One-dimensional migration of interstitial clusters in SUS316L and its model alloys under electron irradiation

The one-dimensional (1D) migration of interstitial clusters in austenitic stainless steel SUS316L and its model alloys, namely, Fe–18Cr–13Ni, Fe–18Cr–13Ni–0.012C, and Fe–18Cr–13Ni–1.7Mn (mass %), was examined using in situ observation by high-voltage electron microscopy. Such 1D migration was confirmed to occur along the ?110? direction at irregular intervals in all these alloys under 1250-kV electron irradiation at room temperature. The frequency of 1D migration was found proportional to electron beam intensity, and was about 1/10 that in high-purity iron under the same irradiation intensity. The distance of 1D migration in the four alloys was less than 10?nm, which was much shorter than that in high-purity iron. No clear difference in the frequency or distance of 1D migration was observed among the four alloys, suggesting that minor solute/impurity elements have no apparent effect on 1D migration in SUS316L.     

Magnetization and Mössbauer study of double layer perovskites La1.5Ca1.5Mn2 − x Fe x O7 prepared by sol–gel method

Magnetization and Mössbauer studies have been made for understanding magnetic behavior of three double perovskite systems La_1.5Ca_1.5Mn_2???x Fe _x O₇ corresponding to x = 0.05, 0.10 and 0.50. These have been prepared following sol–gel route. Substitution of Fe does not lead to any major change in the tetragonal cell but increased iron leads to greater distortion in octahedral site. The three samples undergo paramagnetic–ferromagnetic transition. Curie temperature (T _c) for the system with 0.05 Fe is ～150 K which is lower than (190 K) for the system without iron; with 0.50 Fe T _c goes below 50 K. Iron goes as Fe^3?+? and replaces Mn in ab plane. With increasing Fe the valence states of Mn get re-distributed in a way that number of the Jahn–Teller ions Mn^3?+? increases and that of the pairs of Mn^3?+?–O–Mn^4?+? experiencing double exchange decreases.     

Athermal migration of vacancies in iron and copper induced by electron irradiation

Abstract

Irradiation with high-energy particles induces athermal migration of point defects, which affects defect reactions at low temperatures where thermal migration is negligible. We conducted molecular dynamics simulations of vacancy migration in iron and copper driven by recoil energies under electron irradiation in a high-voltage electron microscope. Minimum kinetic energy required for migration was about 0.8 and 1.0 eV in iron and copper at 20 K, which was slightly higher than the activation energy for vacancy migration. Around the minimum energy, the migration succeeded only when a first nearest neighbour (1NN) atom received the kinetic energy towards the vacancy. The migration was induced by higher kinetic energies even with larger deflection angles. Above several electron-volts and a few 10s of electron-volts, vacancies migrated directly to 2NN and 3NN sites, respectively. Vacancy migration had complicated directional dependence at higher kinetic energies through multiple collisions and replacement of atoms. The probability of vacancy migration increased with the kinetic energy and remained around 0.3–0.5 jumps per recoil event for 20–100 eV. At higher temperatures, thermal energies slightly increased the probability for kinetic energies less than 1.5 eV. The cross section of vacancy migration was 3040 and 2940 barns for 1NN atoms in iron and copper under irradiation with 1.25 MV electrons at 20 K: the previous result was overestimated by about five times.     

Characterization of yellow and colorless decorative glasses from the Temple of the Emerald Buddha, Bangkok, Thailand

Yellow and colorless ancient glasses, which were once used to decorate the Temple of the Emerald Buddha, Bangkok, Thailand, around 150 years ago, are studied to unravel the long-lost glass-making recipes and manufacturing techniques. Analyses of chemical compositions, using synchrotron x-ray fluorescence (SRXRF), indicate that the Thai ancient glasses are soda lime silica glasses (60 % SiO₂; 10 % Na₂O; 10 % CaO) bearing lead oxide between 2–16 %. Iron (1.5–9.4 % Fe₂O₃) and manganese (1.7 % MnO) are present in larger abundance than the other 3d transition metals detected (0.04–0.2 %). K-edge x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure spectroscopy (EXAFS) provide conclusive evidence on the oxidation states of Fe being 3+ and Mn being 2+ and on short-length tetrahedral structures around the cations. This suggests that iron is used as a yellow colorant with manganese as a decolorant. L ₃-edge XANES results reveal the oxidation states of lead as 2+. The results from this work provide information crucial for replicating these decorative glasses for the future restoration of the Temple of the Emerald Buddha.     

