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Alexandra Navrotsky – One of the best experts on this subject based on the ideXlab platform.

  • direct calorimetric measurement of Enthalpy of adsorption of carbon dioxide on cd mof 2 a green metal organic framework
    Journal of the American Chemical Society, 2013
    Co-Authors: Di Wu, Sergey V. Ushakov, Jeremiah J Gassensmith, Douglas Gouvea, Fraser J Stoddart, Alexandra Navrotsky
    Abstract:

    The Enthalpy of adsorption of CO2 on an environmentally friendly metal–organic framework, CD-MOF-2, has been determined directly for the first time using adsorption calorimetry at 25 °C. This calorimetric methodology provides a much more accurate and model-independent measurement of adsorption Enthalpy than that obtained by calculation from the adsorption isotherms, especially for systems showing complex and strongly exothermic adsorption behavior. The differential Enthalpy of CO2 adsorption shows Enthalpy values in line with chemisorption behavior. At near-zero coverage, an irreversible binding event with an Enthalpy of −113.5 kJ/mol CO2 is observed, which is followed by a reversible −65.4 kJ/mol binding event. These enthalpies are assigned to adsorption on more and less reactive hydroxyl groups, respectively. Further, a second plateau shows an Enthalpy of −40.1 kJ/mol and is indicative of physisorbed CO2. The calorimetric data confirm the presence of at least two energetically distinct binding sites for…

  • Enthalpy of water adsorption and surface Enthalpy of lepidocrocite γ feooh
    Geochimica et Cosmochimica Acta, 2007
    Co-Authors: Juraj Majzlan, Lena Mazeina, Alexandra Navrotsky
    Abstract:

    Abstract Lepidocrocite (γ-FeOOH) appears to be thermodynamically metastable with respect to goethite (α-FeOOH) and yet the former phase forms and persists both in nature and laboratory. Here we show that the thermodynamic factors relevant to these observations cannot be dismissed, although kinetics undoubtedly plays a significant role in the formation and preservation of metastable phases. To understand the relationships of the FeOOH polymorphs in the bulk and nanoscale, we investigated the energetics of lepidocrocite nanoparticles. We measured Enthalpy of water adsorption and Enthalpy of formation of lepidocrocite samples with surface area of 42–103 m2/g. Having both quantities measured allowed us to calculate the surface Enthalpy for a water-free surface of this phase as 0.62 ± 0.14 J/m2 and the energy of a relaxed (hydrated) surface as 0.40 ± 0.16 J/m2. Our measurements show that a portion of the adsorbed water (∼40% under laboratory conditions) is chemisorbed (strongly bound) with Enthalpy of adsorption of −65.8 ± 2.6 kJ/mol of H2O relative to vapor (or −21.8 ± 2.6 kJ/mol relative to liquid water). The standard Enthalpy of formation from elements for a hypothetical lepidocrocite with nominal composition FeOOH and zero surface area is −552.0 ± 1.6 kJ/mol. Our results demonstrate that when considering the thermodynamic properties of iron oxides in the environment, a conclusive statement about their stability cannot be made without specifying the particle size of individual phases.

  • Energetics of Bulk and Nano-Akaganeite, β-FeOOH: Enthalpy of Formation, Surface Enthalpy, and Enthalpy of Water Adsorption
    Chemistry of Materials, 2006
    Co-Authors: Lena Mazeina, Suraj Deore, Alexandra Navrotsky
    Abstract:

    Akaganeite, β-FeOOH, is a commonly occurring ferric mineral in the environment and is a sorbent, ion exchexchanger, and catalyst. It is often fine-grained (nanophase) and frequently contains excess water. Its Enthalpy of formation was studied by solution calorimetry in aqueous HCl. The Enthalpy of water adsorption was studied by a new calorimetric technique combining a Calvet microcalorimeter and an automated gas dosing system, used for surface adsorption measurements. Akaganeite samples with surface areas of 30−280 m2/g were used. Sample characterization was performed by X-ray powdpowder diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer−Emmett−Teller method, scanning electron microscopy, and transmission elecelectron microscopy. Surface Enthalpy and Enthalpy of water adsorption are reported for the first time. By adsorbing water, akaganeite decreases its effective surface Enthalpy from 0.44 J/m2 to 0.34 J/m2. The Enthalpy of formation of akaganeite can vary by 10−12 kJ/mol as…

Hyun-jung Chung – One of the best experts on this subject based on the ideXlab platform.

