EPMA Results Research Articles

Resonant X-ray diffraction of α-phase Mo 0.15Ru 0.85Si and crystal stability calculation in Mo–Ru–Si system (FeSi and CsCl types)

Resonant X-ray diffraction at the Mo K edge on α-phase Mo 7Ru 43Si 50 (FeSi type) has been performed in the aim of increasing the scattering contrast between Ru and Mo. The X-ray composition obtained from multipattern refinement with the Rietveld method (Mo 7.8(1)Ru 42.2(1)Si 50) is in agreement with EPMA results (Mo 6.9(2)Ru 42.8(2)Si 50.3(2)), thus validating the method for further crystallographic studies in the Mo–Ru–Si system. The KKR calculations show that the stability of both structural forms of RuSi is related to the presence of either an energy gap (FeSi) or a very low density of states (DOS) at the Fermi level (CsCl). This particular electronic structure behavior is absent in other CsCl-type compounds, since they exhibit a markedly large DOS at E F. Conversely, the corresponding DOS values at E F are found to be smaller in existing FeSi-type phases (TcSi and RhSi). The KKR–CPA results of FeSi-type Ru 1− x Mo x Si (0 < x < 0.3) alloys clearly reveal that the DOS at E F strongly increases with Mo content, which comes from rigid band structure and decreasing number of electrons as well as higher d-Mo states replacing d-Ru ones. Such a DOS behavior suggests crystal instability with increasing Mo content, which is in line with the limited Mo solubility in Ru 1− x Mo x Si.

Heterogeneous nucleating role of TiB 2 or AlP/TiB 2 coupled compounds on primary Mg 2Si in Al–Mg–Si alloys

Refinement and modification performance of Al–Ti–B master alloy alone or with Al–P master alloy on primary Mg 2Si in Al–12.67% Mg–10.33% Si alloy was investigated in this paper. The experimental results show that perfect effect can be obtained after addition of 1% Al–5Ti–1B master alloy into the Al–Mg–Si alloy. The morphologies of primary Mg 2Si particulates change from dendritic to polygonal shape, and their average sizes decrease from ∼100 to ∼20 μm. The ultimate tensile strength of the alloy increases. EPMA and TEM results show that TiB 2 particles act as the nuclei of primary Mg 2Si. Crystal lattice correspondence indicates TiB 2 has a good lattice matching coherence relationship with Mg 2Si, and the disregistry is only 4.64%. Furthermore, the addition of Al–5Ti–1B master alloy can significantly improve the refinement and modification effect of AlP on primary Mg 2Si. It is also found that coupling particles of AlP and TiB 2 exist in the center of primary Mg 2Si.

A new single step process for synthesis and growth of ZnGeP 2 crystal

A new one-step process for synthesis and growth of zinc–germanium–phosphide, ZnGeP 2 (ZGP), is reported for the first time herein using a three-zone resistance furnace by the horizontal gradient freeze technique. A safe and proper temperature scheme has been obtained for both synthesis and growth of ZGP crystals via the melt growth route from Zn, Ge and P powder. The prepared material has been investigated using powder X-ray diffraction which shows the correct ZGP tetragonal phase. EPMA results are also obtained to estimate the compositional homogeneity of the grown crystal.

Combined cathodoluminescence spectroscopy, electron microprobe and laser ablation ICP mass spectrometry analysis: an attempt to correlate luminescence and chemical composition of monazite

Quantitative electron microprobe analyses (EPMA), cathodoluminescence (CL) panchromatic images and monochromatic spectra, as well as laser ablation – inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of minor and trace elements were performed on selected monazite crystals from Dora Maira Massif, Western Alps (Italy). Back-scattered electron (BSE) images suggest no patchy or chemical zoning or strong disomogeneity. The EPMA data indicate that the crystals are Ce-monazite with a mostly homogeneous composition in light rare earth elements (LREE). Low (far below 1 wt%) and variable Th, Ca and Y contents were detected. The LA-ICP-MS data indicate that all heavy rare earth elements (HREE) occur as minor or trace elements (from thousand to few ppm). Interesting Si, Sr, U, and Pb concentrations are also detected. Th, Y and Ca values are comparable to EPMA results. The use of panchromatic and monochromatic CL images with CL spectra in combination with microanalytical techniques suggest that the luminescence of monazite is mostly due to four bands centered at 316, 339, 634, and 683 nm, partially overlapping and not clearly related to impurity activators or to microchemical differences. However, we can attempt to attribute the first two bands to Gd3+ and Ce3+, respectively. In addition, several minor peaks centered at 384, 411, 485, 498, 562, and 596 nm also occur in between. These minor peaks may be tentatively assigned to Tb3+, Dy3+, and Sm3+.

