Conventional Metallurgical Methods Research Articles

Removal of Impurities from Refractory Gold Ore using Bio-reduction and Bio-oxidation processes

Gold in refractory gold ore is difficult to be extracted by conventional metallurgical method due to the presence of sulfide minerals with elevated levels of iron (Fe), sulfur (S), and arsenic (As) as impurities, resulting in low gold (Au) recovery. Conventional methods such as cyanide leaching has been proven ineffective for gold extraction from refractory ore due to gold being intricately bound within the sulfide minerals. Consequently, this study explores the application of bioleaching as an alternative to conventional cyanide leaching. Shewanella oneidensis (S. oneidensis) and Acidithiobacillus ferroxidans (A. ferroxidans) serve as bio-reduction and bio-oxidation agents, respectively in the bioleaching process. The composition of minerals in the ore was determined through XRD analysis (Model: Rigaku’s Miniflex 600) and EDX analysis (Model EDX 3). Meanwhile, SEM analysis (Zeiss EVO LS15 SEM) was utilized to examine the morphology structure. The concentrations of impurities (Fe, S, and As) were assessed using a spectrophotometer (Model: DR3900 Hach) meanwhile the Au concentration was determined through ICP-OES (Model: G8015A5110 ICP-OES). Sieved refractory gold ore samples with less than 32 um and varying in weight (0.5 g, 1.0 g, 1.5 g, 2.0 g), underwent bio-reduction and bio-oxidation processes. The results indicated a rougher surface morphology of raw sample as observed through SEM analysis. Furthermore, XRD and EDX results demonstrated a decrease in impurity concentrations, suggesting a potential increase in gold purity. Notably, the bio-reduction process exhibited a superior enhancement in Au concentration with the values of 138.89% compared to biooxidation with the value 122.22%. Thus, the bio-reduction process proved more effective in increasing Au concentration compared to bio-oxidation.

New Al-alloys with dispersed stable quasicrystal approximant phases: Overcoming the barrier of conventional casting processing and microstructure design

Multi-stage manufacturing processes, high production costs and narrow two-phase field of Al-alloys containing Al-FCC and quasicrystals or approximants phases have been barriers to the widespread use of these alloys in technological applications. In the present work, we demonstrated that new Al-alloys with dispersed stable quasicrystal approximant phases can be produced by conventional metallurgical fabrication methods. Six alloys containing different volume fractions (5% up to 40%) of the approximant α-phase were designed and produced by conventional solidification in a graphite mold. The hardness and tribological properties of Al-FCC matrix with different volume fractions of the quasicrystal approximant phase were evaluated. A wide range of wear rates, from 2.1 × 10−3 mm3/Nm to 6.3 × 10−4 mm3/Nm, could be achieved by tuning the volume fraction of the α-phase ranging from 5% up to 40%, respectively. Low coefficient of friction values around 0.3 were observed after the running-in periods, regardless of the α-phase content, indicating that the quasicrystal approximant phase played a critical role. The alloy containing 25% of α-phase was chosen to be processed by different manufacturing processes to show that the morphology of the stable approximant α-phase can also be controlled. This finding opens new perspectives for the commercial application of products derived from such light- and wear-resistant materials.

Advances in Intelligent Regeneration of Cathode Materials for Sustainable Lithium‐Ion Batteries

AbstractExplosively increased market penetration of lithium‐ion batteries (LIBs) in electric vehicles, consumer electronics, and stationary energy storage devices has recently aroused new concerns on nonrenewable metal resources and environmental pollution because of the forthcoming wave of retired popularized LIBs. Recycling the retired LIBs in an environmentally sustainable and cost‐effective way thus becomes much urgent and imperative. As a preferable route, the direct regeneration strategy has been innovatively proposed to repair degraded cathode materials in retired LIBs under non‐destructive conditions, which exhibits tremendous superiority compared to conventional metallurgical method that just emphasizes the recovery of target metal elements. Nevertheless, the development of direct regeneration methods for degraded cathode materials is still in infancy, and there remain many scientific and technological obstructions to conquer. It is even absent in the thorough summaries and assessments of this kind of avenue so far. In this review, the current states of various direct regeneration approaches from the regenerative processes, principles, merits, and challenges aspects are summarized, highlighting the extraordinary importance in constructing the really‐green closed loop industry for future sustainable energy and, more significantly, in turn providing profound insights into rationally designing more advanced regeneration approaches at the industrial scale.

