Bulk Foils Research Articles

Investigation of the body-centred tetragonal structure of Fe–Co–V–N Bulk foils using the rolling and ammonia-gas-nitriding method

Improving the properties of permanent magnets is essential for the advancement of electric motors in reducing energy consumption and carbon emissions. This study investigated the effect of V and N addition to FeCo foils on the stability of tetragonally distorted FeCo-based bulk magnets. The incorporation of these two elements stabilised the body-centred tetragonal structure in thin-film and bulk systems. Fe–Co–V ingots were rolled and nitrided by ammonia gas at 650 °C for 5 h. A body-centred tetragonal lattice with an axial ratio of c/a ≈ 1.1 was observed by transmission electron microscopy, and the collected data suggested the induction of a large uniaxial magnetic anisotropy. This study is expected to improve our understanding of rare-earth-free magnets.

OVERVIEW ON METHODS OF SYNTHESIS OF NANOPARTICLES

In recent years, interest in the development of novel drug delivery systems using nanoparticles has gained more attention. The nanoparticles offer several advantages over other conventional drug delivery systems. Nanoparticles have gained importance in technological advancements due to their modifiable physical, chemical and biological properties with improved performance over their bulk foils. Nanoparticles can simply move in the body due to their small size and reach very complex organs through diverse routes. The high stability, controlled drug release makes nanoparticles the most suitable drug delivery system. Along with all these advantages, they offer variety in routes of administration. Both hydrophilic, as well as hydrophobic drugs, can be delivered in the form of nanoparticles. Nanoparticles have been used as a physical approach to modify and advance the pharmacokinetics and pharmacodynamics possessions of various types of drug molecules. Thesol-gel technique is a stress-free and very inexpensive process to formulate metal oxides and permits control over the doping process or adding of transition metals, as related to other research techniques. The study of different methods of synthesis of nanoparticles is essential to obtain desired nanoparticles with specific sizes and shapes. They are suitable candidates for various marketable and local applications, which include imaging, catalysis medical applications and environmental applications. This review mainly focuses on approaches used for the production of nanoparticles and different methods of synthesis of nanoparticles such as physical, chemical and biological method.

Electrochemical Reduction of CO2 Using Cu-Au Nanoparticles: Effects of Size and Composition

The electrochemical reduction of CO2 to light hydrocarbons allows renewable energy storage without increasing net atmospheric CO2. Alloys and nanoscale catalysts have emerged as potential electrocatalysts with high efficiencies and selectivities to valuable products. Here, we describe CuAu alloy nanoclusters with diameters of 2 nm and 5 nm for use as CO2 electroreduction catalysts. The Cu:Au ratio was controlled to yield nanoparticles with a range of alloy compositions ranging from Cu25Au75 to Cu72Au28. The yields and onset potentials were measured and compared to Cu, Au and CuAu bulk foils, where the nanoparticles showed a 50 fold increase in CO yield compared to Au foil, and greater than a 100 mV anodic shift in CO2 reduction onset potentials. As seen in Figure 1, the alloys showed greater improvements in yield as Au content increased. These improvements are attributed to low coordination active sites and to the bimetallic nature of these active sites. Figure 1

Surface effects and statistical laws of defects in primary radiation damage: Tungsten vs. iron

We have investigated the effect of surfaces on the statistics of primary radiation damage, comparing defect production in the bcc metals iron (Fe) and tungsten (W). Through molecular dynamics simulations of collision cascades we show that vacancy as well as interstitial cluster sizes follow scaling laws in both bulk and thin foils in these materials. The slope of the vacancy cluster size distribution in Fe is clearly affected by the surface in thin foil irradiation, while in W mainly the overall frequency is affected. Furthermore, the slopes of the power law distributions in bulk Fe are markedly different from those in W. The distinct behaviour of the statistical distributions uncovers different defect production mechanisms effective in the two materials, and provides insight into the underlying reasons for the differing behaviour observed in TEM experiments of low-dose ion irradiation in these metals.

Microstructure Analysis of Melt Spun FeN foils with α’’-Fe16N2 Phase

ABSTRACTWe are reporting an approach to prepare bulk foils of α″-Fe16N2that can be directly obtained from a melt spinning process. The diffraction peaks from α″-Fe16N2phase were found in X-ray diffraction spectrum of the foil, for which a nitrogen composition of 8.7at% was found by Auger electron spectroscopy. The microstructure of this melt spun foil was analyzed. We found 600 nm subgrains inside 8 μm grains for this foil. The coercivity of the α″-Fe16N2foil was found as 222 Oe with a saturation magnetization of 223 emu/g. We analyzed the coercivity based on the microstructure and proposed a model to explain how to further improve it in melt spun FeN foils.

