Equilibrium Thickness Research Articles

Енергоефективні рішення подового електроду дугової сталеплавильної печі постійного струму

Проведено чисельні дослідження електровихрових течій (ЕВТ) в сталеплавильній ванні дугової печі постійного струму і теплопередачі з фазовим переходом через подовий електрод (ПЕ). Щільність теплового потоку в ПЕ і локальна швидкість ЕВТ в анодній ямі становлять 1,8 −2 МВт/м2 і 0,75 м/с, відповідно. Рівноважна товщина твердої сталевої частини ПЕ знаходиться в критичній залежності від ширини мідно-сталевої перехідної зони, яка має не перевищувати 20−25 мм. Вдосконалено технологію виготовлення ПЕ з вузькою перехідною зоною, що забезпечує сталу експлуатацію ПЕ та підвищення енергоефективності печі.

Role of dielectronic recombination in the interaction of fast heavy-ion beams with cold plasmas

The influence of dielectronic recombination (DR) of projectile ions on characteristics of fast heavy-ion beams passing through cold plasmas is studied on the basis of fully relativistic multi-configuration calculations of DR rate coefficients. Present results are compared with the first (and, to our knowledge, the only ones) results for DR rates of 1.5-MeV/u iodine ions penetrating fully ionized hydrogen plasma with the electron temperature Te = 10 eV and density Ne = 1020 cm−3 calculated in the hydrogenic approximation (Th. Peter and J. Meyer-ter-Vehn, Phys. Rev. A 43, 2015 (1991)). Confirming the importance of DR processes of ions moving through plasma, our calculations give much higher DR-rate values than those calculated by Th. Peter and J. Meyer-ter-Vehn, which significantly changes the non-equilibrium and equilibrium ion charge-state fractions, the mean and equilibrium charges of projectile ions, as well as the equilibrium thickness of hydrogen plasmas. In order to perform DR-rate calculations for arbitrary ions passing through plasma, a new computer code DRIMP (Dielectronic Recombination of Ions Moving in Plasmas) is developed and described in the paper.

Thickness of the Ice-Shedding Lubricant Layer in Equilibrium with an Underlying Cross-Linked Polymer Film

A thin lubricant oil layer in equilibrium with an underlying cross-linked polymer film is ideal for ice shedding and smudge repellency. While the oil film renders the desired repellency, the polymer layer bestows the mechanical strength and serves as a reservoir for the lubricant. Despite this knowledge, there have been no theoretical studies on factors that affect the equilibrium thickness hs of the lubricant layer. In this work, we treat the substrate-bound polymer as a rubber film that can only expand or contract along the vertical direction. The Flory–Rehner theory for treating the 1D swelling of a rubber by a solvent is then used to derive the system’s free energy, which is further used to construct the phase diagrams of such systems. From these phase diagrams and the known feed volume ratios between the lubricant and the polymer, we calculate hs and plot hs as a function of the Flory–Huggins parameter for the polymer and the lubricant, the cross-linking density of the polymer, and the molecular volume and amount of lubricant. Aside from using these plots for regulating hs and for justifying prior experimental observations, we also propose methods to tune the different variables to sustain the release of the lubricant until it is essentially exhausted. Additionally, we draw attention to possible measures that can be used to design thermoresponsive ice-shedding coatings that store the lubricant in the polymer matrix during the warm seasons to minimize lubricant loss but release the lubricant during winter to enable ice shedding. While the current theory involves approximations, the predicted trends will be of guidance value for designing and preparing robust and long-lasting ice-shedding coatings.

