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Name: Aaron
Status: student
Grade: 9-12
Location: MN
Country: USA
Date: April 2009


Question:
Does glass have any malleability?


Replies:
The general concept you are talking about is the ability of a material to reshape in response to a stress. Stress is a force applied to an object. In the case of malleability, the stress is compressive (think 'pushing'), often rolling or pounding. A similar concept is ductility, where the stress is tensile (think 'pulling'), such as pulling a wire.

If I can restate your question, you are asking if glass can deform based on a compressive load. The answer is that glass has very, very little malleability or ductility. Rather than deforming/bending, the glass is more likely to break or shatter.

Some materials are highly malleable and ductile - such as Play-doh and gold. Other materials are more one than the other (lead, for example is more malleable than ductile). Materials like ceramics are neither very ductile nor malleable.

Your question says 'any' malleability. If you look at the atomic level, then all materials can deform slightly based on loads. Crystal matrices can deform/bend slightly, and defects in the crystal can cause both increased and decreased deformation (a defect could make something more brittle, or it could make it more malleable). Also, temperature plays a big role in how attracted atoms are to each other, which affects malleability. You can take a material like Play-doh (malleable at room temperature) and freeze it, which would make it more likely to shatter at a given load, or take lead and heat it, and find its malleability is much lower at elevated temperature. So the answer all depends on the conditions you choose.

So strictly speaking, yes, all materials have some slight malleability or ductility. In practical terms, though, glass is not malleable. Generally speaking, metals and some polymers are malleable, while ceramics are not.

This question was already partially answered earlier by Ask-A-Scientist as well -- please see:

http://www.newton.dep.anl.gov/askasci/mats05/mats05072.htm

Hope this helps,
Burr Zimmerman


Definition: A substance is "malleable" if it deforms under a stress and does NOT return to its original shape when the stress is removed. Soft metals, like gold, are malleable. A non-crystaline substance has four zones of deformation properties as a function of increasing temperature: the "glassy" zone, the "leathery" zone, the "rubbery" zone, and the "flow" zone. If you graph the "strain" that is the movement or distortion on the "Y" axis and the "stress" that is the applied force along the "X" axis. The general shape of the curve will be high, but constant, values of strain with increasing stress. This is the "glassy" region, which tends to be relatively hard and brittle (glass shatters). There is a relatively narrow region of stress where the strain starts to decrease. This is the "leathery" region of stress/strain. The substance in this zone is tough. It can absorb the applied stress, but tends not to distort very much. Leather is a good example of this region. Next is the rubbery zone in which the substance will deform when a stress is applied, but tends to return to its original shape when the stress is removed. At still higher temperature is the "flow" zone. In this zone the substance is irreversibly distorted when the stress is applied.

The temperature range of the various zones and the numerical values of both strain and stress depends upon the material, the stress, the strain, and also the rate at which the stress is applied.

To answer your question directly, the glassy zone "tends" to be hard and brittle, but just how hard and how brittle, depends upon the substance and various factors mentioned in the previous sentence.

Vince Calder


Hi Aaron,

Glass, like many (but not all) amorphous substances, is sometimes referred to as a supercooled liquid, and the claim has been made that centuries-old windows have slowly flowed slightly under the force of gravity, so the bottoms of the windows are slightly thicker. Careful analysis has shown this to be false. There remains some argument whether in fact glass is a solid or a supercooled liquid, but normally it is considered a rigid unmalleable solid (at room temperature of course), simply because under any normal exposure to stress, it cannot be made to flow or otherwise change permanent shape in any way.

Many other substances (such as some plastics) are entirely amorphous and relatively rigid below their Glass Transition Temperature, but still can be considered malleable to a small degree, since application of stress can cause (over time) a permanent deflection.

Regards,
Bob Wilson



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