Effects Of Variations In Composition Research Articles

Development of non-stoichiometric SrBi4+2xTi4O15+3x (−0·04 ≤x≤ 0·04) ceramics

The non-stoichiometric compositions of Bi layered structural SrBi4Ti4O15 ferroelectric materials (SrBi4+2xTi4O15+3x, x=−0·04, −0·02, 0, 0·02 and 0·04) are investigated as the main precursors to find the influence of Bi2O3 content on the characteristics of SrBi4Ti4O15 ceramics. The effect of compositional variation on the sintering and the dielectric characteristics of SrBi4Ti4O15 ceramics are deduced with the aid of X-ray diffraction patterns, scanning electron microscopy observation and dielectric–temperature curves. From the scanning electron microscopy observations, the SrBi3·92Ti4O14·88 and SrBi3·96Ti4O14·94 ceramics reveal two phased grain growth, bar typed and irregularly disc typed grains coexist; the other SrBi4+2xTi4O15+3x ceramics reveal irregularly disc typed grains. From the X-ray patterns, the Bi2Ti2O7 and SrTiO3 phases are observed in the SrBi3·92Ti4O14·88 and SrBi3·96Ti4O14·94 ceramics. Except the SrBi3·96Ti4O14·94 ceramics, the other SrBi4+2xTi4O15+3x ceramics have revealed a splitting peak in the (119) plane. It is also shown that the compositional variation has apparent influences on the grain morphologies, the bulk densities, the Curie temperatures and the maximum dielectric constants of SrBi4+2xTi4O15+3x ceramics.

Seismic structure of Precambrian lithosphere: New constraints from broad-band surface-wave dispersion

Depth distributions of seismic velocities and their directional dependence (anisotropy) in the crust and mantle beneath cratons yield essential constraints on processes of their formation and evolution. Despite recent progress in mapping the lateral extent of cratonic roots around the globe, profiles of seismic velocities within them remain uncertain. In this study we employ a novel combination of waveform-analysis techniques and measure inter-station Rayleigh- and Love-wave phase velocities in broad period ranges that enable resolution from the upper crust to deep upper mantle. Sampling a selection of 10 Archean and Proterozoic locations, we derive new constraints on the isotropic and radially anisotropic seismic structure of Precambrian lithosphere. Shear-wave speed V S is consistently higher in the lithosphere of cratons than in the lithosphere of Proterozoic foldbelts. Because known effects of compositional variations in the lithosphere on V S are too small to account for the difference, this implies that temperature in cratonic lithosphere is consistently lower, in spite of sub-lithospheric mantle beneath continents being thermally heterogeneous, with some cratons underlain, as we observe, by a substantially hotter asthenosphere compared to others. Lithospheric geotherms being nearly conductive, this confirms that the stable, buoyant lithosphere beneath cratons must be substantially thicker than beneath younger continental blocks. An increase in V S between the Moho and a 100-150 km depth is consistently preferred by the data in this study and is present in seismic models of continents published previously. We argue that this is largely due to the transition from spinel peridotite to garnet peridotite, proposed previously to give rise to the “Hales discontinuity” within this depth interval. The depth and the width of the phase transformation depend on mantle composition; it is likely to occur deeper and over a broader depth interval beneath cratons than elsewhere because of the high Cr content in the depleted cratonic lithosphere, as evidenced by a number of xenolith studies. Seismic data available at present would be consistent with both a sharp and a gradual increase in V S in the upper lithosphere (a Hales discontinuity or a “Hales gradient”). The V S profile in the upper mantle lithosphere is not shaped by the temperature distribution only; this needs to be considered when relating seismic velocities to lithospheric temperatures. Radial anisotropy in the upper crust is observed repeatedly and indicates vertically oriented anisotropic fabric ( V SH < V SV); this may yield a clue on how cratons grew, lending support to the view that distributed crustal shortening with sub-vertical flow patterns occurred over large scales in hot ancient orogens. In the lower crust and upper lithospheric mantle, radial anisotropy consistently reveals horizontal fabric ( V SH > V SV); the fabric can be interpreted as a record of (sub-)horizontal ductile flow in the lower crust and lithospheric mantle at the time of the formation and stabilisation of the cratons. We also find indications for radial anisotropy below 200 km depth, corroborating recent evidence for anisotropy in the asthenosphere beneath cratons due to current and recent asthenospheric flow.

