Small Distribution Coefficient Research Articles

Graded Preparation and Industrial Applications of Large-Ball Polyolefin Catalyst Carriers

In the process of preparing polyolefin catalyst carrier, the particle size is often unqualified because of the adhesion of smaller particles to each other and the crushing effect of mechanical vibration. To improve the output of target products, reduce loss, and improve yield, a high-precision and high-efficiency carrier particle classification process was developed according to the embedded principle. The hydraulic hydrocyclone equipment designed in this work could eliminate short-circuit flow and achieve good integration of the internal flow field, thereby enhancing the separation accuracy and high separation efficiency. The process was successfully applied to the industry with smooth operation. The large-ball polyolefin catalyst carrier prepared by grading showed a small distribution coefficient, high yield, and excellent polymerization performance, and the average particle size of the graded large ball catalyst support was 65–75 μm with the SPAN < 0.7, which could meet the needs of DQC700 series catalyst products.

Effect of grain alignment distribution on magnetic properties in (MM, Nd)–Fe–B sintered magnets

Hcj of (MMxNd1−x)–Fe–B sintered magnets decreases distinctly with x increasing when misch metal (MM) content (x) ranges from 0.3 to 1. Practical application is taken into consideration so that the (MM0.6Nd0.4)–Fe–B components are chosen to analyze the changes in behavior of the magnetic properties. Both Magnet II and Magnet III belong to (MM0.6Nd0.4)–Fe–B sintered magnets, however, it should be noted that Magnet II is prepared by the single alloying method (SAM) and Magnet III is prepared by the double main phase alloy method (DMPAM). Core–shell structures of the magnets prepared by DMPAM can result in the higher Hcj and lower knee-point coercivity (Hk) compared with that by SAM. Furthermore, for Magnet II, the abnormal grain growth contributes to a better grain alignment and smaller distribution coefficient (σ) defined as the degree of grain alignment, which will enforce a higher tendency of the Hcj decreasing and Hk increasing. The expression of their normalized coercivity h(σ) is deduced by combining Gao’s starting field model with Kronmüller’s nucleation mechanism. Based on the overall h(σ) ~ σ curve, the best desirable h(σ) value is calculated when σ = 0.09. Theoretically, for Magnet III, the resultant larger σ should be attributed to the more uniform grain alignment. In addition, the deviations of grain size distributions on the c-plane become more remarkable with more MM concentrates, which can be presented by SEM images. Meanwhile, by means of the pole figures, it is also verified that the grain alignment distribution becomes much more diverse with x increasing. Therefore, it can be predicted whether the grain alignment distribution is significant for Hk and Hcj of (MMxNd1−x)–Fe–B sintered magnets (x ≠ 0.6) prepared by SAM/DMPAM or not.

Acceleration and Reaction Mechanism of the N-Nitrosation Reaction of Dimethylamine with Nitrite in Ice.

Some reactions (e.g., oxidation of nitrite, denitrification of ammonium) are accelerated in freeze-concentrated solution (FCS) compared to those in aqueous solution. Ice is highly intolerant to impurities, and the ice excludes those that would accelerate reactions. Here we show the acceleration of the N-nitrosation reaction of dimethylamine (DMA) with nitrite to produce N-nitrosodimethylamine (NDMA) in FCS. NDMA is a carcinogenic compound, and this reaction is potentially accelerated in frozen fish/meat. The eaction rate of the N-nitrosation reaction becomes fastest at specific pH. This means that it is a third-order reaction. Theoretical pH values of the peak in the third-order reaction are higher than the experimental one. Freeze-concentration of acidic solution causes pH decrement; however, the freeze-concentration alone could not explain the difference of pH values. The theoretical value was obtained under the assumption that no solute took part in ice. However, solutes are incorporated in ice with a small distribution coefficient of solutes into ice. This small incorporation enhanced the decrement of pH values. Using the distribution coefficient of chloride and sodium ion and assuming those of nitrite and DMA to explain the enhancement, we succeeded in estimating the distribution coefficients of nitrite: 2 × 10-3 and DMA: 3 × 10-2.

