Charged Mixtures Research Articles

Use of mechanical alloying and subsequent annealing for obtaining intermetallic compound CuAl2

The possibility of obtaining a “line” (narrow-homogeneity-range) intermetallic compound CuAl2 with the use of mechanical alloying (MA) and subsequent annealing has been investigated by X-ray diffraction and scanning electron microscopy. Regimes (composition of a charge mixture, time of preliminary MA, time and temperature of annealing) allowing one to obtain a virtually single-phase compound have been determined. The low-temperature annealings in a temperature range of 100–250°C have shown that the most probable mechanism of mass transfer upon heating of layered composites obtained by MA is grain-boundary diffusion, which can be explained by a large fraction of grain boundaries in mechanically alloyed powders.

Synthesis of fine-grained calcium hexaferrite and investigation of its structural and magnetic parameters

The results of investigations aimed at creating a system of fine-grained crystals of calcium hexaferrite doped with lanthanum (barium) are presented. An integrated technological approach that involves two cycles is implemented. At the first stage, i.e., the stage of preparing the charge mixture, a high-efficiency cryochemical technology that allows one to obtain a chemically homogeneous (at the atomic level) ferrite charge mixture was used. At the second stage, namely the stage of ferritization, 1.2–4.8 wt % of a low-melting flux was added to an oxide charge mixture of ferrite that made it possible to reduce the temperature of complete ferritization and, thus, to create the conditions for formation of nano- and microcrystals of a specified composition. The specimens of the synthesized magnetic powder demonstrated magnetic properties at the level of the best microcrystalline systems of barium hexaferrite.

Thermodynamics and diffusion in size-symmetric and asymmetric dense electrolytes

MD simulation results for model size-symmetric and asymmetric electrolytes at high densities and temperatures (well outside the liquid-gas coexistence region) are generated and analyzed focusing on thermodynamic and diffusion properties. An extension of the mean spherical approximation for electrolytes originally derived for charged hard sphere fluids is adapted to these systems by exploiting the separation of short range and Coulomb interaction contributions intrinsic to these theoretical models and is found to perform well for predicting equation of state quantities. The diffusion coefficients of these electrolytes can also be reasonably well predicted using entropy scaling ideas suitably adapted to charged systems and mixtures. Thus, this approach may provide an avenue for studying dense electrolytes or complex molecular systems containing charged species at high pressures and temperatures.

SU‐E‐T‐03: Proximity Effects and Intra‐Track DSB Interactions within the Repair‐Misrepair Fixation (RMF) Model

Purpose: Formulas linking Linear‐Quadratic (LQ) cell survival parameters to double strand break (DSB) induction are derived from the Repair‐ Misrepair‐Fixation (RMF) model for mixed radiation fields. Measured data for several cell lines irradiated by radiations of varying quality are used to examine the impact of proximity effects on intra‐ and inter‐track binary misrepair. Methods: With the RMF, estimates of alpha and beta for any particle type are determined by a well‐defined physical parameter (mean specific energy), two biological parameters (theta and kappa) that are independent of radiation quality, and a biological parameter (sigma) that depends on radiation quality. To minimize the number of ad hoc adjustable parameters, we used the published Monte Carlo Damage Simulation (MCDS) to estimate sigma. The effects of radiation quality on alpha and beta were examined by performing a regression analysis of survival data for 55 and 250 kVp x‐rays (V79 cells), for 55 kVp, 250 kVp and gamma‐rays from 60Co (CHO cells) and human kidney T‐1 cells irradiated by x‐rays, protons, deuterons and alpha particles with an LET up to 200 keV/um. Results: In CHO, V79 and T‐1 cells irradiated by widely varying types of radiation, the probability per unit time DSB formed by the same track interact in pairwise fashion is 100 to 300 times larger than the probability per unit time DSB formed by different tracks interact in pairwise fashion. Conclusion: The RMF is a useful conceptual and mathematical framework to quantify the effects of radiation quality on intrinsic radiation sensitivity for monoenergetic charged particles and mixtures of charged particles of varying quality. Although not an especially important cell killing mechanism for low LET radiations, intra‐track binary misrepair becomes the dominant one‐track cell killing mechanism for intermediate and higher LET radiations.