Effect of compositional variations on the optical properties of Sb–Ge–Se thin films

Compositional dependences of the optical and physical properties of as-deposited amorphous SbxGe25−xSe75 films (x = 0, 5, 10, 15 and 20 at%), prepared by thermal evaporation, have been studied. The refractive index, n, and film thickness, d, have been determined from the upper and lower envelopes of the transmission spectra, measured at normal incidence, in the spectral range from 400 to 2500 nm. An optical characterization method for uniform films based on Swanepoel's ideas has been employed, and it has allowed us to determine the average thickness, , and the refractive index, n, of the films, with accuracies better than 1%. It has been found that the refractive index of the SbxGe25−xSe7 samples increases with increasing x, over the entire spectral range, which is related to the increased polarizability of the larger Sb atomic radius 1.38 Å compared with the Ge atomic radius 1.22 Å. The dispersion parameters such as E0 (single-oscillator energy) and Ed (dispersive energy) were discussed in terms of the single-oscillator Wemple–DiDomenico model. The absorption coefficient, α, and therefore the extinction coefficient, k, have been determined from the transmittance and reflectance spectra in the strong absorption region. The optical energy gap is derived from Tauc's extrapolation and a decrease in with increasing Se content. Finally, in terms of the chemical bond approach, cohesive energy has been applied to interpret the decrease in the glass optical gap with increasing Sb content in SbxGe25−xSe75.

Geochemical investigation of weathering processes in a forested headwater catchment: mass-balance weathering fluxes

AbstractGeochemical research on natural weathering has often been directed towards explanations of the chemical composition of surface water and ground water resulting from subsurface water-rock interactions. These interactions are often defined as the incongruent dissolution of primary silicates, such as feldspar, producing secondary weathering products, such as clay minerals and oxyhydroxides, and solute fluxes (Meunier and Velde, 1979). The chemical composition of the clay-mineral product is often ignored. However, in earlier investigations, the saprolitic weathering profile at the South Fork Brokenback Run (SFBR) watershed, Shenandoah National Park, Virginia, was characterized extensively in terms of its mineralogical and chemical composition (Piccoli, 1987; Pochatila et al., 2006; Jones et al., 2007) and its basichydrology. O’Brien et al. (1997) attempted to determine the contribution of primary mineral weathering to observed stream chemistry at SFBR. Mass-balance model results, however, could provide only a rough estimate of the weathering reactions because idealized mineral compositions were utilized in the calculations. Making use of detailed information on the mineral occurrence in the regolith, the objective of the present study was to evaluate the effects of compositional variation on mineral-solute mass-balance modelling and to generate plausible quantitative weathering reactions that support both the chemical evolution of the surface water and ground water in the catchment, as well as the mineralogical evolution of the weathering profile.

Hydrogen separation and purification in membranes of miscible polymer blends with interpenetration networks

This study demonstrates the successful implications of blending technique cum chemical modification for the fabrication of high performance polymeric membranes for gas separation applications. The effect of variation in composition on miscibility and microstructure, gas permeability and selectivity of blend membranes is investigated. It is found that augmentation in PBI composition results in enhancement in gas separation performance of membranes which is attributed mainly to the effect of diffusivity selectivity. Analysis of the microstructure of membranes confirms the variations in chain packing density, d-spacing and segmental mobility of polymer chains as a result of blending. Separation performance of membranes is further ameliorated through chemical modification of blend constituents. Modification of PBI phase with p-xylene dichloride brings about slight improvements in selectivity performance, especially for H2/CO2 and H2/N2. In contrast, the selectivity of membranes is improved significantly after cross-linking of Matrimid phase with p-xylene diamine. The results indicate that higher tendency of Matrimid toward cross-linking reaction contributes more in controlling the transport properties of membranes through diffusion coefficient by increase in chain packing density and diminishing the excess free volumes. Results obtained in this study reveal the promising features of developed membranes for gas separation applications with great potential for hydrogen separation and purification on industrial scale.

