Metal Purity Research Articles

Effect of residual excess carbon on the densification of ultra-fine HfC powder

The residual carbon content of ultra-fine hafnium carbide (HfC) powder was controlled by the optimization of the synthesis process, and the effect of residual carbon on the densification of HfC powder was analyzed. The amount of residual carbon in the HfC powder could be reduced by the de-agglomeration of HfO2 powder before the carbo-thermal reduction (CTR) process. The average particle size of HfO2 powder decreased from 230 to 130 nm after the de-agglomeration treatment. Ultra-fine (d50: 110 nm) and highly pure (metal basis purity: >99.9 % except for Zr) HfC powder was obtained after the CTR at 1600 °C for 1 h using the C/Hf mixing ratio of 3.3. In contrast, the C/Hf ratio increased to 3.6 without the de-agglomeration treatment, indicating that a large amount of excess carbon was required for the complete reduction of the agglomerated HfO2 particles. HfC ceramics with high relative density (>98 %) were obtained after spark plasma sintering at 2000 °C under 80 MPa pressure when using the HfC powder with low excess carbon content. In contrast, the densification did not complete at a higher temperature (2300 °C) and pressure (100 MPa) when the HfC powder contained a large amount of residual carbon. The results clearly indicated that residual carbon suppressed the densification of HfC powder in case the carbide powder had low oxygen content, and the residual carbon content could be controlled by the optimization of the synthesis process. The average grain size and Vickers hardness of the sintered specimen were 6.7(±0.7) μm and 19.6 GPa, respectively.

Reduction of oxides obtained from waste Ni-MH battery’s positive electrode using waste plastics to produce nickel based alloy

Generation of electronic waste (e-waste) is a direct result of the world’s dependence on electronics and daily use gadgets. Global consumption of e-waste was around 60 Mt in 2016 and is increasing each year in developed and developing countries. The waste accumulated not only affects the environment (soil and water) but also is detrimental to human health, thereby calling for sustainable recycling solutions. The current work details a novel approach to recover nickel alloy, using two waste streams: positive electrode materials of waste Ni-MH battery as Ni source in oxide form and e-waste plastics as a reductant. As an alternative to the use of conventional carbon, characterization studies, gas evolution kinetics, weight loss, fine black carbon generation were performed on e-waste plastics before carrying out the reduction of Nickel oxide at 1550 °C in an argon atmosphere in a high-temperature horizontal tube furnace. The selected temperature (1550 °C) favors the reduction without the addition of any additives and diminishes the formation of toxic compounds such as dioxins. FTIR gas spectra of the e-waste plastics confirmed the gradual decrease of functional groups, such as poly-methylene, phenol, and styrene as temperature increased from 400 °C to 850 °C. A mechanism of reduction starting from the cold zone of the furnace to hot zone was established which is observed to be predominantly gas based. High metal purity was confirmed by ICP-OES (Inductively coupled plasma optical emission spectroscopy) > 99% and XPS (X-ray photoelectron spectroscopy) 70–84 atomic %. XRD (X-ray powder diffraction) and EDS (Energy Dispersive X-ray spectroscopy) confirmed the formation of nickel alloy in the product phase and morphology was studied by SEM (scanning electron microscopy) which conveyed the uniformity of the product surface. This scientific study of using e-waste plastics as a reducing agent depicts a promising route to produce nickel alloy from the positive electrode of Ni-MH battery while reutilizing e-waste streams in a sustainable way.

Collaborative ductile rupture mechanisms of high-purity copper identified by in situ X-ray computed tomography

The competition between ductile rupture mechanisms in high-purity Cu and other metals is sensitive to the material composition and loading conditions, and subtle changes in the metal purity can lead to failure either by void coalescence or Orowan Alternating Slip (OAS). In situ X-ray computed tomography tensile tests on 99.999% purity Cu wires have revealed that the rupture process involves a sequence of damage events including shear localization; growth of micron-sized voids; and coalescence of microvoids into a central cavity prior to the catastrophic enlargement of the coalesced void via OAS. This analysis has shown that failure occurs in a collaborative rather than strictly competitive manner. In particular, strain localization along the shear band enhanced void nucleation and drove the primary coalescence event, and the size of the resulting cavity and consumption of voids ensured a transition to the OAS mechanism rather than continued void coalescence. Additionally, the tomograms identified examples of void coalescence and OAS growth of individual voids at all stages of the failure process, suggesting that the transition between the different mechanisms was sensitive to local damage features, and could be swayed by collaboration with other damage mechanisms. The competition between the different damage mechanisms is discussed in context of the material composition, the local damage history, and collaboration between the mechanisms.