High Temperature Thermoelectric Property of Sr-Filled Skutterudite Sr&lt;sub&gt;y&lt;/sub&gt;Co&lt;sub&gt;4&lt;/sub&gt;Sb&lt;sub&gt;12&lt;/sub&gt;

Sr-filled skutterudite compounds SryCo4Sb12 (y=0-0.20) were synthesized by melting method. XRD and EPMA results revealed that the obtained samples are single skutterudite phase with homogeneous chemical composition. The lattice parameters increase linearly with increasing Sr content in the range of y=0-0.20. The thermal conductivity, electrical conductivity and Seebeck coefficient were measured in the temperature range of 300-850K. The measurement of Hall effect was performed by Van de Pauw method at room temperature. The obtained Sr-filled skutterudite exhibits n-type conduction. The absolute value of the Seebeck coefficient of SryCo4Sb12 decreases with the increase of Sr content. The electrical conductivity increases with the increase of Sr content. The lattice thermal conductivity of SryCo4Sb12 is significantly depressed as compared with unfilled CoSb3. The maximum dimensionless thermoelectric figure of merit is 0.7 for Sr0.20Co4Sb12 at 850K. Further optimization of chemical composition would improve the thermoelectric performance.

Distribution and Solubility Limit of Al in Al2O3-Doped ZnO Sintered Body

A few mol% Al2O3-doped ZnO sintered body forms a substitutional solid solution and the semi-conducting property is drastically affected by the content of the dissolved Al. It was suggested from the results of XRD and EPMA that Al existed in the ZnO sintered body in the form of ZnAl2O4. Furthermore, the distribution of ZnAl2O4 was visualized by AFM and SEM. It was, however, difficult for these techniques to detect dissolved Al in ZnO grains directly. The SIMS mapping suggested that the trace amount of Al (approximately 0.3 atomic%) dissolved into ZnO grains because of high sensitivity for trace impurities. This result was consistent with the change in lattice constants of ZnO with Al dissolution.

Metal-phosphate coating on LiCoO 2 cathodes with high cutoff voltages

Metal-phosphate coating on LiCoO 2 cathodes improved the cycle-life performance with high charge-cutoff voltages. The optimum annealing temperature and coating thickness for the excellent electrochemical properties of the metal-phosphate-coated LiCoO 2 cathodes were determined. Among the metal-phosphate-coating materials, the Al–P–O coating enhanced the electrochemical properties most efficiently. The EPMA results (after cycles) with a 4.8 V cutoff confirmed that most of the nanoscale coating layers, particularly the P component, had dissolved during cycling.

Fission Gas Bubbles Characterisation in Irradiated UO2 Fuel by SEM, EPMA and SIMS

The behaviour of gases produced by fission is of great importance for nuclear fuel operation. Within this context, an experimental method for the characterisation of the fission gas including gas bubbles in an irradiated UO2 nuclear fuel was developed in our laboratory using SIMS, EPMA and SEM results. SIMS and EPMA have been used to measure the radial distribution of xenon and SEM gives information on bubble formation across the fuel pellet radius. Using SIMS, xenon concentration can be determined in the matrix and in the bubbles. A quantification method, allowing the determination of the total inventory of xenon, is proposed and qualified with EPMA results. It is concluded that the complementary micro-analytical techniques SIMS, EPMA and SEM are very powerful tools for the characterisation of the fission gas bubbles in irradiated nuclear fuel.

Oxidation and hot corrosion behavior of gradient NiCoCrAlYSiB coatings deposited by a combination of arc ion plating and magnetron sputtering techniques

NiCoCrAlYSiB coating was prepared by arc ion plating and Al and Cr gradient NiCoCrAlYSiB coating by a combination of arc ion plating and magnetron sputtering. The results of EPMA show that the Al and Cr are uniformly distributed in the NiCoCrAlYSiB coating but have a graded distribution in the surface layer of the gradient coating. Compared to the bare DSM 11, both the NiCoCrAlYSiB coating and the gradient coating improved the oxidation resistance greatly. After 100 h hot corrosion, the gradient coating showed the best corrosion resistance. The oxidation and hot corrosion mechanisms were discussed.