Thermal and rheological behavior of ultrafine fly ash filled LDPE composites

AbstractThe specimens containing different volume fractions of ultrafine fly ash in LDPE were prepared with the help of two roll mixing mill and the hot‐plate compression‐molding machine. Thermal and rheological properties were evaluated using DSC and parallel‐plate rotational‐rheometer. The effect of composition variation on melt enthalpy, crystallinity, shear viscosity, shear stress and first normal stress difference was studied and reported here. The addition of ultrafine fly ash in LDPE decreased the melt enthalpy of the specimen. Slight decrease in the crystallinity of LDPE was observed on addition of fly ash. The shear stress as well as the shear viscosity both increased with the addition of ultrafine fly ash in LDPE. Two regions of shear thinning were observed at 200°C for fly ash filled LDPE. The first normal stress difference (N1) reduced with fly ash content and with the increased temperature. The values of N1 remained almost invariable at low shear region however a proportional increase was observed beyond the shear stress of 10 kPa. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Effect of Compositional Variations on Field-Induced Phase Transition of (Pb,La)(Zr,Sn,Ti)O3 Antiferroelectric Ceramics

(Pb,La)(Zr,Sn,Ti)O 3 ceramics near AFE-FE phase boundary were studied as a function of composition, electric field and temperature. Below the critical temperature T FE − AFE of FE to AFE phase transition, the electric field-induced FE state can maintain metastable state when electric field was removed. As temperature increased over T FE − AFE , the metastable FE recovered to AFE. As Ti content increased, the structure of unpoled PZST ceramics changed from tetragonal AFE phase to rhombohedral FE phase, the temperature T FE − AFE increased, while the switching field E AFE − FE and E FE − AFE decreased. The forward switching field E AFE − FE and hysteresis Δ E were observed to be dependent on T FE − AFE and Tc, respectively.

Grain structure and homogeneity of pulsed laser treated surfaces on Al-aerospace alloys and FSWs

The effect of pulsed excimer laser surface treatment, on typical Al-aerospace alloys and friction stir weld substrates, has been studied. A thin <10 μm deep surface layer can be achieved, where the majority of the re-solidified material does not exhibit phase separation, and has a higher level of homogeneity relative to the substrate material. However, due to the extremely short melt times, the layer is not as homogeneous as has previously been claimed and melted constituent particles leave solute rich trails throughout the layer. The treated layer also contains a series of second phase bands that are the result of a transient region, caused by the growth front from each pulse initially accelerating through speeds below ultimate stability, combined with the effects of composition variations within the liquid from the solute trails. The layer was further found to develop a grain structure that was very sensitive to that of the substrate and the presence of Al 3Zr β′ dispersoids within the treated alloy, which can alter the grain structure from coarse epitaxial, to very fine columnar.

Compositional effects on the shock-compression response of alumina-filled epoxy

Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties, resulting in complex behavior during shock compression and release. A previous study examined the shock properties of a particular composition in some detail. In the current study, the effects of compositional variations on shock properties were examined. Planar-impact experiments producing states of nearly equal strain were conducted to investigate the effects of changes in the size and shape of alumina particles, and in the total volume fraction of alumina. Laser interferometry and wave timing were used to obtain transmitted wave profiles, Hugoniot states, and release wave velocities. In addition, wave profiles and velocities were obtained in “thin-pulse” experiments that examined the combined effects of compression and release properties in different compositions. Changes in the size and shape of alumina particles were found to have little effect except in the viscous spreading of wave profiles during shock compression. Increasing the volume fraction of alumina resulted in steadily increasing Hugoniot states, wave rise times, and release wave velocities. An important observation was that differences between release wave and shock wave velocities increased significantly as the alumina loading was increased. Consequences of this effect were evident in the thin-pulse experiments, which showed that increased alumina loading resulted in stronger wave attenuation.

