Maximum Film Thickness Research Articles

Critical thickness predicted for crack formation in Ga2O3 and Al2O3 alloys

The maximum thickness of films before tensile strain results in damage was calculated by studying crack formation in the films of Ga 2 O 3 and Al2O3 alloys

Housing Profile Design for Improved Apex Seal Lubrication Using a Finite Length Roller Elastohydrodynamic Lubrication Model

Abstract Finite-length roller contacts are found in apex seal-housing interfaces in rotary engines, as well as in many other mechanical systems, such as those at the interfaces of meshing gear teeth, cam followers, and roller bearings. Rollers are usually designed with crowns and modified ends to mitigate the negative effects of misalignment, thermal deformation, and edge-induced non-uniform displacement. A crowned-roller elastohydrodynamic lubrication model is enriched and employed to investigate seven housing surface profiles, including a sinusoidal recess, sinusoidal ends, the combination design of a sinusoidal recess and sinusoidal ends, multiple sinusoidal recesses, a concave shape, and a concave shape with sinusoidal ends or round corners, aiming to improve the tribological performance of the interface via increasing the minimum film thickness but reducing the average and maximum film thicknesses, and lowering friction coefficient. The modified discrete convolution and fast Fourier transform method with duplicated padding is utilized to deal with the potential free-end-surface effect. The simulation results suggest that the combinations of a concave shape and sinusoidal ends, or round corners, are the best designs because they can help distribute the lubricant most uniformly without causing a negative edge effect.

Role of Metal Ion-Linked Multilayer Thickness and Substrate Porosity in Surface Loading, Diffusion, and Solar Energy Conversion.

Metal ion-linked multilayers offer an easily prepared and modular architecture for controlling energy and electron transfer events on nanoparticle, metal oxide films. However, unlike with planar electrodes, the mesoporous nature of the films inherently limits both the thickness of the multilayer and subsequent diffusion through the pores. Here, we systematically investigated the role of TiO2 nanoparticle film porosity and metal ion-linked multilayer thickness in surface loading, through-pore diffusion, and overall device performance. The TiO2 porosity was controlled by varying TiO2 sintering times. Molecular multilayer thickness was controlled through assembling ZnII-linked bridging molecules (B = p-terphenyl diphosphonic acid) between the metal oxide and the Ru(bpy)2((4,4'-PO3H2)2bpy)]Cl2 dye (RuP), thus producing TiO2-(Bn)-RuP films. Using attenuated total reflectance infrared absorption and UV-vis spectroscopy, we observed that at least two molecular layers (i.e., TiO2-B2 or TiO2-B1-RuP) could be formed on all films but subsequent loading was dependent on the porosity of the TiO2. Rough estimates indicate that in a film with 34 nm average pore diameter, the maximum multilayer film thickness is on the order of 4.6-6 nm, which decreases with decreasing pore size. These films were then incorporated as the photoanodes in dye-sensitized solar cells with cobalt(II/III)tris(4,4'-di-tert-butyl-2,2'-bipyridine) as a redox mediator. In agreement with the surface-loading studies, electrochemical impedance spectroscopy measurements indicate that mediator diffusion is significantly hindered in films with thicker multilayers and less porous TiO2. Collectively, these results show that care must be taken to balance multilayer thickness, substrate porosity, and size of the mediator in designing and maximizing the performance of new multilayer energy and electron management architectures.

Experimental study on the water film thickness under spray impingement based on planar LIF

Spray impingement is widely applied in many fields, and the liquid film formed on the impact surface is closely related to the heat and mass transfer. In present paper, an experimental setup of the spray impingement with an air-atomizing nozzle was established to study the water film formed on a flat surface. And the planar laser-induced fluorescence technology was applied to measure the film thickness at different spray heights (10–40 mm) and water flow rates (60–120 ml/min). Based on the film topography, the water film was divided into the impact zone and the free flow zone. The film thickness in the impact zone was thinner than that in the free flow zone. The water film at the center of the impact surface intensely fluctuated, and the steady layer thickness was 0.33–0.73 mm. The film thickness in the free flow zone presented a camelback topography of first increasing and then decreasing with the increase of the radial distance. Besides, the film thickness in the free flow zone decreased with increasing the spray heights and increased with increasing the water flow rates. The maximum film thickness was 2.27 mm and the average film thickness in the free flow zone was 0.85–1.50 mm. The study provides much more experimental data with the study on the liquid film thickness under spray impingement.

