Rich Alloys Research Articles

Structural and electrochemical properties of (SnxCo100-x)50C50 anodes for Li-ion batteries

Phase formation and electrochemical characteristics of (SnxCo100-x)50C50 (x = 34, 71, 85 wt %) composite anodes prepared by ball milling of melt spun alloys and graphite powder is studied for Li-ion battery applications. The maximum specific capacity of these anodes is 260 mAh g−1 for the Co rich alloy, 400 mAh g−1 for the equi-atomic alloy and a fading capacity of 335 mAh g−1 to 205 mAh g−1 in Sn rich alloy. Anodes made of Co rich and equi-atomic composition deliver stable capacity of 74% of the theoretical value due to the presence of nanocrystalline Sn–Co compounds. Sn rich composition exhibits a large fading in capacity below 55% of the theoretical value, due to the presence of soft Sn phase. The formation of nanocrystalline structure by ball milling is prevented in the Sn rich alloy due to the presence of this soft phase. A highly non uniform porous structure is formed during cycling of the Sn rich anodes, causing poor reversibility. Ball milling leads to the dissolution of Sn–Co compounds in the matrix phase, whereas the softer Sn and C elements do not dissolve. The structure of Sn–Co phase is further completely lost by charge-discharge cycling, forming non-crystalline Li–Sn phase in all the alloys. The equi-atomic Sn–Co composition is shown to be most suitable for making SnCoC anode compared to the Sn rich or Co rich compositions.

Tuning of interfacial perpendicular magnetic anisotropy and domain structures in magnetic thin film multilayers

We investigate the magnetic domain structures and the perpendicular magnetic anisotropy (PMA) arising in CoFeB films interfaced with selected heavy metal (HM) layers with large spin Hall angles in HM/CoFeB/MgO (HM = W, Pt, Pd, WxTa1−x) stacks as a function of CoFeB thickness and composition for both as-deposited and annealed materials stacks. The coercivity and the anisotropy fields of annealed material stacks are higher than for the as-deposited stacks due to crystallisation of the ferromagnetic layer. Generally a critical thickness of MgO > 1 nm provides adequate oxide formation at the top interface as a requirement for the generation of PMA. We demonstrate that in stacks with Pt as the HM, the PMA depends crucially on the alloy composition of the ferromagnet requiring a Co rich alloy to achieve PMA, i.e. it is important to have a large number of Pt–Co hybrid bonds at the interface compared to Pt–Fe hybrid bonds. In Pd/CoFeB/MgO layers, we observe for appropriate PMA a special stripe domain configuration that also includes circular skyrmion-like spin structures. Three different means of selective tuning of the PMA are discussed apart from the conventional FM thickness variation: Changing the number of repetitions of a multilayer stack is shown to change the PMA and strong PMA is found for certain compositions of WxTa1−x that also result in very low coercive fields (<1 mT) of the CoFeB. The PMA has also been shown to be tuned via annealing, very strong anisotropy fields of up to 1 T and low pinning of domain structures were measured in W/CoFeB/MgO, making these multilayers stacks a promising candidate for MRAM development.