Determination of micellar system behavior in the presence of salt and water-soluble polymers using the phase diagram technique

The application of micellar systems has been growing during the last years because of their importance in various practical situations. Continued development of their application is necessary. If the principal economic interest of microemulsions is for some time enhanced oil recovery, the following also have significant applications such as pharmaceutical preparations, painting, and products for engine lubrication. The effect of variation in composition of anionic surfactants (α oleifin sulfonates) and the presence of a water-soluble charged polymer (Xanthan gum) and an uncharged polymer [poly (ethylene glycol)] on the phase behaviour of pseudo- ternary systems of water-oil surfactants was investigated. Several domains were observed when the composition of surfactants and cosurfactants (e.g., pentanol) in a mixture is varied. The appearance of these domains in the phase diagram has been attributed to the formation of different Winsor systems.

A linear theory of physical properties in inhomogeneous sediments and its application to relative paleointensity determination

A linear model is developed to study the effect of variations in composition upon extensive physical properties of continuously deposited sediment sequences. By applying this model to natural and synthetic remanence acquisition, an optimal method of relative paleointensity determination is derived. The sediment is regarded as a mixture of independent components, each of which behaves uniformly in depth with respect to its physical properties. The concentration of each sediment component is assumed to independently vary linearly with an external signal. Remanence acquisition in each sediment component is linear in external field and concentration of the component. It is demonstrated that in this case the ideal normalization procedure for relative paleointensity determination is to divide the natural remanent magnetization by a biased normalizer. Common magnetic cleaning techniques improve the relative paleointensity record by removing nonlinear behavior and by reducing the bias to the normalizer. The proposed linear sediment model for any extensive physical property clearly separates the influences of concentration of sediment components from those of environmental signals. It thus opens many possibilities for extensions to nonlinear models.

Structural, dielectric and magnetic properties of NiCuZn ferrite grown by citrate precursor method

Fine powders of Ni 0.6 − x Cu x Zn 0.4Fe 2O 4, where 0 ≤ x ≤ 0.4 was prepared by the citrate precursor method. The powders were calcined at 600 °C for a duration of 1 h and sintered at 900 °C for 3 h. The effect of compositional variation on structural, dielectric and magnetic properties of the Cu substituted NiZn ferrite was investigated. X-ray diffraction measurements confirmed the formation of single-phase cubic spinel structure at such low temperature of calcinations and sintering. A maximum density of 4.7 g/cm 3 was obtained for the Cu substituted ferrite. The grain sizes were estimated from the SEM micrographs. The addition of copper promoted grain growth, resulting in increase in grain size. Curie temperature, however, was understandably lowered with the increase in Cu content. A saturation magnetization value of 92 emu/g was obtained for the composition x = 0.2. This value is higher than that reported for ferrites prepared by the conventional ceramic method. Ferrite with Cu concentration of x = 0.4, showed the highest value of initial permeability.

Diffusion and Permeation of Deuterium in EUROFER97: Effect of Irradiation and of Implanted Helium

Permeability, diffusivity, and solubility of deuterium in the low-activation martensitic stainless steel EUROFER97 were derived from measurements of gas permeation in the transient and steady-state regimes at temperatures from 100 to 350°C and at pressures from 2 × 103 to 2 × 105 Pa. The specimens were used in four conditions to investigate the effect of irradiation-induced defects: standard annealed condition, preirradiated with protons, implanted with helium, and implanted plus annealed to produce helium bubbles. In general, displacement defects as well as implanted helium tend to decrease permeation and diffusivity. Permeation and diffusion measurements were also performed under simultaneous irradiation, showing no net effect if the slight temperature increase due to irradiation is taken into account. Diffusion measurement of implanted hydrogen gave equal or slightly lower values than gas permeation, which is in qualitative agreement with results from preirradiated specimens. Trapping parameters are derived by a detailed comparison to a saturable-trap model. Results are compared to previous studies on 7%Cr F82H and 11%Cr MANET-II steels, and effects of compositional variations are indicated.

