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Until now, glass transitions were detected in isolated humic and fulvic acids as well as in distinct soil samples with usually high Corg contents. The glassiness is a common characteristic of soil org. matter (SOM). However, two types of glassiness were obsd. in various soil types. Addnl. to a typical glass transition with low intensity, a slowly reversing glass transition-like step transition with significantly higher intensity was detected in 52 out of ...Until now, glass transitions were detected in isolated humic and fulvic acids as well as in distinct soil samples with usually high Corg contents. The glassiness is a common characteristic of soil org. matter (SOM). However, two types of glassiness were obsd. in various soil types. Addnl. to a typical glass transition with low intensity, a slowly reversing glass transition-like step transition with significantly higher intensity was detected in 52 out of 102 tested soil samples. The intensity of this transition type is correlated to the org. matter content of the samples. The transition behavior addnl. depends on characteristics of the locations and changes within soil profiles. Relations to particulate org. matter (POM), mineral-assocd. org. matter (MOM), and the thermostable fraction of the soil samples were not significant. A surprising result of the study is that the step transition temps. of all analyzed air-dried soil samples range between 51 and 67 DegC in closed systems, pointing to a superordinate mechanism which controls the matrix rigidity of the org. mols. This may be represented by the formation of hydrogen bond based cross-links between water mols. and SOM suggested in a previous study. Thus, glassiness in SOM may be caused by phys. and physicochem. mechanisms. [on SciFinder (R)]» weiterlesen» einklappen

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