Duplex Film Research Articles

An Ellipsometric Study of Electrochromism in Iridium Oxide

The film growth and conversion processes which take place when an iridium electrode is cycled in 0.5M sulfuric acid are studied with a self‐nulling ellipsometer operated at a wavelength of 6328Å. Analysis of the optical data recorded at cycle endpoints shows that the film on the iridium surface is transparent with , in its reduced state, and becomes absorbing with, on oxidation. The optical data recorded during conversion show that the reduction data retrace the oxidation data with little hysteresis, and exhibit a distinctive structure which shows that the conversion process does not take place by the motion of an interface between colored and bleached layers of a duplex film, nor does it take place by single‐stage conversion of a homogeneous film. Both the optical and the electrochemical data show that the conversion process takes place in two distinct stages on oxidation and on reduction for cycles which result in film growth. The refractive index of the film was determined to be , after the first stage of the conversion process. The optical analysis is tested by extrapolating the endpoint and stage one curves to intersect the conversion curve for a thicker film grown by applying an a‐c current to the sample.

Thermodynamics of displacement wetting

A thermodynamic analysis is presented of the various types of immersion heat measurements which can be carried out on systems having two immiscible phases. The analysis is applied to the available data. It is shown that the film pressure and film energy are negligible for the adsorption of a hydrocarbon component at the interface between water and several high-energy solids. The analysis also permits the calculation of the corresponding quantities for the adsorption of water at the interface between liquid hydrocarbon and high-energy solid phases. Possible calorimetric tests of the Harkins duplex film hypothesis for the adsorption of water at such interfaces are discussed.

Gradient theory of fluid microstructures

The general gradient theory of fluid microstructures is outlined. This theory reduces the determination of fluid microstructures to a boundary value problem. The density and pressure tensor profiles and the tension of planar thin films and layered structures in one-component fluids are investigated. The boundary conditions determining these structures are given a geometric interpretation in the free energy-density diagram. Discussed are the implications of the theory for the validity of Antonov's rule, the duplex film hypothesis, and the asymptotic theory of disjoining pressure and of the origin of a characteristic length scale in spinodal decomposition.

The occurrence of duplex films on flyash surfaces

This note reports observations made on several flyash-bearing Portland cement pastes in which duplex films apparently are found to occur around all visible grains, including the flyash particles. The films consist of a thin 0.5 ..mu..m uniform continuous layer of calcium hydroxide deposited quickly on the exposed surface, plus a thin single layer of parallel, more-or-less widely spaced C-S-H gel particles. The pastes were 0.5 pastes prepared from 50 wt percent flyash-50 wt percent Portland cement mixtures hydrated for 1 day at room temperature. Examination suggests that the coating that develops around these flyash grains, which should be inert at the short period of hydration involved, is in fact the same kind of calcium hydroxide -C-S-H gel duplex film previously shown to form on any inert surface in contact with solutions developing in hydrating cement paste. The long term cementitious reaction, associated with the late strength gain of such flyash-containing concretes must take place through this skin, presumably by diffusion of material in or out of the grain through it. It appears that the same hydration shells may represent the effects of deposition from solution onto surfaces of grains that are chemically inactive. 3 figures. (DP)

Micromorphology of the Interfacial Zone Around Aggregates in Portland Cement Mortar

Scanning electron microscopy showed that micromorphological features of the interfacial zone, which occur next to glass slide “model aggregates” occur also in mortars made with standard Ottawa silica sand. These features included formation of a duplex film on the sand‐grain surfaces, development of large well‐formed Ca(OH)2 crystals at intervals near the interface with their c axes roughly parallel to it, development of stacked‐platelet secondary Ca(OH)2 in open spaces immediately adjacent the duplex film, and hydration leading to the presence of hollow‐shell hydration grains (Hadley grains) in the interfacial region.

