Coalescence of magnetron-sputtered silver islands affected by transition metal seeding (Ni, Cr, Nb, Zr, Mo, W, Ta) and other parameters

Silver thin films were deposited on various base layers using magnetron sputtering. The onset of coalescence of silver islands was evaluated using in situ conductivity measurements. The substrates included glass and silicon, with base layers of ZnO:Al 4 at.% at various thickness and additional thin seed layers of transition metals. It is shown that certain conditions promote coalescence, and in particular the following seed conditions: tungsten (1.0 nm), molybdenum (0.1 nm), zirconium (0.5 nm), and nickel (0.1-0.2 nm). In the absence of transition metal seeding, earlier onset of coalescence occurred at the thinnest of the ZnO:Al 4 at.% base layers (5 nm) and the lowest sputtering power (50 W), indicating that the substrate-film system is not in thermodynamic equilibrium.     

Effects of coal blending on the reduction of PM10 during high-temperature combustion 2. A coalescence-fragmentation model

A coalescence-fragmentation model has been developed to predict the behaviors of coal mineral particles during the combustion of pulverized bituminous coals or coal blends. Based on the computer-controlled scanning electron microscope (CCSEM) characterization of coal minerals, the particle size distributions (PSDs) and mineral species of ash particles can be simulated. In particular, the interactions among excluded minerals (mainly referring to the excluded Ca-bearing-species and Fe-bearing-species) and included minerals are accounted for in this model. The PSDs and the mineral species of ash particles are derived from the coalescence and fragmentation of coal mineral particles. Based on this proposed model, both of the predicted PSDs and the mineral species of ash particles are in good agreement with their corresponding experimentally measured values. And the comparisons further demonstrate that the combined effects of coalescence of included minerals and fragmentation of excluded minerals have direct impacts on the ash-forming process. In addition, for the coals rich in excluded Ca- and/or Fe-bearing-species, the interactions among included minerals and excluded minerals are another important mechanism governing ash formation for high-rank coals.     

Hydrodynamic interaction and coalescence of two droplets under large step shear strains

We observed change in distance between two droplets in each step after application of large multi-step shear strains. Experiments were performed using a sliding plate apparatus. Large step shear strains were applied to two polyisobutylene droplets in poly(dimethyl siloxane) matrix in the same plane between the plates. The distance between the two droplets decreases with increasing the total shear strain, which is given by the product of the step strain magnitude and the number of application of the step strains. The two droplets coalesce when the distance becomes less than the diameter of the droplets. The slope for plots of the distance versus the total strain is independent of the step strain magnitude. This indicates that the effect per unit strain on the distance is the same, irrespective of the strain magnitude. It is suggested that a stronger hydrodynamic interaction between the droplets is the main cause for the droplet approach.     

Bubble Size Distribution in Oil‐Based Bubble Columns

A practical population balance model was used to evaluate the bubble size distribution in a bubble column. In addition, the bubble size distribution in the bubble column was measured at different gas velocities by photography and analysis of the pictures. Four types of liquid, i.e., water and three petroleum‐based liquids, were used in the experiments. The gas phase was air. It was found that the existing models in the literature are not able to satisfactorily predict the experimentally measured bubble size distribution. The model can be corrected by applying a correction factor to the energy dissipation rate. The corrected model fits the experimental bubble size distribution considerably better than the existing models. The variation of this correction factor is reported for different systems at different gas velocities.     

Helium bubbles in nickel annealed at T>0.7Tm

Helium-induced cavities in fusion materials are considered to be detrimental. Valuable information on He bubbles and on the basic mechanisms underlying their evolution is obtained by post-implantation annealing, subsequent to He implantation at about 300 K. For Ni and Cu, it has been shown that up to annealing temperatures T_a≤0.7T_m (T_m is the melting point), highly overpressurized bubbles form in the volume and coarsen very slowly by migration and coalescence, whereas near vacancy sources the overpressure relaxes and the coarsening occurs rapidly by Ostwald ripening (OR) which leads to the appearance of small and large He cavities. Annealing of He loaded Ni at T_a from 0.72T_m to 0.92T_m leads to the formation of only one population of nearly equilibrium bubbles which is related to the recovery of the ability of dislocations to emit vacancies into their surroundings. The effective activation energy of the increase of the mean bubble radius was found to be 0.60±0.02 eV, which is lower than that for the OR at lower temperatures (1.1 eV). Analysis shows that the mechanism covering the coarsening of He bubbles at very high temperatures is still OR, but limited by the rate of ledge nucleation on the bubble walls.     

