Thin Ni Foils Research Articles

Effect of stresses on the dielectric and piezoelectric properties of Pb(Zr0.52Ti0.48)O3 thin films

Flexible piezoelectric microelectromechanical systems can experience a wide range of stress conditions. In order to explore the functional properties over this range, the dielectric and piezoelectric properties of 0.6 μm thick {001} sol-gel Pb0.99⧠0.01(Zr0.52Ti0.48)0.98Nb0.02O3 (PZT) films on Si substrates and thin Ni foils were measured as a function of stress arising from thermal expansion mismatch during fabrication or applied by bending of a cantilever. Due to the differences in residual thermal stress, the remanent polarization, Pr, was approximately 21 ± 0.2 μC/cm2 and 39.5 ± 2.3 μC/cm2 for PZT films on Si and Ni, respectively, with the higher Pr on Ni originating from more “c” domains (out-of-plane polarization) due to the compressive stresses. The link between stress and domain orientation was further explored by bending films on Ni around mandrels with known radii of curvature to apply uniaxial strains of −0.2% to 0.5%. Films on Si were only exposed to strains between −0.06% and 0.06%, because of substrate failure. For films on 50 μm thick Ni foil, under a 0.5% tensile strain, the Pr decreased by 7%–10% and the permittivity increased up to 23% relative to zero applied stress samples. This trend reversed upon compressive strain. In addition, the piezoelectric coefficient, e31,f, is reported to be −9.0 ± 0.45 μC/cm2 and −7.1 ± 0.35 μC/cm2 on Ni and Si, respectively, and increased in magnitude with applied uniaxial compressive strain. These changes are consistent with substantial levels of ferroelastic reorientation.

Experimental Investigation and Thermodynamic Modeling of the Ni-Rich Part of the Ni-N Phase Diagram

The N uptake of thin Ni foils was monitored by use of nitriding experiments performed in NH3-H2 gas atmospheres as function of the atmosphere’s composition between 673 K and 873 K (400 °C and 600 °C). With increasing nitriding potential $$ r_{\text{N}} = {{p_{{{\text{NH}}_{3} }} } \mathord{\left/ {\vphantom {{p_{{{\text{NH}}_{3} }} } {p_{{{\text{H}}_{2} }}^{3/2} }}} \right. \kern-0pt} {p_{{{\text{H}}_{2} }}^{3/2} }} $$ (with $$ p_{{{\text{NH}}_{3} }} $$ and $$ p_{{{\text{H}}_{2} }}^{{}} $$ being the partial pressures of the ammonia and hydrogen in the nitriding atmosphere at the Ni specimen’s surface) first an increasing uptake of N by the terminal Ni[N] solid solution was observed up to about 1 at. pct N. Upon surpassing a threshold nitriding potential, the Ni3N compound was formed. A thermodynamic interpretation of the observed data is only possible by taking into account the (small) degree of decomposition of the NH3 at the surface of the specimens, to arrive at the effective values of r N genuinely acting at the surface of the specimen. The data obtained were used to determine model descriptions for (i) the Gibbs energy of dissolution of N into Ni[N] (at infinite dilution), which was modeled as an ideal interstitial solid solution, and (ii) the Gibbs energy of formation of Ni3N (in equilibrium with Ni[N]). The thermodynamic model descriptions of Ni[N] and Ni3N, associated with these Gibbs energies, were used to calculate the Ni-rich part of the phase diagram Ni-N. A comparison of the values of the Gibbs energy of dissolution of N in various 3d-metal based terminal solid solutions reveals a considerable decrease of the stability of such solutions with increasing atomic number.