Maximizing the Lubricant Film Thickness Between a Rigid Microtextured and a Smooth Deformable Surface in Relative Motion, Using a Soft Elasto-Hydrodynamic Lubrication Model.

We design a pattern of microtexture features to increase hydrodynamic pressure and lubricant film thickness in a hard-on-soft bearing. We use a soft elastohydrodynamic lubrication model to evaluate the effect of microtexture design parameters and bearing operating conditions on the resulting lubricant film thickness and find that the maximum lubricant film thickness occurs with a texture density between 10% and 40% and texture aspect ratio between 1% and 14%, depending on the bearing load and operating conditions. We show that these results are similar to those of hydrodynamic textured bearing problems because the lubricant film thickness is almost independent of the stiffness of the bearing surfaces in full-film lubrication.

Preparation and Self-Healing Properties of Clinker/PVP Microsphere in Cement Paste.

This paper presents a new insight into the autolytic mineral self-healing method for cementitious materials. The clinker/PVP (polyvinyl pyrrolidone) autolytic microsphere was prepared via the film coating method with cement clinker as a healing agent and PVP as the autolytic coating film. The morphology and chemical structure of the microsphere were characterized by environmental scanning electron microscopy (FESEM) equipped with energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR), respectively. The clinker retaining original mineral healing composition was successfully coated with a PVP film confirmed by FTIR. The maximum film thickness was 7.54 μm, which was determined by laser particle size measurement. The autolytic behavior was measured using isothermal calorimetry and successfully controlled by pretreatment degree (i.e., silane coupling agent amount). Experimental results showed that the compressive strength recovery of cement paste with a 30% microsphere was 54% higher than ordinary cement paste specimens. The damage degree of the specimen was also decreased by adding the autolytic microsphere.

Researches on hydrodynamics of liquid film flow on inclined plate using diffuse-interface method

The liquid film flow can consistently remove heat to reduce the pressure and temperature in the containment when a severe accident occurs in reactors. However, due to the various variable factors of the environment, such as angle of wall inclination and physical properties of liquids, the liquid film flow is complex in practice. In order to investigate the influences of inclined angle of plate, contact angle, surface tension and density on the hydrodynamics of liquid film, numerical simulation of liquid film flow on the inclined plate are studied by using the diffuse-interface method. Good agreements of the maximum liquid film thickness and the wave velocity are observed between experiment and simulation, proving that diffuse-interface method can be available to simulate the hydraulic characteristics of the liquid film flow. And the analysis of the influence of the above factors on liquid film flows show that the solitary wave phenomenon can be observed in the simulation; the wettability of liquid film flow becomes worse when the inclined angle and the contact angle increase; the change of contact angle is related to the surface tension; the wettability of the liquid film can be improved by increasing density of the liquid for the condition that the wettability is not good.

Formation Efficiency of Anodic Porous Alumina in Sulfuric Acid Containing Alcohol: Comparison of the Effects of Monohydric and Polyhydric Alcohols as Additives

Focusing on the coulombic efficiency of film formation, we systematically investigated the effects of polyhydric alcohols added to a sulfuric-acid-based electrolyte on the anodization behavior of aluminum, the coating ratio, the porosity, and the maximum attainable film thickness of the anodic oxide film by comparison with the effects of monohydric alcohols. Anodization was conducted in sulfuric acid containing various alcohols with different physical properties at a constant current density of 100 A·m−2 and at 20 °C. The viscosity and conductivity of the mixed electrolyte were affected by the addition of alcohol, resulting in an increase of the steady-state voltage with increasing alcohol concentration because of the high viscosity and low conductivity of the mixed electrolyte. Although the coating ratio, which is an index value used to evaluate the efficiency of the film formation, and the maximum attainable film thickness also increased with the addition of any of the alcohols, the addition of a polyhydric alcohol was more effective than that of a monohydric alcohol. When sulfuric acid with 50 vol% ethylene glycol was used as an electrolyte, an alumina film with less than 10% porosity was formed with high coulombic efficiency of film formation.

