High-purity Metal Research Articles

Structural and Mössbauer studies of Mn0.5Co0.5Fe2O4 ferrites prepared by high energy ball milling and glycolthermal methods

We have investigated the properties of three Mn0.5Co0.5Fe2O4 ferrites synthesized directly from high purity metal oxides (Sample A) and from MnFe2O4 and CoFe2O4 ferrites (Sample B) by mechanical milling and by glycolthermal process (Sample C). XRD results show essentially single phase spinel structure. Sample C is the best sample followed by Sample B based on the presence of minor impurity peaks near 2θ ≈ 38° and 52°. More impurity peaks appear to grow after annealing above 400 °C. Samples A and B have been found to have similar Fe-57 Mössbauer spectra before and after annealing at 1050 °C. The spectrum for each sample changes significantly after annealing. This is attributed to changes of both grain sizes and impurity phases with thermal annealing. At least two sextets and two doublets are used to fit the Mössbauer spectra.

Magnetocaloric and magnetoelastic effects in (Tb0.45Dy0.55)1-xErxCo2 multicomponent compounds

The magnetocaloric effect (MCE) and magnetoelastic (ME) anomalies at the magnetic phase transitions in (Tb0.45Dy0.55)1-xErxCo2 compounds (0.1 ≤ x ≤ 0.3) are studied. For the compounds synthesized with the use of high-pure rare-earth metals, the measurements of MCE performed by a direct method and the study of magnetostriction and thermal expansion by a strain-gauge technique are carried out. Large MCE and a maximum of magnetostriction are observed in the vicinity of phase transitions in the studied compounds, which can be considered as potential materials for magnetic refrigeration. It is shown that the magnetoelastic energy contribution to the MCE for (Tb0.45Dy0.55)1-xErxCo2 cannot be neglected.

Hydrometallurgical process for extraction of metals from electronic waste-part I: material characterization and process option selection

Used electronic equipment became one of the fastest growing waste streams in the world. In the past two decades recycling of printed circuit boards (PCBs) has been based on pyrometallurgy, highly polluting recycling technology which causes a variety of environmental problems. The most of the contemporary research activities on recovery of base and precious metals from waste PCBs are focused on hydrometallurgical techniques as more exact, predictable and easily controlled. In this paper mechanically pretrated PCBs are leached with nitric acid. Pouring density, percentage of magnetic fraction, particle size distribution, metal content and leachability are determined using optical microscopy, atomic absorption spectrometry (AAS), X-ray fluorescent spectrometry (XRF) and volumetric analysis. Three hydrometallurgical process options for recycling of copper and precious metals from waste PCBs are proposed and optimized: the use of selective leachants for recovery of high purity metals (fluoroboric acid, ammonia-ammonium salt solution), conventional leachants (sulphuric acid, chloride, cyanide) and eco-friendly leachants (formic acid, potassium persulphate). Results presented in this paper showed that size reduction process should include cutting instead of hammer shredding for obtaining suitable shape and granulation and that for further testing usage of particle size -3 +0.1mm is recommended. Also, Fe magnetic phase content could be reduced before hydro treatment.

Study of the process for gold hydrochlorination in gold-containing magnetic fraction processing

Hydrochlorination provides high gold extraction into a solution and makes it possible to obtain high-purity metal (98–99 wt %) using simple technology for recovering it from a chloride solution. The quickness of the process leads to an increase in the productivity of the apparatus and, accordingly, to an improvement in the technical and economic indexes. Gold-containing magnetic fraction roasting improves the gold extraction parameters: the degree that is passed into the solution comes to 65% from a roasted fraction and 30% from a nonroasted one. The influence of NaCl and NaClO concentrations on the gold extraction has been established at various durations of the process. A flowsheet has been proposed for gold-containing magnetic-fraction processing by hydrochlorination.

The Aqueous Corrosion Behavior of Plutonium Metal and Plutonium-Gallium Alloys Exposed to Aqueous Nitrate and Chloride Solutions

Previous work in this laboratory examined the polarization behavior of high-purity plutonium metal exposed to various solutions, however, the polarization behavior of plutonium-gallium alloys has not been studied. The objective of this work is to establish the effect of gallium on the electrochemical behavior of plutonium metal exposed to nitric acid, sodium nitrate, and sodium chloride solutions. Results indicated that plutonium-gallium alloys were not passive in HNO3 solutions, unlike unalloyed plutonium. The dissolution of 0.5 and 1 wt % Ga alloys exposed to HNO3, and all materials exposed to NaCl, was found to be controlled by the presence of a corrosion product film. Relative oxide thickness measurements of unalloyed Pu exposed to HNO3 were obtained. Chloride was found to aggressively attack Pu and its alloys with increasing chloride concentration resulting in increased corrosion. Nitrate ions were shown to have a weak effect on the corrosion behavior of Pu, as compared to protons and chloride ions.

