Role of an Organomineral Gel in the Formation of Natural Electrical Fields in Soils

Федотов, Г. Н.; Tret’yakov, Yu. D.; Pozdnyakov, A. I.; Zhukov, D. V.; Pakhomov, E. I.

doi:10.1023/b:doch.0000010330.90024.68

Doklady Chemistry

2003

DOI: 10.1023/b:doch.0000010330.90024.68

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Role of an Organomineral Gel in the Formation of Natural Electrical Fields in Soils

Г. Н. Федотов

Yu. D. Tret’yakov

A. I. Pozdnyakov

et al.

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“…EPMA showed C, O, Ca, Si, Al, Mg, and Fe in the colloids. These results correlate with the suggestion [7][8][9][10][11][12] CHEMISTRY 1 µ m Fig. 1.…”

supporting

confidence: 89%

“…EPMA showed C, O, Ca, Si, Al, Mg, and Fe in the colloids. These results correlate with the suggestion [7][8][9][10][11][12] When designing our experiments to study the colloidal structure, we proceeded from the fact that a pressure applied to a soil destroys the starting colloidal structure of the soil solution; the solution has its mobility increased as a result, and it partially separates from the soil. In this case, the fluid pressed out of the soil can contain debris of the colloidal structures with various sizes.…”

supporting

confidence: 61%

“…It was demonstrated recently [7][8][9][10][11][12] that various phenomena observed in soils find explanation if the soils are treated from the standpoint of the existence of organomineral colloidal structures in the soils, more exactly, in the soil solution. However, the arguments cited in those works were circumstantial.…”

mentioning

confidence: 99%

“…The samples studied were soil solutions that were separated from a greenhouse substrate [7] under a pressure of 10 atm.…”

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confidence: 99%

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Colloidal Soil Structures as Probed by Electron Microscopy

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The ion-exchange ability of a soil is an important factor in soil fertility. Van Bemmelen [1] discovered that the absorption and exchange of ions in soils pertain to colloidal particles. Gedroits [2] showed that the absorbent complex of soils consists of mineral, organomineral, and organic colloidal particles.It is commonly accepted that these particles occur in soils in the form of a sol in the soil solution and in the form of thick gel films. The films form as a result of direct contact between colloidal particles and coat coarse soil particles [3,4].It was inferred more than half a century ago [5] that not only can sols and thick gels form in the water-colloidal particles system but periodic colloidal structures can also appear due to the long-range, contactless interaction between colloidal particles, also referred to as long-range aggregation [6].It was demonstrated recently [7-12] that various phenomena observed in soils find explanation if the soils are treated from the standpoint of the existence of organomineral colloidal structures in the soils, more exactly, in the soil solution. However, the arguments cited in those works were circumstantial.Here, we have shown using electron microscopy that the soil solution has a colloidal structure. This structure is formed through the long-range aggregation of colloidal particles (their anchorage at a distance from one another).The electron microscopic investigation was carried out on a Leo Supra 50VP (Carl Zeiss, Jena) scanning electron microscope equipped with an autoemission source operated at accelerating voltages of 3-10 kV and an InLens secondary electron detector. The primary signal processing involved the accumulative averaging over the scan line.For better illustration, the electron microscopic images were inverted. X-ray electron probe microanalysis (EPMA) was carried out on an INCA Energy + energy dispersive spectrometer (from Oxford Instruments) attached to the Leo Supra 50VP microscope operated at an accelerating voltage of 20 kV in a particular region.The samples studied were soil solutions that were separated from a greenhouse substrate [7] under a pressure of 10 atm.In the investigations of the colloidal structure, the soil solution was allowed to settle for 24 h; then, it was diluted 1000-fold with water and applied to a fresh fracture of natural mica.After the water evaporated, the samples were sputtered with carbon using a Univex-300 Leybold thermal evaporator.From the electron micrograph in Fig. 1, one can see that the starting soil solution before dilution contained a large amount of colloidal particles of various sizes. EPMA showed C, O, Ca, Si, Al, Mg, and Fe in the colloids. These results correlate with the suggestion [7][8][9][10][11][12] CHEMISTRY 1 µ m Fig. 1. Electron micrograph of the soil solution separated from the greenhouse substrate and applied to a copper substrate. 50000 × .