Processing and Characterization of Charcoal Added Bulk MgB2 Superconductor

In this study, we focus on methods to further improve the flux pinning and critical current density (Jc) of disk shaped MgB2 bulk superconductors by a comparative study with locally obtained charcoal at optimized processing conditions. The doping of charcoal was varied at 0, 0.2, 0.4 and 0.6 wt%. Bulk MgB2 samples were produced by in-situ solid state reaction in Ar gas and ambient pressures at 775 °C, employing high purity of Mg metal and nano B powder mixed in a fixed ratio of Mg:B = 1:2 and optimal conditions. The phase has been investigated by X-ray diffractometer (XRD). The effects of the dopants on superconducting properties especially the field dependence of Jc have been determined by superconducting quantum interference device (SQUID) and critical temperature (Tc). Measurements of the magnetic susceptibility showed sharp superconducting transitions (ΔTc ∼ 1 K). Jc at self-field and 20 K was determined to be ~280 and 467 kA/cm2 for the 0 and 0.4 wt% charcoal added samples respectively. The structural and superconducting results were correlated with the addition of charcoal in the final product.

Effect of energy parameters of pulsed laser welding of Zr-1%Nb alloy on metal contamination with gases and properties of welds

Effect of pulsed laser welding parameters (pulse energy and duration, frequency, welding speed and, as a result, overlapping factor) on properties of E110 (Zr-1%Nb) alloy welds is presented. Butt welded joints of two identical plates with a thickness of 0.5 mm were investigated. EDS analysis of a surface layer of the welds was done, initial hydrogen concentration in the weld metal was measured and influence of absorbed gases (oxygen, nitrogen, carbon and hydrogen) on tensile strength, microhardness, hydrogen absorption rate and corrosion resistance of the welds was evaluated. The weld metal contained initial hydrogen concentration within the limits set by standards. However, mixing argon flows with atmospheric gases caused the weld metal contamination with oxygen, nitrogen and carbon. As a result, inclusions of complex chemical composition and surface branching microcracks were formed. They were stress raisers where weld failures occurred. Furthermore, it was the reason of increased hydrogen absorption rate and decreased corrosion resistance of the weld metal. The obtained results showed that absence of discoloration on surfaces of the welded joints did not guarantee metal purity and, as a consequence, required performance properties. Future research is required to determine the optimal overlapping factor; shielding gas compositions (Ar, He or their mixture) and flow rates; configuration and inclination angle of nozzles as well as distance from the nozzles to the weld zone.

Dependence of Inhibition Effects of Oxalate, Tungstate, Molybdate and Phosphate on Purity of Zinc Metal

The inhibition effects of oxalate, tungstate, molybdate and phosphate on corrosion of 99.99 %, 99.999 % zinc and 99.95 % molybdenum metals were investigated in NaCl solutions by potential-time, AC-impedance spectra and current-potential curves. The corrosion rates of metals are highly dependent on the purity of its. The inhibition effect of these anions on 99.999 % purity zinc is less than the effect on 99.99 % purity zinc. This implies that alloying elements are effective on inhibiting efficiencies of these anions. Inhibition effect of these anions decreases also with increasing NaCl concentration. None of the studied anions behaved as inhibitors on 99.999 % purity zinc in 1 M NaCl solution. The corrosion mechanism on the zinc metals is charge-transfer, but reaction on the molybdenium is diffusion controlled in the studied solutions. Keywords : Zinc, corrosion, oxalate, tungstate, molybdate, phosphate DOI : 10.7176/JSTR/5-4-12

Pengaruh pH dan Tegangan Listrik dalam Elektrolisis Limbah Padat Baja (Slag Eaf) Sebagai Upaya Mereduksi Kandungan Logam Fe pada Limbah Padat Industri Galvanis

