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- MakaleYalnız künye2027Scopus SJRQ2Design, structural characterization, and simulated radiation-transport assessment of high-entropy (GdErSmEuYb)2X2O7 (X = Hf, Zr, Ce, Si) rare-earth oxides
Güler, Ömer; Güler, Seval Hale; Yayla, Nihal; Baykal, Duygu Sen; Durmus, Hasan; Tekin, Huseyin Ozan; ALMisned, Ghada
This study investigates the structural, microstructural, surface-chemical, and radiation attenuation behaviour of high-entropy rare-earth oxide (HEO) powder compositions synthesized as TBC-related candidate coating materials, whose radiation attenuation potential was assessed within a computational Inconel-718-based sandwich model. Four compositions, namely (GdErSmEuYb)2Hf2O7, (GdErSmEuYb)2Ce2O7, (GdErSmEuYb)2Zr2O7, and (GdErSmEuYb)2Si2O7, were synthesized via high-energy ball milling followed by calcination at 1200 °C. X-ray diffraction results revealed the formation of distinct crystal structures depending on B-site chemistry, including defective fluorite and silicate-type phases. SEM-EDS mapping confirmed homogeneous elemental distribution, while XPS analysis demonstrated mixed valence states and different oxygen vacancy concentrations across the compositions. To evaluate radiation attenuation performance, a sandwich-type geometry consisting of a 10 mm Inconel-718 core with symmetrically defined simulated HEO layers was modelled using Monte Carlo simulations. Gamma-ray transmission was analyzed over an energy range of 0.276-1.332 MeV, and fast neutron attenuation was assessed at 4.5 MeV. The results showed that transmission factors decreased with increasing coating thickness, with the effect being more pronounced at lower photon energies. Among the investigated compositions, the Hf-based system exhibited the most favorable predicted attenuation response for both gamma rays and fast neutrons under the defined simulation conditions. Theoretical half-value layer calculations also showed good agreement with the simulation results. Overall, the findings indicate that high-entropy rare-earth oxide coatings may provide an additional radiation attenuation contribution when incorporated as layers in Inconel-718-based systems. However, since direct thermal-barrier properties such as thermal conductivity, thermal diffusivity, thermal cycling resistance, and thermal-stress behavior were not evaluated in the present work, the present study should be interpreted as a structural and radiation-transport assessment of TBC-related coating candidates rather than a direct demonstration of thermal-barrier performance.
- MakaleYalnız künye2026Scopus SJRQ1Engineering Ti-Zr-Hf high-entropy alloys (HEA) with rare-earth and boron additives for microstructure-controlled mixed-field radiation shielding: Fabrication, physical, structural and experimental γ-ray & fast-n shielding properties
Özkul, İskender; Güler, Ömer; Kavaz, E.; Kalay, Ece; Güler, Seval Hale; ALMisned, Ghada; Tekin, H.O.
This study investigates three newly designed Ti-Zr-Hf-based high-entropy alloys such as TiZrHfGdSm (N1), TiZrHfEr (N2), and TiZrHfGdEuB (N3), with the aim of understanding how selected rare-earth and boron additions influence microstructural evolution and dual γ-ray/fast-neutron shielding performance. All alloys were synthesized by arc melting and evaluated through thermodynamic modelling, X-ray diffraction, scanning electron microscopy with elemental mapping, and mixed-field attenuation measurements. The results show that each composition forms an HCP-type solid-solution matrix with composition-dependent lattice distortion and secondary phase formation. Among the studied systems, the Er-modified alloy N2 develops the most spatially uniform elemental distribution and demonstrates the most balanced combination of γ-ray attenuation, effective atomic number, buildup behaviour, and fast-neutron removal efficiency. N1 and N3, containing multiple rare-earth elements and, in the case of N3, boron-induced borides, exhibit distinct grain features and provide valuable insights into how multi-element additions shape photon and neutron interaction pathways. Comparative examination confirms that shielding performance in these HEAs is governed by the interplay of elemental cross sections, density, and microstructural uniformity. The findings highlight Ti-Zr-Hf-RE(B) alloys as promising platforms for multifunctional radiation-shielding materials and provide a compositional framework for future optimization in nuclear, medical, and aerospace applications.
