Ultrapure Aluminum Research Articles

Development of fully superconducting 5 MW aviation generator with liquid hydrogen cooling

The use of liquid hydrogen as a fuel will be inevitable in the aviation of the future. This statement means that manufacturers will also implement liquid hydrogen for cooling all superconducting aviation equipment of an electric propulsion system. The development of fully electric aircraft is the most promising solution in this case. Scientists from the Department of electrical machines and power electronics of Moscow aviation institute have conducted calculations and theoretical researches of critical specific mass-dimensional parameters (MW/ton and MW/m3 at 21 K) of fully superconducting aviation synchronous generator of the electric propulsion system. The results are in this article.
 The article discusses the results 3D finite element modeling (FEM) simulation of a 5 MW fully superconducting synchronous generator with combined excitation. Superconducting armature and axial excitation windings based on second generation high temperature superconductors (HTS-2G) are located on the stator, which makes it possible to contactlessness and the absence of sliding seals. A dry gap will reduce gas-dynamic losses and increase the nominal peripheral speed of the rotor. The use of liquid hydrogen as a coolant makes it possible to significantly increase the linear load of the generator, and high current densities to reduce the cross-sectional area of the coils, which will make it possible to place them in individual cryostats in the future. Individual cryostats will allow to remove the heat release of magnetic losses from the cryogenic zone and reduce the consumption of refrigerant. For the purpose of internal redundancy of the HTS coils, the machine has a complete set of reserve winding made of ultrapure aluminum, also cooled by liquid hydrogen. If the superconducting coils get out of the stand, the generator will provide 15 % power on standby

Development of New Plasma Technology Methods in Synthetic Materials Production and Research

This paper presents the results of the application of new unique techniques based on plasma nanotechnology in metallurgy and materials science. In recent years, a team of authors have developed the solutions for extraordinary problems arising in the conditions of metallurgical enterprises related to the production of synthetic materials and control of manufactured products, namely, the methods for the production of various structural materials and optimization of methods for their non-destructive testing by atomic emission spectral analysis (AESA). The paper points out some aspects of ongoing research, in particular, an innovative technique that allows obtaining ultrapure samples of white corundum by plasma melting of alumina in a reactor. This method also allows obtaining ultrapure aluminum at the output, which can be used for the purposes of hydrogen energy. In the course of the research, the criteria for thermal protection, temperature conditions and optimal parameters of the plasmatron were determined. In order to carry out the studies of metals and alloys by AESA method, a new global analytical method was developed, which made it possible to take into account the influence of various important parameters, including third elements, background plasma radiation, etc. This method has been preliminary tested on emission spectrometers made in Russia and can significantly reduce the error in the determination of low concentrations of elements. In addition to the consideration of these parameters, the method makes it possible to perform high-precision calibration of atomic emission spectrometers of the same type (produced in series), using not a set of several tens of approved standard samples, but only two standard samples. For each area, patent applications were formed and filed.

Preparation of the Surfaces of High-Purity Polycrystalline Aluminum for the Mechanical Analysis by Means of Nanoindentation

Abstract The sample preparation and, in certain cases, the nanoindenter itself have an impact on the measurement results of a nanoindentation process on electropolished aluminum surfaces. In this work, the indentation hardness and the indentation modulus of recrystallized ultra-pure aluminum were determined. To this end, the surfaces were prepared by electrolysis. Two sources of influence were investigated respectively: the sample preparation (roughness and deformed layer) and the nanoindenter (influence of the edge and damage to the sample caused by the measuring head). Very smooth (R a < 1 nm) surfaces could be generated. A statistical pop-in analysis revealed that the surfaces are virtually deformation-free. The design of the measuring head of the used Picodentor HM500 considerably limits the available measuring surface. On a square ultra-pure aluminum sample with a dimension of 9.5 mm, only an area of 1.5 × 1.5 mm in the center of the sample can be measured by the indenter without any influences. The values for the indentation hardness and the indentation modulus of the suitably prepared samples were 240.1 MPa and 63.5 GPa, respectively, with a standard deviation of only 1 – 2%. The results can be obtained in a reproducible manner for several individual samples and fit well into data from literature.

