Concentration Gradients Of Elements Research Articles

Low‐Energy Ion‐Scattering Spectroscopy of Modified Silicate Glasses

Low‐Energy Ion‐Scattering (LEIS) spectroscopy is a technique with a unique sensitivity to the elemental composition of the top atomic layer of a solid surface. LEIS measurements of ternary silicate glasses modified with Na2O, Cs2O, CaO, and BaO show that the compositions of the as‐cast (melt) surface and the in‐vacuum fracture surface often differ. While the as‐cast surface is usually depleted of alkali ions (Na+ or Cs+) compared to the nominal (batch) glass composition, there is often strong accumulation of the same mobile cations on the fresh fracture surface. Depth profiles obtained by sputter etching reveal elemental concentration gradients normal to the glass surface. The final concentrations often fail to reach the nominal glass composition, suggesting the likely presence of preferential sputtering effects and thereby the distortion of the measured concentration gradient. At present, the lack of reliable standards and preferential sputtering effects in the LEIS of multicomponent glasses limit somewhat the absolute chemical composition and structural information that can be obtained with this otherwise unique and powerful method of surface analysis.

Development of microstrain in aged lithium transition metal oxides.

Cathode materials with high energy density for lithium-ion batteries are highly desired in emerging applications in automobiles and stationary energy storage for the grid. Lithium transition metal oxide with concentration gradient of metal elements inside single particles was investigated as a promising high-energy-density cathode material. Electrochemical characterization demonstrated that a full cell with this cathode can be continuously operated for 2500 cycles with a capacity retention of 83.3%. Electron microscopy and high-resolution X-ray diffraction were employed to investigate the structural change of the cathode material after this extensive electrochemical testing. It was found that microstrain developed during the continuous charge/discharge cycling, resulting in cracking of nanoplates. This finding suggests that the performance of the cathode material can be further improved by optimizing the concentration gradient to minimize the microstrain and to reduce the lattice mismatch during cycling.

Coarsening behavior of lamellar orthorhombic phase and its effect on tensile properties for the Ti–22Al–25Nb alloy

This study quantitatively investigated the coarsening behavior of the lamellar O and its effect on tensile properties of the Ti–22Al–25Nb alloy. The results indicated that the growth of lamellar O was sensitive to the temperature and holding time. The alloy with different lamellar thicknesses (from 0.16 to 1.1μm) can be obtained via varying the aging temperature and holding time. At the initial growth stage, the thickness of the lamellar O increased rapidly by diffusional process because of the high storage energy and different concentration gradients of elements in different phases (O/B2). Due to the consuming of storage energy and the decreasing of concentration gradient with the holding time, the growth rate decreased. The growth exponent and activation energy were both increased as the aging temperature and the holding time increased respectively. The room temperature (RT) and 650°C 0.2% yield strength (YS) and elongation (EL) agree well with the Hall–Petch relationship and those can be adjusted in the range of 560–1045MPa and 510–950MPa for RT and 650°C 0.2% YS respectively and 3–8% and 8–14.5% for RT and 650°C EL via varying the thickness of lamellar O.

Single Second Laser Annealed CuInSe2 Semiconductors from Electrodeposited Precursors as Absorber Layers for Solar Cells

Cu(In,Ga)Se2 (CIGSe) is a polycrystalline absorber layer in thin film solar cells with solar conversion efficiencies exceeding 20%. High temperature annealing for periods of minutes to hours is currently required to convert amorphous or nanocrystalline precursor material into high quality Cu(In,Ga)Se2 absorber layers. In this work, we perform the critical annealing step, using a 1064 nm laser, on electrodeposited precursor layers containing Cu, In, and Se, for times of 0.3–60 s thus synthesizing CuInSe2 absorber layers. An annealing time of 1 s is found to be sufficient to remove elemental concentration gradients in the bulk of the layer and to increase the average implied crystallite size (crystal coherence length, as determined by X-ray diffraction, XRD). Therefore the rate-determining step in producing higher quality layers with short annealing times is the rate of grain growth and not atomic diffusion. Optoelectronic analysis of the absorber layers revealed p-type doping with improved radiative recombination compared to the precursors. Laser annealed CuInSe2 layers did not produce working photovoltaic devices. This is first attributed to a loss of Se that occurs during laser annealing, resulting in detrimental substoichiometric quantities of Se in the absorber. Second, the likely presence of a thick surface layer of the CuIn3Se5 phase is expected to detrimentally impact device performance. These findings must be addressed if annealing times of the CuInSe2 absorber layer are to be reduced to seconds.

