Effect Of Metal Impurities Research Articles

Effect of metal impurities on the adsorption energy of cesium and work function of the cesiated Mo (0 0 1) surface

Based on the DFT method, the effects of copper and tungsten impurities present in the negative ion source of neutral beams on the cesiated surface were studied, including their effects on the adsorption energy of cesium on the surface and the surface work function. The results indicate that copper impurities significantly increase the average adsorption energy of cesium, whereas tungsten has limited enhancement on the average adsorption energy of cesium and may even reduce it. The work function calculations show that, at cesium coverages below 4/16 θ, copper impurities cause a significant increase in the work function. However, at cesium coverages above 6/16 θ, high-coverage copper impurities lead to a further decrease in the work function, causing the cesium coverage corresponding to the lowest work function to shift towards higher cesium coverage. Under any tungsten impurity and cesium coverage, tungsten impurities can significantly increase the surface work function, with the maximum increase reaching 0.50 eV. The dipole moment density analysis shows that in most cases, impurities significantly reduce the dipole moment density of the cesiated surface, except when the coverage of cesium and copper impurities is above 6/16 θ. The charge transfer results show that the copper impurity layer has more positive charge compared to the tungsten impurity layer, which significantly affects the dipole moment density of the surface system. In addition, adsorbed atoms cause electrons in the molybdenum atomic layer to migrate to the surface, resulting in the molybdenum substrate having a pronounced negative dipole moment.

P-53 - Effect of metal impurities on the radiolabeling efficiency of DOTA with terbium-161 and lutetium-177: a comparative study

P-53 - Effect of metal impurities on the radiolabeling efficiency of DOTA with terbium-161 and lutetium-177: a comparative study

Effects of Metallic Impurities in Alkaline Electrolytes on Electro-Oxidation of Water and Alcohol Molecules

The presence of metallic impurities in the electrolyte greatly affects electrocatalytic performance. A systematic study on this topic can not only provide guidance for rigorous practices on electrochemical measurements, but also in-depth fundamental understanding on the mechanisms of the electrochemical reactions. Herein, nine types of metallic ions including Cu2+, Ni2+, Fe3+, Fe2+, Co2+, Mn2+, Zn2+, Ce3+ and Al3+ are intentionally introduced into the electrolytes with a controlled manner and their effects on electro-oxidation of water, 5-hydroxymethylfurfural (HMF) and glycerol are investigated in details. Among these metal ions, Co2+ has the most pronounced effects on H2O electro-oxidation while Cu2+ species displays superior activity toward HMF and glycerol electro-oxidation, but negligible effects on H2O electro-oxidation. Such a unique feature of Cu2+ can also be noted from electro-oxidation of other small molecules, such as ethylene glycol, ethanol and furfural. More importantly, the effects of metallic impurities are independent of the composition of the electrodes, only rely on the pH of the electrolytes. In-situ electrochemical Raman spectroscopy, control electrochemical experiments and X-ray photoelectron spectroscopy analyses reveal that the origin of impurity effects is attributed to the formation of hydroxides during the electrochemical measurements.

Metallic impurities induced corrosion of a Ni-26W-6Cr alloy in molten fluoride salts at 850 oC

The effect of metallic impurities on corrosion of a Ni-26W-6Cr alloy in molten FLiNaK salts at 850 °C was investigated. Results show that the Ni-26W-6Cr alloy exhibits the same excellent compatibility with fluoride salts as Hastelloy N alloy. Fe impurities in molten salts accelerate the diffusion of Cr in the alloy, which determines the corrosion degree of the alloy. Unexpected depletion of W from the alloy was observed, which mostly results from the presence of Mo impurity in the salts. Mo impurity should be limited because of the significant effect of W on the neutron spectra of reactors.

