Ask A Scientist© Environmental Earth Science Archive

name         Jason M.
status       student
age          20s

Question -   I heard somewhere that this is possible... if you throw a wrench (some type of metal 
object) up in the air in Antarctica could it be cold enough for the wrench to shatter when it hits 
the ground?
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Metals can become very brittle at low temperatures.  However, my guess would be that one would have 
to throw a wrench very, very hard to break it.  My response to an earlier question about why metals 
become brittle when immersed in liquid nitrogen follows.

This is a great question because many inquires to this BBS ask what is the "strongest" metal.  There 
really is no way to answer this question because, in fact, strength is just one factor in the 
suitability of a given metal for an application.  Actually, many metals can become brittle at 
temperatures well above that of liquid nitrogen (-196 deg C or -321 deg F).  This tendency to be 
brittle (i.e., fracture under impact)  is referred to as a metal's "toughness" and this toughness 
is temperature sensitive.

When a metal is ductile, it can bend and stretch.  This change in shape is accompanied by actual 
translation or flow of the metal at the atomic level. As the temperature decreases, it becomes more 
difficult to break these bonds and, consequently, easier to develop stresses in the metal that can 
lead to actual fracture, rather than flow.

The crystalline structure of the metal, along with many other factors, influences the temperature at 
which that metal becomes brittle. Metallurgists have learned to manipulate steel composition to 
achieve a desired temperature sensitivity.  For instance, steel alloys high in nickel are used in 
cryogenic applications because they are more resistant to becoming brittle at very low temperatures.

The effects of temperature on metal toughness can be critical in many applications.  For instance, 
it is hypothesized that the sinking of the Titanic ocean liner might have been averted if the steel 
in the hull had had greater low-temperature ductility.  Tests on hull samples from the Titanic 
retrieved in recent years indicate that the steel had a high sulfur content, which caused it to 
become brittle at temperatures as high as -1 deg C, which is substantially above the freezing 
point of salt water.  As a result, when the Titanic struck the iceberg, the steel in its hull 
fractured rather than deformed, causing the fatal gash.  If the metal had just buckled, it is 
possible the ship would not have sunk.  These properties were not well-understood or appreciated 
until the 1940's.

As a matter of fact, this property has even co-starred in a 1951 movie with Jimmy Stewart and Marlene 
Dietrich titled "No Highway in the Sky".  It comes on TV periodically and is the story of a 
metallurgist who learns that low-temperature induced metal fatigue is causing the mysterious 
crashes of a new airliner.  It is based on the book "No Highway" by Nevil Shute, published in 
1948.

Andy Johnson
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I have not heard that, but I would not be too surprised. Most substances become brittle as the 
temperature decreases, in addition, uneven contraction sets up stresses within the object. It is 
entirely conceivable that a metal tool could become sufficiently brittle at -40 C. ~ -40 F. to 
break apart if dropped.

Vince Calder
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