Limited Composition Range Research Articles

Slag viscosity modeling toolbox

Slag viscosity models are applied in many industries. However, the models are only applicable to a limited range of slag compositions and conditions, and their performance is not easily assessed. The present study describes tools that have been developed to assist slag viscosity model users in the selection of the best model for given slag compositions and conditions, and to help users determine how well the model will perform. The tools, which are in the form of several publicly available files and programs, include a slag viscosity prediction calculator with 24 slag viscosity models, and a database of 4124 slag viscosity measurements. The database includes over 750 compositions from 53 published studies. New slag viscosity models, integrated into the tools, include an artificial neural network for fully molten slags, and a viscosity prediction modifier for slags containing solid particles. Glass forming, entrained flow gasification and blast furnace case studies are provided to demonstrate how the slag viscosity modeling tools can be applied and to highlight certain features that should be considered when using slag viscosity models and experimental data.

Ab Initio Study of the Sodium Intercalation and Intermediate Phases in Na0.44MnO2 for Sodium-Ion Battery

The Na0.44MnO2 structure is a promising cathode material for sodium ion batteries due to a high capacity (∼130 mAh/g) and good cycle performance. In this work, we present the results of density functional theory (DFT) calculations on the structural and electrochemical properties of Na0.44MnO2, combined with experiments. Seven intermediate phases and the two-phase reactions among them were found, where the calculated voltage profile agreed well with experiments. We found that the S-shaped tunnel is not empty in the deintercalated Na0.22MnO2 structure but has a partial occupancy of sodium ions. The new sodium sites were found in a limited sodium composition range (x = 0.44–0.55) which is attributed to the electrostatic interactions between sodium ions and manganese atoms. The asymmetric lattice evolution in Na0.44MnO2 as a function of sodium insertion/deinsertion is shown to be due to the Jahn–Teller effects. On the basis of this interpretation, we suggest that the Cr substitution will reduce the volume change significantly.

The Crustal Magma Storage System of Volcán Quizapu, Chile, and the Effects of Magma Mixing on Magma Diversity

Crystal zoning as well as temperature and pressure estimates from phenocryst phase equilibria are used to constrain the architecture of the intermediate-sized magmatic system (some tens of km 3 ) of Volcan Quizapu, Chile, and to document the textural and compositional effects of magma mixing. In contrast to most arc magma systems, where multiple episodes of open-system behavior obscure the evidence of major magma chamber events (e.g. melt extraction, magma mixing), the Quizapu magma system shows limited petrographic complexity in two large historical eruptions (1846–1847 and 1932) that have contrasting eruptive styles. Quizapu magmas and peripheral mafic magmas exhibit a simple binary mixing relationship. At the mafic end, basaltic andesite to andesite recharge magmas complement the record from peripheral cones and show the same limited range of compositions. The silicic end-member composition is almost identical in both eruptions of Quizapu. The effusive 1846–1847 eruption records significant mixing between the mafic and silicic end-members, resulting in hybridized andesites and mingled dacites. These two compositionally simple eruptions at Volcan Quizapu present a rare opportunity to isolate particular aspects of magma evolution—formation of homogeneous dacite magma and late-stage magma mixing—from other magma chamber processes. Crystal zoning, trace element compositions, and crystal-size distributions provide evidence for spatial separation of the mafic and silicic magmas. Dacite-derived plagioclase phenocrysts (i.e. An 25 – 40 ) show a narrow range in composition and limited zonation, suggesting growth from a compositionally restricted melt. Dacite-derived amphibole phenocrysts show similar restricted compositions and furthermore constrain, together with more mafic amphibole phenocrysts, the architecture of the magmatic system at Volcan Quizapu to be compositionally and thermally zoned, in which an andesitic mush is overlain by a homogeneous dacitic magma that is the source for most of the 1846–1847 and 1932 erupted magmas. Dacite formation is best explained by mineral–melt separation (crystal fractionation) from an andesitic mush, which is inferred to have thermally and compositionally buffered the dacite magma thereby keeping it at relatively low crystallinity (<30 vol. %). The dominant cause of compositional diversity is melt separation. Back-mixing of mush (i.e. crystals with signatures of growth both in the andesitic mush and in the dacite magma) into the overlying dacite magma is rarely observed. Recharge events that increase crystal and magma diversity in the dacite magma are limited to an episode of mafic recharge and mixing just prior to the 1846–1847 eruption, where evidence for magma mixing is present on all scales. Chamber-wide mixing was incomplete (mixing efficiency of ∼0·53–0·85) as flow lobes vary significantly in composition along the proposed mixing array. Estimates of viscosity variations during the course of magma mixing suggest that mixing dynamics and the degree of magma interaction on all scales were established at the beginning of the recharge event.