  • effect of partial gelatinization and retrogradation on the enzymatic digestion of waxy rice starch
    Journal of Cereal Science, 2006
    Co-Authors: Hyun-jung Chung
    Abstract:

    The effect of partial gelatinization and retrogradation on in vitro enzymatic digestibility of waxy rice starch was investigated, and the relationship between the residual crystallinity and digestibility measured. An aqueous dispersion of starch (5%, dry weight basis) was partially gelatinized by heating at different temperatures (60, 65, or 70 °C for 5 min). The relative melting Enthalpy values of the starch samples, based on the melting Enthalpy of native starch, were 69.0, 36.7, and 8.5%, respectively. Retrograded starch samples were also prepared by storing a fully gelatinized starch paste (5% starch) at 4 °C for 2, 4, or 7 d, and the relative melting Enthalpy values for the starch samples were 36.7, 67.2, and 79.9%, respectively. The partial gelatinization and retrogradation changed the enzymatic digestion behavior of the waxy rice starch samples, and the changes were significant in the initial stage of digestion. The digestion rate was reduced as the melting Enthalpy increased. The amounts of slowly digestible starch (SDS) and resistant starch (RS) correlated positively with the relative melting Enthalpy of the partially gelatinized or retrograded starch samples. The glycemic index (GI) estimated using an in vitro digestion test correlated negatively with the relative melting Enthalpy. At similar melting Enthalpy levels, the partially gelatinized starch samples were more resistant to enzymatic digestion than the retrograded starch samples, indicating that the thermal history and the crystalline morphology affected the enzymatic digestion behavior of starch.

  • Effect of partial gelatinization and retrogradation on the enzymatic digestion of waxy rice starch
    Journal of Cereal Science, 2006
    Co-Authors: Hyun-jung Chung, Hyesook Son Lim, Seung Taik Lim
    Abstract:

    The effect of partial gelatinization and retrogradation on in vitro enzymatic digestibility of waxy rice starch was investigated, and the relationship between the residual crystallinity and digestibility measured. An aqueous dispersion of starch (5%, dry weight basis) was partially gelatinized by heating at different temperatures (60, 65, or 70 °C for 5 min). The relative melting Enthalpy values of the starch samples, based on the melting Enthalpy of native starch, were 69.0, 36.7, and 8.5%, respectively. Retrograded starch samples were also prepared by storing a fully gelatinized starch paste (5% starch) at 4 °C for 2, 4, or 7 d, and the relative melting Enthalpy values for the starch samples were 36.7, 67.2, and 79.9%, respectively. The partial gelatinization and retrogradation changed the enzymatic digestion behavior of the waxy rice starch samples, and the changes were significant in the initial stage of digestion. The digestion rate was reduced as the melting Enthalpy increased. The amounts of slowly digestible starch (SDS) and resistant starch (RS) correlated positively with the relative melting Enthalpy of the partially gelatinized or retrograded starch samples. The glycemic index (GI) estimated using an in vitro digestion test correlated negatively with the relative melting Enthalpy. At similar melting Enthalpy levels, the partially gelatinized starch samples were more resistant to enzymatic digestion than the retrograded starch samples, indicating that the thermal history and the crystalline morphology affected the enzymatic digestion behavior of starch. © 2006 Elsevier Ltd. All rights reserved.

Pascal Marquet – One of the best experts on this subject based on the ideXlab platform.

