Phase Homogeneity Research Articles

Hydrodynamic and Mass Flow in a Mixing Stirred Tank

The manufacture and development of materials very often involves agitation or mixing. The mixing system of the vessel is always an important aspect of design, because the involved processes (chemical reaction, heat or component transport) need adequate mixing, and phase homogeneity. In our work we propose a mobile of agitation which does not exist in the literature it is the case of a chamfered paddle impeller. The hydrodynamic and mass characteristics of this impeller have been investigated in the case of viscous Newtonian fluids. 2D finite volume based computational fluid dynamics (CFD) simulations have been carried out. It was found that the chamfered paddle impeller could reduce mixing time compared to that obtained by the straight impeller in laminar flow region. The effect of the degree of chamfering impeller on mixing time was also studied and a significant reduction of mixing time was observed.

Controlled synthesis of lead magnesium tantalate

The results of elaborating a method for controlled synthesis of the ferroelectric phase of lead magnesium tantalate having the perovskite structure and distinguished by high phase homogeneity are reported.

Mn in misch-metal based superlattice metal hydride alloy – Part 1 structural, hydrogen storage and electrochemical properties

The structural, gaseous phase hydrogen storage, and electrochemical properties of a series of Mn-modified misch-metal based superlattice metal hydride alloys were investigated in part one of this two-part series of papers. X-ray diffraction analysis showed that these alloys are all multi-phased compositions with different abundances of AB2, AB3, A2B7, AB4, and AB5 phases. Substitution of Ni in the B-site by Mn promotes AB5 phase formation and decreases both gaseous phase and electrochemical capacities due to the reduction in the abundance of main hexagonal A2B7 phase. AC impedance and magnetic susceptibility measurement were employed to characterize the surface of Mn-free and Mn-modified alloys and show deterioration in surface catalytic ability as the Mn-content increases. Mn-modification adversely affected misch-metal based superlattice metal hydride alloy properties such as phase homogeneity, capacity, cycle stability, high-rate performance, and surface reaction.

Characteristic variations of gas-chromatographic retention indices for phases of variable composition

On an example of mixtures of dinonyl phthalate and 2,2′-bis-(2-cyanoethoxy)diethyl ether, it was shown that the dependence of gas-chromatographic retention indices (RIs) on the composition (α) of mixed stationary phases can be both linear and with various abnormalities. These features of the dependence of RI-α can be explained by the existence of areas of homogeneity and disintegration of mixed phases. Another reason for the nonlinearity of the dependence RI-α is that the components of phases of variable composition are expressed in mole fractions, which is typical for polymethylphenylsiloxanes, widely used in contemporary gas chromatography. It is shown that the expression of composition in mass fractions enables the approximation of these dependencies in the homogeneity regions by linear regression equations with sufficient accuracy.

Tuning the Solubility of Copper Complex in Atom Transfer Radical Self-Condensing Vinyl Polymerizations to Control Polymer Topology via One-Pot to the Synthesis of Hyperbranched Core Star Polymers

In this paper, we propose a simple one-pot methodology for proceeding from atom transfer reaction-induced conventional free radical polymerization (AT-FRP) to atom transfer self-condensing vinyl polymerization (AT-SCVP) through manipulation of the catalyst phase homogeneity (i.e., CuBr/2,2'-bipyridine (CuBr/Bpy)) in a mixture of styrene (St), 4-vinyl benzyl chloride (VBC), and ethyl 2-bromoisobutyrate. Tests of the solubilities of CuBr/Bpy and CuBr2/Bpy under various conditions revealed that both temperature and solvent polarity were factors affecting the solubility of these copper complexes. Accordingly, we obtained different polymer topologies when performing AT-SCVP in different single solvents. We investigated two different strategies to control the polymer topology in one-pot: varying temperature and varying solvent polarity. In both cases, different fractions of branching revealed the efficacy of varying the polymer topology. To diversify the functionality of the peripheral space, we performed chain extensions of the resulting hyperbranched poly(St-co-VBC) macroinitiator (name as: hbPSt MI) with either St or tBA (tert-butyl acrylate). The resulting hyperbranched core star polymer had high molecular weights (hbPSt-g-PSt: Mn = 25,000, Đ = 1.77; hbPSt-g-PtBA: Mn = 27,000, Đ = 1.98); hydrolysis of the tert-butyl groups of the later provided a hyperbranched core star polymer featuring hydrophilic poly(acrylic acid) segments.

