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Simon L Clegg - One of the best experts on this subject based on the ideXlab platform.
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densities and apparent molar volumes of atmospherically important electrolyte solutions 2 the systems h hso4 so42 h2o from 0 to 3 mol kg 1as a function of temperature and h nh4 hso4 so42 h2o from 0 to 6 mol kg 1at 25 c using a pitzer ion interaction model and nh4hso4 h2o and nh4 3h so4 2 h2o over the entire concentration range
Journal of Physical Chemistry A, 2011Co-Authors: Simon L Clegg, Anthony S WexlerAbstract:A Pitzer ion interaction model has been applied to the systems H 2SO4?H2O (0?3 mol kg?1, 0?55 °C) and H2SO4?(NH4)2SO 4?H2O (0?6 mol kg?1, 25 °C) for the calculation of apparent molar volume and density. The Dissociation reaction HSO4?(aq) ? H+(aq) + SO42?(aq) is treated explicitly. Apparent molar volumes of the SO42? ion at infinite dilution were obtained from part 1 of this work,(1)and the value for the bisulfate ion was determined in this study from 0 to 55 °C. In dilute solutions of both systems, the change in the Degree of Dissociation of the HSO4? ion with concentration results in much larger variations of the apparent molar volumes of the solutes than for conventional strong (fully dissociated) electrolytes. Densities and apparent molar volumes are tabulated. Apparent molar volumes calculated using the model are combined with other data for the solutes NH4HSO4 and (NH4) 3H(SO4)2 at 25 °C to obtain apparent molar volumes and densities over the entire concentration range (including solutions supersaturated with respect to the salts).
Anthony S Wexler - One of the best experts on this subject based on the ideXlab platform.
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densities and apparent molar volumes of atmospherically important electrolyte solutions 2 the systems h hso4 so42 h2o from 0 to 3 mol kg 1as a function of temperature and h nh4 hso4 so42 h2o from 0 to 6 mol kg 1at 25 c using a pitzer ion interaction model and nh4hso4 h2o and nh4 3h so4 2 h2o over the entire concentration range
Journal of Physical Chemistry A, 2011Co-Authors: Simon L Clegg, Anthony S WexlerAbstract:A Pitzer ion interaction model has been applied to the systems H 2SO4?H2O (0?3 mol kg?1, 0?55 °C) and H2SO4?(NH4)2SO 4?H2O (0?6 mol kg?1, 25 °C) for the calculation of apparent molar volume and density. The Dissociation reaction HSO4?(aq) ? H+(aq) + SO42?(aq) is treated explicitly. Apparent molar volumes of the SO42? ion at infinite dilution were obtained from part 1 of this work,(1)and the value for the bisulfate ion was determined in this study from 0 to 55 °C. In dilute solutions of both systems, the change in the Degree of Dissociation of the HSO4? ion with concentration results in much larger variations of the apparent molar volumes of the solutes than for conventional strong (fully dissociated) electrolytes. Densities and apparent molar volumes are tabulated. Apparent molar volumes calculated using the model are combined with other data for the solutes NH4HSO4 and (NH4) 3H(SO4)2 at 25 °C to obtain apparent molar volumes and densities over the entire concentration range (including solutions supersaturated with respect to the salts).
M I Alymov - One of the best experts on this subject based on the ideXlab platform.
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synthesis of micron particles with fe fe4n core shell structure at low temperature gaseous nitriding of iron powder in a stream of ammonia
Inorganic Materials: Applied Research, 2016Co-Authors: A G Gnedovets, A B Ankudinov, V A Zelenskii, E P Kovalev, H Wisniewskaweinert, M I AlymovAbstract:Synthesis of the single-phase γ′-Fe4N on the surface of the micron-sized particles of iron at low-temperature gaseous nitriding of carbonyl iron powder in a stream of ammonia is studied. It is shown that synthesis of particles with such structure is possible with simultaneous control of the number of process parameters: temperature, Degree of Dissociation of ammonia, and treatment time. It is found that, at temperature T = 400°C and nitriding potential of the atmosphere rN ≈ 1.3 atm−1/2, the shells with a thickness of about 1 μm are formed on the particles within ~15–20 min and the powder consists of the γ-Fe4N phase within ~60 min of treatment. The mechanisms of formation of microparticles with a core–shell structure are considered. A qualitative model for the thermochemical treatment of the micron iron powder with consideration of the diffusion processes of the transport of ammonia molecules in the pore space of the powder and atomic nitrogen diffusion inside the particles is developed. Geometric and dimensional effects at nitriding of iron powders are discussed.