Synthesis and characterization of LiMn1-x Fe x PO4/carbon nanotubes composites as cathodes for Li-ion batteries

Carbon nanotubes (CNT) coated with LiMn_1-x Fe _x PO₄ (0.2?≤?x?≤?0.8), as possible cathode materials, was synthesized by using a sol–gel process (Polyol method), after annealing under flowing nitrogen. X-ray diffraction (XRD) patterns of the composites confirmed the formation of the olivine structured LiMn_1-x Fe _x PO₄ phase and no secondary phases were detected. The morphological investigation revealed the formation of agglomerates with particles size ranging between 300 and 700 nm. XRD investigation of composites shows difference of the morphology by doping CNT and carbon black in the composites. Transmission electron microscopy shows the growth of nano-sized particles on CNT (20–70 nm) and the agglomeration of primary particles to form secondary particles. The X-ray photoelectron spectroscopy showed that the Fe and Mn ions are in divalent states in the LiMn_1-x Fe _x PO₄ composites. The cyclic voltamograms showed the oxidation peaks of iron and manganese ions at 3.53–3.63 and 4.05–4.33 V, respectively, while the reduction peaks were found at 3.21–3.42 V (iron reduction) and 3.85–3.93 V (manganese reduction) depending on the iron content in the composition. The LiMn_0.6Fe_0.4PO₄/CNT composite (x?=?0.4) (with 20 %?wt CNT) delivered a specific capacity of 120 mAhg^?1 (at a discharge rate of C/20 and RT).     

Evidence for direct observation by Mössbauer spectroscopy of surface tin atoms in platinum–tin particles

The diamond-bearing gravels found along South Africa's West Coast are being beneficiated by means of dense medium separation (DMS) to reclaim the alluvial diamonds. Granular ferrosilicon (Fe–Si) is used as the DMS material and at the end of each operation the Fe–Si is reclaimed from the process stream using a magnetic separator and is then recycled but losses of Fe–Si due to attrition, adhesion to the separation products, density changes and changes to the magnetic properties can occur. The gravel obtained from the mining operation is washed and screened before heavy mineral separation. The concentrate, tailings and Fe–Si samples were investigated by means of SEM and Mössbauer spectroscopy to determine where changes to the Fe–Si, or contamination could occur. The composition of the Fe–Si was determined to be Fe (76.1 at.%), Si (20.3 at.%), Mn (1.5 at.%), Al (1.5 at.%) and Cr (0.6 at.%) resulting in a more or less ordered DO₃ phase with a calculated composition of Fe₃Si for this Fe–Si, consistent with the Mössbauer results where two sextets with hyperfine magnetic fields of 18.6 T and 28.4 T were observed. After DMS, magnetite and ilmenite, the minerals found in the gravel, were still present in the concentrate. In the tailings virtually no magnetite or ilmenite was found and only a doublet, identified as an oxihydroxide, due to the abrasion of the Fe–Si, was found. After magnetic separation, to wash and clean the Fe–Si for re-use, it was found that magnetite and ilmenite were still present in the Fe–Si, which results in a change in density of the Fe–Si, resulting in a higher density and loss of valuable diamonds.     

Amethyst and morion quartz gemstone raw materials from Turkey: color saturation and enhancement by gamma,neutron and beta irradiation