Thermodynamic prediction of thixoformability in alloys based on the Al–Si–Cu and Al–Si–Cu–Mg systems

Most commercial semi-solid processing (of which thixoforming is one type) utilises the conventional casting alloys A356 and A357. There is, however, a demand to widen the range of alloys, including those with higher performance which tend to show poor characteristics for thixoforming. Thermodynamic calculation packages, such as MTDATA, provide a tool for predicting thixoformability. Here, the effects of compositional variations, in particular the effect of added copper on the thixoformability of alloy A356 and the effect of added silicon on the thixoformability of alloy 2014, have been investigated using MTDATA thermodynamic and phase equilibrium software combined with the MTAL database. Criteria for thixoformability are identified and a range of alloy compositions based on Al–Si–Cu and Al–Si–Cu–Mg evaluated in relation to these criteria. Compositions which satisfy these criteria include: 308 (Al–5.5Si–4.5Cu); 319 (Al–6Si–3.5Cu); 238 (Al–10Cu–4Si–0.3Mg); 355 (Al–5Si–1.3Cu–0.5Mg); 2014 based alloys Al–4.4Cu–0.5Mg–(4–6)Si; and a range of alloys (7.5 ⩽ Si + Cu ⩽ 9 and 1.5 ⩽ Si/Cu ⩽ 2.33) and alloys (9 < Si + Cu ⩽ 10 and Si/Cu = 1.5) based on the Al–Si–Cu–Mg system.

Organization of Amphiphiles, Part VII: Effect of Variation of Composition and Salt on the Phase Behavior of Some Ethoxylated Surfactants

The effect of variation in composition of the emulsifier and presence of salt on the phase and clouding behavior of a pseudo‐ternary system of the type H2O‐oil‐emulsifier has been investigated at 300±1 K. The emulsifier constitutes polyoxyethylated alkyl phenol/polyoxyethylated alkyl ethers and isobutanol in different mole ratios. Large numbers of domains are observed when composition of surfactant and cosurfactant in emulsifier is varied. Appearance of these domains in the phase diagram has been attributed to the formation of different type of organized assemblies. The electrical conductivity of BL‐9‐isobutanol(1∶1)‐hexane‐2% brine versus various compositions of the emulsifier is found to increase slowly with the addition of water, followed by rapid increase to a plateau leading to a sigmoidal plot. This significant change in electrical conductivity for small change in weight fraction of water is attributed to the percolation transition. The three arms of the electrical conductivity plot are suggested due to W/O to O/W microemulsion transition through bicontinuous structure, and the bicontinuous phase area is delineated. The ordering of water molecule around surfactant molecules has been arrived at through electrical conductivity and cloud point measurements.

Effect of compositional variation in sintering behaviour of Al–Zr oxide composites

Sintering behaviour of sequentially varied metal ion concentration in Al x –Zr 100− x ( x = 0, 10, 20, …, 100) based oxide composites were studied using conventional solid state sintering process in the temperature range 1400–1600 °C. Critical experimental parameters like green density, sintering time and temperature were varied to achieve higher sintered product. Systematic studies of densification, structural, microstructural, hardness and shrinkage properties were carried out to understand the real sintering process development mechanism involved in this oxide matrix during initial, intermediate and final stage of sintering. Interesting development in connection with microstructural and phase evolution, pore-grain network in relation to physical densification and hardness behaviour are analysed and it is noted that compositional variation in Al x –Zr 100− x oxide matrix ( x = 0, 10, 20, …, 100) produces structural (monoclinic to tetragonal) phase separation (complete or partial) at different sintering temperatures (1400–1600 °C). Long heating schedule (20 h) at high sintering temperature (1600 °C) promotes highest percentage of monoclinic–tetragonal transformation at x = 30 in Al x –Zr 100− x oxide composites.