Extraction Effect of Ni-Zn By Electrodeposition from Aqueous Acid Solutions

The electrodeposition of Zn-Ni is classified by Brenner (1) as anomalous codeposition, because zinc, the less noble metal, is preferentially deposited to nickel the more noble metal. The inhibition of H+ reduction occurs with increasing Zn ions concentration in solution (2). Anomalous codeposition is favored in chloride medium and inhibited in boric acid (3). The reaction kinetic of Zn-Ni codéposition was investigated in acid solutions .The effects of solution composition and pH were analyzed. The inhibition of H+ reduction occurs with increasing Zn ions concentration in solution. Increasing pH values causes Zn deposition during Ni-Zn codeposition. Anomalous codeposition is favored in chloride medium and inhibited in boric acid. When alloy deposition becomes the main process, the interfacial pH is governed by the individual metal deposition that controls the kinetic behavior. The interfacial pH increases during separate Ni deposition, meaning that it occurs with simultaneous consumption of H+. Anomalous codeposition process is not due to a saturation of species at the electrode surface. Results show that it is possible to obtain alloys rich in either nickel or zinc , from an acidic solution,depending on the Ni/Zn concentration ration. For Ni/Zn concentration ratios in the range of 1-5, zinc rich alloys are obtained despite Zn is the less noble metal and even when it is present lower concentrations than nickel. For the highest Ni/Zn concentrations ratio ≥100, the formation of the alloy occurs by a normal deposition, resulting in Ni-rich alloys. Boric acid extends the proton discharge potential to more cathodic values. Thus it can reduce anomalous codeposition since the presence of 0,8M of acid reduces the intensity of the peak corresponding to δ phase that is rich in zinc and enhances the intensity of γ phase containing more nickel than the δ phase.

Large Scale Solid-state Synthesis of Catalytically Active Fe3O4@M (M = Au, Ag and Au-Ag alloy) Core-shell Nanostructures

Solvent-less synthesis of nanostructures is highly significant due to its economical, eco-friendly and industrially viable nature. Here we report a solid state synthetic approach for the fabrication of Fe3O4@M (where M = Au, Ag and Au-Ag alloy) core-shell nanostructures in nearly quantitative yields that involves a simple physical grinding of a metal precursor over Fe3O4 core, followed by calcination. The process involves smooth coating of low melting hybrid organic-inorganic precursor over the Fe3O4 core, which in turn facilitates a continuous shell layer post thermolysis. The obtained core-shell nanostructures are characterized using, XRD, XPS, ED-XRF, FE-SEM and HR-TEM for their phase, chemical state, elemental composition, surface morphology, and shell thickness, respectively. Homogeneous and continuous coating of the metal shell layer over a large area of the sample is ascertained by SAXS and STEM analyses. The synthesized catalysts have been studied for their applicability towards a model catalytic hydrogen generation from NH3BH3 and NaBH4 as hydrogen sources. The catalytic efficacy of the Fe3O4@Ag and Ag rich alloy shell materials are found to be superior to the corresponding Au counterparts. The saturation magnetization studies reveal the potential of the core-shell nanostructured catalysts to be magnetically recoverable and recyclable.

Annealing Effects on the Microstructure and Properties of Vanadium and Molybdenum Rich FCC High Entropy Alloy

In the past decade, research into High Entropy alloys (HEAs) have gained significant attention due to their outstanding properties and approach to design alloys for high temperature applications. Strengthening of face centered cubic (FCC) based HEAs, by addition of intermetallic phase or precipitate forming elements is a very captivating direction of alloy designing for high temperature structural applications. However, the knowledge regarding the influence of intermetallic phases on the properties of FCC HEAs is rare. The current study focuses on annealing effects on the microstructure of Cr20Co20Fe25Ni25V5Mo5 (at. %) alloy, this alloy was synthesized using induction melting, and was homogenized at 1200 °C for 12h. X-ray diffraction analysis indicated that the principle phase was (FCC) identified. Scanning electron microscopy (SEM) together with Energy Dispersion X-ray Spectroscopy (EDS) showed that there is an additional phases that is Mo-rich. In order to understand the effect of the high temperature annealing on phase stability, the homogenized samples were annealed at 700 °C, 800 °C, 900 °C, 1000 °C each for 6h and quenched. The annealing treatments had considerable effect on the crystal structure and the elemental distribution. The Mo-rich phase is precipitated at the grain boundaries at all temperatures. Additionally, at 1000 °C annealing temperature Mo-rich phase had precipitated inside the grains. The lower annealing temperatures inhibited diffusion of Mo, which restricted the Mo-rich phase formation. Additionally, the hardness is increased to 195 HV at 1000 °C due precipitation hardening. At other annealing temperatures the hardness is reduced to 145 – 158 HV.

