Specific surface area and microstructure of the surface of soil solid substrates of different genesis

Abstract

The sorption characteristics of sand, peat, the arable layer of Moscow urbanozem and a mixture of these substrates were studied in conjunction with the surface topography of their solid phase, studied by scanning electron microscopy (SEM). The arable layer has the greatest ability to absorb nitrogen, and the peat substrate showed very low values of the sorbed gas. A different picture of the mutual arrangement of substrate sorption isotherms is observed when water vapour is used as a sorbing gas. Peat is distinguished by high values of sorbed moisture in the entire studied range of relative humidity. This leads to differences in the ranking of substrates by specific surface area in descending order of its values. So, the specific surface area by water sorption in the series: peat / arable layer / mixture / sand was: 420 / 72 / 45 / 4 m2/g, respectively. The given surface was ranked according to nitrogen sorption in a different sequence: 8.31 / 2.41 / 1.45 / 0.55 for the series: arable layer, mixture, peat and sand, respectively. The analysis of microstructural characteristics by the SEM method at various magnifications revealed the most developed, rough surface in the arable layer. It turned out to be geometrically the most diverse, even at magnification of ×20 000. The variety and heterogeneity of the relief of the interface of the phases leads to the appearance of hysteresis of the sorption/desorption curves. Its severity in the range of nitrogen vapor concentration in which hysteresis is detected, and in the maximum width of the hysteresis loop, also turned out to be the most significant in the arable layer. The very low nitrogen specific surface of peat, which is close to a sandy substrate, is associated with the presence of organic films draping and leveling the surface of peat particles, which was revealed by analyzing images obtained by scanning electron microscopy. The sorption of water showed their high hydrophilicity, which led to high values of substrate humidity in the entire studied range of relative humidity.

Keywords

• hydrosorption
• nitrogen desorption
• scanning electron microscopy
• hysteresis of sorption curves
• peat
• sand