Targeted chemical pressure yields tuneable millimetre-wave dielectric.

Epitaxial strain can unlock enhanced properties in oxide materials, but restricts substrate choice and maximum film thickness, above which lattice relaxation and property degradation occur. Here we employ a chemical alternative to epitaxial strain by providing targeted chemical pressure, distinct from random doping, to induce a ferroelectric instability with the strategic introduction of barium into today's best millimetre-wave tuneable dielectric, the epitaxially strained 50-nm-thick n = 6 (SrTiO3)nSrO Ruddlesden-Popper dielectric grown on (110) DyScO3. The defect mitigating nature of (SrTiO3)nSrO results in unprecedented low loss at frequencies up to 125 GHz. No barium-containing Ruddlesden-Popper titanates are known, but the resulting atomically engineered superlattice material, (SrTiO3)n-m(BaTiO3)mSrO, enables low-loss, tuneable dielectric properties to be achieved with lower epitaxial strain and a 200% improvement in the figure of merit at commercially relevant millimetre-wave frequencies. As tuneable dielectrics are key constituents of emerging millimetre-wave high-frequency devices in telecommunications, our findings could lead to higher performance adaptive and reconfigurable electronics at these frequencies.

Corrosion Inhibition of Magnesium by Anodizing In Safe and Unsafe Alkaline Electrolytes

Magnesium has high strength to weight ratio , good machinability , high creep stress and high impact resistance . Such properties make the magnesium an excellent choice in many applications . Disadvantages of magnesium represented in low corrosion resistance in most environments and ignites easily in air . Surface modification techniques which are used to improve surface properities of Magnesium are conversion surface treatments like chromating , phosphating , galvanizing electroplating such as Cu , Zn , Ni , Cr , electroless metal plating and cladding by Aluminum foil . Anodizing in an electrolyte (with pH>12) is considered a passivation process that produces chemical stable protective oxide film on magnesium surface . Usually unsafe electrolytes such as KOH are frequently used . Anodizing of commercial magnesium (ASTM 9980A) was carried out in 3M KOH(unsafe) , 1M Na2SiO3 and 0.6M K2SiO3(safe) electrolytes for time periods ranging from 10 to 50 minutes at constant voltage of 5V .The anode was magnesium specimen where the cathode was stainless steel type AISI 304 . Energy Dispersive X-Ray(EDX) and X Ray Diffraction (XRD) approved that magnesium Oxide (MgO) is the anodic film when using 3M potassium hydroxide electrolyte and a magnesium Silicate with a glassy morphology formed in the anodic film using safe electrolytes of 0.6M potassium silicate and 1M sodium silicate . Maximum film thickness reaches to 46 , 27,47 μm after anodizing at 30 min using 3M potassium hydroxide ,1M Sodium silicate , 0.6M Potassium Silicate respectively . It was found that the corrosion rate of commercially pure magnesium decreased from 37 to 7 , 2.2 , 1.3 mpy when using 3M potassium hydroxide , 1M sodium silicate , 0.6M potassium silicate respectively . At the same time the contact angle increases from 70 degrees to 114o, 105o , 113o degrees using the same electrolytes . An increase in microhardness of the anodic films was observed in 3M potassium hydroxide , 1M sodium silicate and 1M potassium silicate respectively . The adhesion of the anodic film measures according to ASTM D3359 method 13 for thickness <125 μm was classified in 3B which denote that the amount of the layer released by the adhesive tape lies from 5-15% of the formed layers using the three electrolytes.