Bandgap tuning of Monolayer MoS2(1-x)Se2x alloys by optimizing parameters

Among the two-dimensional (2D) materials, transition-metal dichalcogenide (TMD) monolayer alloys attract significant attention as they allow for bandgap engineering, which is highly beneficial for their applications in nanoelectronics, optoelectronics, and photonics. In this research, we present a facile and repeatable molybdenum sulphoselenide (MoS2(1-x)-Se2x) monolayer growth through systematic investigation of CVD growth parameters such as gas flow rates, substrate temperature and precursor concentration (S/Se ratio). We have obtained a full control of the x values within the range of 0–1 allowing for bandgap tailoring between 1.82 eV (MoS2) and 1.56 eV (MoSe2) where the size of the grown monolayer flakes has been measured as large as 150 μm on SiO2 (300 nm)/Si substrates. We find that S/Se ratio and the growth temperature are the most critical parameters to control the composition (x value) of the monolayer alloy TMDs. In our study, we find two growth regimes, where S rich alloys are grown by controlling S to Se ratio at 750 °C and Se rich alloys are synthesized at higher growth temperatures (900 °C) by utilizing Se rich vapor conditions. Growth of Se rich alloys at a higher growth temperature is attributed to the chalcogen exchange mechanism (CEM) referring to substitution of S atoms in as grown alloy host lattice site with Se atoms present in the Se rich vapor. CEM is proposed as the basic alloying mechanism for selenium rich monolayer alloys. Regarding the structural properties, FWHM of the photoluminescence (PL) spectral peaks of our flakes range between 19 and 37 nm together with uniform spatial PL emission intensities indicating high crystalline quality. Tuning the bandgap of high-quality and large area TMD monolayers by simply changing the basic CVD parameters is of great benefit for future 2D optoelectronic devices.

On the origin of a remarkable increase in the strength and stability of an Al rich Al-Ni eutectic alloy by Zr addition

The effect of Zr addition to Al rich binary α-Al - Al3Ni eutectic cast alloy (Al-3.1 at.% Ni) in enhancing the microstructural stability and strength at high temperature is demonstrated. On subsequent heat treatment after casting, nanometric coherent L12 ordered Al3Zr precipitates form inside the α-Al that strengthen the alloy. Additionally, remarkable stability of eutectic microstructure was observed even after 100 h of annealing at 400 °C. The synergetic effect of the strengthening of the α-Al matrix by coherent Al3Zr precipitates and the low coarsening rate of the Al3Ni rods results in a significant increase in high temperature hardness and yield strength of the alloy. The tensile yield strength of the annealed Al-3.1Ni-0.15Zr alloy (400 °C, 10 h) tested at 250 °C is found to be 185 ± 10 MPa, which is 1.5 times higher than the corresponding binary Al-3.1Ni alloy. The experimentally determined average rod size (radius) during annealing at 400 °C follows the classical matrix diffusion controlled LSW-based coarsening model for both binary Al-3.1Ni and ternary Al-3.1Ni-0.15Zr alloys. The calculated coarsening rate constant values based on modified LSW coarsening model are 10.3 and 4.1 nm3/s for Al-3.1Ni and Al-3.1Ni-0.15Zr alloys, respectively. Atom probe tomographic (APT) investigations of the heat-treated ternary alloy unambiguously reveal segregation of Zr solute at the αAl/Al3Ni interface in addition to the presence of the strengthening Al3Zr ordered precipitates in the α-Al matrix. The segregation hinders the interdiffusion of Al and Ni in the eutectic and, thereby, increasing the stability of the eutectic phase at high temperature.

Room temperature and 600 °C erosion behaviour of various chromium carbide composite coatings

In this study, the erosion behaviour of laser clad chromium carbide-Ni rich alloy composite coatings with a wide range of carbide contents at room temperature and 600 °C were investigated. The variation in carbide content of the coatings was due to dilution from the substrate and the high cooling rate in the laser cladding process preventing re-solidification of the molten carbides. Erosion rate was observed to be a function of carbide content alone and was significantly higher at 600 °C as compared to room temperature. Erosion wear ratio (E90/E30) was also dependent on carbide content but decreased at higher temperature and higher carbide contents. A comparison of erosion behaviour with detonation and plasma sprayed counterparts showed the superior performance of laser clad coatings at 600 °C. The poor erosion performance of the detonation and plasma sprayed coatings was due to weak splat bonding. Thick oxide layer formed on the steel substrate after pre-oxidation resulted in its poor erosion performance.

