NRC Negev

Beersheba, Israel

NRC Negev

Beersheba, Israel
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Aizenshtein M.,NRC Negev | Aizenshtein M.,University of California at Davis | Shvareva T.Y.,University of California at Davis | Navrotsky A.,University of California at Davis
Journal of the American Ceramic Society | Year: 2010

Lanthanide-doped thoria is relevant both to nuclear energy and to solid oxide fuel cell technology. It is also a simple model system in which oxygen vacancy concentration is directly proportional to doping with no complication from oxidation-reduction reactions, ordered phases, or phase transitions in the tetravalent oxide. Despite this relevance, only few thermodynamic data are available for such systems. In the present study, LaxTh 1-xO2-0.5x (0

Ben-Galim Y.,Ben - Gurion University of the Negev | Wengrowicz U.,NRC Negev | Raveh A.,Advanced Coatings Center at Rotem Industries Ltd. | Orion I.,Ben - Gurion University of the Negev
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

A new approach for neutron detection enhancement to scintillator gamma-ray detectors is suggested. By using a scintillator coupled with a boron carbide (B4C) disc, the 478 keV gamma-photon emitted from the excited Li in 94% of the 10B(n,α)7Li interactions was detected. This suggests that the performance of existing gamma detection systems in Homeland security applications can be improved. In this study, a B4C disc (2 in. diameter, 0.125 in. thick) with ∼19.8% 10B was used and coupled with a scintillator gamma-ray detector. In addition, the neutron thermalization moderator was studied in order to be able to increase the neutron sensitivity. An improvement in the detector which is easy to assemble, affordable and efficient was demonstrated. Furthermore, a tailored Monte-Carlo code written in MATLAB was developed for validation of the proposed application through efficiency estimation for thermal neutrons. Validation of the code was accomplished by showing that the MATLAB code results were well correlated to a Monte-Carlo MCNP code results. The measured efficiency of the assembled experimental model was observed to be in agreement with both models calculations. © 2014 Published by Elsevier B.V.

Stern A.,Ben - Gurion University of the Negev | Aizenshtein M.,NRC Negev
Materials Science and Technology | Year: 2011

The magnetic pulse welding of Al-A1050 to Mg alloys was successfully performed, and the structural-mechanical properties of the interfacial bonding layer produced between dissimilar metals were studied. The morphology of the interface layer has a typical wavy pattern with an average thickness of 20 μm. Compositional microanalysis showed that the composition of the interfacial layer is Al-50 at-%Mg and is practically uniform, being a direct outcome of the local melting effect, intensive mixing of the melt and a rapid rate of solidification. The composition of the bonding layer corresponds to the Al supersaturated intermetallic β phase (Mg17Al12). The elastic modulus (and the hardness) of the interfacial layer was measured using the nanoindentation technique, and its value of 60±1.4 GPa is in good agreement with the value calculated from first principles in the literature (57.3 GPa) for the Mg17Al12 intermetallic phase. © 2011 Institute of Materials, Minerals and Mining.

Aizenshtein M.,NRC Negev | Froumin N.,Ben - Gurion University of the Negev | Frage N.,Ben - Gurion University of the Negev
Journal of Materials Engineering and Performance | Year: 2012

TiB 2 among other borides like ZrB 2 and HfB 2 represents a unique class of ceramics, which displays good wetting by liquid metals, such as Cu and Au, without chemical interaction that may be detected by conventional characterization techniques. The nature of the wetting in these systems is commonly attributed to the "metallic-like" character of borides. In this study, improved wetting of TiB 2 by Cu and Au (50° and 15°, respectively) was confirmed and evidence of a limited chemical interface interaction was observed using TEM analysis. Moreover, it was shown that the addition of B to Au and Cu improves wetting. It was suggested that not only "metallic-like" character of TiB 2 but also the chemical interaction stands behind good wetting in these systems. © ASM International.

Stern A.,Ben - Gurion University of the Negev | Shribman V.,Bmax SRL | Ben-Artzy A.,NRC Negev | Aizenshtein M.,NRC Negev
Journal of Materials Engineering and Performance | Year: 2014

Magnetic pulse welding (MPW) is a solid-state impact welding technology that provides metallurgical joints while exhibiting a negligible heat-affected zone. The MPW process is a high speed single shot welding technique used mainly for joining tubular components in a lap configuration and characteristic length scales of few millimeters to centimeters. It is similar in operation to explosive welding and shares the same physical principles. The nature of bonding in MPW is not sufficiently understood yet and some controversial explanations are reported in the literature. The two major ideas are based on either solid state bonding or local melting and solidification. The present work summarizes our current understanding of the bonding mechanism and the structure in various similar and dissimilar metal pairs joined by MPW. © 2014, ASM International.

Barzilai S.,Ben - Gurion University of the Negev | Aizenshtein M.,NRC Negev | Froumin N.,Ben - Gurion University of the Negev | Frage N.,Ben - Gurion University of the Negev
Advances in Applied Ceramics | Year: 2011

Scandia, yttria and erbia are thermodynamically stable oxides and could be used as a structural material for crucibles, in order to avoid contamination of the melt. These oxides have similar wetting behaviour in contact with aluminium containing melts, but different interaction characteristics and different interfacial products. When yttria and erbia substrates are exposed to Al containing melts, the substrate decomposes, large amounts of Y or Er are released into the melt and a thick interaction layer consisting of a new YAlO3 or ErAlO3 phase is formed beneath the drop. These results were not obtained in the Sc2O3/Al system where only a slight amount of Sc was dissolved in the melt and a thin interfacial layer consisting of Al2O3 was formed. The differences in the mechanism and in the nature of the reaction products of the studied systems are attributed to the thermodynamic properties of the ternary Al-Me-O systems. These properties dictate the sequence of dissolution-precipitation reactions during the wetting experiment and the final equilibrium state for each system. © 2011 Institute of Materials, Minerals and Mining.