The CROSS experiment: search for 0v2β decay with surface sensitive bolometers

CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) is a project aiming to develop a new bolometric technology enabling an active background rejection in 0v2β search. The isotopes of interest are 100Mo and 130Te, and bolometers are based on Li2MoO4 and TeO2 crystals. The key feature of CROSS detectors is the possibility of pulseshape discrimination of near surface interactions. An ultrapure superconductive aluminum film, deposited on the crystal surface, is acting as a pulse-shape modifier for phonon sensors, providing separation of surface events from bulk ones. First prototypes were produced and successfully tested aboveground with the rejection of α surface radioactivity higher than 99.9%. A demonstrator with 32 0.28-kg Li2 100MoO4 crystals will be installed in a dedicated cryostat in the Canfranc underground laboratory (Spain) to confirm the reproducibility of surface sensitive bolometers. CROSS demonstrator can obtain sensitivities to the effective Majorana mass down to 70 meV in the most favorable conditions. The CROSS technology can be applied for future ton-scale experiments, reaching sensitivities to the effective Majorana mass down to 10 meV.

Grain refining of Al-Si alloys using Al-10% Ti master alloy: role of Zr addition

ABSTRACTThe present study was carried out on ultra-pure aluminum, 1050, and 356 alloys. The results revealed that when Al-4%B is added to ultra-pure aluminum, it forms AlB12 and AlB2 which have no grain refining effect in pure aluminum. When no grain refiner is added to pure aluminum, the microstructure is a mixture of columnar and equiaxed grains. The addition of 30 ppm Ti to pure aluminum is sufficient to promote equiaxed grains when the metal is solidified at high rate ~ 10°C/s but requires an addition of 1000 ppm B at 0.8°C. Increasing the Si content to 7% reduces the initial grain size of pure aluminum from 2800 μm to 1200 μm. In commercial aluminum, B reacts with traces of Ti to form TiB2 phases which are active grain refining agents. However, in Al-7%Si, Ti reacts with Si forming (Al,Si)2Ti phase which is a poor refining agent.

Damage Characteristics of Dynamically Induced Incipient Spall in Ultrapure Aluminum

A series of plate-impact experiments were performed to study the damage characteristics of incipient spall in ultrapure aluminum (99.999%). Surface profile measurement system based on the axial chromatic aberration was used to measure the cross section of “soft-recovered” samples and reconstruct the metallographic and 3D surface topography. Statistical analyses show that the size distribution, coalescence condition and connectivity factor of the voids are regularly affected by loading conditions. Based on this finding, the mechanisms that control the damage properties and evolution process of dynamic fracture are analyzed in detail. The results of this research offer an experimental quantitative microstructure description of the ductile fracture process.

Spall behaviour of single crystal aluminium at three principal orientations

A series of plate impact experiments have been conducted to study the spall strength of the three principal crystallographic orientations of single crystal aluminium ([100], [110] and, [111]) and ultra-pure polycrystalline aluminium. The samples have been shock loaded at two impact stresses (4 GPa and 10 GPa). Significant differences have been observed in the elastic behaviour, the pullback velocities, and the general shape of the wave profiles, which can be accounted for by considerations of the microscale homogeneity, the dislocation density, and the absence of grain boundaries in the single crystal materials. The data have shown that there is a consistent order of spall strength measured for the four sample materials. The [111] orientation has the largest spall strength and elastic limit, followed closely by [110], [100], and then the polycrystalline material. This order is consistent with both quasi-static data and geometrical consideration of Schmid factors.

The Development of Superconducting Detector Magnets From 1965 to the Present

This paper describes the development of detector magnets from the mid-1960s to the LHC detector magnets. The discovery of cryogenic stability in March, 1965, made large detector magnets possible. A number of bubble chamber magnets were built as a result. In the 1970s, the quest for thin magnets started. This led to the development of quench protection through quench-back and the development of indirect cooling with two-phase helium in tubes. The late 1970s and 1980s led to the development of a conductor with ultrapure aluminum as a stabilizer. This led to large coils that were wound inside a strong aluminum mandrel. The LHC saw the development of magnets that are open and they return their own flux without iron. This paper describes the development of detector magnets that have been used in high-energy physics.