Color-enhancement investigations without using heating treatment from dull or pale to ideal saturation and/or changes to the formation of the rarer attractive colors are widely conducted to revalue abandoned gem material sources in the world. Such an investigation is carried out on pale or dull purple-colored amethyst and smoky-colored morion samples, which are two important gem species of the crystalline quartz (SiO₂) mineral that are currently abandoned in natural deposits in Turkey because of their unattractive coloration. The results of color enhancements observed on these samples, after irradiation with artificial gamma, neutron and beta beams, were examined by comparing with samples with the ideal color saturation and also with colorless samples, using optical absorption (OA) and radioluminescence (RL) spectroscopy. The ICP-AES analyses reveal that the main impurity elements of over 100 ppm in abundance in these quartz species are aluminum, iron and titanium for amethyst, and aluminum, iron, titanium and manganese for morion. The OA spectra indicate that vivid purple coloration of amethyst is due to the transmittance at about 395–420 nm band gap as a result of absorbance peaks at 375, 480 and 530 nm. These absorbances may be related to the unusual oxidized small proportions of certain impurity ions, after being exposed mainly to gamma irradiation, such as Al(IV) from the total aluminum, Ti(V) from the total titanium and Fe(IV) from the total iron, respectively. However, the RL spectroscopy of amethyst samples before and after they were exposed to artificial gamma, neutron and beta radiation beams demonstrates that the ions most affected by irradiation are Fe(IV) first and Al(IV) and Ti(V) second, and these ions represent the RL peaks at 600, 720 and 495 nm, respectively. The OA spectra indicate that dark smoky coloration in morion is due to a lack of transmittance at the visible region as a result of the absorbance peaks at 375, 450–490, 620 and 730 nm. These absorbances also may be related to the unusual oxidized small proportions of certain impurity ions by irradiation, such as Al(IV) from the total aluminum, Ti(V) from the total titanium and Mn(III) from the total manganese, respectively. In addition, the buoyancies of these absorbance peaks in the visible region produce the color hues between light smoky and dark smoky colorations in morion samples. These oxidized ion states are more resistant and stable against environmental destructive conditions in comparison with amethyst. Thus, the dark smoky coloration of morion becomes dull or pale after relatively longer periods. But, the RL spectroscopy of morion before and after being exposed to gamma, neutron and beta irradiation beams demonstrates that the most induced ions from the irradiation are Mn(III) and Al(IV) first and Ti(V) second. These ions represent the RL peaks at about 400, 720 and about 500 nm, respectively.     

One-dimensional migration of interstitial clusters in SUS316L and its model alloys at elevated temperatures

For self-interstitial atom (SIA) clusters in various concentrated alloys, one-dimensional (1D) migration is induced by electron irradiation around 300 K. But at elevated temperatures, the 1D migration frequency decreases to less than one-tenth of that around 300 K in iron-based bcc alloys. In this study, we examined mechanisms of 1D migration at elevated temperatures using in situ observation of SUS316L and its model alloys with high-voltage electron microscopy. First, for elevated temperatures, we examined the effects of annealing and short-term electron irradiation of SIA clusters on their subsequent 1D migration. In annealed SUS316L, 1D migration was suppressed and then recovered by prolonged irradiation at 300 K. In high-purity model alloy Fe-18Cr-13Ni, annealing or irradiation had no effect. Addition of carbon or oxygen to the model alloy suppressed 1D migration after annealing. Manganese and silicon did not suppress 1D migration after annealing but after short-term electron irradiation. The suppression was attributable to the pinning of SIA clusters by segregated solute elements, and the recovery was to the dissolution of the segregation by interatomic mixing under electron irradiation. Next, we examined 1D migration of SIA clusters in SUS316L under continuous electron irradiation at elevated temperatures. The 1D migration frequency at 673 K was proportional to the irradiation intensity. It was as high as half of that at 300 K. We proposed that 1D migration is controlled by the competition of two effects: induction of 1D migration by interatomic mixing and suppression by solute segregation.     

Solute-diffusion-controlled dislocation creep in pure aluminium containing 0.026 at.% Fe

Pure aluminium containing about 200?at.ppm Fe in solution is shown to creep about 10⁶ times slower at 200°C than the same aluminium containing a negligible amount of iron in solution. The high creep resistance of the Al–200?at.ppm?Fe alloy is attributed to the presence of subgrain boundaries containing iron solute atoms. It is proposed that the opposing stress fields from subgrain boundaries and from the piled-up dislocations during creep are cyclically relaxed, by iron solute diffusion, to allow climb of the lead dislocation in the pile-up. The mechanism is a form of mechanical ratcheting. The model is applied to Al–Fe alloys and correctly predicts that the creep rate is controlled by the rate of iron solute diffusion and by a temperature dependence equal to the activation energy for iron diffusion, namely Q _c?=?221?kJ?mol^?1. Basic creep studies on solid-solution alloying with solute atoms that diffuse slowly in the lattice of aluminium (e.g. manganese, chromium, titanium and vanadium) appear worthy of study as a way of enhancing creep strength and of understanding creep mechanisms involving solute-atom-containing subgrain boundaries.     

