Effects Of Changes In Composition Research Articles

Preparation and properties of chalcogenide glasses in the GeS2–Sb2S3–CdS system

Abstract In searching for new kind of photoelectric material, chalcogenide glasses in the GeS 2 –Sb 2 S 3 –CdS system have been studied and their glass-forming region was determined. The system has a relatively large glass-forming region that is mainly situated along the GeS 2 –Sb 2 S 3 binary side. Thermal, optical and mechanical properties of the glasses were reported and the effects of compositional change on their properties are discussed. These novel chalcogenide glasses have relatively high glass transition temperatures ( T g ranges from 566 to 583 K), good thermal stabilities (the maximum of deference between the onset crystallization temperature, T c , and T g is 105 K), broad transmission region (0.57–12 μm) and large densities ( d ranges from 2.99 to 3.34 g cm −3 ). These glasses would be expected to be used in the field of rare earth doped fiber amplifiers and nonlinear optical devices.

Effect of compositional changes on corrosion of steel at short exposure times in marine mud

The present study has been carried out to investigate the corrosion behaviour of carbon–manganese steels in chloride environments at short exposure times. The influence of copper phosphorous microalloying on the corrosion resistance of carbon–manganese steels has been also addressed. The microalloying of copper and phosphorus in the steel has shown significant improvement in corrosion resistance, indicating greater hindrance to anodic dissolution. Laser Raman spectroscopy studies have shown the presence of different oxyhydroxides on the samples of carbon–manganese and copper phosphorous microalloyed steels. It was confirmed that the presence of predominant and adherent δ-FeOOH resulted in a slower dissolution rate for copper and phosphorous microalloyed steel.

Oxidation of MCrAlY coatings on Ni based superalloys

Industrial gas turbine engines used for power generation generally employ Ni based superalloys for the turbine blades. The operating conditions for these blades are very arduous with high temperatures (>900°C) leading to oxidation and corrosion. Therefore in order to increase the service life of components, coatings are employed which allow the use of Ni based superalloys at higher temperatures and therefore more efficient engines. These systems are very complicated and in order to understand coating performance and service life, many modelling approaches have been utilised. However, there is still a lack of understanding of the thermally grown oxide (TGO) with regards to its chemistry, microstructure, adhesion strength and mechanical properties. Therefore a more detailed understanding of the TGO would be useful for both empirical and computational modelling. The effect of compositional changes in the MCrAlY bond coat and their effect on the TGO have been studied. Two different MCrAlY coatings have been examined after aging at representative operation temperatures. A number of analytical techniques have been used including, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray and electron backscattered diffraction. A dual beam scanning electron microscope has also been utilised for both TEM sample preparation and microstructural evaluation. These techniques will allow a better understanding of the microstructure of the TGO, ultimately leading to improved predictions of coating behaviour and service life.

Electrical properties of some Y2O3 and/or Fe2O3-containing lithium silicate glasses and glass-ceramics

The ac electrical properties of some lithium silicate glasses and glass-ceramics containing varying proportions of Y2O3 and/or Fe2O3 were measured to investigate their electronic hopping mechanism. There is a clear variation of these properties with composition. The obtained results were related to the concentration and role of Y2O3 and/or Fe2O3 in the lithium silicate glass structure. In crystalline solids the electrical properties data obtained were correlated to the type and content of the mineral phases formed as indicated by X-ray diffraction analysis (XRD). The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 30 Hz–100 KHz and the effect of compositional changes on the measured properties was investigated. The measurements revealed that the electrical responses of the samples were different and complex. The addition of Y2O3 generally, decreased the ac conductivity, dielectric constant and dielectric losses of the lithium silicate glasses. The addition of Fe2O3 in Y2O3-containing glasses increases the conductivity, while, the dielectric constant and dielectric losses were found to be decreased. However, the addition of Fe2O3 instead of Y2O3 led to decrease the ac conductivity and increased their dielectric constant and dielectric losses. The obtained data were argued to the internal structure of the lithium silicate glass and the nature or role-played by weakness or rigidity of the structure of the sample. Lithium disilicate-Li2Si2O5, lithium metasilicate-Li2SiO3, two forms of yttrium silicate Y2Si2O7 & Y2SiO5, iron yttrium oxide-YFeO3, lithium iron silicate-LiFeSi2O6 and α-quartz phases were mostly developed in the crystallized glasses. The conductivity of the crystalline materials was found to be relatively lower than those of the glass. At low frequency, as the Y2O3 content increased the ac conductivity, dielectric constant and dielectric loss data of the glass-ceramics decreased. However, the addition of Fe2O3 to the Y2O3 containing glass-ceramic led to increase the conductivity. The addition of high content of Fe2O3 instead of Y2O3 in the glass ceramic led to increase the ac conductivity.