Expanded phase stability of Gd-based garnet transparent ceramic scintillators

Abstract

Complex study of titanium nano-films prepared by magnetron sputtering

The oxidation of Ti films with thickness from 5 to 100 nm was performed in air at room temperature. The thickness and roughness of metal and oxide layers were determined by neutron and X-ray reflectometry. The thin titanium films were found to be oxidized to a greater depth; than the thick ones. However the metal layer was found to exist even in the thinnest (5 nm) samples, as the direct measuring of electrical resistance of the films has confirmed. The optimal parameters of titanium films utilizable in polarizing coatings of neutron optics were estimated. The AFM data on the microrelief and the phase homogeneity of the Ti nano-film surface were obtained.

Quasi-Solid Semi-Interpenetrating Polymer Networks as Electrolytes: Part III. Probing the Mechanism of Ionic Charge Transport Employing Temperature-Step Electrochemical Impedance Spectroscopy

The correlated ion-transport mechanism and its dependence on microscopic phase separation for a new class of quasi-solid semi-IPN electrolytes is probed in considerable detail using temperature-step electrochemical impedance spectroscopy. The response of electrolyte matrices under alternating current perturbation is comprehensively analyzed using a simulated model fit to extract pertinent information relevant to the phase composition and homogeneity, contribution of each phase, interfacial charge-transfer resistance, phase entanglement zones, bulk relaxation time for ionic hopping mechanisms, coupled segmental motions, rate of site reorganization that dictates successful hopping events, and estimates of ionic transport numbers. The normalized complex plane Nyquist plots (ρ′ versus ρ″) show two well-defined regions for bulk (in mid- and high-frequency regions) and electrode–electrolyte interfacial impedance (in low-frequency regions). Rigorous analysis indicates the presence of three microscopic phases in the matrix bulk (pure poly(ethylene oxide)–polyurethane (PEO-PU), pure poly(ethylene glycol) dimethyl ether (PEGDME), and PEO-PU/PEGDME mixed phase) along with the charge-transfer resistance (Rct) which contribute to the bulk resistance. Spectroscopic plots of complex impedance against frequency (Z″ versus log f) depict Debye peaks, providing an estimate of the bulk relaxation time (τpeak). Profiles depicting the real component of conductivity (σ′(ω)) as a function of frequency (log f) follow a modified universal power law where the simulated fit results reveal vital information on the site relaxation rates, cumulative favorability for successful hopping events, and predominant charge carrier type. The behavior of the dielectric contributions provides insights into the various ion polarization processes dominant in the high-, mid-, and low-frequency windows of the sweep. These trends were further correlated with our prior evaluation of the physico-chemical properties of the semi-IPN matrices to propose a rational physical model for these complex systems.

Probing the A1 to L1 transformation in FeCuPt using the first order reversal curve method

The A1-L10 phase transformation has been investigated in (001) FeCuPt thin films prepared by atomic-scale multilayer sputtering and rapid thermal annealing (RTA). Traditional x-ray diffraction is not always applicable in generating a true order parameter, due to non-ideal crystallinity of the A1 phase. Using the first-order reversal curve (FORC) method, the A1 and L10 phases are deconvoluted into two distinct features in the FORC distribution, whose relative intensities change with the RTA temperature. The L10 ordering takes place via a nucleation-and-growth mode. A magnetization-based phase fraction is extracted, providing a quantitative measure of the L10 phase homogeneity.