Mössbauer study of Mg–Ni(Fe) alloys processed as materials for solid state hydrogen storage

Mg–Ni–Fe magnesium-rich intermetallic compounds were prepared following two distinct routes. A Mg₈₈Ni₁₁Fe₁ sample (A) was prepared by melt spinning Mg–Ni–Fe pellets and then by high-energy ball milling for 6 h the obtained ribbons. A (MgH₂)₈₈Ni₁₁Fe₁ sample (B) was obtained by high-energy ball milling for 20 h a mixture of Ni, Fe and MgH₂ powders in the due proportions. A SPEX8000 shaker mill with a 10:1 ball to powder ratio was used for milling in argon atmosphere. The samples were submitted to repeated hydrogen absorption/desorption cycles in a Sievert type gas–solid reaction controller at temperatures in the range 520?÷?590 K and a maximum pressure of 2.5 MPa during absorption. The samples were analysed before and after the hydrogen absorption/desorption cycles by X-ray diffraction and Mössbauer spectroscopy. The results concerning the hydrogen storage properties of the studied compounds are discussed in connection with the micro-structural characteristics found by means of the used analytical techniques. The improved kinetics of hydrogen desorption for sample A, in comparison to sample B, has been ascribed to the different behaviour of iron atoms in the two cases, as proved by Mössbauer spectroscopy. In fact, iron results homogeneously distributed in sample A, partly at the Mg₂Ni grain boundaries, with catalytic effect on the gas–solid reaction; in sample B, instead, iron is dispersed inside the hydride powder as metallic iron or superparamagnetic iron.     

Relaxation method for constructing the interaction potentials of metal–nonmetal atomic pairs

An algorithm that employs the method of successive relaxation for determining the parameters of the pairwise interaction potential of iron and nonmetallic atoms that implicitly considers the redistribution of electron density between atoms is developed. The parameters of the interatomic interaction potential are calculated for ten pairs of elements: Fe–P, Fe–S, Fe–B, Fe–V, Fe–Mo, Fe–Cr, Fe–Mn, Fe–Si, Fe–Ni, and Fe–Al. The structural and thermodynamic properties of solid solutions based on iron and pure materials, and some pairwise interaction potentials constructed earlier in the Lennard–Jones form for identical metal atoms and homogeneous pairs of different metal–metal atoms, are used in these calculations.     

Evolution of ion-irradiated point defect concentration by cluster dynamics simulation

The relationship between ions irradiation and the induced microstructures(point defects, dislocations, clusters, etc.)could be better analyzed and explained by simulation. The mean field rate theory and cluster dynamics are used to simulate the effect of implanted Fe on the point defects concentration quantitatively. It is found that the depth distribution of point defect concentration is relatively gentle than that of damage calculated by SRIM software. Specifically, the damage rate and point defect concentration increase by 1.5 times and 0.6 times from depth of 120 nm to 825 nm, respectively. With the consideration of implanted Fe ions, which effectively act as interstitial atoms at the depth of high ion implantation rate, the vacancy concentration C_v decreases significantly after reaching the peak value, while the interstitial atom concentration C_i increases significantly after decline of the previous stage. At the peak depth of ion implantation, C_v dropped by 86%, and C_i increased by 6.2 times. Therefore, the implanted ions should be considered into the point defects concentration under high dose of heavy ion irradiation, which may help predict the concentration distribution of defect clusters, further analyzing the evolution behavior of solute precipitation.     

