Clustering Of Mn Research Articles

Effect of Ni content on 475°C embrittlement of directed energy deposited duplex stainless steel using a laser beam and wire feedstock

Duplex stainless steel (DSS), specifically the 2209 grade, is increasingly employed in additive manufacturing, particularly in processes like directed energy deposition using a laser beam with wire (DED-LB/w). However, a significant challenge arises when DSS faces brittleness within the temperature range of 250–500 °C. This study employs advanced characterization techniques, including atom probe tomography (APT) and transmission electron microscopy (TEM), to investigate DSS embrittlement after aging at 400 °C for up to 1000 h. The hardness analysis revealed that the higher Ni content in DED-LB/w-fabricated DSS cylinder promotes the age hardening compared to 2205 wrought DSS plate. Furthermore, APT and TEM demonstrated that, alongside the decomposition of ferrite into Fe-rich (α) and Cr-rich (αʹ) phases, clustering of Ni, Mn, and Si atoms contributes to the embrittlement. Although the Ni-Mn-Si-rich clusters could suggest nucleation of G-phase, the G-phase crystal structure was not observed by TEM. This might be attributed to the short aging time or limitations in the characterization technique. This work underscores the impact of characterization techniques on the measurement of spinodal decomposition, with APT providing capability of detecting nanometer sized clusters. By elucidating the complexities of 475 °C-embrittlement in DED-LB/w DSS, this study offers valuable insights for industrial applications and a deeper understanding of age hardening in duplex DSSs under specific manufacturing conditions.

On the Analysis of Clustering in an Irradiated Low Alloy Reactor Pressure Vessel Steel Weld.

Radiation induced clustering affects the mechanical properties, that is the ductile to brittle transition temperature (DBTT), of reactor pressure vessel (RPV) steel of nuclear power plants. The combination of low Cu and high Ni used in some RPV welds is known to further enhance the DBTT shift during long time operation. In this study, RPV weld samples containing 0.04 at% Cu and 1.6 at% Ni were irradiated to 2.0 and 6.4×1023 n/m2 in the Halden test reactor. Atom probe tomography (APT) was applied to study clustering of Ni, Mn, Si, and Cu. As the clusters are in the nanometer-range, APT is a very suitable technique for this type of study. From APT analyses information about size distribution, number density, and composition of the clusters can be obtained. However, the quantification of these attributes is not trivial. The maximum separation method (MSM) has been used to characterize the clusters and a detailed study about the influence of the choice of MSM cluster parameters, primarily on the cluster number density, has been undertaken.

Influence of interstitial Mn on local structure and magnetism inMn1+δSb

We report x-ray total scattering and pair distribution function (PDF) studies of the structural relaxation around interstitial manganese (Mn$_i$) in ferromagnetic Mn$_{1+\delta}$Sb ($0.03 \le \delta \le 0.23$) alloys, guided by density functional theory (DFT). Refinements to the experimental PDF using a crystallographically constrained structural model indicate an expansion in the equatorial plane of the Mn$_i$Sb$_5$ trigonal bipyramidal site, which introduces significant positional disorder in addition to the nominally-random occupation of interstitial voids. Observation of a weak diffuse signal near the symmetry-forbidden (001) reflection position is indicative of correlated disorder from the clustering of Mn$_i$. Density functional relaxation of supercells approximating the $\delta = 0.08$, $0.15,$ and $0.23$ compositions provides improved models that accurately describe the short-range structural distortions captured in the PDFs. Such structural relaxation increases the DFT calculated moment on Mn$_i$, which aligns antiparallel to the primary Mn moments, but leads to insubstantial changes in the average Mn and Sb moments and moments of Mn and Sb proximal to interstitials, thus providing a more accurate description of the observed bulk magnetic properties.

Benefitting from Dopant Loss and Ostwald Ripening in Mn Doping of II-VI Semiconductor Nanocrystals.

