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1
Gas Hydrates Phase Equilibria and Formation from High Concentration NaCl Brines up to 200 MPa

Hu, Yue,Makogon, Taras Y.,Karanjkar, Prasad,Lee, Kun-Hong,Lee, Bo Ram,Sum, Amadeu K. American Chemical Society 2017 Journal of chemical and engineering data Vol.62 No.6
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Gas hydrate phase equilibrium and kinetics at high NaCl concentrations (near and at saturation in solution) and very high pressures (up to similar to 200 MPa) are investigated to study the interplay of hydrate formation and salt precipitation. Limited experimental data above 80 MPa exist for hydrate phase equilibrium in high salinity systems. This study reveals the unusual formation of gas hydrates under these extreme conditions of high salinity and very high pressure. In particular, the results demonstrate that hydrates can form from saturated salt solutions, and the formation of hydrates and salt precipitation are competing effects. It is determined that hydrates will remain in equilibrium with a saturated salt solution, with the amount of salt precipitation determined by the amount of hydrates formed. These data are essential fundamental data for gas hydrates applications in the oil and gas production flow assurance and seawater desalination.
2
Gas hydrates phase equilibria for structure I and II hydrates with chloride salts at high salt concentrations and up to 200MPa

Hu, Yue,Makogon, Taras Y.,Karanjkar, Prasad,Lee, Kun-Hong,Lee, Bo Ram,Sum, Amadeu K. Elsevier 2018 The Journal of chemical thermodynamics Vol.117 No.-
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Abstract Gas hydrates phase equilibria for structure I and II hydrates with chloride salts (NaCl, CaCl2, KCl and MgCl2) were measured at high salt concentrations and up to 200MPa. The measured equilibrium data represent three-phase (Solution – Hydrate – Vapor) or four-phase (Solution – Hydrate – Salt precipitated – Vapor) equilibrium depending on the salt concentration. The hydrate phase boundary with salts was shifted to lower temperatures and higher pressures when the experimental system was below the salt saturation concentration, while the boundaries were unchanged at salt concentrations above saturation, corresponding to quadruple points. The experimental data were compared with hydrate equilibrium predictions calculated by commonly used predictive tools to assess the reliability of these tools for the brines and conditions considered. The comparison demonstrates that predictive tools exhibit large deviation to the measured data, especially at high pressures and high salinity conditions. Highlights <UL> <LI> Gas hydrates phase equilibria with chloride salts were measured up to 200MPa. </LI> <LI> Predictions deviate from measured data at high salt concentration and high pressure. </LI> <LI> Measured data are valuable to test and improve hydrate predictive tools. </LI> </UL>
3
Solid - state Reactions in Ni / Si Multilayered Films, Investigated by Optical and Magneto - optical Spectroscopy

Y. P. Lee,S. M. Kim,Y. V. Kudryavtsev,Y. N. Makogon 한국진공학회(ASCT) 2003 Applied Science and Convergence Technology Vol.12 No.S1
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Solid-state reactions in Ni/Si multilayered films (MLF) with an overall stoichiometry of Ni₂Si, NiSi and NiSi₂, induced by ion-beam mixing (IBM) and thermal annealing, were studied by using spectroscopic ellipsometry and magnetooptical spectroscopy as well as x-ray diffraction (XRD). The mixing was performed with Ar^+ ions of an energy of 80 keV and a dose of 1.5×10^(16) Ar^+/㎠. It was shown that the IBM induces structural changes in the Ni/Si MLF, which cannot be detected by XRD but are confidently recognized by the optical method. A thermal annealing at 673 K of the Ni/Si MLF with an overall stoichiometry of NiSi and NiSi₂ causes formation of the first η-NiSi phase. The first trace for NiSi₂ phase on the background of NiSi one was detected by XRD after an annealing at 1073 K while, according to the optical results, NiSi₂ turns out be the dominant phase for the annealed Ni/Si MLF with an overall stoichiometry of NiSi₂.