In-Situ Alloy Formation of a WMoTaNbV Refractory Metal High Entropy Alloy by Laser Powder Bed Fusion (PBF-LB/M).

High entropy or multi principal element alloys are a promising and relatively young concept for designing alloys. The idea of creating alloys without a single main alloying element opens up a wide space for possible new alloy compositions. High entropy alloys based on refractory metals such as W, Mo, Ta or Nb are of interest for future high temperature applications e.g., in the aerospace or chemical industry. However, producing refractory metal high entropy alloys by conventional metallurgical methods remains challenging. For this reason, the feasibility of laser-based additive manufacturing of the refractory metal high entropy alloy W20Mo20Ta20Nb20V20 by laser powder bed fusion (PBF-LB/M) is investigated in the present work. In-situ alloy formation from mixtures of easily available elemental powders is employed to avoid an expensive atomization of pre-alloyed powder. It is shown that PBF-LB/M of W20Mo20Ta20Nb20V20 is in general possible and that a complete fusion of the powder mixture without a significant number of undissolved particles is achievable by in-situ alloy formation during PBF-LB/M when selecting favorable process parameter combinations. The relative density of the samples with a dimension of 6 × 6 × 6 mm3 reaches, in dependence of the PBF-LB/M parameter set, 99.8%. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) measurements confirm the presence of a single bcc-phase. Scanning electron microscopy (SEM) images show a dendritic and/or cellular microstructure that can, to some extent, be controlled by the PBF-LB/M parameters.

Selective recovery of precious metals through photocatalysis

Precious metals such as gold and platinum are valued materials for a variety of important applications, but their scarcity poses a risk of supply disruption. Recycling precious metals from waste provides a promising solution; however, conventional metallurgical methods bear high environmental costs and energy consumption. Here, we report a photocatalytic process that enables one to selectively retrieve seven precious metals—silver (Ag), gold (Au), palladium (Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru) and iridium (Ir)—from waste circuit boards, ternary automotive catalysts and ores. The whole process does not involve strong acids or bases or toxic cyanide, but needs only light and photocatalysts such as titanium dioxide (TiO2). More than 99% of the targeted elements in the waste sources can be dissolved and the precious metals recovered after a simple reducing reaction that shows a high purity (≥98%). By demonstrating success at the kilogram scale and showing that the catalysts can be reused more than 100 times, we suggest that this approach might be industry compatible. This research opens up a new path in the development of sustainable technologies for recycling the Earth’s resources and contributing to a circular economy.

Exploring additive manufacturing as a high-throughput screening tool for multiphase high entropy alloys

High entropy alloys (HEA) exhibit exceptional and sometimes record-setting physical, thermal and mechanical properties. However, the vast composition space presents a significant practical challenge for optimization, particularly when relying on sequential use of conventional metallurgical fabrication and characterization methods. An efficient method for rapidly evaluating the properties of complex concentrated alloys is presented. Powder based directed energy deposition additive manufacturing was used to synthesize a broad range of compositions in a single metallurgical sample via in situ alloying. An investigation of the phase-property space was done by compositionally grading a transition metal-based HEA (CoCrFeMnNi) with several refractory metals (i.e., Ta, Nb, and Ti-6Al-4V). A high throughput microstructural-mechanical analysis method was also utilized to rapidly assess microstructure and hardness as a function of alloy composition. Compositions promoting solid solutions, multiple phases, and intermetallics were found to have a wide range of hardness and fabrication quality. These results are discussed in the context of alloy-specific microstructural characteristics and configurational entropy, along with relevant processing challenges.

