46 research outputs found
On the long-term correlations and multifractal properties of electric arc furnace time series
In this paper, we study long-term correlations and multifractal properties
elaborated from time series of three-phase current signals coming from an
industrial electric arc furnace plant. Implicit sinusoidal trends are suitably
detected by considering the scaling of the fluctuation functions. Time series
are then filtered via a Fourier-based analysis, removing hence such strong
periodicities. In the filtered time series we detected long-term, positive
correlations. The presence of positive correlations is in agreement with the
typical V--I characteristic (hysteresis) of the electric arc furnace, providing
thus a sound physical justification for the memory effects found in the current
time series. The multifractal signature is strong enough in the filtered time
series to be effectively classified as multifractal
Advances in scalable gas-phase manufacturing and processing of nanostructured solids: A review
Although the gas-phase production of nanostructured solids has already been carried out in industry for decades, only in recent years has research interest in this topic begun to increase. Nevertheless, despite the remarkable scientific progress made recently, many long-established processes are still used in industry. Scientific advancements can potentially lead to the improvement of existing industrial processes, but also to the development of completely new routes. This paper aims to review state-of-the-art synthesis and processing technologies, as well as the recent developments in academic research. Flame reactors that produce inorganic nanoparticles on industrial- and lab-scales are described, alongside a detailed overview of the different systems used for the production of carbon nanotubes and graphene. We discuss the problems of agglomeration and mixing of nanoparticles, which are strongly related to synthesis and processing. Finally, we focus on two promising processing techniques, namely nanoparticle fluidization and atomic layer deposition
Complex Concentrated Alloys (CCAs)
This book is a collection of several unique articles on the current state of research on complex concentrated alloys, as well as their compelling future opportunities in wide ranging applications. Complex concentrated alloys consist of multiple principal elements and represent a new paradigm in structural alloy design. They show a range of exceptional properties that are unachievable in conventional alloys, including high strength–ductility combination, resistance to oxidation, corrosion/wear resistance, and excellent high-temperature properties. The research articles, reviews, and perspectives are intended to provide a wholistic view of this multidisciplinary subject of interest to scientists and engineers
Synchrotron X-ray operando studies of atomic structure evolution of multi-component Al alloys in liquid state
This research has studied one of the challenging scientific issues in materials science, i.e., in real time, understanding quantitatively the 3D atomic structures of multiple component alloys in the liquid state and how the atomic structures evolve with temperatures until the onset of crystal nucleation. Four Al-based alloys were used in the research: (1) Al-0.4Sc, (2) Al-1.5Fe, (3) Al-5Cu-1.5Fe and (4) Al-5Cu-1.5Fe-1Si alloy (all in weight percentage). All alloys were heated up to the liquid state and then cooled down with predefined cooling rates using a dedicated solidification apparatus. During cooling, synchrotron X-ray was used to illuminate onto the samples and the total scattering data were collected at the target temperatures. Based on the total scattering data, the empirical potential structure refinement (EPSR) method was used to model and reconstruct the 3D atomic structures in the liquid state at the selected temperatures for each alloy. The research has demonstrated that the EPSR is a computationally efficient tool for searching and finding the solutions of 3D atomic structures according to the measured total scattering data. For the studied alloys, the research reveals fully the temperature-dependent structure heterogeneity and their evolutions with temperature. The key findings of the research are: (1) For the Al-0.4Sc alloy, at the short-range scale in the liquid state, Sc-centred Al polyhedrons form icosahedral type structures with the Al coordination number in the range of 10–12. As the melt is cooled down, the Sc-centred polyhedrons become more compacted, and the connections between adjacent polyhedrons change from more vertex connection to more edge and then more face-sharing connection. At the medium-range scale, the Sccentred clusters with face-sharing are proved to be the “precursors” for the L12 Al3Sc primary phase in the liquid-solid coexisting region. (2) For the three Fe-containing alloys, atomic structural heterogeneities were found to exist in the 1st atomic shell and beyond. The degree of structural heterogeneities is related with the difference in atom radius, atomic bond length and the chemical preference between different atoms in each alloy. The competition resulted in that the Al-centred clusters expand, i.e., with larger bond length, while the solute atom-centred clusters contract, so with the reduced bond length. (3) At the short-range scale, the structural heterogeneities were characterised by the co-existence and growth of the icosahedra-like (ICO-like) and crystal-like structures. During cooling, the Fe atoms show a higher degree of crystallinity than other atoms in the liquids. At the onset of crystal nucleation, relative percentage of the Fe-centred ICO-like and crystal-like Voronoi