Unique challenges with recent gamma spectroscopy measurements at Los Alamos National Laboratory

A variety of unique radioactive samples have been measured recently at Los Alamos National Laboratory (LANL) using an electrically-cooled high-purity germanium detector. In each case the purpose of the measurements included one or more of the following objectives: (1) an accurate determination of the isotopic weight fractions of different plutonium or uranium materials; (2) an accurate determination of the isotopic quantity in the absence of relevant calibration standards; and (3) a qualitative determination of various sample impurities for additional forensic information. This paper discusses how simple modifications to the PC-FRAM parameter sets enabled a better determination of the isotopic content of the following samples: (1) high-purity plutonium metal, (2) plutonium-beryllium (PuBe) neutron sources, (3) neutron-irradiated natural uranium, and (4) re-processed HEU fuel with elevated 236U content. The isotopic quantity in a variety of samples was determined using a combination of the Spectral Nondestructive Assay Platform (SNAP™) routine from Eberline Services and the Monte Carlo Neutral Particle (MCNP) code developed at LANL. The non-traditional sources that were quantified with these gamma ray modeling codes included dozens of neutron-irradiated targets of natural uranium, several plutonium-beryllium neutron sources, and three high-purity samples of plutonium metal.

Determination of trace impurities in high-purity iron using salting-out of polyoxyethylene-type surfactants

To an iron sample solution was added polyoxyethylene-4-isononylphenoxy ether (PONPE, nonionic surfactant, average number of ethylene oxides 7.5) and the surfactant was aggregated by the addition of lithium chloride. The iron(III) matrix was collected into the condensed surfactant phase in >99.9% yields, leaving trace metals [ e.g., Ti(IV), Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Bi(III)] in the aqueous phase. After removing the surfactant phase by centrifugation, the remaining trace metals were concentrated onto an iminodiacetic acid-type chelating resin. The trace metals were desorbed with dilute nitric acid for the determination by inductively coupled plasma-mass spectrometry or graphite-furnace atomic absorption spectrometry. The proposed separation method allowed the analysis of high-purity iron metals for trace impurities at low μg g −1 to ng g −1 levels.

Surface Characterization of High Purity Metals of Silver and Nickel Electropolished with an Ionic Liquid

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Electromagnetic separation of nonferrous metals before a metallurgical conversion in a field of high-frequency current

This article examines the problem of finding new “dry” methods of recovering particles of nonferrous metals from nonmagnetic fractions of solid industrial and municipal wastes while saving water resources and reducing pollution. The methods also separate particles of different metals from one another based on their electrical conductivity, and they yield high-purity (97–99.5%) copper, aluminum, and lead concentrates for metallurgical conversion. The article discusses the possibilities of the electrodynamic separation of nonferrous metals in high-gradient fields of high-frequency current – high-frequency electromagnetic fields. Results are presented from experimental studies of the recovery of nonferrous metals from nonmagnetic fractions of crushed cable scrap and electrical scrap within the coarseness range –20+5 mm and the separation of these metals from one another on the basis of their electrical conductivity. The important social problems of protecting the environment and saving water and energy resources are solved by using this method: the production of high-quality secondary raw materials for metallurgical conversion makes it possible to recycle valuable commercial products – high-purity nonferrous metals – while also protecting the environment from these dangerous eco-toxins.

Parametrical optimization of laser surface alloyed NiTi shape memory alloy with Co and Nb by the Taguchi method

Different high-purity metal powders were successfully alloyed on to a nickel titanium (NiTi) shape memory alloy (SMA) with a 3 kW carbon dioxide (CO2) laser system. In order to produce an alloyed layer with complete penetration and acceptable composition profile, the Taguchi approach was used as a statistical technique for optimizing selected laser processing parameters. A systematic study of laser power, scanning velocity, and pre-paste powder thickness was conducted. The signal-to-noise ratios (S/N) for each control factor were calculated in order to assess the deviation from the average response. Analysis of variance (ANOVA) was carried out to understand the significance of process variables affecting the process effects. The Taguchi method was able to determine the laser process parameters for the laser surface alloying technique with high statistical accuracy and yield a laser surface alloying technique capable of achieving a desirable dilution ratio. Energy dispersive spectrometry consistently showed that the per cent by weight of Ni was reduced by 45 per cent as compared with untreated NiTi SMA when the Taguchi-determined laser processing parameters were employed, thus verifying the laser's processing parameters as optimum.

