Impurities In Alloys Research Articles

Investigating the Effect of Temperature on Sulfur Deportment in Nickel Laterite Calcination

The majority of the ferronickel production from nickel laterite ores is through the Rotary kiln- electric furnace (RK-EF) process. Calcination and partial reduction of the laterite ore is typically carried out in a rotary fuel fired furnace. Sulfur is one of the most deleterious impurities in nickel alloys and degrades the mechanical properties of the product. Considering the insubstantial concentration of sulfur in laterites, it is assumed that sulfur partially originates from added fuel and reductant in the calcination stage. Investigating the effects of the temperature in the calcination stage on the sulfur distribution can provide valuable information on controlling the level of sulfur in the calcine. In this study, the atmosphere resulted from coal combustion is simulated by purging a gas mixture of N2, CO, CO2, and SO2 to the electrical horizontal tube furnace. The effect of temperature (600, 700, 800, and 900 ⁰C) on the sulfur deportment was studied. Inductively coupled plasma optical emission spectrometry (ICP-OES), and X-ray diffraction tests were used to measure the sulfur content and identify the phase composition of the products. The dominant compound of the calcine that contains sulfur is identified as pyrrhotite. Raising temperature from 600 to 700 ⁰C, increases %S in the calcine from 0.29 to 0.34%; however, promoting the temperature above 700 ⁰C diminishes the sulfur deportation percentage because of decreasing the surface area of solids by recrystallization of magnesia silicate compounds and sintering of oxides.

Increasing secondary silumins quality in the condi-tions of prezent day production

Due to the lack of domestic production of primary aluminum in Ukraine, an actual problem is the development of technological processes for producing high-quality aluminum alloys using secondary raw materials. It is known that secondary aluminum raw materials are characterized by a high content of undesirable impurities, which makes it difficult to obtain alloys with the required level of technological and mechanical properties. Goal. The aim is development of a technology for the production of aluminum alloys from secondary raw materials that meet the requirements of modern standards and technical conditions. Methodology. Development of a complex technology, including the hereditary modification of liquid metal by a fine crystalline charge and impurity modification by modifier MK-1. Results. Complex modification provided a reduction in the size and shape parameter of intermetallic phases and silicon particles, which positively affected the mechanical properties of the alloys. Originality. It was established that complex modification made it possible to neutralize the negative effect of iron, which is the most harmful impurity in secondary alloys. It was established, that silumin AK7 with Fe content up to 1.84 % meets the requirements of the standard for mechanical properties. Practical value. The results of industrial tests showed that the developed technology of complex modification expands the possibilities of producing silumins of the required quality using cheap secondary raw materials.

(Invited) First-Principles Understanding of Deep-Level Defects and Impurities in GaN and Nitride Alloys

The presence of native defects or unwanted impurities can strongly affect semiconductor device performance. Such defects can give rise to deep levels in the band gap, acting as sources of non-radiative recombination, carrier trapping, and sub-band-gap luminescence. Although predicting the properties of deep defects in semiconductors has long been hampered by the band-gap problem of density functional theory (DFT), methodological developments now allow for quantitative predictions. Here we discuss how first-principles calculations have shed light on the role of deep-level defects and impurities in gallium nitride and related alloys.We begin by discussing computational methodologies for calculating the properties of native defects and discuss how to overcome the band-gap problem of DFT. In particular, we examine to what extent calculations performed with semilocal functionals (such as the generalized gradient approximation), combined with correction schemes, can produce accurate results. The properties of vacancy, interstitial, and antisite defects in GaN are discussed, as well as their interactions with impurities such as hydrogen and oxygen. We also discuss first-principles results in the context of experimental observations, and examine how native defects and their complexes impact the performance of nitride devices [1].We also explore how the properties of defects are affected by presence of alloying elements such as indium [2]. With explicit alloy calculations we monitor how defect levels depend on indium content and the distribution of In atoms. The relative shifts of the charge‐state transition levels of different defects are explained by the atomic character of the defect state. Such shifts depend on whether the defect state is composed of valence‐band or conduction‐band states of the host material, or whether it acts as an atomic‐like impurity. Various possible atomic configurations of In and Ga cations in InGaN alloys of given compositions lead to a distribution of charge‐state transition levels. Defects on the nitrogen site lead to a larger spread of defect levels, while defects on the cation site lead to a smaller spread.Finally, we also investigate the properties of heavily C-doped GaN using both optical experiments and hybrid DFT calculations. Previous calculations had established that carbon acceptors (CN) give rise to a yellow luminescence (YL) band near 2.2 eV [3], along with a blue luminescence band near 2.9 eV. Photoluminescence measurements showed these optical transitions shifting as a function of carbon concentration, suggesting a change in the behavior of carbon. With hybrid DFT we calculated the electrical and optical behavior of carbon species containing multiple carbon impurities, which may arise in heavily doped material. We compared the behavior of these complexes to the isolated centers, and find that the CGa-CN complex is a good candidate to explain the shift in the YL peak. Furthermore, we determined the local vibrational modes of carbon impurity centers, and compared these results to recent experiments.[1] J. L. Lyons and C. G. Van de Walle, npj Computational Materials 3, 12 (2017).[2] D. Wickramaratne et al., phys. Stat. sol. (b) 2020 (https://doi.org/10.1002/pssb.201900534).[3] J. L. Lyons, A. Janotti, and C. G. Van de Walle, Phys. Rev. B 89, 035204 (2014).