Self-Propagating High Temperature Synthesis of Composition Materials using Mineral Raw Materials

The possibility of obtaining multicomponent refractory composition materials on the basis of quarts containing raw material by SHS method was studied. The use of a modifying carbon additive in the form of graphite power, carbonized rice husk, apricot stones and shungit was considered. It is shown that a complex use of preliminary mechanochemical activation (MA) and modification of the charge mixture with carbon containing additives contributes to formation of carbide and nitride phases in synthesis products.

Morphologies of Charged Diblock Copolymers Simulated with a Neutral Coarse-Grained Model

We present the results of coarse grained molecular dynamics simulation using a charge free model that is able to capture different regions of the morphological phase diagram of charged diblock copolymers. Specifically, we were able to reproduce many phases of the poly(acrylic acid)-(1,4)-polybutadiene (PAA-PBA) diblock copolymer, Ca(2+) and water systems as a function of pH and calcium concentration with short-range LJ type potentials. The morphologies observed range from bilayers to cylinders to spherical micelles. Such polyanionic/cationic amphiphiles in water typically present multiple challenges for molecular simulations, particularly due to the many charge interactions that are long ranged and computationally costly. Further, it is precisely these interactions that are thought to modulate large amphiphile assemblies of interest such as lipid rafts. However, our model is able to reproduce different morphologies due to pH and with or without the addition of Ca(2+) as well as the lateral phase segregation and the domain registration observed in neutral and charged diblock copolymer mixtures. The results suggest that the overall effect of charges is a local structural rearrangement that renormalizes the steric repulsion between the headgroups. This simple model, which is devoid of charges, is able to reproduce the complex phase diagram and can be used to investigate collective phenomena in these charged systems such as domain formation and registration or colocalization of lipid rafts across bilayer leaflets.

Renormalized jellium mean-field approximation for binary mixtures of charged colloids

In this work the renormalized jellium model of colloidal suspensions, originally proposed by Trizac and Levin [Phys. Rev. E 69, 031403 (2004)], is extended to study mechanisms of charge renormalization in binary mixtures of charged colloids. We here apply our recent reformulation that introduces the requirement of self-consistency directly into the Poisson-Boltzmann equation, i.e., the background charge is explicitly replaced by the effective one, thus facilitating the whole charge renormalization scheme. We briefly discuss the reformulated model for monodisperse charged suspensions composed of either spheres or rods. In particular, we put emphasis on the effects of the surface charge variation, mixture composition, and particle size on the charge regulation of charge-stabilized colloidal suspensions.

Charged colloid-polymer mixtures: A study on electrostatic depletion attraction

In this work, light scattering methods have been used to study the effect of adding charged polymer chains on the structural and dynamic properties of a charged colloidal system. The experimental measurements of the static structure factor S(cc)(q) show that as the polymer concentration increases, the main peak moves to higher q-values, which is interpreted in terms of the electrostatically enhanced depletion attraction induced by the polymer. Moreover, we found that the shift of the peak depends on the interplay between two relevant length scales, the polymer radius of gyration, R(g), and the Debye length, κ(-1). To reach these conclusions, the polymer reference interaction site model has been employed to explain the experimental results and to study how the effective depletion attraction depends on the polymer concentration, R(g) and κ(-1). Additionally, the measurements of the dynamic structure factor f(q, τ) indicate that the colloidal diffusion increases with the polymer concentration. Both static and dynamic analysis point out that the repulsion between colloids becomes weaker as the charged polymer is added.

Carbon adsorbents and ionites from a copolymer of petroleum asphaltites

Radiation-resistant cation exchangers with a static exchange capacity to 5.91 mg-equiv/g and a mechanical strength to 95% were prepared based on a grafted copolymer of asphaltite and acrylonitrile. The adsorbents prepared in accordance with an industrial process using a charge mixture containing the copolymer exhibited higher sorption properties, as compared with those of the commercial adsorbent SKT, in the sorption of silver from multicomponent polymetallic solutions. The selectivity factor for silver was 3.55, as compared with 1.85 for SKT.