Al-Mo-Ni-W (Aluminum-Molybdenum-Nickel-Tungsten)

Starting with high purity metals, [1992Mas] arc-melted under Ar atm 10 quaternary alloys with 14 at.% Al and 7 at.% Mo, or 17 at.% Al and 7 at.% Mo, with W content varying from 2 to 7.5 at.%. To construct vertical sections, the alloys were annealed at a number of temperatures and quenched in water. The phase equilibria were studied with optical metallography, transmission electron microscopy, x-ray powder diffraction, and x-ray microspectral analysis. The vertical sections at 14Al-7Mo ad 17Al-7Mo (atomic percent) constructed by [1992Mas] are shown in Fig. 1 and 2, respectively. The nomenclature used in the figures are: c (fcc), c¢ (Ni3Al) and a (Mo,W). The liquidus is raised by the addition of W in both the sections, more at the lower Al content (Fig. 1). The liquidus reaches a maximum at 2-3 at.% W. The solubility of Mo or W in c¢ at 1200 C in Al-Mo-Ni or Al-Ni-W alloys is about 5 at.%. The analysis of the phase composition of c¢ in the quaternary alloys showed that the solubility of (Mo + W) remains at about 5 at.%, but the ratio of Mo/W in c¢ changes significantly with alloy composition [1992Mas].

Corrosion resistance of vanadium alloys clad by a ferritic corrosion-resistant steel in liquid-metal heat-transfer agents

The results of studying the corrosion resistances of steels of various classes and vanadium-based alloys in liquid-metal heat-transfer agents (lithium, sodium, lead) are analyzed. These structural materials are shown to have satisfactory corrosion resistance in high-purity liquid metals. However, a nitrogen impurity in lithium and an oxygen impurity in sodium and lead cause the degradation of the mechanical properties and the fracture of the vanadium alloys. The use of these alloys clad by a ferritic corrosion-resistant steel is shown to ensure high corrosion resistance of the fuel-element can materials in fast neutron reactors with sodium and lead heat-transfer agents.

High precision determination of silver isotope ratios in commercial products by MC-ICP-MS

Silver isotope ratios in several fortified commercial products were determined by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Mass discrimination and instrument drift were corrected for by a combination of internal normalization with Pd and standard-sample-standard bracketing, without assuming identical mass bias for Pd and Ag. The certified value of 1.07638 for 107Ag/109Ag in NIST SRM 978a was used for mass bias correction of 106Pd/108Pd in two adjacent solutions of SRM 978a. Their average was then used for mass bias correction to calculate the mass bias corrected Ag isotope ratio in the sample. An approximately 2.5-fold improvement in precision of determination of δ107/109Ag was obtained with the use of the proposed technique compared to data obtained solely with a standard-sample-standard bracketing approach. Internal and external precisions (2SD) of ±0.05‰ (n = 10) and ±0.04‰ (n = 19) for δ107/109Ag were obtained, suitable for the detection of varying Ag isotope abundances in commercial products fortified with Ag. Amongst the commercial products examined, no significant differences were detected in Ag isotopic compositions among NIST 978a standard, Ag high purity metal (Johnson Matthey Plc), Ag Nanopowder (Sigma-Aldrich) and Silversoft socks. Significant differences in Ag isotope ratios were found among NIST SRM 978a standard, a colloidal Ag dietary supplement, decanethiol functionalized Ag nanoparticles and X-static socks. The X-static socks and decanethiol functionalized Ag nanoparticles have negative δ107/109Ag values of −0.08 ± 0.05‰ and −0.15 ± 0.02‰ (2SD, n = 4), respectively, and the colloidal Ag dietary supplement has +0.83 ± 0.06‰ (2SD, n = 4). These observations suggest that such data may provide a useful tool for fingerprinting sources of Ag in the environment.