Annealing or growth at high temperatures for an extended period of time is considered detrimental for most synthetic strategies for high-quality Mn-doped II-VI semiconductor nanocrystals. It can lead to the broadening of size distribution and, more importantly, to the loss of dopants. Here, we examine how ripening can be beneficial to doping in a simple “heat-up” approach, where high dopant concentrations can be achieved. We discuss the interplay of the loss of dopants, Ostwald ripening, and the clustering of Mn near the surface during nanocrystal growth. Smaller nanocrystals in a reaction batch, on average, exhibit higher undesirable band-edge photoluminescence (PL) and lower desirable dopant PL. The optimization of dopant loss and the removal of such smaller undesirable nanocrystals through Ostwald ripening along with surface exchange/passivation to remove Mn clustering lead to high Mn PL quantum yields (45 to 55 %) for ZnSxSe1−x, ZnS, CdS, and CdSxSe1−x host nanocrystals. These results provide an improved understanding of the doping process in a simple and potentially scalable synthetic strategy for achieving “pure” and bright dopant emission.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1123-9) contains supplementary material, which is available to authorized users.

Assessment of toxic metals in groundwater and saliva in an arsenic affected area of West Bengal, India: A pilot scale study

Communities in many parts of the world are unintentionally exposed to arsenic (As) and other toxic metals through ingestion of local drinking water and foods. The concentrations of individual toxic metals often exceed their guidelines in drinking water but the health risks associated with such multiple-metal exposures have yet to receive much attention. This study examines the co-occurrence of toxic metals in groundwater samples collected from As-rich areas of Nadia district, West Bengal, India. Arsenic in groundwater (range: 12–1064µgL−1; mean ± S.D: 329±294µgL−1) was the most important contaminant with concentrations well above the WHO guideline of 10µgL−1. Another important toxic metal in the study area was manganese (Mn) with average concentration of 202±153µgL−1, range of 18–604µgL−1. The average concentrations (µgL−1) of other elements in groundwater were: Cr (5.6±5.9), Mo (3.5±2.1), Ni (8.3±8.7), Pb (2.9±1.3), Ba (119±43), Zn (56±40), Se (0.60±0.33), U (0.50±0.74). Saliva collected from the male participants of the area had mean concentrations of 6.3±7.0µg As L−1 (0.70–29µgL−1), 5.4±5.5µg Mn L−1 (0.69–22µgL−1), 2.6±3.1µg Ni L−1 (0.15–13µgL−1), 0.78±1.0µg Cr L−1 (<DL–5.9µgL−1), 0.94±0.90µg Pb L−1 (<DL–4.2µgL−1), 0.56±0.37µg Se L−1 (0.11–1.5µgL−1) and 194±54µg Zn L−1 (112–369µgL−1). The high concentrations of salivary As and Mn are believed to be indicative of intake from the groundwater. The clustering of salivary As and Mn in principal component analysis further indicated influence of the common exposure source. Zinc and selenium comprised a separate component presumably reflecting the local deficiencies in intakes of these essential elements from drinking water and foodstuff. Thus the study reveals that the concentration of other metals beside As must be monitored in drinking water before implementation of any policies to provide safe water to the affected communities.

Nanoscale Clustering and Magnetic Properties of Mn x Fe3−x O4 Particles Prepared from Natural Magnetite

A series of Mn x Fe3−x O4 (0 ≤ x ≤ 1) nanoparticles was successfully synthesized via a simple coprecipitation method. The starting material was a natural magnetite purified from local iron sand. Crystallite nanoparticles were produced by drying without using a high calcination temperature. Rietveld analysis of the X-ray diffractometry (XRD) data for all samples demonstrated that the Mn ions partially substituted the Fe ions in the spinel cubic structure of the Fe3O4 to form Mn x Fe3−x O4 phases. We applied two lognormal spherical and single mass fractal models to the analysis of the small-angle neutron scattering (SANS) data and revealed that the primary Mn x Fe3−x O4 particles ranged in size from 1.5 to 3.8 nm and formed three-dimensional clusters as secondary structures. The samples displayed superparamagnetic behavior, having the saturation magnetization which was most likely influenced by the competing contribution from Mn, the sizes of the primary particles, and their clusters. Further analysis revealed that the zero-field-cooled and field-cooled curves of the Mn x Fe3−x O4 nanoclusters exhibited a superparamagnetic phenomenon with the lowest magnetic blocking temperature approximately 145 K.

