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Bombardment versus quick cooling.

Bombardment versus quick cooling

Does rapidly cooling a liquid to form a glass produce the same kind of disorder as that produced by bombarding the crystal form of the same substance with ions? In other words, what is the relationship between the microcopic structure of an amorphous, or disordered, material and the method used to produce it? A research team at the Oak Ridge (Tenn.) National Laboratory has now determined for the first time that for at least one material, the method used to create disorder makes a difference.

The researchers studied lead pyrophosphate, which contains chains of phosphate ions. In one case, they bombarded the surface of a single crystal of the material with lead ions. The ions did enough damage to the surface to make it appear amorphous in X-ray diffraction measurements. In the other case, they cooled the molten form of the material rapidly to produce a homogeneous glass. The researchers used a technique known as high-performance liquid chromatography to determine the length of phosphate chains in both the ion-damaged material and the glass. They discovered that no matter how high the dose of lead ions, the ion-damaged amorphous structure differed significantly from the glass form.

The results contradict what some researchers have argued in the past. The Oak Ridge experiments show that for some materials, the ion-damage process isn't always equivalent to melting followed by rapid cooling of the same material.
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Title Annotation:cooing liquid to form glass produces different structure from bombarding crystal form of same substance with ions
Author:Peterson, Ivars
Publication:Science News
Date:Apr 1, 1989
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