Deformation-induced dissolution of the intermetallics Ni3Ti and Ni3Al in austenitic steels at cryogenic temperatures

An anomalous deformation-induced dissolution of the intermetallics Ni₃Al and Ni₃Ti in the matrix of austenitic Fe–Ni–Al(Ti) alloys has been revealed in experiment at cryogenic temperatures (down to 77 K) under rolling and high pressure torsion. The observed phenomenon is explained as the result of migration of deformation-stipulated interstitial atoms from a particle into the matrix in the stress field of moving dislocations. With increasing the temperature of deformation, the dissolution is replaced by the deformation-induced precipitation of the intermetallics, which is accelerated due to a sufficient amount of point defects in the matrix, gained as well in the course of deformation at lower temperatures.     

Phase coexistence in mechanicallly alloyed iron–manganese powders

Iron–manganese alloys with Mn concentration of 6–30 at.% were prepared by mechanical alloying. Structure and phase composition of the samples were investigated by X-ray diffraction and Mössbauer spectroscopy. Mechanical alloying results in the formation of b.c.c. and f.c.c. solid solutions with high concentration of structure defects and refined grains. A single b.c.c. phase was observed in Fe–Mn alloys a Mn concentration less than ≤8 at.% and, for higher Mn contents, a mixture of b.c.c. and f.c.c. phases was observed. The main features of phase composition of as-prepared alloys consisted in significant widening of single phase concentration range.     

X‐ray fluorescence analysis of trace metals in environmental water using preconcentration with an iminodiacetate extraction disk

A simple and convenient x‐ray fluorescence analysis procedure for trace amounts of Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb in water was developed using preconcentration with an iminodiacetate extraction disk (IED). The IED was coated on both faces with commercially available laminate film to prevent x‐ray damage to the IED by strong x‐irradiation (4 kW; 50 kV, 80 mA) of the wavelength‐dispersive x‐ray fluorescence spectrometer. Lamination of the IED prolongs its life from 7 to about 200 min at 4 kW irradiation while negligibly decreasing the x‐ray fluorescence. Lowering the power of primary x‐rays to less than 1.5 kW compensated for the Hg evaporation. Linear calibration curves were obtained over the range 500 µg–5 mg for Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb. Detection limits corresponding to three times the standard deviation of the blank intensity were 0.1–0.4 µg for Mn, Co and Ni, 0.5–0.8 µg for Fe, Cu, Zn and Pb and 7 µg for Cd. A spike test for 10 µg of eight analytes, excluding Mn, showed good recoveries (90–100%) for city water and rainwater. Analytical results for municipal tap water and rainwater agreed well with values obtained using atomic absorption spectrometry. Copyright © 2006 John Wiley & Sons, Ltd.     

Thermal and structural characterization of Cu–Al–Mn–X (Ti,Ni) shape memory alloys

In this study, the Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys at the range of 10–12 at.% of aluminum and 4–5 at.% manganese were produced by arc melting. We have investigated the effects of the alloying elements on the transformation temperatures, and the structural and the magnetic properties of the quaternary Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys. The evolution of the transformation temperatures was studied by differential scanning calorimetry with different heating and cooling rates. The characteristic transformation temperatures and the thermodynamic parameters were highly sensitive to variations in the aluminum and manganese content, and it was observed that the nickel addition into the Cu–Al–Mn system decreased the transformation temperature although Ti addition caused an increase in the transformation temperatures. The effect of the nickel and the titanium on the thermodynamic parameters such as enthalpy and entropy values was investigated. The structural changes of the samples were studied by X-ray diffraction measurements and by optical microscope observations at room temperature. It is evaluated that the element Ni has been completely soluble in the matrix, and the main phase of the Cu–Al–Mn–Ni sample is martensite, and due to the low solubility of the Ti, the Cu–Al–Mn–Ti sample has precipitates, and a martensite phase at room temperature. The magnetic properties of the Cu–Al–Mn, Cu–Al–Mn–Ni and Cu–Al–Mn–Ti samples were investigated, and the effect of the nickel and the titanium on the magnetic properties was studied.     

