Chemical Composition Gradient Research Articles

Processing of PM aluminium alloy based gradient materials

Gradient materials were manufactured from powder mixes of aluminium RAl-1 and aluminium alloy Al17Si5Fe3Cu1.1Mg0.6Zr. The preforms were cold pressed with alloy concentrations ranging from 0% to 100%, at 20% intervals, and then closed-die hot forged at 490°C. From these materials preforms, with a continuous gradient of chemical composition, were produced. The effects of chemical composition gradient on flow of the material and on mechanical properties in compression were examined. Compression strengths ranged from 470 to 800MPa. Closed-die plastic working and extrusion of two-layer specimens Al–Al alloy were investigated. Specimens were prepared as two – parallel layer and coat – core type. The LARSTRAN/Shape program was used to model the flow of multi-layer materials during forming. The correlation with experimental data demonstrates the usefulness of the modified program for the analysis of the flow of materials type coat – core.

Effect of plasma nitriding on adhesion strength of CrTiAlN coatings on H13 steels by closed field unbalanced magnetron sputter ion plating

A duplex treatment, i.e. plasma nitriding followed by closed field unbalanced magnetron sputter ion plating, is used to strengthen the bonding of CrTiAlN coatings to H13 steels in the paper. A nitride layer is first formed on H13 steel samples by plasma nitriding and then two chromium transition layers are prepared on the surface of the nitrided H13 steels using closed field unbalanced magnetron sputter ion plating. The adhesion between the substrate and the coating is evaluated using the Rockwell indentation and scratch tests. Meanwhile, the composition, phase structure and the morphologies for CrTiAlN coatings as well as the worn surfaces are characterized by EDX, SEM and XRD, respectively. Dry sliding wear behavior of the duplex-treated H13 steels is analyzed by using ball-on-disk wear tests compared with those of untreated and plasma-nitrided H13 steels. The results show that the adhesion strength and wear resistance for duplex-treated coatings increase significantly due to a gradient-hardness support, one favorable gradient of chemical composition, an intermediate hardening effect and a diffusion reaction of the nitrided layer-coating interface.

On assessment of processing variables on copper–tin functionally graded alloys produced by incremental melting and solidification process

The present work is concerned with the ability of the incremental melting and solidification process to be used in a controlled way to produce functionally graded materials in industrial environments. For this purpose, the influence of the main process parameters, namely relative mould/coil rate and melt temperature, is evaluated in relation to the obtained final component chemical composition gradient. Several graded components of Cu–Sn alloys were produced. The effect of the process parameters on the final component gradient was quantified. It was verified that both the melt temperature and the relative mould/coil rate play a similar role in final component chemical composition gradient. Predictive equations for the gradient, namely the extension of chemical composition gradient zones, are proposed based on the two studied variables.

Distinct mantle sources for Pliocene–Quaternary volcanism beneath the modern Sierra Nevada and adjacent Great Basin, northern California and western Nevada, USA

Latest Pliocene to Quaternary, mildly alkaline, mafic to intermediate volcanic activity extends in a swath from the Lake Tahoe region in the eastern Sierra Nevada across the western Great Basin to the Battle Mountain area, Nevada. From west to east, the volcanic centers exhibit a dramatic gradient in chemical and isotopic composition. Centers situated in or adjacent to the Sierra Nevada have incompatible element and isotopic compositions consistent with an old, subduction-modified lithospheric mantle source (87Sr/86Sr > 0.7045; 143Nd/144Nd < 0.5127; δ18O > +6.5‰). Mafic volcanic centers east of the Sierra Nevada, in the Carson Sink and in the Buffalo Valley region, have an intraplate incompatible element and isotopic signature (87Sr/86Sr < 0.7045; 143Nd/144Nd > 0.5127; δ18O < +6.5‰) consistent with an asthenospheric mantle source. Earlier 20–3 Ma arc volcanism in the Sierra Nevada also tapped the old lithospheric mantle source along with the mantle wedge, indicating that the lithospheric mantle source existed well prior to the onset of Tertiary arc volcanism and probably prior to Mesozoic igneous activity of the Sierra Nevada. Thus, the lithospheric mantle beneath the Sierra Nevada has remained a geochemically consistent, fertile, fusible source for at least the past 20 m.y. Old lithospheric mantle likely still exists east of the Sierra Nevada, but lithospheric thinning and/or exhaustion of fusible components inhibit its melting, such that during the Quaternary, melting could only occur in the asthenosphere.