Combined micro-beam Laue and white beam topography: mapping local lattice orientation and misorientation

Micro-beam Laue diffraction is a well-established technique to determine lattice orientation and lattice structure. A polychromatic X-ray beam is used to illuminate a scattering volume within individual crystallites. The resulting diffraction pattern consists of a number of Laue spots. By refinement of the exact spot positions, lattice orientation and deviatoric elastic strain of the single crystalline scattering volume can be determined. Diffraction spot shape is linked to the orientation spread in the scattering volume arising due to the local dislocation structure. However, angular resolution of Laue diffraction spots is limited due to small sample-to-detector distance (~100 mm) and large Laue camera pixel size (~40 µm). In contrast, X-ray diffraction topography allows high-resolution imaging of an individual reflection from a crystal. On beamline B16 at the Diamond Light Source, we have combined micro-beam Laue diffraction with simultaneous collection of diffraction topographs, using a second high-resolution X-ray camera in the far field. In situ deformation of a single grain within a thin Ni foil has been studied using this setup. While detailed analysis is ongoing, some early results are presented here to allow an assessment of the technique's utility and future development possibilities.

X-ray resonant Raman scattering on Ni employing polarized and unpolarized exciting radiation

The X-ray resonant Raman scattering effect on nickel was studied by means of monochromatic polarized and unpolarized exciting radiation, respectively. Experiments involving polarized exciting radiation were carried out at the four crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt for synchrotron radiation from 4 to 10 keV at the electron storage ring BESSY II. Resonant Raman spectra of thin Ni foils were recorded at the Cu-K α (8041 eV) exciting beam energy. In the Institute of Nuclear Physics of the N.C.S.R. Demokritos, the resonant Raman spectrum of a thick nickel target was also recorded for an unpolarized Cu-K α (8041 eV) exciting beam produced after the ionization of a thick Cu target by 1.7 MeV protons in a triaxial, orthogonal geometry. In the present work, the individual spectral characteristics and the methodological approaches adopted for the extraction of the Ni-RRS cross sections, with respect to each mode of excitation, are presented, compared and discussed. An excellent agreement was found between the Ni KL-RRS cross sections determined for polarized and unpolarized exciting radiation confirming the theoretical predictions within the experimental uncertainties achieved.

Excitation function of the 64Ni( α,p) 67Cu reaction for production of 67Cu

The excitation function of the 64Ni( α,p) 67Cu reaction was measured from threshold up to 24 MeV in order to investigate the possibility of production of the β −-emitting therapeutic radioisotope 67Cu ( T 1/2=61.9 h). Two stacks of thin metallic self-supporting foils of 64Ni (enrichment 77.8%) prepared by electrolytic deposition were irradiated by α-particle beams. The radioactivity was determined via HPGe detector γ-ray spectrometry. Some 67Ga activity (which emits the same γ-rays as 67Cu), formed via the natCu( α, x) 67Ga process on trace copper impurity in the Ni foils, was also observed. Corrections were done for 67Ga activity contribution and for the 67Cu activity escape fraction from the thin Ni-foil. The maximum cross section of the 64Ni( α,p) 67Cu reaction amounts to 34 mb at 22 MeV. The experimental results were compared with theoretical predictions. The integral yield of 67Cu at 24 MeV α-particle energy, calculated from the excitation function, amounts to 544 KBq/μAh (48.5 MBq/μA at saturation). It is thus a low-yield reaction.

Combustion reaction in multilayered nickel and aluminum foils

Ni/Al (3/1) multilayer reaction piles were heated in a vacuum furnace and the temperature (100 readings per s for a precision of 0.2°C) of the reaction pile was measured continuously during the combustion reaction. The ignition temperature (at which the combustion starts) is almost the same independent of heating rate and the thickness of the foils. This temperature corresponds to the melting of Al which triggers the reaction. For thin Ni foils, less than 25 μm thick, the maximum temperature shows a plateau with time, close to the adiabatic reaction temperature or the eutectic temperature close to Ni3Al. For thicker Ni foils, the maximum temperature decreases with the increase of foil thickness and the combustion is incomplete. The reaction time between the ignition temperature and the maximum temperature (or the beginning of the plateau temperature) increases from 8 s for a 12.5 μm Ni foil to 125 s for a 150 μm Ni foil and the relation is almost linear. For Ni foils less than 25 μm thick, the final microstructure is homogeneous with a grain size approximately equal to the combined initial Ni and Al foil thicknesses. In the range used, 1–100°C min−1, the heating rate has very little effect on the combustion reaction. From the temperature-time profile and microstructure analysis, there are evidences of melting of Al, decomposition of Al3Ni and Al3Ni2, and the formation of NiAl and Ni3Al.

