Vibrating electrode atomization

In the VEP, currents used are between 600 and 1200 A at potentials between 30 and 60 V. The vibration frequency of the wire electrode is up to 500 Hz. The materials atomized via VEP include mild steel, Cr-Ni steel, Cu-Ni alloy and tungsten. The VEP is carried out in an inert atmosphere (typically argon) for most alloys, but the arc is struck under water for tungsten wire. Wire diameter is 1-4 mm, and its feed rate is 1.7-4.3 m/min. The feed rate and current density must be determined properly according to the relationship between these two variables. At lower current densities, the wire electrode tends to stick to the rotating electrode. At higher current densities, the wire electrode becomes overheated, causing it to bend or even rupture. 

The VEP-atomized particles are spherical. The mass median diameter of the particles ranges typically from 300 to 500 pm. Both the mass median diameter and size range of the particles reduce with decreasing wire diameter for a given vibration frequency. The narrowest particle size distribution is produced at the resonant 

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Vibrating Electrode Atomization (VEP) 300-500 Mild steel, Cr-Ni steel, Cu-Ni alloy, W — -0.2 — Spherical, high-purity particles, Simple Low volume productivity... 

The modulation of the charge of the adsorbed atom by the vibrations of heavy particles leads to a number of additional effects. In particular, it changes the electron and vibrational wave functions and the electrostatic energy of the adatom. These effects may also influence the transition probability and its dependence on the electrode potential. 

It should be apparent from the discussion above that STM possesses tremendous potential for the elucidation of processes at the electrode-electrolyte interface. Particularly promising are the prospects for in situ studies of electrode surfaces. Vibrational, electronic, and structural information is obtainable on an atomic scale for electrodes of importance to basic electrochemical studies. Although relatively few electrochemical applications have been demonstrated to date, the availability of commercial instrumentation (c.f.,95-97) ought to increase the accessibility of STM to electrochemists and widespread use of the technique is expected in the near future. 

Franck-Condon principle. That means in other words that the time for electron transfer from a molecule to an electrode is short compared with the time of atomic movements in vibrations or rotations. This has the consequence that for electron transfer reactions the energy terms E of the electrons in the donors or acceptors are different from the thermodynamic energy levels °E which we have discussed in the preceding section. 

The other (or Y) curve represents the variation with distance of the energy of the adsorbed H atom as it vibrates on the metal surface. This M-H bond waggles as well as stretches, but in Fig. 9.10 only the stretching away from and toward the electrode... 

Correlations of in situ and ex situ observations. The characterization methods of surface science have already been established within an electrochemical context, because they can provide structural definition of fine distance scales as well as atomic composition of a surface and, sometimes, vibrational spectroscopy of adsorbates. These ex situ methods normally involve transfer of an electrode from the electrochemical environment to ultrahigh vacuum, and the degree to which they provide accurate information about structure and composition in situ is continuously debated. Additional work is needed to clarify the effect of emersion of samples and their transfer to ex situ measurement environments. The most appropriate experimental course requires observations by techniques that can be employed in both environments. Vibrational spectroscopy, ellipsometry, radiochemical measurements, and x-ray methods seem appropriate to the task. Once techniques suited to this problem are established, emphasis should be placed on the refinement of transfer methods so that the possibilities for surface reconstruction and other alterations in interfacial character are minimized. 

Since the electric perturbation vibrates along a unique axis, that is, perpendicular to the surface of the electrode, a simplified contribution of the new wave function with the interlayer distance is expected. This fact leads to longitudinal waves having an u(r) atomic displacement in the lattice. However, in spite of the absence of the other transversal components, three modes of propagation are expected one longitudinal and the other two degenerating in a single transversal mode. 

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