Copper Rich Cu1-xNix Alloys (0.05 < x < 0.15) Electrodeposited from Acid Sulfate-Based Electrolyte with Benzotriazole Additive for Microbump Metallization for 3D Stacked Integrated Circuits

In this paper we report on electrodeposition of CuNi alloys with low Ni content for applications in three-dimensional stacking of integrated circuits (SIC). For practical reasons related to compatibility with SIC processing, a common sulfate-based electrolyte solution was chosen and the high copper/low nickel content in the deposited alloys was achieved through the introduction of organic additive benzotriazole (BTA). BTA is known as a strong inhibitor for Cu deposition, but its effects on CuNi alloy deposition were not known before. We hypothesized that, in addition to bringing the onset potential of Cu closer to that of Ni deposition, the slower diffusion through the BTA passivation layer could enable improved control of the composition of the deposited alloy as well as the current distribution over the substrate. Our hypotheses were tested through systematic electrochemical measurements combined with ex-situ imaging and chemical analysis techniques. As such, CuNi alloys with Ni content between 5–15 at.% were successfully fabricated from a sulfate-based CuNi electrolyte solution with BTA as an organic additive.

Effect of Aging Heat Treatment on the High Cycle Fatigue Life of Ni50.3Ti29.7Hf20 High-Temperature Shape Memory Alloy

Shape memory alloys can be utilized as actuators for several applications in aerospace industry which require high strength and stable actuation cycles together with the transformation temperatures above 100 °C. Aging is one of the methods for Nickel rich NiTiHf alloys that adjusts the transformation temperatures and enhances the cyclic stability due to the formation of nano-sized precipitates. In this study, the high cycle functional fatigue life and behavior of the extruded and aged Ni50.3Ti29.7Hf20 high-temperature shape memory alloy were investigated in order to reveal the effect of aging on the stability of the actuation strain and transformation temperatures. The aging was conducted at 550 °C for 3 h. 200 MPa was chosen in the functional fatigue experiments since no irrecoverable strain was determined under this stress magnitude for the extruded and the aged samples in the load-biased heating cooling experiments. The fatigue experiments were conducted twice to check the repeatability of the shape memory properties of the samples and it was observed that the life cycle of the aged sample was determined as 20,337 and the extruded sample completely lost the shape recovery ability after 5000 cycles.

The application of non-destructive techniques for the study of corrosion patinas of ten Roman silver coins: The case of the medieval Grosso Romanino

This work focuses on the study of ten Grosso Romanino, a silver medieval coin, minted in Rome during the 13th century CE. As the coinage of this denomination occurred during a tumultuous period of the history of Rome, the official documentation from Mint was lost. For this reason, archaeometric investigations were necessary to have an overall knowledge of the Grosso Romanino. This work represents the first attempt of archaeometric study performed on this interesting denomination. The coins were characterized by a combination of non-destructive techniques, i.e., X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDAX), micro-Raman spectroscopy and Voltammetry of Microparticles (VIMP), aiming to investigate the external surface and its microstructure and to explore the nature of the alloy and corrosion products. The results show an Ag- rich alloy with minor amount of copper (2.1–3.1 wt%), lead (0.7–3.2 wt%) and other elements. Moreover, the rare corrosion products on the surfaces indicate the presence of a random distributed patina composed by oxides, sulfides and chlorides.