The Performance of a Wear Resistance Cladding Layer on a Mild Steel Plate by Electric Resistance Welding

This study deals with the performance of a 1 mm-thick wear resistance cladding layer of composite metal powder of 110~160 μm-sized STL-1(Co-Cr alloy) and 100 μm-sized MBF-15 (Ni based brazing alloy) applied by the resistance welding method to clad 1.9 mm-thick mild steel plate. Two metal powders were prepared as the cladding materials, in the ratio of two to one by weight. We studied the microstructures and results of EPMA of cladding layers to obtain the most suitable joint conditions. Also, bending and abrasion tests were performed to evaluate the bond-ability with the substrate and the wear behaviour of the cladding layer. The main results obtained are as follows: The wear resistance cladding layer had sound microstructures when it had been applied under the following welding conditions: welding current higher than 2.1 kA, welding speed of 1.0 m/min, and electrode force less than 392 N. In spite of cracks occurring in the cladding layer after the bending test, the cladding layer, applied under almost all welding conditions, was not separated from the substrate. We obtained the wear behaviour of the mild steel, 16.833 mg/min-wear loss and 0.046 mm/min-abrasion depth. The characteristics of the cladding layer, which had been applied with welding conditions — welding current of 2.5 kA, welding speed of 1.0 m/min, and electrode force of 196 N, had a satisfactory wear resistance behaviour of 15.726 mg/min-wear loss and 0.043 mm/min-abrasion depth.

Stabilized epitaxial films of hexagonal Ni 1−xS on MgO(001)

This study used molecular beam epitaxy to prepare epitaxial Ni 1− x S films with NiAs-type structures on MgO(001) substrates. The films were characterized using X-ray diffraction method. Nickel vacancies showed an ordered arrangement of alternating metal-rich and metal-deficient layers along the c-axis. The orientations of epitaxial films were (001) [1,−1,0]Ni 1− x S||(001)[110]MgO and its equivalents because of the coexistence of the trigonal axis of the Ni 1− x S film and the four-fold rotation axis of the MgO substrate. Film compositions were obtained using intensity ratios between 0 0 1 and 0 0 2 reflections and EPMA results. They were dependent on substrate temperature. The relation between lattice parameters and the composition, as determined by the intensity ratio, nearly agrees with that of previously reported bulk Ni 1− x S. The films were stable at room temperature after 1 year, which contrasts with deterioration of bulk Ni 1− x S. This paper presents SEM and RHEED assessments of the film's morphology and structure.

The preparation and hot corrosion resistance of gradient NiCoCrAlYSiB coatings

An Al and Cr gradient NiCoCrAlYSiB coating was prepared by a two-step deposition: (i) deposition of a NiCoCrAlYSiB layer onto Ni-based superalloy surface by arc ion plating (AIP); and (ii) co-deposition of NiCoCrAlYSiB and Cr–Al by AIP and magnetron sputtering (MS), respectively. The results of EPMA show that Al and Cr have a gradient distribution in the surface layer of the gradient coatings. After annealing, the NiCoCrAlYSiB coatings consist of γ/γ′ and β-NiAl, while the gradient coatings consist of σ-(Cr, Co), AlCr 2, and Al 8Cr 5, besides γ/γ′ and β-NiAl. The phases of σ-(Cr, Co), AlCr 2, and Al 8Cr 5 can act as reservoir phases of Cr and Al to improve the hot corrosion resistance and lifetime of the coatings. In order to investigate the effect of Al and Cr on the hot corrosion of coatings, NiCoCrAlYSiB coatings and the gradient coatings were coated with 0.5 mg (Na 2SO 4+K 2SO 4 20 wt.% salt mixture)/cm 2 and oxidized at 900 °C for 20 h. XRD and EDS results show that there are only the alumina formed on the NiCoCrAlYSiB coatings, so the basic fluxing of Al 2O 3 occurred, which caused an accelerated hot corrosion after 10 h. For the gradient coatings, there formed Al 2O 3 and Cr 2O 3 at the primary stage of hot corrosion. Cr 2O 3 is easier to react with Na 2SO 4 than Al 2O 3, which reduces the oxygen ion activity of Na 2SO 4, so Al 2O 3 was protected. The formation of the continual and protective layer of Al 2O 3 and Cr 2O 3 leads to the hot corrosion kinetics of gradient coatings similar to oxidation kinetics.