Structural and Mössbauer studies of aerosol FeCu nanoparticles in a wide composition range

Structure and magnetic state of aerosol FeCu nanoparticles of 10–30 nm size with Cu content of 0.6–92.1 at.% have been examined by X-ray diffraction and Mössbauer spectroscopy. The FeCu particles have been shown to consist of an iron core surrounded by a copper and Fe oxide shell. With increasing Cu content the iron core having a bcc structure is reduced down to its complete disappearance followed by vanishing ferromagnetism of the particles. Within the copper content from 4.9 to 74.3 at.% the bcc and fcc phases coexist, with the fcc phase having a lattice constant close to that of pure copper and the bcc lattice constant being slightly higher than that for pure Fe due to embedding Cu atoms into the Fe lattice. At Fe-rich FeCu samples a presence of two-spin (ferromagnetic and paramagnetic) components of the fcc Fe is also observed. In the case of a thin copper shell there is only the ferromagnetic fcc Fe, whereas with further thickening of the shell both spin states of the fcc Fe appear existing up to a 20% Cu content. For FeCu samples with a higher Cu content they disappear due to oxidation of the copper grains. The Cu-rich samples with Cu content higher 80 at.% have a fcc structure, with the lattice constant being slightly higher than that of copper and they are paramagnetic. A slight increase of the lattice constant is due to the penetration of small iron aggregations into the Cu grains. In contact with air, the FeCu particles become covered with Fe₃O₄ and Cu₂O. Their long-term exposure to ambient conditions leads to further oxidation process of Cu₂O to CuO.     

Mössbauer study of the invar Fe–Ni and Fe–Ni–C alloys in magnetic field

F.C.C. Fe–30.3%Ni and Fe–30.5%Ni–1.5%C (wt.%) alloys were studied by means of Mössbauer spectroscopy in external magnetic field B _ext?=?2.5, 5, 7 T parallel to the gamma-beam. It is shown that distribution of effective magnetic field in the alloys is broad and that carbon expands the range of B _eff. The external magnetic field increases B _eff in the Fe–Ni alloy and decreases it more evidently in the Fe–Ni–C alloy. Antiferromagnetic spin coupling along the ferromagnetic component is proposed to explain data.     

Ferromagnetism in epitaxial germanium and silicon layers supersaturated with managanese and iron impurities

The possibility of laser synthesis of diluted magnetic semiconductors based on germanium and silicon doped with manganese or iron up to 10–15 at % has been shown. According to data on the electronic levels of 3d atoms in semiconductors, Mn and Fe impurities are most preferable for realizing ferromagnetism in Ge and Si through the Ruderman-Kittel-Kasuya-Yosida mechanism. Epitaxial Ge and Si layers 50–110 nm in thickness were grown on gallium arsenide or sapphire single crystal substrates heated to 200–480°C. The content of a 3d impurity has been measured by x-ray spectroscopy. The ferromagnetism of layers and high magnetic and acceptor activities of Mn in Ge, as well as of Mn and Fe in Si, are manifested in the observation of the Kerr effect, anomalous Hall effect, high hole conductivity, and anisotropic ferromagnetic resonance at 77–500 K. According to the ferromagnetic resonance data, the Curie point of Ge:Mn and Si:Mn on a GaAs substrate and of Si:Fe on an Al₂O₃ substrate is no lower than 420, 500, and 77 K, respectively.     

Phase transformation in Ni–Mn–Sn ferromagnetic shape memory alloy thin films induced by dense ionization

The effects of 200 MeV Au ions irradiation on the structural and magnetic properties of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin films have been systematically investigated. In order to understand the role of initial microstructure and phase of the film with respect to high energy irradiation, the two types of Ni–Mn–Sn FSMA films having different phases at room temperature were irradiated, one in martensite phase (Ni_58.9Mn_28.0Sn_13.1) and other in austenite phase (Ni₅₀Mn_35.6Sn_14.4). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images along with the diffraction patterns of X-rays and electrons confirm that martensite phase transforms to austenite phase at a fluence of 6×10¹² ions/cm² and a complete amorphization occurs at a fluence of 3×10¹³ ions/cm², whereas ion irradiation has a minimal effect on the austenitic structure (Ni₅₀Mn_35.6Sn_14.4). Thermo-magnetic measurements also support the above mentioned behaviour of Ni–Mn–Sn FSMA films with increasing fluence of 200 MeV Au ions. The results are explained on the basis of thermal spike model considering the core and halo regions of ion tracks in FSMA materials.