Binding of Heparin to Metals

Heparin is a major prophylactic and treatment agent for thrombosis. Structurally, this anticoagulant is a polydisperse, highly negatively charged polysaccharide mixture that contains a variable density of sulfate group substituents per molecule. Previous study has shown that heparin molecules have a high affinity for a wide range of metal ions with varying oxidation states. However, reports in literature on binding of heparin to metals have investigated only a small sampling of heparin-metal ion interactions. Since interaction of heparin with fluid phase and cell surface macromolecules in vivo is dependent on the heparin structure when bound in a metal ion complex, a survey of the physical parameters for heparin binding to metals is imperative. Atomic absorption and spectrophotometry experiments were performed for metal quantification, and in this study, the relative values for affinity constants and number of binding sites for heparin binding to several alkaline, alkaline earth, main group, and transition metals in their most common oxidation states are reported. We found an overall trend for heparin-metal affinity to be Mn(2+)>Cu(2+)>Ca(2+)>Zn(2+)>Co(2+)>Na(+)>Mg(2+)>Fe(3+)>Ni(2+)>Al(3+)>Sr(2+), with the trend in N (b) being opposite compared with the K (a).

Electrolytes in a nanometer slab-confinement: Ion-specific structure and solvation forces

We study the liquid structure and solvation forces of dense monovalent electrolytes (LiCl, NaCl, CsCl, and NaI) in a nanometer slab-confinement by explicit-water molecular dynamics (MD) simulations, implicit-water Monte Carlo (MC) simulations, and modified Poisson-Boltzmann (PB) theories. In order to consistently coarse-grain and to account for specific hydration effects in the implicit methods, realistic ion-ion and ion-surface pair potentials have been derived from infinite-dilution MD simulations. The electrolyte structure calculated from MC simulations is in good agreement with the corresponding MD simulations, thereby validating the coarse-graining approach. The agreement improves if a realistic, MD-derived dielectric constant is employed, which partially corrects for (water-mediated) many-body effects. Further analysis of the ionic structure and solvation pressure demonstrates that nonlocal extensions to PB (NPB) perform well for a wide parameter range when compared to MC simulations, whereas all local extensions mostly fail. A Barker-Henderson mapping of the ions onto a charged, asymmetric, and nonadditive binary hard-sphere mixture shows that the strength of structural correlations is strongly related to the magnitude and sign of the salt-specific nonadditivity. Furthermore, a grand canonical NPB analysis shows that the Donnan effect is dominated by steric correlations, whereas solvation forces and overcharging effects are mainly governed by ion-surface interactions. However, steric corrections to solvation forces are strongly repulsive for high concentrations and low surface charges, while overcharging can also be triggered by steric interactions in strongly correlated systems. Generally, we find that ion-surface and ion-ion correlations are strongly coupled and that coarse-grained methods should include both, the latter nonlocally and nonadditive (as given by our specific ionic diameters), when studying electrolytes in highly inhomogeneous situations.

Arbitrary mixture of two charged interacting particles in a magnetic Aharonov–Bohm ring: persistent currents and Berry's phases

Aharonov–Bohm physics at the two-particle level is investigated for distinguishable interacting charged particles through the exact solution of a toy model with confined states. The effect of the inaccessible magnetic flux is distributed between the center-of-mass and the internal pair level, and the nontrivial manner in which the two levels mutually affect each other demonstrates the interplay between interactions, the nontrivial topology, the Aharonov–Bohm flux and the characteristics of a charged quantal mixture. Analytical expressions for energy spectra, wavefunctions, (flux-dependent) critical interactions for binding and current densities are derived, and these offer the rare possibility of studying persistent currents from the point of view of an interacting nanoscopic system. Two cyclic adiabatic processes are identified, one coupled to the center-of-mass behavior and the other defined on the two-body interaction potential, with the associated Berry's phases also analytically determined; these are found to be directly linked to the electric and probability (persistent) currents in nontrivial ways that are shown to be universal (independent of the actual form of the interaction). The direct connection of the two-body Berry's phase to the electric current for a neutral system is found to disappear in the case of identical particles—hence revealing the character of a charged mixture as being crucial for exhibiting this universal behavior.