Modeling of Asphaltene Precipitation Due to Changes in Composition Using the Perturbed Chain Statistical Associating Fluid Theory Equation of State

Asphaltene precipitation and deposition adversely affect production assurance and are key risk factors in assessing difficult environments such as deepwater. Deposition in the near well bore regions and production tubulars implies high intervention and remediation costs. Prediction of asphaltene precipitation onset represents a challenge for the flow assurance area. The applicability of the PC-SAFT equation of state model to predict asphaltene onset of the precipitation in live oils is demonstrated by studying representative examples from field experiences with asphaltene problems during production. These examples not only validate the proposed model but also confirm the theory that asphaltene phase behavior can be explained based only on molecular size and van der Waals interactions. The PC-SAFT equation of state estimates also properties such as densities and bubble points of live oil systems using a minimum number of real components and “realistic” pseudocomponents. The amount and composition of the asphaltene precipitated phase is also determined as part of the equilibrium calculations. This paper presents experimental observations and simulation results at reservoir conditions using the PC-SAFT equation of state on the effect of compositional changes in live oils caused by two common processes in the oil industry: oil-based-mud (OBM) contamination and reinjection of associated gas. In the first case, the downhole oil samples can be contaminated with OBM, causing laboratory measurements of the bubble point and asphaltene precipitation to be different from the reservoir fluid. In the second case, the reinjection of gas into the field increases the gas−oil-ratio (GOR) of the oil. The addition of gas into the oil can cause asphaltene precipitation and deposition due to the increase of light components that reduces asphaltene solubility. Asphaltenes in this example are treated as both monodisperse and polydisperse pseudocomponents. From the obtained results, it can be concluded that the live oil modeled using the PC-SAFT equation of state properly predicts the asphaltene phase behavior under these compositional changes. The PC-SAFT equation of state model is a commercially available, proven tool.

Effect of composition changes on properties and defect structure of crystalline Sm-doped ZrO2

Polymorphous structure, electrical conductivity, absorption coefficient, refractive index, and mechanical characteristics of crystalline system ZrO2 + x Sm2O3 (x = 4–43 mol %) is investigated. Vickers microhardness is investigated by the well-known quasi-static indentation method. Plastic microhardness and the effective elastic modulus are studied by the depth-sensing indentation technique. Special attention is devoted to the ordered defect fluorite structure, pyrochlore phase Sm2Zr2O7, observed for x = 43 mol %. Potential applications of the investigated system are discussed.