Kinetics of phosphorus release from sediments and its relationship with iron speciation influenced by the mussel (Corbicula fluminea) bioturbation

The effects of bivalve (Corbicula fluminea) bioturbation on the lability of phosphorus (P) in sediments were investigated. The high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques were employed to obtain soluble and labile P/Fe profiles at a vertical resolution of 2 and 1mm, respectively. The bivalve bioturbation increased the concentrations of soluble reactive P (SRP) in pore water and DGT-labile P up to 116% and 833% of the control within the sediment depths from the sediment water interface (SWI) to −64mm and −44mm, respectively. The sediments with bioturbation had a smaller distribution coefficient than the control (1964 vs. 3010 cm3g−1), reflecting a weaker ability in retaining P. Meanwhile, the sediments with bioturbation had a greater ratio of the concentration of DGT-labile P to that of SRP (0.20 vs. 0.03), demonstrating a stronger ability to resupply pore water SRP by the sediment solids when they are affected by the bioturbation. The DGT-induced fluxes in sediments (DIFS) modeling further showed a much shorter response time (277.9 vs. 18,670s) and a much higher rate (0.192 vs. 0.002day−1) of the solids in release of P with the bioturbation. Correspondingly, the flux of P to the overlying water from the bioturbation treatment increased up to 157% of the control. The bivalve bioturbation significantly increased the concentrations of soluble Fe(II) and DGT-labile Fe up to 84% and 334% of the control from the SWI to −46mm, respectively. The SRP and DGT-labile P were highly correlated with respective soluble and DGT-labile Fe. It was concluded that the release of P from the sediments with bioturbation to the pore water and the overlying water was promoted by the reductive dissolution of easily reducible Fe(oxyhydr)oxides due to the depletion of oxygen in the top sediments from bivalve respiration.

Effect of boron addition on the microstructure and mechanical properties of 6.5% V-5% W high speed steel

The effect of adding 0.04% additional boron to 6.5% V-5% W high speed steel was investigated. The microstructure characterization, phase identification, and carbide identification of the materials were performed using SEM/EDS and XRD. The cell size and carbide volume fraction were examined using image analysis software. The boron distribution was observed by PTA Boron Tracking. The addition of 0.04% more boron to a HSS alloy exerted a cell refining effect on the sample. The cell refinement of dendritic structures in the alloy containing boron may be attributed to the constitutional supercooling effect associated with the fairly small distribution coefficient for boron in iron. The addition of boron increases the bending strength of the material by more than 10%, as well as increasing its hardness.

Growth and piezoelectric features of La2CaB10O19 crystals doped with Pr3+ ions

High quality La2CaB10O19 single crystals doped with Pr3+ ions were grown by means of the top seeded solution growth method. The concentration of Pr3+ ions in the starting melt was equal to 4at%, which, due to small distribution coefficient, in consequence gave single crystals containing 2.5at% of Pr3+ions. The piezoelectric coefficients were measured for the pure and Pr+3 doped crystals. The principal changes under influence of the nanosecond pulsed 1064nm Nd:YAG laser were observed for the LCBO nanocrystallites incorporated into the polymer matrices. The introduction of the Pr3+ ions favors enhanced piezoelectric constants. In turn the nanocrystallites with enhanced piezoelectricity lead to the enhanced laser threshold damage.

Preparation and fluorescence properties of La2CaB10O19 crystals doped with Pr3+ ions

High quality La2CaB10O19 single crystals doped with Pr3+ ions were grown by means of the top seeded solution growth method. The concentration of Pr3+ ions in the starting melt was equal to 4at%, which in consequence gave single crystals containing 2.5at% of Pr3+ ions, due to small distribution coefficient. The absorption and luminescence spectra were recorded in the wavelength range from 200 to 3000nm at an ambient temperature of 24°C and analyzed using the Judd–Ofelt theory. With the intensity parameters obtained in the present work, the estimated radiative life time of the 3P0 emitting state is 28μs. Possible applications of this crystal as a luminophore are discussed.