Coupled Tensile Stress Increases and Topography Evolution during Aluminum Corrosion

Embrittlement of high-strength Al alloys resulting from water exposures thought to be caused by absorption of hydrogen produced by corrosion.1 Studies of Al dissolution processes indicate that corrosion itself produces large concentrations of subsurface hydrogen and defects, which may be relevant to degradation mechanisms. Hebert and coworkers detected extensive subsurface hydride formation during alkaline corrosion of Al, suggesting high hydrogen concentrations near the corroding surface.2 Studies of alkaline aluminum dissolution by electron microscopy and positron annihilation spectroscopy reveal large numbers of subsurface nanoscale voids which suggest condensation of near-surface vacancies produced during dissolution.3 Measurements of stress changes accompanying corrosion can detect defect formation, along with other microstructural changes relevant to degradation. Here we report in situ stress measurements during corrosion of 99.998% purity aluminum in alkaline solutions. The experiments utilized a new technique, phase-shifting curvature interferometry, the high curvature resolution of which enables measurement of corrosion-induced stress on bulk aluminum sheet and foils, and extension of the period of stress measurement to tens of minutes in order to capture the full evolution of stress transients during dissolution.4 Topographic changes were characterized quantitatively by Fourier transform analysis of scanning electron microscope (SEM) images, to identify length scales of the ridge-scallop surface pattern produced by dissolution. Stress measurements during dissolution in NaOH solutions revealed large reproducible tensile force increases (in-plane stress integrated through thickness) that scale directly with the sample yield stress. This is apparently the first indication of near-surface plastic deformation directly induced by corrosion. The force increases to a steady state reached after around 10 min. Close agreement of force transients for as-received and electropolished sheet samples demonstrate that stress is not influenced by near-surface microstructure. Steady-state force levels are found to increase with NaOH concentration. The force transients can be interpreted in terms of growth of a surface-adjacent plastic layer, within which the metal is at the yield stress. The thickness of this plastic layer can be approximated as the ratio of the measured force per sample width to the yield stress. Tensile force within the plastic layer is proposed to originate from the lattice contraction due to metal vacancies injected by dissolution.5 According to this mechanism, plastic layer growth should be governed by vacancy diffusion. Using a one-dimensional model for vacancy diffusion, closely comparable independent estimates of the vacancy diffusivity values are obtained from the measured steady-state force and time. These estimates are on the same magnitude as the vacancy diffusivity extrapolated from high-temperature measurements, 4 x 10-16 m2/s. Thus, the force measurements seem to be quantitatively consistent with the introduction of tensile stress by continuous vacancy formation at the dissolving surface. Vacancy injection can be rationalized by the high surface overpotential present during alkaline Al dissolution. SEM images reveal the expected surface pattern of concave scallops surrounded by convex ridges. The characteristic scallop width increases to a steady-state during dissolution, following nearly the same trajectory as that of the measured tensile force. Indeed, a universal scaling factor of 120 MPa was found to relate force to scallop diameter, implying that the plastic layer thickness and mean scallop radius remain nearly the same during dissolution. Since nearly all the hydride particles and voids observed to form during dissolution are located at ridges,2,3 we propose that diffusing hydrogen and vacancies aggregate on ridges to produce immobile hydride particles and voids, that are then removed by metal dissolution. The scaling of force to scallop diameter implies that length scale for diffusion toward the sample bulk, governing the injection rate of hydrogen and vacancies, must remain comparable to the length scale for lateral diffusion to ridges, which controls the removal rate. The present results suggest strong enhancement of diffusion by vacancies near corroding surfaces, which may be relevant to crack propagation processes. ACKNOWLEDGMENT This work was supported by the National Science Foundation through NSF-CMMI-100748. REFERENCES 1. J. R. Scully, G. A Young, S. W. Smith, in Gaseous Embrittlement of Materials in Energy Technologies, p. 707, R. P. Gangloff and B. P. Somerday, Eds.., Woodhead, Oxford (2012). 2. S. Adhikari, J. J. Lee, K. R. Hebert, J. Electrochem. Soc., 155, C16 (2008). 3. S. Adhikari, K. R. Hebert, L. S. Chumbley, H. Chen, Y. C. Jean, A. C. Geiculescu, Electrochim. Acta, 55, 6093 (2010). 4. O. O. Capraz, P. Shrotriya, K. R. Hebert, J. Electrochem. Soc., 160, D501 (2013). 5. H. K. Birnbaum et al., J. Alloys Compd., 253-254, 260 (1997).

