FIRST-PRINCIPLES STUDY ON THE THERMODYNAMIC DEFECT AND CRYSTAL STRUCTURE OF U-12.5 AT% Nb ALLOY

Wang, Jintao; Wang, Yu; Wang, Tao; Wang, Yuling; Gao, Yunliang

doi:10.18280/ijht.330124

Cited by 8 publications

(6 citation statements)

References 8 publications

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“…In view of the previous research [21,22] and the test results of this paper, the author finds that the tribological properties of nanometer lanthanum borate can be greatly improved through thermal activation under 300°C-600°C because the formation of the composite repair film layer, which contains FeB and La2O3, further enhances the anti-friction and lubrication performance of heat-treated nanometer lanthanum borate. On the contrary, the nanometer lanthanum borate treated under 900°C produces B2O3, a hard, ceramic material, through a cracking reaction.…”

Section: Discussion Of the Anti-friction And Anti-wear Mechanismmentioning

confidence: 69%

Effect of heat treatment temperature on the structure and tribological properties of nanometer lanthanum borate

Wang¹,

Huang²

2017

IJHT

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Nanometer lanthanum borate was prepared by ultrasonic-assisted chemical precipitation. X-ray diffraction and a laser particle size analyzer were used to study the heat treatment temperature on the micro-structure of the nanoparticles, and the tribological properties of nanoparticles were explored for friction and wear using a MMU-10G testing machine. The results show that the heat treatment temperature not only determines the crystallization degree and crystal type of nanometer lanthanum borate, but also greatly affects the anti-friction and wear-resistance properties of the base oil. When the heat treatment temperature is between 300°C and 600°C, amorphous La2[B4O5(OH)4]3 nanoparticles are formed. Featuring strong chemical activity, adsorption on the friction surface, and a significant anti-wear self-repair effect, the nanoparticles can promote the formation of a tribochemical reaction film. When the heat treatment temperature exceeds 900°C, the particle size distribution in the bed becomes broader and shifts to a larger size. Hard-phase crystal LaBO3 and B2O3 particles are formed, which intensifies the abrasive wear and the tribological properties are reduced.

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Section: Discussion Of the Anti-friction And Anti-wear Mechanismmentioning

confidence: 69%

Effect of heat treatment temperature on the structure and tribological properties of nanometer lanthanum borate

Wang¹,

Huang²

2017

IJHT

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“…We introduce a 16-atom supercell approximation for the U-6Nb alloy by replacing 2 of the 16 uranium atoms with niobium in an ordered U 14 Nb 2 compound, either in the monoclinic α" phase or the orthorhombic α phase. This assumption is analogous to the study by Wang et al [32]. Geometrical energy optimization (structural relaxation) is performed for the genuine phases (α for uranium and α" for the U-6Nb alloy).…”

Section: Methodsmentioning

confidence: 99%

“…From a modeling standpoint, there are fewer studies on the uranium-niobium system, but there are some recent phenomenological works reported [25,[27][28][29]. Uranium-niobium has also been investigated from first-principles electronic structure theory [30][31][32][33]. However, no theoretical or experimental data on elastic properties are found in the literature, even though they are central for understanding the mechanical behavior and the SME of the U-Nb alloys.…”

Section: Introductionmentioning

confidence: 99%

Mechanical and Thermal Properties for Uranium and U–6Nb Alloy from First-Principles Theory

et al. 2021

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Elasticity, lattice dynamics, and thermal expansion for uranium and U–6Nb alloy (elastic moduli) are calculated from density functional theory that is extended to include orbital polarization (DFT+OP). Introducing 12.5 at.% of niobium, substitutionally, in uranium softens all the cii elastic moduli, resulting in a significantly softer shear modulus (G). Combined with a nearly invariant bulk modulus (B), the quotient B/G increases dramatically for U–6Nb, suggesting a more ductile material. Lattice dynamics from a harmonic model coupled with a DFT+OP electronic structure is applied for α uranium, and the obtained phonon density of states compares well with inelastic neutron-scattering measurements. The Debye temperature associated with the lattice dynamics falls within the range of experimentally observed Debye temperatures and it also validates our quasi-harmonic (QH) phonon model. The QH Debye–Grüneisen phonon method is combined with a DFT+OP electronic structure and used to explore the anisotropic thermal expansion in α uranium. The anomalous negative thermal expansion (contraction) of the b lattice parameter of the α-phase orthorhombic cell is relatively well reproduced from a free-energy model consisting of QH-phonon and DFT+OP electronic structure contributions.

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“…Uranium is a typical member of the early actinide metallic elements due to its very wide range of applications in the aerospace, military weapons and nuclear industries [1][2][3][4][5][6][7][8][9][10][11][12][13]. In general, the -uranium occurs under normal pressure conditions [3].…”

Section: Introductionmentioning

confidence: 99%

Study on Electronic Properties of α-Uranium using Ab-initio Approach

Vora

2022

BIBECHANA

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In the present work, a density functional theory (DFT) based simulation is performed to study the electronic properties of (-uranium through the electronic band structure, total electron density of states (DOS), integrated density of states (IDOS), partial density of states (PDOS) and Fermi-surface measurements. A Generalized Gradient Approximation (GGA) with Projector-Augmented Wave (PAW) pseudopotential is used in present computation. The hybridization between the 5f orbital and 6d orbital also has fairly influences on the electronic Properties of α-Uranium. BIBECHANA 19 (2022) 208-213

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FIRST-PRINCIPLES STUDY ON THE THERMODYNAMIC DEFECT AND CRYSTAL STRUCTURE OF U-12.5 AT% Nb ALLOY

Cited by 8 publications

References 8 publications

Effect of heat treatment temperature on the structure and tribological properties of nanometer lanthanum borate

Effect of heat treatment temperature on the structure and tribological properties of nanometer lanthanum borate

Mechanical and Thermal Properties for Uranium and U–6Nb Alloy from First-Principles Theory

Study on Electronic Properties of α-Uranium using Ab-initio Approach

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