The Experts below are selected from a list of 41973 Experts worldwide ranked by ideXlab platform
Tjisse Hiemstra - One of the best experts on this subject based on the ideXlab platform.
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Natural and pyrogenic humic acids at goethite and Natural Oxide surfaces interacting with phosphate
Environmental Science & Technology, 2013Co-Authors: Tjisse Hiemstra, Pierrebenoit Duhaut, Bastiaan MollemanAbstract:Fulvic and humic acids have a large variability in binding to metal (hydr) Oxide surfaces and interact differently with oxyanions, as examined here experimentally. Pyrogenic humic acid has been included in our study since it will be released to the environment in the case of large-scale application of biochar, potentially creating Darks Earths or Terra Preta soils. A surface complexation approach has been developed that aims to describe the competitive behavior of Natural organic matter (NOM) in soil as well as model systems. Modeling points unexpectedly to a strong change of the molecular conformation of humic acid (HA) with a predominant adsorption in the Stern layer domain at low NOM loading. In soil, mineral Oxide surfaces remain efficiently loaded by mineral-protected organic carbon (OC), equivalent with a layer thickness of ≥∼0.5 nm that represents at least 0.1–1.0% OC, while surface-associated OC may be even three times higher. In Natural systems, surface complexation modeling should account for th...
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Natural and pyrogenic humic acids at goethite and Natural Oxide surfaces interacting with phosphate
Environmental Science & Technology, 2013Co-Authors: Tjisse Hiemstra, Pierrebenoit Duhaut, Shamim Mia, Bastiaan MollemanAbstract:Fulvic and humic acids have a large variability in binding to metal (hydr) Oxide surfaces and interact differently with oxyanions, as examined here experimentally. Pyrogenic humic acid has been included in our study since it will be released to the environment in the case of large-scale application of biochar, potentially creating Darks Earths or Terra Preta soils. A surface complexation approach has been developed that aims to describe the competitive behavior of Natural organic matter (NOM) in soil as well as model systems. Modeling points unexpectedly to a strong change of the molecular conformation of humic acid (HA) with a predominant adsorption in the Stern layer domain at low NOM loading. In soil, mineral Oxide surfaces remain efficiently loaded by mineral-protected organic carbon (OC), equivalent with a layer thickness of ≥∼0.5 nm that represents at least 0.1–1.0% OC, while surface-associated OC may be even three times higher. In Natural systems, surface complexation modeling should account for th...
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nanoparticles in Natural systems i the effective reactive surface area of the Natural Oxide fraction in field samples
Geochimica et Cosmochimica Acta, 2010Co-Authors: Tjisse Hiemstra, Juan Antelo, Rasoul Rahnemaie, Willem H Van RiemsdijkAbstract:Abstract Information on the particle size and reactive surface area of Natural samples is essential for the application of surface complexation models (SCM) to predict bioavailability, toxicity, and transport of elements in the Natural environment. In addition, this information will be of great help to enlighten views on the formation, stability, and structure of nanoparticle associations of Natural organic matter (NOM) and Natural Oxide particles. Phosphate is proposed as a natively present probe ion to derive the effective reactive surface area of Natural samples. In the suggested method, Natural samples are equilibrated (⩾10 days) with 0.5 M NaHCO3 (pH = 8.5) at various solid–solution ratios. This matrix fixes the pH and ionic strength, suppresses the influence of Ca2+ and Mg2+ ions by precipitation these in solid carbonates, and removes NOM due to the addition of activated carbon in excess, collectively leading to the dominance of the PO4–CO3 interaction in the system. The data have been interpreted with the charge distribution (CD) model, calibrated for goethite, and the analysis results in an effective reactive surface area (SA) and a reversibly bound phosphate loading Γ for a series of top soils. The oxidic SA varies between about 3–30 m2/g sample for a large series of representative agricultural top soils. Scaling of our data to the total iron and aluminum Oxide content (dithionite–citrate–bicarbonate extractable), results in the specific surface area between about 200–1200 m2/g Oxide for most soils, i.e. the Oxide particles are nano-sized with an equivalent diameter in the order of ∼1–10 nm if considered as non-porous spheres. For the top soils, the effective surface area and the soil organic carbon fraction are strongly correlated. The Oxide particles are embedded in a matrix of organic carbon (OC), equivalent to ∼1.4 ± 0.2 mg OC/m2 Oxide for many soils of the collection, forming a NOM–mineral nanoparticle association with an average NOM volume fraction of ∼80%. The average mass density of such a NOM–mineral association is ∼1700 ± 100 kg/m3 (i.e. high-density NOM). The amount of reversibly bound phosphate is rather close to the amount of phosphate that is extractable with oxalate. The phosphate loading varies remarkably (Γ ≈ 1–3 μmol/m2 Oxide) in the samples. As discussed in part II of this paper series ( Hiemstra et al., 2010 ), the phosphate loading (Γ) of field samples is suppressed by surface complexation of NOM, where hydrophilic, fulvic, and humic acids act as a competitor for (an)ions via site competition and electrostatic interaction.
A K Raychaudhuri - One of the best experts on this subject based on the ideXlab platform.