Equilibrium thickness of foam films and adsorption of ions at surfaces: Water and aqueous solutions of sodium chloride, hydrochloric acid, and sodium hydroxide

HypothesisThe origin of negative surface charge at water/air interface is still not clear. The most probable origin is specific adsorption of OH− ions. From diffuse layer potential, we can evaluate the surface density of ions in the Stern layer which can be a measure for the specific adsorption of ions and determines whether the surface charge is solely due to the specific adsorption of OH− ions. ExperimentsEquilibrium thickness of foam films of pure water and aqueous solutions of NaCl, HCl, and NaOH was measured as a function of disjoining pressure for water and as a function of concentration for the aqueous solutions at 298.15 K. Quartz-glass cells thoroughly cleaned and immersed in pure water before use were used for the measurement. FindingsApplication of a modified Poisson-Boltzmann equation to the equilibrium film thickness gave the diffuse layer potential and the surface density of ions in the Stern layer. From the concentration dependence of the surface density, it was concluded that not only OH− ions but also Cl− ions and HCO3− and/or CO32− ions adsorb specifically at the water/air interface.

Novel approach for calculating the equilibrium foam nanofilm-meniscus contact angle and the film free energy

The film meniscus is a capillary system that is part of everyday observed phenomena, such as in foams, emulsions, liquid suspensions of nanoparticles (nanofluids), and liquid-wetting solids. The capillarity of a microscopic free foam lamella with a meniscus is important for a fundamental understanding of the role of the surface forces vs. thickness and stability of dispersed systems. The film-meniscus transition region, known as the Gibbs-Plateau border, and macroscopic contact angle, defined by the extrapolated meniscus Laplace surfaces, are the characteristics of capillary systems that reveal how the surface forces contribute to the stability of the dispersed systems. The foam nanofilm formed from a nanofluid due to nanoparticle self-layering under the film surface confinement thins in a multiple regular stepwise manner (not like soap films) above the CMC. The equilibrium thickness of the nanofilm is governed by the film area rather than the capillary pressure, as was reported for common and Newtonian films. Our video clip shows that the nanofilm thins layer by layer as the film area decreases. Our observation reveals that the nanofilm with a small film area remains at the equilibrium thickness with several layers. An iterative method is proposed to locate the film meniscus contact line. The film-meniscus profile of the transition region is examined using the reflected light interferometry and by applying the two radii of curvature. The micro- and macroscopic contact angles between nanofilm and meniscuses are calculated. The foam nanofilm’s structural free energy is calculated vs. the number of layers. The knowledge gained from this research will help to improve the understanding of the dispersion stability of foams, emulsions, and liquid suspensions of nanoparticles.

Moisture sorption and thickness swelling of wood-based materials intended for structural use in humid conditions and bonded with melamine resin

When used in construction, the properties of wood-based materials they are mainly affected by moisture. Moisture sorption and the associated swelling has an impact on the resistance of materials to biocidal attacks, on their mechanical properties or air permeability, and on comfort of use and durability of the structure. Equilibrium moisture content (EMC) and thickness swelling (TS) depending on the relative humidity for plywood (PW), particleboard (PB) and oriented strand board (OSB), for load-bearing purposes in humid environments and bonded with melamine-urea-formaldehyde resin (MUF), are studied in detail in this paper. Equilibrium moisture content and thickness swelling are influenced by the type of material, density, quantity of adhesive composition, and paraffin. The highest values of equilibrium moisture content were found in plywood, whilst the highest thickness swelling was achieved by OSB. A high dependency of nonrecoverable thickness swelling on the equilibrium moisture of the material was also ascertained. The proportion of nonrecoverable thickness swelling increases exponentially, in particular if the material’s equilibrium moisture content exceeds 12%.

A growth/annealing equilibrium model for helium-induced nanostructure with application to ITER

Abstract It is now well-known that under exposure to a helium (He) plasma at elevated temperatures, a tungsten (W) surface is modified by the growth of a fibreform nano-structure referred to as “fuzz”. Formation of W fuzz occurs when a specific set of conditions are met and raises concerns for the behaviour of the ITER W divertor targets. The key open question remains, however, of whether or not fuzz will actually form in ITER. An analysis of existing data shows that the fuzz annealing kinetics can be described by a diffusive-like kinetics law. A growth/annealing equilibrium model is then proposed to take into account Edge Localized Mode (ELM)-induced erosion and the effect of the transient temperature excursion on fuzz growth and annealing. In addition, both the decrease of fuzz erosion rate and thermal conductivity with increasing thickness are treated consistently. The main finding is that as fuzz grows thicker, its thermal conductivity decreases and peak temperature attained during an ELM increases. Given the competition between growth and annealing rates, an equilibrium thickness exists above which fuzz annealing dominates for a given ELM energy density. In the absence of ELMs, the fuzz thickness would increase with the typical t0.5 time dependence.