The Effect of Metal Impurities on the All-Vanadium Redox Flow Battery Performance

Vanadium redox flow batteries (VRFB) are a rapidly emerging technology for grid scale energy storage and the integration of the renewable energy generation. However, the cost of the electrolyte is a major barrier for implementation of VRFBs [1, 2]. The quality of the electrolyte has a significant impact on the cell performance and cost. The presence of impurities even with low concentrations in the vanadium electrolyte solution can alter the stability of the electrolyte and influence cell performance, energy density, operating temperature range, electrochemical kinetics and production costs [1-4]. Because a universal standard for the electrolyte specifications has not been defined in the market, a high purity electrolyte is always favored by researchers and customers to avoid potential detrimental impacts of impurities on the system performance. High purity greatly contributes to the high cost of electrolyte for VRFBs. Thus, understanding the impact of the impurities present in electrolyte on the performance of VRFBs is vital for commercialization of VRFBs [5]. This paper aims to conduct a systematic study on the effect of iron, aluminum and manganese ions (Mn2+, Fe2+ and Al3+) on the performance of VRFBs.A three-electrode system was utilized to conduct cyclic voltammetry (CV) experiments. Carbon paper (thermally treated at temperature of 500o C for 1 h in an air atmosphere), a platinum wire, and a saturated calomel electrode (SCE), were used as the working, counter and reference electrodes, respectively. The battery performance was evaluated in a flow cell using a ‘zero-gap’ cell design with an electrode area of 5 cm2. The electrolytic solution (1 M VOSO4 solution in 3 M H2SO4) was circulated through the cell. Thermally treated carbon papers were used as cathode and anode electrodes. For charge-discharge experiments, constant current density (10, 20, 30, 40 and 60 mAcm−2) was applied with 1.65 and 0.8 V as upper and lower voltage limits. The effects of each impurity were studied at five different concentrations (0.02, 0.04, 0.06, 0.08 & 0.1 M) through CV and charge-discharge experiments.The CV results shown in Figure 1 indicate that side reactions of gas evolution from water electrolysis will increase as the concentrations of the metal impurities increase. Comparison of the effect of three transition metal ions (Mn2+, Fe2+ and Al3+) showed that the highest peak separation was obtained in the presence of Fe2+. The peak separations for Mn2+and Al3+ were almost the same. Figure 2 shows the battery performance obtained in the zero-gap cell for a range of current densities versus cycle number, for a pure electrolyte and in the presence of aluminum and iron. The coulombic efficiency improved as the current density increased. Generally, the presence of impurities affected the coulombic efficiency and could result in side reactions and capacity fading, which will have a negative effect on the battery performance. The voltage and energy efficiencies obtained for a range of current densities are shown in Figures 2 (b) and (c), respectively. Similar to the coulombic efficiency results, the highest voltage efficiency was observed with the pure electrolyte. Based on the cyclic voltammetry results, the kinetics of the vanadium reaction falls, and the peak separation increased with increasing concentration of the contaminant metal ions Al3+ and Fe2+. Thus, the voltage efficiency decreased in the presence of these metal ions in the electrolyte. The energy efficiencies have the same trend and illustrates that the contaminant metal ions are competitive with vanadium ions for adsorption on the electrode surface and thus affect the vanadium redox reaction kinetics [6]. The side reactions caused by the metal ions have a negative influence on the performance of VRFBs.[1] A. Parasuraman, T.M. Lim, Ch, Menictas, M. Skyllas-Kazacos, A review of electrolyte additives and impurities in vanadium redox flow batteries, Electrochimica Acta, 27-40, 2013.[2] Cao, L., Skyllas-Kazacos, M., Menictas, Ch., Noack, A review of electrolyte additives and impurities in vanadium redox flow batteries, Energy Chemistry, pp.1269-1291, 2018.[3] A.K. Singh., N. Yasri., K. Karan, E.P. L. Roberts, Electrocatalytic Activity of Functionalized Carbon Paper Electrodes, ACS Appl. Energy Mater. 2019, 2324−2336.[4] John, J. St., Imergy uses recycled vanadium to cut materials costs for flow batteries, Greentech media, 2014.[5] J.H. Park, J.J. Park, H.J Lee, B.S. Min, J.H. Yang, Influence of Metal Impurities or Additives in the Electrolyte of a Vanadium Redox Flow Battery, The Electrochemical Society, page 1263-1268, 2018.[6] Ding, M., Liu, T., Zhang, Y., Cai, Z., Yang, Y., Yuan, Y., Effect of Fe(III) on positive electrolyte for vanadium redox flow battery, R. SOC. open sci. 181309, 2019. Figure 1

A coupled model of electromagnetic and heat on nanosecond-laser ablation of impurity-containing aluminum alloy.