Interaction between impurity elements (C, N and O) and hydrogen in hcp-Zr: a first-principles study

Zirconium (Zr) alloys as cladding materials are widely used in fission reactors. The service life of Zr-based materials cladding is seriously affected by the hydrogen (H) behaviors; while the impurities (C, N and O) in Zr alloys have a great influence on the hydrogen behaviors. In this work, we have investigated the impurity–hydrogen interactions in hexagonal-closed packed Zr (hcp-Zr) by a first-principles approach. It was found that H atom tends to occupy tetrahedral interstitial position in perfect Zr and occupy octahedral interstitial position in Zr with vacancy, while the impurities tend to occupy octahedral interstitial positions in Zr both with and without vacancy. The impurities can trap H atoms. Four possible paths were studied for the diffusion of H atom in hcp-Zr, and it is found that the diffusion barriers of H varied with the presence of impurities.

Effects of ferrosilicon alloy, Si content of steel, and slag basicity on compositions of inclusions during ladle furnace refining of Al-killed steel

To obtain solid Al2O3 or MgO·Al2O3 inclusions in ladle furnace (LF) refining process and achieve ultra-low total oxygen content in steel through subsequent Ruhrstahl Heraeus degassing, the effects of ferrosilicon alloy, Si content of steel, and slag basicity on the compositions of inclusions during LF refining were investigated in Al-killed steel. Al2O3 inclusions could be transformed into CaO–Al2O3–MgO–CaS inclusions after adding ferrosilicon alloy in the LF refining process as this alloy contains some CaSi alloy impurities. The addition of all ferrosilicon alloys required for the steel in the tapping process could eliminate the influence of Ca in ferrosilicon alloy on the compositions of inclusions. Si in liquid steel had a significant influence on the compositions of inclusions during LF refining when CaO–Al2O3–SiO2–MgO slag with high basicity of 7.0 was used. This was because [Ca] produced by the reaction of CaO and [Al] could be consumed more readily by SiO2 in Si-free steel than in Si-containing steel, which was confirmed by the difference of total calcium content between Si-free and Si-containing steels. As a result, Al2O3 and MgO·Al2O3 inclusions were retained in Si-free steel, whereas calcium aluminate inclusions were found in Si-containing steel. For CaO–Al2O3–SiO2–MgO slag with low basicity of 2.8, Al2O3 and MgO·Al2O3 inclusions were obtained after LF refining in Si-containing steel when all ferrosilicon alloys required for the steel were added in the tapping process. This was because the reaction of CaO and [Al] was weak, and residual [Ca] in the steel could be rapidly consumed by SiO2 in low-basicity slag owing to the low activity of CaO and high activity of SiO2, leading to a low total calcium content of 0.0003% in Si-containing steel.

