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Application of Thermal Analysis to Elucidate Water-Repellency Changes in Heated Soils

^a Dep. of Soil Science, Faculty of Natural Sciences, Comenius Univ., Mlynska dolina B-2, 842 15 Bratislava, Slovak Republic
^b Dep. of Geography, Univ. of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK
^c CSIRO Land & Water, GPO Box 1666, Canberra ATC 2601, Australia
^d Institute of Chemistry, Slovak Academy of Sciences, Dubravska cesta 9, 845 38 Bratislava, Slovak Republic
^e Institute of Landscape Ecology, Slovak Academy of Sciences, Stefanikova 3, 81499 Bratislava, Slovak Republic
^f GEA– Grupo de Edafología Ambiental, Dep. of Agrochemistry and Environment, Univ. Miguel Hernández, Avda de la Universidad s/n, E-03202 Elche, Alicante, Spain

View larger version (11K): [in this window] [in a new window]   Fig. 1. The effects of heating duration at selected temperatures (125 and 175°C) on water drop penentration time (WDPT) in A horizons of a Humic Dystrustept and a Typic Psammaquent. Values for the WDPT were obtained as the mean of three determinations. The WDPTs in the A horizon of a Typic Ustipsamment are not included as they were >43,200 s before heating.

View larger version (14K): [in this window] [in a new window]   Fig. 2. Effect of heating temperature on heating duration necessary for water repellency elimination for samples from individual soil horizons of a Typic Ustipsamment, a Humic Dystrustept, and a Typic Psammaquent.

View larger version (12K): [in this window] [in a new window]   Fig. 3. Results of thermal analysis in standard air for A horizons of the Typic Ustipsamment, Humic Dystrustept, and Typic Psammaquent. Plotted curves correspond to thermogravimetric analysis (TGA), derivative thermogravimetric analysis (DTG), and differential thermal analysis (DTA) at a heating rate of 10°C min–1.

View larger version (11K): [in this window] [in a new window]   Fig. 4. Logarithm of the conversion rate of soil organic matter (d/dt) vs. the reciprocal value of temperature (T) at different heating rates (2.5, 7.5, and 15°C min–1) for A horizons of the three soils. Dashed lines interpolate points with the same conversion degree of soil organic matter (0.1, 0.3, 0.5, 0.7 and 0.9).

View larger version (13K): [in this window] [in a new window]   Fig. 5. Activation energies (E) and logarithms of the pre-exponential factor (lnA) at selected degrees of soil organic matter (SOM) conversion () as determined by the Friedman method for A horizons of the three soils. The pre-exponential factor was determined assuming first-order kinetics.

View larger version (12K): [in this window] [in a new window]   Fig. 6. Calculated heating durations necessary to destroy 50% of soil organic matter (conversion = 0.5) as a function of temperature.

View larger version (10K): [in this window] [in a new window]   Fig. 7. Calculated remainder of soil organic matter (SOM) at the time of water-repellency destruction as a function of heating temperature.

View larger version (9K): [in this window] [in a new window]   Fig. 8. Calculated conversions () of soil organic matter at the time of water-repellency destruction as a function of heating temperature.