Composition dependence of magnetic properties in perpendicularly magnetized epitaxial thin films of Mn-Ga alloys

Mn-Ga binary alloys show strong magnetism and large uniaxial magnetic anisotropy even though these alloys do not contain any noble, rare-earth metals or magnetic elements. We investigate the composition dependence of saturation magnetization ${M}_{\mathrm{S}}$ and uniaxial magnetic anisotropy ${K}_{\mathrm{u}}$ in epitaxial films of Mn${}_{x}$Ga${}_{1\ensuremath{-}x}$ alloys ($x\ensuremath{\sim}0.5$--0.75) grown by magnetron sputtering. The ${M}_{\mathrm{S}}$ values decrease linearly from approximately 600 to 200 emu/cm${}^{3}$ with increasing $x$, whereas the ${K}_{\mathrm{u}}$ values decrease slightly from approximately 15 to 10 Merg/cm${}^{3}$ with increasing $x$. These trends are distinct from those for known tetragonal hard magnets obtained in a limited composition range in Mn-Al and Fe-Pt binary alloys. These data are analyzed using a localized magnetic moment model.

Thermodynamic and mechanical stabilities of γ′-Ir3(Al,W)

The structural, thermodynamic, and mechanical properties of a recently identified γ′-Ir3(Al,W) compound are investigated using first-principles density functional calculations. The configurational disorder in this compound is treated by both the special quasirandom structure approach and the cluster expansion technique, and the two complimentary methods give results in excellent agreement with each other. In support of experiments, our T=0 K calculations indicate that γ′-Ir3(Al1−xWx) is thermodynamically stable in the Ir–Al–W ternary system over a limited composition range near x=0.5. At finite temperatures, γ′-Ir3(Al,W) will be further stabilized by configurational and vibrational entropies but will be slightly destabilized due to thermal electronic excitations. The single-crystal elastic constants of γ′-Ir3(Al,W) are obtained using an efficient stress-strain approach. We find that the alloying of W in γ′-Ir3(Al,W) significantly enhances its strength, although at the cost of reduced ductility due to the directionality of atomic bonding between Ir and W atoms.

Assessment of the Phase Equilibria among γ-Fe/ Fe2Nb/ Ni3Nb Phases in Fe-Ni-Nb Ternary System at Elevated Temperatures

ABSTRACTPhase equilibria among γ-Fe, ε-Fe2Nb Laves and δ-Ni3Nb phases in Fe-Ni-Nb ternary system at 1473 K and 1373 K were experimentally examined, and also assessed by calculation in order to calculate the phase equilibria among these phases at 973 K. A ternary compound with hP24 structure with its limited composition range of Fe-21.5Nb- (56.8-59.8) Ni exists between Fe2Nb and Ni3Nb phase regions at both temperatures. Including the hP24 phase, the calculated isotherms at both temperatures are in good agreement with experimental ones. By using the optimized interaction parameters among the three elements in each phase, the isothermal section calculated at 973 K revealed a γ-Fe+ Fe2Nb + Ni3Nb three-phase coexisting region extended to Fe-rich composition of 80 at. % Fe. This suggests a possibility to develop austenitic heatresistant steels strengthened by both intermetallics phases.

