Phase diagram of the NaCl-water system from computer simulations

Autor: V. Bianco, M. M. Conde, C. P. Lamas, E. G. Noya, E. Sanz
Přispěvatelé: Ministerio de Ciencia, Innovación y Universidades (España), European Commission, Ayuntamiento de Madrid, Comunidad de Madrid, Universidad Politécnica de Madrid
Rok vydání: 2022
Předmět:
Zdroj: Digital.CSIC. Repositorio Institucional del CSIC
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ISSN: 1089-7690
Popis: 12 pags., 12 figs., 1 tab.
NaCl aqueous solutions are ubiquitous. They can crystallize into ice, NaCl, or NaCl · 2H2O depending on the temperature-concentration conditions. These crystallization transitions have important implications in geology, cryopreservation, or atmospheric science. Computer simulations can help understand the crystallization of these solids, which requires a detailed knowledge of the equilibrium phase diagram. We use molecular simulations in which we put at contact the solution with the solid of interest to determine points of the solid-solution coexistence lines. We follow two different approaches, one in which we narrow down the melting temperature for a given concentration and the other in which we equilibrate the concentration for a given temperature, obtaining consistent results. The phase diagram thus calculated for the selected model (TIP4P/2005 for water molecules and Joung-Cheatham for the ions) correctly predicts coexistence between the solution and ice. We were only able to determine NaCl · 2H2O-solution coexistence points at higher temperatures and concentrations than in the experiment, so we could not establish a direct comparison in this case. On the other hand, the model underestimates the concentration of the solution in equilibrium with the NaCl solid. Our results, alongside other literature evidence, seem to indicate that ion-ion interactions are too strong in the model. Our work is a good starting point for the improvement of the potential model and for the study of the nucleation kinetics of the solid phases involved in the phase diagram.
This project was funded by the Ministry of Science, Innovation and Universities (Grant Nos. FIS2016-78117-P and PID2019- 105898GB-C21). V.B. acknowledges the support from the European Commission through the Marie Skłokodowska Curie Fellowship No. 748170 ProFrost. E.G.N. acknowledges Agencia Estatal de Investigación and Fondo Europeo de Desarrollo Regional (FEDER) (Grant No. PID2020-115722GB-C21). C.P.L. acknowledges Ministerio de Universidades for a predoctoral Formación Profesorado Universitario (Grant No. FPU18/03326) and also Ayuntamiento de Madrid for a Residencia de Estudiantes grant. The authors acknowledge the computer resources and technical assistance provided by the RES. M.M.C. acknowledges financial support from the MICINN (Grant No. PID2019-105898GA-C22) and CAM and UPM through the Cavities (Project No. APOYO-JOVENES-01HQ1S-129- B5E4MM) from “Acción financiada por la Comunidad de Madrid en el marco del Convenio Plurianual con la Universidad Politecnica de Madrid en la linea de actuacion estimulo a la investigacion de jovenes doctores.” The authors gratefully acknowledge the Universidad Politecnica de Madrid (www.upm.es) for providing computing resources on Magerit Supercomputer.
Databáze: OpenAIRE
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