Bioprocessing of oxidized platinum group element (PGE) ores as pre-treatment for efficient chemical extraction of PGE

Platinum-group elements (PGE) are relevant for many high technology applications, prompting the search for potential alternative resources and environmentally friendly processing technologies. The largest deposit of PGE worldwide is the Bushveld Complex in South Africa. The pristine sulfide-bearing ore is mined using conventional metallurgical methods, while the near-surface oxidized PGE ore is currently stockpiled. Economic extraction of PGE from these stockpiles using conventional technologies is not feasible to date. Hence, biohydrometallurgical approaches to recover valuable transition metals and liberate platinum-group minerals for subsequent chemical PGE extraction have been considered. The four stockpile samples taken from a heap of oxidized PGE ores from the Platreef formation showed a similar mineralogical composition with >90 wt% silicates and minor amounts of Fe-(oxy)/hydroxides, both associated with Ni, Mn and Cu. Platinum-group minerals were present as sperrylite (PtAs2), cooperite (PtS low Pd), native platinum and Pd‑bismuthotellurides and mostly associated with silicates. Stirred tank bioleaching under various conditions was proven to be most feasible for an oxidative process at moderately-high temperatures using a consortium of iron- and sulfur-oxidizing acidophiles dominated by Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. Bioleaching achieved up to 86% total metal recovery (including Co, Cu, Mn and Ni) and led to a liberation of platinum-group minerals. The bioleach residues were subsequently chemically leached by a HNO3/NaCl and a cyanide leach, allowing for the enhanced extraction of up to 89% Pt and 96% Pd after bioleaching. Chemical and mineralogical analysis validated the potential of oxidative bioleaching as a promising processing option for a pre-treatment of oxidized PGE ore, allowing separate and efficient recovery of valuable base metals and enhancing the subsequent chemical PGE extraction.

Mesophilic bioleaching performance of copper, cobalt and nickel with emphasis on complex orebodies of the Democratic Republic of Congo: a review of dynamic interactions between solids loading, microbiota activity and growth

The copper, cobalt and nickel ores are still currently mined in the world. Its complex mineralogy creates extraction challenges by means of conventional metallurgical methods. Meanwhile, dealing with mesophilic strains in leaching process requires a compromise between solid loading and microbiota activity and growth. That is why, the influence of solid loading with fine or coarse particulates, the cell disturbance during the metal–microbes interactions depending upon the influence of gangue nature as well as metallic ions concentration on bacterial tolerance and the chemical and biological pathways involved in bioleaching mechanism of complex ores are summarised in detail in this paper. The current trends in mechanism research and diverse discovered set of microbiota and bacterial population coupled with bacterial adaptation methods contribute to optimise and improve the metals leaching performance and knowledge. In addition, the different existing complex mineralogical structures elaborate a main indirect mechanism with two different transitory mechanisms, before metal is converted into metal sulphate as wealthily explained in this comprehensive review. More data for cost analysis concomitant with extraction efficiency of metals using mesophilic bioleaching process are needed. However, it does not mean that other options are excluded in order to set a bio-hydrometallurgical chain. In fact, to consider also the concentration and purification of the pregnant leaching solution via phase separation and solvent extraction will be helpful. This obeys to the idea of option trees, where possible options are then systematically gaged with respect to critical criteria.

Fabrication of Al-matrix composite reinforced with quasicrystals using conventional metallurgical fabrication methods

Al-matrix composites reinforced with quasicrystals are mostly fabricated by methods that apply rapid solidification techniques or by means of powder metallurgy. In this work, we show a metallic system that forms such microstructure containing the quasicrystalline, Al7Cu2Fe and aluminum phases by casting an appropriate composition followed by a thermal treatment. An Al85Cu6.75Fe3.375Cr4.875 (%at.) alloy was arc-melted, annealed and subsequently characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. We show that it is possible to fabricate Al-matrix composites reinforced with quasicrystals using conventional metallurgical processes. This opens new perspectives for application of quasicrystalline alloys and composites.