<em>Galvanization is a metal coating process that is widely used in industry. The effects of this metal coating process are not entirely beneficial to society. The issue of pollution generated by the metal coating activity becomes very important. The objective of this research is to reduce Fe metal content from solid waste steel using electrolysis process with variation of pH of electrolyte solution and voltage. This research uses experimental method with test of metal content composition using X-Ray Flouresence, and Fe metal reduction using electrolysis process. This research activity used stainless steel plate as cathode and solid steel waste chunk as anode. Variations of pH of FeSO<sub>4</sub>.7H<sub>2</sub>O electrolyte solution used during electrolysis process are pH = 2, pH = 2.5, pH = 3, pH = 3.5 and pH = 4. Variation of electric voltage used is 3 volts, 6 volts, 9 volts and 12 volts. The result of purity level analysis of the initial Fe metal at anode was 84,48 %, while after electrolysis process there was an increase of metal purity attached to the cathode of 96,58 %. The result showed that the effect of pH variation of the electrolyte solution on the mass produced in the electrolysis process in the A<sub>1</sub>, A<sub>2</sub>, A<sub>3</sub>, A<sub>4</sub> and A<sub>5</sub> samples was 0,09; 0,07; 0,02; 0,02; and 0,02 g. The greater the concentration of H<sup>+</sup> of the electrolyte solution the more mass produced. In variable voltage of electricity on samples A<sub>11</sub>, A<sub>21</sub>, and A<sub>31</sub> mass produced that is equal to 0,14; 0,13; and 0,10 g. While the mass of A<sub>41</sub> sample did not increase in the cathode produced during the electrolysis process. The greater the voltage used in the electrolysis process the greater the mass produced.</em>

U-involved sphere-dispersed metallic glass matrix composites

The preparation of bulk U-based metallic glasses has fails for a long time due to weak glass forming ability and the low chemical purity of raw uranium metal. To make bulk glassy samples containing uranium, the compositing approach is adopted in this study. U-involved sphere-dispersed metallic glass matrix composites are successfully in-situ synthesized with suction-casting and tilt-casting by the phase separation alloying of uranium and Zr41.2Ti13.8Ni10.0Cu12.5Be22.5 (Vit-1). These composites are in a large composition range of 3–40 at.% U and with a flexible diameter dimension of not <15 mm. The dispersing phase is α-U solid solution while the matrix is Zr-based. A typical U30.03Zr28.83Ti9.66Ni7.00Cu8.75Be15.73 composite exhibits a compressive fracture strength of 1.7 GPa and high corrosion resistance in neutral and alkaline media. Its matrix phase shows higher thermostability and nominal glass forming ability than Vit-1 glass. This work suggests strong application potential of U-bearing glassy materials in nuclear-related fields, and also gives guidance for the development of more advanced uranium alloys.

Copper extraction by wet chemical method

Abstract In many countries large deposits of copper with no locally established copper based industries occur because known methods for extraction are prohibitively expensive and unaffordable. This study reports on an affordable and sustainable method for the extraction of copper. This was achieved through the use of a wet chemical method which makes use of hydrazones prepared in situ from chicken dung leached solution. The method involves the reduction of copper (II) ions leached from copper ore to zero valence using chlorine treated solution prepared from chicken droppings at a temperature range of 60–70 °C. The ore samples were pulverized to 250 micro millimetres and leached with hydrochloric acid to obtain leachate containing copper ions. The dissolved copper was reduced to copper metal and obtained by filtration. It was confirmed by XRFS analysis that, the metal purity was found to range between 60 and 80% depending on the ore used. In another experiment, chicken waste solution was used to extract copper from the ore. To the mixture, chlorine gas was then bubbledthrough a glass delivery tube to prepare the hydrazone in situ at a temperature range of 60–70 °C and a pure copper metal was obtained. The findings from this study have shown that there is great potential for the production of copper at low cost and this could be applied in both small-scale cottage industries and large industries using readily available resources such as chicken dung.

Amplification of impurity upon complex formation: how a 2% ligand impurity lowers the corresponding complex purity to 50%

Statistical incorporation of small amounts of ligand impurities has devastating consequences on the purity of metal–organic complexes derived from the respective ligands.

Green synthesis of silver nano particles from Atalantia monophylla (L) Correa leaf extract, their antimicrobial activity and sensing capability of H2O2

In the present study deals with the green synthesis of silver nano particles from methanolic leaf extracts of Atalantia monophylla. The synthesized nano-particles are characterized by UV–vis spectroscopy, PL, FTIR, XRD, SEM with EDAX and TEM. The nano-particles are indicated in absorption peak at 404 nm in the absorption spectrum. Further micro graphical analysis confirmed the average size was estimated about 35 nm and SEAD pattern authorized well crystalline materials. The FTIR studies help to confirm the functional group of synthesized silver nano particles. The XRD data shown the crystalline nature of nano particles and EDAX measurement indicates the purity of silver metal. The antimicrobial effect of silver nanoparticles was tested on pathogenic organisms using agar well diffusion method. Minimum inhibitory concentration (MIC) and Minimum bactericidal/fungicidal concentration (MBC/MFC) were also investigated in different concentrations of leaf extract. The results indicated that synthesized silver nano particle of A. monophylla leaf extract has the potential of antimicrobial activity against pathogenic microorganism. In addition, this is the first report on leaf synthesized silver nano particles of A. monophylla. The antimicrobial activity against pathogenic microorganisms and the ability to detect hydrogen peroxide using the silver nanoparticles were confirmed which would find applications in the development of new antimicrobial drugs and new biosensors to detect the presence of hydrogen peroxide in various samples respectively.