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a method to quantitatively evaluate hamaker constant using the jump into contact effect in atomic force microscopy
arXiv: Materials Science, 2008Co-Authors: Soma Das, P A Sreeram, A K RaychaudhuriAbstract:We find that the jump-into-contact of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the jump-into-contact distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the jump-into-contact using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with Natural Oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the jump-into-contact is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.
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a method to quantitatively evaluate the hamaker constant using the jump into contact effect in atomic force microscopy
Nanotechnology, 2007Co-Authors: Soma Das, P A Sreeram, A K RaychaudhuriAbstract:We find that the 'jump-into-contact' of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the 'jump-into-contact' distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the 'jump-into-contact' using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with Natural Oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the 'jump-into-contact' is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.
Soma Das - One of the best experts on this subject based on the ideXlab platform.
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a method to quantitatively evaluate hamaker constant using the jump into contact effect in atomic force microscopy
arXiv: Materials Science, 2008Co-Authors: Soma Das, P A Sreeram, A K RaychaudhuriAbstract:We find that the jump-into-contact of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the jump-into-contact distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the jump-into-contact using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with Natural Oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the jump-into-contact is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.
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a method to quantitatively evaluate the hamaker constant using the jump into contact effect in atomic force microscopy
Nanotechnology, 2007Co-Authors: Soma Das, P A Sreeram, A K RaychaudhuriAbstract:We find that the 'jump-into-contact' of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the 'jump-into-contact' distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the 'jump-into-contact' using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with Natural Oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the 'jump-into-contact' is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.
Bastiaan Molleman - One of the best experts on this subject based on the ideXlab platform.
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Natural and pyrogenic humic acids at goethite and Natural Oxide surfaces interacting with phosphate
Environmental Science & Technology, 2013Co-Authors: Tjisse Hiemstra, Pierrebenoit Duhaut, Bastiaan MollemanAbstract:Fulvic and humic acids have a large variability in binding to metal (hydr) Oxide surfaces and interact differently with oxyanions, as examined here experimentally. Pyrogenic humic acid has been included in our study since it will be released to the environment in the case of large-scale application of biochar, potentially creating Darks Earths or Terra Preta soils. A surface complexation approach has been developed that aims to describe the competitive behavior of Natural organic matter (NOM) in soil as well as model systems. Modeling points unexpectedly to a strong change of the molecular conformation of humic acid (HA) with a predominant adsorption in the Stern layer domain at low NOM loading. In soil, mineral Oxide surfaces remain efficiently loaded by mineral-protected organic carbon (OC), equivalent with a layer thickness of ≥∼0.5 nm that represents at least 0.1–1.0% OC, while surface-associated OC may be even three times higher. In Natural systems, surface complexation modeling should account for th...
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Natural and pyrogenic humic acids at goethite and Natural Oxide surfaces interacting with phosphate
Environmental Science & Technology, 2013Co-Authors: Tjisse Hiemstra, Pierrebenoit Duhaut, Shamim Mia, Bastiaan MollemanAbstract:Fulvic and humic acids have a large variability in binding to metal (hydr) Oxide surfaces and interact differently with oxyanions, as examined here experimentally. Pyrogenic humic acid has been included in our study since it will be released to the environment in the case of large-scale application of biochar, potentially creating Darks Earths or Terra Preta soils. A surface complexation approach has been developed that aims to describe the competitive behavior of Natural organic matter (NOM) in soil as well as model systems. Modeling points unexpectedly to a strong change of the molecular conformation of humic acid (HA) with a predominant adsorption in the Stern layer domain at low NOM loading. In soil, mineral Oxide surfaces remain efficiently loaded by mineral-protected organic carbon (OC), equivalent with a layer thickness of ≥∼0.5 nm that represents at least 0.1–1.0% OC, while surface-associated OC may be even three times higher. In Natural systems, surface complexation modeling should account for th...
Kazuhiro Ogawa - One of the best experts on this subject based on the ideXlab platform.
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elucidation of cold spray deposition mechanism by auger electron spectroscopic evaluation of bonding interface Oxide film
Acta Materialia, 2019Co-Authors: Yuji Ichikawa, Kazuhiro Ogawa, Ryotaro Tokoro, Masatoshi TannoAbstract:Abstract The relationship between the cold spray deposition mechanism, microstructure, and strength of the resulting film must be understood for this innovative process to be practical. Previous studies have suggested that the coating mechanism is reliant on breaking the Natural Oxide film such that metallic bonding occurs through direct contact between the metal surfaces. In this study, the proposed model was experimentally verified by a small tensile adhesion test and auger electron spectroscopy analysis of the bonding interface. Since shear deformation does not occur at the tip (south pole) of the incoming particle, the Oxide film is not broken, such that the bonding strength is weak. In contrast, at the outer edge of the particle, metallic bonding occurs, attaining a level of strength that exceeds that of the base material due to the huge plastic deformation. This phenomenon is known as the “south-pole problem,” and can lead to a decrease in the overall adhesion strength despite the local adhesion being strong. However, detailed observations revealed, in parts of the deposits, particles that had adhered across their entire surface. This suggests that, provided the collision state can be controlled, it is possible to overcome the south-pole problem and improve the adhesion strength.