In the emerging field of laser-driven inertial confinement fusion, Joule heating generated via electromagnetic heating of the metal frame is a critical issue. However, there are few reported models explaining thermal damage to the aluminum alloy. The aim of this study was to build a coupled model for electromagnetic radiation and heat conversion of an ultrashort laser pulse on an aluminum alloy based on Ohm's law. Additionally, the application SiO2 films on aluminum alloy to improve the laser-induced damage threshold (LIDT) were simulated, and the effects of metal impurities in the aluminum alloy were analyzed. A model examining the relation between electromagnetic radiation and heat for a nanosecond laser irradiating an aluminum alloy was developed using a coupled model equation. The results obtained using the finite difference time domain (FDTD) algorithm can provide a theoretical basis for future improvement of the aluminum alloy LIDT.

Highly sensitive amperometric detection of drugs and antioxidants on non-functionalized multi-walled carbon nanotubes: Effect of metallic impurities?

This work demonstrates that the electrochemistry of different molecules of pharmaceutical interest, including omeprazole, ciprofloxacin, dopamine, catechol, hydroquinone, and the antioxidants tert-butylhydroquine, gallic acid, propyl gallate, and pyrogallol, is affected by the functionalization of multi-walled carbon nanotubes (MWCNTs). Voltammetric and amperometric measurements confirmed the improved analytical characteristics of the GCE modified with non-functionalized (NF) MWCNTs (as-received) in comparison with functionalized MWCNTs (F-MWCNTs). Increase in voltammetric responses (up to 10-fold), higher slope values for the amperometric detection of the analytes (up to 7-fold) and, for some molecules, widening of the linear working range, were verified. Electrochemical impedance spectroscopy measurements also revealed higher electrochemical activity of non-functionalized MWCNTs. The presence of metallic impurities on NF-MWCNTs, removed by functionalization with HNO3/H2SO4, may contribute the improved performance of NF-MWCNT-modified electrodes; however, decrease in electroactive area of F-MWCNTs has to be considered. Although acid functionalization introduced oxygenated groups on the MWCNT structure, the presence of metallic impurities (Fe and Co) and higher electroactive area of NF-MWCNTs play major role on the increase in sensitivity of the electrochemical sensors. As a conclusion, we propose the use of pristine MWCNTs to produce more sensitive amperometric sensors.

Effect of metal impurities on the oxidation of various carbon forms in products of detonation diamond synthesis

The optimal catalyst for a selective oxidation of the nondiamond component of a diamond detonation synthesis product has been determined. The phase composition and oxidation resistance of diamond nanopowders recovered by different methods have been studied. It has been shown the existence of residual nondiamond carbon in diamond powders recovered by a gas-phase oxidation in the presence of copper (II) chloride (CuCl2) and their higher oxidation resistance than of recovered by a mixture of chromium anhydride with the sulphate acid.

Simulations of the Eutectic Transformations in the Platinum–Carbon System

In this paper, we present the simulation of the eutectic phase transitions in the Pt–C system, in terms of both freezing and melting, using the multi-phase-field model. The experimentally obtained heat-extraction and -injection rates associated with the induction of freezing and melting are converted into the corresponding rates for microstructure-scale simulations. In spite of the extreme differences in the volume fractions of the FCC–Pt-rich phase on the one hand and graphite (C) on the other, satisfactory results for the kinetics of solidification and melting have been obtained, involving reasonable offsets in temperature, inducing freezing and melting, with respect to the equilibrium eutectic temperature. For freezing in the simulations, the needle/rod-like morphology, as experimentally observed, was reproduced for different heat extraction rates. The seemingly anomalous peak characterizing the simulated freezing curves is ascribed to the speed up of the solidification process due to the curvature effect. Similarly, a peak is observed in the experimental freezing curves, also showing up more clearly with increasing freezing rates. Melting was simulated starting from a frozen structure produced by a freezing simulation. The simulations reproduce the experimental melting curves and, together with the simulated freezing curves, help to understand the phase transition of the Pt–C eutectic. Finally, the effect of metallic impurities was studied. As shown for Au, impurities affect the morphology of the eutectic structure, their impact increasing with the impurity content, i.e., they can act as modifiers of the structure, as earlier reported for irregular eutectics.