Impact of the Roughness of Alumina and Al2O3–C Substrates on the Adhesion Mechanisms in a Model System

To improve metal purity by reducing solid and liquid inclusions, intelligent filters with a functionalized surface are studied for an application in metal melt filtration. Besides special coatings that increase the attraction of inclusions at the filter surface or react with gases inside the melt, also the filter roughness might increase the filtration efficiency. In this study, we investigate the influence of roughness on adhesion forces for hydrophilic and hydrophobic filter surfaces in a water‐based model system with an atomic force microscope. In the case of hydrophilic filter substrates, adhesion forces decrease with an increase of roughness whereas on hydrophobic filter surfaces an inverse effect is observed. The primary cause for this is the formation of small cap‐shaped bubbles due to poor wetting. To investigate the stability of these bubbles on smooth as well as rough samples of filter material, imaging in contact mode with increasing applied force is performed. On rough surfaces, the bubbles remain stable even at 30–50 nN because of pinning effects.

Au Fixed Point Development at NRC

Two Au fixed points filled using metal of different nominal purities in carbon crucibles have been developed at the National Research Council Canada (NRC). The primary motivation behind this project was to provide the means for direct thermocouple calibrations at the Au freezing point (\(1064.18~^\circ \hbox {C}\)). Using a Au fixed point filled with the metal of maximum available purity [99.9997 % pure according to glow discharge mass spectroscopy (GDMS)], multiple freezing plateaus were measured in a commercial high-temperature furnace. Four Pt/Pd thermocouples constructed and calibrated in-house were used to measure the freezing plateaus. From the calibration at Sn, Zn, Al and Ag fixed points, the linear deviation function from the NIST-IMGC reference function (IEC 62460:2008 Standard) was determined and extrapolated to the freezing temperature of Au. For all the Pt/Pd thermocouples used in this study, the measured EMF values agree with the extrapolated values within expanded uncertainty, thus substantiating the use of 99.9997 % pure Au fixed point cell for thermocouple calibrations at NRC. Using the Au fixed point filled with metal of lower purity (99.99 % pure according to GDMS), the effect of impurities on the Au freezing temperature measured with Pt/Pd thermocouple was further investigated.

Synthesis and photoluminescent characteristics of Dy3+ doped Gd2O3 phosphors

Pure and dysprosium doped gadolinium oxide nanoparticles for three different concentrations (2, 5 and 10 mol.%) were synthesized by auto-combustion method using citric acid as fuel. The nanoparticles obtained were characterized using powder x-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), UV–vis–NIR spectroscopy and photoluminescence (PL) spectroscopy techniques. XRD pattern revealed the crystalline cubic phase with space group Ia3 (Space Group: 206) for both the pure and doped Gd2O3 nanoparticles. The metal oxide phase formation and purity of Gd2O3 nanoparticles were further confirmed from the FTIR spectra. Morphology of the pure Gd2O3 powder is loosely dispersed clusters of tiny particles with microscopic pores, whereas for the doped samples aggregates were broken to form small clusters. Optical absorption measurements were recorded in the UV–vis–NIR wavelength region and the optical band gap variations with dopant concentration were discussed. The PL spectra of pure and Dy3+ doped Gd2O3 nanoparticles have been studied and the effect of emitted light on the yellow-to-blue intensity ratio (Y/B) of Dy3+ emission was demonstrated.