The contact zone between portland cement paste and glass “aggregate” surfaces

The morphology of the contact zone developed between Portland cement paste and glass slide “aggregates” has been explored using SEM and other techniques. A duplex film of about 1 μm total thickness is rapidly deposited on the glass surface. This is a continuous film of Ca(OH) 2 overlain by a parallel array of rod-shaped CSH gel particles projecting normal to the interface. The nearby cement paste exhibits high porosity, but after a few days becomes partly filled with a secondary deposit of stacked platelets of relatively pure Ca(OH) 2. Cement particles near the interface hydrate in a peculiar manner. A hydration product shell is quickly formed, but the encapsulated cement particles dissolve away to leave partly or completely empty shells. This behavior occurs with various Portland cement types and presumably occurs near aggregate surfaces in concrete.

An O18 Study of Field‐Assisted Pore Formation in Compact Anodic Oxide Films on Aluminum

The mechanism of field‐assisted pore formation in 15% wt aqueous solutions was studied by O18 tracing techniques. Compact base layers were first formed in an O18 labeled solution and further oxidized in a nonlabeled solution, leading to field‐assisted pore formation. The O18 content and depth distribution was measured in these duplex films. It was found that the initial number of O18 atoms per square centimeter is conserved to within 2% and that the major part of the oxygen of the initial base layer is located on the top of the duplex film with the same O18 isotopic concentration. This observation shows clearly that the pore formation does not take place through a simple oxide dissolution process whether chemical or field assisted. Pore formation consists of some kind of oxide decomposition involving only cation transfer into the solution. The values of the cationic and anionic currents are calculated. Possible mechanisms for ion movement are discussed.

Rate of penetration of a fluid into a porous body: II. Verification of the generalization of the washburn equation, for organic liquids in glass capillaries

The rate of penetration of a liquid hydrocarbon or an alcohol into a glass capillary is more rapid if the capillary has been outgassed, than if its surface is covered with a duplex film of the liquid. The increase in rate is as large as 10%. If the pore walls are covered by an adsorbed film, the thickness of which is comparable to the pore radius, this leads to an accelerated rate of penetration in comparison to systems in which the pore radii are large. In the systems studied, there was a notable difference between hydrocarbons and octyl alcohol, which appeared when the glass was outgassed at 200°C under vacuum.

Microemulsions versus micelles

To differentiate between microemulsions and micellar solutions, an examination was undertaken of the molecular interactions taking place in the interphase of very small droplets. When the interphase is 25 A thick, there is an abrupt change in the ratio of the volume of the interphase to the volume of the core in the neighborhood of a droplet diameter of 100 A. Below this diameter, the degree of aggregation, or curvature of the noncoherent interphase, is primarily determined by interactions between water and the heads of the surfactant species. Above this diameter, curvature is determined by specific interactions among oil molecules and surfactant tails as well as by the interactions among the surfactant heads and water in a well-defined coherent interphase. It is such a duplex film, capable of having different tensions at each of its sides, that distinguishes the microemulsion from the micellar solution. A tension or pressure gradient across a freshly formed interphase is able to control its curvature, and thus droplet size, over a much wider range than can the interaction among surfactant heads and water alone. The data of two of Schulman's alcohol and soap stabilized dispersions were used for this analysis. In one, the oil phase was benzene, in the other hexadecane. It was recalled that as the water content of these inverted micelles was increased, the increase in droplet size was accompanied by an increase in the ratio of alcohol to soap in the interphase. This is important because zero interfacial tension, considered necessary for microemulsions, only occurs at intermediate values of this ratio. In the benzene system this ratio was quickly exceeded, resulting in a macroemulsion at low water content. In the hexadecane system, because of better association between oil molecules and the tails of the surfactant species, the aggregates retained their equilibrium status, despite a high ratio, by changing into cylindrical or lamellar micelles. This behavior was ascribed to a limit in the system of the ratio of alcohol to soap and the amount of oil, suggesting how phospholipids might form liposomes or membrane layers. As more water was added to the lamellar micelles, o/w microemulsions formed providing certain new criteria were met. Emphasis was placed on the choice of components. Because of space limitations in the center of the droplet, long alcohol tails and more than stoichiometric amounts of, or large, cations increased the chances of forming these rare systems. A hypothetical phase equilibria diagram was presented in which the regions of microemulsions, micellar solutions, and liquid crystalline phases were defined qualitatively. In this diagram microemulsions and micellar solutions were distinguished on the basis of aggregate size.