Grain growth and solid-state dewetting of Bi-Crystal Ni-Fe thin films on sapphire

We studied the solid-state dewetting behavior of thin Ni80Fe20 films deposited on basal plane oriented sapphire substrate and annealed in the range of temperatures of 1023–1323 K. All studied films exhibited strong <111> texture and maze bicrystal microstructure, with only two grains misoriented by 60° around the common <111> axis present in the film. The morphology of partially dewetted films changed from the one typical for polycrystalline thin films to the one typical for single crystalline heteroepitaxial films with increasing temperatures and annealing times. This change of dewetting behavior was associated with the fast grain growth in the films. The films of pure Ni of identical thickness, annealed under identical conditions exhibited significantly slower grain growth and lower thermal stability. Both the high-resolution X-ray diffraction and the cross-sectional high-resolution transmission electron microscopy observations revealed the phase separation of the Ni80Fe20 films into two parallel layers of the face-centered cubic (adjacent to the substrate) and hexagonal close-packed (on the top of the film) phases of similar compositions. Our density functional theory (DFT) calculations indicated that this phase separation is driven by the decrease of the film surface and interface energy, leading to the thermodynamically equilibrium thickness of the metastable hexagonal close-packed phase. This phase exhibits higher surface anisotropy than its stable face-centered cubic counterpart and is instrumental in accelerating the grain growth in the film via suppression of grain boundary grooving.

The effect of fuel composition and additive packages on deposit properties and homogeneous charge compression ignition combustion

Homogeneous charge compression ignition combustion is highly dependent on in-cylinder thermal conditions that are favorable to auto-ignition, and the presence of deposits can dramatically impact the in-cylinder environment. Because fuels available at the pump can differ considerably in composition, and fuel composition and the included additive package directly affect how deposits accumulate in a homogeneous charge compression ignition engine, strategies intended to bring homogeneous charge compression ignition to market must account for this fuel and additive variability. In order to investigate this impact, two oxygenated refinery stream test fuels with two different additives were run in a single cylinder homogeneous charge compression ignition engine. The two fuels had varying chemical composition; one represents a “dirty” fuel with high aromatic content that was intended to simulate a worst-case scenario for deposit growth, while the other represents a California Reformulated Gasoline Blendstock for Oxygenate Blending fuel, which is the primary constituent of pump gasoline at fueling stations across the state of California. The additive packages are typical of technologies that are commercially available to treat engine deposits. Both fuels were run in an experimental, single-cylinder homogeneous charge compression ignition engine in a passive conditioning study, during which the engine was run at steady state over a period of time in order to track changes in the homogeneous charge compression ignition combustion event as deposits accumulated in-cylinder. Both the composition and the additive influenced the structure of the combustion chamber deposit layer, but more importantly, both the rate at which the layer developed and the equilibrium thickness it achieved. The overall thickness of the combustion chamber deposit layer was found to have a significant impact on homogeneous charge compression ignition combustion phasing.

Grain Growth and Solid-State Dewetting of Bi-Crystal Ni-Fe Thin Films on Sapphire