Metal alloy nanowire joining induced by femtosecond laser heating: A hybrid atomistic-continuum interpretation

Nanojoining is a promising nano-fabrication technique with the capability of assembling functional nanodevices with dissimilar nanoscale and/or molecular components. However, significant challenges are encountered in experimental studies owing to the extremely small scale (10−9 m), high heating rates (1016 K s−1), and high temperature gradients (1011 K m−1) inherent in the nanojoining process. A hybrid atomistic-continuum model comprised of a molecular dynamics simulation (MD) and a two-temperature model (TTM) was used to study the mechanical and thermal characteristics of copper/copper-nickel alloy nanowires during a femtosecond laser nanojoining process. The results show that the laser nanojoining of two identical copper nanowires leads to the deterioration of thermal conductivity and thermal stress due to lattice structural variations. The nanojoining process induces an interface when applied to nanowires with different crystal orientations, which leads to phonon scattering at the joining interface, significantly reducing the thermal conductivity but providing for better mechanical properties. Additional alloy impurities strongly affect the thermal and mechanical properties during the laser nanojoining process. The thermal conductivity decreases significantly with increasing of nickel content while the mechanical properties are improved with respect to the Young's modulus and elastic limit. The utility of the hybrid MD-TTM simulations employed in the present work can approximate the laser nanojoining process in accordance with reasonable physical scenarios and accurate thermal and mechanical property predictions, which can also provide an atomic-level understanding of ultra-small, ultra-fast phenomena.

Deep‐Level Defects and Impurities in InGaN Alloys

In this study, density functional theory calculations with a hybrid functional are used to examine the charge‐state transition levels of native point defects and impurities in InGaN alloys, with the goal of identifying centers that play a role in defect‐assisted recombination. Explicit alloy calculations are used to monitor the dependence of defect levels on indium content and distribution of In atoms. The relative shift (or lack thereof) of the charge‐state transition levels of the different defects is explained by the atomic character of the defect state and whether it is derived from valence‐band or conduction‐band states of the host material or acts as an atomic‐like impurity. The various possible atomic configurations of In and Ga cations for a given composition of InGaN lead to a distribution of charge‐state transition levels. Defects on the nitrogen site lead to a larger spread in levels compared with defects on the cation site.

THERMODYNAMIC INTERACTION COEFFICIENTS IN LOW-CONCENTRATED LIQUID BINARY ALLOYS

The article considers basic expansion of thermodynamics and thermodynamic interaction coefficients of the first, second and third orders of low-concentrated binary alloys. The values of interaction coefficients of the first and second orders in 37 such systems were estimated according to experimental thermodynamic data on the concentration dependence of excess chemical potential of an impurity in liquid alloys of binary systems. Estimates were obtained by the numerical differentiation method. This method is based on Newton first interpolation formula. Calculation formulas for the corresponding estimates are given. A simple theory is proposed that relates the thermodynamic interaction coefficient of the second order with the first-order one in the liquid alloy of certain system. The theory is based on the lattice model of a solution and the principles of statistical mechanics. The FCC lattice is adopted as a model lattice. The model of pair interaction between metal atoms in the alloy was used. The radius of this interaction corresponds to radius of the nearest atomic shell. Using the proposed theory, thermodynamic interaction coefficients of the second-order for all 37 systems considered in this work, as well as the values of the third order interaction coefficients for 23 systems out of 37 mentioned above, were calculated. For these 23 systems, theoretical estimates of the second-order interaction coefficients are in agreement with experimental ones both by sign and by order of magnitude. This circumstance can be considered as evidence of applicability of the numerical differentiation method for estimation of thermodynamic interaction coefficients of the first and second orders in liquid binary alloys. The accuracy of estimating the values of the third derivative by numerical differentiation is insufficient. That makes it impossible to compare the calculated values of the interaction coefficients of the third order with the experimental ones, obtained by this method. It can be assumed that the theoretical calculations just give an idea of the magnitudes’ order of these coefficients.