Understanding Friction and Wear Mechanisms of High-Purity Titanium against Steel in Liquid Nitrogen Temperature

Although the friction and wear properties of several metallic alloys in unlubricated conditions are widely investigated, such understanding for high-purity metals in cryogenic environment is rather limited. This article reports the tribological properties of high-purity α-titanium (α-Ti), prepared by cold rolling and recrystallization annealing, under liquid nitrogen (LN2) and room temperature (RT) environments against steel (bearing grade: SAE 52100) at varying loads (up to 15 N) and sliding speeds (0.6 to 4.19 m/s). It has been found that the steady-state coefficient of friction (COF) of titanium under LN2 environment (∼0.27 to 0.33) is lower than that at RT COF (∼0.33 to 0.58) irrespective of sliding speed. For cryogenic sliding conditions, the COF decreased steadily with sliding speed to a mean value of about 0.28 and no appreciable variation in COF is noticed for sliding speed of more than 1.5 m/s. The wear rate under both environment conditions was of the order of 10−3 mm3 N−1 m−1 irrespective of variation in operating parameters, but the RT wear rate was found to be higher compared to the LN2 case. Overall, the experimental results demonstrate improved tribological properties of high-purity titanium at LN2 temperature compared to the RT. Flow localization at tribological interfaces because of the large strain rate and subsequent damage accumulation at the titanium test piece are some of the attributes of the wear of Ti at LN2 temperature. In addition, the galling of titanium was also observed to occur under large contact stress and sliding speed conditions.

Small-angle X-ray scattering characterization of precipitates in Cu–Ti alloys

In order to understand the aging characteristics of Cu–Ti alloys, extended X-ray absorption fine structure (EXAFS) and small-angle X-ray scattering (SAXS) measurements were performed for characterizing changes in the local structure around titanium and the precipitate size in the Cu–Ti alloys by aging at approximately 720 K after solution treatment. Cu–1.3, 2.6, and 4.5 at.% Ti alloys were prepared using high-purity base metals. The amount of titanium dissolved in the copper matrix during aging was estimated from the electrical resistivity of the alloys. The aging characteristics showed that the precipitation rate of Cu–Ti intermetallic compounds in the copper matrix increased with increasing bulk titanium amount. The local structures of titanium in precipitates, presumably Cu 4Ti, are indistinguishable in the present alloys by EXAFS analysis because of the similarity of EXAFS functions for a Cu 4Ti intermetallic compound and a substitutional solid solution in copper. However, the EXAFS analysis revealed that the atomic distance of a Cu–Ti pair was significantly smaller than that estimated from the atomic radii of copper and titanium, implying that there is a strong atomic correlation in the pair. SAXS measurements were carried out for analyzing the growth behavior of precipitates in alloys during aging. The SAXS results revealed that a small amount of precipitates was formed in Cu–1.3 at.% Ti in the initial aging stage, whereas precipitates with approximately 2 nm radius were formed in Cu–2.6 and 4.5 at.% Ti alloys. By aging up to 2000 s, the precipitates in Cu–1.3, 2.6 and 4.5 at.% Ti alloys grew to approximately 3.5 nm in radius. These aging characteristics were discussed on the basis of the number density of precipitates calculated from the size of precipitates and the amount of super-saturated titanium in the copper matrix.

Al-C-Cr-Fe-Mo (Aluminum-Carbon-Chromium-Iron-Molybdenum)

Starting with high purity metals, [2008Kob] induction melted three ternary alloys Fe-26Al-5Cr, Fe-27Al-10Mo, and Fe-27Al-2C (at.%) to form the end members of the diffusion multiple. The assembly was first annealed at 1200 C for 24 h, where Cr, Mo, and C dissolve in the B2 (Fe3Al) matrix. The second anneal of a portion of the assembly was at 800 C for 300 h to allow the precipitation of carbides. The microstructures were examined by optical microscopy and high resolution scanning electron microscopy. The compositions of the phases coexisting at the interfaces were measured by energy dispersive spectroscopy, with structure identification by electron backscatter diffraction. The phases that occur in the composition range studied by [2008Kob] are Fe3Al (B2, CsCl-type cubic) as the matrix phase and the precipitating carbide phases as described below. Fe3AlC (denoted j) has the E21 or L¢12-type cubic structure, with C atoms in the octahedral voids of the AuCu3type cell. Cr7C3 has the D101-type orthorhombic structure. M6C is E93-type carbide, with M = Al, Cr, Fe, and Mo. It occurs at two different compositions denoted M6C (H) (high C andCr) andM6C (L) (lowC andCr). TheM2C-type carbide is not in equilibrium with the B2 matrix at 800 C. Partial isothermal tetrahedra were constructed by [2008Kob] at 800 C. At Cr-rich compositions, the fourphase equilibrium of M6C (H) + M6C (L) + Cr7C3 + B2 was identified, Fig. 1. The compositions (in atomic percent) listed by [2008Kob] for the four co-existing phases are— M6C(H): 14.5Fe13.6Al9.7Cr45Mo17.2C, M6C(L): 22.1Fe 16.4Al3.3Cr45Mo13.2C, Cr7C3: 16.3Fe1.0Al50.5Cr2.2Mo30C, and B2 matrix: 68.6Fe27.9Al2.6Cr0.9Mo. At Cr-poor compositions, Fe3AlC is stable and two four-phase equilibria were identified (Fig. 2): M6C (H) + Cr7C3 + Fe3AlC + B2 and M6C (H) + M6C (L) + Fe3AlC + B2.