Effect of the composition and annealing conditions of precursor films on the structure of thin CuIn1 − x GaxSe2 (0 ≤ x ≤ 0.7) layers

A technique has been developed for the preparation of CuInxGa1 − xSe2 layers through closed-space selenization of precursor films containing intermetallic compounds. We also have produced CuInxGa1 − xSe2 films by selenizing metallic precursor films. Examination of the CuInxGa1 − xSe2 layers by X-ray diffraction, atomic force microscopy, and scanning electron microscopy has shown that the use of inter-metallic precursors offers a number of important advantages: phase purity and homogeneity of CuInxGa1 − xSe2 layers, in combination with good adhesion of the layers to substrates (glass or glass/molybdenum).

Experimental Investigation of the Phase Equilibria in the Al-Mn-Zn System at 400°C

Al-Mn-Zn ternary system is experimentally investigated at 400°C using diffusion couples and key alloys. Phase relationships and homogeneity ranges are determined for binary and ternary compounds using EPMA, SEM/EDS, and XRD. Reported ternary compound T3 (Al11Mn3Zn2) is confirmed in this study and is denoted as τ2 in this paper. Two new ternary compounds (τ1 and τ3) are observed in this system at 400°C. τ1 is determined as a stoichiometric compound with the composition of Al31Mn8Zn11. τ3 has been found to have homogeneity range of AlxMnyZnz (x=9–13 at%; y=11–15 at%; z=75–77 at%). The binary compounds Al4Mn and Al11Mn4 exhibit limited solid solubility of around 6 at% and 4 at% Zn, respectively. Terminal solid solution Al8Mn5 is found to have maximum ternary solubility of about 10 at% Zn. In addition, ternary solubility of Al-rich β-Mn′ at 400°C is determined as 4 at% Zn. Zn-rich β-Mn′′ has a ternary solubility of 3 at% Al. The solubility of Al in Mn5Zn21 is measured as 5 at%. Based on the current experimental results, the isothermal section of Al-Mn-Zn ternary system at 400°C has been constructed.

Effects of vacancy and exchange-coupling between grains on magnetic properties of SrFe12O19 and α-Fe2O3 composites

All samples were synthesized via supercritical (390°C) and low-temperature (190°C) hydrothermal methods followed by annealing at 1000°C, and contained both SrFe12O19 and α-Fe2O3 phases as reported in literature. The magnetic properties sensitively depended on the relative content of each phase, which was generally attributed to phase homogeneity and microstructural characteristics in literature as far as we know. In this paper, we observed a double-peak behavior in the curve of irreversible susceptibilities χirr versus an external magnetic field H, which was assigned to the cation vacancies and their distribution. The coercivity of the sample almost changed linearly with the average value of magnetic fields at which the χirr (H) peak located. Therefore, we conclude that the magnetic parameters, at least the coercivity, are mainly determined by cation vacancies which have usually been neglected before in SrFe12O19.

Effect of Silver Addition to Superconducting SmFeAsO1−x F x

We investigate the effect of silver addition to polycrystalline Sm-1111 superconductor. We show that Ag improves the phase homogeneity of the samples drastically reducing the weight of the low temperature, hence, leading to less fluorinated phases. The intragranular critical current density is enhanced by adding a small amount of Ag in all pinning regimes but a higher content of Ag leads to a decrease of this quantity. A tentative explanation for this dependence is proposed.

The reaction network in propane oxidation over phase-pure MoVTeNb M1 oxide catalysts