Novel simulated moving-bed method for reduced solvent consumption

Simulated moving-bed (SMB) chromatography is attractive for reducing sorbent and solvent consumption relative to fixed-bed systems. In this contribution, we describe a novel and versatile method for further reducing solvent consumption in the case of reversed-phase chromatography. The method is based on the variation of the distribution coefficients of solutes to be separated upon varying the composition of a multi-component mobile phase. If the solvent strength of the desorbent is set higher than the solvent strength of the feed, the components will have smaller distribution coefficients in the extraction section of the SMB and hence will be more easily eluted. This will result in a lower desorbent flow and possibly also in a shorter desorbent zone, and, ultimately, in more concentrated products. The so-called “Triangle-method” by Storti et al. [AIChE J., 39 (1993) 471] to obtain the region of complete separation, is extended for this novel SMB method. Theoretical evaluation of the proposed methodology supports the anticipated solvent reduction relative to fixed-bed RP-HPLC for the cases of the purification of the polyketide antibiotic nystatin and the separation of bovine insulin from porcine insulin.

Pore nucleation in solidifying high-purity copper

High-purity copper (6 or 7 N) was melted and solidified unidirectionally in the atmosphere of a H2-Ar gas mixture for the purpose of studying the mechanism of pore nucleation in solidifying metal. Hydrogen content in the melt was controlled by changing the partial pressure in the atmosphere. Pores were formed when the hydrogen partial pressure in the atmosphere was 0.3 atm or more. Oxides of aluminum and silicon were observed at the bottom of the pores and the pores were nucleated heterogeneously. Water vapor with a very low partial pressure existed in the furnace atmosphere, and the melt must have contained a small amount of oxygen in equilibrium with this water vapor. The solid/liquid (S/L) interface was planar and convection was eliminated. The redistribution of the solute during solidification can, therefore, be estimated. The concentration of oxygen in the liquid at the S/L interface is estimated to be much larger than its initial concentration, due to the very small equilibrium distribution coefficient of oxygen in copper, and aluminum and silicon were oxidized even though their concentrations were very low. The probability of homogeneous nucleation by α particles was very small in these experiments.

Reactive Solute Transport in a Single Fracture

The transport of reactive and nonreactive solutes under the action of fully developed laminar flow in a parallel plate fracture has been analyzed. Three types of surface reactions are examined: (1) irreversible first‐order kinetic, (2) instantaneous reversible, and (3) reversible first‐order kinetic. Approximate analytical models for the dispersion of nonreactive and reactive solutes with an irreversible first‐order reaction are developed, and numerical “exact” solutions for the three surface reaction types are obtained. The conditions under which the approximate solutions hold are determined by comparison with the numerical solutions. The solute migration patterns and the extent of retardation due to surface reactions are then analyzed and compared with the nonreactive case. Dimensionless reaction coefficients incorporated into the solutions are estimated from data available in the literature. It is found that the approximate solutions are consistent with the numerical solutions; that the criterion for applicability of a local equilibrium assumption is based on the values of dimensionless time and a dimensionless number representing the ratio of the rate at which the surface reaction reaches equilibrium to the rate of the molecular diffusion in the transverse direction; and that the effect of surface reaction can be described by a retardation factor Rf = 1 + Kd* for the case in which the reaction can be assumed at equilibrium, with small Peclet number,small dimensionless distribution coefficient Kd*, and large dimensionless time. Conditions are also found under which reactive solute transport can be well approximated by nonreactive solute transport and reversible reactions can be treated as irreversible. These results and the dimensionless analysis method employed herein may serve as a basis for development of more complex models of reactive solute transport in saturated fractured media.