Study on curved surface design of sliding pair based on stepped topography model

PurposeThe stepped topography of the friction pairs mainly causes the fluid film thickness to change in the direction of motion. In this region, there have very few topographical design methods for continuous or non-linear distribution of the fluid film. The purpose of this study is to analyze the effect of the curved surface on the performance of the liquid film.Design/methodology/approachFirst, a numerical simulation is used to solve the optimal bearing capacity and friction coefficient of the liquid film under the condition of the minimum film thickness. Then, the curved surface described by the sinusoidal curve equation is applied in the transitional region of maximum and minimum film thickness. The bearing capacity and the friction coefficient of the liquid film are respectively simulated and compared in the same condition of the minimum film thickness.FindingsThe research results show that the liquid film using the curved surface transition model, the optimal bearing capacity is significantly increased by 32 per cent while the optimal friction coefficient is clearly reduced by 38 per cent in comparison with using stepped surface model.Originality/valueThe friction pair with curved transition enables better lubrication performance of the liquid film and better adaptability under unstable conditions.

Effects of ethanol on the efficiency of the formation of anodic alumina in sulfuric acid

In the interest of enabling practical applications of anodic oxide films, it is important to develop methods to improve the coulombic efficiency of film formation. In this study, ethanol was added to the sulfuric-acid-based electrolyte to examine its effects on the anodization behavior of aluminum, the maximum attainable film thickness, and the resulting etching ability. Anodization was conducted in sulfuric acid solutions containing various concentrations of ethanol under mild anodization conditions (i.e., 20 °C, as opposed to the lower-temperature hard anodization conditions). When a constant current of 100 A·m−2 was applied, the initial voltage and steady-state voltage were strongly dependent on the ethanol concentration that was added. The growth rate of the alumina film was governed by a field-assisted electrochemical process and, thus, was not affected by the addition of ethanol in the sulfuric-acid-based electrolyte. However, the maximum attainable film thickness increased with increasing ethanol concentration while the charge during anodization was constant. Thus, it was concluded the coulombic efficiency of the film formation could be improved by suppressing the chemical dissolution of the anodic film. Furthermore, the degree of acid dissociation in the water-and-ethanol system is thought to play an important role in controlling the formation and resultant structure of the film.

ELECTROCHEMICAL FORMATION OF THIN INTERFERENCE-DYED OXIDE FILMS IN Ti6Al4V ALLOY IN SULFATE ELECTROLYTES

Introduction. Oxidation of titanium implants is used to impart biological compatibility properties to the surface and to mark for medical products. Artificially formed oxide films have a certain thickness and uniformity of chemical composition. Electrochemical oxidation allows to obtain films of a given thickness on products of any configuration, using simple equipment. The properties of oxide coatings, namely, the thickness and structure of the oxide layer, are determined by the type of oxidation electrolyte and the mode of oxidation of the alloy. The aim of the work is to study the effect of the process mode on the electrochemical oxidation of the Ti6Al4V alloy in sulphate electrolytes. Materials and research methods. The dynamics of the formation of oxide films in a sulfate electrolyte were investigated by analyzing the forming dependences U = f (τ) obtained by oxidizing the material in galvanostatic mode using a sequential circuit with a B5-47 power source and a Keithley-2000 multimeter. Results. The nature of the molding dependencies of the alloy depends on the density of the oxidation current. At j a 0.5 A·dm –2 , interference-colored oxide films are formed on the alloy surface. The maximum film thickness is determined by a given voltage value and does not depend on other parameters of electrolysis. For a number of identical voltage values, the dependence of the electrolysis duration on the current density is linear, which indicates the formation of low-porous films. The color of the oxide film is determined by the voltage value and does not depend on the current density and electrolyte concentration. The correspondence of the color of the film and the voltage in the range of its values of 10-100 V. The analysis of formation dependences has made it possible to establish that when oxidation of the alloy in sulfate electrolytes, low porous oxide films are formed.

Analysis of magnetohydrodynamic partial slip laser bump texture slider and journal bearing

A model of magnetohydrodynamic partial slip laser texture bearing (slider and journal) is developed. The influence of laser bump texture and slip laser texture partial configuration on the magnetohydrodynamic performance analysis of bearing is presented. An electrically conducting fluid is confined to bearing surfaces under uniform magnetic field perpendicular to slider bearing and inclined to the line of maximum film thickness to journal bearing. A one-dimensional analysis based on the narrow groove theory is considered to evaluate the nondimensional pressure distribution in bearing. Results of the nondimensional load capacity and coefficient of friction of magnetohydrodynamic partial laser bump texture and partial slip laser texture bearing configurations are analyzed. Partial slip configuration under MHD lubrication without laser bump texture brings in the performance improvement.