The Effect of Molecular Weight, M/G Ratio and pH on the Cyclability of Alginate Bound High Capacity Silicon Anodes

Classical rocking chair Li-ion batteries are dominating the market as they are currently the battery concept with the highest energy density, both per weight and volume. As the technology is rather mature, only small increases in energy density are expected without changing the electrode chemistry. Though the positive electrode currently limits the capacity of a Li-ion battery most, the state of the art graphite negative electrodes only deliver a moderate capacity of 300-350 mAh/g and improvements to this are also highly desirable. Silicon is a promising alternative negative electrode material. Under cathodic polarisation it forms a Li rich alloy, delivering a very high specific capacity of about 3600 mAh/g. Alloying, in contrast to an intercalation reaction, is associated with immense volume changes of the material. The currently used binder (PVDF) has been shown to be unsuitable for Si based electrodes as it cannot withstand the volume changes associated with cycling. Lately, a variety of biopolymers have been described as potential binders for Si based electrodes. These usually come with the advantage of being water soluble and hence makes the electrode production more environmentally benign. One class of biopolymers which have shown encouraging results are derivates of alginic acid. Most commonly applied as water soluble Na salts, alginates have shown encouraging results in accommodating the volume changes and hence can improve the cyclability of Si based electrodes. [1-3] Most published studies describe the alginates they are using rather incompletely. Alginic acid consists of the two epimers D-mannuronic acid (M) and L-guluronic acid (G). The content and distribution of the repetition units have a strong impact on the 3D structure and hence the properties. Furthermore, the chain length influences the properties of the corresponding alginates. Another crucial factor is the pH of the binder solution, which influences the degree of protonation of the carboxyl groups of the alginate. Protonated carboxyl groups ease esterification of the alginate with the native oxide layer on the Si surface which has a strong influence on the binding strength. [4] This systematic study addresses the effect of pH, Mw and M/G ratio of Na alginates as a binding agent for high capacity Si anodes using commercially available materials. The examined electrodes consisted of Si as main active material, Graphite and carbon black as conductivity enhancers and different Na alginates as binding agents. Na alginates with different Mw and M/G ratio were supplied by FMC BioPolymer AS (DuPont) and a commercially available battery grade Si (Silgrain ®, e-Si 400) was provided by ELKEM AS Technology. Kovalenko, I., et al., A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries. Science, 2011. 334(6052): p. 75-79.Erk, C., et al., Toward Silicon Anodes for Next-Generation Lithium Ion Batteries: A Comparative Performance Study of Various Polymer Binders and Silicon Nanopowders. Acs Applied Materials & Interfaces, 2013. 5(15): p. 7299-7307.Zhang, L., et al., A coordinatively cross-linked polymeric network as a functional binder for high-performance silicon submicro-particle anodes in lithium-ion batteries. Journal of Materials Chemistry A, 2014. 2(44): p. 19036-19045.Mazouzi, D., et al., New insights into the silicon-based electrode's irreversibility along cycle life through simple gravimetric method. Journal of Power Sources, 2012. 220: p. 180-184.

Atomization of Al-rich alloys: Three paradigmatic case studies

In this work we present our results on three aluminum rich alloys processed by atomization: Al90Fe5Nd5, Al93Fe3Cr2Ti2, and Al68.5 Ni31.5, for structural and functional applications. Amorphous and a nanocomposite microstructure, formed by nanocrystals of α-Al embedded in a remaining amorphous matrix, are obtained in the atomized Al90Fe5Nd5 powder particles. Bars produced by extrusion of this powder present yield strength above 700 MPa. Atomized Al93Fe3Cr2Ti2 powder particles contain a high proportion of quasicrystalline precipitates, stable up to 500 °C. At 300 °C, Al93Fe3Cr2Ti2 extruded bars present ultimate tensile strength as high as 280 MPa. Raney alloy, Al68.5 Ni31.5, is of high interest as a catalyst. When it is atomized, the particles present a fine dendrite microstructure, which is very suitable for catalyst reactions once the Al rich phases have been leached away.