Concentration of platinum-group elements by magmatic fluids in layered intrusions

Evidence leading to a model which supports the formation of Pt-Pd reefs in a layered intrusion by the action of magmatic fluids is presented, as well as some of the constraints imposed on such a model. The Stillwater Complex is used as an example of this model. Within the Stillwater Complex, no laterally continuous sulfide-enriched cumulates occur above the lowermost parts of the Ultramafic series until one reaches the platiniferous J-M reef. This sulfide-poor stratigraphic interval beneath the J-M reef is characterized by unusually Cl-rich apatite. Although reported sulfide modes and whole-rock sulfur contents in the cumulates below the J-M reef are approximately an order of magnitude lower than that expected for a sulfide-saturated magma; sulfide saturation prior to the formation of the J-M reef is suggested by relatively high Pd and Pt concentrations reported in the cumulates below the J-M reef as well as by the presence of sulfide as inclusions in silicate and oxide cumulus minerals. Hence it is suggested that the footwall cumulates to the J-M reef were originally sulfide saturated but later lost sulfur to a fluid phase exsolving from inter-cumulus liquid. Sporadic sulfide-bearing pegmatoids in some of these rocks are additional evidence for late loss of sulfur. These observations, as well as the association of the J-M reef at the first significant stratigraphic break in the Cl/(Cl + F) ratio of apatite and the relatively high solubility of Pt and Pd as aqueous Cl complexes, are consistent with the formation of the J-M reef by exsolution of Cl- and volatile-rich fluids from footwall intercumulus liquids which leached and transported ore components (both the PGE and S) upward to the level of the reef.Using published whole-rock platinum-group element (PGE) concentrations for the Ultramafic and Lower Banded series, the cumulates below the J-M reef must have been enriched by a factor of, at most, 1.24 for Pt and 1.75 for Pd if these rocks were to be the source for the metals in the J-M reef. Model Raleigh fractionation calculations suggest that the cumulates beneath the J-M reef could have had the required metal concentrations if, during the crystallization of a parent magma containing no more than 15 ppb of either metal, the average bulk solid/liquid distribution coefficients for Pt and Pd were no more than 5; these values are consistent with assumption of sulfide saturation prior to the formation of the J-M reef.During solidification of intercumulus liquid, the separation and loss of a Cl-rich fluid will deplete the residual assemblage of S and PGE. If 0.1 to 0.5 wt percent fluid containing 5 percent S evolved during solidification of the footwall cumulates (the amount of fluid expected to be exsolved by the crystallization of approximately 2 to 10 percent fluid-saturated intercumulus liquid), the fluid/liquid distribution coefficients for Pt and Pd would need to be almost as large as the (sulfide liquid)/(silicate liquid) distribution coefficients to remove significant amounts of Pt and Pd. Much smaller distribution coefficients are needed if sulfide is completely lost to fluid during degassing. The latter possibility is consistent with the low S contents of the footwall cumulates beneath the J-M reef. Numerical models of the degassing of intercumulus liquids suggest that thick cumulus sequences can act as chromatographic columns to separate the PGE and S during the degassing of intercumulus silicate liquids, the PGE being enriched at a sulfide-dissolution front as upward migrating sulfide-undersaturated fluids resorb cumulus sulfides. Zones of PGE and S enrichment can occur where degassing fronts encounter stratigraphic physical-chemical discontinuities such as changes in the fluid saturation temperature of the intercumulus silicate liquids.

Blow up and growth in the directional solidification of dilute binary alloys

Numerous asymptotic equations have been derived to describe the evolution of the solid-liquid interface which occurs during the directional solidification of a dilute binary alloy. In the limit of a small distribution coefficient, many of these equations have been of the form [l-4] where α and K are positive constants. More recently the equation has also been derived in this context by a modified asymptotic method,which more accurately preserves some of the original nonlinearities [5]. Both of these equations fall into the class of equations where f(u) is a positive convex function,where r, K and α are constants and where K and α are positive. For (0.1) and (0.2), we demonstraie that if the solution breaks down in finite time, then blowup of the L∞norm occurs. Furthermore, if K is sufficiently large, a=0, and if the initial data is sufficiently small, then solutions exist globally and decay to zero exponentially.Estimates on the growth of the H −1norm are also given. Sufficient conditions for blow up for ...