polyhedrons (VPs) reaches 8-10%, and the others in the range of 5.8-8.5%. (4) The Fe-centred short-range orders (SROs) tend to connect together via five different modes to form larger Fe-centred medium-range orders (MROs). The percentage of the face-sharing increases almost linearly as the temperature is cooled down, approximately 18-20% at the onset of nucleation in the 3 melts. The Fe-centred MROs gradually approach to the structures of the Al13Fe4 primary phase (monoclinic structure) and are proved to be the nucleation precursors for the Al13Fe4 phases. (5) For the quaternary Al-Cu-Fe-Si alloy melt, the research found that the liquid first transfers into a quasicrystal-like, metastable monoclinic Al13Fe4 phase. Such primary phase was confirmed to have a higher degree of five-fold and crystalline symmetry than the liquid. Upon cooling, the Fe-centred five-fold and crystalline symmetry both get enhanced in liquid, leading to a smaller Al13Fe4-liquid configuration entropy difference and interfacial free energy
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Summaries of FY 1996 engineering research
This report documents the Basic Energy Sciences (BES) Engineering Research Program for fiscal year 1996; it provides a summary for each of the program projects in addition to a brief program overview. The report is intended to provide staff of Congressional committees, other executive departments, and other DOE offices with substantive program information so as to facilitate governmental overview and coordination of Federal research programs. Of equal importance, its availability facilitates communication of program information to interested research engineers and scientists. Each BES Division administers basic, mission oriented research programs in the area indicated by its title. The BES Engineering Research Program is one such program; it is administered by the Engineering and Geosciences Division of BES. In preparing this report the principal investigators were asked to submit summaries for their projects that were specifically applicable to fiscal year 1996. The summaries received have been edited if necessary, but the press for timely publication made it impractical to have the investigators review and approve the revised summaries prior to publication. For more information about a given project, it is suggested that the investigators be contacted directly
Titanium Alloys
Titanium alloys, due to unique physical and chemical properties (mainly high relative strength combined with very good corrosion resistance), are considered as an important structural metallic material used in hi-tech industries (e.g. aerospace, space technology). This book provides information on new manufacturing and processing methods of single- and two-phase titanium alloys. The eight chapters of this book are distributed over four sections. The first section (Introduction) indicates the main factors determining application areas of titanium and its alloys. The second section (Manufacturing, two chapters) concerns modern production methods for titanium and its alloys. The third section (Thermomechanical and surface treatment, three chapters) covers problems of thermomechanical processing and surface treatment used for single- and two-phase titanium alloys. The fourth section (Machining, two chapters) describes the recent results of high speed machining of Ti-6Al-4V alloy and the possibility of application of sustainable machining for titanium alloys
Array stamping of carbon nanotubes and quantum transport in low-dimensional carbon nanotube-TMDC devices
In the first part of this thesis, we present a new approach to the fabrication of devices based on carbon nanotubes (CNTs) in the low disorder regime. Our fabrication method consists of growing CNTs on a transparent quartz chip and stamping them on an array of tens of devices. The quartz chip and the recipient chip are designed in such a way that during the stamping process the CNTs do not touch any substrate and stays suspended on the electrodes of the recipient devices. The parallel transfer of tens of CNTs highly increases the average number of usable devices per chip. The resulting CNT-based devices are characterized via transport measurements at different temperatures down to the milli-Kelvin regime. The separation of growth chip from the measurement chip allows one to freely choose the material for the electrodes, opening the way for the implementation of CNT-based devices with superconducting or ferromagnetic leads.
It was suggested recently that Majorana Fermions should emerge in CNTs contacted with a thin superconductor which retains its superconducting gap in presence of large in-plane field. We demonstrate an all-dry technique for contacting CNTs with few-layer-thick flakes of niobium diselenide (NbSe2) as superconducting layered material of the family of the transition metal dichalcogenides. The choice of NbSe2 is motivated by its large critical in-plane magnetic field. We show that the NbSe2-to-CNT contact resistance is comparable to that observed for other methods. We discuss the temperature and magnetic field dependence of the quantum transport in our devices. Furthermore, we could observe long-range superconducting correlations in a few micrometer-long CNT which is encapsulated in stack of NbSe2 and hexagonal boron nitride. We show that a substantial supercurrent flows through the nanotube section underneath the NbSe2 crystal and through a two-micrometer long portion which is not in contact with it. As predicted for superconductors with a cross section in the nanometer range, the current-triggered collapse of superconductivity is mediated by resistance steps due phase slip center nucleation.