Surface pressure—area behavior of fatty acid monolayers on multicomponent substrates

The surface pressure-area behavior of a number of fatty acid monolayers on water-glycerol substrates has been examined experimentally using a Langmuir-Wilhelmy balance and theoretically by using a modification of the Langmuir duplex film model together with various theories correlating solution activity data. Results are obtained for substrates up to 100% glycerol, and its presence at low to moderate concentration is found to cause slight expansion in the condensed and intermediate regions but significant expansion in the liquid expanded region. The expansion effect achieves a maximum at a particular characteristic glycerol concentration for each surfactant. The π-A curves for low to moderate glycerol concentrations are well-correlated with the new equations of state proposed, but the curves obtained on concentrated glycerol solutions show greater deviations from ideality than are accounted for in the present form of the model.

回転電極による電解クロム酸処理皮膜の生成挙動

The effect of rotating speed of specimen on the formation of duplex film consisting of metallic Cr and hydrated Cr oxide, and the incorporation of sulfate radical into the film was mainly investigated by galvanostatic electrolysis for a few seconds in dilute chromic acid electrolyte containing a small amount of sulfuric acid.The results obtained were as follows:(1) The increase in the rotating speed of specimen resulted in the increase in hydrated Cr oxide and slulfate radical incorporated into the oxide film, and the decrease in the molar ratio (oxide Cr/SO42-).The current in the 3rd branch of the polarization curve also increased with the rotating speed of specimen.These phenomena were also observed in the increase of sulfuric acid added to the electrolyte. Therefore, it was considered that in the formation of the duplex film, the action of the increase in the rotating speed was similar to that of the increase in sulfuric acid added to the electrolyte.(2) On addition of sulfuric acid to the electrolyte, both the amount of hydrated Cr oxide and the current efficiency for the deposition of metallic Cr increased; and each of them remarkably decreased at an apporoximately equal amount of sulfuric acid addition.(3) An approximately linear relation was found between the amount of metallic Cr (m) and the electrolysis time (t) as showh by the equation: m=Kt-C, in which K=rate constant for metallic Cr deposition and C/K=time lag for obtaining constant current efficiency for metallic Cr deposition(4) The metallic Cr deposition was closely related to the amount of hydrated Cr oxide and the molar ratio (oxide Cr/SO42-), because the maximum current efficiency for metallic Cr deposition was obtained at the formation of thicker hydrated Cr oxide and the molar ratio (oxide Cr/SO4-2) of about 3.

The effects of anion concentration on anodic polarization of copper, zinc, and bra's

The polarization characteristics of copper, zinc and single and two-phase brasses have been obtained in sodium chloride solutions within the concentration range 1–30% w/w and the surface films present were identified by X-ray and cathode reduction techniques. The surface finishes are related to the anode potential and the results show that copper anodes are covered with a film of cuprous chloride at all potentials just above the rest potential and the only film on zinc is one of metallic zinc. On the brasses a duplex film of zinc particles and cuprous chloride is found over a copper rich alloy layer. The results support the theory that zinc and copper are oxidized simultaneously at all potentials greater than the rest potential.

Discussion of “Some Evidence for Duplex Film Structuring Within the Anodic Alumina Barrier Layer” [G. A. Dorsey, Jr. (pp. 466–471, Vol. 116, No. 4)

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Closure to “Discussion of ‘Some Evidence for Duplex Film Structuring Within the Anodic Alumina Barrier Layer’ [G. A. Dorsey, Jr. (pp. 466–471, Vol. 116, No. 4)

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Some Evidence for Duplex Film Structuring Within the Anodic Alumina Barrier Layer

Direct observations of anodic barrier layer oxide, by transmission electron microscopy, provide further evidence for the duplex film structuring suggested earlier, based on infrared data. Anodic films were prepared with a boric acid electrolyte maintained at 60°C and two film layers were observed: the uppermost layer being extremely thin. Only the layer lying next to the metal (primary phase barrier layer) showed a thickness relationship with respect to forming voltage: 14.8 Aå/v. The thickness of the uppermost layer (secondary phase barrier layer) was on the order of 200Aå and was essentially independent of forming voltage. With the boric acid electrolyte employed at 90° C, a pronounced increase was found in the thickness of the uppermost layer. The thickness of the layer next to the metal surface remained consistent with the ∼14 Aå/v relationship. Infrared, coating weight, effluent gas detection, and impedance data were also obtained for these coatings and correlated with the data obtained by transmission electron microscopy.