The radial distribution of dust species in young brown dwarf discs

We present a study of the radial distribution of dust species in young brown dwarf disks. Our work is based on a compositional analysis of the 10 and 20 micron silicate emission features for brown dwarfs in the Taurus-Auriga star-forming region. A fundamental finding of our work is that brown dwarfs exhibit stronger signs of dust processing in the cold component of the disk, compared to the higher mass T Tauri stars in Taurus. For nearly all of our targets, we find a flat disk structure, which is consistent with the stronger signs of dust processing observed in these disks. For the case of one brown dwarf, 2M04230607, we find the forsterite mass fraction to be a factor of ~3 higher in the outer disk compared to the inner disk region. Simple large-scale radial mixing cannot account for this gradient in the dust chemical composition, and some local crystalline formation mechanism may be effective in this disk. The relatively high abundance of crystalline silicates in the outer cold regions of brown dwarf disks provides an interesting analogy to comets. In this context, we have discussed the applicability of the various mechanisms that have been proposed for comets on the formation and the outward transport of high-temperature material. We also present Chandra X-ray observations for two Taurus brown dwarfs, 2M04414825 and CFHT-BD-Tau 9. We find 2M04414825, which has a ~12% crystalline mass fraction, to be more than an order of magnitude brighter in X-ray than CFHT-BD-Tau 9, which has a ~35% crystalline mass fraction. Combining with previous X-ray data, we find the inner disk crystalline mass fractions to be anti-correlated with the X-ray strength.

A 2D surface morphology–composition gradient panel for protein-binding assays

We designed a two-dimensional (2D) morphology–composition gradient panel, which has a gradient in surface morphology at constant chemical composition along its length and a gradient in surface chemical composition without change of surface morphology in the orthogonal direction. The panels, which exhibit a 2D gradient in surface wettability, were fabricated by thermolysis of parylene-C followed by oxygen-plasma treatment for various times. As a demonstration study, binding of three different biotinylated serum proteins (B-IgG, B-A, and B-TF) to the 2D panel was investigated. The 2D gradient panels will facilitate development of optimized binding surfaces for various biotechnological applications.

X-ray spectra of wind-driven bubbles with chemical gradients

AbstractAs a tool helping to interpret diffuse X-ray emission of PNe, and as a supplement to our RHD simulations, we have started to construct a grid of theoretical X-ray spectra of wind-blown bubbles with temperature and density profiles according to thermal conduction theory. We investigate how the X-ray spectra depend on chemical composition (e.g. H-rich vs. H-deficient) and how temperature and abundance determinations reflect gradients of temperature and chemical composition within the bubbles. These synthetic models shall allow to quickly perform detailed parameter studies without the need for dedicated hydrodynamical simulations. We report on ideas and goals.

Real-Time Measurements of Spontaneous Potential for Inflow Monitoring in Intelligent Wells