Chiral separation of amino acids in ultrafiltration through DNA-immobilized cellulose membranes

Ultrafiltration experiments for the chiral separation of racemic tryptophan, phenylglycine and phenylalanine were investigated through immobilized DNA membranes having various pore sizes. l-tryptophan preferentially permeated through immobilized DNA membranes with a pore size<2.0 nm (molecular weight cut-off (MWCO)<5000) while d-tryptophan preferentially permeated through immobilized DNA membranes with a pore size>2.0 nm (MWCO>5000). These results are completely opposite tendency in the ultrafiltration of racemic phenylalanine through the immobilized DNA membranes. This may be originated from the different interaction between DNA and tryptophan compared to that between DNA and phenylalanine. However, in both cases the pore size of the immobilized DNA membranes regulated preferential permeation of the enantiomer through the membranes. The immobilized DNA membranes are categorized as channel type membranes and not as affinity membranes. Chiral separation models were proposed from using the chiral separation results of racemic amino acids, preferential adsorption of amino acid enantiomers and EPMA results.

Effect of electrolysis potential on reduction of solid silicon dioxide in molten CaCl 2

Electrochemical reduction of solid SiO 2 by using a contacting electrode method was investigated in molten CaCl 2 at 1123 K. The samples were prepared by potentiostatic electrolysis at 0.35–1.30 V (vs. Ca 2+/Ca) for 1 h. From the results of XRD, SEM and EPMA, it was confirmed that SiO 2 was electrochemically reduced to Si at 1.25 V or more negative potential, which agreed with the thermodynamic calculation. The current–time curves during electrolysis and the cross-sectional SEM measurements of the samples clearly showed that reduction rate is higher at more negative potential. In addition, Si–Ca alloy formation was confirmed at 0.35 V.

Effects of Cr, Cu, Ni and Ca on the corrosion behavior of low carbon steel in synthetic tap water

Aqueous corrosion behaviors of the low-alloy steels with small amounts of Cr, Cu, Ni and Ca in synthetic tap water were studied by electrochemical corrosion tests (potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS)) and analytical techniques (XPS, EPMA). Potentiodynamic polarization test represented that all curves showed active corrosion behavior and corrosion potential was shifted to noble direction and corrosion rate tended to decrease as the result of alloying. Results of EIS measurement showed that the more the content of element, the larger the polarization resistance. It can be seen that these results were caused by the formation of a coherent protective film, which contained alloying elements. Actually, XPS results showed that Cr, Cu, and Ca formed protective metal oxide at the surface of rust layer under stagnant condition. The results of EPMA indicated that Cr, Cu, and Ca were distributed densely at inner layer of the rust layer, while Ni was distributed at the whole layer under flow condition. Consequently, alloying elements improved corrosion resistance of low carbon steel. It was reflected that corrosion rates of all specimens were quite low; especially, Cu-, Ni-, and Ca-containing specimens revealed the lowest corrosion rate due to the formation of insoluble rust layer at the initial stage of corrosion.

Compositional design considerations for microsegregation in single crystal superalloy systems

This paper investigates the role of varying refractory addition levels on the microsegregation behaviour of single crystal (SX) superalloys systems during solidification. Specifically, a series of six Ni-base alloy compositions are set in a controlled manner, such that the chemical effects of Re, W, and Ru can be independently assessed. Each experimental alloy is produced in the SX condition utilizing a modified Bridgman casting process, with subsequent compositional analysis of the solidification structures via standard electron microprobe analysis (EPMA) methods. Qualitative partitioning results indicate typical SX alloy segregation behavior with elements such as Cr, Co, Re, Mo, and W all segregating towards the dendrite core regions, while the γ′ forming elements of Al, Ti, and Ta show favorable partitioning to the interdendritic γ–γ′ eutectic regions. Both Ni and Ru exhibit ideal segregation behaviour with no favorable partitioning to either phase. Quantitative EPMA results indicate that as the nominal Re level increases, the severity of microsegregation to the dendrite core regions rises dramatically for Mo, Cr, and Re. Remarkably, evidence is presented demonstrating the role that Ru plays in counteracting the microsegregation effects of both increased Re and higher overall total refractory levels.

