The growth of fractal humic acids: Cluster correlation and gel formation |
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Authors: | Ragnar Österberg Kell Mortensen |
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Affiliation: | (1) Department of Chemistry, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden;(2) Department of Solid State Physics, Risø National Laboratory, DK-4000 Roskilde, Denmark |
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Abstract: | The growth of humic acids, prepared by a gentle method from two different kinds of soils (I and II), has been studied using small-angle neutron scattering at an acidity corresponding to pH 5.0 and 0.10 M ionic strength (NaCl). Humic acids aggregate either to large clusters with a fractal dimension of 2.35 and an average diameter of 1720 (I) or to clusters with an average diameter of 700 (II). After storage for 2 days at 4 °C, the latter aggregates (II) formed a gel. In a step toward gelation, we observed cluster-cluster interaction from the neutron-scattering data in the form of a correlation peak. These differences in size can be explained by assuming that the smaller particles (II) are trapped into a nonequilibrium state characterized by the temperature-solvent condition. The importance of a humic acid gel network for the conservation of water and nutrients in the environment is discussed. |
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