A validation experiment on indium recovery by electrowinning of aqueous electrolytes: Optimization of electrolyte composition

Abstract A batch-type and lab-scale indium recovery method was developed via electrowinning (EW) to prove mass production-capability and economic recovery of indium from InCl3 crystals precipitated from the solvent extraction using a suitable phosphoric acid-based extractant. More precisely, the InCl3 crystals thus precipitated were further dissolved in three different aqueous electrolyte mixtures for subsequent electrowinning experiments: 0.05 M InCl3 – 0.7 M LiCl; 0.05M InCl3; 0.05 M InCl3 – 0.7 M NaCl. The effect of adding LiCl and NaCl supporting electrolytes to InCl3 on overall EW efficiency was thus comprehensibly investigated. Direct electroreduction of InCl3 using 0.05 M InCl3 aqueous electrolyte resulted in the highest indium metal purity of 99.996 % deposited on the copper cathode. Thus, metallic contents obtained from the validation experiments were further characterized using various analytical tools such as inductively coupled plasma/atomic emission spectroscopy (ICP/AES), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF).

Electroless Nickel Deposition: An Alternative for Graphene Contacting

We report the first investigation into the potential of electroless nickel deposition to form ohmic contacts on single layer graphene. To minimize the contact resistance on graphene, a statistical model was used to improve metal purity, surface roughness, and coverage of the deposited film by controlling the nickel bath parameters (pH and temperature). The metalized graphene layers were patterned using photolithography and contacts deposited at temperatures as low as 60 °C. The contact resistance was 215 ± 23 Ω over a contact area of 200 μm × 200 μm, which improved upon rapid annealing to 107 ± 9 Ω. This method shows promise toward low-cost and large-scale graphene integration into functional devices such as flexible sensors and printed electronics.

Effect of super-gravity field on metal–slag separation

The effects of super-gravity field on metal–slag separation at different gravity coefficients were investigated in this study. In a super-gravity field, the liquid metal concentrated along the direction of super-gravity, while the molten slag migrated and aggregated along the opposite direction thereafter separated from the metal. Moreover, a straight interface between the metal and slag appeared in the perpendicular direction to the super-gravity. Consequently, increasing the gravity coefficient could definitely increase the driving force of phase separation between metal and slag, and so enhance the removal of oxide and the purity of metal significantly.

High Purity Tungsten Nanostructures via Focused Electron Beam Induced Deposition with Carrier Gas Assisted Supersonic Jet Delivery of Organometallic Precursors

A substantially enhanced purity of tungsten nanostructures, with up to 95% of metal content relative to carbon contaminants with no postprocessing, is achieved by using a supersonic inert carrier gas jet in the continuum flow regime to deliver the organometallic precursor for focused electron beam induced deposition (FEBID). Through impact-enhanced desorption of residual organic ligands at the deposition site, high kinetic energy of the gas jet assists in completing the secondary electron induced dissociation of precursor molecules, resulting in both increased metal purity and enhanced deposit growth rate. The inert gas jet at low Knudsen numbers also serves as a carrier gas to increase precursor flux to the substrate. Operating in the continuum flow regime reduces jet spreading and allows the use of smaller diameter nozzles to increase localization of precursor delivery to the deposition site. This drastic increase in localized precursor flux to the substrate is shown to compensate for the diminished sti...

COMPARATIVE ASSESSMENT OF Al-Si ALLOY GASSING DEGREE WITH THE APPLICATION OF THE ‘FIRST BUBBLE’ AND ‘SOLIDIFICATION UNDER DECREASED PRESSURE’ METHODS

All aluminum alloys in a liquid state are characterised by easy oxidation and absorption of hydrogen from the surroundings (which are the main reasons for casting defects). The amount of hydrogen adsorbed by a liquid alloy depends mainly on temperature and melting time. The performed investigations were aimed at comparing two known methods of measuring a metal gassing degree; the first bubble method and sample solidification under decreased pressure. Liquid metal melting and holding processes were performed under different conditions that caused variability of its gassing degree, resulting in a variability of purity and quality of the liquid metal. The investigations were carried out with using the hypoeutectic aluminum-silica AK7 alloy.

Study on the oxidisation behaviour of particles during thermal spray process

Atomised metallic particles at high-temperature are oxidised easily in thermal spray process, resulting in the generation of defects such as low purity of sprayed metal and reduction in adhesive strength of deposited coating. In this investigation, argon and compressed air were employed as atomisation gas to spray 1Cr18Ni9Ti stainless steel wire by arc spraying. The result indicated that the best atomising effect of spraying particles can be achieved when argon atomising gas was employed. Their particle size were in the range of 20–40 μm, which were about half as large as those using compressed air as atomisation gas. Oxygen content of atomising particles were as follows: 16.66% using argon atomising gas, 25.34% using compressed air and 42.48% using oxygen atomising gas. The presence of Cr diffusion in the coating deposited using argon atomising gas led to a dense interface which determined the adhesive strength of 12.5 MPa.