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Name: Jason M.
Status: Student
Age: 20
Location: N/A
Country: N/A
Date: January 2004


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?



Replies:
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


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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