Immiscible Combinations Research Articles

Atomic-Scale Homogeneous RuCu Alloy Nanoparticles for Highly Efficient Electrocatalytic Nitrogen Reduction.

Ruthenium (Ru) is the most widely used metal as an electrocatalyst for nitrogen (N2 ) reduction reaction (NRR) because of the relatively high N2 adsorption strength for successive reaction. Recently, it has been well reported that the homogeneous Ru-based metal alloys such as RuRh, RuPt, and RuCo significantly enhance the selectivity and formation rate of ammonia (NH3 ). However, the metal combinations for NRR have been limited to several miscible combinations of metals with Ru, although various immiscible combinations have immense potential to show high NRR performance. In this study, an immiscible combination of Ru and copper (Cu) is first utilized, and homogeneous alloy nanoparticles (RuCu NPs) are fabricated by the carbothermal shock method. The RuCu homogeneous NP alloys on cellulose/carbon nanotube sponge exhibit the highest selectivity and NH3 formation rate of ≈31% and -73μmol h-1 cm-2 , respectively. These are the highest values of the selectivity and NH3 formation rates among existing Ru-based alloy metal combinations.

Ultrafast laser ablation of silver targets in miscible and immiscible liquid mixtures

• Effect of polar-polar miscible liquids on ablation. • Effect of polar-nonpolar immiscible liquids on ablation. • Influence of liquid parameters on silver nanoparticles and nanostructures. In this article we report the results obtained from ultrafast laser ablation of silver targets immersed in polar/polar miscible and polar/non-polar immiscible combinations of liquids with laser pulses of ∼2 ps duration. Former combination included acetone and water while the latter combination was toluene and water. The prepared silver nanoparticles in pure acetone, pure water (double distilled) were compared with the silver nanoparticles fabricated in acetone–water (double distilled) mixture. Similarly, synthesized silver nanoparticles in pure toluene, pure water were compared with the silver nanoparticles fabricated in toluene-water mixture. The TEM images of Ag NPs generated in acetone demonstrated that average size of Ag nanoparticles fabricated in acetone, water, and double distilled water–acetone mixture were ∼4.5 ± 1.8 nm, ∼16 ± 4 nm, and 5 ± 1.7 nm, respectively. In the case of double distilled water-toluene combination, formed silver nanoparticles were trapped inside the graphitic matrix. Obtained morphologies and average sizes of silver nanoparticles in polar/polar miscible and polar/non-polar immiscible combinations demonstrated the effect of the difference in the formatted cavitation bubble (CB). In general, products of ablation are determined by the dynamics of CB and its oscillations those depend on the intrinsic behaviour of aqueous medium of interest.

Synthesis of a binary alloy nanoparticle catalyst with an immiscible combination of Rh and Cu assisted by hydrogen spillover on a TiO2 support.

This work demonstrated the use of TiO2 as a promising platform for the synthesis of non-equilibrium RhCu binary alloy nanoparticles (NPs). These metals are regarded as immiscible based on their phase diagram but form NPs with the aid of the significant hydrogen spillover on TiO2 with concurrent proton–electron transfer. The resulting RhCu/TiO2 exhibited 2.6 times higher catalytic activity than Rh/TiO2 during hydrogen production from the hydrolysis of ammonia borane (AB), due to a synergistic effect. Theoretical simulations showed a higher energy value for the adsorption of AB on the RhCu alloy and a lower activation energy for the rate determining N–B bond dissociation by the attack of H2O during AB hydrolysis compared to monometallic Rh. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the formation of RhCu alloy NPs with a mean diameter of 2.0 nm on the TiO2. H2-temperature programmed reduction and in situ X-ray absorption fine structure analyses at elevated temperature under H2 demonstrated that Rh3+ and Cu2+ precursors were simultaneously reduced only on the TiO2 support. This effect resulted from the improved and limited reducibility of Cu2+ and Rh3+, respectively. The rate of hydrogen spillover of TiO2 is faster as compared to γ-Al2O3 and MgO as evidenced by sequential H2/D2 exchanges during in situ Fourier transform infrared analyses. Density functional theory calculations also showed that the migration of H atoms on TiO2 proceeds with a lower energy barrier than that on Al2O3, and the reduction of Cu2+ species is facilitated by H spillover on the support rather than by direct reduction by H2. These results confirm the vital role of TiO2 in the formation of the alloy and may represent a new strategy for the synthesis of different non-equilibrium solid solution alloys.