Copper Corrosion: III . Electrochemical Theory of General Corrosion

The oxidative dissolution of copper in acidic, aqueous media is limited in rate by the presence at the metal‐solution interface of a growing film of cuprous oxide. A brief survey of what is known about the nature and modes of growth of such films provides the basis for a “duplex film” model of the corroding copper system. This leads to an interpretation of some features of the observed kinetics of the corrosion reactions reported in the preceding paper, including the constancy of rates of dissolution and film growth following induction periods, the kinetic link between them, the absence of effects due to concentration polarization of dissolved oxygen, and the results of “replacement experiments.” The interpretation is made in terms of the operation of a hypothetical double electrochemical cell, corresponding with the duplex film model, and leaves unresolved problems associated with possible special functions of carbon dioxide and the mechanism of oxygen reduction.

The oxidation of iron at 175 to 350° C

The oxidation of iron, previously freed from oxide by hydrogen treatment, has been studied at 175 to 350° C; five methods (gravimetric, electrometric, film -transfer followed by chemical or microscopic examination, X -rays and electron diffraction) have been used to identify and estimate the different oxides. If specimens are exposed to air at room temperature without subsequent hydrogen treatment, complications are introduced, magnetite being formed where otherwise it would be absent. On hydrogen-reduced iron powder, ferrous oxide, magnetite and α-ferric oxide appear when oxygen is admitted, but the oxidation is not isothermal, since a glow appears on admission of oxygen even when the initial temperature is only 40° C. On hydrogen-reduced Swedish sheet, α-ferric oxide alone appears at 175 and 225° C, while at 300, 325 and 350° C, a duplex film of magnetite (not γ-ferric oxide) overlaid with α-ferric oxide is formed; at 250° C, the film consists of a single layer (α-ferric oxide) for 8 h, but then magnetite appears below it at certain places (distinguishable by the more advanced interference colours) and spreads laterally, the rate of magnetite formation increasing rapidly with time. Most of the films studied display interference tints in the usual sequence, when they are on the metal; after transfer to glass, they show different colours, which in the case of the duplex films are themselves different according as they are viewed from the magnetite side or the α-ferric oxide side. This can easily be explained. Some experiments on pure iron give results similar to those on Swedish iron. The growth law on sheet is parabolic ( W 2 = Kt + K ' ) at 325 and 350° C but logarithmic ( W = K ' In ( Kt + K ´)) at 175, 225, 250, 275 and 300° C.

Effect of Surface Films on the Evaporation of Water

BY a variety of laboratory experiments, it has been demonstrated that the presence upon a water surface of a suitable monolayer or duplex film may diminish considerably the rate of evaporation1–3. That significant retardation of evaporation is not obtained under natural conditions is indicated by the lack of application of the techniques on a larger scale.

The Rate of Evaporation of Water through Duplex Films

The stability of duplex films of hydrocarbon oils containing spreaders is discussed in this paper. Duplex films containing spreaders of high molecular weight and of complex nature, e.g. stand oil, eucalyptus residue, polymerized oleic acid, may remain spread for long periods but are thermodynamically metastable. The penetration of water molecules from a water surface through a duplex film has been discussed in terms of the evaporation resistances of the interfacial layer of spreader, the bulk layer of oil and the stagnant layer of air above the film. Evaporation through duplex films of thickness 1-100 μ has been studied in conditions of " still air " at atmospheric pressure and in a vacuum, and in non-turbulent winds at several controlled wind velocities. The efficiency of duplex films in reducing evaporation is greater in wind than in still air and Increases with the wind velocity. When duplex films thicker than 10 μ are placed on water surfaces, even a wind at 8 miles per hour does not increase the rate of evaporation. Thus with such films the resistance of the stagnant layer of air above the film is small compared with that of the oil layer and of the interfacial film of spreader. With all duplex films thicker than 10 μ the total evaporation resistance is proportional to the film thickness and depends on the nature of the spreader. An analysis of the experimental results suggests that the interfacial layer of spreader makes an appreciable contribution to the evaporation resistance of the duplex films under investigation. Approximate relative figures characterizing the magnitude of this contribution are calculated for several spreaders.