Modeling and Simulation of Spray Forming of Clad Deposits with Graded Interface Using Two Scanning Gas Atomizers

A three-dimensional shape model based on a surface coordinate tracking method has been developed for clad deposits with graded interface which are spray formed using two scanning gas atomizers. The calculation of element distributions in the deposits has been incorporated into the shape model. On this basis, the deposit shape and the element distributions in the deposit have been simulated. It shows that the scanning mode of the atomizers and the degree of overlapping of the two sprays play important roles in the spray forming of clad deposits. A concentration gradient of chemical elements in the deposits can be achieved under proper processing conditions. Finally, the modeling and simulation of the spray forming of clad deposits have been validated by experimental investigations.

The hyporheic zone composition of a mining-impacted stream: Evidence by multilevel sampling and DGT measurements

The importance of the hyporheic zone in influencing stream solute loads and stream ecosystems has been increasingly recognised. The hyporheic zone physicochemical composition of a stream stretch of the Rookhope Burn, a tributary of the River Wear in the North Pennines, UK, affected by historical mining of Pb ore, was characterised at two contrasting flow and temperature regimes. Vertical element concentration gradients were obtained using multilevel samplers down to a depth of 40cm below the water–sediment boundary. Additional in situ Diffuse Gradients in Thin films (DGT) measurements of surface water and pore water were obtained.Circumneutral pH and oxidising conditions characterised the hyporheic zone of the study reach, composed of coarse-textured bed sediments. The surface hyporheic zone (top 15–20cm) was dominated by the chemistry of the overlying water, while interactions with the solid phase were important for some elements in the deeper section of the hyporheic zone.Manganese was attenuated in the hyporheic zone as shown by SEM analysis of Mn-rich grain coatings from the bed sediment. Fine resolution data obtained through the use of the DGT probe deployed in the sediment at one sampling location, showed localised loss in Mn and Zn concentrations at 1.5–4.5cm below the water–sediment interface. There was clear evidence for hyporheic pore water enrichment in Pb, which was unaffected seasonally, while Zn was greater in the summer sampling. These temporal variations of the hyporheic zone composition warrant consideration when accounting for the contribution of disperse inputs to mining impacted catchments, highlighting the need for hyporheic zone studies taking into account differences in seasons.The significance of the observed sediment-scale hyporheic processes on the reach-scale geochemical mass balance was estimated by using surface water geochemical loading calculations. Water metal mass balance from four previous sampling events indicated a constant loss of Mn load, a continuous gain of Pb load and a more temporally variable loss of Zn load for a 700m stream stretch which included the study site. These results closely agreed with the present observations at the stream bed sediment scale, supporting the importance of hyporheic dynamic solute exchanges in affecting surface water quality for the study stream.

Wettability of Ni/(TixMe1 − x)(CuNv) System (Me = Mo, W)

Wetting tests for Ni on TiN, Ti(C0.7N0.3), and various (TixMe1−x)(CuNv) compounds were carried out at 1823K (Me denotes Mo or W). The contact angles decreased with increasing Me content, and the contact angle for (TixMo1−x)(C0.7N0.3) was smaller than that for (TixW1−x)(C0.7N0.3) for the same Ti/Me ratio. It was found that molybdenum and tungsten are effective in improving the wettability of Ni/(TixMe1−x)(CuNv) and that molybdenum is more effective than tungsten. The wettability of Ni/(TixMe1−x)(C0.7N0.3) is better than those of Ni/(TixMe1−x)(C0.55–0.65N0.45–0.35) compounds. Cross sections of the samples after wetting tests were observed by XRD and SEM/EDS. No new phase was observed, and microstructures could be divided into three regions: a Ni-rich region, mixed region, and substrate region. The solubility increased with the Me content. The element concentration gradients around the interfacial region decreased with an increase in the Me content. The contact angle decreased with an increase in the solubility and the element concentration gradients. It is suggested that the wetting mechanism of the Ni/(TixMe1−x)(CuNv) system is reactive wetting accompanied by a dissolution.