ALUMINOBAROTHERMIC SYNTHESIS OF HIGH-NITROGEN STEEL

High-nitrogen austenitic steels are promising materials, combining high strength, plasticity and corrosion resistance properties. However, to produce high-nitrogen steel by conventional metallurgical methods under high nitrogen pressure, powerful and complex metallurgical equipment is required. From energy-saving viewpoint, an alternative and simpler method for producing high-nitrogen steels can be aluminothermy (reduction of metal oxides by metallic aluminum) under nitrogen pressure. Thermodynamic modeling of aluminothermic reactions in a nitrogen atmosphere was carried out by the authors. Aluminothermy under nitrogen pressure was used to produce high-nitrogen nickel-free Cr – N and Cr – Mn – N stainless steels with a nitrogen content of about 1 %. Microstructure (X-ray diffraction, metallography and transmission electron microscopy techniques) and mechanical properties were examined. Thermodynamic analysis has shown that the aluminothermic reduction reactions do not go to the end. The most important parameter of the synthesis is the ratio of Al and oxygen in the charge, the correct choice of which provides a compromise between completeness of oxides reduction, content of aluminum and oxygen in steel (the degree of deoxidation), and its contamination with aluminum nitride. Cr – N steel ingots in the cast state had the structure of nitrogen perlite (ferrite-nitride mixture), and Cr – Mn – N steel – ferrite-austenite structure with attributes of austenite discontinuous decomposition with Cr2 N precipitations. Quenching resulted in complete austenization of both steels. The compliance of the austenite lattice parameter obtained from the diffractograms for quenched Cr – Mn – N steel with the parameter predicted from the known concentration dependence for Cr – Mn – N austenitic steels indicated that all alloying elements (including nitrogen) were dissolved in austenite during aging at quenching temperature and fixed in the solid solution by quenching. Study of the mechanical properties of quenched Cr – Mn – N steel has shown a combination of high strength and ductility. It is concluded that by the aluminothermic method a high-nitrogen steel can be obtained, which, by mechanical properties, is not inferior to industrial steel – analog manufacted by electroslag remelting under nitrogen pressure.

Distribution of platinum-group elements in pristine and near-surface oxidized Platreef ore and the variation along strike, northern Bushveld Complex, South Africa

The Platreef of the Bushveld Complex is currently the largest PGE open pit deposit. In order to investigate the behavior of PGE during weathering, three boreholes covering a sequence of oxidized and pristine Platreef ore from the Mogalakwena mine were studied. Further, sulfides and platinum-group minerals (PGM) at various locations along the strike of the Platreef, at Townlands, Tweefontein and Nonnenwerth were compared to those of the Mogalakwena mine (Overysel, Sandsloot). In the pristine ore, PGE generally occur as PGM, or in solid solution within sulfides. PGM are usually associated with sulfide and mainly comprise (Pt,Pd)-bismuthotellurides, cooperite-braggite, and sperrylite. Electron probe microanalysis (EPMA) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) indicate concentrations of Pd in pentlandite (up to 185 ppm), whereas pyrrhotite contains up to 15 ppm of Os, Ir, and Ru, and chalcopyrite is usually devoid of PGE. Two compositionally different groups of pyrite differing in Ni, Co, and Pt contents were identified. Sulfur isotope data indicate different degrees of assimilation from the country rocks. Near-surface, oxidized PGE ores have a large economic potential. However, attempts to extract the PGE have proven unfeasible due to low PGE recoveries (< 30%) achieved by conventional metallurgical methods. In the oxidized ores, rare relict PGM are present. EPMA and LA-ICP-MS measurements demonstrated that secondary iron oxides/hydroxides and secondary silicates contain erratically distributed concentrations of Rh, Pt, and Pd (up to several 100 ppm). The polymodal distribution of PGE in the weathered PGE ores explains the low recovery rates by conventional flotation processing.