Scaling relationship among indentation properties of electromagnetic materials at micro- and nanoscale

Electromagnetic materials have been widely employed in micro-functional devices. Using multi-field nanoindentation technique, we have investigated the local deformation behavior of various electromagnetic materials in the form of bulk materials, foils, and thin films under electric or magnetic field. Based on dimensional analysis and experimental data, a field tunable scaling relationship among hardness, reduced contact elastic modulus, and indentation work has been found. Furthermore, a method to determine the hardness and reduced modulus of electromagnetic materials is proposed, which avoids the error from estimating the indentation contact area. This work is meaningful for the characterization of mechanical properties and design of devices made of electromagnetic materials.

Comparison between bulk and thin foil ion irradiation of ultra high purity Fe

Accumulation of radiation damage in ultra high purity iron under self ion irradiation without and with simultaneous He implantation was investigated in bulk and thin foil form to assess, on the one hand, the effect of free surfaces and, on the other hand, the influence of He. Specimens were irradiated at room temperature to a dose of 0.8dpa and ∼900 appm He content. We found in thin foils after irradiation with single beam a majority of a0 〈100〉 type loops, while in the presence of He it is the ½ a0 〈111〉 type loops that prevail. In single beam irradiated bulk samples most of the loops are of ½ a0 〈111〉 type. In both bulk and thin foils density of defects visible in transmission electron microscope is considerably higher when He is implanted with prevailing ½ a0 〈111〉 dislocation loops, indicating that He stabilizes them.

Magnetic domain structure of epitaxial Ni–Mn–Ga films

For the magnetic shape memory effect, knowledge about the interaction between martensitic and magnetic domain structure is essential. In the case of Ni-Mn-Ga bulk material and foils, a staircase-like magnetic domain structure with 90{\deg}- and 180{\deg}-domain walls is known for modulated martensite. In the present paper we show that the magnetic domain pattern of thin epitaxial films is fundamentally different. Here we analyze epitaxial Ni-Mn-Ga films by atomic and magnetic force microscopy to investigate the correlation between the twinned martensitic variants and the magnetic stripe domains. The observed band-like domains with partially perpendicular outof-plane magnetization run perpendicular to the microstructure domains defined by twinning variants. These features can be explained by the finite film thickness, resulting in an equilibrium twinning period much smaller than the domain period. This does not allow the formation of a staircase domain patter. Instead the energies of the magnetic and martensitic microstructures are minimized independently by aligning both patterns perpendicularly to each other. By analyzing a thickness series we can show that the observed magnetic domain pattern can be quantitatively described by an adapted band domain model of Kittel.

Effect of liquid film on near-threshold laser ablation of a solid surface

Enhancement of material ablation and photoacoustic excitation by an artificially deposited liquid film in the process of pulsed-laser ablation (PLA) is investigated in this paper. Ablation threshold, ablation rate, surface topography, and acoustic-transient emission are also measured for dry and liquid film-coated surfaces. The physical mechanisms of enhanced ablation in the liquid-assisted process are analyzed at relatively low laser fluences with negligible effect of laser-produced plasma. Particularly, correlation between material ablation and acoustic-transient generation is examined. In the experiment, aluminum thin-films and bulk foils are ablated by Q-switched Nd:YAG laser pulses. The dependence of ablation rate and laser-induced topography on liquid film thickness and chemical composition is also examined. Photoacoustic emission is measured by the probe beam deflection method utilizing a CW HeNe laser and a microphone. In comparison with a dry ablation process, the liquid-assisted ablation process results in substantially augmented ablation efficiency and reduced ablation threshold. The results indicate that both increased laser-energy coupling, i.e., lowered reflectance, and amplified photoacoustic excitation in explosive vaporization of liquid are responsible for the enhanced material ablation.

TiO2 Nanocrystalline Pigmented Polyethylene Foils for Radiative Cooling Applications: Synthesis and Characterization

Radiative cooling devices should ideally operate with a shield substrate that completely blocks solar radiation but is transparent in the “atmospheric window” (8−13 μm) region. In this paper, we introduce a new type of shield for radiative cooling applications based on the use of polyethylene foils pigmented with nanocrystalline TiO2. Homogeneous shields were prepared by spreading colloidal suspension of TiO2 (rutile ca. 60 nm) between two polyethylene sheets followed by hot pressing. Optical and structural properties of the films were investigated using X-ray diffraction, TEM, and UV/vis/NIR and FTIR spectroscopy. The shields show high IR transmittance and high solar reflectance, which are favorable characteristics for solar radiation shields in radiative cooling devices. The mechanism for obtaining improved optical properties of nanocrystalline foils (in comparison with submicrometer bulk foils) is discussed with respect to both the materials and the shield preparation method. The simplicity and low-cos...