AN XPS STUDY OF AMORPHOUS THIN FILMS OF MIXED OXIDES In2O3–SnO2 SYSTEM DEPOSITED BY CO-EVAPORATION

XPS core level measurements are used to observe the surface changes in amorphous thin films of mixed oxides In 2 O 3– SnO 2 system deposited by co-evaporation. The effects of changes in composition (in mol%), film thickness, substrate temperature, post-deposition annealing, and etching with Ar+ ions on the binding energies of In (3 d ) and Sn (3 d ) doublets in mixed oxides In 2 O 3– SnO 2 system are presented. XPS core level In (3 d ) and Sn (3 d ) spectra at various compositions exhibit the characteristic 3 d 5 / 2 and 3 d 3 / 2 doublets. The positions of the In (3 d ) and Sn (3 d ) lines are those as expected for In 3+ ions in In 2 O 3 and Sn 4+ ions in SnO 2. The initial decrease in binding energy with an increase in Sn content in In 2 O 3 lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The increase in binding energy above the critical Sn content (10 mol% SnO 2) is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The decrease in binding energy with film thickness is caused by the increase in free-carriers density, which is generated by oxygen vacancy acting as two electrons donor. The decrease in binding energy with a substrate and annealing temperatures is due either to the severe deficiency of oxygen, which deteriorates the film properties and reduces the mobility of the carriers or to the diffusion of Sn atoms from interstitial locations into the In cation sites and the formation of indium and tin species of lower valence states so that the In 3+ and the Sn 4+ oxidation states may be changed to the In 2+ and the Sn 2+ oxidation states respectively. The new oxidation states, In 2+ and Sn 2+, formed due to ion etching and annealing the samples can be attributed to the internal electron transfer from oxygen 2p to the In 5s and Sn 5s levels both in In 2 O 3 and SnO 2.

THE IR STUDY OF AMORPHOUS THIN FILMS OF MIXED OXIDES In2O3–SnO2 SYSTEM

The IR spectra of thin amorphous films of mixed oxides In 2 O 3– SnO 2 system have been studied in the spectral range 4000–400 cm-1 by Fourier transform infrared technique. The effects of changes in composition, film thickness, substrate temperature and annealing on the IR absorption bands are observed. A shift in frequency and intensity of the bands with varying preparation parameters and an increase in ordering at higher annealing temperatures are observed in the infrared curves. Some new peaks appear, which reveal the presence of lower valency states both in In 2 O 3 and SnO 2. The disappearance of bands at higher annealing temperatures is assigned to the removal of point defects in which oxygen plays an important role. The shift in band frequency with an increase in (i) the Sn content is attributed to the incorporation of Sn 4+ ions in the In 2 O 3 lattice, (ii) the film thickness is attributed to the large concentration of donor centers, (iii) the substrate temperature is attributed to the increase in diffusion of Sn atoms from interstitial locations into the In cation sites, and (iv) the annealing temperature is attributed to the oxygen vacancies and indium interstitials.

Tunability and microwave dielectric properties of BaO–SrO–Nd 2O 3–TiO 2 ceramics

Ferroelectrics such as barium–strontium titanates (BSTO) and Mg-doped BSTO are well known as promising candidates for the application in microwave tunable devices including phase shifters, filters, and others operating at microwave frequencies. In this study new bulk ceramics based on BaTiO 3 (BTO)–SrTiO 3 (STO) with addition of BaNd 2Ti 4O 12 (BNT) solid solution was investigated. The phase correlations, size, and nature of boundaries between phases were studied using scanning electron microscopy (SEM). The effect of compositional change on the unit cell parameters of the perovskite phase, microwave dielectric properties, and tunability under DC field had been studied. The materials with dielectric constant ∼320–700, Qf = 1950–3000 GHz at 3.5 GHz and tunability ∼8.0–31.7% at E = 1 V/μm were achieved.

Correlation on compositional change with crystal structure and optical property of CdS thin films grown by femtosecond pulsed laser

The effect of compositional change with the crystal structure and optical property of CdS films synthesized by femtosecond pulsed laser deposition has been studied. The results indicate that growth temperature played an important role on compositional change, crystal structure and optical properties of the CdS films. And the compositional segregation of the CdS films could be drawn from the selective evaporation of sulfur from the film surface as a result of heating up the substrates.