Dissimilar Friction Stir Welding of Immiscible Titanium and Magnesium

The dissimilar friction stir welding of the immiscible combination (i. e., titanium and magnesium) was performed. The thin foil aluminum was inserted between pure titanium and pure magnesium in order to react the two immiscible materials. The welding parameters (i.e., aluminum foil thickness, probe offset and welding speed) were optimized to acquire a sound joint. Also, the influence of the welding conditions on the formation of reaction layer at the interface, aluminum distributions in the magnesium matrix and tensile strength of the joints was systematically examined. With the increasing thickness of the aluminum filler material, the size and amount of the welding defects generated inside the magnesium stir zone (SZ) increased due to the poor material flow. The dissimilar joint between titanium and magnesium fabricated with a thin aluminum filler material and with the optimized probe offset and welding speed shows a high tensile strength because of the properly thin intermetallic compound layer formed at the weld interface and inhibition of the brittle intermetallic compounds formation inside the SZ on the magnesium side during the FSW. The tensile property results indicated that the highest tensile strength of approximately 150 MPa, which is ~88% of the joint strength of pure magnesium can be obtained in the optimized dissimilar titanium and magnesium joint, and it fractured at the heat affected zone (HAZ) in the magnesium.

Pilot-Scale Experimental Study and Mathematical Modeling of Buoyant Settling of Immiscible Heavy Fluid in Mud To Stop Annular-Gas Migration Above Leaking Cement

Summary Annular casing pressure (ACP) is defined as the accumulated pressure on the casing head. If pressure returns after bleed-down, then the casing annulus is said to be showing sustained casing pressure (SCP). SCP is caused by late gas migration in the annular-fluid column above the top of leaking cement and may result in atmospheric emissions or underground blowouts. Removal of SCP is required in places where SCP is regulated, particularly before the well-plugging and abandonment operations. Annular-intervention methods for SCP removal, which are less expensive than the conventional downhole-intervention methods, typically involve injecting heavy fluid into the affected annulus that would displace the annular fluid (AF), balance the pressure at the top of cement, and stop the gas leakage. Previous studies stated that the use of immiscible combinations of two fluids is more effective for the purpose; however, inattentive applications may result in excessive use of heavy fluid. In this study, a 20-ft carbon-steel pilot-well annulus was manufactured and used for displacement experiments with various water-based drilling muds and heavy fluids with different properties. Pressure-change data were collected from four different levels of the annulus, and volumes of fluids going in and out of the annulus were measured. Experiments indicated the formation of a mixture zone that would build bottoms up and expand during ongoing displacement. The proposed pressure-buildup model suggests an exponential distribution of density of this zone, and shows its high dependency on fluids’ properties and injection rate. The mathematical models were also converted into dimensionless process measures and proposed for use in real-well applications. The study demonstrates the viability and recommends the correct application of the method.

Electronic Structure and Phase Stability of PdPt Nanoparticles.

To understand the origin of the physicochemical nature of bimetallic PdPt nanoparticles, we theoretically investigated the phase stability and electronic structure employing the PdPt nanoparticles models consisting of 711 atoms (ca. 3 nm). For the Pd-Pt core-shell nanoparticle, the PdPt solid-solution phase was found to be a thermodynamically stable phase in the nanoparticle as the result of difference in surface energy of Pd and Pt nanoparticles and configurational entropy effect, while it is well known that the Pd and Pt are the immiscible combination in the bulk phase. The electronic structure of nanoparticles is conducted to find that the electron transfer occurs locally within surface and subsurface layers. In addition, the electron transfer from Pd to Pt at the interfacial layers in core-shell nanoparticles is observed, which leads to unique geometrical and electronic structure changes. Our results show a clue for the tunability of the electronic structure of nanoparticles by controlling the arrangement in the nanoparticles.

Prediction of Drug–Polymer Miscibility through the use of Solubility Parameter based Flory–Huggins Interaction Parameter and the Experimental Validation: PEG as Model Polymer

Important consideration for developing physically stable solid dispersion is miscibility of drug in carrier matrix. It is possible to predict thermodynamics of binary system through free energy calculations based on Flory-Huggins interaction parameter (χ(dp)). In present study, PEG 6000 as model polymer and dataset comprising commonly used drugs/excipients was selected. The three-dimensional solubility parameter based on group contribution method was utilized for systemic calculation of χ(dp) of the polymer with each compound in data set. On the basis of the values of χ(dp), it was possible to categorize all the compounds into three distinct categories, Types I and II: compounds predicted to be miscible and immiscible respectively with the polymer in all proportions and Type III: compounds expected to exhibit composition dependent miscibility behavior. The Bagley plot showed that majority of points for Type I fall in a region, which can approximately be delimited by a circle. Experimental verification through thermal analysis revealed that though it was possible to predict correctly miscibility behavior of Type II class compounds, distinction between Types I and III was less evident. Hence, solubility parameter based χ(dp) may be used as an initial tool for fast screening of immiscible combination of polymer and drug.

Synthesis of non-equilibrium phases in immiscible metals mechanically mixed by high pressure torsion

The structural changes in mechanically mixed metals of immiscible combinations of elements caused by bulk mechanical alloying (MA) through the use of high pressure torsion (HPT) were investigated in Ag–Ni and Nb–Zr systems. There was no alloying between Ag and Ni on atomic scale even after 100 rotations of HPT. On the other hand, the β-Zr phase started to appear after HPT 2 rotations in the Nb–Zr system, even though β-Zr is a high temperature phase. Further, Nb and Zr were completely mixed to form a bcc structured single phase after HPT 100 rotations. The sequence of alloying in the Nb–Zr system during HPT was discussed. These results clearly suggest that non-equilibrium phases can form in the Nb–Zr system by bulk MA by the use of HPT.

