually look at the “this day in history” pages to get post ideas. On this day in 1912, they discovered the frozen remains of explorer Robert Scott and his companions Edward Wilson and Henry Bowers on the Ross Ice Shelf in Antarctica. Scott’s goal was to be the first to reach the South Pole but was beaten by Roald Amundsen by more than a month. On their return trip, they failed to make it to a supply cache and succumbed to either the cold or starvation in March 1912, not to be found until the next Antarctica summer. Scott wrote several letters before he died, defending his expedition and adding to the lore of the British stiff upper lip.

We took risks, we knew we took them; things have come out against us, and therefore we have no cause for complaint, but bow to the will of Providence, determined still to do our best to the last … Had we lived, I should have had a tale to tell of the hardihood, endurance, and courage of my companions which would have stirred the heart of every Englishman.

One of the legends that sprang from this expedition was that the supply cans of kerosene suffered from a materials problem called tin pest and spilled their contents. Tin at cold temperatures can transform from ductile to brittle and even turn to powder.

[youtube http://www.youtube.com/watch?v=vVtCPw7RsW4&w=420&h=315]

Was it tin pest that doomed Scott and his expedition or just bad soldering? Tin pest and the similar tin whiskers still plague explorers, this time in space. In the video above, they generated tin pest at -35 degrees C, and it gets much colder than that in space. As the environmentally conscious pushed to eliminate lead from solder and from electronics parts, we started seeing tin pest and tin whiskers develop again. The failure of the Galaxy IV satellite in 1998 is attributed to tin pest/tin whisker formation which short-circuited the control avionics, followed by Galaxy VII in 2000 and Galaxy IIIR in 2006.

Sometimes bismuth, antimony, or a combination of silver and copper are used in the place of lead to keep tin pest from forming, but these do not have the reliability of the old lead-tin solder and they can be actually worse for the environment. Military equipment is exempt from being lead-free, but what happens if you have off-the-shelf equipment or parts in the right environment? I found citations about tin pest/tin whisker problems with the F-15 radar system, the Phoenix missile, and an unnamed military plane. We don’t need history to repeat itself.

1 thought on “A different kind of pest”

  1. Yeah, COTS was a “cost cutting” measure put in place because of $700 hammers and other stories of defense cost overruns. The result is that commercial gear often fail when you need it. Ironically, “mil-spec” is hot right now. Everything from camping gear to motherboards is hyped as being mil-spec….

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