ТЕПЛОФИЗИКА ЩЕЛОЧНЫХ ЖИДКИХ МЕТАЛЛОВ. ЧАСТЬ 2: ФИЗХИМИЯ, ТЕХНОЛОГИЯ И ИННОВАЦИОННЫЕ ПРИЛОЖЕНИЯ (РЕТРОСПЕКТИВНО-ПЕРСПЕКТИВНЫЙ ВЗГЛЯД)

The article presents the results of experimental and analytical studies carried out at the SSC RF - IPPE in the field of physical chemistry, mass transfer, technology and innovative applications of alkaline liquid metal coolants. An integrated approach to the study of coolants as a complex multi component heterogeneous system, the state of which is determined by the interaction of coolant - impurities - structural (technological) materials - protective gas, was substantiated. Thermodynamic analysis and experimental studies of the coolants properties and the kinetics of their interaction with air, water, hydrogen, structural and technological materials determined the sources of impurities and their intensity. It is shown that for temperature parameters of modern NPPs, the required concentration of impurities in sodium and sodium-potassium alloy, can be provided by purification the coolants by cold traps. The deeper purification of ciilants required for use in high-temperature installations of niobium, tungsten, vanadium, tantalum is achieved by getters (hot traps). This method can also be applied when limiting the weight and size characteristics, for example, for a space NPP. A fundamentally new combined purification system from impurities was proposed and substantiated for a high-temperature NPP for the production of hydrogen with a sodium coolant temperature of ~900 °C. As a result of the development of alkaline liquid metal coolants, liquid metal technology has been proposed in various technical applications: sodium at nuclear power plants with fast neutron reactors, sodium and sodium potassium in the metallurgical and chemical industries; sodium-potassium, cesium, lithium - in space installations; lithium - in fusion reactors - thermonuclear reactors.

Matrix-assisted photochemical vapor generation for determination of trace bismuth in Fe[sbnd]Ni based alloy samples by inductively coupled plasma mass spectrometry

As the impurities in alloy may affect its mechanical and physical properties, the determination of trace elements is important to ensure the quality of alloy. However, accurate determination of trace impurities in alloy samples is a big challenge due to their complicated matrix and low concentrations. In this work, matrix-assisted photochemical vapor generation (PVG) was developed for the determination of impurity in alloy samples by inductively coupled plasma mass spectrometry (ICPMS). Bismuth was selected as the target element, which is detrimental to the strength of alloy even at very low concentration. The transition ions existed in alloy worked as the “sensitizers” for the efficient PVG of bismuth, and only formic acid and acetic acid were required for the analysis of alloy samples after digestion. This largely reduced the risks of sample contamination and analyte loss in multiple sample pretreatment involved in conventional analytical methods. The PVG efficiency of bismuth was greatly enhanced, making the sensitive and simple determination of trace analytes in alloy samples feasible. The limit of detection (LOD, 3σ) for Bi was found to be 0.4 ng L−1 corresponding to 0.54 ng g−1 for analysis of 0.5 g of alloy sample. A relative standard deviation (RSD) of 1.1% was obtained from seven replicate measurements of 0.5 μg L−1 Bi3+ in sample matrix. The proposed method was successfully applied for the determination of Bi in two certified reference materials (FeNi based alloys GBW01621 and GBW01622).

Formation of Surface Layers on Fe70Si15B15 Alloy upon Heating in an Inert Atmosphere with Air Impurities

The composition of surface layers formed during high-temperature interaction between Fe70Si15B15 alloy and air impurities in an inert atmosphere is determined using equilibrium thermodynamic means. It is shown that at T = 1473 K, Fe3O4, FeSiO3, and B2O3 are at the interface between the alloy and the gas. Intermediate layers of internal oxidation contain FeSiO3, B2O3, SiO2, and BN. The iron-based region adjacent to the alloy contains silicides Fe3Si and FeSi; borides Fe2B and FeB; and nitride BN. At a relatively low concentration of air impurities in the inert gas, the destruction of a surface film consisting mainly of SiO2 is detected in the temperature range of 1600–1800 K as an anomaly on the damping decrement polytherm of free torsional vibrations of the crucible with the melt.