Aqueous Corrosion Behavior of Plutonium Metal and Plutonium–Gallium Alloys Exposed to Aqueous Nitrate and Chloride Solutions

Previous work in this laboratory examined the polarization behavior of high-purity plutonium metal exposed to various solutions; however, the polarization behavior of plutonium–gallium alloys has not been studied. The objective of this work is to establish the effect of gallium on the electrochemical behavior of plutonium metal exposed to nitric acid, sodium nitrate, and sodium chloride solutions. Results indicated that plutonium–gallium alloys were not passive in solutions, unlike unalloyed plutonium. The dissolution of 0.5 and Ga alloys exposed to , and all materials exposed to NaCl, was found to be controlled by the presence of a corrosion product film. Relative oxide thickness measurements of unalloyed Pu exposed to were obtained. Chloride was found to aggressively attack Pu and its alloys with increasing chloride concentration resulting in increased corrosion. Nitrate ions were shown to have a weak effect on the corrosion behavior of Pu, as compared to protons and chloride ions.

Electronic Structure and Magnetism in Transition Metals Doped 8-Hydroxy-Quinoline Aluminum

We report the room-temperature ferromagnetism in transition metals (Co, Ni)-doped 8-hydroxy-quinoline aluminum (Alq3) by thermal coevaporation of high purity metal and Alq3 powders. For 5% Co-doped Alq3, a maximum magnetization of approximately 0.33 microB/Co at 10 K was obtained and ferromagnetic behavior was observed up to 300 K. The Co atoms interact chemically with O atoms and provide electrons to Alq3, forming new states acting as electron trap sites. From this, it is suggested that ferromagnetism may be associated with the strong chemical interaction of Co atoms and Alq3 molecules.

One-pot synthesis and characterization of metal phosphide-doped carbon xerogels

Transition metal phosphide (Fe 2P, Co 2P and Ni 12P 5)-doped carbon xerogels were synthesized by a one-pot pyrolysis of the sol–gel polymer of resorcinol and formaldehyde in the presence of metal nitrates and (NH 4) 2HPO 4. Various techniques, including: X-ray diffraction, N 2 adsorption–desorption, scanning electron microscopy, transmission electron microscopy and Mössbauer spectra, were employed for characterizing the physico-chemical properties of this kind of phosphide–carbon composites. Comparing with the corresponding metal-doped carbon xerogels, metal phosphides can exert a different influence on the graphitization temperature, textural properties and surface morphology of the resultant carbon xerogels. Investigations on the mechanism of iron phosphide formation indicated that CH 4, CO and C acted probably as reducing agents in the carbothermal reduction of metal phosphates. In addition, Mössbauer studies confirmed that this one-pot synthesis method was an excellent way for preparing high purity metal phosphide-doped carbon xerogels.

Hydrometallurgical recovery of copper and cobalt from reduction-roasted copper converter slag

The paper is concerned with a simple hydrometallurgical method for selective recovery of copper and cobalt from industrial copper converter slag. The following consecutive stages are proposed: roasting of the slag in reduction conditions to produce Cu–Co–Fe–Pb alloy, electrolytic dissolution of the alloy in an ammonia–ammonium chloride solution, ammoniacal leaching of the slime, selective copper and cobalt electrowinning. Cu27–Co6–Fe64–Pb1.5 alloy was a five-phase system and did not dissolve uniformly during electrolysis. This resulted in the separation of the metals, wherein iron remained in the slime, while copper and cobalt were components of slime, electrolyte and cathodic deposit. A mechanism of the alloy dissolution was developed. A series of secondary processes took place in the system: precipitation of iron compounds, copper cementation with cobalt and iron; adsorption of copper and cobalt ions on the iron precipitates. Final products were metals of high purity (99.9% Cu, 92% Co).