Paleozoic alkaline volcanism: geochemistry and petrogenesis of Um Khors and Um Shaghir trachytes of the central Eastern Desert, Egypt

The Um Khors and Um Shaghir trachyte (UKT and UST) plugs and sheets represent two conspicuous outcrops of Paleozoic alkaline volcanism in the central Eastern Desert of Egypt. The trachyte magmatisms erupted along the Pan-African NW-trending shear zone (302 ± 15 and 273 ± 15 Ma, respectively) and intruded the Late Proterozoic rocks of the studied area. The trachyte rocks consist mainly of sanidine, anorthoclase, albite, and quartz with a noticeable amount of aegirine–augite, aegirine, hedenbergite, and arvedsonite. The studied trachytes are moderately evolved in composition (with 62–67.5 wt.% SiO2) and exhibit a limited compositional range in most of the major elements. They are alkaline in nature and considered as silica-oversaturated rocks. The rare earth elements (REE) patterns are somewhat uniform and highly fractionated, being enriched in light REE over heavy REE and show prominent negative Eu anomalies. The UKT and UST are enriched in high field strength elements Nb, Zr, and Y, consistent with typical within-plate alkaline magmatisms of extensional tectonic regimes. They were generated through the fractional crystallization of mantle-derived magmas. Although the UST is younger than the UKT, they show approximately similar chemical compositional ranges of the most major and trace elements, with somewhat higher MgO, Cr, Ni, and Ba contents in the former. This may argue against the evolution of the UST via a continuous fractional crystallization of the residual magmatic melt of the UKT. Thus, the UKT and UST are genetically related but could be emplaced through two various magmatic pulses of the same parent source (i.e., asthenospheric mantle source) at different times. The ascending magmatisms were subjected to variable significant degrees of crustal contamination during their generation.

Smectic Demixing in the Phase Behavior and Self-Assembly of a Hydrogen-Bonded Polymer with Mesogenic Side Chains

We present a detailed study of the structure and properties of a supramolecular complex formed via hydrogen bond association between poly(acrylic acid) chains and an imidazole-terminated biphenyl mesogen. The system exhibits a rich phase behavior as a function of temperature and stoichiometry, expressed as the molar ratio S between the number of mesogens and binding sites present. Smectic mesophases are formed for all S ≥ 0.033, a surprisingly small number. The dependence of the characteristic length scale of the mesophase on stoichiometry does not follow the expected 1-D swelling law. At low stoichiometries, S ≤ 0.2, the system exhibits little or no change in structure up to temperatures as high as 200 °C, beyond which changes become temperature irreversible. In contrast, at higher S, the system features complex thermally driven transitions among tilted monolayer and bilayer arrangements and complete, reversible isotropization of the system at elevated temperatures. Over a limited range of temperatures and compositions, a supramolecular length scale emerges that is well beyond the upper limit imposed by a bilayer construct and thus cannot be accounted for within the conventional paradigm. Binding isotherms reveal that the polymer has a limited capacity for the ligand with saturation occurring for S ≥ 0.33. These results suggest that the common assumption of homogeneously distributed tightly bound ligands with layer-like phase separation from the polymer backbone do not apply in this system over all compositions. The anomalous phase display is consistent with demixing between polymer rich and polymer poor domains due to the presence of excess unassociated mesogen, which can act as a solvent for the system.

Multicomponent (n ≥ 3) Sorption Isotherms in Reversed-Phase Liquid Chromatography: The Effect of Immobilized Eluent on the Retention of Analytes