The surface microstructure of TiC-(Ti,W)C-WC-Ni cermets sintered in a nitrogen atmosphere

The effects of nitrogen and a solid-solution carbide on the surface microstructure of TiC-(Ti,W)C-WC-Ni cermets were investigated. The binder enrichment layer with the cubic carbide was observed at the surface, the formation of which is attributed to the concentration gradient of nitrogen and constituent elements. This tendency is found to decrease as the dissolution rate increases when nano-sized TiC was employed. Coarsening behavior and the formation of a discrete layer were studied as a function of (Ti 0.93W 0.07)C carbide content and nitrogen pressure. The results were interpreted in terms of the relative thermodynamic stability of the carbide phases in the system.

Characterisation of metal droplets sampled during top lance blowing

Laboratory trials were performed in an induction furnace to study droplet formation during lance blowing. Oxygen was blown on a molten iron bath consisting of iron alloyed with carbon and silicon. Iron droplets were collected using a specially designed sampler. The average iron droplet composition and the oxide layer thickness were determined using scanning electron microscopy combined with energy dispersed spectroscopy. In addition, the concentration gradient of elements was determined using electron probe microanalysis. It should be noted that a special technique had to be developed in order to prepare the droplet sample. The size distribution and composition of the droplets were also determined using the microprobe. The carbon was found to be homogeneously distributed throughout the droplet independently of the size of the droplet. For the experiments using both carbon and silicon it was found that the silicon in most droplets could be found in the periphery of the droplets. It was also found that the tendency was that both the carbon content as well as the silicon content in the droplets decreased with a decreased droplet size. Thus, it was concluded that it is necessary to modify top blown decarburisation processes so that a maximum area between droplet and atmosphere is obtained.

Determination of concentration gradients in bone tissue generated by a biologically degradable magnesium implant

Rare earth element (REE) concentration gradients in bone were quantitatively investigated by LA-ICP-MS using different reference materials and ablation patterns. For line ablations a matrix effect was observed during calibration procedures. The maximum concentration of REE in bone around a biologically degradable magnesium alloy implant was ∼200 µg/g after six weeks of implantation compared to a background concentration of 3–4 µg/g. No further accumulation of degraded REE in bone tissue around the implant was detected after 12 weeks of implantation. PIXE measurements showed an aluminium accumulation in the corrosion zone of the implant. Furthermore, new bone formation was identified by a variable Ca/P-ratio. The Ca/P ratio of the hydroxyapatite as the main inorganic constituent of bone tissue was not reached 12 weeks after implantation, indicating that the replacement of the implant by newly formed bone is still in progress.

Geochemical gradients in soil O-horizon samples from southern Norway: Natural or anthropogenic?

Abstract Forty soil O- and C-horizon samples were collected along a south-to-north transect extending inland for approximately 200 km from the southern tip of Norway. The elements As, Au, Bi, Cd, Cu, Ga, Ge, Hf, Hg, In, Mg, Mn, Mo, Na, Ni, Pb, Sb, Se, V, W, Zn and Zr all show a distinct decrease in concentration in soil O-horizons with increasing distance from the coast. The elements showing the strongest coastal enrichment, some by more than an order of magnitude compared to inland samples, are Au, Bi, As, Pb, Sb and Sn. Furthermore, the elements Cd (median O-/median C-horizon = 31), C, Sb, Ag, K, S, Ge (10), Hg, Pb, As, Bi, Sr (5), Se, Au, Ba, Na, Zn, P, Cu and Sn (2) are all strongly enriched in the O-horizon when compared to the underlying C-horizon. Lead isotope ratios, however, do not show any gradient with distance from the coast (declining Pb concentration). Along a 50 km topographically steep east–west transect in the centre of the survey area, far from the coast but crossing several vegetation zones, similar element enrichment patterns and concentration gradients can be observed in the O-horizon. Lead isotope ratios in the O-horizon correlate along both transects with pH and the C/N-ratio, both proxies for the quality of the organic material. Natural conditions in southern Norway, related to climate and vegetation, rather than long range atmospheric transport of air pollutants (LRT), cause the observed features.