Friction, Wear and Mechanical Properties of Al-Si LM6 Cast Alloy Processed in Semi-solid Stage

Dry sliding wear characteristics, mechanical properties and microstructural behavior of powder-chip based reinforcement silicon rich LM6 aluminum alloy, fabricated by semi-solid casting were investigated. Wear tests were conducted on powder-chip reinforced cast samples using the pin on disc apparatus under 5, 10 and 15 N with 0.4, 0.8 and 1.2 m/s sliding speeds for 250, 500 and 750 m sliding distances versus EN31 tool steel hardened to 62 HRC. An observation from the microstructure images indicated that the porosity of the cast composite reduces due to the distribution of un-melted chips inside the short cavities by the addition of reinforcement and confirmed with the obtained results of density. The fracture in cast specimens indicates that the micro-cracks were prevalently propagated along the broken eutectic silicon particles. Additionally, wear resistance was increased reasonably due to the inclusion of reinforcement under metallic wear environment. Worn surfaces SEM, EDS, XRD and, AFM analysis suggests that surfaces plastically deformed along with silicon brittle asperities which stuck on the softer surface of the contact layers, while dominant wear mechanisms were found from these surfaces and wear debris.

Experimental investigation and thermodynamic re-assessment of the ternary copper-nickel-lead system

Due to their high corrosion resistance and thermal stability, Cu-Ni-alloys have essential role in many materials engineering applications. Lead is an alloying element in these alloys although it may also be considered as an impurity in certain cases. In copper rich alloys, lead tends to diffuse into the grain boundaries and weaken the hot-working properties. In addition to alloys design, accurate knowledge of phase relations and solubilities in the ternary Cu-Ni-Pb system has important role in improving the copper and nickel smelting and refining processes.In the present work, an isothermal equilibration technique was used to measure the mutual solubilities of liquid lead and solid CuNi foil in the temperature range 1280–1530 K. The samples were equilibrated and an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) and an Electron Probe Micro Analyzer (EPMA) were used to quantify the chemical composition of the phases. Selected solubility data obtained in this work were combined with the literature data to obtain a thermodynamic description of the Cu-Ni-Pb ternary liquid and fcc solid solution phases by applying the CALPHAD method. The ternary assessment agrees well with the experimental observations in this work.

High Temperature Oxidation of Hot-Dip Aluminized T92 Steels

The T92 steel plate was hot-dip aluminized, and oxidized in order to characterize the high-temperature oxidation behavior of hot-dip aluminized T92 steel. The coating consisted of Al-rich topcoat with scattered Al3Fe grains, Al3Fe-rich upper alloy layer with scattered (Al, Al5Fe2, AlFe)-grains, and Al5Fe2–rich lower alloy layer with scattered (Al5Fe2, AlFe)-grains. Oxidation at 800 °C for 20 h formed (α-Al2O3 scale)/(AlFe layer)/(AlFe3 layer)/(α-Fe(Al) layer), while oxidation at 900 °C for 20 h formed (α-Al2O3 scale plus some Fe2O3)/(AlFe layer)/(AlFe3 layer)/(α-Fe(Al) layer) from the surface. During oxidation, outward migration of all substrate elements, inward diffusion of oxygen, and back and forth diffusion of Al occurred according to concentration gradients. Also, diffusion transformed and broadened AlFe and AlFe3 layers dissolved with some oxygen and substrate alloying elements. Hot-dip aluminizing improved the high-temperature oxidation resistance of T92 steel through preferential oxidation of Al at the surface.