Effect of compositional changes on the structure and properties of alkali-alumino borosilicate glasses

The effect of replacing BaO by SrO or Al2O3 by MgO on the structure and some physical properties of the glasses of the system Li2O-B2O3-(SrO)BaO-(MgO)Al2O3-SiO2—containing TiO2 have been investigated. Fourier transform infrared (FTIR) spectroscopy revealed that the addition of SrO at the expense of BaO gives no changes in the main structural building units. The addition of MgO instead of Al2O3 decreases the fraction of BO3 and increases the fraction of BO4 groups. Dilatometric measurements showed that the thermal expansion coefficients (α-values) were increased by gradual addition of SrO or MgO instead of BaO or Al2O3, respectively, however the transformation (Tg) and softening (Ts) temperature values of the glasses were decreased. The density was found to decrease as SrO/BaO or MgO/Al2O3 replacements increased. The conductivity, dielectric constant and dielectric loss (dielectric constant × loss tangent) of the glasses were investigated using the frequency response in the interval 200 Hz-100 KHz and the effect of compositional change on the measured properties was investigated. Measurements showed that the electric responses of samples were different and complex. The addition of SrO instead of BaO generally, increases the conductivity, dielectric constant and dielectric losss of the glasses. Increasing the MgO at the expense of Al2O3, the conductivity and dielectric constant of the glasses were decreased. However, the dielectric losss was increased. The electrical properties were found to be factors that are able to distinguish the various electrical parameters as a result of the change in composition. The obtained data were correlated to the internal structure of the glasses and the nature and role played by glass forming cations.

Modelling the Effect of Compositional Changes in Transient Flow of Gas Condensate Reservoirs

Modelling the Effect of Compositional Changes in Transient Flow of Gas Condensate Reservoirs

Investigations on hydrogen storage over Li–Mg–N–H complex—the effect of compositional changes

Three Li–Mg–N–H samples with LiH/Mg(NH 2) 2 molar ratio of 1/1, 2/1 and 3/1 were prepared and investigated. Remarkable differences were observed in the temperature dependence of hydrogen desorption, subsequent absorption and P-C isotherms over these three samples. It was revealed that the reduction of LiH content induced the desorption of ammonia. Higher content of LiH pushes the hydrogen desorption to a higher temperature region.

Surface Segregation in SnO2–Fe2O3 Nanopowders and Effects in Mössbauer Spectroscopy

AbstractSnO2–Fe2O3 nanopowders prepared by the polymeric precursor method were studied by combined conventional and high‐resolution techniques. The powders treated at 500 °C were analyzed by EDS local probe associated with HRTEM to directly detect surface segregation of Fe ions onto SnO2 nanoparticles over a broad range of concentrations. The segregation of these ions controls the system microstructure by changing the surface energies and acting as nucleation sites for the formation of a Fe oxide phase (magnetite) at high Fe concentrations. A technologically interesting core–shell‐type particle structure, with a magnetic shell and semiconductor core, was observed for the first time. The influence of the segregated Fe ions in Mössbauer spectra is also addressed as a new proposal for the interpretation of the effects of composition changes in both the bulk and at the interface of particles. In this proposal, the two observed sites in Mössbauer spectra would be independently related to bulk‐substituted and surface‐segregated Fe ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Lasing properties of Pr3+-doped tellurofluorophosphate glasses

Spectroscopic and laser properties of Pr3+ ions incorporated into tellurofluorophosphate (TFP) glasses have been investigated from the absorption and emission spectra recorded in the UV–VIS–NIR regions. The intensities of the 4f–4f induced electric dipole transitions are parametrized in terms of Judd–Ofelt intensity parameters Ωλ (λ=2, 4, 6) from the experimentally determined oscillator strengths. Various spectroscopic parameters such as electric dipole linestrengths (Sed), magnetic dipole linestrengths (Smd), radiative transition probabilities (AR), radiative lifetimes (τR), branching ratios (βR) and integrated absorption cross-sections (σa) for stimulated emission were evaluated for various excited levels of Pr3+ ions. The effect of compositional changes of the glasses on the optical properties of Pr3+ ions has been discussed. These calculated intensity parameters (Ωλ) and radiative lifetimes (τR) are compared with other Pr3+ doped host materials. From the magnitudes of the stimulated emission cross-sections (σe), branching ratios (βR), the most potential laser transitions are identified and utility of these glasses as laser active materials is discussed.