ChemInform Abstract: Carbocatalysis: The State of “Metal‐Free” Catalysis

AbstractReview: [latest advances in the application of chemically modified graphene as catalyst, with an emphasis on the possible effects of metallic impurities; 68 refs.

Carbocatalysis: the state of "metal-free" catalysis.

The rise in global demand for crucial chemical compounds has driven immense research in the fundamental science of catalysis. Graphene and its derivatives (chemically modified graphene, CMGs) have recently emerged as a new class of heterogeneous catalyst that promises economically viable and greener routes to these compounds. Although CMGs possess unique catalytic properties, the actual active sites are often points of discussion. Current minimal understanding on the possible effects of metallic impurities on the electrocatalytic performances of these CMGs calls forth the need to raise awareness on possible metallic impurities misrepresenting the actual chemical catalytic performances of the CMGs. This Minireview highlights the latest advances in the application of CMGs as catalysts, with an emphasis on the possible effects of metallic impurities on CMG catalysis.

The Nucleation of Sn in Undercooled Melts: The Effect of Metal Impurities

The dependence of the solidification temperature on the concentration x of impurity atoms, M, of Sn-M x alloys after cooling from the melt was measured separately for M = Co, Ni, Ag, and Cu. For a comparison, similar measurements were performed on SAC305-Ni x alloys. Large variations in undercooling were observed. It was found that the Ag atoms dissolved in the Sn-Ag melt significantly lowered undercooling, although the presence of Ag3Sn intermetallic compounds did not. While Cu6Sn5 intermetallic compounds in Sn-Cu melts did not significantly lower undercooling, the undercooling of a Sn-Cu melt in contact with a Cu interface was significantly reduced. The addition of Ni to Pb-free solder SAC305 caused a factor of two reduction in the undercooling, similar to that observed after the addition of Ni to high-purity Sn.

Effect of Metal Impurities on the Tensile Strength of Carbon Nanotubes: A Theoretical Study

Metal catalysts used in the synthesis of carbon nanotubes (CNTs) are one of the main impurities in CNT fibers. Using quantum mechanical computations, we show that these metal impurities have a large impact on the mechanical performance of CNTs and CNT fibers. One single Ni atom adsorption on the wall of a single-walled CNT (SWCNT) can decrease the tube’s critical strain about 40% by weakening the C–C bond on the wall of a tube. Further systematic calculations and theoretical analysis showed that the reduction of tube strength is nearly independent of the tube’s diameter. Thus, the tensile strength of the CNT fiber is expected to be greatly improved by washing away these metal impurities.

Crystal growth of organic energetic materials: pentaerythritol tetranitrate

Abstract The energy output performance and thermal stability of organic energetic materials have a strong dependence on the porosity, particle morphology, and micro-scale crystal structure. This paper reviews the growth habit of pure pentaerythritol tetranitrate (PETN) crystals and the effect of metal impurities on microcrystal morphology of PETN films. The pure crystal growth shows that PETN molecules diffuse on the surface and nucleate in a two-dimensional layer-by-layer fashion; the final structure is controlled by the deposition flux. Also, the effect of metal cation impurities has a strong impact on the thermal stability and crystal structure, and is dependent on the doping level.

Effects of metal impurities on the optical properties of polyethylene in the warm dense-matter regime

For the warm dense-matter regime, we have examined the effects on the equation of state, conductivity, and optical properties of the introduction of a metal impurity (Al) into a poorly conducting mixture $({\text{CH}}_{2})$ by means of quantum molecular-dynamics simulations employing temperature-dependent density-functional theory for temperatures between 1 and 4 eV and densities from ambient solid to a few times compressed. The properties such as dc conductivity and Rosseland mean opacity exhibit significant departures from the pure ${\text{CH}}_{2}$ results only for metal concentrations above about 50%. The system is representative of a wide range of environments that include planetary interiors, inertial confinement fusion capsules, and laser-produced plasmas.

