Showing papers in "Journal of The Electrochemical Society in 1963"

Surface Energy of Germanium and Silicon

Abstract: Surface energy is one of the most fundamental parameters of a solid since it depends directly on the binding forces of the material. Indeed, it is a measure of the work necessary to separate a material into two parts along a plane. Very few measurements have been made of this quantity and these by indirect means, because of difficulties of measurement and interpretation. This report deals with a direct measurement of specific surface energy of Ge and Si made by the cleavage technique. By measuring the force just necessary to move a crack "in reversible fashion" the surface energy can be obtained. The measured value for the {111} planes of Ge and Si are 1060 ergs/cm2 and 1230 ergs/cm2. From these measured values the energy of the planes {100} and {110}can be estimated. They are: Using the measured value of specific surface energy, assuming this is due to the appropriate number of broken , the bond strength of Ge and Si was obtained as ; .

Electroluminescent Lines in ZnS Powder Particles II . Models and Comparison with Experience

Abstract: Existing theories of ‐powder‐EL are shown to be unable to explain the new findings of electroluminescent striations or lines described in Part I of this work. Several new hypotheses are discussed. Among these, a model seems to be likely which is based on simultaneous bipolar field‐emission from opposite ends of conducting imperfection lines into the insulating crystallite, with trapping of injected holes in activator centers, and recombination with mobile electrons at field‐reversal. This model, which is shown to be consistent with facts, is discussed in detail. A new impact ionization model is also described which is very similar to that of the field‐mission model. At present, it is experimentally indistinguishable from the field‐emission model.

Electrical Resistivity of Stabilized Zirconia at Elevated Temperatures

Abstract: The electric resistivity of stabilized zirconia of various compositions was measured by a four-probe technique in the temperature range 550 to 1200 deg C. Resistivities of fully stabilized compositions were found to increase with increasing additions of the stabilizing oxide, and the lowest resistivities appear to occur in materials stabilized with small cations. (auth)

A Technique for the Evaluation of Hydrogen Embrittlement Characteristics of Electroplating Baths

Abstract: A simple electrochemical technique is described for measuring the quantity of hydrogen permeating a thin membrane of iron or steel during cathodic charging or electroplating. For cadmium electroplating, the quantity is small when this metal is deposited from a fluoborate or a DL‐α‐amino‐n‐butyrate bath, but comparatively high when a cyanide bath is used. The mechanism which governs hydrogen permeation in alkaline solutions containing capillary active anionic species is discussed, and the remarkable similarity between hydrogen permeation and hydrogen induced brittle fracture of high strength steel is demonstrated.

Oxidation of Molybdenum 550° to 1700°C

Abstract: Weight change and oxygen consumption measurements were used to study the oxidation of molybdenum from 550° to 1704°C for pressures of 5 to 76 Torr. For temperatures of 550°–700°C two processes occurred simultaneously, oxide scale formation and molybdenum trioxide volatility. Above 800°C at pressures up to 76 Torr molybdenum trioxide volatilized as fast as it formed. At 900°C and 76 Torr using 1.2 cm2 samples the primary chemical reaction gave a rate of about 1018 at. molybdenum/cm2/sec. Above this temperature for 1.2 cm2 specimens the reaction was limited by gaseous diffusion of oxygen. Little change was found in the rate of oxidation to 1615°C. Pressure had only a small effect on the rate of reaction for these reaction conditions. However, in the chemically controlled region pressure had an important effect on the rate of oxidation. To extend the temperature region where the primary chemical reaction was rate controlling, samples of small area were used. A sample having a total area of 0.12 cm2 gave a reaction rate of . For these very fast reactions, appreciable temperature rises occurred, and the actual sample temperature had to be estimated. A log K vs. 1/T plot of the primary chemical reaction data gave an energy of activation of 19.7 kcal/mole. Reaction conditions where gaseous diffusion processes are rate controlling were determined. All of the earlier studies were made for these reaction conditions. The activated state theory of surface reactions was applied to the primary chemical reaction in the oxidation of molybdenum. A mechanism of mobile adsorption was found to be the primary chemical reaction. This adsorption process probably occurred on a surface already covered with a layer of adsorbed oxygen atoms since was volatilized.

