Supercritical Drying Applied to Natural “Gels”: Allophanic Soils

Organic carbon stabilization in the fractal pore structure of Andosols

“…Thus, the term "allophane content" could include various poorly crystalline alumino silicate compounds: allophane (hollow spheres of 3-5 nm diameter) as well as protoimogolite allophane (allophane with an Al:Si ratio close to 2) and proto-imogolite (with a same short range structure, an Al:Si ratio close to 2 and a low fibrosity). However, previous studies showed no imogolite structure features, such as hollow tubes of 2 nm in diameter, in these soils and the IR spectra did not present the specific doublets at 577 and 967 cm − 1 as found when imogolite is present (Gustafsson et al, 1995;Denaix et al, 1999) and the TEM micrographs did not show any fibrous structure but only spherical particles (3-5 nm) forming aggregates with a hierarchical structure (Woignier et al, 2005;Woignier et al, 2007). It was therefore assumed that most of the poorly crystalline alumino silicates were allophane and not protoimogolite or imogolite.…”

“…Besides plagioclase minerals, Andosol samples exhibit a large bulge in the base line between 2 and 8 Å attributed to non crystalline solids, especially allophane and imogolite (Woignier et al, 2005). Thus, the term "allophane content" could include various poorly crystalline alumino silicate compounds: allophane (hollow spheres of 3-5 nm diameter) as well as protoimogolite allophane (allophane with an Al:Si ratio close to 2) and proto-imogolite (with a same short range structure, an Al:Si ratio close to 2 and a low fibrosity).…”

“…In this study, a critical point dryer (Balzers) was used as described by Woignier et al (2005). The N 2 absorption-desorption isotherms of the samples at liquid nitrogen temperature (78 K) and at gas saturation vapor tension range were measured using an ASAP 2010 static volumetric absorption analyzer (Micromerities).…”

“…Various mechanisms for chemical and physical stabilization of SOC, such as Al toxicity and formation of organo-mineral complexes, precipitation and binding have all been described as key processes for sequestering SOC (Boudot, 1992;Percival et al 2000;Scheel et al 2007;Mikutta et al 2006). Studies using an Andosol series (Woignier et al, 2005) and a series of silicate soils (Mayer and Xing, 2001) showed that the specific surface area (SSA) of soil particles is highly correlated to the SOC content. Although interactions between SOC and mineral surfaces have sometimes been described as a major factor in SOC stabilization in soils, other authors did not find any correlation between the SSA of poorly crystalline minerals and the SOC content (Kaiser and Guggenberger, 2003;Mikutta et al 2005).…”

Compost addition reduces porosity and chlordecone transfer in soil microstructure

“…Before physical characterization, the soil samples were dried by supercritical drying. The apparatus used was a critical point dryer (Balzers), and the whole procedure was the same as that detailed in Woignier et al (2005).…”