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 135146, ’Real-Time Measurements of Spontaneous Potential for Inflow Monitoring in Intelligent Wells,’ by M.D. Jackson, SPE, M.Y. Gulamali, E. Leinov, J.H. Saunders, and J. Vinogradov, Imperial College London, prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed. Spontaneous-potential (SP) signals are generated during hydrocarbon production because of gradients in the water-phase pressure (relative to hydrostatic), chemical composition, and temperature. Measurements of SP during production, taken with permanently installed downhole electrodes, could be used to detect water that is encroaching on a well while the water is several tens to hundreds of meters away. Introduction SP measurements, logged before production or injection using wireline tools, are primarily electrochemical (EC) in origin. Contrasts in chemical composition between formation and drilling fluids give rise to “junction” or “diffusion” potentials in permeable beds, while the exclusion of (typically) negative ions from the pore space of fine-grained rocks (e.g., mudstones and shales) results in “membrane” potentials. Together, these EC potentials typically dominate the SP log, although in some cases, electrokinetic (EK), or streaming, potentials, which arise from gradients in fluid pressure (relative to hydrostatic), also may contribute. However, gradients in fluid pressure, chemical composition, and temperature also will be present during hydrocarbon production, particularly during waterflooding or steamflooding where colder or hotter water of a chemical composition different from that of the formation brine is injected into the reservoir. Consequently, if the casing is either nonmetallic or is insulated electrically from the formation, SP signals will be observed during production. This study characterized the magnitude of these SP signals to determine if their measurement, using permanently installed downhole electrodes, might be useful in monitoring fluid flow. SP Components The SP acts to maintain overall electro-neutrality when a separation of electrical charge occurs in response to gradients in pressure, chemical composition, or temperature. In a water-wet reservoir rock, charge separation occurs at the mineral/water interface because the water reacts with the mineral surfaces to leave an excess of (typically) negative charge on the mineral surface and an excess of positive charge in the water adjacent to the mineral surface. This arrangement of charges at the mineral/water interface is known as the electrical double layer. The negative charge on the mineral surface is immobile, but some of the excess positive charge in the adjacent water is mobile and will move with the fluid. If the water is subjected to a pressure gradient, which causes it to flow relative to the mineral surfaces, then some of this positive charge is transported with the flow. The net excess of positive charge moving with the flow gives rise to a so-called streaming current. To balance this streaming current, a conduction current is established and the electrical potential required to maintain this conduction current is the EK, or (more specifically) streaming, potential. The term EK is used here for consistency with the terminology used to describe the EC and thermoelectric (TE) potentials.

Characteristics of the functionally graded coating fabricated by plasma transferred arc centrifugal cladding

Iron-based powders were deposited on the internal wall of a cylinder by means of plasma transferred arc centrifugal cladding. The as-fabricated coating was a functionally graded triple layer coating with microstructures varying from hypereutectic firstly to near eutectic, and then to hypoeutectic structures along the radial direction. Significant enrichment of carbides [M7C3 and M23(C, B)6] was observed in the inner layer. The centrifugal force was responsible for the chemical composition gradient which resulted in the microstructures gradient. Theoretical analysis revealed that Cr, C and B atoms moved toward the inner layer whereas Fe, W and Mo atoms moved toward the outer layer under the effect of centrifugal force, which was confirmed by the quantitative analysis and line-scan profile. Wear resistance of the inner layer of the coating was fairly higher than that of the substrate.

Nanometer‐scale cathodoluminescence analysis of GaAs and its application to the assessment of laser diode

AbstractWe studied steep gradients of both chemical composition and residual stress in a Si‐doped GaAs blocking layer of a laser diode by means of spectrally and spatially resolved cathodoluminescence (CL) spectroscopy. Using a low‐energy electron beam as an excitation source for the CL emission, a spatial resolution in the sub‐micron scale could be achieved. The knowledge of local doping concentration, local stress state, and their distribution on the nanometer scale is crucial in diode design since lasing characteristics and near‐field width. Emphasis was placed in making quantitative the CL spectroscopic assessments in GaAs by means of a set of preliminary calibrations, regarding both probe size and material composition. These procedures enabled extracting from the CL spectra and quantitatively mapping values of both carrier concentration and residual stress in the diode device. The visualization of those parameters into highly spatially resolved maps (i.e., recorded with nanometer‐scale resolution) required the implementation of a spectroscopic algorithm that was purposely built up in this study and preliminarily validated according to the shown sets of calibration procedures.