Use of actinides in uncommon oxidation states for their extraction and separation from alkaline solutions

The extraction behavior of Am(IV–VI) from high pH solutions in the presence of carbonates, pyrophosphates or polyphosphates of alkali metals and of Np(VI–VII) from alkaline solutions with acylpyrazolones (1-phenyl-3-methyl-4-benzoylpyrazolone-5, PMBP) and extractants of the phenol type [bis(2-oxy-4-alkyl-benzoil)amin, CAAF] has been studied. The extraction ability of phenolic extractants with respects to Np(VII) is determined generally by its state in the alkaline solution. Maximum extraction is observed when Np(VII) is present as hydroxo complex and minimum extraction, when the solution contains oxo-ions. During the extraction the reduction of Np(VII) to Np(VI) is possible. Hexavalent neptunium can be extracted by phenol extractants too, but more slowly and with smaller distribution coefficients in comparison with Np(VII). The stabilization of transplutonium elements (TPE) in the highest oxidation states in alkaline solutions contaning carbonate and pyrophosphate ions, in combination with extraction by PMBP and CAAF, allows to realize the separation of transplutonium elements which are very similar in their properties. Methods of separation for americium and curium have been developed. They are based on the ability of trivalent curium to be extracted quantitatively from 0.1M sodium pyrophosphate solution (pH 10) and 1.0M potassium carbonate solution (ph 13.4) by PMBP in chloroform and by CAAF in carbon tetrachloride, respectively, with high distribution coefficients, whereas americium which is electrochemically oxidized to Am(VI) in these media, remains in the aqueous phase, since it reduces only to Am(V) when contacting the extractant. The separation factor of the couple Cm(III) Am(VI) is about 103.

Modified asymptotic approach to modeling a dilute-binary-alloy solidification front.

Directional solidification in the presence of an impurity may be described by a set of impurity-concentration and thermal-diffusion equations coupled at a free boundary. Small deviations of the interface from planarity can be described by a single fourth-order equation. This equation is derived by a long-wavelength, small-amplitude expansion in the limit of a small distribution coefficient. We present an alternative asymptotic approach that isolates and preserves the crucially important nonlinearities in their original form, and thus preserves the proper behavior at large amplitudes during pattern formation. The resulting evolution equation is in better agreement with the physical phenomena of front destabilization and droplet creation than are previously presented models. The formation of different solidification patterns is numerically elucidated.

A study of the transport phenomena of solar grade silicon prepared by the bridgman-stockbarger process

A mathematical model to simulate the heat transfer process of the directional solidification of silicon in a Bridgman-Stockbarger furnace was established. Finite element technique was employed to compute the temperature profile and the solid-liquid interface. The distributions of impurity concentrations were also predicted. Impurity with a small distribution coefficient showed a marked purification effect by this directional solidification process. Qualitative agreement between theoretical results and experimental measurements which used boron and aluminum as testing impurities was obtained.

Matrix Diffusion Effects on Contaminant Migration from an Injection Well in Fractured Sandstone

ABSTRACTDeep‐well injection into fractured sandstone is an option for the disposal of contaminated mine dewatering discharge from an open pit uranium mine. As part of the assessment of potential contaminant migration from deep‐well injection, the effect of matrix diffusion was evaluated. An analytical mathematical model was developed for the simulation of the radial movement of a contaminant front away from an injection point under steady flow conditions in a planar fracture with uniform properties. The model includes the effects of advection in the fracture, diffusion of contaminants from the fracture into the rock matrix, and equilibrium adsorption on the fracture surface as well as in the rock matrix. Effective diffusion coefficients obtained from laboratory experiments on 11 intact core samples varied from 3.4 × 10−8 to 3.2 × 10−7 cm2/s. Model simulations were made with diffusion coefficient values in this range and with single‐fracture injection rates estimated from fracture frequencies in boreholes, and from bulk hydraulic conductivity values obtained from field tests. Because of matrix diffusion, the rate of outward movement of the front of the nonreactive contaminants from the injection well is much slower than the rate of water flow in the fractures. Simulations of the movement of contaminants that undergo adsorption indicate that even a small distribution coefficient for the rock matrix causes the contaminants to remain very close to the injection well during the one‐year period. The results of the simplified model demonstrate that matrix diffusion is an important process that cannot be neglected in the assessment of a waste disposal scheme located in fractured porous rock. However, in order to make a definitive assessment of the capability of matrix diffusion and associated matrix adsorption to significantly limit the extent of contaminant migration around injection wells, it would be necessary to conduct field tests such as a preliminary or experimental injection.

