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Rozenak P.,Hydrogen Energy Batteries Ltd. | Unigovski Ya.,Ben - Gurion University of the Negev | Shneck R.,Ben - Gurion University of the Negev
Energy Materials 2014, Conference Proceedings | Year: 2014

The effects of in situ cathodic charging on the tensile properties and susceptibility to cracking of an AISI type 321 stainless steel, welded by the gas tungsten arc welding (GTAW) process, was studied by various treatments. Appearance of delta-ferrite phase in the as-welded steels in our tested conditions was observed with discontinuous grain boundaries (M23C6) and a dense distribution of metal carbides MC ((Ti, Nb)C), which precipitated in the matrix. Shielding gas rates changes the mechanical properties of the welds. Ultimate tensile strength and ductility are increases with the resistance to the environments related the increase of the supplied shielding inert gas rates. Charged specimens, caused mainly in decreases in the ductility of welded specimens. However, more severe decrease in ductility was obtained after post weld heat treatment (PWHT). The fracture of sensitized specimens was predominantly intergranular, whereas the as-welded specimens exhibited massive transgranular regions. Both types of specimen demonstrated narrow brittle zones at the sides of the fracture surface and ductile micro-void coalescences in the middle. Ferrite δ was form after welding with high density of dislocation structures and stacking faults formation and the thin stacking fault plates with ε-martensite phase were typically found in the austenitic matrix after the cathodical charging process. Source


Rozenak P.,Hydrogen Energy Batteries Ltd. | Shani E.,Ben - Gurion University of the Negev
Energy Materials 2014, Conference Proceedings | Year: 2014

The novel energy generation, by means of a unique hydrogen production method, creates an opportunity to tackle some important social and environmental factors that determine our sustainable development and personal health. Hydrogen can be produced from a spontaneous chemical reaction in an Al-water system, at a relatively low cost, by bringing aluminum and water into contact, with sodium hydroxide as the catalyst and using an energy source derived from aluminum waste. In our experiments, hydrogen of extremely high-purity was obtained and was used in commercial fuel cell facilities to produce electricity. The hydrogen was produced from recyclable material without supplementary energy and with almost no air pollution. We propose that aluminum technologies for fuel cells could become an integral part of the solution for an economical, clean, low-polluting source of energy. The process is lightweight and largely recyclable and offers opportunities for the commercialization of multiple technologies. Source


Rozenak P.,Hydrogen Energy Batteries Ltd.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

The transmission electron microscopy (TEM) and X-ray characterization of lattice distortion forms caused by low-energy Ar+ bombardment of grown thin silicon films on a silicon (001) substrate were studied. The isotropic case (of spherical distortions) takes place in epitaxial silicon "as grown" processes. The intensity distribution consists of two maxima-one from the distorted layer and the other from the original unaffected silicon lattice. Significant changes in the 2θ location, peak broadening, and integrated intensity from the (004)*reflections were obtained as functions of aging temperatures. First, aging heat treatment, affects the distribution of distortions obtained from local regions at the "as grown" layer, which changes to a special topography of continued distortions at higher aging temperatures. At aging temperatures above 923 K (650 °C), this extra diffraction peak disappears. The TEM observations reveal the appearance of dislocation lines with dark and bright contrasts around the lines and interdislocation strain contrasts and disorder of Ar atoms in Si matrix regions with coherent interfaces. © 2010 The Minerals, Metals & Materials Society and ASM International. Source


Rozenak P.,Hydrogen Energy Batteries Ltd.
TMS Annual Meeting | Year: 2010

The ability of micro-cracks formation in high purity aluminum during electrochemical charging by hydrogen has been studied. The experiments revealed that the existence of a large size distribution of hydrogen bubbles on the surface (blisters) and under the surface obtaining during electrochemical charging can leads to micro-cracks formation in the absence of an external applied stress in aluminum samples. Transmission Electron microscopy (TEM) samples after electrochemically charging showed micro-cracks with typical ductile mode of fracture. Source


Rozenak P.,Hydrogen Energy Batteries Ltd.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2014

In austenitic type stainless steels, hydrogen concentration gradients formed during electrochemical charging and followed by hydrogen loss during aging, at room temperature, surface stresses, and martensitic phases α′-BCC and ε-HCP developed. The basic relationship between the X-ray diffraction peak broadening and the hydrogen gradients, formed during charging and aging at room temperature in such austenitic stainless steels, were analyzed. The results demonstrate that the impact of stresses must be considered in the discussion of phase transformations due to hydrogenation. Austenitic stainless steels based on iron-nickel-chromium, have relatively low stacking fault energy γSFE and undergo: quenching to low temperatures, plastic deformation, sensitization heat treatments, high pressure (≥3-5 × 109 Pa) by hydrogen or other gases, electrochemical charging (when the sample is cathode) and when is irradiation by various ions the samples in vacuum. All the above mentioned induce formation of ε and α′ in the face-centered cubic (FCC) austenite γ matrix. The highest stresses cause formation of mainly α′ phase and ε-martensite, and both are involved in plastic deformation processes and promoting crack propagation at the surface. In 310 steel, the crack propagation is based on deformation processes following ε-martensitic formation only. Formations of ε- and α′-martensites were noted along the fracture surfaces and ahead of the crack tip. The cracks propagated through the ε-martensitic plates, which formed along the active slip planes, while α′ phase was always found in the high-stress region on the ends of the ligaments from both sides of the crack surfaces undergoing propagation. © 2013 The Minerals, Metals & Materials Society and ASM International. Source

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