Phase Separation in Symmetric Mixtures of Oppositely Charged Rodlike Polyelectrolytes

Phase separation in salt-free symmetric mixtures of oppositely charged rodlike polyelectrolytes is studied using quasi-analytical calculations. Stability analyses for the isotropic-isotropic and the isotropic-nematic phase transitions in the mixtures are carried out and demonstrate that electrostatic interactions favor nematic ordering. Coexistence curves for the symmetric mixtures are also constructed and are used to examine the effects of linear charge density and electrostatic interaction strength on rodlike polyelectrolyte complexation. It is found that the counterions are uniformly distributed in the coexisting phases for low electrostatic interaction strengths dictated by the linear charge density of the polyelectrolytes and Bjerrum's length. However, the counterions also partition along with the rodlike polyelectrolytes with an increase in the electrostatic interaction strength. It is shown that the number density of the counterions is higher in the concentrated (or "coacervate") phase than in the dilute (or supernatant) phase. In contrast to such rodlike mixtures, flexible polyelectrolyte mixtures can undergo only isotropic-isotropic phase separation. A comparison of the coexistence curves for weakly charged rodlike mixtures with those of analogous flexible polyelectrolyte mixtures reveals that the electrostatic driving force for the isotropic-isotropic phase separation is stronger in the flexible mixtures.

Formation of Fluid Lamellar Phase and Large Unilamellar Vesicles with Octadecyl Methyl Sulfoxide/Cholesterol Mixtures

Systems composed of a monoalkylated amphiphile and a sterol have been shown to form stable liquid-ordered (lo) lamellar phases; these include negatively charged mixtures of unprotonated palmitic acid/cholesterol (Chol) or cholesterol sulfate (Schol) and mixtures of positively charged cetylpyridinium chloride/Schol. Large unilamellar vesicles (LUVs) could be formed by these systems, using conventional extrusion methods. The passive permeability of these LUVs was drastically limited, a phenomenon associated with the high sterol content. In the present paper, we showed that octadecyl methyl sulfoxide (OMSO), a neutral monoalkylated amphiphile, can form, in the presence of cholesterol, LUVs that are stable at room temperature. Differential scanning calorimetry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy of deuterium were used to characterize the phase behavior of OMSO/Chol mixtures. A temperature-composition diagram summarizing the behavior of the OMSO/Chol system is proposed; it includes a eutectic with an OMSO/Chol molar ratio of 5/5. It is found that the fluid phase observed at temperature higher than 43 degrees C is metastable at room temperature, and this situation allows extruding these mixtures to form stable LUVs at room temperature. This distinct behavior is associated with the strong H-bond capability of the sulfoxide group. The properties associated with this neutral formulation expand the potential of these non-phospholipid liposomes for applications in several areas such as drug delivery.

The Peculiarities of Combustion and Phase Formation during SHS of Mechanically Activated Mixtures Quartz – Calcite

<p>The work with the influence of mechanochemical treatment (MCT) of minerals (quartz-SiO<sub>2</sub>, calcite-CaCO<sub>3</sub>) on the process of their combustion under the conditions of SHS with aluminium. It is shown that activation of the charge mixture in the mill increases the power state of the material and contributes to the change of kinetic characteristics of combustion process: the decrease in the induction period of ignition and the increase in combustion rate. The change in combustion temperature is of a complex character due to activation of both exothermal reactions related to formation of such compounds as anothite, helenite, wollastonite. The use of deferent organic modifiers of the charge mixture results in formation of nitride and carbide compounds in the process of SHS. It is shown that changing the conditions of MCT, modifiers and ratios between the charge components it is possible on the basis of activated and modified systems to synthesize composition SHS-materials different in their phase compositions.</p>

Improved understanding of mixed oil in Nigeria based on pyrolysis of asphaltenes

Crude oil from reservoirs in the onshore Niger Delta is a mixture of low and high maturity charge. Aromatic biomarkers in these oils, such as alkylphenanthrenes and alkylnaphthalenes, show relatively high thermal maturity, whereas the saturated sterane and hopane biomarkers indicate lower maturity close to the peak of the oil window. The high predicted maturity of the crude oils based on alkylphenanthrene and alkylnaphthalene indices is probably caused by mixing of high maturity condensate with less mature black oil. This correlates with the gas washing phenomenon of studied Nigerian oils caused by migrating condensate stream. The results of our study indicate that asphaltenes can be used to infer the organofacies of the low maturity petroleum charge in mixed crude oils. Compositional characteristics of the asphaltene pyrolysates indicate an origin of the related oils from Type II/III or Type III source rock kerogen. The n-alkyl-chain length distributions of the asphaltene pyrolysates predict source rocks that generated high wax paraffinic–naphthenic–aromatic oils or paraffinic oils. The n-alkyl-chain length of asphaltene pyrolysates changes in proportion to oxicity and the relative input of terrigenous organic matter to the source rock.