Continuous synthesis of CdSe xTe 1−x nanocrystals: Chemical composition gradient and single-step capping

A capillary microreactor was firstly utilized to continuously synthesize near-infrared emitting CdSe x Te 1− x nanocrystals (NCs). By using trioctylphosphine oxide and trioctylphosphine as the solvents for anion precursor as well as oleic acid and oleylamine as the solvents for cation precursor, high quantum yield zinc-blend CdSe x Te 1− x NCs with a chemical composition gradient internal structure and tunable emission from 634 to 783 nm were synthesized. Thus, the nonlinear relationship between the composition and the emission energies were verified. Moreover, a facile single-step capping approach was developed by using the dissolution of cadmium oxide and free element sulfur in oleic acid, and a very thin CdS shell was successfully epitaxial grown around the as-prepared CdSe x Te 1− x NCs to enhance the photostability. After the capping process, the core/shell structured CdSe x Te 1− x /CdS NCs remained 15–40% of their initial PL intensity after 3 h of illumination.

Design and fabrication of compositionally graded inorganic oxide thin films: Mechanical, optical and permeation characteristics

Different types of inorganic oxide films composed of a chemical composition gradient single layer were designed, fabricated and characterized. Compositionally graded thin films were created by power-controlled co-sputtering of alumina (Al2O3) and silica (SiO2) at room temperature, allowing the structural design of the film to be tailored at the nanometer scale. Two distinct graded thin films were fabricated: one with a compositionally asymmetric structure consisting of a SiO2-rich bottom interface and a Al2O3-rich top surface, and the other with a compositionally balanced sandwich structure consisting of both the top surface and bottom interface rich in SiO2 and a core rich in Al2O3 (referred to as SGS for ‘sandwich graded structure’). Smoothly graded thin films without interfacial boundaries were verified by Auger electron spectroscopy profiles. X-ray photoelectron spectroscopy demonstrated that the Al2O3/SiO2 graded structures consisted of Si–O and Al–O bonds, as well as Al–O–Si bonds in the transition layer. Neat Al2O3 or SiO2 and their graded ones were all investigated for their mechanical, optical and permeation properties. A SGS thin film presented the best mechanical stability (i.e., about three times improved film toughness of a neat Al2O3 single layer), demonstrating that balanced internal stresses and alternating bonding structures, achieved via a graded structure without interfaces, are crucial for enhancing mechanical stability. Furthermore, neat and graded thin films exhibited the similar level of optical transmittance and the permeation properties for the graded films were well matched with the behaviors of mechanical stability.

Effect of temperature on the polarization distribution in BTS functional gradient ceramics

The effect of the chemical composition gradient in barium titanate-stannate (BTS) piezoelectric ceramic on the depth distribution of the effective pyroelectric coefficient was investigated. A correlation between the coordinate dependence of polarization in the sample and the polarization temperature is demonstrated.

Single step synthesis of CdSeS nanorods with chemical composition gradients

We report a simple method of fast synthesis of CdSeS nanorods with chemical composition gradients. The CdSeS nanorods were prepared by single-step addition of Se and S source mixture into Cd precursor solution at elevated temperatures. The size of the nanorods can be tuned by changing the S/Se feed molar ratio. As a result of the reactivity difference between Se and S precursors, the nanorods have a core/shell structure with chemical composition gradients, leading to enhancements of their photoluminescence quantum yield and photostability, which make them attractive for use in optoelectronic devices and bio-labeling.

Display of Solid-State Materials Using Bipolar Electrochemistry

We report the formation and characterization of one-dimensional chemical composition gradients of CdS on Au surfaces using bipolar electrodeposition. When an external electric field is applied across an electrically floating Au electrode immersed in a bipolar electrochemical cell, a position-dependent interfacial potential difference is generated along the length of the Au. This potential gradient can be used to induce variations of chemical composition within thin films electrodeposited onto the Au bipolar electrode (BPE). Thin films formed by bipolar electrodeposition represent continuous one-dimensional solid-state material libraries and were screened using resonance Raman microscopy and Auger electron spectroscopy. As predicted from simple thermodynamic considerations, we observed three distinct deposition zones scanning from the cathodic pole to the midpoint of the BPE: (i) CdS+Cd, (ii) stoichiometric CdS, and (iii) elemental S. Bipolar electrodeposition can be used to generate material libraries rapidly and without direct electrical contact to the substrate using extremely simple instrumentation.

