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3. Nucleation-growth versus spinodal decomposition in Fe-Cr alloys: an experimental verification by atom probe tomography and small angle neutron scattering

Author

Sarkar, Sudip Kumar, Ray, Debes, Sen, Debasis, and Biswas, Aniruddha

Subjects
Condensed Matter - Materials Science
Abstract

Identifying the operative mode of phase separation (spinodal decomposition (SD) or nucleation-growth (NG)) remains a largely unexplored area of research in spite of its importance. The present work examines this critically in Fe-Cr system using atom probe tomography (APT) and small angle neutron scattering (SANS), and establishes the framework to distinguish the two different modes of alpha-prime phase separation in thermally aged Fe-35 at.% Cr and Fe-20 at.% Cr alloys. Independent APT analysis determines the mode of phase separation on the basis of: (i) presence / absence of periodic chemical fluctuation through radial distribution function analysis; and (ii) inter-phase interface characteristics (diffuse / sharp). SANS analysis, in contrast, yields virtually indistinguishable correlation peaks for both the modes, which necessitates further investigation of the several different aspects of SANS profiles in the light of APT results. For the first time, key features of SANS profiles have been identified that can unambiguously distinguish SD from NG in Fe-Cr system: (i) nature of temporal evolution of FWHM of the correlation peak; and (ii) appropriate value of 'gamma' for fitting with the dynamic scaling model ('gamma'= 6 for SD, Fe-35 at.% Cr alloy; 'gamma'= 4 for NG, Fe-20 at.% Cr alloy).

Published
2021
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29. Self‐assembly and solution behavior of cationic surfactants in water‐trifluoroethanol environment: An experimental and theoretical approach.

Author

Kumar, Vinod, Padsala, Shailesh, Mayursing, Girase, Ray, Debes, Aswal, Vinod Kumar, Kuperkar, Ketan, and Bahadur, Pratap

Subjects
CATIONIC surfactants, SMALL-angle neutron scattering, CRITICAL micelle concentration, SURFACE tension, SURFACE pressure, MOLECULAR interactions
Abstract

The micellization behavior of conventional cationic surfactant: tetradecyltrimethylammonium bromide (TTAB), and Gemini surfactant (GS): N,N′‐ditetradecyl‐N,N,N′,N′‐tetramethyl‐N,N′‐ethanediyl‐diammonium dibromide (14‐2‐14) in water and water‐trifluoroethanol (TFE) solvent mixture has been examined using tensiometric and small‐angle neutron scattering (SANS) techniques. Critical micelle concentration (CMC), and various interfacial parameters such as surface tension at CMC (γCMC), surface pressure at CMC (πCMC), maximum surface excess concentration (Γmax), and minimum area occupied by the head group (Amin) were evaluated for our examined systems at 303.15 K. It was observed that with the increase in TFE concentration, the CMC of the tested cationic surfactants decreased, thereby favoring the micellization in the presence of the surface‐active TFE. Furthermore, the geometry and aggregation number (Nagg) of surfactant micelles were inferred using SANS that revealed the decrease in micelle size of cationic surfactants. Additionally, the computational simulation study provided an insight into the molecular interactions in the examined system that validated our experimental findings. [ABSTRACT FROM AUTHOR]

Published
2024
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