Carbon in silicon: Properties and impact on devices

The properties, origin and analysis of carbon in silicon and its influence on the electrical characteristics of devices are investigated and reviewed. The typical carbon concentrations in electronic-grade silicon are still some 10 16 cm −3. The small distribution coefficient ( k 0 = 0.058) causes an inhomogeneous incorporation of carbon along the crystal axis and across the crystal diameter during crystal growth. Carbon concentrations exceeding about 5 × 10 16 cm −3 in float-zoned silicon can lead to the formation of process-induced defects in the fabrication of power rectifiers and thyristors. These defects which are frequently arranged in a swirl-like pattern strongly deteriorate the electrical characteristics of these devices. It is shown that carbon is involved primarily in the generation of the defect nuclei whereas the defects finally observed form via precipitation of oxygen and agglomeration of silicon interstitials. Reasons for the benign behavior of high carbon concentrations in the processing of integrated circuits are discussed. In powder device processing the formation of carbon-induced defects is safely avoided by application of silicon containing carbon less than 5 × 10 16 cm −3.

The release of arsenic from contaminated sediments and muds

Abstract Stream muds and sediments, contaminated with arsenic from an industrial waste water, have been studied, under laboratory conditions, for release of this contaminant to overlying waters. The arsenic content of the muds was determined initially whereupon simulated reservoirs were prepared from these muds and natural stream water. The systems studied were: anaerobic conditions at 25o, 20o, 15°, 10°, and 4°C, aerobic conditions at 20°and 10°C with dissolved oxygen (DO) levels of 100%, 50%, 25%, and 10% saturation. Distribution coefficients, the dimensionless ratio of AS /AS ,, were determined. In both the water mud aerobic and anaerboic systems, lower temperatures produced smaller distribution coefficients (those in the 4–10oC range were about 40% of the coefficients at the higher 20–25°C range). Very little difference was found in the distribution coefficients at a given temperature between reservoirs having either 10%, 25%, 50%, or 100% of saturation of dissolved oxygen. Anaerobic conditions led to...

Osmium, ruthenium, iridium and uranium in silicates and chromite from the eastern Bushveld Complex, South Africa

Osmium, ruthenium, iridium and uranium contents were determined in eight ortho pyroxene, seven plagioclase, and three chromite mineral separates from the eastern Bushveld Complex. Neutron activation analysis was used to measure the platinum metals, and uranium was determined by a fission track technique. The platinum metals were found to be present within each minéral in the proportions Os: Ru: Ir = 1:7:1, while the concentrations of these metals in the minerals are in the ratios orthopyroxene:plagioclase:chromite = 1:16:700. The concentration of uranium was found to range from 11 to 66 ppb (parts per billion) and not to vary significantly from mineral to mineral. The data for the platinum metals are consistent with a model in which the eastern Bushveld Complex was formed by the fractional crystallization of two separately injected magmas. A computer fit of this model to these data indicates that the initial concentrations of Os, Ru and Ir in the first magma were 0.24, 2.0 and 0.21 ppb and in the second magma were 0.16, 1.1 and 0.18 ppb, respectively. The fit also yields the distribution coefficients for the partitioning between the liquid and cumulus orthopyroxene, cumulus plagioclase and cumulus chromite. These coefficients (mineral/liquid) for osmium are 4.5, 66 and 2700; for ruthenium, they are 5, 65 and 2700; and for iridium, they are 4, 60 and 1600. To make this fit, it was necessary to hypothesize the existence of two types of chromite: one type with a large distribution coefficient, presumably formed as a cumulus phase at high temperature, and another, more prevalent type with a smaller distribution coefficient, which may have been formed by postcumulus growth at a lower temperature. This hypothesis is supported by data for coexisting chromite-silicate pairs, which indicate that the chromite grains expelled these platinum metals as they cooled.