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“…EPMA showed C, O, Ca, Si, Al, Mg, and Fe in the colloids. These results correlate with the suggestion [7][8][9][10][11][12] CHEMISTRY 1 µ m Fig. 1.…”

supporting

confidence: 89%

supporting

confidence: 61%

mentioning

confidence: 99%

“…The samples studied were soil solutions that were separated from a greenhouse substrate [7] under a pressure of 10 atm.…”

mentioning

confidence: 99%

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Colloidal Soil Structures as Probed by Electron Microscopy

et al. 2005

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“…It has been demonstrated [2][3][4][5][6] that soil solutions are structured colloids and that they affect many properties of soils. However, these studies did not concern colloidal structures per se and structural rearrangements occurring in gel systems were deduced from variations in the properties of the soils.…”

mentioning

confidence: 99%

Fractal Structures of Soil Colloids

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Fractal Colloidal Structures in Soils of Various Zonalities

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It has been demonstrated [1][2][3][4][5] that soil solutions are structured colloids and that they affect many properties of soils. Attempts to isolate a soil solution in order to study it using electron microscopy were inefficient [6]. Therefore, the need appeared for techniques to observe colloidal structures directly in soils rather than separate fragments of colloidal structures isolated from the soil and, thus, exposed to external factors.Small-angle neutron and X-ray scattering may be classified as such techniques [7]. In particular, these techniques provide information on the fractal dimension of soils, which is an integral characteristic of soil colloids [8].Here, we consider the fractal dimension of soil colloidal structures as dependent on the formation conditions and functioning of soils under various exposures.We employed small-angle neutron scattering (SANS) to find the fractal dimensions of the test soils. Fractal objects are known to have specific SANS patterns. Their log-log plots of the scattering intensity versus pulse energy are straight lines over a fairly wide range of pulse energies [9]:(1)For mass fractals, x (the Porod exponent) coincides with the fractal dimension D ; for surface fractals, x = 6 -D .The measurements were carried out on a YuMO small-angle neutron spectrometer installed at the fourth channel of an IBR-2 pulsed reactor. Since a two-detector system was used (Fig. 1), the range of the scattering vector magnitude Q was from 0.007 to 0.6 Å -1 for neutron wavelengths from 0.7 to 5 Å and detector-to-sample distances of 3.6 and 12.97 m for the nearer and the farther detectors, respectively.Test samples were placed in Hellma cells with a useful thickness of 2 mm; the beam size was 14 mm. The cells were mounted inside a thermobox maintained at 25°ë . I k ( ) logx k. log -∼ Primary data processing was performed using the SAS software [10]. The data were normalized to a vanadium reference in order to obtain the spectra in absolute values.The fractal dimensions and the fractal range (i.e., the self-similarity range) were determined.The test samples were various air-dry soils and soil pastes.The results of the SANS analysis are displayed in Tables 1-3.The results show that the fractal characteristics of the soil colloidal structures are substantially controlled by the soil zonality and profile and by external factors.Soil colloidal structures are most frequently mass fractals (Tables 1-3). It is only in air-dry soddy-podzolic and brown forest soils that the plot of the scattering intensity as a function of wave vector magnitude obeys the law characteristic of surface fractals. Note that the data obtained for these soils may be interpreted in a different way: an exponential particle size distribution of colloids can exist in these soils.There are cases where the fractal dimension reaches three, which is the limiting value for fractal objects. This value obtained in SANS analysis may characterize the transition from mass to surface fractals [11].The data compiled in Tables 1 and 2 show tha...

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Role of an Organomineral Gel in the Formation of Natural Electrical Fields in Soils

Cited by 3 publications

References 0 publications

Colloidal Soil Structures as Probed by Electron Microscopy

Colloidal Soil Structures as Probed by Electron Microscopy

Fractal Structures of Soil Colloids

Fractal Colloidal Structures in Soils of Various Zonalities

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