Hydraulic Characteristics of Liquid Film Generated by Slit Injector

Liquid film generated by a jet slit injector on a wall was analyzed experimentally. Liquid film characteristics were investigated by measuring the liquid film thickness distribution for various experimental conditions. At first, the distributions were qualitatively analyzed using backlight imaging. Furthermore, quantitative measurements were performed using a liquid film thickness sensor based on the electric conductance method, which was applied to the high-speed wire-mesh method. The injection angle (15, 30, 45 °), jet velocity (7, 10.5, 13.5 m/s), and injection distance (45, 55, 65 mm) were varied, and the responses of the liquid film were observed. Having increased the injection angle, the main stream thickness decreased and the position of the maximum film thickness moved upstream. A faster jet velocity corresponded to a wider liquid film area and larger perturbation of the liquid film. The injection distance did not affect the characteristics of the liquid film considerably. A hydraulic jump effect was also observed, and a large hydraulic jump affected the film thickness distribution of the main stream. The results of this study can be applied to the development of liquid rocket engines or thrusters using the film-cooling method.

Response of grease film at low speeds under pure rolling reciprocating motion

Using an optical interferometric technique, the grease film distribution under a pure rolling reciprocating motion is observed on a ball-disk test rig, to explore the transient response of grease, which is expected to fill the contact with thickener fiber and run for a long time under steady-state conditions. It is found that the reciprocating motion reduces the accumulation of the thickener fiber gradually with time. The maximum film thickness forms around the stroke ends. After 1,000 working cycles, very severe starvation occurs so that either the central or minimum film thickness becomes nearly constant over one working period. Thus, the life of grease lubrication under a transient condition is far below that under steady-state conditions. However, it is also found that by selecting a smaller stroke length, the thickener fiber spreads out in the contact instead of being removed from the contact at the 1,000th working period. When increasing the maximum entraining speed of the reciprocating motion to a certain value, during which the thickener fiber is not expected to accumulate under a steady-state condition, severe starvation occurs very quickly, causing surface damage.

Гидрохимический синтез пленок халькогенидов металлов. Часть 40. Влияние условий гидрохимического осаждения пленок ZnS тиоацетамидом на их толщину и морфологию

ZnS thin films are promising as a buffer layer in solar cells; photovoltaic cells, photoelectric sensors, light-emitting diodes are being developed on their basis. In this work, the growth kinetics of ZnS films has been studied during hydrochemical precipitation with thioacetamide from acidic (biphthalate, acetate) and alkaline (ammonia) aqueous solutions. From the biphthalate bath at pH = 2.5–3.0 at 343 K and from the ammonia reaction mixture at 293 K on glass substrates, mirror layers of zinc sulfide with a thickness of up to 250 and 330 nm were obtained, respectively. The maximum thickness of the ZnS films from the ammonia system is achieved by increasing the ammonia content in it to 5 mol/l. For all the ammonia concentrations used, an extreme dependence of the thickness of the ZnS films on the concentration of thioacetamide in the system was established. When precipitating ZnS films from the acetate system, lowering the pH of the solution from 5.0 to 4.5 increases their thickness by a factor of 1.5-2.0. On the kinetic curves of changes in the thickness of the ZnS films during deposition from the biphthalate system, an area is distinguished, which is characterized by the presence of a plateau, which presumably corresponds to the sulfidization process of the zinc hydroxide phase formed at the initial stage of synthesis. The optimal composition of the reaction mixtures and the recommended time of deposition of ZnS films from the studied reaction mixtures are proposed. According to electron microscopy, the main structural elements of the zinc sulfide films precipitated with thioacetamide, regardless of the composition of the reaction mixture, are globular aggregates. The layers precipitated from the biphthalate reaction mixture have more uniform microstructure with a predominant particle size of 30-50 nm. Films obtained from the ammonia reaction mixture are formed from globules with a diameter of from 0.5 to 5.0 μm with particles of ~ 100 nm interspersed. The content of the main elements (Zn, S) in the ZnS films obtained from the biphthalate and ammonia reaction mixtures, according to the data of energy dispersive microanalysis, was 49.48, 50.52 and 50.35, 49.65 at.%, respectively.

