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Phase Transition of KNO 3 Monitored by Synchrotron X‐ray Powder Diffraction
Author(s) -
Christensen A.,
Norby P.,
Hanson J. C.,
Shimada S.
Publication year - 1996
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889895015664
Subject(s) - analytical chemistry (journal) , phase transition , powder diffraction , phase (matter) , diffraction , atmospheric temperature range , synchrotron , materials science , chemistry , x ray crystallography , transition temperature , crystallography , thermodynamics , optics , chromatography , condensed matter physics , physics , superconductivity , organic chemistry
The solid‐state phase transitions of KNO 3 were studied at atmospheric pressure in the temperature range 303 to 533 K by synchrotron X‐ray powder diffraction. The detectors used were (i) a curved position‐sensitive detector and (ii) a moving imaging‐plate system built for time‐, temperature‐ and wavelength‐dependent powder diffraction. On heating, the transition from α ‐KNO 3 to β ‐KNO 3 occurs at 401 K. On cooling with a cooling rate of 7 K min −1 , the transition from β ‐KNO 3 to γ ‐KNO 3 was observed at 388 K. The phase transition from γ ‐KNO 3 to α ‐KNO 3 occurred at temperatures that strongly depended upon the cooling rate. With a high cooling rate of 15 K min −1 from 403 to 303 K, the γ ‐KNO 3 phase was obtained as a pure phase at 303 K, but it was eventually transformed to α ‐KNO 3 at this temperature, and the phase transition at 303 K was complete within 15 min. With a slow cooling rate of 0.5 K min −1 from 403 to 303 K, the γ ‐KNO 3 phase was formed at 391 K and transformed at 370 K to α ‐KNO 3 . With a cooling rate of 7 K min −1 from 403 to 303 K, the γ ‐KNO 3 phase transformed to α ‐KNO 3 in a temperature range between 377 and 353 K. The two phases could exist simultaneously in temperature ranges that were apparently dependent upon the thermal history of the sample. The unit‐cell parameters of γ ‐KNO 3 from 383 K to room temperature are reported.