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Keshra Sangwal – One of the best experts on this subject based on the ideXlab platform.

  • Solubility of Ammonium Oxalate in water-acetone mixtures and metastable zone width of their solutions
    Chemical Engineering Research and Design, 2014
    Co-Authors: Keshra Sangwal, Ewa Mielniczek-brzóska, Sylwia Barylska

    Abstract:

    Abstract Experimental results on the solubility c of Ammonium Oxalate in mixed water–acetone solvents containing acetone content x T are presented and discussed using the theory of regular solutions. It was found that: (1) the dependence of the solubility c of Ammonium Oxalate in solutions of different mixed water–acetone solvents on temperature T follows an Arrhenius-type relation, (2) the dependence of c on acetone content x at different temperature T follows the relation: ln( c  +  δ ) =  a  −  bx , where the parameters a and b are measures of deviation of a solution from ideality and the correction factor δ is related to the activity coefficient f a of the solution, which decreases with an increase in c , and (3) the dependence of the solubility c of Ammonium Oxalate in solutions of different compositions x of water–acetone mixtures is related to the dielectric constant ɛ * of the solvent mixture, following the relation ln  c  =  C  +  C 1 ɛ *, where C and C 1 are related to the parameters a and b , respectively. Study of the metastable zone width, defined as maximum undercooling Δ T max a solution saturated at a particular temperature T can withstand, of some selected solutions of mixed water–acetone solvents at different T revealed that Δ T max decreases with an increase in antisolvent content x . The results are discussed using the self-consistent Nývlt-like approach.

  • Study of the nature of Cu(II) complexes in aqueous Ammonium Oxalate solutions by ultraviolet-visible spectroscopy
    Journal of Physics: Conference Series, 2011
    Co-Authors: Ewa Mielniczek-brzóska, Keshra Sangwal

    Abstract:

    Experimental results of an investigation of aqueous Ammonium Oxalate solutions containing Cu(II) impurity by ultraviolet–visible spectroscopy are described and discussed from the standpoint of speciation of complexes. The results show that absorption of light by aqueous Ammonium Oxalate solutions containing Cu(II) impurity in the range −5 < ln(ci/c) < 2.5 of the ratio of concentrations ci and c of impurity and solute, respectively, leads to decrease or increase in the intensity of bands of the ultraviolet–visible spectral regions, and these changes may be expressed by full width at half maximum, molar extinction coefficient, peak wavelength and oscillator strength. The changes are caused by the coordination of C2O42− ligand with Cu(H2O)62+ aquocomplex, and are related with the impurity–solute concentration ratio ci/c. The coordination of C2O42− ligand with Cu(H2O)62+ aquocomplex in the range 0 < ln(ci/c) < 2.5 leads to the formation of Cu(C2O4) complex, but the coordination of the C2O42− ligand with Cu(C2O4) complex in the concentration ratio range −5 < ln(ci/c) < 0 results in the formation of predominantly Cu(C2O4)22− complex. The effect of successive coordination of the C2O42− ligand is well-defined in the ultraviolet spectral region but poor in the visible region.

  • Investigation of metastable zone width of Ammonium Oxalate aqueous solutions
    Crystal Research and Technology, 2009
    Co-Authors: Keshra Sangwal, K. Wójcik

    Abstract:

    The metastable zone width of pure Ammonium Oxalate aqueous solutions, as represented by maximum supercooling ΔTmax, is investigated as functions of cooling rate R and saturation temperature T0 by the polythermal method. The experimental results are discussed by using two recently advanced approaches: (1) self-consistent Nývlt-like approach based on a power-law relationship between nucleation rate J and maximum supersaturation lnSmax, and (2) a novel approach based on the relationship between J and lnSmax described by the classical three-dimensional nucleation theory. Analysis of the experimental data revealed that both approaches describe the experimental data on metastable zone width by the polythermal method reliably and provide useful information about the physical processes and parameters involved in nucleation kinetics. The values of various physical quantities predicted by both of these approaches are reasonable for a fairly-soluble compound. A careful examination of the data on ΔTmax as a function of T0 obtained by polythermal method and from density measurements showed that ΔTmax has a slight tendency to decrease with increasing saturation temperature T0. The values of lnSmax at saturation temperature 303 K suggest that the metastable zone width of Ammonium Oxalate aqueous solutions is determined by primary nucleation in the polythermal method and by secondary nucleation during density measurements. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Bo Zou – One of the best experts on this subject based on the ideXlab platform.