The experimental technique of tracer pulse chromatography was used to simultaneously measure the uptake of eluent components by a C(18)-bonded reversed-phase liquid chromatography (RPLC) packing and the retention factors for a series of test analytes over the full range of eluent composition for methanol and acetonitrile with water. The primary objective of the research was to determine whether or not the uptake of eluent components immobilized as part of the stationary phase would influence the retention of analyte standards. Both acetonitrile and methanol were absorbed in or adsorbed on the C(18)-bonded phase with the maximum amount of acetonitrile sorbed being about four times that of methanol. The thermodynamic void volume of the column and the excess sorption isotherms of acetonitrile, methanol, and water in binary aqueous/organic mixtures were determined directly from the tracer pulse experiments. The absolute sorption isotherms of the eluent components were indirectly estimated by a combination of techniques. Regression analysis of the nonstationary inflection point of the excess isotherms provided an estimate of the volume of eluent sorbed by the stationary phase but only over a limited eluent composition range. In order to expand the applicable composition range, several commonly used "unretained" probe solutes were tested to determine the accuracy of the assumption that the retention volumes of these solutes provided a viable measure of the kinetic void volume (mobile-phase volume) of the column. The difference between the thermodynamic and kinetic void volumes provided an estimate of the absolute volume of eluent present in the stationary phase. The experimental results showed that some solutes, viz., water and thiourea, did provide an accurate measure of the mobile-phase volume but only over a limited range of eluent composition. Using deuterated water as the unretained dead time marker for water-rich eluents combined with the regression results from excess isotherm data, the absolute volume of eluent sorbed by the stationary phase could be estimated over the full range of eluent composition. The effect of this uptake of eluent on the retention of the test solutes appeared to be minimal for this particular set of test analytes.

The electronic, elastic, and structural properties of Ti–Pd intermetallics and associated hydrides from first principles calculations

Using an ab initio density functional approach, we report on the ground-state phase stabilities, enthalpies of formation, electronic, and elastic properties of the Ti–Pd alloy system. The calculated enthalpies of formation are in excellent agreement with available calorimetric data. We found a linear dependence between the calculated enthalpies of formation of several intermetallic structures and the Pd-concentration, indicating that each of these compounds has a very limited composition range. The elastic constants for many of these Ti–Pd intermetallics were calculated and analyzed. The B2 TiPd phase is found to be mechanically unstable with respect to the transformation into the monoclinic B19′ structure. A series of hydrides, Ti 2PdH x ( x = 1, 1.5, 2, 3, 4), have been investigated in terms of electronic structure, enthalpies of hydrogen absorption, and site preference of H atoms. Our results illustrate the physical mechanism for hydrogen absorption in term of the charge transfer, and explain why TiPd 2 does not form a stable hydride.

Formation of cerium titanate, CeTi2O6, in sol–gel films studied by XRD and FAR infrared spectroscopy

The process of formation of cerium titanate films as a function of annealing temperature and composition has been studied by combining X-ray diffraction analysis and far infrared spectroscopy. The films have been prepared by a sol–gel synthesis using metal chlorides as precursors; the synthesis allows obtaining cerium titanate films upon annealing in air. A brannerite type, CeTi2O6, phase has been identified by X-ray diffraction and Rietveld analysis on thin films. CeTi2O6 is formed upon annealing at 700 °C and in a limited range of ceria-titania mixed compositions. The far infrared spectra are useful to observe the formation of crystalline phases at the beginning of the crystallization process at lower firing temperatures, when the XRD analysis is not enough sensitive.

Alteration Mechanisms of Chromian‐Spinel during Serpentinization at Wadi Sifein Area, Eastern Desert, Egypt

AbstractWadi Sifein podiform chromite deposits, Central Eastern Desert of Egypt, are hosted by fully serpentinized peridotite that is a part of the dismembered Pan‐African ophiolite complexes. Relics of primary minerals and the chemical characters indicate that the ophiolitic rocks were derived from depleted mantle peridotite of harzburgite and subordinate dunite compositions. The mantle rocks were initially formed at a mid‐oceanic ridge and subsequently thrust at a supra‐subduction zone. The chromite mineralization at Wadi Sifein area displays either pod‐shaped bodies with massive and lumpy chromitite appearance or dissemination of chromian‐spinel in serpentinite matrix. The podiform chromitite exhibits a very limited compositional range in terms of Cr# [Cr/(Cr + Al) atomic ratio] and Mg# [Mg/(Mg + Fe) atomic ratio]. The chromian‐spinel, however, frequently displays optical and geochemical zoning. Four zones can be identified from core to edge: inner core representing the original composition of the chromian‐spinel; narrow Cr‐rich ferritchromit zone; wide ferritchromit zone; and outer Cr‐magnetite/magnetite zone. The zonation of chromian‐spinel is interpreted to be a result of serpentinization rather than magmatic or metamorphic processes. The geochemical data obtained from the chromitite and chromian‐spinel was statistically processed using discriminant and R‐mode factor analyses. Two trends, minor and major, were achieved considering the formation of ferritchromit. The minor trend is controlled by the redistribution of trivalent cations, where Cr2O3 increased on the expense mainly of Al2O3 and to less extent Fe2O3 to form zone II during the peak of serpentinization. The major trend of alteration, however, is explained by the exchange between Mg‐Fe2+ rather than Cr, Al, and Fe3+ to form zone III. Kammererite formation was accompanied the formation of zones III and IV at a 314°C temperature of formation.