The effects of metal impurities in poly[(2,5-bis(3-decylthiophen-2-yl)thieno[2,3-b]thiophene] on field-effect transistor properties

We have used particle induced X-ray emission analysis and particle induced gamma-ray emission analysis to determine the elemental impurity concentrations in poly[(2,5-bis(3-decylthiophen-2-yl)thieno[2,3-b]thiophene] samples that have undergone different washing and extraction procedures to remove impurities. Field-effect transistors (FETs) were fabricated from the materials and their electrical characteristics show no significant differences between the devices made from different material samples. Reducing the metal residue levels below the ones measured in the starting material (300 mg/kg Fe, 7 mg/kg Zn, 3000 mg/kg Pd and 12000 mg/kg Sn) does not improve the FET performance. This suggests that it is not necessary to completely remove metal residues in the polymer for FET applications.

Raman Investigation of the Effect of Metal Impurities at Gettering Sites on Phonon and Electron Related Properties of 4H-SiC n-n<sup>+</sup> Junctions

We report on the application of introducing gettering sites as an approach to control some phonons and charge carrier related properties in 4H-SiC epilayer. Helium implantation (at room temperature or 750°C) was first carried out, followed by a proper annealing and gold diffusion, in order to check the gettering efficiency. Raman measurements showed the presence of the desired defect, introduced by ion implantation at RT. The shift of the Fano interference allowed us to calculate the free carriers’ density in each sample. The lowest value was found for the sample implanted at RT. The gettering sites can act as majority carrier traps and reducers of recombination processes, which can be interesting for devices designed for the detection of radiations.

A first-principles study on the bond characteristics in carbon containing Mo, Ag, or Al impurity atoms

The atomic bond characteristics between carbon and metal atoms are investigated by the first-principles calculation using a tetrahedron bond model. Both the charge density distribution of the highest occupied molecular orbital and the partial density of states were examined to reveal the bond characteristics. The chemical bond characteristics between Mo and carbon are nonbonding, which would reduce the bond directionality. On the other hand, noble metals such as Ag show antibonding characteristic with carbon. The bond between Al and carbon has ionic characteristics and was found to prefer a two-dimensional configuration. The effect of metallic impurities in carbon materials could be explained from the difference in the atomic bond characteristics.

Effect of Metal Impurities on Shading and Thermal Conductivity of Aluminum Nitride

Because aluminum nitride (AlN) has a high thermal conductivity and a high electrical resistivity, it is used for substrates and packaging for high power or high density circuits. Silicon chips need to be protected from faults caused by exposure to ultra-violet rays. AlN packaging and substrates have to be shaded for UV protection. The characteristics of AlN are influenced by a number of factors. Specifically, metallic impurities affect the shading and thermal conductivity, and are particularly easily mixed with AlN as minerals or solutions during processing. It is very important to understand how metallic impurities influence the characteristics of AlN, and either refine processing to eliminate such effects, or add metal to achieve the desired industrial characteristics. Iron (Fe), silicon (Si), magnesium (Mg), and titanium (Ti) are metals that are easily mixed, so it is important to understand their influence. The metallic impurities Fe, Si, Mg, and Ti were added to raw powder AlN and uniformly distributed at a molecular level. The powder was sintered and tested for any effects on shading or reduction in thermal conductivity. Some Ti compounds were found at the grain boundaries, but these did not reduce the AlN thermal conductivity and provided efficient shading. In contrast, Si and Mg compounds were not found at the grain boundaries but formed solid solutions in the AlN grains, so they significantly reduced the AlN thermal conductivity and provided no shading. The effect of Fe was intermediate between that of Ti and Si and was characterized by its tendency to form solid metal ion solutions in the AlN grains.