Membrane‐Based Conditioning of an Innovative Oil‐Based Preservative for Food Technology

Demulsification of emulsions is of great interest for industrial applications. For developing a new, alternative preservation process, investigations are conducted for separating a mixture of water and an oil‐based preservative by membrane technology. Using a water‐in‐oil emulsion, the conventional membrane separation with hydrophobic membranes does not show a reasonable result. It was found that the oil‐based preservative leads to a hydrophilization of the membrane by its amphipathic character. Subsequently, a possible separation with a hydrophilic membrane system as a coalescing system was investigated. Different parametric studies were performed. The efficiency of the coalescence depends on the membrane material, the pore size, the transmembrane pressure, and the temperature during membrane passage as well. Best results so far have been achieved by using a polyethersulfone membrane with a pore size of 0.6 μm.     

Drop breakage and coalescence in the toluene/water dispersions with dissolved surface active polymers PVA 88% and 98%

The influence of two PVAs of the same molecular weight (13,000–23,000) and different degree of hydrolysis equal to 88% and 98% on breakage and coalescence of toluene droplets in the liquid/liquid dispersion were considered for PVA concentration range 0.001–0.01%. Analysis of experimental results shows that drop coalescence is significant only in the system containing 0.001% PVA. Drop coalescence for polymer concentration range 0.002–0.01% is strongly limited. Therefore, population balance was solved using breakage and coalescence expressions with assumed partially mobile drop interfaces for the lowest PVA concentration. For c ≥ 0.002% drop size distributions were properly predicted using only breakage model. Multifractal formalism was used to take into account intermittent character of turbulence and explain drop behavior. Larger drop size reduction by PVA of lower degree of hydrolysis observed experimentally was confirmed by the model.     

Influence of chain length in nonyl-phenol ethoxylate surfactants on the film formation behaviour of methylmethacrylate-2-ethylhexyl acrylate copolymer latexes: part 1. Differential scanning calorimetry and atomic force microscopy

A comparison of the film forming characteristics of methylmethacrylate-2-ethylhexyl acrylate latex copolymers stabilised with nonyl-phenol ethoxylate molecules of varying chain lengths is presented. The ability of the stabiliser to segregate and diffuse from the interfacial layer into the surrounding media influences both the rate of coalescence process and structure of the film formed. Dynamic mechanical analysis, minimum film formation temperature measurements, particle size analysis, differential scanning calorimetry (DSC) and atomic force microscopy reveal the complexity of the mechanism involved in the coalescence process. A model that describes the various stages of coalescence and compaction of the latex particles indicates the effects of chain length on the film forming properties. For the stabiliser with a chain length of 20, coalescence is observed at room temperature; whereas for the stabiliser with chain lengths of 30 and 40, coalescence only occurs if the films are raised above 315 K. For the longer chain stabilisers, the effect of stabiliser-stabiliser interaction inhibits the coalescence process and DSC data indicate the occurrence of crystalline phase structure in the thin film.     

On the effect of phase fraction on drop size distribution of liquid–liquid dispersions in agitated vessels

The theory of Kolmogorov–Hinze is the base for many studies that have been done on mean drop size and drop size distribution of liquid–liquid dispersions in agitated vessels. Although this theory has been used extensively in the literature, but it does not always give a satisfactory result in the studies and therefore needs to be modified. This paper addresses the effect of phase fraction on drop size distribution in agitated vessels and on the proportionality coefficient and Weber number exponent in the relation d₃₂/D ∝ We^m. The experimental data that were taken from Pacek et al. (1998) and Desnoyer et al. (2003) have been applied to this relation to investigate the effect of phase ratio. It is shown that even at low phase fractions, the Kolmogorov–Hinze theory necessarily does not give the best result with the −0.6 exponent for the Weber number. Furthermore, for the non-coalescing system, a range of exponent for the Weber number typically from −0.6 to −0.43 can be considered where the system may be approximated as a pseudo-coalescing system at Φ = 0.4 in which the obtained results are in good agreement with the results of Pacek et al. (1998).