Determination of impurities in magnesium alloys by inductively coupled plasma mass spectrometry

Determination of impurities in magnesium alloys by inductively coupled plasma mass spectrometry

Determination of impurities in magnesium alloys by inductively coupled plasma mass spectrometry

Determination of impurities in magnesium alloys by inductively coupled plasma mass spectrometry

Dendritic structure formation of magnesium alloys for the manipulation of corrosion properties: Part 1 – microstructure

Abstract Besides impurities in magnesium alloys containing aluminum, the microstructure also plays a role in the corrosion properties of the alloy. By targeted manipulation of grain size, secondary dendrite arm spacings and segregation in terms of amount and position, the corrosion properties are expected to be improved. For this, experiments were carried out by casting alloys with 0, 3, 6, 9, and 12 % aluminum into a mold with different applied cooling rates. The samples were analyzed regarding microstructure and composition, and the grain size and secondary dendrite arm spacings, as a function of aluminum content and cooling rate, were modeled. The results show a decrease in grain size and secondary dendrite arm spacings with an increased cooling rate. The segregated β phase was predominantly situated at the grain boundaries as divorced eutectic and in lamellar form. The assumed influences on the corrosion properties will be examined in Part 2.

Simplified micrometric surface characterization of different implant surfaces available on the Brazilian market

Aim: This study characterized the implant surfaces available on the Brazilian market in terms of topography, chemical composition, and roughness. Methods: The following brands were selected according to their surfaces: Kopp (Ko), Signo Vinces (Sv), Neodent (Ne), Osseotite (Os) NanoTite (Nt), SIN (Si), Titanium Fix (Tf), conventional Straumann (Str), Active SLA (SLA). The morphological analysis and the alloy impurities and implant surface contaminants were analyzed by SEM-EDS. Surface roughness parameters and 3-D reconstructions were obtained by laser microscopy (20x). Two distinct areas were evaluated: i) the cervical portion (no surface treatment), and ii) the middle third (treated surface). Results: The characterization of the implant surfaces by SEM showed morphological differences between the thread geometries and surface morphology at 800x and 2000x magnification. The EDS elemental analysis showed a predominance of titanium (Ti) for all implants. The SLA surface showed only peaks of Ti while other implants brands showed traces of impurities and contaminants including Al, C, PR, F, Mg, Na, Ni, O, P, and SR. The implant surface roughness in the cervical portion did not exceed Ra 0.5–1.0 μm, constituting a minimally rough surface and obtaining acceptable standards for this region. Only Nt, Str, and SLA presented Ra above 2 μm in the middle third area showing a rough surface favorable for osseointegration. Conclusion: This study concluded that there is no established standard for morphology, chemical composition and implant surface roughness that allows a safe comparison between the available dental implant surfaces. National implant brands generally contain more impurities and surface contaminants than their international counterparts and were consequently more sensitive to the surface treatment techniques.

First principles investigation on the electronic structure and magnetism of dilute Fe impurity in [formula omitted][formula omitted] alloys

Employing the all electron augmented plane wave + local orbital (APW + lo) method based on the density function theory (DFT), we have performed ab initio calculations of electronic structure and magnetic properties of dilute Fe impurity in PdHx alloys (0⩽x⩽1.0). Here we present our results for the H induced changes in the density of state (DOS), local magnetic moment and the macroscopic magnetic properties. The calculations performed for PdHx without the Fe impurity reveal H concentration dependent lattice expansion and Pd-H bonding which results in large change in electronic band structure and the DOS at the Fermi energy. The nonmagnetic DOS calculated for Fe doped PdHx is analyzed within Stoner model and the condition for local moment formation is found to hold for all concentrations of H. With an increase of the H content in the Pd matrix, the local moment of Fe declines from 3.43μB at x = 0 to 2.72μB at x = 1.0. More significantly, the giant magnetic moment, associated with the Fe impurity in Pd, progressively decreases with H concentration as the positive spin polarization of Pd-4d band electrons diminish and crossover to negative sign for x > 0.75. We show that H induced changes in s-d and d-d hybridization plays a crucial role on the magnetic properties of Fe doped PdHx alloys. In particular, we suggest that the rapid decline of the giant moment in PdHx alloys results from the weakening of ferromagnetic d-d exchange interaction between Fe-3d and Pd-d band electrons caused by changes in density of states arising from H induced filling up of the Pd-4d band.