Effect of Process Parameter Variation on Purity during Rotary Fractional Crystallization of Aluminum

High pure and ultrapure Aluminum is increasingly used in highly corrosion resistant applications or to replace copper in conductive parts such as high voltage cable and transformers due to their higher electrical conductivity properties. Ultrapure Aluminum is also used in semiconductors industry. Hence, the market demands innovative refining technologies, which consume less energy, take less time and lead to higher resource efficiencies. The most common methodology to produce ultrapure Aluminum is zone refining, based on the principle of fractional crystallization. Zone refining is however a very time-consuming process. In order to achieve a purity of 6N, several passes along the crucible with each full day treatment must be carried out. Also this method cannot be conducted continuously. This paper presents first time a new and eco-efficient method, which offers high potential to meet the mentioned multi-dimensional demands. Firstly, distribution coefficients of main impurities in Aluminum—a deciding factor to forecast and assess the removal behavior of impurities-were studied theoretically as a function of temperature using thermo-chemical calculation in FactSageTM. Secondly, the innovative method using a rotating and gas cooled crystallizer (“cooled finger”) was developed to validate the principle. The influencing process parameters such as temperature gradient, cooling gas flow rate, etc. were experimentally investigated and the theoretical results could be verified.

Particle stabilization of plastic flow in nanostructured Al-1 %Si Alloy

A nanostructured Al-1 %Si alloy containing a dispersion of Si particles in ultrapure aluminum (99.9996 %) was produced by heavy cold rolling to study the effect of second-phase particles on the occurrence of plastic instability during tensile testing of a nanostructured metal. Tensile tests were conducted on the as-deformed sample and on samples after recovery annealing treatments. Work hardening and strain rate sensitivity were studied by tensile test at different strain rates, and deformed and annealed samples were characterized by transmission electron microscopy. By comparing the observed behavior with that of nanostructured commercial purity Al, a significant increase in the tensile elongation was found. This is related to a homogenization of the deformation microstructure due to the presence of finely dispersed Si particles. As a result localized deformation is reduced and tensile ductility increased.

Effect of grain size and arrangement on dynamic damage evolution of ductile metal

Plate-impact experiments have been carried out to examine the effect of grain size and grain arrangement on the damage evolution of ultrapure aluminum. Two groups of samples, “cross-cut“ and “longitudinal-cut,“ are obtained from the rolled aluminum rod along different directions. The peak compressive stress is approximately 1.25 GPa−1.61 GPa, which can cause incipient spall damage that is correlated to the material microstructure. The metallographic analyses of all recovered samples show that nearly all damage nucleates at the grain boundaries, especially those with larger curvature. Moreover, under lower shock stress, the spall strength of the “longitudinal-cut“ sample is smaller than that of the “cross-cut“ sample, because the different grain sizes and arrangement of the two samples cause different nucleation, growth, and coalescence processes. In this study, the difference in the damage distribution between “longitudinal-cut“ and “cross-cut“ samples and the causes for this difference under lower shock-loading conditions are also analyzed by both qualitative and semi-quantitative methods. It is very important for these conclusions to establish a reasonable and perfect equation of damage evolution for ductile metals.

Reducing potassium contamination for AMS detection of 39Ar with an electron-cyclotron-resonance ion source

The first application of 39Ar Accelerator Mass Spectrometry (AMS) at the ATLAS facility of Argonne National Laboratory was to date ocean water samples relevant to oceanographic studies using the gas-filled magnet technique to separate the 39K–39Ar isobars. In particular the use of a quartz liner in the plasma chamber of the electron cyclotron resonance ion source enabled a 39K reduction of a factor ∼130 compared to previous runs without liners, and allowed us to reach a detection sensitivity of 39Ar/Ar=4×10−17. In order to improve this sensitivity and allow the measurement of lower ratios, higher ion source currents and a lower overall 39K background are necessary. This paper summarizes our efforts to investigate new methods combining low level potassium cleaning techniques with the use of ultra-pure aluminum liners in the plasma chamber of the ion source. The aim of the study was to improve by 1–2 orders of magnitude the 39Ar detection sensitivity required in the selection of ultra-pure materials for detectors used in weakly interacting massive particle dark matter searches.

