Dependence of electron work function of Al-Mg alloys on surface structures and relative humidity

Xue, Mingshan; Xie, Juan; Li, Wen; Yang, Chao; Ai, Yongfeng; Wang, Fajun; Ou, Junfei; Yao, Junping

doi:10.1016/j.physb.2011.08.017

Cited by 24 publications

(17 citation statements)

References 28 publications

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“…It was also reported that the WF might be altered by the change in the Fermi level or band gap associated with surface structures [13,14]. Recently, we found that the WF of Al-Mg alloys decreased with the increase of surface smoothness, whereas surface oxide layers resulted in the increase of the WF [15]. Nevertheless, relative to the study of a kind of material, a comparative study of several kinds of materials may be more helpful to reveal the inherent mechanisms responsible for the effect of surface conditions on the WF.…”

Section: Introductionmentioning

confidence: 72%

Understanding of the correlation between work function and surface morphology of metals and alloys

Xue¹,

Wang²,

Wang³

et al. 2013

Journal of Alloys and Compounds

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Section: Introductionmentioning

confidence: 72%

Understanding of the correlation between work function and surface morphology of metals and alloys

Xue¹,

Wang²,

Wang³

et al. 2013

Journal of Alloys and Compounds

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“…It was reported that the measured Volta potential of Al 2 CuMg decreases to become less noble than the matrix when the oxide layer is removed. 27,40 It is widely recognized that the experimental Volta potential can be influenced by many factors, such as the measuring environment, 23 the structure and thickness of the oxide film formed on the surface, 22 the adsorption of gaseous species 24 and the tip-sample distance. 13 This circumstance highly motivates the theoretical calculation of the Volta potential for relative nobility evaluation.…”

Section: Resultsmentioning

confidence: 99%

First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications

Jin

Liu

Zhang

et al. 2017

J. Electrochem. Soc.

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This work presents a theoretical assessment of galvanic (relative) nobility of four intermetallic particles (IMPs), Al 2 Cu, Al 2 CuMg, Mg 2 Si and MgZn 2 , in aluminum alloys through work function calculation based on density functional theory (DFT). The concepts of work function, Volta potential and relative nobility are discussed with respect to the IMPs and aluminum matrix. The calculated Volta potentials are compared with reported experimental Volta potentials measured by scanning Kelvin probe force microscopy (SKPFM). Various crystal faces and terminal types are examined in the DFT calculation, showing that these two factors have a significant effect on the work function value. Considering the large divergence in the reported experimental data, the comparison shows a general agreement between the calculated and experimental Volta potential data for the investigated IMPs. The DFT calculations provide theoretical explanations for several experimental phenomena. The results demonstrate that DFT calculation is a valuable theoretical approach for assessment of the relative nobility of different phases in the alloys, providing complementary information to experimental data from SKFPM. Moreover, the implications of the calculated Volta potentials are discussed with respect to the corrosion potentials. The addition of various alloying elements into the aluminum (Al) matrix to improve mechanical performance of Al alloys may simultaneously increase their susceptibility to localized corrosion. This is mainly due formation of intermetallic particles (IMPs) that may trigger micro-galvanic corrosion along the interface between the IMPs and the alloy matrix.1 The potential differences between the IMPs and the matrix may result in localized dissolution of the matrix or dealloying of the IMP. 2The most common IMPs present in 2xxx and 7xxx series Al alloys include Al 2 CuMg (S-phase), Al 2 Cu (θ-phase), Al 7 Cu 2 Fe (β-phase), MgZn 2 (η-phase) and Mg 2 Si.3-5 IMPs containing Cu and Fe, such as Al 2 Cu. 6 and Al 7 Cu 2 Fe, 7 are considered to be cathodic with respect to the matrix, acting as local cathodes and thus promoting cathodic reactions such as oxygen reduction. In contrast, Mg-rich IMPs, such as Al 2 CuMg, are considered anodic relative to the matrix, resulting in selective dissolution and concomitant Cu-enrichment of the IMP.8 These localized corrosion events may eventually trigger other corrosion forms, such as stress corrosion cracking or intergranular corrosion.9 Therefore, micro-galvanic corrosion effects between IMPs and the Al matrix is considered to be of utmost importance for the overall service performance of Al alloys.In 1987, Stratmann started to use the Kelvin probe to investigate corrosion properties of metals under thin electrolyte films.10 His measurements revealed a linear relationship between Volta potential and corrosion potential of Cu, Zn, Fe and other metals. Later, the scanning Kelvin microprobe was developed and used for Volta potential measurements of several metals in humid atmospheres.11 Du...

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“…However, the surface morphology may play a crucial role in the successful correlation of the two potentials, since the Volta potential is influenced significantly by microstructure [38]. The CPD and OCP mappings presented in Figure 5 indicate that their compositional variations are indeed affected by different factors.…”

Section: Resultsmentioning

confidence: 99%

Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

Mardare

Kollender

et al. 2018

Science and Technology of Advanced Materials

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A thin film combinatorial library deposited by co-sputtering of Hf, Nb and Ta was employed to characterise fundamental properties of the Hf-Nb-Ta system. Compositional mappings of microstructure and crystallography revealed similarities in alloy evolution. Distinct lattice distortion was observed upon addition of hexagonal Hf, leading to amorphisation of alloys containing more than 32 at.% Hf and less than 27 and 41 at.% Nb and Ta, respectively. Volta potential and open circuit potential mappings indicated minimal values for the highest Hf concentration. Localised anodisation of the library by scanning droplet cell microscopy revealed valve metal behaviour. Oxide formation factors above 2 nm V−1 were identified in compositional zones with high amounts of Nb and Ta. Fitting of electrochemical impedance spectroscopy data allowed electrical permittivity and resistivity of mixed oxides to be mapped. Their compositional behaviours were attributed to characteristics of the parent metal alloys and particularities of the pure oxides. Mott–Schottky analysis suggested n-type semiconductor properties for all Hf–Nb–Ta oxides studied. Donor density and flat-band potential were mapped compositionally, and their variations were found to be related mainly to the Nb amount. Synergetic effects were identified in mappings of Hf-Nb-Ta parent metals and their anodic oxides.

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Dependence of electron work function of Al-Mg alloys on surface structures and relative humidity

Cited by 24 publications

References 28 publications

Understanding of the correlation between work function and surface morphology of metals and alloys

Understanding of the correlation between work function and surface morphology of metals and alloys

First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications

Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

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