Barzilai S.,NRC Negev | Hayun S.,Ben - Gurion University of the Negev
Journal of Materials Science | Year: 2015

Tantalum–titanium alloys have widespread potential in biomedical applications due to their superior biocompatibility, favorable mechanical properties, high corrosion resistance, and ability to exhibit shape memory behavior. However, this system is plagued by processing difficulties due to significant differences in melting temperatures, specific weights, and vapor pressures of Ta and Ti. In the present study, mechanical alloying (MA) using high‐energy ball milling of Ti–xTa (where x = 50, 60, 70, and 85 wt%) was investigated. The alloyed powders were characterized by X-ray diffraction, electron microscopy (SEM and TEM), and differential scanning calorimetry. It was established that α-Ti (hcp) gradually dissolves into α-Ta (bcc), with the alloyed particles becoming chemically homogeneous as a bcc structure. This structure corresponds to a meta-stable phase and should decompose to yield two solid solutions, Ti-rich hcp and Ta-rich bcc. To overcome this thermodynamic preference, MA-generated Ta–Ti bcc solid solution powders possess relatively high internal strain energy. © 2015, Springer Science+Business Media New York.

Stern A.,Ben - Gurion University of the Negev | Aizenshtein M.,NRC Negev | Moshe G.,Ben - Gurion University of the Negev | Cohen S.R.,Weismann Institute of Science | Frage N.,Ben - Gurion University of the Negev
Journal of Materials Engineering and Performance | Year: 2013

The microstructure and the phase composition of the interfaces of Al-1050/Al-1050 and Al-1050/Mg-AZ31 magnetic pulse welding (MPW) joints were characterized by SEM and TEM analyses. The mechanical properties were tested by nanoindentation. Properties of the Al-1050/Al-1050 interface joint were established. The interface is almost free from Al3Fe precipitates, which are present in the base metal. The hardness value is higher than that of the base metal; however, values of the Young's modulus of the interface and base metal are similar. It was suggested that the interface evolution in the Al-1050/Al-1050 system includes local melting and rapid solidification of the base materials. A wavy shaped heterogeneous interface was detected in the Al-1050/Mg-AZ31 joints. Some areas are free from visible intermetallic phases (IMPs), while others contain pockets of relatively coarse intermetallic precipitates. The presence of a relatively large fraction of globular porosity at the interface indicates that local melting takes place in the course of MPW. TEM characterization of regions free of IMPs at the interface reveals regions consisting of fcc supersaturated Al-Mg solid solution, apparently formed as a result of local mechanical alloying during MPW. In other regions, the composition and structure correspond to the Mg17Al12 phase, which was probably formed by local melting and rapid solidification. © 2013 ASM International.

Aizenshtein M.,NRC Negev | Hamawi D.,NRC Negev
Metallography, Microstructure, and Analysis | Year: 2014

β-U could be metastably retained at room temperature when alloyed with various elements such as gallium. Since iron is a common impurity, we investigated two different kinetic processes which occurs simultaneously; one is the β → α transformation and the other is the precipitation of the U6Fe phase from the iron dilute U(Ga)–Fe alloy. Furthermore, we determined the solubility of iron and gallium solubility in quenched uranium from 800 to 720 °C (γ and β phase regions, respectively). It was shown that the β → α phase transformation is sluggish and has a character of massive transformation. The retention from the β phase region does not fully stabilize β phase, and α phase is also formed during quenching, while the γ-quenched sample remains metastable at room temperature, and only high-temperature heat treatment transforms β to α. The precipitates found in the system are U6Fe and U2Ga3, no ternary intermetallics were detected, and the morphology of the precipitates does not depend on the heat treatment course. The gallium and iron contents found in the γ- and β-quenched samples are XGa= 0.72 wt% XFe= 0.18 wt% and XGa= 0.42 wt% XFe= 0.06 wt%, respectively. The different gallium contents in the γ and β explain the differences in the β → α phase transformation kinetics. Quenching U–Ga alloys (above the solubility limit of gallium) from the γ region stabilizes β-U better than quenching from the β region. © 2014, Springer Science+Business Media New York and ASM International.

Aizenshtein M.,NRC Negev | Hamawi D.,NRC Negev
Metallography, Microstructure, and Analysis | Year: 2014

The morphology of U6Fe precipitates were investigated in the different allotropic states of uranium matrix. The morphology of γ-U is equiaxed and the characteristic size is ~65 μm. The excess dissolved iron in β-U precipitates discontinuously through a eutectoid reaction during cooling at the grain boundaries, while α-phase precipitates have a “needle-like” morphology (in many cases, aspect ratio ≫10) with a well-defined direction in the uranium matrix. This morphology may compensate for the large density differences of ~9 % between α-U and U6Fe (~19 and ~17.4 g/cm3, respectively) and the fact that precipitation takes place at relatively low temperatures. It was shown that U6Fe precipitates do not introduce new nucleation sites in β and α phases of uranium. © 2014, Springer Science+Business Media New York and ASM International.

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