Surface-tension- and injection-driven spreading of a thin viscous film

We consider the spreading of a thin viscous droplet, injected through a finite region of a substrate, under the influence of surface tension. We neglect gravity and assume that there is a precursor layer covering the whole substrate and that the rate of injection is constant. We analyse the evolution of the film profile for early and late time, and obtain power-law dependencies for the maximum film thickness at the centre of the injection region and the position of an apparent contact line, which compare well with numerical solutions of the full problem. We relax the conditions on the injection rate to consider more general time-dependent and spatially varying forms. In the case of power-law injection of the form$t^{k}$, we observe a switch in the behaviour of the evolution of the film thickness for late time from increasing to decreasing at a critical value of$k$. We show that point-source injection can be treated as a limiting case of a finite-injection slot and the solutions exhibit identical behaviours for late time. Finally, we formulate the problem with thickness-dependent injection rate, discuss the behaviour of the maximum film thickness and the position of the apparent contact line and give power-law dependencies for these.

Establishing the patterns in the formation of oxide films on the alloy Ti6Al4V in carbonic acid solutions

This paper reports results of studying the features of the formation of thin interference-colored oxide films on the alloy Ti6Al4V alloy in solutions of carboxylic acids. It has been established that a change in voltage on the cell corresponding to the molding dependence of the alloy depends on the anodic current density. At current densities <0.5 A∙dm –2 , a continuous oxide film is not formed at the alloy surface and the assigned voltage value is not reached. An increase in current density to values higher than 0.5 A∙dm –2 predetermines a linear change in voltage over time with followed by reaching the assigned magnitude U. The maximum film thickness for these conditions is defined by the voltage magnitude and does not depend on the electrolysis mode. Color of the oxide film is defined by the specified value for the molding voltage and does not depend on current density, nature and concentration of carboxylic acid. A match between the molding dependences of oxidation obtained in different electrolytes suggests that the formation of oxide proceeds in line with the same mechanism. The obtained data are explained by the fact that the formation of oxide under the galvanic static mode takes place under conditions of the presence of a constant potential gradient in the oxide film. An increase in the voltage magnitude applied to the cell predetermines a proportional increase in the maximum oxide thickness, since it leads to an increase in the amount of electricity passed through the cell and a corresponding increase in the mass of the oxidized metal. Results of the study into determining the effect of the nature of carboxylic acid on the formation process of an oxide film on the alloy Ti6Al4V using the method of electrochemical oxidation have demonstrated that the nature of the electrolyte does not affect the characteristics of its formation. The obtained data allow us to suggest that the choice of an electrolyte for the development of a technology for electrochemical oxidation of titanium implants should be based on the results of studying the functional properties of the obtained coatings

Salt-Induced, Continuous Deposition of Supramolecular Iron(III)-Tannic Acid Complex.

One-step assembly of iron(III)-tannic acid (Fe3+-TA) complex forms nanothin (∼10 nm) films on various substrates within minutes. In this deposition scheme, however, the film does not grow continuously over time even though Fe3+-TA complex is still abundant in the coating solution. In this paper, we report that the salt addition dramatically changes the one-off coating characteristic to continuous one, and each salt has its optimum concentration ( CMFT) that produces maximum film thickness. For detailed investigation of the salt effects, we employed various salts, including LiCl, NaCl, KCl, CaCl2, SrCl2, BaCl2, NaBr, and NaNO3, and found that only cations played an important role in the continuous deposition of the Fe3+-TA complex, with smaller CMFT values for the cations of higher valency and larger size. On the basis of the results, we suggested that the positively charged cations screened the negative surface charges of Fe3+-TA complex particles, leading to coagulation and continuous deposition, further supported by the ζ-potential measurement and time-resolved dynamic light-scattering analysis.