MoVTeNb oxide catalysts exclusively composed of the M1 phase (ICSD No. 55097) have been studied in the direct oxidation of propane to acrylic acid applying a broad range of reaction conditions with respect to temperature (623–633–643–653–663K), O2 concentration in the feed (4.5–6.0–9.0–12.0%), steam concentration in the feed (0–10–20–40%), and contact time (0.06–0.12–0.18–0.24–0.36–0.48–0.72–1.44sgcatNml−1). The molar fraction of propane was kept at 3.0%. Model experiments were performed to study the reactivity of possible intermediates propene, acrolein, and CO. The impact of auxiliary steam on the chemical nature of the catalyst surface was analyzed by in situ photoelectron spectroscopy, while in situ X-ray diffraction has been carried out to explore the structural stability of the M1 phase under stoichiometric, oxidizing, and reducing reaction conditions. Phase purity apparently accomplishes absolute stability in terms of the crystalline bulk structure and the catalytic performance over month even under extreme reaction conditions. In contrast, the catalyst surface changes dynamically and reversibly when the feed composition is varied, but only in the outermost surface layer in a depth of around one nanometer. The addition of steam causes enrichment in V and Te on the surface at the expense of Mo. Surface vanadium becomes more oxidized in presence of steam. These changes correlate with the abundance of acrylic acid detected in the in situ photoelectron spectroscopy experiment. Analysis of the three-dimensional experimental parameter field measured in fixed bed reactors revealed that the complexity of the reaction network in propane oxidation over MoVTeNb oxide is reduced compared to less-defined catalysts due to phase purity and homogeneity. The oxidative dehydrogenation of propane to propene followed by allylic oxidation of propene comprises the main route to acrylic acid. The oxygen partial pressure was identified as an important process parameter that controls the activity in propane oxidation over phase-pure M1 without negative implications on the selectivity. High O2 concentration in the feed keeps the catalyst in a high oxidation state, which provides an increased number of active sites for propane activation. Auxiliary steam increases activity and selectivity of M1 by changing the chemical nature of the active sites and by facilitating acrylic acid desorption.

3β-Acetoxy-6-nitrocholest-5-ene: Crystal structure, thermal, optical and dielectrical behavior

3β-Acetoxy-6-nitrocholest-5-ene (2) has been synthesized from 3β-acetoxycholest-5-ene (1). We provided an analysis of the compound by means of FT-IR, FT-Raman, NMR and X-ray crystallography. In addition microstructural, thermal, optical and dielectrical properties were also investigated. The compound 2 crystallizes in the monoclinic space group P21 with cell dimensions, a=15.7729 (13) Å, b=9.8933 (8) Å, c=17.8070(14) Å, α=90.00, β=96.176(4), γ=90.00. The powder X-ray diffraction (PXRD) of the compound was recorded to ascertain phase homogeneity. The SEM micrograph showed the presence of brick shaped, elongated nitrocholestane particles with 177.12×25.53×5.69μm dimensions. Thermogravimetric analysis showed stability of the compound up to 200°C. The dielectrical studies showed that with increase in frequency, the dielectric constant decreases and becomes almost constant at high frequencies.

Microstructural and Mechanical Studies of PVA Doped with ZnO and WO3 Composites Films

Polymer composites of ZnO and WO3 nanoparticles doped polyvinyl alcohol (PVA) matrix have been prepared using solvent casting method. The microstructural properties of prepared films were studied using FTIR, XRD, SEM, and EDAX techniques. In the doped PVA, many irregular shifts in the FTIR spectra have been observed and these shifts in bands can be understood on the basis of intra/intermolecular hydrogen bonding with the adjacent OH group of PVA. The chemical composition, phase homogeneity, and morphology of the polymer composites of the polymer film were studied using EDAX and SEM. These data indicate that the distribution of nanosized ZnO and WO3 dopants is uniform and confirm the presence of ZnO and WO3 in the film. The crystal structure and crystallinity of polymer composites were studied by XRD. It was found that the change in structural repositioning and crystallinity of the composites takes place due to the interaction of dopants and also due to complex formation. The mechanical studies of doped polymer films were carried out using universal testing machine (UTM) at room temperature, indicating that the addition of the ZnO and WO3 with weight percentage concentration equal to 14% increases the tensile strength and Young’s modulus.