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erratum to synthesis of micron particles with fe fe4n core shell structure at low temperature gaseous nitriding of iron powder in a stream of ammonia
Inorganic Materials: Applied Research, 2016Co-Authors: A G Gnedovets, A B Ankudinov, V A Zelenskii, E P Kovalev, H Wisniewskaweinert, M I AlymovAbstract:Synthesis of the single-phase γ′-Fe4N on the surface of the micron-sized particles of iron at low-temperature gaseous nitriding of carbonyl iron powder in a stream of ammonia is studied. It is shown that synthesis of particles with such structure is possible with simultaneous control of the number of process parameters: temperature, Degree of Dissociation of ammonia, and treatment time. It is found that, at temperature T = 400°C and nitriding potential of the atmosphere rN ≈ 1.3 atm−1/2, the shells with a thickness of about 1 μm are formed on the particles within ~15–20 min and the powder consists of the γ-Fe4N phase within ~60 min of treatment. The mechanisms of formation of microparticles with a core–shell structure are considered. A qualitative model for the thermochemical treatment of the micron iron powder with consideration of the diffusion processes of the transport of ammonia molecules in the pore space of the powder and atomic nitrogen diffusion inside the particles is developed. Geometric and dimensional effects at nitriding of iron powders are discussed.
May Matthias - One of the best experts on this subject based on the ideXlab platform.
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Band Positions of Anatase (001) and (101) Surfaces in Contact with Water from Density Functional Theory
Journal of Chemical Physics, 2020Co-Authors: Geiger Julian, Sprik Michiel, May MatthiasAbstract:Titanium dioxide in the anatase configuration plays an increasingly important role for photo(electro)catalytic applications due to its superior electronic properties when compared to rutile. In aqueous environments, the surface chemistry and energetic band positions upon contact with water determine charge-transfer processes over solid--solid or solid--electrolyte interfaces. Here, we study the interaction of anatase (001) and (101) surfaces with water and the resulting energetic alignment by means of hybrid density functional theory. While the alignment of band positions favours charge-transfer processes between the two facets for the pristine surfaces, we find the magnitude of this underlying driving force to crucially depend on water coverage and Degree of Dissociation. It can be largely alleviated for intermediate water coverages. Surface states and their passivation by dissociatively adsorbed water play an important role here. Our results suggest that anatase band positions can be controlled over a range of almost one eV via its surface chemistry.International Exchanges grant IE161814 of the Royal Society. German National Academy of Sciences Leopoldina, grant LPDS 2015-09 German Research Foundation, project 43402347
Helmuth Mohwald - One of the best experts on this subject based on the ideXlab platform.
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study of the ph dependence of head group bonding in arachidic acid monolayers by polarization modulation infrared reflection absorption spectroscopy
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: Robert Johann, D Vollhardt, Helmuth MohwaldAbstract:Abstract Little information is available on the bonding interaction of fatty acid head groups with solvent molecules and other fatty acid molecules in monolayers at the air–water interface. Recent findings indicate the formation of hydrogen bonds between pairs of neutral fatty acid and carboxylate in the pH range from pH 5.6 to 10. In this work arachidic acid monolayers are investigated on subphases of pH 5.6, 9, 9.7 and 12.0, that contain a variable amount of sodium ions, by means of polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The fitted peak intensities are related to surface concentrations of singly and doubly hydrogen bonded and non-hydrogen bonded carbonyl and carboxylate. From the change of the concentrations with the pH tentative conclusions are drawn on the bonding situation of fatty acids in monolayers on water and alkaline solution. The Degree of Dissociation as derived from the peak intensities is compared with calculated results according to the Gouy–Chapman–Stern theory.
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shifting of fatty acid monolayer phases due to ionization of the headgroups
Langmuir, 2001Co-Authors: Robert Johann, D Vollhardt, Helmuth MohwaldAbstract:Monolayers of simple fatty acids exhibit a rich polymorphism with at least seven solid phases. The reason for such a variety of phases is not known yet and therefore is the object of the current investigation. In the present work the pH of the subphase is varied between 2 and 10.5 and the influence of the Degree of Dissociation on phase transition pressures and temperatures of arachidic acid monolayers is investigated in detail in the range from 2 to 45 °C by means of Brewster-angle microscopy and surface pressure−area isotherms. The shift of phase boundaries is ascribed to the change in the steric, electrostatic, and bonding interactions between the lipid headgroups. The impressive correlation between the L2/Ov nearest neighbor to next nearest neighbor (NN/NNN) transition pressure and the position correlation length as functions of the pH value suggests that the L2/Ov NN/NNN transition in fatty acid monolayers is strongly influenced or even originates in headgroup bonding interactions. The influence of h...