A General Thermodynamic Theory of the Spreading of Liquids to Form Duplex Films and of Liquids or Solids to Form Monolayers

A comprehensive thermodynamic theory is developed for the spreading of any liquid or solid b over the surface of any liquid a. Spreading is considered to occur by two types of processes: (A) duplex film or D spreading, and (B) non-duplex or M spreading. A duplex film is always unstable, and transforms into a non-duplex film and a lens. Every non-duplex film of known structure is a monolayer (M). Either type of film may spread if its formation involves a decrease of free energy. The free surface energy of mercury at 20°C is 476 erg cm—2, and the spreading of water or any organic liquid on the surface as either a duplex film or a monolayer, gives a decrease of free surface energy, so all such liquids spread on mercury. On water all organic liquids spread as monolayers; an organic solid also spreads as a monolayer unless it is too non-volatile in the two-dimensional system. A liquid b will spread over the surface of a liquid a as a duplex film if the initial spreading coefficient Sb/a = WA — WCb is positive, that is if the work of adhesion WA between the two liquids is greater than the work of cohesion (WCb) in b. If b is saturated with a, then Sb′/a is designated as the semi-initial spreading coefficient, which has almost the value of the initial coefficient. If the liquids are mutually saturated the final spreading coefficient, Sb′/a′, is always negative. Thus a liquid b will never spread over its own monolayer, and if the whole surface of water in any vessel is covered by a duplex film, it is certain that a monolayer has not spread over any part of it. After a definite period, the length of which is dependent on many factors, a duplex film begins to segregate into a monolayer, patches of thicker duplex film, and lenses, and finally into a monolayer and a lens. The film pressure πe of a monolayer of b in equilibrium with a lens of b is equal to the difference between the semi-initial and the final spreading coefficient, or πe = Sb′/a — Sb′/a′. Since Sb′/a′ is always negative, the equilibrium film pressure is always greater than the semi-initial coefficient. Hydrocarbons of not too high molecular weight are found to spread on water as either duplex films or monolayers. Thus many nonpolar oils spread on water to form either type of film. Benzene, which according to one of the most prominent theories does not spread at all, spreads readily, and exhibits the following values, which are almost the same as those for isopentane: initial coefficient 8.94, semi-initial 8.90, and equilibrium film pressure 10.6, in erg cm—2. Carbon disulfide (nonpolar) and methylene iodide (highly polar) have initial coefficients —7.3 and —23.8, and therefore do not give duplex films, but they vaporize in the two-dimensional surface, and give equilibrium film pressures of 2.3 and 0.6 dyne cm—1, respectively. Presumably their monolayers are gaseous. In general for liquids which spread as duplex films, it takes less work (i.e., the increase of free energy is less) to pull a liquid away from its equilibrium monolayer than to pull it away from itself. For benzene the difference is 1.7 and for n-heptyl alcohol, 5.4 erg cm—2. An oil which is non-spreading in the sense of duplex film formation, may be caused to spread as a duplex film by the addition of an oil of sufficiently high initial spreading coefficient. This also increases the equilibrium film pressure of the monolayer. The oils added for this purpose are, in general, of the polar-nonpolar type, such as stearic acid. With such mixtures the values of the thermodynamic spreading coefficients, or the free energy levels, are highly dependent upon the nature and the concentration of the oil added. If the aqueous subphase is alkaline, stearic, or another similar acid is converted into a salt, and if the positive ions have a charge of two or higher, this has a pronounced effect upon the spreading coefficients and the film pressure.