Architectured duplex stainless steels micro-composite: Elaboration and microstructure characterization

In this work we propose a top-down strategy in which an austenitic stainless steel (type AISI 316L) and a ferritic stainless steel (type AISI 430LNb) are mechanically alloyed by Severe Plastic Deformation (SPD) to elaborate an architectured duplex stainless steel. This proposed strategy serves two main objectives: i) enhancing the properties by microstructure refinement down to sub-micron scale, and ii) elaborating a model material for understanding the behavior of Duplex Stainless Steel (DSS) obtained by the conventional metallurgical methods. The Accumulative Drawing and re-Bundling (ADB) technique has been successfully implemented for these specific materials, allowing to obtain multi-scale micro-composites of 316L/430LNb steels. The limits of this process in terms of microstructure refinement, have been identified as due to the complete regression of the micro-scale austenitic phase during annealing.

Tensile properties and drawability of thin bimetallic aluminum-scandium-zirconium / stainless steel foils and monometallic Al-Sc-Zr fabricated by magnetron sputtering

Al-Sc-Zr alloys are interesting for the production of high strength micro components by micro deep drawing. These alloys show a good hardenability due to the formation of nanometer-scale spheroidal Al3(Sc, Zr) precipitates, which are highly coherent with the aluminum matrix. However, the formation of these precipitates in Al-Sc-Zr foils fabricated by conventional metallurgical methods dramatically reduces their ductility and drawability. In this work, magnetron sputtering was used to produce Al-Sc-Zr foils and Al-Sc-Zr / stainless steel bimetallic foils which are nearly free of these precipitates. Tensile tests were carried out to measure and compare the mechanical properties of monometallic Al-Sc-Zr foils and bimetallic Al-Sc-Zr / stainless steel foils deposited with varying plasma target powers and containing different volume fractions (layer thickness) of Al-Sc-Zr. Micro deep drawing was used to determine the drawability of selected monometallic and bimetallic foils. The results show that the density of monometallic Al-Sc-Zr foils can be improved significantly by increasing the DC target power and by using the high power impulse magnetron sputtering (HiPIMS) technology, resulting in foils with higher ductility. Bimetallic foils achieved higher strength and ductility than monometallic Al-Sc-Zr foils. Their mechanical properties vary with the target power and the volume fraction (thickness) of Al-Sc-Zr. The limit drawing ratio of HiPIMS deposited monometallic foil was 1.7 or 1.8 depending on the side of the foil facing the die, whereas a limit drawing ratio of 1.9 was observed for bimetallic foils.

Thermodynamic Modeling of Ag-Ni System Combining Experiments and Molecular Dynamic Simulation

Ag-Ni is a simple and important system with immiscible liquids and (Ag,Ni) phases. Previously, this system has been thermodynamically modeled utilizing certain thermochemical and phase equilibria information based on conjecture. An attempt is made in this study to determine the missing information which are difficult to measure experimentally. The boundaries of the liquid miscibility gap at high temperatures are determined using a pyrometer. The temperature of the liquid ⇌ (Ag) + (Ni) eutectic reaction is measured using differential thermal analysis. Tie-lines of the Ag-Ni system at 1023 K and 1473 K are measured using a conventional metallurgical method. The enthalpy of mixing of the liquid at 1773 K and the (Ag,Ni) at 973 K is calculated by molecular dynamics simulation using a large-scale atomic/molecular massively parallel simulator. These results along with literature information are used to model the Gibbs energy of the liquid and (Ag,Ni) by a calculation of phase diagrams approach, and the Ag-Ni phase diagram is then calculated.