Fracture behavior of laser-clad joint of Stellite 21 on AISI 316L stainless steel

Present paper describes microstructural and mechanical characterization of laser-clad composite joint made of Stellite 21 and type 316L stainless steel (SS). The study has been broadly performed on two kinds of laser-clad specimens viz. (i) involving direct deposition of Stellite 21 on SS and (ii) involving gradient in chemical composition across substrate/clad interface. Both kinds of specimens exhibited nearly similar tensile strength, which was higher than that of SS in the interface region. Inter-dendritic carbides provided low energy fracture path in laser-clad deposits of Stellite 21. Both direct and graded interfaces of laser-clad specimens exhibited superior fatigue strength than the SS substrate. Instrumented impact testing brought out distinct difference in the mode of crack propagation across direct and the graded clad specimens. In contrast to initiation-controlled brittle crack propagation across the interface region in “direct clad” specimens, crack propagation across “graded interface” was marked with significant plastic deformation.

Elemental diffusion and segregation processes in partially ionized solar plasma

Although diffusion is usually associated with equalizing of the chemical composition, the pressure and temperature gradients inside the Sun cause elemental diffusion segregation. While light hydrogen is flowing up to the solar envelope, helium and heavier elements are settling down to the core. The target of our simulation is an accurate estimation of the settling rate in solar plasma during the course of solar evolution. The rate of helium depletion in the envelope is a key parameter of the solar evolution and depends on position and conditions around the base of the convective mixing zone. The rate of heavy element settling is sensitive to the degree of ionization and interaction with the radiation flux. We estimate the effect of ion ionization on the settling rate for several heavy elements up to iron in the framework of the LTE assumption and the thermodynamic calculation according to SAHA-S EOS.

Analysis of zonal shrinkage in alloy steels

Thermal behaviour of the solidifying steel structure is important for understanding of the defects during ingot solidification. During solidification and cooling, most metals shrink. As a consequence in upper part of solid ingot, pores and pipes of typical shapes and size are formed. Forming of pipes is closely related to the casting and solidification processing parameters. In the present paper the influence of liquid temperature, chemical composition and temperature gradient on the shrinkage intensity are investigated. The ratio of the pipe depth to total ingot height as a criterion of the pipe size is used. The values of the temperature gradients on the base of the numerical model solidification are obtained. The experimental measurements of temperature change have been carried out on laboratory steel ingot. The results by numerical model are compared with the experimental ones and showed a good agreement.

Structural and optical properties of Mg yNi 1– yH x gradient thin films in relation to the as-deposited metallic state

Thin Mg y Ni 1− y H x films with a gradient in chemical composition are investigated by optical spectrophotometry, dc resistivity and X-ray diffraction measurements before and after exposure to hydrogen. In the metallic state crystalline Mg 2Ni is present for 0.6 ≤ y ≤ 0.8 and coexists with amorphous Mg and/or Ni. The hydride state is mainly characterized by the presence of Mg 2NiH 4 around the stoichiometric [Mg]/[Ni] = 2 composition and some MgH 2 on the Mg-rich side. The abrupt microstructural changes found in the as-deposited metallic state around the Mg–Mg 2Ni eutectic point correlate well with the compositional dependence of the optical properties in the hydride state. We conclude that the formation of the hydride depends directly on the detailed nature of the metallic parent phase. Furthermore, we demonstrate that high-throughput compositional screening via fiber-optic spectrophotometry is useful for hydride identification. When no structural long-range order is present, this provides a new tool for the search for hydrogen storage materials.

On the ability of producing copper–silver functionally graded alloys by using an incremental melting and solidification process

An incremental melting and solidification process (IMSP) has been used in order to obtain components with controlled gradient in chemical composition along one direction of the piece. The composition variation was externally induced by a sequential addition of different materials. To better assess the process of the chemical composition gradation the tests were performed in castings with and without externally induced chemical composition variation. The level of macro-segregation was also assessed in the different experiments. Results demonstrated that a substantial gradual variation of chemical composition and metallurgical properties, along the component, may be obtained.