In-situ strain measurements in the Ni/NiO system during high temperature oxidation

Stresses generated during the high temperature oxidation of metals and alloys can cause scale fracture, buckling and spallation, exposing the underlying metal to renewed oxidation. A transmission X-ray diffraction technique has been used to measure strains in both the scale and the metal during all phases of the oxidation process. Strains were measured in thin Ni foils, 25–125 μm thick, before, during and after oxidation at 900–940 °C in oxygen. Strains were measured in the attached oxide scales during and after oxidation. Compressive residual strains exist in both the oxide and in the metal at room temperature after oxidation is complete. Application of the sin 2(Ψ) technique provides an independent confirmation of this conclusion and demonstrates in addition that an equiaxial plane stress state is operative in the oxide, but not in the metal. Substantial variations of residual stresses exist in the metal prior to oxidation and are likely due to grain to grain variations in the large-grained samples used in this study. This variation may help explain the large residual tensile strains, typically 0.4%, that have been measured in the NiO scales during oxidation. Simultaneously, residual tensile strains of approximately 0.08% have been measured in the metal. The condition of balance of forces across the metal/scale interface cannot be applied as a check on self-consistency because the measured strains do not represent appropriate averages for balance of force calculations. Evidence for stress relaxation in the metal due to creep was observed in the 125 μm foils.

Fabrication, Structure and Properties of Aluminum-Aluminide Layered Composites

AbstractThe fabrication of aluminum-aluminide layered composites by reactive bonding of elemental Al and Ni foils was investigated. It was observed that after hot-pressing, thin Ni foils were converted to NiAl. The as-processed Al-NiAl layered structure could be heat-treated to produce an equilibrium Al-Al3Ni layered composite. Tensile tests revealed that composites could be produced that failed in a “tough” manner and were stronger and stiffer than aluminum.

Theory of radiation-induced self-organization of defect structures

During high-dose electron irradiation of thin Ni foils at 520 K, groups of about 10 Stacking-Fault Tetrahedra (SFT) are formed, which are referred to as patches. Within the patches the SFT occupy the sites of a square lattice whose sides are parallel to the two 〈100〉 directions of the crystalline host lattice in the foil plane. A theory of this planar square lattice of SFT is the subject matter of the preceding paper (Part I). The patches themselves are arranged in a planar face-centred cubic lattice that also shares its orientation with the host lattice. In the present paper (Part II) a mesoscopic theory is presented that accounts for this ordering of SFT-lattice patches in terms of an instability of disordered patch arrangements that results from a point-defect-mediated dynamic patch-patch interaction. This interaction arises from the competition of SFT-lattice patches for static crowdions migrating one-dimensionally along close-packed host lattice directions and for three-dimensionally diffusing vacancies and dumbbell interstitials. The so far exclusive occurrence of ordered SFT-lattice patches in Ni is related to the low packing density of this material, which leads to a high stability of the static crowdions and thus to a long range of the dynamic interaction between SFT-lattice patches.

