Further insights into the durability of Pt3Co/C electrocatalysts: Formation of “hollow” Pt nanoparticles induced by the Kirkendall effect

This paper provides further insights into the degradation mechanisms of nanometer-sized Pt₃Co/C particles under various proton-exchange membrane fuel cell (PEMFC) operating conditions. We confirm that Co atoms are continuously depleted from the mother Pt₃Co/C electrocatalyst because they can diffuse from the bulk to the surface of the material. The structure of the Pt–Co/C nanoparticles in the long-term is determined by a balance between Co surface segregation and formation of oxygenated species from water splitting. When the PEMFC is operated at high current density (low cathode potential, below the onset of surface oxide formation from water), a steady-state is reached between the rate of Co dissolution at the surface and Co surface segregation. Consequently, Co and Pt atoms remain homogeneously distributed within the Pt–Co/C particles and the thickness of the Pt-shell is maintained to a small value not detectable by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. When the PEMFC is operated at low current density (high cathode potential), the formation of surface oxides from water and the resulting “place-exchange” mechanism enhance the rate of diffusion of Co atoms to the surface. Consequently, the fresh Pt₃Co/C particles form core/shell particles with thick Pt-shells and Co content < 5 at% and, ultimately, “hollow” Pt nanoparticles (Kirkendall effect). To the best of our knowledge, this is the first report on the formation of “hollow” Pt particles in a PEMFC.     

Improvements in star photometry for aerosol characterizations

This work addresses the applicability of the Astronomical Langley method to retrieve accurate calibration constants for a star photometer at a high mountain site. For this application, this method provides more accurate and reliable calibration constants than the classical Langley method. The Astronomical Langley method has been also tested in an urban environment using one year of star photometer measurements in the city of Granada (37.16°N, 3.60°W, 680 m a.s.l.). Under low and stable aerosol load conditions the calibration constants obtained are close to those retrieved at altitude. Finally, an analysis of the applicability of the one-star and classical two-star methods to retrieve aerosol optical depth (δ_A(λ)) at night is performed. For the one-star method the estimated errors in δ_A(λ) are close to 0.02 for λ<800 nm and 0.01 for λ>800 nm. For the two-star method the uncertainties are larger than those obtained by the one-star method, and thus can lead to unreliable values of the δ_A(λ). As a concluding remark, we consider that the one-star method is more appropriate, especially in an urban environment.     

Ordered arrays of copper nanowires enveloped in polyaniline nanotubes

Copper nanowires enveloped in polyaniline (PANI) nanotubes were obtained by ‘second order’ electrodeposition into the pores of anodic porous alumina. The templated synthesis of copper nanowires was performed by both potentiostatic and galvanostatic methods. The morphology of the polyaniline nanotubes, copper nanowires as well as the copper-filled polyaniline nanotubes was investigated by means of scanning electron microscopy. The copper nanowires were protected from corrosion and oxidation by the PANI nanotubes. Energy-dispersive X-ray spectroscopy was performed for the microanalysis of the copper deposition into the polyaniline nanotubes. Cyclic voltammetry was employed to assess the electrochemical properties of the obtained nanostructures as well as the influence of the copper nanowires synthesis method on the properties of filled polyaniline nanotubes.     

Effect of the deposition parameters on the voiding propensity of solder joints with Cu electroplated in a Hull cell

A quantitative study of the impact of key Cu plating parameters on the voiding propensity of solder joints with Cu electroplated in a commercially available plating solution (CAPS) is performed first on 0.3 cm² Cu rotating disk electrode. It is shown that similar to samples plated in a generic plating solution (GPS) containing bis(3-sulfopropyl) disulfide, polyethylene glycol, and Cl⁻ ions, void-prone samples are deposited predominantly at higher overpotentials, in the range from positive to −0.20 V. In the second part, a Hull cell with 46 cm² cathode is used to scale up the voiding study in both, GPS and CAPS. It is demonstrated that plating conditions could be chosen in a way to generate both, void-prone and void-proof Cu on the same cathode panel. Thus, the controlled voiding propensity illustrated for the first time in a prototype of industrial Cu plating helps in realizing the sporadic nature of the voiding phenomenon.     

New polymer/steel solution for automotive applications

Dry and wet steel/polymer adhesion was investigated using pull-off test and dielectric measurements. The influence of the composition of a hexafluorotitanic acid based surface treatment (Patent WO9607772A1) was also studied. It was noticed that when manganese or organic phase was missing from surface treatment, breaking force level decreases and steel surface was not protected from water effects. After ageing and drying, a complete recovery in breaking force was noticed except for treatment without the organic phase.     