Well-wetted olivine grain boundaries in partially molten peridotite in the asthenosphere

Pore morphology in partially molten peridotites strongly controls many physical properties of the Earth's deep materials. The dihedral angle of the olivine–silicate melt system is a key factor in understanding the physical behavior of the upper mantle. For a limited range of melt compositions, previous studies of wetting behavior have determined dihedral angles of 30–50°. However, the dihedral angle of partially molten peridotites should be variable under a wide range of pressure and temperature conditions, because wetting behavior depends strongly on liquid structure and composition. The dihedral angles of olivine–silicate melt in partially molten peridotite were determined at pressures of 1 to 7 GPa and temperatures between 1473 and 1993 K. The dihedral angle decreased (approaching 0°) with increasing temperature, which corresponds to completely wetted grain boundaries. This angle variation probably depends on a decrease in the solid-melt interfacial energy, which is a product of large change in melt structure. These results suggest that the presence of partial melt would have large influences on the physical properties of the upper mantle even if the melt fraction was very low. If grain boundary diffusion creep dominates in the asthenosphere, the shear strength of partially molten peridotites at asthenospheric pressure (~ 3 GPa) would be much lower than that predicted from experiments at relatively lower pressure (~ 0.3 GPa) because of the extremely low grain boundary contiguity.

LABORATORY SPECTRA OF THE CO 2 BENDING-MODE FEATURE IN INTERSTELLAR ICE ANALOGUES SUBJECT TO THERMAL PROCESSING

The infrared absorption features of solid carbon dioxide have been detected by space-based observatories in nearly all lines of sight probing the dense interstellar medium (ISM). It has also been shown that the absorption feature of solid CO2 near 658 cm−1 (15.2 μm) should be a sensitive indicator of the physical conditions of the ice (e.g., temperature and composition). However, the profile structure of this feature is not well understood, and previous laboratory studies have concentrated on a limited range of temperatures and compositions for comparisons with observed spectra from both the Infrared Space Observatory and the Spitzer Space Telescope. In the laboratory study described here, the infrared spectra of ices bearing H2O, CH3OH, and CO2 have been measured with systematically varying compositions and temperatures that span the range of the values expected in the ISM. The mid-IR spectra (λ = 2.5–25 μm) were measured for 47 different ice compositions at temperatures ranging from ∼5.5 K to evaporation, at 5 K intervals.

Li14.7Mg36.8Cu21.5Ga66: An Intermetallic Representative of a Type IV Clathrate

Synthetic explorations in the quaternary Li-Mg-Cu-Ga system yield the novel intermetallic Li(14.7(8))Mg(36.8(13))Cu(21.5(5))Ga(66) [P6m2, Z = 1, a = 14.0803(4) A, c = 13.6252 (8) A] from within a limited composition range. This contains a unique three-dimensional anionic framework consisting of distinct interbonded Ga(12) icosahedra, dimerized Li@(Cu,Mg)(10)Ga(6) icosioctahedra, and 15-vertex Li@(Cu,Mg)(9)Ga(6) and Li@Cu(3)Ga(12) polyhedra. These polyhedral clusters are hosted by M(20) (5(12)), M(24) (5(12)6(2)), and M(26) (5(12)6(3)) (M = Li/Mg) cages, respectively. The geometries and arrangements of these cages follow those in known type IV clathrate hydrates.

