Evaluation of the impact of freezing technique on pore-structure characteristics of highly decomposed peat using X-ray micro-computed tomography
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University of Orleans, CNRS, BRGM, Earth Sciences Institute of Orléans (ISTO), 1A rue de la Férollerie, 45071 Orleans Cedex 2, France
University of Damas, Department of Soil Science, Faculty of Agronomy, PO Box 30621, Damas, Syria
CNRS, Extreme Conditions and Materials, High Temperature and Irridiation (CEMHTI), UPR 3079, Avenue de la Recherche Scientifique, 45071 Orleans, Cedex 2, France
Hassan Al Majou   

Université d’Orléans, CNRS, BRGM, Institut des Sciences de la Terre d’Orléans (ISTO), 1A rue de la Férollerie, 45071, Orléans, France
Final revision date: 2022-07-07
Acceptance date: 2022-07-12
Publication date: 2022-08-29
Int. Agrophys. 2022, 36(3): 223–233
  • Freezing used to obtain small size samples alters structure of peat materials
  • Structure alteration is clearly shown in X-ray computed tomography
  • Tubular pores several hundreds micrometers in diameter are altered
  • Smaller pores possibly produced by the formation of ice crystals are artefacts
The modelling of peatland functioning requires detailed knowledge of the peat structure. To this end, freezing is nowadays increasingly used to obtain X-ray micro computed tomography (X-ray -CT) images. The aim of this study was to analyze the structure of a peat material before freezing and post-defreezing using X-ray -CT and to look for possible alterations in the structure by analyzing the air-filled porosity. A highly decomposed peat material close to water saturation was selected for study. Three samples were analyzed before freezing and post-defreezing using an X-ray -CT Nanotom 180NF. Results showed that the continuity and cross section of the air-filled tubular pores several hundreds to about one thousand micrometers in diameter were altered post-defreezing. Many much smaller air-filled pores not detected before freezing were also recorded post-defreezing. Detailed analysis showed a dramatic increase in the number of air-filled pores ranging between 1 voxel (216 103 µm3) and 50 voxels (10.8 106 µm3) in volume. The volume of these pores newly occupied by air using X-ray -CT and their total volume was found to be consistent with the one calculated as resulting from the increase in the specific volume of water when it turns into ice.
The authors acknowledge all of the contributions which enabled us to carry out this study.
This work was financialy supported by the Labex Voltaire (AND-10-LABX-100-01, 2009 to 2025) and the French program PAUSE (2017 to 2022).
The authors do not declare any conflict of interest.
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