Effect of compositional variations on log responses of igneous and metamorphic rocks. II: acid and intermediate rocks

Abstract An extensive data-set of petrophysical down-hole measurements exists for boreholes drilled into continental crystalline crust. We selected boreholes covering a range of different types of plutonic rocks and gneisses in amphibolite or high-grade metamorphic rocks. According to Serra’s concept of electrofacies, a specific set of log responses should characterize one rock type. Here, we concentrate on the detection of compositional variations between rock types. Bulk composition of the protoliths influences the mineralogical composition of the metamorphic rock, and we demonstrate how this impacts on the down-hole measurements. Integration of logging data with geochemical core data and mineralogical descriptions allows the calibration of the log responses to rock types. The relationship of the log responses with core data shows a remarkably good correlation, and diagnostic trends are detected. From the logs, potassium and neutron porosity are particularly helpful in distinguishing different types of gneisses and igneous rocks with respect to their protoliths. The proportions of amphibole/pyroxene, mica + K-feldspar and feldspar + quartz in the rocks seem to control the direction of correlation in a cross-plot, i.e. positive or negative, depending on increasing or decreasing mineral proportions. This is true for all boreholes, and a generalized classification scheme could be developed for these crystalline rocks.

Effect of compositional variation on the synthesis of magnesite–chrome composite refractory

Magnesite–chrome composites have been prepared by utilizing sintered magnesite and friable chrome ore in presence of titania as additive. Three types of batch compositions containing 5% Cr 2O 3, 18% Cr 2O 3 and 30% Cr 2O 3 have been selected for developing mag–chrome composites. The aggregates were developed by first vibro milling the raw materials and then additives were incorporated in wt.% along with 5% PVA solution as binder to the different batches. It was then properly mixed by fluidized bed mixer and after sieving in 20-mesh BS sieve briquettes were formed uniaxially at a pressure of 100 MPa. The briquettes were first air dried and subsequently oven dried at 110±5 °C for 24 h. Finally, the green briquettes were fired at 1700 and 1750 °C in electrically program controlled muffle furnace. The physical properties as well as thermo-mechanical properties and microstructural studies of the sintered aggregates have been evaluated. The common feature observed in the microstructures is the exsolution of spinel phase in magnesia grains. The hot properties of the composites are superior when the Cr 2O 3 content is increased to 30%. Additives played a significant role in improving the bulk density and strength.

The effect of Cu substitution on the microstructure and magnetic properties of MnFe2O4 ferrite

The effect of compositional variation on grain size and porosity of Mn1 − xCu x Fe2O4 ferrite, where x = 0.0, 0.25, 0.50, 0.75, 1.00, prepared by standard ceramic method are reported. From microstructure analysis it follows that porosity increases with the Cu concentration where as coercivity increases up to x = 0.50. Above x = 0.5 the decrease in coercivity is explained on the basis of Neel's mathematical model treating the demagnetizing influence of non-magnetic material in cubic crystals. The coercivity, varies inversely with the grain size upto x = 0.5. The decrease in coercivity above x = 0.5 with grain size can be correlated with the inter-granular domain wall movement because of large porosity.

The effect of Zn substitution on microstructure and magnetic properties of Cu 1− xZn xFe 2O 4 ferrite

The effect of compositional variation on porosity, magnetic properties, and grain size of Cu 1− x Zn x Fe 2O 4 ferrite, where x=0.0,0.25,0.50,0.75, 1.00, prepared by standard ceramic method are reported. From microstructure analysis, it follows that both porosity, p and coercivity, H c decrease with the substitution of Zn. The coercivity, H c is inversely proportional to grain size while the curie temperature T c increases from 538 to 560 K. The decrease in H c with grain size can be correlated fairly well with Neels’ mathematical model treating the demagnetizing influence of non-magnetic material in mixed ferrites.