Slow Reversion of Potassium Nitrate
Potassium nitrate exists in several crystalline forms depending upon both the temperature and the pressure (1,2). The three easily observed forms are the orthorhombic KNO3II, stable under standard conditions, a trigonal form, KNOoI, staole above 127.7°C at atmospheric pressure (3), and a second trigonal form, KNO3III, which is typically formed when KNO3I is cooled. The persistence of this form varies with, among other things, its degree of confinement; that is, the expansion of the crystallites transforming from I?III may be unrestrained in a shallow pan, but in a sample cup or well the points of contact are under pressure, so a confined sample transforms more quickly to the orthorhombic phase (4).
KeywordsOrthorhombic Phase Heating Peak Trigonal Form Unidirectional Compression Single Crystal Potassium Nitrate
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