International Practical Temperature Scale of 1948: Text Revision of 1960

The International Practical Temperature Scale of 1948 is a text revision of the International Temperature Scale of 1948, the numerical values of temperatures remaining the same. The adjective “Practical” was added to the name by the International Committee on Weights and Measures. The scale continues to be based upon six fixed and reproducible equilibrium temperatures to which values have been assigned, and upon the same interpolation formulas relating temperatures to the indications of specified measuring instruments. Some changes have been made in the text to make the scale more reproducible than its predecessor. The triple point of water, with the value 0.01 °C replaces the former ice point as a defining fixed point of the scale. It is also recommended that the zinc point, with the value 419.505 °C, be used instead of the sulfur point. The recommendations include new information that has become available since 1948.An internationally accepted scale on which temperatures can be measured conveniently and accurately is necessary for science and industry. As early as 1911 the directors of the national laboratories of Germany, Great Britain, and the United States agreed to undertake the unification of the temperature scales in use in their respective countries. A practical scale, named the International Temperature Scale, was finally agreed upon, was recommended to the Seventh General Conference on Weights and Measures by its International Committee on Weights and Measures, and was adopted in 1927.¹The General Conference on Weights and Measures is the official international body now representing 36 nations that subscribe to the Treaty of the Meter. The General Conference normally meets every six years, and at those times may adopt recommendations submitted by the International Committee. The International Committee is the executive body elected by the General Conference. It consists of 18 scientists, only one from any one nation, and it normally meets every two years. The International Committee now has six advisory committees of specialists most of whom represent large national laboratories. The Advisory Committee on Thermometry was authorized in 1933 and first met in 1939.In 1948 a revision of the International Temperature Scale was prepared by the Advisory Committee and proposed to the International Committee. The International Committee recommended this revision to the Ninth General Conference which adopted it.² At this time the General Conference also adopted the designation of degree Celsius in place of degree Centigrade or Centesimal.³ The revised scale was designed to conform as nearly as practicable to the thermodynamic scale as then known, while incorporating certain refinements, based on experience, to make the scale more uniform and reproducible than its predecessor. In the revision there were only three changes which affected values of temperatures on the scale. One was to increase the value assigned to the silver point by 0.3 degree, merely to make the scale more uniform. Another was to specify Planck’s radiation formula instead of Wien’s formula so the scale would be consistent with the thermodynamic scale above the gold point. The third was to increase the value for the second radiation constant to bring it nearer to the value derived from atomic constants.In 1954 the Advisory Committee proposed a resolution redefining the Kelvin thermodynamic scale by assigning a value to the triple point of water. This kind of definition was what Kelvin, in 1854, had said “must be adopted ultimately.” This resolution was recommended by the International Committee and adopted by the Tenth General Conference.⁴ As soon as this resolution had been adopted it was pointed out that it would be necessary to revise the introduction of the text of the International Temperature Scale of 1948 to conform with the action just taken.In preparing a tentative proposal for a new text of the introduction it soon became evident that the other three parts of the text would also profit by a revision. For example, the triple point of water could now be made one of the defining fixed points of the scale and thus become the one defining fixed point common to both the international and the Kelvin scales. The Recommendations could include new information that had become available since 1948. At the higher temperatures some new determinations of differences between the international and thermodynamic scales could be included. The values reported for these differences, however, were still not certain enough to warrant a change of the scale itself. The new text, therefore, does not change the value of any temperature on the 1948 scale by as much as the experimental error of measurement.In 1958 the tenative proposal was discussed in detail at sessions of the Advisory Committee in June, and many suggested changes were agreed upon. It was proposed to the International Committee in October. Minor corrections were made during the next two years, and in 1960 the International Committee gave the scale its new name. The International Committee recommended this text revision to the Eleventh General Conference and it was adopted in October 1960.A translation of the official text ⁵ follows.     

Change in the nature of hydrodynamic cavitation in nonuniform magnetic fields

It is known that in nonuniform magnetic fields the precavitation properties of aqueous media change, leading to an increase in the irreversible physicochemical changes.Notation l length of zone II - D and d diameters of tubes I, III, and II - p_I, p_II, p_III pressures in regions I, II, and III - p_cr critical pressure at which cavitation occurs - p_cr and p _cr ⁰ critical pressures in the magnetic field and when there is no magnetic field - [V_I, V_II, V_III] velocities of the liquid in regions I, II, and III - V_II, lim velocity of the liquid at which breakdown of the hydrated layer occurs for a certain value of the induction - V_cr and V _cr ⁰ critical velocities at which cavitation occurs in the magnetic field and when there is no magnetic field - p_a atmospheric pressure - p_sv saturation-vapor pressure at the given temperature - density of the liquid - kinematic viscosity - Re Reynolds number - Re_cr critical Reynolds number - c_gf and c_gd concentrations of free and dissolved gases in the magnetic field and when there is no magnetic field - c_gf and c_gd, and c _gf ⁰ and c _gd ⁰ concentrations of free and dissolved gases in the magnetic field and when there is no magnetic field - _sc space-charge density - electrical conductivity in the volume of the liquid - _b electrical conductivity in the boundary layer - _l , _g, _d dielectric constants of the liquid in the volume, of the gas in the bubbles, and of the diffusion layer - j, j_b, j_i, and j_T current density of the general, boundary layer, induced and current flow - f_MHD and f_EHD volume forces of magnetohydrodynamic and electrodynamic nature (per unit volume) - p_MHD pressure in the liquid due to the action of the magnetohydrodynamic forces - ₀ limiting shear stress in the liquid - B magnetic induction - E electric field strength in the volume of the liquid Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 842–850, November, 1978.