Bicellar Mixtures Containing Pluronic F68: Morphology and Lateral Diffusion from Combined SANS and PFG NMR Studies

Small angle neutron scattering (SANS) and pulsed field gradient (PFG) nuclear magnetic resonance (NMR) diffusion measurements were applied to examine morphology and diffusion in dimyristoyl- plus dihexanoyl-phosphatidylcholine bicellar mixtures, either neutral or negatively charged, incorporating a Pluronic triblock copolymer (F68). Negatively charged bicellar mixtures, doped with dimyristoylphosphatidylglycerol (DMPG), exhibited SANS profiles consistent with a perforated lamellar morphology for the magnetically alignable phase. Correspondingly, F68 diffusion in this magnetically aligned phase was normal Gaussian, in that the mean square displacements increased linearly with the experimental diffusion time, with a lateral diffusion coefficient of 1.9 x 10(-11) m(2) s(-1) consistent with a lipid bilayer inserted configuration. Neutral bicellar mixtures, that is, lacking DMPG, in contrast, displayed SANS profiles characteristic of ribbons arranged in such a fashion as to produce extended lamellae. Within the lamellae, the ribbons exhibited an in-plane periodicity (interribbon) of between 120 and 140 A. Correspondingly, F68 diffusion was non-Gaussian, exhibiting a square root diffusion time dependence of the mean square displacement indicative of one-dimensional curvilinear diffusion. The presence or absence of DMPG, rather than of F68, dictated the ribbon versus lamellar morphology, with F68 reflecting this difference via its lateral diffusion behavior. Although ribbons have been reported previously, this is the first study to show that they aggregate, most likely into extended lamellar sheets, and eventually fold into multilamellar vesicles.

Enhanced crystal stability in a binary mixture of charged colloidal spheres

We report on the phase behavior of a binary charged sphere mixture of size ratio Gamma=0.68 and charge ratio Lambda approximately 1 as a function of composition p and number density n . For p=0.1-0.3 we observe freezing at densities well below the freezing densities of the pure components. At all compositions our data indicate the formation of substitutional alloy crystals of body centered cubic structure. No indications for compound formation were observed. Rather, our findings point at the first observation of an upper azeotrope. Measurements of the crystallization kinetics reveal a combined density and composition dependence of growth velocities and nucleation rate densities, with small but significant anomalies at p*=0.2 . These correlated deviations can be rationalized within classical theories of solidification and suggest an increased similarity between melt and solid for this particular composition.

Effect of ball size distribution on milling rate

This paper focuses on the determination of the selection function parameters α, a, μ, and Λ together with the exponent factors η and ξ describing the effect of ball size on milling rate for a South African coal. A series of batch grinding tests were carried out using three media single sizes, i.e. 30.6, 38.8, and 49.2 mm. Then two ball mixtures were successively considered. The original manufacturer’s recommended ball mixture was used to investigate the effect of ball size distribution on the selection function whereas the equilibrium ball mixture was used to validate the model. Results show that with the six parameters abovementioned, the charge mixture is fully characterized with about 5% deviation. Interestingly, the estimated parameters can be used in the simulator model allowing one to find the optimal ball charge distribution for a set of operational constraints.

A study of heat-transfer processes in a countercurrent cyclone heat exchanger

Heat-transfer processes in a countercurrent cyclone heat exchanger are investigated on a pilot installation. Volumetric coefficients of heat transfer from gases to a flow of solid particles are determined during operation with tangentially swirled flow of gas suspension, separation of solid particles on the heat-exchanger walls, and deceleration of flue gas flows as they collide with the charge mixture fed to the apparatus.