Mass Spectrometric Tracer Pulse Chromatographic Investigations of Eluent Sorption with Bonded RPLC Packings

The experimental technique of mass spectrometric tracer pulse chromatography was used to investigate the uptake of RPLC eluents by a C 18-bonded packing. The experiments were carried out with eluents consisting of binary aqueous mixtures with acetonitrile, methanol, and tetrahydrofuran over the full range of eluent composition at 25 degrees C. The primary experimental data obtained were excess volumes of sorption for the eluent components. The excess volume data were then used to determine the absolute volume of each eluent component in the stationary phase as a function of composition. The absolute volumes were calculated by utilizing a series of strategies specific to limited eluent composition range. The linear inflection region of the excess volume isotherms was used to calculate the volume and composition of the eluent in the stationary phase for organic-rich eluents. Three different assumptions were used and evaluated for the water-rich eluent compositions. The assumptions were (i) constant volume of the sorbed layer, (ii) constant amount of water sorbed, and (iii) no water sorption. The latter assumption was adopted as the most satisfactory. The calculated void volume data were compared with the retention volume of thiourea and uracil, commonly used dead time markers. Neither thiourea nor uracil proved to be an accurate measure of the kinetic void volume.

Engineering aerosol-through-plasma torch ceramic particulate structures: Influence of precursor composition

This is the second in a series of articles demonstrating the unique character of the aerosol-through-plasma (A-T-P) process for producing nanoparticles. This study is focused on the impact of two parameters, cation ratio (1:3, 1:1, 3:1) and solvent (evaporated prior to generation of aerosol), on the structures of Ce:Al oxides particles. These two simple changes were found to impact virtually every aspect of particle structure, including the fraction of hollow versus solid, fraction of nanoparticles, phase structure, and even the existence of surface phase segregation. CeAl mixed oxides were found only over a limited range of compositions, and that range was a function of the solvent. At all other cation ratios, only ceria was a crystalline phase, and most if not all the alumina is amorphous. It is notable that the fraction of hollow micron-sized particles and nanoparticles is greatly influenced by the cation ratio and solvent identity. Indeed, significant numbers of nanoparticles were only produced using an aqueous precursor with a Ce:Al ratio of 1:1. Another unique finding is that phase segregation exists in individual particles on the length scale of nanometers. This study compliments an earlier study of the influence of operating conditions on particle structure. Taken together, the studies suggest a means to engineer (as well as limits to the engineering possibilities) ceramic particle structures using the A-T-P method.

The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites

Samarium-neodymium isotopic analyses of unleached and acid-leached mineral fractions from the recently identified olivine-bearing shergottite Northwest Africa 1195 yield a crystallization age of 347 ± 13 Ma and an ε Nd 143 value of +40.1 ± 0.9. Maskelynite fractions do not lie on the Sm–Nd isochron and appear to contain a martian surface component with low 147Sm/ 144Nd and 143Nd/ 144Nd ratios that was added during shock. The Rb–Sr system is disturbed and does not yield an isochron. Terrestrial Sr appears to have affected all of the mineral fractions, although a maximum initial 87Sr/ 86Sr ratio of 0.7016 is estimated by passing a 347 Ma reference line through the maskelynite fraction that is least affected by contamination. The high initial ε Nd 143 value and the low initial 87Sr/ 86Sr ratio, combined with the geologically young crystallization age, indicate that Northwest Africa 1195 is derived from a source region characterized by a long-term incompatible-element depletion. The age and initial Sr and Nd isotopic compositions of Northwest Africa 1195 are very similar to those of Queen Alexandra Range 94201, indicating these samples were derived from source regions with similar Sr–Nd isotopic systematics. These similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano. The meteorites Yamato 980459, Dar al Gani 476, Sayh al Uhaymir 005/008, and Dhofar 019 also have relatively old ages between 474 and 575 Ma and trace element and/or isotopic systematics that are indicative of derivation from incompatible-element-depleted sources. This suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible-element-depleted sources. Closed-system fractional crystallization of this suite of meteorites is modeled with the MELTS algorithm using the bulk composition of Yamato 980459 as a parent. These models reproduce many of the major element and mineralogical variations observed in the suite. In addition, the rare earth element systematics of these meteorites are reproduced by fractional crystallization using the proportions of phases and extents of crystallization that are calculated by MELTS. Other shergottites that demonstrate enrichments in incompatible-elements and have evolved Sr and Nd isotopic systematics have some geochemical systematics that are similar to those observed in the depleted group. Most notably, although they exhibit a very limited range of incompatible trace element and isotopic compositions, they have highly variable major element compositions. This is also consistent with evolution from a common mantle source region by variable amounts of fractional crystallization. If this scenario is correct, it suggests that the combined effects of source composition and fractional crystallization are likely to account for the major element, trace element, and isotopic diversity of all shergottites.