Simultaneous neutron transmission and diffraction contrast tomography as a non-destructive 3D method for bulk single crystal quality investigations

Traditional neutron tomography allows to reconstruct the attenuation cross section, a measure for the material distribution, at high spatial resolution and non-destructively. However, it does not state anything about the ordering structure of the atoms inside this material. Extending the setup with a second neutron imaging detector, diffracted neutrons from the ordered crystal lattice could be captured. Emerging iterative reconstruction techniques allow reconstructing the local Bragg reflectivity in the sample, a measure for the spatial distribution in crystal quality (orientation, homogeneity of phases). Simultaneous acquisition ensures optimal use of the neutron flux and a direct comparison of different sample properties.

Correlating morphology, proton conductivity, and water transport in polyelectrolyte-fluoropolymer blend membranes

Obtaining detailed correlations among multi-scale morphology, ion conduction, and water transport will allow for informed design of novel membrane materials for alternative energy and sustainability applications. We compare morphological and performance features of polyelectrolyte-fluoropolymer blend membranes processed with different degrees of tetrabutylammonium hydroxide (TBA-OH) using the techniques of SEM, elemental analysis, proton conductivity, and water self-diffusion and spin relaxation by NMR. Increased TBA-OH significantly improves membrane phase homogeneity observed by SEM, consistent with observed enhancements in proton conductivity and water diffusion. We further observe drastic changes in local restrictions to water diffusion among the different blend membranes, and use theories of diffusion in porous media to understand improvements in characteristic domain size Rc and tortuosity ℑ with phase homogeneity. NMR relaxometry studies yield two-component T1 values, which further probe structural heterogeneities on smaller (1–10nm) scales than diffusion experiments (1–10μm). These multifaceted analyses linking morphology, chemistry, and transport properties provide critical information toward advanced membrane design.

The Effect of Si on the Formation of the ${\rm La}({\rm Fe},{\rm Si})_{13}$ Phase Synthesized by the Reduction-Diffusion (R/D) Process

In this contribution, the influence of Si content on the formation of the of LaFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(13-x)</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(x)</sub> (1:13 phase) synthesized by the reduction-diffusion (R/D) process is addressed. The raw materials used were Fe and Si, in powder form, La oxide (La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ), and Ca granules as reduction agent. The amount of Si per unit formula, represented by x, was varied from 1.3 to 1.7, for three different compositions. After a leaching step, subsequent to the actual R/D process and necessary to extract the reaction byproducts, such as CaO and nonreacted Ca, an alloy in powder form is obtained, with an average particle size of about 10 μm. In order to know the relative phase-amount evolution with the increasing Si content for these three different alloys, X-ray diffraction (XRD), supported by Rietveld refinement, was performed. Magnetic measurements carried out on a vibrating sample magnetometer (VSM) were used as an alternative means to infer the amount of formed 1:13 phase. The agreement found for the two methods (XRD and VSM) was good and showed that, for predetermined conditions, the amount of 1:13 phase formed, is directly related to the Si content added in powder form, as raw material. Moreover the transition-temperature (TC) of the target 1:13 phase, at which the magnetocaloric effect is highest, was accessed by differential scanning calorimetry (DSC) in order to check homogeneity and stoichiometry deviations from the predicted composition. The different values measured for distinct preparation conditions, point out to different Si contents incorporated to the targeted 1:13 phase, what directly affects phase formation and stability. The well-defined DSC-peaks, however, point out to good phase homogeneity.

Phase homogeneity and crystal structure of Sb88Te12 synthesized by melt-quench method

Phase homogeneity and crystal structure of Sb88Te12 alloy synthesized by melt-quench method have been analyzed using X-ray diffraction (XRD) and Raman spectroscopy. Rietveld refinement of crystal structure of Sb88Te12 has revealed the formation of Sb8Te3 and Sb phases respectively with 11R and A7 structures (space group is $$R\bar 3m$$ ). Phase fractions of the phases Sb8Te3 and Sb have been determined to be 44.44% and 55.56% respectively. Raman spectrum of Sb88Te12 has showed a highest intensity peak at 156 cm−1 and another peak at 151.1 cm−1, which correspond to A1g modes of Sb8Te3 and element Sb, respectively. Analysis of Raman spectrum has substantiated the results obtained from structure refinement regarding the presence of two different phases.