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İncele - MakaleAçık Erişim2026Scopus SJRQ1Effect of dilute rare-earth addition on structural evolution, mechanical, magnetic, and radiation shielding properties of CoFeNiMnTi high-entropy alloy
Özkul, İskender; Kalay, Ece; Güler, Ömer; Karaduman, Oktay; Canbay, Canan Aksu; Hameed, Louis Ibrahim; Almisned, Ghada; Baykal, Duygu Sen; Tekin, H.O.
This study investigates the effect of 1 at.% rare-earth (RE = Sm, Gd, Dy) addition on the structural, mechanical, magnetic, and radiation shielding properties of CoFeNiMnTi high-entropy alloys produced by arc melting. X-ray diffraction results reveal an FCC-dominant structure accompanied by secondary Laves-type phases, with increased phase complexity observed in Gd- and Dy-containing alloys. Mechanical evaluation shows a significant hardness enhancement, reaching 581 HV for Gd and 548 HV for Dy, compared to 447 HV for the reference alloy. Magnetic measurements indicate soft-ferromagnetic behaviour for all compositions, with magnetization increasing in the order S0<S1<S2<S3, highlighting the strong influence of Dy on magnetic response. Elemental mapping confirms a homogeneous distribution with minor local compositional variations contributing to phase evolution. Thermodynamic analysis suggests that rare-earth addition increases lattice distortion and chemical complexity without strongly differentiating among RE types. In terms of radiation shielding, linear attenuation coefficients and effective atomic number values demonstrate improved gamma-ray attenuation, particularly at low energies, with Dy exhibiting the highest performance. In contrast, fast neutron removal cross section values remain nearly unchanged, indicating limited sensitivity to dilute RE addition. It can be concluded that the incorporation of Dy results in the most balanced multifunctional performance, whereas Gd primarily enhances mechanical strength, emphasizing the importance of rare-earth selection in the design of high-entropy alloys for radiation-related applications.
- MakaleYalnız künye2025Scopus SJRQ1The Extraction of Rare-Earth Elements (REEs) from Spent Nickel–Metal Hydride (Ni–MH) Batteries by Bifunctional Ionic Liquids (Bif-ILs): Process Optimization and Kinetics Modeling
Erust, Ceren
The cathode material of nickel–metal hydride (Ni–MH) batteries includes nickel, cobalt, and rare-earth elements (REEs) such as La, Ce, Nd, and Pr, which are among the critical raw materials (CRMs). Ionic liquids as the environmentally friendly approaches are proposed by various investigations for the extraction of critical metals from spent Ni–MH batteries. In this study, three different Bifunctional Ionic Liquids (Bif-ILs) were designed for comparative studies, namely Aliquat 336–Cyanex 272 (AL–CY), Aliquat 336–PC88A (AL–PC), and Aliquat 336–D2EHPA (AL–D2). The extraction results indicated that temperature has a direct effect on the extraction of critical metals in the presence of all Bif-ILs. Among three types of Bif-ILs, AL–D2 has an optimal extraction power (La: 98.8%, Ce: 94.2%, Nd: 99.2%, and Pr: 98.4%) after precipitation of 99.99% of Ni and Co. Furthermore, kinetics modeling is used for reaction mechanisms investigation. Results indicated that the mixed controlled model by shrinking core model (diffusion controlled and chemical reaction controlled) was the best model fitted to all data (coefficient of determination (R2) > 0.90). according to the Arrhenius equation, activation energies for all REEs in the presence of all Bif-ILs are between 13 and 42 kJ/mol that reflects a mixed controlled reaction.
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