A UNIFIED TECHNIQUE OF DETERMINING MASS FRACTIONS OF THE IMPURITIES IN PLATINUM-RHODIUM ALLOYS BY ATOMIC EMISSION SPECTROSCOPY (AES)

A unified technique of AES determination of the impurities in platinum-rhodium alloys is presented. A distinctive feature of the technique is the possibility for analysis of the alloys of the grades not determined by GOSTs, which are widely used in industry. Almost no standard samples (their development is a long and expensive process) are available for such alloys. The technique provides determination of the impurities in platinum-rhodium alloys with rhodium contents of 0.1% – 35 % wt. without using an adequate standard sample for each particular alloy. The unified technique of AES determination of silver, gold, copper, iron, nickel, lead, palladium, antimony, tin, zinc and other in platinum-rhodium alloys (containing up to 36% of rhodium) is thus developed. Certified standard samples were used to plot the calibration curves. The accuracy indices of the developed unified technique are not inferior to those of the procedures developed earlier for platinum and platinum – rhodium alloys.

Climbing the Volcano of Electrocatalytic Activity while Avoiding Catalyst Corrosion: Ni3P, a Hydrogen Evolution Electrocatalyst Stable in Both Acid and Alkali

We report microcrystalline Ni3P as a noble-metal-free electrocatalyst for the H2 evolution reaction (HER) with high activity just below those of Ni5P4 and Pt, the two most efficient HER catalysts known. Ni3P has previously been dismissed for the HER, owing to its anticipated corrosion and its low activity when formed as an impurity in amorphous alloys. We observe higher activity of single-phase Ni3P crystallites than for other nickel phosphides (except Ni5P4) in acid, high corrosion tolerance in acid, and zero corrosion in alkali. We compare its electrocatalytic performance, corrosion stability, and intrinsic turnover rate to those of different transition-metal phosphides. Electrochemical studies reveal that poisoning of surface Ni sites does not block the HER, indicating P as the active site. Using density functional theory (DFT), we analyze the thermodynamic stability of Ni3P and compare it to experiments. DFT calculations predict that surface reconstruction of Ni3P (001) strongly favors P enrichment of...

Interaction of Ca, P trace elements and Sr modification in AlSi5Cu1Mg alloys

Thermal and microscopy analyses were carried out to investigate the interaction of Sr modification with Ca and P trace elements in high-purity and commercial-purity Al–5Si–1Cu–Mg alloys. The results show how the addition of Sr to commercial-purity alloy induces significant changes in the nucleation and growth temperatures of eutectic Si since pre-eutectic Al2Si2(CaSr) intermetallics tend to poison AlP particles, making them inactive as nucleation sites for eutectic Si. In contrast, the addition of Sr to high-purity alloy shows no apparent influence on the characteristic temperatures of Al–Si eutectic reaction, even though the microstructural investigations reveal flake-to-fibrous transition in the eutectic Si structure. This indicates that the eutectic growth temperature, commonly used to predict eutectic modification level, is not a key feature of Sr modification, but it is indirectly caused due to the presence of additional impurities in commercial-purity alloys which affect the nucleation kinetics of eutectic Si.

Size effects of nano-spaced basal stacking faults on the strength and deformation mechanisms of nanocrystalline pure hcp metals

The size effects of nano-spaced basal stacking faults (SFs) on the tensile strength and deformation mechanisms of nanocrystalline pure cobalt and magnesium have been investigated by a series of large-scale 2D columnar and 3D molecular dynamics simulations. Unlike the strengthening effect of basal SFs on Mg alloys, the nano-spaced basal SFs are observed to have no strengthening effect on the nanocrystalline pure cobalt and magnesium from MD simulations. These observations could be attributed to the following two reasons: (i) Lots of new basal SFs are formed before (for cobalt) or simultaneously with (for magnesium) the other deformation mechanisms (i.e. the formation of twins and the < c + a > edge dislocations) during the tensile deformation; (ii) In hcp alloys, the segregation of alloy elements and impurities at typical interfaces, such as SFs, can stablilise them for enhancing the interactions with dislocation and thus elevating the strength. Without such segregation in pure hcp metals, the < c + a > edge dislocations can cut through the basal SFs although the interactions between the < c + a > dislocations and the pre-existing SFs/newly formed SFs are observed. The nano-spaced basal SFs are also found to have no restriction effect on the formation of deformation twins.