Infiltration of Die-Upset Nd-Fe-B Magnets With Mischmetal Eutectic Alloys

In recent years, infiltration of hot-deformed Nd-Fe-B magnets with liquid Nd- and Pr-rich alloys has been intensively studied as a cost-effective way of increasing the magnet coercivity $H_{{\text{c}}}$ and, ultimately, its maximum operating temperature. In this letter, a similar improvement is obtained through infiltration of commercial die-upset Nd-Fe-B magnets with eutectic alloys based on inexpensive Ce52La28Nd15Pr5 mischmetal (MM). After being infiltrated with 10 wt% of MM85Fe15, MM85Al 15, and MM70Cu30 alloys at 700 °C, the die-upset magnets exhibited an $H_{c}$ that was both higher and more temperature stable than before the treatment. For example, after infiltration with the MM85Al15 alloy, the room-temperature $H_{{\text{c}}}$ increased from 12.1 kOe to 17.8 kOe, whereas the absolute value of the $\Delta H_{\text{c}}/ H_{\text{c}}\Delta T$ between 27 °C and 100 °C decreased from 0.65%/°C to 0.54%/°C. Although the infiltration treatment reduces the maximum energy product of the magnets, this reduction becomes less significant at elevated temperatures, effectively disappearing at 150 °C to 175 °C. The microstructural effects of the treatment with MM-rich alloys are analyzed in the context of earlier studies involving Nd(Pr)-rich alloys. As of now, the improved $\Delta H_{\text{c}}/ H_{\text{c}}\Delta T$ in the infiltrated magnets still lacks a convincing, controversy-free explanation.

Catalytic activity of pure Ni and Ni-33%Cu for dehydrogenation during graphene growth by chemical vapour deposition

Dissociative chemisorption of CH4/H2 gas mixture during graphene growth was investigated on commercially available Ni and Ni-33wt.% Cu substrates. Catalytic activity of both the substrates was severely decreased by employing very low gas pressure, thereby allowing the examination of very initial stages of dissociative-chemisorption. The chemisorption characteristics of the nickel rich nickel-copper alloy were interestingly found to be similar to those of pure copper, i.e., preferential adsorption of hydrogen over methane. These observations led to an in-depth understanding of the graphene growth mechanism on these substrates.

Influence of Powder-Chip Based Reinforcement on Tensile Properties and Fracture Behaviors of LM6 Aluminum Alloy

Tensile properties and fracture behaviors of silicon rich LM6 aluminum alloy were investigated in details for as cast alloy and modified by LM6 powdery-chip capsules. The obtained results showed that 20% modified LM6 cast composite ensured the excellent tensile properties (tensile strength of 203 MPa with 3.8% elongation). An impressive increase in the elongation (6.8%) was found for 25% modified cast composite with good ultimate tensile strength, 6.2% higher than unmodified (182 MPa). Characterization of the casts and fracture surfaces were carried out to study the effect of reinforcement particles. An influence of un-melted chip structure was observed inside the cavities and on fractured surfaces. The XRD results showed that cast consisted of inter-metallics of AlO2, Al2Si and Al4Si. It was attributed to micro-cracks prevalently propagated along the broken eutectic silicon particles and some rejected solid particles on the fractured surfaces with ductile and inter-granular fracture. Debonding and cracking of silicon particles were also detected on the fractured surface of the specimens.

Internal field 59Co NMR study of cobalt-iron nanoparticles during the activation of CoFe2/CaO catalyst for carbon nanotube synthesis

CoFe2/CaO catalysts for multi-walled carbon nanotubes (MWCNT) were characterized during the activation period (T = 670 °C; C2H4/Ar = 1:1, 400 sccm) by internal field 59Co nuclear magnetic resonance. During this induction period, although C2H4 is already reacting, the MWCNT yield remains negligible. The NMR spectra of the catalysts revealed the occurrence of several structural and magnetic species. They were not detectable by conventional X-ray diffraction but the heterogeneity of the metal particles was corroborated by high-resolution transmission electronic microscopy coupled with energy dispersive X-ray spectroscopy. Two samples quenched at different activation time contained, beside non-reacted pure metal Co particles, strong and weak ferromagnetic alloys. During activation, the pure Co metal content dropped and an increase of the ordering of the cobalt-iron alloy in the catalyst was evidenced thus revealing a multistage activation mechanism for the reaction. We propose this ordering process during the induction period to be an intermediate step between the strong ferromagnetic Co rich alloy and the weak ferromagnetic Fe rich one and that it favors the onset of MWCNTs growth.