The microstructure, mechanical properties and corrosion resistance of 316 L stainless steel fabricated using laser engineered net shaping

The mechanical properties and corrosion resistance of 316L stainless steel fabricated using the Laser Engineered Net Shaping (LENS) technique have been studied. The crack-free, full density samples made using SS316L alloy powder and the LENS technique are characterized by an unusual distinct dual-phase microstructure. STEM analysis revealed a significant increase of Cr and Mo content and a decrease of Ni in the grain boundaries. Based on the Cr and Ni content (austenite stabilizing elements), the Schaeffler diagram and the EBSD results, the existence of intercellular delta ferrite on subgrain boundaries and austenite in the fine-grains are observed. The XRD patterns, in addition to the FCC austenite phase, revealed the second BCC ferrite phase. Moreover, the sigma (FeCr) phases are present in the analyzed 316L stainless steel. The occurrence of ferrite, which does not occur in regular stainless steel fabricated using conventional metallurgical methods, improves the mechanical and corrosion properties of the LENS-fabricated sample made using 316L stainless steel powder. The obtained results prove that the microstructure of the SS316L fabricated using LENS is heterogeneous; its impact on the mechanical properties is visible. The analyzed samples are characterized by anisotropic mechanical properties that are favorable. For both the perpendicular and parallel directions of tensile tests, samples had a ductile fracture with many dimples inside of the larger dimples. The corrosion potential of SS316L LENS and classically manufactured steel is similar. The SS316L fabricated using LENS is characterized by a relatively low value of corrosion current density, which translates into much smaller corrosion rates.

Forming a single layer of a composite powder based on the Ti-Nb system via selective laser melting (SLM)

Alloys based on the titanium-niobium system are widely used in implant production. It is conditional, first of all, on the low modulus of elasticity and bio-inert properties of an alloy. These alloys are especially important for tooth replacement and orthopedic surgery. At present alloys based on the titanium-niobium system are produced mainly using conventional metallurgical methods. The further subtractive manufacturing an end product results in a lot of wastes, increasing, therefore, its cost. The alternative of these processes is additive manufacturing. Selective laser melting is a technology, which makes it possible to synthesize products of metal powders and their blends. The point of this technology is laser melting a layer of a powdered material; then a sintered layer is coated with the next layer of powder etc. Complex products and working prototypes are made on the base of this technology. The authors of this paper address to the issue of applying selective laser melting in order to synthesize a binary alloy of a composite powder based on the titanium-niobium system. A set of 10x10 mm samples is made in various process conditions. The samples are made by an experimental selective laser synthesis machine «VARISKAF-100MB». The machine provides adjustment of the following process variables: laser emission power, scanning rate and pitch, temperature of powder pre-heating, thickness of the layer to be sprinkled, and diameter of laser spot focusing. All samples are made in the preliminary vacuumized shielding atmosphere of argon. The porosity and thickness of the sintered layer related to the laser emission power are shown at various scanning rates. It is revealed that scanning rate and laser emission power are adjustable process variables, having the greatest effect on forming the sintered layer.

Advances in microbial leaching processes for nickel extraction from lateritic minerals - A review

Lateritic nickel minerals constitute about 80% of nickel reserves in the world, but their contribution for nickel production is about 40%. The obstacles in extraction of nickel from lateritic minerals are attributed to their very complex mineralogy and low nickel content. Hence, the existing metallurgical techniques are not techno-economically feasible and environmentally sustainable for processing of such complex deposits. At this juncture, microbial mineral processing could be a benevolent approach for processing of lateritic minerals in favor of nickel extraction. The microbial mineral processing route offers many advantages over conventional metallurgical methods as the process is operated under ambient conditions and requires low energy input; thus these processes are relatively simple and environment friendly. Microbial processing of the lateritic deposits still needs improvement to make it industrially viable. Microorganisms play the pivotal role in mineral bio-processing as they catalyze the extraction of metals from minerals. So it is inevitable to explore the physiological and bio-molecular mechanisms involved in this microbe-mineral interaction. The present article offers comprehensive information about the advances in microbial processes for extraction of nickel from laterites.