Effect of Crystal Structure on the Anodic Oxidation of Nickel

Abstract: The formation of and on different crystal planes of nickel, and of polycrystalline nickel, was studied in alkaline solution. Oxide films of less than two monolayers were reduced potentiostatically, then current‐potential curves were measured in the range −200 to 1600 mv at different rates of the linearly increasing potential. Electron diffraction and microscopy were used to develop a suitable experimental procedure for dealing with bare and smooth nickel surfaces. The extent of oxide film formation in air on different planes was in the order (110) > (100) > (111). The reactivity on anodization, characterized by the potential at which the equivalent of one monolayer of hydroxide is formed, was in the same order. On continued oxidation the structure of the crystal surface is lost; subsequent reduction forms a strongly disordered surface. The results are discussed with regard to the mechanism of anodization, the extent of differences between crystal planes, and the conditions under which they are maintained or lost.

The Initiation of Pores in Anodic Oxide Films Formed on Aluminum in Acid Solutions

Abstract: When pure aluminum is passivated at constant applied voltage in solutions ranging from pH 0–7, the current density representing film growth falls during the first few seconds in a manner that is qualitatively and nearly quantitatively the same for all solutions. The fall of current is succeeded by a rise to a constant value; the rise occurs the earlier, and is the greater, the lower the pH. The fall is interpreted as caused by barrier‐layer formation, and the rise as caused by pore initiation when the field across the barrier layer has fallen low enough to allow the entry of protons into the film. Electron micrographs of the film surface show that very few pores are present on specimens that have not been anodized long enough for the initial current fall to halt, and that the pore system is fully established as soon as the succeeding rise is complete. A mechanism for pore formation is proposed.

The Anodic Oxidation of Iron in a Neutral Solution II . Effect of Ferrous Ion and pH on the Behavior of Passive Iron

Abstract: The anodic polarization curve, the static passive potential, and the behavior of the decay of the polarized passive potential of iron were examined in neutral boric acid/borate solutions with and without Fe++ ion addition. It was found that the passivation potential is a function of the [Fe++] and pH and corresponds to the equilibrium potential of the reaction of . The polarized passive potential in the steady state is related to a pseudoequilibrium potential that corresponds to a higher defect concentration in the oxide surface and to a lower [Fe++] at the oxide/solution interface. The potential gradient across the film appears to be very small. The decay of the polarized passive potential on open circuit is explained as due mainly to the change in the defect‐concentration and consequently of the film composition at the oxide/solution interface either by the outward migration of iron through the film or by the reaction with Fe++ ion in solution when the latter had been added or supplied by a small amount of self‐corrosion.

The Formation of Metal Oxide Films Using Gaseous and Solid Electrolytes

Abstract: The growth of oxide films has been observed to occur on the surface of certain metals when they are (a) subjected to an oxygen plasma, (b) subjected to an oxygen plasma and maintained at a positive potential with respect to the plasma anode, and (c) brought into intimate contact with a second metal that has oxygen dissolved in it, and maintained at a positive potential with respect to that metal. Dielectric barriers formed by these methods have been used to construct both active and passive elements in a thin film oscillator‐amplifier circuit based on the superconducting tunnel diode.

Anodic Passivation of Nickel in Sulfuric Acid Solutions

Abstract: The potential decay curve of a passive nickel electrode on open circuit was followed in solutions of pH ranging from 0.4 to 1.4. The three arrest potentials observed in the decay curve correspond to the equilibrium potentials for the , , and the electrodes, respectively; the second potential is called the Flade potential, and the passivation occurs beyond this potential. A process for formation of the film is proposed that can be represented by the successive reactions, , . Then the critical potential beyond which the oxide formation takes place is calculated, under conditions when the solution in the vicinity of the surface becomes saturated with corresponding to the solubility product of , and is found to be equal to the Flade potential. The proposed mechanism can also explain the ability of the passive film to protect the metal against active dissolution due to breakdown of the film.The mechanisms of dissolution of nickel in the passive and overpassive potential regions are discussed from measurements of the Tafel constant and the pH dependence of the dissolution rate .The results are summarized as follows: passive region; .