Synthesis of Mn-doped ZnO diluted magnetic semiconductors in the presence of ethyl acetoacetate under solvothermal conditions

Mn-doped ZnO samples with 5%, 20% and 40% nominal Mn concentrations were prepared in the presence of ethyl acetoacetate under solvothermal conditions. UV absorption spectroscopic analysis discloses that chemical modification was achieved by reaction of Zn or Mn precursor with ethyl acetoacetate in ethanol medium. XRD and HRTEM characterizations indicate that ZnMnO 3 impurity phase was formed in the 20% and 40% Mn-doped ZnO samples while no secondary phase was present in the 5% Mn-doped sample. The 5% Mn-doped sample consists of spheroid-like particles with size of 10–50 nm and has a real Mn concentration of 3.2%. Ferromagnetism and paramagnetism coexist in the 5% Mn-doped ZnO sample at room-temperature, which may arise from ferromagnetic exchange interaction as well as small secondary phases. The 20% and 40% Mn-doped samples show large paramagnetic effects at room temperature. Small paramagnetic secondary phases and clustering of Mn are probably responsible for this.

The effect of a material growth technique on ion-implanted Mn diffusion in GaAs

Diffusion of ion-implanted Mn in semi-insulating (SI) and liquid encapsulated Czochralski (LEC)-grown GaAs has been determined employing the modified radiotracer technique. The effect of the growth technique and conditions on Mn diffusion in low temperature molecular beam epitaxy (LT-MBE)-grown GaAs has also been studied. Two distinct diffusion components appear in ion-implanted Mn diffusion in GaAs: slow and fast. As the diffusivity for the SI material is slightly higher than that for the LT-grown material, it is observed that the diffusivity of the fast component retards with increasing initial concentrations of Ga sublattice defects. At the same time the Mn concentration in the tail part of the diffusion profile is higher in the LT-grown material. Ga vacancy-assisted clustering of Mn is proposed as a likely reason for the observed effects.

Characterisation of the early stages of solute clustering in 1Ni–1.3Mn welds containing Cu

Microstructural characterisation of neutron irradiated low alloy steels is important for developing mechanistic understanding of irradiation embrittlement. This work is focused on the early stages of irradiation-induced clustering in a low Cu (0.03 wt%), high Ni (∼1 wt%) weld. The weld was irradiated at a very high dose rate and then examined by atom probe (energy-compensated position-sensitive atom probe (ECOPoSAP) and local electrode atom probe (LEAP)) with supporting microstructural information obtained by small angle neutron scattering (SANS) and positron annihilation (PALA). It was demonstrated that extreme care must be taken optimising parameters used to characterise the extent of clustering. This is particularly important during the early stages of irradiation-damage when the clusters are poorly defined and significant compositional variations are present in what is traditionally described as matrix. Analysis of the irradiated materials showed increasing clustering of Cu, Mn, Ni and Si with dose. In the low Cu steel the results showed that initially the irradiation damage results in clustering of Mn, Ni and Si, but at very high doses, at very high dose rates, redistribution of Si is significantly more advanced than that for Mn and Ni.

Growth of gas phase nanoparticles with an accretion mechanism

Nano-droplet growth in a supersaturated vapor has been investigated in a gas aggregation source using laser-ionization time-of-flight mass spectrometry. During its propagation into an atomic vapor, a small particle grows by sticking atoms on its surface. This accretion process has been highlighted through the clustering of homogeneous particles Mn and heterogeneous Mn(M2O) and Mn(MOH)2 particles in a metallic vapor and a helium buffer gas (M = Na or K). A modelization is introduced so as to connect the measured cluster mass distributions to the pertinent physical parameters. The mass distribution width is particularly sensitive to the efficiency of the first steps in the growth sequence. We used this property to compare the ability of this vapor-condensed matter phase transition to occur around various homogeneous and heterogeneous nucleation seeds.

Local structural properties of (Mn,Fe)Nb2O6 from Mössbauer and X-ray absorption spectroscopy

The MnNb(2)O(6)-FeNb(2)O(6) solid solution has been investigated by Fe-K- and Mn-K-edge X-ray absorption (XANES and EXAFS), and Mossbauer spectroscopy. The first-shell M-O bond lengths deduced from EXAFS show a fairly small compositional dependence. A degree of static disorder, which increases with increasing manganese content, is clearly seen by the loss of correlation for the next-neighbour (NN) interaction. Hyperfine parameters from Mossbauer spectra are consistent with variations in the average environment, as recorded by X-ray data. Line broadening of the Mossbauer spectra provides evidence for next-neighbour effects and is consistent with there being no significant clustering of Fe or Mn within the samples. There appear to be differences in the way the columbite structure accommodates Fe(2+) and Mn(2+) ions. In ferrocolumbite all the Fe octahedra are close to being identical, while there are local structural heterogeneities at a longer length scale, presumably in ordering the precise topology of polyhedra immediately adjacent to the octahedron. By contrast, the manganocolumbite seems to have some diversity in the precise coordination at the MnO(6) octahedra, but a greater uniformity in how the adjacent polyhedra are configured around them.

