Effect of humic acids, sesquioxides and silica on the pore system of silt aggregates measured by water vapour desorption, mercury intrusion and microtomography

Abstract

Summary Most of the information on soil aggregation and porosity comes from studies of natural soil in which the effects of the different constituents that form the structure overlap. The aim of this research was to study the effects of these constituents separately on well‐characterized artificial aggregates in order to understand them better. To do this, the pore system of model silt aggregates, amended with different amounts of humic acids, iron and aluminium hydroxides or colloidal silica, was investigated at three levels of magnification with water vapour desorption (nanometre sizes), mercury intrusion (micrometre sizes) and microtomography (tens of micrometres). Humic acid and aluminium hydroxide increased aggregate porosities measured by all methods. An increase in porosity with increasing additions of each constituent was indicated only by water desorption. We did not observe any well‐defined trends in the dynamics of average pore radii. The pore surface fractal dimension determined by mercury intrusion was negatively correlated with that measured by water desorption. The pore system in granular media comprises larger voids joined by narrower necks; therefore, we attempted to relate their sizes with a novel approach that combined microtomography with mercury intrusion and extrusion data. We observed a decrease in the size of pore necks that give access to voids of the same sizes with increasing additions of all constituents. With additions of humic acid this effect was the smallest. The mercury intrusion data showed the formation of separate concretions of iron hydroxides and silica in silt aggregates.

Contemporary Approach to the Porosity of Dental Materials and Methods of Its Measurement

“…Additionally, both powders and larger pieces of solids can be tested; however, the latter have been shown to exhibit less variation, resulting in a better representation of the original pore structure [79]. MIP can also be performed in an extrusion mode when data are collected with decreasing pressure steps [80,81]. Analysis usually reveals then hysteresis between intrusion and extrusion cycles which is attributed to variations in the sample saturation process, alterations due to advancing and receding contact angles and mercury entrapped in the pores structure [74,82].…”

Soil structure as an indicator of soil functions: A review

“…This equation gives the equivalent pore diameter as function of the pressure, contact angle, and surface tension of mercury. Although rarely done in soil science, mercury porosimetry can also be performed in the "extrusion" mode, by decreasing the applied pressure (e.g., Jozefaciuk et al, 2015;Otalvaro et al, 2016). A hysteresis is typically found between intrusion and extrusion: mercury can be entrapped in the soil pore space, because of the ink-bottle effect and different contact angles between advancing and receding menisci (Kloubek, 1981).…”

Biochars from Mediterranean Agroindustry Residues: Physicochemical Properties Relevant for C Sequestration and Soil Water Retention

“…Additionally, we observed different intrusion and extrusion pathways (hysteresis), which can be explained by the theory of the ink-bottle shape. 57 According to this theory, if we compare pore shapes with the shape of a bottle, pores with similar dimensions of voids and necks would have similar intrusion and extrusion curves. Meanwhile, these curves would become more different from each other as necks are smaller than the voids.…”