Defect generation and analysis in mechanically alloyed stoichiometric Fe–Ni alloys

FeNi, with the chemically-ordered L10 tetragonal structure, is a promising material for next-generation rare-earth-free permanent magnets. Due to the extremely low atomic Fe and Ni mobility below the critical chemical order/disorder temperature of 320°C, no conventional metallurgical methods are able to induce its formation. Diffusion rates could be enhanced with the creation of excessive vacancies. High-energy mechanical alloying was employed to produce a nanocrystalline Fe–50at.%Ni alloy. The high energy mechanical milling is expected to change the defect characteristics that would be used to study the effect that mechanical alloying has on the defect concentrations. X-ray diffraction revealed that over the entirety of the milling period, the Fe and Ni powders formed an fcc solid solution. The Williamson–Hall equation and Scherrer equation revealed that reductions in grain sizes were caused during alloying. The initial increase in internal strain, and by extension dislocations, was followed by a decrease in strain with further alloying, which was due to the combination effect of creation of dislocation from mechanical deformation and annihilation of dislocations at increasing grain boundaries. Doppler broadening positron annihilation spectroscopy (DB-PAS) showed that the overall number of open-volume defects decreased with increased milling time. Finally, changes of relative permeability, for the mechanically alloyed FeNi phase, were explained by the pinning effect of dislocations.

Effect of composition and heat treatment on MnBi magnetic materials

The metallic compound MnBi is a promising rare-earth-free permanent magnet material, unique among all candidates for its high intrinsic coercivity (Hci) and its large positive temperature coefficient. The Hci of MnBi in thin-film or powder form can exceed 12 and 26kOe at 300 and 523K, respectively. Such a steep rise in Hci with increasing temperature is unique to MnBi. Consequently, MnBi is a highly sought-after hard phase for exchange coupling nanocomposite magnets. However, the reaction between Mn and Bi is peritectic, and hence Mn tends to precipitate out of the MnBi liquid during the solidification process. As result, when the alloy is prepared using conventional induction or arc-melting casting methods, additional Mn is required to compensate the precipitation of Mn. In addition to composition, post-casting annealing plays an important role in obtaining a high content of MnBi low-temperature phase (LTP) because the annealing encourages the Mn precipitates and the unreacted Bi to react, forming the desired LTP phase. Here we report a systematic study of the effect of composition and heat treatments on the phase content and magnetic properties of Mn–Bi alloys. In this study, 14 compositions were prepared using conventional metallurgical methods, and the compositions, crystal structures, phase content and magnetic properties of the resulting alloys were analyzed. The results show that the composition with 55at.% Mn exhibits both the highest LTP content (93wt.%) and magnetization (74emug−1 with 9T applied field at 300K).

Study of hydrogen storage of the TiFe alloy by neutron powderdiffraction

Metal hydrides are interesting materials from a fundamental as well as practical point of view. Hydrogen storage applications have been the main driving force of research on these materials but lately, uses such as thermal storage are considered. In this presentation, we will review the use of neutron diffraction for the development of new metal hydrides. A good candidate for hydrogen storage applications is the low cost intermetallic compound TiFe which operates near room temperature (RT) under mild pressure conditions. However, the biggest disadvantage of TiFe alloy synthesized by conventional metallurgical method is it poor activation characteristics [1]. The alloy reacts with hydrogen only after complicated activation procedure involving exposure to high temperature (~4000C) and high pressure for several days. In the '90, some researches showed that the change in the nanocristallinity can modify the sorption property of the TiFe[2]. Other research works found that palladium increase the contaminant resistance. However, addition of palladium is too expansive for practical applications [3]. Recently, we found that, when doping TiFe with Zr and Zr7Ni10, the activation could be easily done at room temperature. We present here a neutron diffraction study of these compounds that shows the structural difference between the activated compound and the one cycled under hydrogen.