Nickel Surface Layer Research Articles

A motion-induced sub-surface deformation wear mechanism

A sub-surface deformation phenomenon was identified as a wear mechanism in the plated metallurgies of electrical contact tabs on printed circuit cards. Under vibratory sliding conditions, the plastic flow of the copper substrate produces a bending and thinning of the intermediate layer of nickel and causes an upsurgence or upward motion of the copper, nickel and noble metal surface layers. This results in a high spot on the surface which now experiences increased local wear. Ultimately, there is local exposure within the wear region of the nickel and copper to the ambient environment, providing a potential for corrosion. The resultant appearance of the surface and cross-sections through the wear scar indicate that the sub-surface layers are locally being driven through the surface layer. An additional related phenomenon was observed in the analysis of card tabs that were tested at an elevated temperature. The copper substrate, directly under the wear track, experienced recrystallization and grain growth; the normally mottled grain structure was replaced with large, well defined grains. The physical evidence for these mechanisms, along with quantitative results showing differences in wear rates when these phenomena occur and when they do not, are presented. In addition, associated friction behavior is presented.

Polarized neutron diffraction by D2 chemisorbed on a nickel powder

The theory of surface differential diffraction (SDD) is extended to the case of polarized neutron diffraction. Nuclear and magnetic surface contributions are thus separated. A method for coherent description of the geometry of the grains is proposed. A saturated D layer chemisorbed on Ni carried by silica is studied with the following results: (111) faces represent the majority of the surface; D atoms sit above the centers of surface Ni triangles with no Ni atom in the underlying layer, the Ni-D distance is equal to 0.215 (7) nm; the magnetic-moment modification induced by chemisorption is mainly localized in the surface layer of nickel. Two possible interpretations of the magnetic structure factor are discussed: one assumes no magnetic moment on D atoms but Ni displacements; the other is based on opposite assumptions.

Electronic structure investigation at a zirconia-nickel interface

X-ray photoelectron spectroscopy (XPS) is used to study electronic structure effects at a zirconia-nickel interface. A method is described to fabricate ZrO 2 coatings on metallic substrates under ultrahigh vacuum conditions with a sufficiently low coverage to allow examination of the interfacial region. Charging effects which relate to the size of oxide particles deposited on the metal (and not to accumulated charge on the oxide) have been identified for small ZrO 2 particles on nickel, palladium and NiO substrates equivalent to a coating approximately 6A˚thick. The charging effects show up as a broadening of the XPS Zr 3d core-level spectrum. By examining the XPS Ni 2p 3/2 and XPS valence band spectra it is found that an oxidized nickel surface layer is reduced during ZrO 2 deposition.

Distribution of concentration of gold in the process of laser alloying of the nickel surface layer

The paper presents the results of studies on the mechanism of laser alloying of nickel with gold. From the investigations carried out, it has been found that thermocapillary phenomena play a predominant role in the alloying process. Experiments have satisfactorily confirmed the distribution area of the capillary motion velocity obtained by theoretical calculations. The paper contains examples of the actual distribution of the alloying material concentration in the areas alloyed with a single laser pulse.

A LEED analysis for the Ni(111)−(2 × 2)− O surface structure: Evidence for oxygen-induced relaxations of both vertical and lateral types in the close packed surface layer of nickel

A multiple-scattering analysis of LEED intensities has been made for the Ni(111)−(2 × 2)− O surface structure. The O atoms are found to chemisorb in the “expected” 3-coordinate hollow sites with the O-Ni bond length equal to 1.83 Å. There are also significant modifications to the metallic structure. The three surface Ni atoms which bond directly to each O are both lifted up vertically from the other surface Ni atoms, by about 0.12 Å essentially as reported earlier by high-energy ion scattering, and relaxed laterally in a “twist” displacement of magnitude about 0.07 Å. The surface Ni atoms which are not bonded to O lie 1.95 Å above the second Ni layer; this distance is significantly less than the bulk value of 2.03 A. The uncertainty in the relaxation parameters is believed to be about 0.03 Å. This study also suggests that LEED crystallography is able to fix the finer details of surface structures for O chemisorption on metal surfaces more closely than has often been appreciated.

EXAFS characterization of the adsorption sites of nickel ammine and ethylenediamine complexes on a silica surface

The evolution of the first and the second coordination shells of Ni 2+ ions in a nickel ion exchanged silica is monitored by EXAFS at the nickel K edge in the early stages of a Ni/SiO 2 catalyst preparation. There is a strong pH and ligand effect on the nature of the adsorbed state of Ni 2+ ions. At pH 9 in the wet gel, the coordination sphere of Ni 2+ ions completed by ammonia or ethylenediamine is not modified by electrostatic adsorption on the support. Below pH 9, ammonia can be substituted by water molecules to form penta- or tetraaammine complexes which can be thus grafted to the surface via a ligand substitution involving surface oxygens. Under theseconditions, the majority of nickel ions are engaged in the formation of a nickel surface layer which has a silicate structure. After drying at 353 K and whatever the pH of the exchange solution, the silicate is always formed. Below pH 7, no substantial cation exchange occurs on silica. On the contrary, the tris ethylenediamine nickel complex which is very stable above pH 7, does not lead to the silicate layer formation. The shift from electrostatic adsorption toward grafting only occurs under drying at 353 K leading to isolated grafted complexes. In all cases, a distance of 3.25–3.31 Å between nickel and 2 silicon ions is consistent with a grafting to a pair of vicinal silanol groups.

Hydride Formation in the Surface Layer of Nickel and Nickel-Iron Alloys by Cathodic Polarization

Hydride Formation in the Surface Layer of Nickel and Nickel-Iron Alloys by Cathodic Polarization

61Ni Mössbauer study of the hyperfine magnetic field near the Ni surface.

$^{61}\mathrm{Ni}$ M\"ossbauer measurements have been performed at 4.2 K on spherical Ni particles covered with a protective layer of SiO, with average diameter of 500 and 50 \AA{}. The hyperfine magnetic field at $^{61}\mathrm{Ni}$ nuclei for 500-\AA{} particles has been found to be 78.3(4) kOe, compared with the field for Ni foil of 75.0(2) kOe. The small difference is due to the demagnetization and dipolar fields in 500-\AA{} particles. The spectrum of 50-\AA{} particles has a surface component with the corresponding value of the hyperfine magnetic field of 40.3(5.4) kOe. This strongly indicates that, in accordance with recent theoretical studies, there is a decrease of the hyperfine magnetic field in the surface layer of nickel.

カソード分極によるニッケルおよびニッケル-鉄合金表面層での水素化物の形成

カソード分極によるニッケルおよびニッケル-鉄合金表面層での水素化物の形成