Corrosion Inhibition in HCl Using Methyl Pyridines

Abstract: The inhibiting effect of pyridine and seven of its methyl derivatives on the corrosion of iron in O2‐free, at 35°C was determined. Corrosion rates were measured by colorimetric analysis for iron with mercaptoacetic acid. The relative inhibitor efficiency and cathodic potential shift increased with increasing inhibitor concentration and, for a given concentration, with increasing electron density at the nitrogen atom. Both increased slightly with decreasing concentration, but a temperature increase of 10°C had no effect on either. The proposition that chemisorption is involved in corrosion inhibition is supported by these experiments. As a supplementary item the great importance of careful purification of the organic compounds used in such researches as this is documented.

Electrical Properties of Thin Organic Films

Abstract: Thin organic polymer film specimens were prepared for electrical conductivity measurements by the glow discharge polymerization process. The experimental procedure for film preparation is described in detail. Data on film properties and deposition efficiencies (g/kwhr) are presented for their possible bearing on the polymerization mechanisms. Dark conductivities (σ) were measured over the temperature range 75°–275°C. Plots of generally gave straight lines above about 125° with slopes characteristic of the chemical composition of the polymer film. Conductivities at 150°C ranged from 10−17 mho/cm (films rich in halogen) to 10−13mho/cm (ferrocene, tetracyanoethylene). A possible relationship between structure and conductivity is discussed.

Electrodeposition of Dispersion‐Hardened Nickel ‐ Al2 O 3 Alloys

Abstract: : Nickel-Al2O3 alloys were electrodeposited from a Watt's type nickel-electrolyte, which contained the second phase particles suspended in the solution. The effects of particle concentration, particle size, and plating conditions on microstructure and physical properties of the deposits were studied. Using submicroscopic Al2O3 particles, the room temperature yield strength increased from 10,000 psi for pure nickel to 40,000 psi for an alloy containing 2 volume percent Al2O3. It is believed that this increase was due to dispersion strengthening effects similar to those observed in sintered or internally oxidized metal-metal oxide systems. (Author)

A New Family of Self‐Activated Phosphors

Abstract: A series of compounds were discovered which have the generalized formula R 2 2+ R 4+ R 2 5+ O 9 . Examination of single crystals of Pb 2 ZrP 2 O 9 showed it to have hexagonal symmetry with α H = 10.08A and c H = 23.29A. Five of the seven compounds studied (Ba 2 ZrP 2 O 9 , Sr 2 ZrP 2 O 9 , Pb 2 TiP 2 O 9 , Ba 2 ZrAs 2 O 9 , and Pb 2 ZrAs 2 O 9 ) were isostructural with Pb 2 ZrP 2 O 9 , and the seventh, Sr 2 ZrAs 2 O 9 , had optical properties closely related to the group. With the exception of Pb 2 TiP 2 O 9 , all of the compounds exhibited a broad band blue fluorescence, with an intensity maximum near 4800A, when excited by 2537A radiation. By contrast, Pb 2 TiP 2 O 9 showed a weak orange fluorescence, more easily excited by 3650A radiation. Emission, absorption, and excitation data are presented.

The Activated Sintering of Tungsten with Group VIII Elements

Abstract: Small additions of Group VIII transition elements permit the densification of tungsten powder compacts at temperatures well below those employed for sintering commercial purity tungsten powder. The mechanism of this process has been examined using the model concepts of current general sintering theories. The added solid element accelerates mass transport along its interface with a tungsten particle. This process, together with sintering in the presence of a liquid phase or a volatile component, comprises the three types of carrier phase sintering in which one of several possible pure component solid‐state sintering mechanisms is selectively accelerated.