  • Negative Linear Compressibility in Organic Mineral Ammonium Oxalate Monohydrate with Hydrogen Bonding Wine-Rack Motifs.
    The journal of physical chemistry letters, 2015
    Co-Authors: Yuancun Qiao, Kai Wang, Hongsheng Yuan, Ke Yang, Bo Zou

    Abstract:

    Negative linear compressibility (NLC) is a relatively uncommon phenomenon and rarely studied in organic systems. Here we provide the direct evidence of the persistent NLC in organic mineral Ammonium Oxalate monohydrate under high pressure using synchrotron X-ray powder diffraction, Raman spectroscopy and density functional theory (DFT) calculation. Synchrotron X-ray powder diffraction measurement reveals that Ammonium Oxalate monohydrate shows both positive and negative linear compressibility along b-axis before 11.5 GPa. The red shift of the external Raman modes and abnormal changes of several selected internal modes in high-pressure Raman spectra further confirmed the NLC. DFT calculations demonstrate that the N—H···O hydrogen bonding “wine-rack” motifs result in the NLC along b-axis in Ammonium Oxalate monohydrate. We anticipate the high-pressure study of Ammonium Oxalate monohydrate may represent a promising strategy for accelerating the pace of exploitation and improvement of NLC materials especially…

  • negative linear compressibility in organic mineral Ammonium Oxalate monohydrate with hydrogen bonding wine rack motifs
    Journal of Physical Chemistry Letters, 2015
    Co-Authors: Yuancun Qiao, Kai Wang, Hongsheng Yuan, Ke Yang, Bo Zou

    Abstract:

    Negative linear compressibility (NLC) is a relatively uncommon phenomenon and rarely studied in organic systems. Here we provide the direct evidence of the persistent NLC in organic mineral Ammonium Oxalate monohydrate under high pressure using synchrotron X-ray powder diffraction, Raman spectroscopy and density functional theory (DFT) calculation. Synchrotron X-ray powder diffraction measurement reveals that Ammonium Oxalate monohydrate shows both positive and negative linear compressibility along b-axis before 11.5 GPa. The red shift of the external Raman modes and abnormal changes of several selected internal modes in high-pressure Raman spectra further confirmed the NLC. DFT calculations demonstrate that the N-H···O hydrogen bonding “wine-rack” motifs result in the NLC along b-axis in Ammonium Oxalate monohydrate. We anticipate the high-pressure study of Ammonium Oxalate monohydrate may represent a promising strategy for accelerating the pace of exploitation and improvement of NLC materials especially in organic systems.

Ewa Mielniczek-brzóska – One of the best experts on this subject based on the ideXlab platform.

  • Electron spin echo and spin relaxation of low-symmetry Mn2+-complexes in Ammonium Oxalate monohydrate single crystal
    Journal of magnetic resonance (San Diego Calif. : 1997), 2014
    Co-Authors: Stanisław K. Hoffmann, Stefan Lijewski, Janina Goslar, Ewa Mielniczek-brzóska

    Abstract:

    Abstract Pulse EPR experiments were performed on low concentration Mn2+ ions in Ammonium Oxalate monohydrate single crystals at X-band, in the temperature range 4.2–60 K at crystal orientation close to the D-tensor z-axis. Hyperfine lines of the resolved spin transitions were selectively excited by short nanosecond pulses. Electron spin echo signal was not observed for the low spin transition (+5/2 ↔ +3/2) suggesting a magnetic field threshold for the echo excitation. Echo appears for higher spin transitions with amplitude, which grows with magnetic field. Opposite behavior displays amplitude of echo decay modulations, which is maximal at low field and negligible for high field spin transitions. Electron spin–lattice relaxation was measured by the pulse saturation method. After the critical analysis of possible relaxation processes it was concluded that the relaxation is governed by Raman T7-process. The relaxation is the same for all spin transitions except the lowest temperatures (below 20 K) where the high field transitions (−3/2 ↔ −1/2) and (−5/2 ↔ −3/2) have a slower relaxation rate. Electron spin echo dephasing is produced by electron spectral diffusion mainly, with a small contribution from instantaneous diffusion for all spin transitions. For the highest field transition (−5/2 ↔ −3/2) an additional contribution from nuclear spectral diffusion appears with resonance type enhancement at low temperatures.

  • Solubility of Ammonium Oxalate in water-acetone mixtures and metastable zone width of their solutions
    Chemical Engineering Research and Design, 2014
    Co-Authors: Keshra Sangwal, Ewa Mielniczek-brzóska, Sylwia Barylska

    Abstract:

    Abstract Experimental results on the solubility c of Ammonium Oxalate in mixed water–acetone solvents containing acetone content x T are presented and discussed using the theory of regular solutions. It was found that: (1) the dependence of the solubility c of Ammonium Oxalate in solutions of different mixed water–acetone solvents on temperature T follows an Arrhenius-type relation, (2) the dependence of c on acetone content x at different temperature T follows the relation: ln( c  +  δ ) =  a  −  bx , where the parameters a and b are measures of deviation of a solution from ideality and the correction factor δ is related to the activity coefficient f a of the solution, which decreases with an increase in c , and (3) the dependence of the solubility c of Ammonium Oxalate in solutions of different compositions x of water–acetone mixtures is related to the dielectric constant ɛ * of the solvent mixture, following the relation ln  c  =  C  +  C 1 ɛ *, where C and C 1 are related to the parameters a and b , respectively. Study of the metastable zone width, defined as maximum undercooling Δ T max a solution saturated at a particular temperature T can withstand, of some selected solutions of mixed water–acetone solvents at different T revealed that Δ T max decreases with an increase in antisolvent content x . The results are discussed using the self-consistent Nývlt-like approach.

  • Study of the nature of Cu(II) complexes in aqueous Ammonium Oxalate solutions by ultraviolet-visible spectroscopy
    Journal of Physics: Conference Series, 2011
    Co-Authors: Ewa Mielniczek-brzóska, Keshra Sangwal

    Abstract:

    Experimental results of an investigation of aqueous Ammonium Oxalate solutions containing Cu(II) impurity by ultraviolet–visible spectroscopy are described and discussed from the standpoint of speciation of complexes. The results show that absorption of light by aqueous Ammonium Oxalate solutions containing Cu(II) impurity in the range −5 < ln(ci/c) < 2.5 of the ratio of concentrations ci and c of impurity and solute, respectively, leads to decrease or increase in the intensity of bands of the ultraviolet–visible spectral regions, and these changes may be expressed by full width at half maximum, molar extinction coefficient, peak wavelength and oscillator strength. The changes are caused by the coordination of C2O42− ligand with Cu(H2O)62+ aquocomplex, and are related with the impurity–solute concentration ratio ci/c. The coordination of C2O42− ligand with Cu(H2O)62+ aquocomplex in the range 0 < ln(ci/c) < 2.5 leads to the formation of Cu(C2O4) complex, but the coordination of the C2O42− ligand with Cu(C2O4) complex in the concentration ratio range −5 < ln(ci/c) < 0 results in the formation of predominantly Cu(C2O4)22− complex. The effect of successive coordination of the C2O42− ligand is well-defined in the ultraviolet spectral region but poor in the visible region.