  • on the computation of moist air specific thermal Enthalpy
    Quarterly Journal of the Royal Meteorological Society, 2015
    Co-Authors: Pascal Marquet
    Abstract:

    The specific thermal Enthalpy of a moist-air parcel is defined analytically following a method in which specific moist entropy is derived from the Third Law of Thermodynamics. Specific thermal Enthalpy is computed by integrating specific heat content with respect to absolute temperature and including the impacts of various latent heats (i.e. solid condensation, sublimation, melting, and evaporation). It is assumed that thermal enthalpies can be set to zero at 0 K for the solid form of the main chemically inactive components of the atmosphere (solid-α oxygen and nitrogen, hexagonal ice). The moist thermal Enthalpy is compared to already existing formulations of moist static energy (MSE). It is shown that the differences between thermal Enthalpy and the thermal part of MSE may be quite large. This prevents the use of MSE for evaluating accurately the Enthalpy budget of a moist atmosphere, a situation that is particularly true when dry air and cloud parcels mix because of entrainment/detrainment processes along the edges of cloud. Other differences are observed when MSE or moist-air thermal Enthalpy is plotted on a psychrometric diagram or when vertical profiles of surface deficit are plotted.

  • On the computation of moist‐air specific thermal Enthalpy
    Quarterly Journal of the Royal Meteorological Society, 2014
    Co-Authors: Pascal Marquet
    Abstract:

    The specific thermal Enthalpy of a moist-air parcel is defined analytically following a method in which specific moist entropy is derived from the Third Law of Thermodynamics. Specific thermal Enthalpy is computed by integrating specific heat content with respect to absolute temperature and including the impacts of various latent heats (i.e. solid condensation, sublimation, melting, and evaporation). It is assumed that thermal enthalpies can be set to zero at 0 K for the solid form of the main chemically inactive components of the atmosphere (solid-α oxygen and nitrogen, hexagonal ice). The moist thermal Enthalpy is compared to already existing formulations of moist static energy (MSE). It is shown that the differences between thermal Enthalpy and the thermal part of MSE may be quite large. This prevents the use of MSE for evaluating accurately the Enthalpy budget of a moist atmosphere, a situation that is particularly true when dry air and cloud parcels mix because of entrainment/detrainment processes along the edges of cloud. Other differences are observed when MSE or moist-air thermal Enthalpy is plotted on a psychrometric diagram or when vertical profiles of surface deficit are plotted.

  • on the computation of moist air specific thermal Enthalpy
    arXiv: Atmospheric and Oceanic Physics, 2014
    Co-Authors: Pascal Marquet
    Abstract:

    The specific thermal Enthalpy of a moist-air parcel is defined analytically following a method in which specific moist entropy is derived from the Third Law of thermodynamics. Specific thermal Enthalpy is computed by integrating specific heat content with respect to absolute temperature and including the impacts of various latent heats (i.e., solid condensation, sublimation, melting, and evaporation). It is assumed that thermal enthalpies can be set to zero at $0$ K for the solid form of the main chemically inactive components of the atmosphere (solid-$\alpha$ oxygen and nitrogen, hexagonal ice). The moist thermal Enthalpy is compared to already existing formulations of moist static energy (MSE). It is shown that the differences between thermal Enthalpy and the thermal part of MSE may be quite large. This prevents the use of MSE to evaluate the Enthalpy budget of a moist atmosphere accurately, a situation that is particularly true when dry-air and cloud parcels mix because of entrainment/detrainment processes along the edges of cloud. Other differences are observed when MSE or moist-air thermal Enthalpy is plotted on a psychrometric diagram or when vertical profiles of surface deficit are plotted.

Seung Taik Lim – One of the best experts on this subject based on the ideXlab platform.

  • Effect of partial gelatinization and retrogradation on the enzymatic digestion of waxy rice starch
    Journal of Cereal Science, 2006
    Co-Authors: Hyun-jung Chung, Hyesook Son Lim, Seung Taik Lim
    Abstract:

    The effect of partial gelatinization and retrogradation on in vitro enzymatic digestibility of waxy rice starch was investigated, and the relationship between the residual crystallinity and digestibility measured. An aqueous dispersion of starch (5%, dry weight basis) was partially gelatinized by heating at different temperatures (60, 65, or 70 °C for 5 min). The relative melting Enthalpy values of the starch samples, based on the melting Enthalpy of native starch, were 69.0, 36.7, and 8.5%, respectively. Retrograded starch samples were also prepared by storing a fully gelatinized starch paste (5% starch) at 4 °C for 2, 4, or 7 d, and the relative melting Enthalpy values for the starch samples were 36.7, 67.2, and 79.9%, respectively. The partial gelatinization and retrogradation changed the enzymatic digestion behavior of the waxy rice starch samples, and the changes were significant in the initial stage of digestion. The digestion rate was reduced as the melting Enthalpy increased. The amounts of slowly digestible starch (SDS) and resistant starch (RS) correlated positively with the relative melting Enthalpy of the partially gelatinized or retrograded starch samples. The glycemic index (GI) estimated using an in vitro digestion test correlated negatively with the relative melting Enthalpy. At similar melting Enthalpy levels, the partially gelatinized starch samples were more resistant to enzymatic digestion than the retrograded starch samples, indicating that the thermal history and the crystalline morphology affected the enzymatic digestion behavior of starch. © 2006 Elsevier Ltd. All rights reserved.

M. Ermelinda S. Eusébio – One of the best experts on this subject based on the ideXlab platform.

  • Enthalpy of sublimation/vaporization of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine
    The Journal of Chemical Thermodynamics, 2007
    Co-Authors: Luciana I.n. Tomé, Mário T. S. Rosado, Sandra C. C. Nunes, Teresa M. R. Maria, João Canotilho, M. Ermelinda S. Eusébio
    Abstract:

    Abstract The molar Enthalpy of sublimation, Δ cr g H m ∘ , of trans-cyclohexyl-1,4-diamine and the molar Enthalpy of vaporization, Δ l g H m ∘ , of cis-cyclohexyl-1,2-diamine, at the temperature 298.15 K, were determined by calorimetry. Δ cr g H m ∘ ( T = 298.15 K ) = ( 105.0 ± 0.8 ) kJ · mol – 1 was obtained for the trans-isomer and Δ l g H m ∘ ( T = 298.15 K ) = ( 62.2 ± 1.0 ) kJ · mol – 1 for the cis form. The molar Enthalpy of fusion of the first compound, at T = 342.1 K, was determined by differential scanning calorimetry. The molar Enthalpy of vaporization of the 1,4-isomer was estimated by combining the value of the Enthalpy of sublimation with that of the Enthalpy of fusion. The values obtained for molar standard Enthalpy of vaporization and those available for the Enthalpy of the diamines in the gas state were used to calculate the difference between the enthalpies of both compounds in the liquid state.

  • Solvation Enthalpy and the thermodynamics of hydration of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine
    The Journal of Chemical Thermodynamics, 2007
    Co-Authors: Luciana I.n. Tomé, João Canotilho, A. J. Lopes Jesus, R.a. Esteves De Castro, M. Helena S. F. Teixeira, M. Ermelinda S. Eusébio
    Abstract:

    Abstract The Enthalpy of solution of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine in water was determined by calorimetry. The Enthalpy of hydration was determined from this quantity and from the Enthalpy of sublimation/vaporization presented in another paper by the authors. Considering the solvation process resulting from cavity creation in the solvent and variation of solute conformation transfer steps, the Enthalpy corresponding to solute–solvent interaction was estimated. The entropies of solvation and interaction were calculated from the values given for the enthalpies in the present paper and those available for the Gibbs free energies.

  • Enthalpy of solvation of butanediols in different solvents
    Thermochimica Acta, 2000
    Co-Authors: A. J. Lopes Jesus, M. Ermelinda S. Eusébio, J.s. Redinha, M. L. P. Leitão
    Abstract:

    Abstract The enthalpies of solution for 1,2-, 1,3-, 1,4- and 2,3-butanediol in water, formamide and dimethylsulphoxide were determined by calorimetry. From the results and data available in the literature for the Enthalpy of vaporisation, the Enthalpy of solvation was determined. The Enthalpy of solvation was decomposed into two terms, cavity formation in the solvent to hold the solute and solute–solvent interaction.