Effects of carbon and sulfur on the decomposition of hydrocarbons on nickel

The kinetics and mechanisms of the decomposition of C2H2, C2H4, and n-C4H10 on polycrystalline Ni resulting in the carburization of the metal have been studied at 1300 to 1500 K and 10−4–10−1 Pa. Special attention has been given to the reaction-retarding effect of surface-segregated carbon. Simultaneous investigations of the reaction rates (by measuring partial pressure changes) and of the nonmetal surface coverages (by applying Auger electron spectroscopy) were carried out in an UHV flow reactor. It was found that hydrocarbon decomposition and carburization are blocked at a certain temperature-dependent concentration of dissolved carbon by the formation of a surface graphitic carbon monolayer in which two C atoms are adsorbed per Ni atom. This monolayer formation is accompanied by surface faceting. The influence of adsorbed sulfur on CH4 decomposition was studied in a flow apparatus by carburizing thin Ni foils in CH4–H2 and CH4–H2–H2S mixtures (1060 to 1280 K, 1-atm total pressure) under conditions where surface reactions are rate controlling. The reaction kinetics were monitored by applying the resistance–relaxation method. For pH2S/pH2 ratios between 8×10−9 and 9×10−5 the initial rate of carburization was found to decrease by a factor of up to 100. The kinetic data are interpreted in terms of the poisoning of active surface sites by adsorbed sulfur. This analysis yields information on the adsorption isotherm for sulfur.

A high resolution bremsstrahlung monochromator for photo-nuclear experiments

An improved bremsstrahlung monochromator, based on the original University of Illinois design, is being used with the Illinois C.W. microtron for (γ, γ) and (γ, f) measurements. The monochromator includes an electron energy disperser followed by an electron energy analyser operating in the energy loss mode. The disperser, which includes two quadrupoles and one 90° n = 0.5 dipole, focuses a demagnified image of the electrons transmitted by a 2 mm defining slit onto a thin Ni foil, termed the radiator. Electrons scattered by the radiator are analysed by a 180° inclined-plane flat pole-piece magnetic spectrometer and are detected in the focal plane by a hodoscope consisting of a 72-wire proportional gas-counter backed by a 12 segment plane of Ne-102 plastic scintillators. Bremsstrahlung emitted by the Ni foil is incident on a target and photons or fission particles emitted by the target are detected in coincidence with pulses from the scintillators and wire counter. The limit of energy resolution, determined primarily by the 3 mm wire spacing, is 14 keV for 3.5 MeV electrons. The limit of resolving time is set by the 3.5 ns jitter of the plastic scintillator-photomultiplier system. The factors which have contributed to improved resolution are: the use of a proportional gas-counter with closely spaced wires, the use of a reduced image of the defining slits on the radiator, the use of thin radiator foils, 5.4 mg/cm 2, and the location of the radiator close to the minimum gap between the pole-pieces. The performance of the monochromator is illustrated by data from the resonance fluorescence of 208Pb and the photofission of 232Th.

Another measurement of the polarization of deuterons channeled through thin Ni foils

Abstract A measurement of the tensor polarization of deuterons which are channeled through a magnetised Ni single crystal and emerge as deuterium atoms is described. The results are in qualitative agreement with the surprisingly large polarization first observed by Karninsky. Experimental details and various control experiments are discussed.

Bulk Diffusion of Carbon-14 through Polycrystalline Nickel Foil between 350 and 700°C

The bulk diffusion of C-14 through polycrystalline Ni foil was investigated in the temperature range of 350 to 700°C. A thin Ni foil was bombarded by a molecular beam of acetylene tagged with C-14. A masking device situated very close to the ribbon surface shielded part of the surface from this beam, producing a well-defined pattern of high and low concentration of absorbed acetylene on the top surface of the foil. After diffusion annealing, this pattern would appear on the underside of the ribbon. Autoradiographic techniques were used to obtain radiation intensities from both surfaces. The ratio of these intensities determined bulk diffusion coefficients after the method of Kryukov. Most previous data had been obtained at temperatures of 700°C or higher. There is acceptable agreement between these data and the higher-temperature experiments of the present work. However, the present results show an activation energy of approximately 20 kcal/mole from 350 to 700°C, while there is substantial evidence that above 700°C the activation energy for this process is of the order of 40 kcal/mole.

Light scattered in the interaction between subnanosecond laser pulses and solid targets

Measurements are reported of the intensity of the light scattered within the solid angle defined by the focussing lens during the interaction of subnanosecond laser pulses with thin Ni foils. The dependence upon the laser pulse energy and the target orientation is also reported.