Rotating electrodes, oscillations

A typical 20-MW, a-c furnace is fitted with three 45-in. (114.3-cm) prebaked amorphous carbon electrodes equdateraHy spaced, operating on a three-phase delta connection. The spacing of the electrodes is designed to provide a single reaction zone between the three electrodes. The furnace is rotated to give one revolution in two to four days or it may be oscillated only. Rotation of the furnace relative to the electrodes minimizes silicon carbide buildup in the furnace. 

Azevedo et al. observed oscillations during CO electrooxidation also on rotating polycrystalline Pt disc electrodes under potentiostatic conditions [165], The oscillations arose only in a small window of the external potential and required the rotation of the electrode. Since the conditions were such that the IRq drop was negligible, it is... 

Another example for the HMRRD electrode is given in Fig. 9 for Fe in alkaline solutions [12, 27]. The square wave modulation of the rotation frequency co causes the simultaneous oscillation of the analytical ring currents. They are caused by species of the bulk solution. Additional spikes refer to corrosion products dissolved at the Fe disc. This is a consequence of the change of the Nemst diffusion layer due to the changes of co. This pumping effect leads to transient analytical ring currents. Besides qualitative information, also quantitative information on soluble corrosion products may be obtained. The size of the spikes is proportional to the dissolution rate at the disc, as has been shown by a close relation of experimental results and calculations [28-30]. As seen in Fig. 7, soluble Fe(II) species are formed in the po-... 

With this instrument, at injection the outer electrode is about at ground, while the inner electrode is set at about —3200 V for positive ions. To have a reasonably circular or oval trajectory around the centre electrode, the ions need to have a kinetic energy around 1600 eV. The ions start to rotate around the inner electrode and together oscillate along the z axis. 

Figure 6. Coexistence of stationary behavior (between 0 and 1.1s) and oscillations (from 2.4 s on) during the reduction of S20 at a rotating Pt electrode, rotation rate f = 20 Hz. Between points a and b the system was perturbed by enhancing the rotation frequency to about 150 Hz, triggering the transition from the fixed point to the limit cycle. (After Wolf etal. with the kind permission of VCH Publishers.)...

The second example is again taken from formic acid oxidation. In Ref. 88 two sequences of mixed-mode oscillations are described which were found when formic acid was oxidized at an elevated temperature (50 °C) at a rotating platinum electrode. The interesting aspect here is that the large amplitudes in the first sequence are as large as the small amplitudes in the second sequence. Hence, the period-1 state that separates the two sequences corresponds to the 1 state of the first sequence and the 0 state of the second one. 

Closer to the Flade potential, the width of the active area started to oscillate or breathe in a way similar to that of the modulated waves described in the above experiments. The difference between these two types of modulated waves is that here the wave constantly rotates around the center and possesses a localized structure, while in the above experiments it traveled once across the whole electrode and reappeared only after some time. 

A B-Z type reaction involving oc-ketoglutaric acid as a substrate was studied by Treindl and Dorovky (1981, 1982). The polarographic method with a rotating platinum electrode was used in following the temporal oscillations both of Ce(IV) and Br2 concentrations simultaneously. 

Makarov invented a new type of mass spectrometer by modifying the Kingdom trap with specially shaped outer and inner electrodes (see Fig. 2.28). Also, in this case a purely electrostatic held is obtained by a dc voltage applied to the inner electrode. Ions injected into the device undergo a periodic motion that can be considered the result of three different periodic motions (1) rotation around the inner electrode (2) radial oscillation and (3) axial oscillations. These three components exhibit well-defined frequencies ... 

If an angular velocity is applied perpendicular to the vertical axis, the rotor responds with a vibrating precession, due to the principle of conservation of angular momentum (Fig. 4.1.6). This tilt oscillation has the same frequency as the inplane rotational vibration and an amplitude proportional to the angular rate to be measured. This motion is detected by electrodes located beneath the structure as a change in capacitance. 

Fig. 5.10.1 Schematic drawing of a rotational disc gyro. The rotor (in blue) is oscillating around the z axis, driven by fixed comb structures. A yaw rate around the y axis generates a Coriolis force in the z direction. The resulting seesaw-like out-of-plane motion of the rotor is detected by measuring the difference in capacities between the rotor and detecting electrodes beneath it...

Recently, a new high performance mass analyzer, called Orbitrap , has been developed. The Orbitrap consists of an inner and an outer electrode, which are shaped to create a quadro-logarithmic electrostatic potential. Ions rotate about the inner electrode and oscillate harmonically along its axis (the z-direction) with a frequency characteristic of their mjz values ... 

Electrostatic ion trap comprised of a spindle-shaped inner electrode and a split outer electrode ions (from API) rotate around and oscillate along the inner electrode... 

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