THE EFFECT OF CERTAIN SURFACTANTS ON ZINC DISSOLUTION IN SULPHURIC ACID SOLUTIONS CONTAINING METAL IMPURITIES

The effect of surfactants nonylphenolpolyethylene glycol (D1), dinaphthylmetane-4,4′- disulphonic acid (D2) and polyethylene glycol with molecular weight 400 (D3) added alone or as a mixture (D1+D2+D3) on zinc dissolution rate in suphuric acid solutions containing metal impurities more positive than zinc (Cd2+, Cu2+, Ni2+, as well as Cd2++ Cu2+ and Cu2+ + Ni2+) was investigated at 50 °C and a high content of impurities (30 mg .dm−3 for each). Zinc dissolution carried out with and without surfactants indicated a different effect of D1, D2 and D3. In all experiments surfactants D1 and D3 decrease zinc dissolution rate, but the effect of D1 is substantially higher compared to D3. When only Cd2+ or Ni2+ are present surfactant D2 inhibits zinc dissolution but in the presence of Cu2+, Cd2++ Cu2+ or Cu2+ + Ni2+ its effect becomes opposite. In all experiments surfactant mixture D1+D2+D3 decreases zinc dissolution rate but its effect is lower compared to D1.The effect of metal impurities on zinc dissolution was determined by comparing the results with and without impurities. Metal impurities increase zinc dissolution rate, the lowest and the highest effect being obtained in the presence of Cd2+ and Ni2+ respectively. The effect of Cd2++ Cu2+ is slightly stronger compared to the effect of Cu2+. The influence of Cu2+ + Ni2+ is substantially stronger than the effect of Cu2+ only or Ni2+ only which indicates that the presence of Cu2+ in zinc sulphate solutions increases deposition of Ni2+ on zinc surface.The inhibition effect of D1+D2+D3 on zinc dissolution causes both a decrease of the negative effect of metal impurities on zinc current efficiency during zinc electrowinning stage and corrosion protection of cathodic zinc till the melting stage of zinc hydrometallurgy.On a étudié l’effet des agents de surface nonylphénolpolyéthylène glycol (D1), acide dinaphtylmétane-4,4′-bisulfonique (D2) et polyéthylène glycol avec poids moléculaire de 400 (D3), ajoutés seuls ou en un mélange (D1+D2+D3), sur la vitesse de dissolution du zinc dans des solutions d’acide sulfurique contenant des impuretés métalliques plus positives que le zinc (Cd2+, Cu2+, Ni2+, ainsi que Cd2+ + Cu2+ et Cu2+ + Ni2+), à 50 ????????C et avec un contenu élevé en impuretés (30 mg·dm−3 pour chacun). La dissolution du zinc, effectuée avec et sans agents de surface, indiquait un effet différent du D1, du D2 et du D3. Dans toutes les expériences, les agents de surface D1 et D3 diminuent la vitesse de dissolution du zinc, mais l’effet du D1 est substantiellement plus élevé que l’effet du D3. Quand seulement Cd2+ ou Ni2+ sont présents, l’agent de surface D2 inhibe la dissolution du zinc, mais en présence de Cu2+, de Cd2+ + Cu2+ ou de Cu2+ + Ni2+, il a un effet opposé. Dans toutes les expériences, le mélange des agents de surface D1+D2+D3 diminue la vitesse de dissolution du zinc, mais son effet est plus faible en comparaison avec le D1.Les impuretés métalliques augmentent la vitesse de dissolution du zinc, l’effet le plus faible et le plus élevé étant obtenus en présence de Cd2+ et de Ni2+ respectivement. L’effet de Cd2+ + Cu2+ est légèrement plus fort en comparaison avec l’effet de Cu2+. L’influence de Cu2+ + Ni2+ est substantiellement plus forte que l’effet du Cu2+ seul ou du Ni2+ seul, ce qui indique que la présence du Cu2+ dans les solutions de sulfate de zinc augmente la déposition du Ni2+ sur la surface du zinc.L’effet d’inhibition du D1+D2+D3 sur la dissolution du zinc cause à la fois une diminution de l’effet négatif des impuretés métalliques sur la performance du courant de zinc lors de l’étape d’extraction électrolytique et un effet de protection contre la corrosion du zinc cathodique jusqu’à l’étape de fonte d’hydrométallurgie du zinc.