We studied the solid-state dewetting behavior of thin Ni80Fe20 films deposited on basal plane oriented sapphire substrate and annealed in the range of temperatures of 1023-1323 K. All studied films exhibited strong texture and maze bicrystal microstructure, with only two grains misoriented by 60° around the common axis present in the film. The morphology of partially dewetted films changed from the one typical for polycrystalline thin films to the one typical for single crystalline heteroepitaxial films with increasing temperatures and annealing times. This change of dewetting behavior was associated with the fast grain growth in the films. The films of pure Ni of identical thickness, annealed under identical conditions exhibited significantly slower grain growth and lower thermal stability. Both the high-resolution X-ray diffraction and the cross-sectional high-resolution transmission electron microscopy observations revealed the phase separation of the Ni80Fe20 films into two parallel layers of the face-centered cubic (adjacent to the substrate) and hexagonal close-packed (on the top of the film) phases of similar compositions. Our density functional theory (DFT) calculations indicated that this phase separation is driven by the decrease of the film surface and interface energy, leading to the thermodynamically equilibrium thickness of the metastable hexagonal close-packed phase. This phase exhibits higher surface anisotropy than its stable face-centered cubic counterpart and is instrumental in accelerating the grain growth in the film via suppression of grain boundary grooving.

Modelling surface melting of macro-crystals and melting of nano-crystals for the case of perfectly wetting liquids in one-component systems using lead as an example

It is known that the majority of crystals melt without superheating. It is because liquids usually perfectly wet their own crystals, leading to surface melting at a lower temperature compared to the bulk melting point of the same crystal. In this paper first this phenomenon is modelled. The equilibrium thickness of the liquid nano-layer is found to approach asymptotically infinity as temperature approaches the bulk melting point of the macro-crystal. Further, the size of the solid crystal is gradually reduced below 100 nm and the size dependence of melting nano-crystals is modelled. Calculations are performed for pure lead (Pb), for which experimental results were published for both of the above mentioned phenomena. The validity of our models is confirmed by these literature experimental results. Co-existence of a core solid and a liquid shell is found in a finite temperature range below the macroscopic melting point in one-component nano-systems, explained by the extended phase rule of Gibbs. The lower temperature of this T-range is called here the solidus temperature, while the upper temperature of this T-range is called here the liquidus temperature of the one-component nano-crystal. Both the solidus and liquidus temperatures of the nano-crystal decrease with decreasing particle size and merge together at a critical particle size (found at 4.7 nm and at 493 K for pure lead with bulk melting point of 600.6 K). Below this critical size the nano-particle melts at a single temperature. A general rule is established claiming that when a one-component macro-crystal melts with surface melting, then the same nano-crystal melts with a solid-liquid co-existence within a finite temperature range and vice versa. Three principle types of binary nanophase diagrams are predicted for each type of macro-phase diagram, depending on whether the two components melt with or without surface melting.

Charge-state dynamics of 1.4- and 11-MeV/u uranium ions penetrating H2 and He gas targets

Abstract Theoretical description and interpretation are presented of the recent experimental data on stripping of fast 238U ions, penetrating H2 and He gaseous targets: obtained in GSI, Darmstadt, Germany at 1.4 MeV/u with a H2 stripper, and in RIKEN, Saitama, Japan at 11 MeV/u with H2 and He strippers. Electron-loss and capture cross sections for uranium ions, interacting with H2 and He targets are calculated and used as input data in the BREIT code to obtain dynamic characteristics of uranium-ion beams: non-equilibrium and equilibrium charge-state fractions, mean and equilibrium charges, and equilibrium thicknesses. Special attention is paid for the calculation of the dynamic characteristics of 1.4-MeV/u uranium ions stripped by a H2 in a windowless gas target at GSI, using a newly designed pulsed gas cell with a pressure changing from ∼ 0.1 to ∼ 100 mbar along the ion beam. To explain the experimental data, a Gaussian pressure model for the H stripper is applied with account for the target-density effect. A possible deviation of the Bragg’s additivity rule for electron-capture cross sections for a H2 target is also considered and we predict that the equilibrium charge of a 1.4-MeV/u uranium beam in atomic hydrogen is larger than in molecular hydrogen, i.e., it is indicated that atomic hydrogen can be a more effective stripper than molecular hydrogen. Charge-changing cross sections and dynamic characteristics of 11-MeV/u uranium ions passing through He and H2 targets are calculated as well. Calculated equilibrium mean charge states q ¯ ( He ) = 67.8 and q ¯ ( H 2 ) = 75.7 are in agreement with RIKEN experimental data within 10%.