Stresses in Anodic Films

Abstract: Stresses in anodic films produced on several metals were measured by clamping the upper end of a thin foil of the metal and observing the motion of the lower end through a telescope. The results show that the stress in all films was tensile at small film thickness. For most metals the sign of the stress was independent of formation voltage, but the stress in anodic films on Zr decreased steadily from strong tension at low voltages to strong compression at higher voltages. Except for films formed on Ta, the reproducibility was generally poor, variations of plus or minus 25% from specimen to specimen being typical. Stresses reported for Ta are reproducible to plus or minus 10%. Also, the stress with forming voltage applied was always more compressive than at zero voltage except for W where no effect of the applied field was observed. Assuming that each newly deposited layer is hydrated, it is hypothesized that as the layer becomes buried it is dehydrated by proton migration, producing tension in the film. (P.C.H.)

Formation and Dissolution of Platinum Oxide Film: Mechanism and Kinetics

Abstract: Oxide film formation on a smooth platinum electrode in perchloric acid solution has been studied as a function of potential, current, time, and electrode history, using constant current and controlled potential techniques. Anodic film formation proceeds through two, single electron steps: a slow step followed by a fast (reversible) one. During film reduction the fast step occurs first, followed by the slow step. In the case of constant current reduction the slow step does not occur, and the film is exactly half‐reduced. Complete reduction requires several hours at a controlled potential. Three electrode states are thus clearly defined: oxidized, half‐reduced (active), and completely reduced or clean. A single kinetic equation quantitatively relates the current, potential, and time parameters, predicts the initial rate of open‐circuit potential decay following film formation, and strongly suggests that the oxide is a chemisorbed film.

Oxidation of Boron Carbide by Air, Water, and Air‐Water Mixtures at Elevated Temperatures

Abstract: A study of the oxidation of boron carbide powder showed measurable reactions at temperatures as low as 250 deg C with H/sub 2/O vapor and 450 deg C in dry air. Removal of the B/sub 2/O/sub 3/ oxidation product by H/sub 2/O vapor occurs at a rate in excess of the oxidation rate below 550 to 600 deg C. The presence of B/sub 2/O/sub 3/ on the B/sub 4/C surface was found to inhibit the oxidation by H/sub 2/O but not by air. Linear dependence of rate on the partial pressure of H/sub 2/O was observed. The activation energy for the H/sub 2/O--B/ sub 4/C reaction was 11 kcal/mole/ deg C while that for the air--B/sub 4/C reaction was 45 kcal/mole. Oxidation by dry air occurs at a lower rate than with H/sub 2/O vapor until approximately 700 deg C (for 235 mm H/sub 2/O partial pressure). (auth)

On the Defect Structure of ZrO2 and HfO2

Abstract: The defect structure of ZrO/sub 2/ and HfO/sub 2/ was studied through measurements of electrical conductivity as a function of oxygen pressure The electrical conductivity exhibits an unusual and complex oxygen pressure dependence, and to explain the results it is proposed that these oxides are ionic conductors and that a coupled transport of oxygen vacancies and interstitials is faster than an independent transport of these defects Thermogravimetric measurements on ZrO/sub 2/ suggest that the nonstoichiometry of this oxide is more than a factor of ten smaller than that observed by Aronson (auth)

Disintegration of Magnesium While Dissolving Anodically in Neutral and Acidic Solutions

Abstract: A closer investigation of the dark deposits which separate from a magnesium anode in the form of leaflets in neutral and in acidic solutions showed that the views set forth by Baborovsky (1905) concerning metallic Mg in the deposits are correct. A multitude of Mg particles of about in diameter were visible in the flakes, causing their dark color. In perchloric acid the magnesium anodes first turned slightly dark at the rim. Beautiful patterns of deformation twins appeared. At high current densities flakes containing innumerable metallic particles separated from the anode. The particles broke off from anodic regions leaving a series of dark holes where the metal was locally strained or deformed or where the interatomic bonding was weakened. The partial disintegration of Mg into fine particles contributes to the explanation of the negative difference effect; it explains the apparent deviation from Faraday's law and shows that the assumption of expulsion of lower valency ions from the anode during anodic dissolution is unnecessary at present. The active metal particles themselves have great reducing ability.