ISSN:
1435-1536
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Description / Table of Contents:
Zusammenfassung Plötzliche Kristallisation geschieht oft in unterkühlten Flüssigkeiten oder in übersättigten Lösungen (gewöhnlich von Ionenverbindungen), wenn feste Substanzen, die in die Flüssigkeiten eingetaucht sind, mechanisch geschnitten oder gebrochen werden. Die Spaltung der chemischen Bindungen in den festen Substanzen scheint notwendig für die Keimbildung zu sein. Plötzliche Kristallisation wird auch durch mechanische Erschütterung in den Flüssigkeiten hervorgerufen. Diese Phänomene werden durch Einfluß delokalisierter Elektronen auf die Keimbildung erklärt.
Notes:
Summary Sudden crystallization takes place frequently in supercooled liquids or in supersaturated solutions (usually of ionic compounds) when solid substances immersed in the liquids are cut or fractured mechanically. Rupture of chemical bonds in the solid is essential for the nucleation and the effect disappears momentarily. Crystallization is also frequently given rise by mechanical shock in the above mentioned liquids, and may be explained as follows: electrons of the shocked molecules become labile and may behave like free electrons in metals momentarily as demonstrated experimentally. Generated free radicals and free electrons cluster into a metal-like structure and are compressed into the closest-packed structure with higher regularity by forces analogous to metallic bond. The cluster may act as the embryo and the nucleus of the crystal, if its structure resembles to that of the crystal or if it is easily convertable to the latter. Nucleation in supercooled liquids given rise by fracturing of solids is explained in an analogous way. Fractured surface of solids is momentarily covered with free radicals. The labile electrons and positively polarized part of liquid molecules in contact with the surface may form a two-dimensional metallic structure and the resulting compressed layer may act as the nucleus, if its structure is appropriate.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02291729
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