Clustering of Mn in (Ga,Mn)As

Clustering of (Ga,Mn)As is studied with the supercell density-functional calculations using the projector augmented-wave method. We find large binding energies for a single substitutional Mn atom to existing dimers and trimers giving rise to trimer and tetramer formation. For larger clusters this binding energy drops. In all cases studied, ferromagnetic alignment is found to be energetically more favourable than the antiferromagnetic one.

Ga sublattice defects in (Ga,Mn)As: thermodynamical and kinetic trends.

We have used positron annihilation spectroscopy and infrared absorption measurements to study the Ga sublattice defects in epitaxial Ga(1-x)MnxAs with Mn content varying from 0% to 5%. We show that the Ga vacancy concentration decreases and As antisite concentration increases with increasing Mn content. This is in agreement with thermodynamical considerations for the electronic part of the formation energy of the Ga sublattice point defects. However, the absolute defect concentrations imply that they are determined rather by the growth kinetics than by the thermodynamical equilibrium. The As antisite concentrations in the samples are large enough to be important for compensation and magnetic properites. In addition, the Ga vacancies are likely to be involved in the diffusion and clustering of Mn at low annealing temperatures.

Combined atomic-scale modelling and experimental studies of nucleation in the solid state.

The process of solid-state nucleation in highly supersaturated solid solutions has been investigated on the atomic scale by a combination of three-dimensional atom probe analysis and atomistic modelling using dynamical Ising models. In binary Cu-Co alloys, a simple atom-exchange model with a single thermodynamic parameter derived from phase-diagram data was able to reproduce the atomic-scale microstructures observed in the atom probe, and also match the measured peak precipitate density. Modelling solute effects in complex copper-bearing steels required a more sophisticated model based on a vacancy-hopping mechanism and a larger number of thermodynamic and kinetic parameters derived from independent experimental data and theoretical calculations. The model gave an excellent match to the experimentally observed microstructures, and it reproduced features such as the clustering of Ni and Mn before the precipitation of Cu. The model also allowed time-dependent behaviour to be investigated, and it showed that solute clustering of Ni and Mn occurs during the cooling of the alloy. These clusters then act as heterogeneous nucleation sites for the formation of copper precipitates. Understanding such complex solute interaction effects through combined experiment and modelling is an essential step to controlling nucleation and hence the fine-scale microstructures in advanced engineering alloys.

Temperature induced clustering of Mn in Pb 1−xMn xTe

From electron-spin-resonance investigations we show that the isolated, substitutional Mn 2+ in the diluted magnetic semiconductor Pb 1−xMn xTe can be produced by ion implantation and subsequent annealing at temperatures lower than 340°C. Higher temperatures, which are employed in regular crystal growth, cause a clustering of Mn.

ESR and reflectance spectra of manganese in polycrystalline TiO 2 (rutile)

The ESR and reflectance spectra of polycrystalline TiO 2 containing manganese oxide (up to 8% atomic ratio) have been investigated. The results show that there is only a limited solubility of substitutional Mn 4+ in TiO 2. The manganese ions are isolated, since the solubility limit prevents clustering of Mn 4+ in TiO 2 matrix. Manganese in excess (with respect to the solubility value) is present as MnTiO 3. The electronic spectrum of Mn 4+ in the rutile lattice is discussed on the basis of the behavior of isoelectronic Cr 3+ in solid solution in TiO 2.

The influence of Mn 3+ ion clustering on electrical properties of manganese ferrites

The effect of the clustering of Mn 3+ ions in octahedral positions of the spinel lattice on the temperature dependences of the Seebeck voltage and the electrical conductivity was studied on three single crystals of manganese-rich manganese ferrites. It was found that the conception of Mn 3+ ion clusters may account for the deviations from the values predicted by the phenomenological theory of the hopping mechanism of electrical conductivity in these materials.