Effect of cold plasma surface pre-treatment of wheat straw particles on straw board properties

Effects of the plasma treatment were evaluated for particles from winter wheat stalks relative to the properties of particleboards manufactured from such treated particles. Using urea-formaldehyde adhesive, boards with a nominal density of 540 kg/m3 and a thickness of 6 mm were manufactured. Two degrees of plasma treatment were selected: cold plasma applied at atmospheric pressure by jet system, with a generator output voltage of 26.9 V and a current of 6.9 A; and in the second treatment, a maximum voltage of 28.6 V was used with a current of 8.7 A. The physical properties (equilibrium moisture content and thickness swelling depending on relative humidity) and mechanical properties (bending strength and tensile strength perpendicular to the plane of the board) were determined. The results showed that the plasma pre-treatment of particles had a statistically significant effect on the resulting composite properties. The mechanical properties of the boards increased with both plasma treatments, but the physical properties changed negatively. Boards manufactured from particles treated with a higher degree of plasma treatment resulted in significantly higher equilibrium moisture contents and thickness swelling than the reference boards.

Method of determination of equilibrium moisture content of building materials of fencing structures

When studying the thermal condition of the enclosing structures, it is necessary to have the values of the equilibrium moisture content Wp of the material of the design corresponding to the given temperature T and the relative humidity φ of the environment. Typically, the isotherms of sorption are empirical ratios, which approximates experimentally obtained graphs Wp = f (φ, T). The methods of experimental determination of equilibrium moisture content are quite complex in terms of ensuring the long-term maintenance of the stationary state of the surrounding gas environment and the accuracy of measuring the change in the mass of moisture material. In addition, each experiment produces only one value of Wp for certain T and φ, that is, obtaining the equilibrium moisture content of a particular porous material throughout the range of changes in relative humidity at this temperature takes a significant time interval. Below is an algorithm for numerical determination of the sorption isotherms based on the data on the pore size distribution function for a given capillary-porous material with the use of a formula for the equilibrium thickness δ of a condensate layer on a solid surface located in the gas medium with the corresponding parameters T and φ. This formula is obtained by Professor N. I. Nikitenko on the basis of his molecular-radiation theory of the heat and mass transfer, in accordance with which the energy transfer, as well as mass of matter or field, is carried out by material carriers that are continuously released or absorbed by particles of substance. The molecular-radiation theory explains the differences between the classical theory of thermal conductivity and experimental data, and on the verge it passes into the Fourier equation. Numerous experiments with different capillary-porous materials were carried out and verification of the obtained results was carried out. They confirm that the proposed algorithm allows us to determine the equilibrium moisture content of any porous materials for which the pore size distribution function is known throughout the range φ at a given temperature.

Viscous dewetting of metastable liquid films on substrates with microgrooves

We present a combined experimental and theoretical investigation of dewetting on substrates with parallel microgrooves. A thin, static liquid film has an equilibrium thickness so as to minimize the sum of the surface free energy and the gravitational potential energy. When the thickness of a liquid film is less than the equilibrium thickness, the film seeks the equilibrium through contraction of the wetted area, which is referred to as dewetting. We experimentally observed the dewetting of thin, metastable liquid films on substrates with parallel microgrooves. The experiments revealed that the films retract in the direction along the grooves and leaves liquid residues with various morphologies. We classify the residue morphologies into three modes and elucidate the dependence of the mode selection on the groove geometry and the equilibrium contact angle of the liquid. We also experimentally examined the dynamic motion of the receding contact lines of the dewetting films, and developed a mechanical model for the receding speed. Our results provide a basis for controlling liquid films using microstructures, which is useful for lubricant-impregnated surface production, painting, spray cooling, and surface cleaning.