The Ising superconductor NbSe2 is the ideal playground to examine the emergence of phase slip events. The exact nucleation position of phase slip lines in plain NbSe2 films is hard to predict and crucially depends on the individual sample. By patterning a one-dimensional constriction in NbSe2, the free energy barrier, which must be overcome to create a normal conducting region inside the superconducting 1D channel, will be sufficiently small. We demonstrate that as such fabricated nanowires still show superconducting features and that we can relate their origins to phase slip centers and lines
Deformation-Induced Electric Currents in Marble Under Simulated Crustal Conditions: Non-Extensivity, Superstatistical Dynamics and Implications for Earthquake Hazard
This thesis investigates electric current signals generated spontaneously in specimens of Carrara marble during deformation under crustal conditions. It extends previous work where similar currents were observed during uniaxial deformation of marble. Since marble is a non-piezoelectric material, one of the main questions is how these currents are related to the mechanical processes of deformation. Another question is whether it is possible to extract from these electric currents information about the deformation dynamics. This is particularly important in light of recent claims that geoelectric anomalies observed in the field are related to crustal deformation and can inform us about changes in the organisation of the fault network in a focal region prior to an earthquake. Using an approach that combines rock deformation experiments and statistical modelling, I examine how these electric currents evolve with deformation at the laboratory scale and make several original discoveries regarding their behaviour. To establish how the current signals varied with experimental condition and deformation mechanism across the brittle-ductile transition, I conducted constant strain rate triaxial compression experiments recording differential electric current flow through the rock samples at various confining pressures, strain rates and pore fluid conditions. I acquired mechanical data, ultrasonic velocities and acoustic emissions simultaneously, along with electric current, to constrain the relationship between electric current and deformation. For the statistical modelling, I used a novel entropy-based model, derived from non-extensive statistical mechanics (Tsallis, 1988), which has the advantage of including a term to account for interactions in the system. Interactions are effectively modelled by the non-extensive q-parameter. Small (nanoAmpere) electric currents are generated and sustained during deformation under all the conditions tested. Spontaneous electric current flow in the dry samples is seen only in the region of permanent deformation and is due to the presence of localised electric dipoles. This current flow is correlated to the damage induced by microcracking, with a contribution from other intermittent ductile mechanisms. Current and charge densities are consistent with proposed models of crack separation charging and migrating charged edge dislocations. The onset of current flow occurs only after a 10% reduction in P-wave velocity, implying that some degree of crack damage and/or crack connectivity is required before current will flow through the samples. Electric current evolution exhibits three separate time-scales of behaviour, the absolute and fluctuating components of which can be related to the evolution of stress, deformation mechanism, damage and localisation of deformation leading up to sample failure. In the brittle regime, electric current exhibits a precursory change as the stress drop accelerates towards failure, which is particularly distinct at dynamic strain rates. Current and charge production depend strongly on the experimental conditions. Power-law relationships are seen with confining pressure and strain rate, with the first corresponding to increased microcrack suppression and the second to time-dependent differences in deformation mechanism across the brittle-ductile transition. In the presence of an ionic pore fluid, electrokinetic effects dominate over solid-state mechanisms but development of the crack network and charge contribution from solid-state deformation processes drive the variation in electrokinetic parameters. Current flow in the dry samples is approximately proportional to stress within 90% of peak stress. In the fluid-saturated samples, proportionality holds from 40% peak stress, with a significant increase in the rate of current production from 90% peak stress, and is associated with fluid flow during dilatancy. This proportionality, together with the power-law relationship between current and strain rate is reminiscent of power-law creep, where deformation rate varies as a power-law function of stress, and suggests that the electric signals could be used as a proxy for stress. High frequency fluctuations in the electric current signal can be described by `fat-tailed' q-Gaussian statistics, consistent with an origin in non-extensive statistical mechanics. These distributions can be explained as arising from superstatistical dynamics (Beck, 2001; Beck and Cohen, 2003), i.e., the superposition of local mechanical relaxations in the presence of a slowly varying driving force. The macroscopic distribution parameters provide an excellent prediction of the experimentally observed mean energy dissipation rate of the system (as modelled by the superstatistical β-parameter), particularly at slow strain rates. Furthermore, characteristic q-values are obtained for different deformation regimes across the brittle-ductile transition, and the evolution of q during deformation reveals a two-stage precursory anomaly prior to sample failure, consistent with the stress intensity evolution as modelled from fracture mechanics. These findings indicate that the dynamics of rock deformation are reflected in the statistical properties of the recorded electric current. My findings support the notion that electric currents in the crust can be generated purely from deformation processes themselves. Scaling up the laboratory results to large stressed rock volumes at shallow crustal pressures and constant crustal strain rates, deformation induced transient telluric current systems may be as large as 1 MA, even accounting for >99% dissipation, which corresponds to a huge accumulated net charge of 10 ZC. This implies that a significant amount of charge from deforming tectonic regions contributes to the Earth's telluric currents and electric field, although due to conduction away from the stressed rock volume, it is unlikely that accumulated charge of this quantity would ever be measured in the field. Electric current evolution and its precursory characteristics can be related to models for electric earthquake precursors and fault-zone damage organisation, developed from field observations, providing experimental support for them. However, given the oscillatory nature of the current evolution observed during cataclastic flow processes in the laboratory, there is a high probability of false alarms. Furthermore, the potential for electric anomalies to be useful as earthquake precursors remains contentious due to the difficulties of separating deformation-induced signals from other telluric noise and the wider issue of establishing a statistically significant link with earthquakes
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Energy Materials Coordinating Committee (EMaCC): Fiscal year 1996. Annual technical report
The DOE Energy Materials Coordinating Committee (EMaCC) serves primarily to enhance coordination among the Department`s materials programs and to further effective use of materials expertise within the Department. These functions are accomplished through the exchange of budgetary and planning information among program managers and through technical meetings/workshops on selected topics involving both DOE and major contractors. In addition, EMaCC assists in obtaining materials-related inputs for both intra- and interagency compilations. The EMaCC reports to the Director of the Office of Energy Research in his or her capacity as overseer of the technical programs of the Department. This annual technical report is mandated by the EMaCC terms of reference. This report summarizes EMaCC activities for FY 1996 and describes the materials research programs of various offices and divisions within the Department