Magnetic and transport and structure properties of the room temperature ferromagneto Sr1−xHoxCoO3−δ

The perovskite Sr1−xHoxCoO3−δ shows room temperature ferromagnetism (Tc∼335K) in a severely limited composition range 0.2⩽x⩽0.25. The formal Co valence is almost constant at +3 regardless of the Ho concentration (x⩾0.2); thus, the high-spin state or the intermediate spin state of 3d6 Co should be mainly responsible for the magnetism. The ferromagnetism was found to accompany the formation of a superstructure 2ap×2ap×4ap (ap denotes a cubic perovskite cell). Besides, an additional superstructure 4(2ap)×4(2ap)×(4ap) was found at x=0.225, where the ferromagnetic volume in magnetic susceptibility was largest. The data suggest that the formation of the multiple superstructures probably plays a key role to establish the peculiar ferromagnetism.

New generation of low fouling nanofiltration membranes

The nanofiltration (NF) membranes and their properties are quite diverse, but can generally be described as having rejection characteristics that range from “loose” RO to “tight” ultrafiltration. The uniqueness of these membranes is highlighted by their ability to selectively reject different dissolved salts, and have high rejection of low molecular weight, dissolved components. Nanofiltration membranes are mainly used to partially soften potable water, allowing some minerals to pass into the product water and thus increase the stability of the water and prevent if from being aggressive to distribution piping material. Additionally, NF membranes are finding increasing use for purifying industrial effluents, and minimizing waste discharge. The key to using NF membranes for particular application is the selection of a membrane with appropriate rejection characteristic and the design of a suitable process. NF membranes are generally characterized by a high charge density and pore sizes in the range of nanometers. The surface charge is most often negative and has the greatest effect on the selective passage nature of these membranes. The design of a NF system can often be more complex than a RO system. Because the required transmembrane pressure is so low, a system design that will result in balanced flux throughout the array is difficult to achieve. One common approach is to design NF systems with multiple element types. Such so called “hybrid” designs can help more finely control flow in the NF system. Also, membrane fouling can cause a change of rejection selectivity and/or reduction of membrane permeability that could affect both the water quality and operating cost due to increased energy requirement and higher consumption of chemicals needed for stabilization of permeate. The rejection characteristics of NF membranes depend on chemistry and surface charges of the separating barrier layer, ionic composition and concentration of feedwater and operating parameters of the NF system: recovery rate and permeate flux. Although, theoretical models have been developed to calculate selective ion rejection of NF membranes, they are mostly adequate only for simple water systems in limited range of water compositions and concentrations. In algorithms applied for projection of permeate composition in commercial NF systems, the theoretical models are augmented by empirical correction coefficients developed from field results. Selection of proper NF membrane type and prediction of performance is further complicated by membrane fouling. In NF projects involving treatment of feedwater with high concentration of dissolved organics the membrane selection process usually include pilot unit operation to evaluate stability of salt rejection and water permeability of candidate membrane elements. The paper will discuss present offering of commercial NF membranes, case studies and models applied to calculate their performance. This will also include information on recently developed NF membranes with low fouling characteristic that are successfully applied in the world largest (150,000 m 3/d, 40 mgd) NF plant in Boca Raton, FL. The process of extensive field testing and parallel membrane performance optimization that led to selection of these nanofiltration elements for the Boca Raton plant will be described as well.