Nonstoichiometry and solubility of impurity in In-doped PbTe films on Si substrates

The chemical quantitative composition, phase constitution, and crystal structure of doped with In lead telluride films on Si (1 0 0) or SiO 2/Si (1 0 0) substrates have been studied in this work. By EPMA and atomic absorption measurements, it has been found that the concentration of In atoms y In varied from 0.0011 to 0.045 in these deposited Pb 1− y In y Te films. The results of EPMA, SEM, and X-ray diffraction (XRD) measurements show that formation of In solid solutions in lead telluride matrix revealed not only in PbTe–InTe cross-section, but in PbTe–In 2Te 3 pseudobinary system also. The results of XRD show that the lattice parameter a PbTe of PbTe〈In〉/Si and PbTe〈In〉/SiO 2/Si heterostructures is described by nonmonotone function and does not obey the Vegard's law within concentration interval 0.0011⩽ y In⩽0.045.

Effect of solidification rate on the phase structure and electrochemical properties of alloy Zr 0.7Ti 0.3(MnVNi) 2

In this work, the alloy Zr 0.7Ti 0.3Mn 0.4V 0.4Ni 1.2 is selected and prepared through both arc-melting and melt-spinning processes at different solidification rates. The electrochemical tests have indicated that higher solidification rates lead to a higher discharge capacity when the solidification rates were <10 m s −1 and a lower discharge capacity when solidification rates were >10 m s −1. When solidification rates get higher, the cycling stability improves, but the activation property and the high-rate dischargeability of the melt-spun alloy both get worse noticeably. The XRD results indicate that the as-cast alloy and the melt-spun alloys all contains two Laves phases, C14 and C15, but the phase composition and phase abundance of the alloys are quite different from each other. The SEM and EPMA results indicate that the microstructure of melt-spun alloy is a uniform mixture of very fine dendritic and columnar crystalline structures, while the as-cast alloy is of much coarser dendritic crystalline structure with noticeable composition segregation. It is the difference in phase composition, phase abundance, and microstructure that results in the noticeable difference in electrochemical properties.

Synthesis and characterization of La 4BaCu 5O 13+ δ and La 4BaCu 5− xMxO 13+ δ: M=Fe, Co, Ni, Zn

La 4BaCu 5− x M x O 13+ δ : M=Fe, Co, Ni, Zn were prepared by the solid-state route at 1000°C. Solid solution limits of x=1.0(1) [Fe], x=1.1(1) [Co], x=1.56(7) [Ni] and x=0.47(1) [Zn] were determined from XRD and EPMA results. Rietveld refinement of combined XRD/neutron powder diffraction data was carried out on undoped La 4BaCu 5O 13+ δ and x=1 for M=Fe, Co, Ni. For La 4BaCu 5O 13+ δ , which is an oxygen-deficient perovskite, the presence of square planar CuO 4 groups, disordered over the Cu(2) sites with CuO 5 square pyramids, is indicated, together with, for δ<0, either square planar CuO 4 or square pyramidal CuO 5 and octahedral CuO 6 groups disordered over the Cu(1) sites. For M=Fe, Ni, there was preferential substitution onto the one-fold octahedral site; for M=Co, substitution took place on both the one-fold octahedral and four-fold square pyramidal sites.

The effect of solidification rate on the microstructure and electrochemical properties of Co-free [formula omitted] alloys

In this work, Fe-containing Co-free Ml(NiMnAlFe) 5 alloy samples were prepared by both arc-melting and melt-spinning processes at different solidification rates, and tested for electrochemical performance. The electrochemical tests indicated that higher solidification rates led to a better cycling stability, but lower discharge capacity and high-rate dischargeability. The X-ray diffraction results indicated that the as-cast alloy and the melt-spun alloys were both of the CaCu 5 -type structure single phase, but the lattice constants of the alloys were varying. The scanning electron microscope and EPMA results indicated that the microstructure of melt-spun alloy formed at the relative lower solidification rate (5 m/ s) was of very fine dendritic structure and that for the alloy formed at a relative higher solidification rate (15 m/ s) was of cellular structure, and both had a more homogeneous composition than the as-cast alloy, which had a typical dendrite structure with noticeable composition segregation. The Co-free MlNi 4.1 Mn 0.35 Al 0.3 Fe 0.25 prepared by melt-spinning at 15 m/ s rate is a promising candidate for low-cost electrode alloy.