Influence of Potamogeton crispus growth on nutrients in the sediment and water of Lake Tangxunhu

An incubation experiment was performed on Potamogeton crispus (P. crispus) using sediment collected from Lake Tangxunhu in the center of China, in order to determine the effects of plant growth on Fe, Si, Cu, Zn, Mn, Mg, P, and Ca concentrations in the sediments and overlying waters. After 3 months of incubation, Ca, Mg, and Si concentrations in the water column were significantly lower, and P and Cu concentrations were significantly higher than in unplanted controls. The effect of P. crispus growth on sediment pore waters and water-extractable elements varied. Concentrations of Ca, Mg, Si, Fe, Cu, and Zn were significantly higher, and P was significantly lower, than in pore waters of the control. Water-extracted concentrations of Fe, Mg, and Si in the sediments were lower, and P was higher, than in the control. Presence of P. crispus generally enhanced concentration gradients of elements between pore waters and overlying waters but not for P. The growth of P. crispus was associated with an increase in water pH and formation of root plaques, resulting in complex effects on the sediment nutritional status.

Assessment of the impact of a phosphatic fertilizer plant on the adjacent environment using fuzzy logic

AbstractThe impact of a phosphatic fertilizer plant on the adjacent environment was examined. Selected rare earth elements, heavy metals and metalloids were determined in substrates and products, waste by-product, and grass and soil samples. Concentration gradients of elements in grass and soil samples along the southerly and easterly directions were examined and compared with the content of interior soil and grass samples, substrates, and products. Results were compared with available data on soil permissible element concentration levels. Two fuzzy principal component analysis (FPCA) methods for robust estimation of principal components were applied and compared with classical PCA. The efficiency of the new algorithms is illustrated. The investigation explored the impact of the plant on the adjacent environment. The most reliable results, in good agreement with types of samples, were produced using the FPCA-O algorithm

Application of PIXE and PIGE under variable ion beam incident angle to several fields of archaeometry

AbstractFor several years, the specific features of PIXE and PIGE have made them very attractive in the field of archaeometry. Among them, non‐destructivity is one of the most important. The possibility of working under atmospheric pressure is also important because of the very different shapes and sizes of the artefacts concerned. However, these ion beam techniques suffer from the same disadvantage: the information coming from x‐rays or γ‐rays produced at different places along the charged particle path is integrated. That prevents one from taking into account the possible element concentration gradients due to multi‐layered systems or diffusion processes. This paper presents several applications of PIXE and PIGE applied under variable ion beam incident angle. PIGE has been mainly used for studying ancient glass items or glass windows in order to detect or evaluate the glass corrosion process. The examples given for PIGE deal with Roman and Merovingian glass objects and cathedral glass windows and PIXE applications concern studies for resolving the multilayered structure of easel paintings. The set‐up allowing one to perform the measurements should be very stable, the rotation axis should pass through the beam axis and the detector should follow the sample movement. Copyright © 2005 John Wiley & Sons, Ltd.

FIB-SIMS investigation of carbazole-based polymer and copolymers electrocoated onto carbon fibers, and an AFM morphological study

The work presented in this paper reports preliminary results obtained by focused ion beam-secondary ion mass spectroscopy (FIB-SIMS) analysis in the study of micro-sized carbon fiber electrocoated by conjugated-nonconjugated polymers such as poly( N-vinylcarbazole-co-methylthiophene), poly( N-vinylcarbazole-co-vinylbenzene sulfonic acid) and polycarbazole. The aim of this study was to investigate by FIB-SIMS analysis the presence and concentration gradient of certain elements via depth profiling of the coating on selected carbon fibers. The presence of dopant ions together with their gradient of concentration in the coating layer was elucidated as well as the thickness of the copolymer layer electrocoated onto the carbon surface. AFM analysis performed on the electrocoated fibers yielded information regarding the surface morphology and roughness.

Diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase

Residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals. We present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects. In particular, we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements (e.g., Mg), the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension. We show that contrary to intuition, diffusive fluxes of trace elements may be coupled to major element concentration gradients, and ignoring such coupling can lead to incorrect estimates of timescales. We illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a Holocene dacitic lava flow of Volcán San Pedro (Chilean Andes, 36°S). The inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 (30 to 148) yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods.

Nanostructural and nanoelemental analysis of metastable M 3C-type carbides with alloy-rich layer in heat resistant 2Cr-martensitic steel

A combination of structural analysis and analytical investigation by transmission electron microscopy was employed to investigate precipitated carbides on 2Cr-steel. Spectral and image analysis by energy dispersive X-ray spectroscopy (EDS), and energy-filtered images in a transmission electron microscopy revealed compositions of precipitated carbides from both boundaries. The presence of concentration gradient of alloy elements within the precipitated carbide, were shown by EDS and energy-filtering transmission electron microscopy. The results indicate that the rate-controlling process should be governed by not only the diffusion of depletion layer but also that of alloy elements within the carbides. It is therefore necessary to consider these phenomena to model the rate-controlling process, for further discussion of the growth mechanisms of the carbides in steels.

Effect of concentration gradients on nanostructure development during primary crystallization of soft-magnetic iron-based amorphous alloys and its modelling

Proper analysis and modelling of the nanocrystallization process of amorphous alloys requires consideration of the experimentally detected concentration gradients of insoluble elements rejected during nucleation and growth of the primary phase. Crystallization enthalpies ΔH(a → c) and free energies ΔG(a → c) decrease sensitively with the advancement of the transformation due to the redistribution of the rejected elements in the remaining amorphous phase. It is shown that inclusion of the variation of the nucleation frequencies during the transformation process is needed if coherent results are to be obtained from Jonson-Mehl-Avrami-type analyses.

XPS Study of the Segregation of Minor Elements at the Surface of a Commercial Copper10 wt. Nickel Alloy

X-ray photoelectron spectroscopy has been used to examine the effects of industrial reduction treatments on the composition and structure of the topmost layers of a commercial copper–10 wt.% nickel alloy (Cu–10Ni). The surface analytical studies carried out on the as-received alloy show, in addition to the usual surface contamination, the formation of nickel(II) hydrated species and pronounced segregations of additive alloying components. Strong enrichments of minor elements are also observed in the outermost layers of the material. Moreover, metallic copper and nickel-based compounds are homogeneously distributed within the segregants in the surface film. Comparison of the surface composition of samples treated in various controlled-reducing atmospheres with a mechanically cleaned alloy surface gives access to the mechanisms responsible for the segregations. The diffusion of the various chemical species is discussed in terms of oxygen potential, leading to concentration gradients of metallic elements. © 1997 by John Wiley & Sons, Ltd.

XPS Study of the Segregation of Minor Elements at the Surface of a Commercial Copper-10 wt.% Nickel Alloy

X-ray photoelectron spectroscopy has been used to examine the effects of industrial reduction treatments on the composition and structure of the topmost layers of a commercial copper–10 wt.% nickel alloy (Cu–10Ni). The surface analytical studies carried out on the as-received alloy show, in addition to the usual surface contamination, the formation of nickel(II) hydrated species and pronounced segregations of additive alloying components. Strong enrichments of minor elements are also observed in the outermost layers of the material. Moreover, metallic copper and nickel-based compounds are homogeneously distributed within the segregants in the surface film. Comparison of the surface composition of samples treated in various controlled-reducing atmospheres with a mechanically cleaned alloy surface gives access to the mechanisms responsible for the segregations. The diffusion of the various chemical species is discussed in terms of oxygen potential, leading to concentration gradients of metallic elements. © 1997 by John Wiley & Sons, Ltd.