Damage property of incompletely spalled aluminum under shock wave loading

The nucleation, growth, and coalescence of microscopic voids are induced inside ductile metal when it is subjected to dynamic tension, and this eventually results in a catastrophic fracture of the specimen. In the present work, this failure property is studied by using ultrapure aluminum (99.999%) as a representative candidate for the ductile metal and, further, the micro-void growth behavior (or the damage evolution) before the catastrophic fracture has been investigated. Measurements of the free surface velocity profile and statistical analysis of micro-voids were used to determine the spall characteristic and damage evolution behavior of dynamic tensile fracture in ultrapure aluminum. Through comparison of the differences between the incompletely and completely spalled signals, the spall characteristics of ultrapure aluminum from incomplete to complete spall were analyzed. Moreover, an obvious critical characteristic is found on the basis of the association between the maximum damage caused within samples and the product of peak stress and tensile duration. The damage variable slowly increased in a linear manner in the initial stages but changed to nonlinear growth and rapidly approached a fracture state as the damage variable extended beyond the critical value, which is approximately 0.09. A physical explanation for this transition is discussed and implicates micro-void linkage behavior during the dynamic failure.

Microscopic Characteristics of Damage Evolution in Ultrapure Aluminum under Tensile Loading

A series of plate-experiments are carried out to acquire ultrapure aluminum (purity, 99.999%) samples with damage. Based on the metallographic of all “soft-recovered" samples, the characteristics of damage evolution and spallation damage mechanism in ultrapure aluminum are analyzed in detail. Results show that the damage will increase regularly with increasing loading strength. Most of voids appear in the grain boundary and grow alone under tensile loading before they coalesce each other to form big irregular voids. These analysis results are helpful to understand the evolution process of ductile metal dynamic fracture and establish the damage evolution model.

Laser Micro-welding Applied to Target Manufacturing

In this work, samples of ultrapure aluminum (content 99.999%) and AA 5083 aluminum alloy (Al-Mg) have been welded under conduction regime, with a pulsed Nd:YAG laser. Due to the very specific final application (use of aluminum assemblies in cryogenic conditions), stringent specifications are imposed for the weld in terms of thermal conductivity and gas tightness at a temperature of 18°K. Process conditions were refined and were validated according to our cryogenic criteria

Microstructural Evolution in Void Coalescence Induced by Plate-Impact Loading in Ultrapure Aluminum

The evolution of microstructure and the mechanical response of ultrapure aluminum subjected to plastic deformation using plate-impact loading was investigated. For the High Purity Aluminum (99.999%), disk sample was shock impacted by a light gun. Observations by transmission electron microscopy reveal that the inside of the early voids consists of nanometer aluminum; it is proposed that they are the result of recrystallization occurring during localization. And some texture may come from the high temperature annealing the secondary grain crystallization behavior and crystallization when the tensile stress effect. This discovery is helpful to the study on the mechanism during the early stage of void nucleation and growth which produced by tensile fracture.

Classical Interpretation of Conduction Currents in Crosslinked Polyethylene (XLPE) and a Comparison with Ideal Polyethylene

Recent experimental conduction current data are numerically analyzed in terms of the established Richardson/Dushman-Schottky (1914) expression for electron emission rates, from a metal cathode, multiplied by the traditional Townsend (1915) derived electron avalanche sizes due to electron-molecule collision ionization in the bulk insulating dielectric for electric fields up to in excess of 1000 MV/m. Agreement between applied theory and experiment limited to 70 MV/m is excellent. Deduced Townsend primary ionization coefficients in ideal, low and high density polyethylene, in solid, liquid and gaseous ethylenes, air, solid Al2O3 and Nb2O5 are shown diagrammatically. From these it is postulated by calculation that 1.5 - 6% of the interelectrode gap distance in practical XLPE is occupied by air filled space rather than by total ideal polyethylene and that this free space is responsible for considerable ionization in the region of 30 MV/m which prevents 1000 MV/m to be attained. Such high dielectric strength should be achievable if in addition a low electron field emitter cathode such as ultra-pure aluminum is used. It is concluded from this and previous work that bonds between atoms/molecules in polymers are as important as the individual discrete particles by themselves in determining dielectric properties.

