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Sodium percarbonate between 293 and 100 K
Robin Gavin Pritchard1, Emran Islam
1Department of Chemistry, UMIST, PO Box 88, Manchester, England. robin.pritchard@umist.ac.uk
Acta Crystallographica. Section B, Structural Science
|October 31, 2003
Summary
Sodium percarbonate undergoes a reversible phase change upon cooling, altering its crystal structure and reducing hydrogen peroxide disorder. This structural transformation is key to understanding its properties at low temperatures.
Area of Science:
- Solid-state chemistry
- Crystallography
- Materials science
Background:
- Sodium percarbonate (Na(2)CO(3).1.5H(2)O(2)) is a widely used oxidizing agent.
- Understanding its structural behavior at different temperatures is crucial for its applications.
Purpose of the Study:
- To structurally characterize sodium percarbonate at low temperatures.
- To investigate the phase transition and its impact on crystal structure and hydrogen peroxide disorder.
Main Methods:
- Single-crystal X-ray diffraction was performed across a temperature range from 293 K to 100 K.
- Analysis of crystallographic data to determine space groups and atomic positions.
Main Results:
- A reversible phase transition was observed between 240 K and 250 K, changing the space group from Cmca to Pbca.
- The crystallographic cell side b shows a reversal in its expansion coefficient upon cooling.
- Disorder in hydrogen peroxide sites significantly decreases with decreasing temperature, indicating dynamic disorder.
Conclusions:
- Sodium percarbonate exhibits a temperature-dependent phase transition affecting its crystal symmetry.
- The dynamic disorder of hydrogen peroxide molecules diminishes at lower temperatures.
- Previous structural studies favoring Aba2 space group for sodium percarbonate should be re-assigned to Cmca.