The Naked Scientists Forum
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28/05/2003 16:09:14 »
Why does crystal grow bigger when you allow a hot liquid to cool slowly? For example, basalt has small crystals because it's formed by rapid cooling of molten rock whereas granite has large crystals. Is it because the molecules have more time to move into position abd bond with neighbouring molecules to form a regular lattice structure?
Exodus, I think you should be able to answer this question. So help!
The Kitty Down Under
Re: Crystal Formation
Reply #1 on:
29/05/2003 03:39:48 »
Oh! We were doing something along these lines in chemistry last week. Quenching is heating the metal (or whatever) to a high temperature then cooling it quickily, annealing is heating it to a high temperature then letting it cool slowly. There may be another one that I've forgotten ... anyway annealed metals are stronger, because there are larger crystals and so fewer fault lines, while quenched metals are very brittle because of many more fault lines. One of them also becomes more malleable, too ... but anyway, I'm fairly sure that the reason annealed metals have larger crystals is; the heating lets the ions move more freely and out of the medium-sized crystals, and as it cools the crystals are able to find each other and slowly get into larger crystals before they stop moving. Quenched metals get to move freely when they're heated (ions move apart and out of crystals) but they are cooled really quickly so they are frozen in their tiny crystals that were the larger ones but broken up from the movement.
Anyway that's just a guess I'm probably way off, we'll see what exodus says[