Reshock response of shock deformed aluminum

The effects of shock loading on compressive yield strength are presented for several aluminum materials. These include commercially pure aluminum 1060, ultrapure aluminum, pure aluminum single crystal of [100] and [111] orientations, and aluminum alloy 6061-T6. The yield strength of these materials was measured by a cyclic shock loading technique in which the sample was first shocked to longitudinal stresses ranging from 4to22GPa, followed by complete release and then reshocked to final states of 4–31GPa. The results reveal that the yield strength of 6061-T6 alloy, as determined through measurement of its Hugoniot elastic limit during reshocking, remains unchanged after first shock loading and release. In contrast, the yield strength of all pure aluminum materials was found to increase during reshocking. In addition, plastic strain hardening was observed in all reshock wave profiles after the initial elastic response, as observed through substantially higher reshock wave speeds. This results in substantially higher reshock Hugoniot stresses than predicted by the original Hugoniot of aluminum at the same compression. The compressive yield strength at the reshock Hugoniot stress was estimated by comparing the first and second Hugoniot states and correcting for thermal effects. The results suggest that strain hardening during second shock compression is independent of first shock amplitudes over the range of 6–22GPa and appears to saturate for a first shock stress greater than 6GPa. The temperature correction for the Hugoniot mean stress shows that the increased temperature produced by second shock compression significantly reduces the flow strength during reshocking and makes the resultant strength strongly dependent on loading history.

Compressive strength measurements in aluminum for shock compression over the stress range of 4–22GPa

Measurements of the high-pressure compressive strength are presented for several aluminum alloys shocked to 22GPa. Five well-characterized aluminum materials were studied, including 6061 alloy with three average grain sizes (50, 30, and <5μm), pure aluminum 1060 (99.5% Al) with a 180-μm grain size, and ultrapure aluminum (99.9998% Al) with a 300-μm grain size. The purpose of these experiments was to investigate deformation mechanisms responsible for the apparently anomalous quasielastic recompression previously observed and to determine how the shock-induced yield strength varies with initial properties. The yield strength was estimated using combined reshock and release techniques previously developed. These results show that quasielastic recompression occurs for all materials investigated and is independent of grain size and impurity level. The shear stress and the shear strength at the shocked state were estimated from the reshock and release wave profiles. These results are consistent with previous investigations and suggest that the shear stress at the Hugoniot state is less than the yield strength. This is thought responsible for the observed quasielastic recompression. The present data, together with other reported measurements, illustrate that the yield strength of aluminum increases with applied shock stress to 90GPa. The Steinberg-Guinan strength model [Steinberg, Cochran, and Guinan, J. Appl. Phys. 51, 1498 (1980)] was used to describe these data and was found to represent the overall data trend with increasing stress, but is not an accurate representation. The collective data suggest that the increase in strength at shock states, ΔY(ΔY=Yyield−YHEL), increases with applied stress and plastic strain. A strength model was developed to describe this increase, which fits the data accurately to 55GPa and reveals that ΔY increases with shock stress in three distinct regions. It also strongly indicates that metallurgical properties, such as impurities and grain size, influence the ambient yield strength, but not the change in strength, which appears to be controlled by the shock-deformed aluminum matrix and possibly grain boundaries.

The fabrication of high-quality periodic porous alumina templates

Porous alumina films can be achieved by anodizing an ultra pure aluminum sheet in proper conditions. Both the distribution and the size of the pores are regular. The depths of the pores are uniquely limited by the anodization time thus very deep pores can be obtained, in the order of mm. Such a porous structure can be employed to serve as the templates for nanosized materials. The Oxalic acid of 0.3mol/L was used in our experiments with the applied DC voltage 40 V. The two-step method was involved to fabricate the templates. The resultant templates exhibit regular porous section. The pore size is ～40—70 nm and the pore-pore spacing is～110 nm. The depth is～0.4 mm. The dependence of the template quality on the solution (oxalic acid) temperature was analyzed and the comparison between the single-step and two-step anodization was made. The results indicate that low solution temperature and two-step method are necessary.