Epitropic Liquid-Crystal Hexadecane Layer in the Rheological Model of a Heterophase Interlayer

The hydrodynamic model of a heterophase interlayer of a liquid, which includes an epitropic liquid-crystal (ELC) layer, is supplemented with its structural-rheological model. The application of these models and the technique developed for processing the results of viscosity measurements for n-hexadecane interlayers in the tribotriads has made it possible to conduct a detailed determination of the properties of its ELC layer and the overlapped layer, such as the equilibrium thickness and viscosity, their temperature variation, and the activations energy of the viscous flow.

Equilibrium parameters of a structured n-hexadecane layer

The temperature dependences of the structural characteristics of the quasi-liquidcrystalline n-hexadecane layers − their equilibrium thickness and the degree of orientational order were determined by such optical methods as measurements of admixture dichroism and the anisotropy of heterophase interlayers. The values of these epitropic liquid-crystalline layer parameters were compared with those established earlier in rheological experiments.

Effects of bubble size and approach velocity on bubble–particle interaction – a theoretical study

ABSTRACTA theoretical analysis of the atomic force microscopy (AFM) approach–retract dynamic interaction between an air bubble and a hydrophilic silica plane was carried out based on the well-established Stokes–Reynolds–Young–Laplace model. An air bubble with different radii attached to the end of a cantilever approached the silica surface with different approach velocities in a 10−3 M KCl solution. Results showed that with increasing approach velocity (0.1, 1, and 10 µm/s), the repulsive force, flattened area of the film, and hydrodynamic suction force between the 100-µm bubble and the silica plane increased. The film continued thinning at the initial stages of bubble retraction because of the attractive hydrodynamic pressure. When the bubble size decreased, the influence of hydrodynamic pressure was less evident. The final film thickness before bubble retraction was similar to the theoretical equilibrium thickness when the Laplace pressure was equal to the disjoining pressure.

Experimental investigation of novel curdlan/chitosan coatings on packaging paper

Abstract In the research, paper was successfully coated with curdlan and chitosan (CR/CH) coating solutions at different ratios (CR/CH ≈ 10:0, 8:2, 6:4, 5:5, 2:8, 4:6, 0:10% w/w). The novelty of this paper is in the use of combination of curdlan and chitosan, which led to a positive effect on the mechanical and water barrier properties. The tensile properties were improved when the ratio between polymers was 5:5. Coated papers were further investigated for their bursting strength, tear and bending resistance. Pure curdlan coating worsen the tensile and moisture properties and allowed to prepare the blend coatings with different amounts of chitosan. The equilibrium thickness of coatings as a function of curdlan content and tensile strength has shown a decrease in tensile strength. This has resulted in reduction of tensile strength especially at higher thickness. The resulting blend curdlan/chitosan coatings exhibited good water barrier and mechanical properties and could be used in many fields.

Water transport kinetics and thickness swelling behavior of natural fiber-reinforced HDPE/CNT nanocomposites

Abstract This study mainly focused on investigating the effect of carbon nanotubes (CNTs) on the long-term hygroscopic behavior of composites based on old corrugated container (OCC) and high density polyethylene (HDPE). Composite profiles were made by melt compounding and then injection molding. For CNT as a reinforcing agent, different loading levels of 0, 1, 3 and 5 phc was used. The amount of HDPE and coupling agent was fixed at 50 wt% and 2 phc for all formulations, respectively. The governing kinetic behavior of water transport in the studied composites was examined by immersing them in water at room temperature for several weeks, and water diffusion coefficients were also calculated by evaluating the water absorption isotherms. In addition, a predictive model for determining the thickness swelling rate of the samples was developed by Shi and Gardner model. Results indicated that the composites filled with CNT had considerably lower water absorption compared with those samples without ones. The absorption processes for all families of composites were found to exhibit Fickian diffusion behavior. It was found that that equilibrium thickness swelling and also shorter equilibrium time (the time to reach the equilibrium thickness swelling) decreased with increase of CNT loading. Furthermore, the swelling model provided a good predictor of the hygroscopic thickness swelling process of HDPE/OCC/CNT hybrid composites. Also, a good linear relationship was fit between swelling rate parameter ( K SR ) and CNT contents. The minimum K SR values were observed in composites made of 5 phc CNT.