Scanning Aggregation Phenomena in Crude Oils with Density Measurements

Aggregation phenomena involved in asphaltene precipitation under ambient conditions are studied in an effort to correlate them with the asphaltene deposition. The effects of compositional changes on the aggregation and the flocculation onset of asphaltene have been investigated for different crude oils. Density measurements of the system {crude oil + toluene + n‐heptane} were used to assess changes of aggregation occurring in a crude oil under influence of the chemical or physical factors. Obtained results made it possible to determine the asphaltene flocculation onset of several crude oils. Density changes of mixtures were used to quantify the changes of the molecular packing of the oil components. It was found that n‐heptane increase the molecular packing of crude oils but also of deasphalted crude oils. Toluene increases the molecular packing also. Therefore, aggregation phenomena occurring in crude oils concern not only asphaltenes but also other components of the oil.

Tears in health and disease.

A brief review of normal tear function and changes resulting from disease. The factors contributing to normal tear physiological function are considered, and the effect of changes in composition, as reported in the literature, is surveyed, with emphasis on the physical performance of the tears. Major classes of tear tests which would reveal functional changes are listed. Where possible, changes of measurable functions in disease are described. Gaps in our current knowledge are indicated. Many techniques exist for examination and assessment of both normal and disease tears, but further development is needed to adapt some of these to clinical situations, and to make them more specific diagnostic tests.

Asphaltene Stability in Crude Oil and Aromatic SolventsThe Influence of Oil Composition

Oil composition changes during production, transportation, and processing of crude oils. The effects of compositional changes on asphaltene stability have been investigated for different crude oils, fractionated asphaltenes, and resins with hydrocarbons that act either as asphaltene solvents or flocculating agents. The refractive index of onset mixtures is used to quantify solution properties with respect to asphaltene stability, and the results are compared to predictions of an asphaltene solubility model. Asphaltene aggregates in depressurized crude oil samples can be explained in terms of natural flocculants in the oil. The effects on asphaltene stability of adding aromatic solvents to an oil have been investigated. Mixtures of asphaltenes and resins show predictable changes in asphaltene stability. The results of this study have important implications for asphaltene stability testing using dilute oil solutions and can be interpreted without any assumptions about special interactions that are often assumed to exist between asphaltenes and resins.

Influence of Solution Composition on the Formation of Crystalline Scales

AbstractScale formation is a difficulty encountered with water containing ions of sparingly soluble salts that can readily precipitate on heat transfer surfaces in evaporative concentration operations. Scale formation, hindering the heat transfer process, increases specific energy consumption and operating costs and causes frequent shut down of the evaporator for cleaning. The effects of changes in composition of the solution due to evaporation and CO2 release on the formation of crystalline scales in seawater evaporators are studied. A model that predicts the CO2 release is presented. The carbonate system in the salt solution on its whole flow path through the evaporator and the scaling (crystallization) tendency are described. Simulation results for different process configurations are shown and the differences are discussed, particularly with regard to the incrustation tendency.

Effect of composition changes on the structural relaxation of a binary mixture.

Within the mode-coupling theory for idealized glass transitions, we study the evolution of structural relaxation in binary mixtures of hard spheres with size ratios delta of the two components varying between 0.5 and 1.0. We find two scenarios for the glassy dynamics. For small size disparity, the mixing yields a slight extension of the glass regime. For larger size disparity, a plasticization effect is obtained, leading to stabilization of the liquid due to mixing. For all delta, a decrease of the elastic moduli at the transition due to mixing is predicted. A stiffening of the glass structure is found as is reflected by the increase of the Debye-Waller factors at the transition points. The critical amplitudes for density fluctuations at small and intermediate wave vectors decrease upon mixing, and thus the universal formulas for the relaxation near the plateau values describe a slowing down of the dynamics upon mixing for the first step of the two-step relaxation scenario. The results explain the qualitative features of mixing effects reported by Williams and van Megen [Phys. Rev. E 64, 041502 (2001)] for dynamical light-scattering measurements on binary mixtures of hard-sphere-like colloids with size ratio delta=0.6.