The Behavior of Copper and Lead during Heat‐Treatment and Surface Treatment of Aluminium Capacitor Foils

The influences of heat‐treatment, electropolishing, etching, and anodizing treatments, applied individually or in combination, on the distributions of copper and lead in aluminum capacitor foils have been investigated for foils of 100 μm thickness, containing up to 100 ppm copper and 1.5 ppm lead. The selected heat‐treatment results in major redistribution of lead in the bulk foils, with a comparatively small effect upon the distribution of copper. Importantly, the lead segregates to a metal layer, probably of about 1–2 nm thickness, located immediately beneath the thermally formed oxide film. The enrichments of lead developed by the heat‐treatment are largely retained in the metal surface region during etching and subsequent anodizing treatments. In contrast, electropolishing results in extensive loss of the segregated lead from the foil surfaces to the electropolishing electrolyte, which is attributed to transient localized corrosion of the metal in the electropolishing bath. Enrichments of copper are developed during electropolishing, etching, and anodizing treatments, with the possibility of incorporation of copper species into the associated oxide films. © 1999 The Electrochemical Society. All rights reserved.

Interdiffusion in two-layer Pd/Ag films III. TEM investigation of diffusion-induced grain boundary migration

Diffusion-induced grain boundary migration (DIGM) is studied by the transmission electron microscopy method in polycrystalline two-layer Pd/Ag thin films with a grain size (100–2000 nm). In addition to the typical features of DIGM known for coarse-grained bulk objects and foils, new features are found which are caused by a quite dense network of triple junctions and by misfit dislocations: fast increase of grain boundary curvature and inclination; back motion of grain boundaries owing to recrystallization forces and termination of DIGM. Homogenization resulted from diffusion-induced migration of misfit dislocations is observed in addition to DIGM.

Cyclic stress-strain response and strain localization effects under stress-control conditions

Polycrystalline nickel was cyclically deformed under stress control. Experiments with different maximum and mean stresses were performed, always applying the maximum stress in the first quarter cycle. During the tests the cyclic mechanical behaviour was studied and the occurrence of strain localization was investigated by surface relief observation and by transmission electron microscopy of bulk foils. The cyclic stress-strain response was shown to be affected characteristically by the mean and maximum stresses. On the surface, persistent slip markings were found not only for zero mean stress but also for wide range of non-vanishing mean stresses. Persistent slip bands with the typical ladder-like dislocation structure appeared in the bulk material only at symmetrical or nearly symmetrical cycling.

Precipitation of boron in silicon

Epitaxial, melt grown and diffused silicon nominally containing more than 10 19 atoms/cm 3 of boron has been examined by optical and electron microscopy. The surface of the epitaxial layers became irregular before this concentration of boron could be incorporated. Extensive precipitation was observed in Czochralski melt-grown material containing > 5 x 10 19 atoms/cm 3 of boron. These precipitates were non-crystallographic and had misfit dislocations associated with them. Beam heating experiments revealed these dislocations more clearly and also reprecipitated the boron in a mainly crystallographic form. Similar crystallographic precipitates, in the form of rods lying along <211> directions and platelets lying on inclined {111} planes, were obtained on diffusing boron into previously thinned electromicroscope samples. Similar diffusions into standard {111} silicon wafers produced very few precipitates. The differences observed on diffusing into bulk or thin foils are discussed.

Experimental Evidence for a new Superconducting Phase Nucleation Field in Type-II Superconductors

Remnant superconductivity in thick films and bulk foils of Pb-Tl alloys was investigated in the field interval H/sub c2/ to 1.7 x H/sub c2/, where H/sub c2/ is the bulk upper critical field. Measurements were made over the range 1.1-- 4.2 deg K. Two critical fields H/sub l/(longitudinal) and H/sub t/ (transverse) which mark, respectively, the cessation of superconductivity with the field applied parallel and perpendicular to the plane of the specimen, were defined. The ratio H/sub l//H/sub t/ is essentially constant, independent of composition, thickness, and temperature and implies a basic effect rather than one caused by specimen defects. (C.E.S.)

The movement of dislocations during the observation of metal films inside an electron microscope

Abstract The influence of specimen contamination on the movement of dislocations in metal films under observation in the electron microscope has been examined. Complete control of the rate of contamination, arising from the electron bombardment of adsorbed hydrocarbon molecules, has been obtained by placing the specimen in a small chamber containing oxygen at a relatively high pressure. It is found that dislocation movement occurs in thin evaporated single crystal gold films only if contamination is allowed to form on the specimens. The movement is believed to occur as a result of the high tensile stress present in the contamination layer. It is concluded that specimen contamination is, at least, a major contributory factor to the cause of the dislocation movement observed in specimens prepared by electro-thinning of bulk foils.