Influences of Miscible and Immiscible Oils on Flow Characteristics Through Capillary Tube—Validation of Calculation Model

A capillary tube is widely used as an expansion device for small refrigeration cycles. This series of papers discusses the influence of mixing refrigeration oil with the refrigerant on the flow through the capillary tube. In the first report, the mass flow rate and temperature and pressure distributions are examined experimentally when miscible or immiscible oil is mixed with refrigerant. In this study, a theoretical model is developed to estimate the influence of oil on the properties of refrigerant/oil mixture and on the mass flow rate. The theoretical model for the miscible combination is also applicable to the immiscible one, since the immiscible oil mixes homogeneously in the liquid phase in the capillary tube. The mass flow rates in both cases of miscible and immiscible combinations are calculated within an error of ±5% in comparison to measured data. In the immiscible combination, however, the model tends to underestimate the mass flow rate slightly as the oil concentration becomes larger than 0.1.

Influences of miscible and immiscible oils on flow characteristics through capillary tube—part I: experimental study

A capillary tube is widely used as an expansion device for small refrigeration cycles. In a practical refrigeration cycle, some amount of refrigeration oil is discharged from a compressor and refrigerant/oil mixture flows through the capillary tube. This study investigated experimentally the influence of mixing of the refrigeration oil with the refrigerant on the flow through the capillary tube. The experiments are carried out with not only a miscible combination of refrigerant and oil but also an immiscible combination. In both cases, the mass flow rate through the capillary tube and temperature and pressure distributions along the tube are measured under several conditions of subcooled degree and oil concentration. In the case of miscible combination, the mass flow rate of refrigerant decreases with increasing the oil concentration because the viscosity of liquid phase increases by the mixing of viscous oil. Even in the case of the immiscible combination, the oil droplet is so small that it mixes homogeneously in the liquid phase in the capillary tube and the refrigerant mass flow rate decreases by the mixing of immiscible oil. There is no significant influence of the oil concentration on the underpressure, which means pressure difference between saturation pressure and flash inception pressure, in both miscible and immiscible combinations.

Ellipsometric studies on immiscible polymer-polymer interfaces

Ellipsometry was employed to estimate the thickness of the interface λ between two bulk layers of dissimilar polymers. The polymer/polymer combinations investigated were poly(methyl methacrylate) (PMMA)/poly(styrene- co-acrylonitrile) (SAN) (AN content < 10 and > 33 wt%), PMMA/poly(methyl methacrylate- co-styrene) (MS) and polystyrene/MS. They provide a series of immiscible combinations with various values of the Flory interaction parameter χ ranging from 1.72 × 10 −3 to 8.71 × 10 −2. The bilayer specimen prepared by the spin-coating technique was annealed at 130°C (> T g) and the time variation of λ was observed during annealing. The observed λ attained a constant value after annealing for ∼1 h and then remained constant. The constant value was assumed to be the equilibrium thickness. The thickness ranged from ∼5 to 40 nm, depending on the magnitude of χ. The thin interface (< ∼10 nm) was nicely explained by the recent theory by Broseta et al., which deals with the effect of molecular weight on λ within the strong segregation limit.

Compatibility studies on polyacrylate and polymethacrylate systems

The predicted general incompatibility of mixtures of polymers has been further confirmed. Thirty-one mixtures of homopolymer pairs showed phase separation in a common solvent. These included closely related polymers such as polyacrylates with both polymethacrylates and other polyacrylates and pairs of different polymethacrylates. Typical immiscible combinations are PMA/PEA and PEMA and PEMA/PMMA. It was also found that the presence of a common monomer constituent did not result in complete compatibility of either a homopolymer with a copolymer or a mixture of two copolymers. Apparently, none of the combinations tried were sufficiently similar to result in heats of interaction small enough to be counteracted by the small entropy change involved. Since another possibility for attaining miscibility is through polar interactions, the effects of ionic and hydrogen-bonding substituents upon polymer-polymer compatibility were considered, and selected experiments were done on a series of carboxyl-containing polymers and their sodium salts. It was concluded that hydrogen bridging occurs preferentially either intramolecularly or between polymer and solvent rather than between two different types of chains each having hydrogen-bonding ability. Thus, poly(acrylic acid) and poly(methacrylic acid) show two-phase separation in water. Although poly(sodium acrylate) and poly(sodium methacrylate) are completely miscible, mixtures of the partially neutralized acids, e.g., PAA and PNaMA mixtures, show separation. In contrast to predictions for less polar polymers, compatibility of mixtures of polymers containing high mole fractions of carboxylic acid monomers showed a pronounced dependence upon solvent. Thus, the two copolymers 45/53 EA–MAA and 47/53 MMA–MAA are incompatible in methanol or ethanol but form homogeneous solutions in DMF or DMS.