Charging timed method

When the potential of an electrode is switched from a value, where an electrode reaetion under investigation proceeds at a negligible rate, to a value, where the rate is measurable, a charge-time behavior ean be observed, which contains besides numerous other eleetroehemieal parameters the rate eonstant of the electrode reaction. Details and a complete derivation have been given elsewhere [73Rod, 75Wea, 76Wea] (Data obtained with this method are labelled CM.)... 

Kakiuchi and Senda [36] measured the electrocapillary curves of the ideally polarized water nitrobenzene interface by the drop time method using the electrolyte dropping electrode [37] at various concentrations of the aqueous (LiCl) and the organic solvent (tetrabutylammonium tetraphenylborate) electrolytes. An example of the electrocapillary curve for this system is shown in Fig. 2. The surface excess charge density Q, and the relative surface excess concentrations T " and rppg of the Li cation and the tetraphenylborate anion respectively, were evaluated from the surface tension data by using Eq. (21). The relative surface excess concentrations and of the d anion and the... 

Fig. 4.2 Electrocapillary curves of 0.1 m aqueous solutions of KF, KC1, KBr, KI and K2S04 obtained by means of the drop-time method (page 233). The slight deviation of the right-hand branch of the S042- curve is caused by a higher charge number of sulphate. (By courtesy of L. Novotny)...

As mentioned above and discussed in Chapter 2, atomic charges were often obtained in the past from dipole moments of diatomic molecules, assuming that the measured dipole moment equal to the bond length times the atomic charge. This method assumes that the molecular electron density is composed of spherically symmetric electron density distributions, each centered on its own nucleus. That is, the dipole moment is assumed to be due only to the charge transfer moment Mct. and the atomic dipoles Malom are ignored. 

It was also shown that the transit time method permits us to obtain important and new information about statistical regularities of the charge... 

The RC-method, or rise-time method, is shown in Fig. 10. Charges injected into the wire by an avalanche at a location x cause a current to flow through the anode wire in both directions, until the initial charge is spread out over the entire length. The position of the avalanche is estimated by measuring and comparing the two currents at both ends of the detector. 

The preceding method (Section 6.3.1) relies completely on the limited equilibration of the ion distribution in solution, due to the hindered diffusion. Additionally, the charging time of the double layer can be exploited for the local machining of surfaces. As mentioned in Section 6.2.2, the time constant for the double-layer charging is given by the product of solution resistance and double-layer capacity. In the above experiments employing the tip of an STM, which is a few nms distance to the surface, as local counter electrode this time constant is well below nanoseconds, even for diluted electrolytes. Nonetheless, for electrode separations in the... 

I(dc) is inserted in equation 5.2 to calculate the specific volume resistivity at that temperature and electrical field strength. This measuring procedure is completely automated, see 5.1.4. The volume resistivity determination is described in the ASTM D257 (US), BS 202A (UK), DIN 53596/51953 (BRD) and in ISO 93 [3]. The time dependency of Ic is mentioned in all these methods. Besides, all methods indicate that I(dc) is determined usually after a standard charging time of 60 seconds. It will be clear that if one assumes I(dc) = Ic(60 seconds), this current nearly always contains a time dependent charging current contribution. 

After the charging the initial surface potential Vq of the samples was measured by the vibrating electrode method with compensation (Reedyk et al.). The measured surface potential values are presented in Table 2. The results obtained show that the charging time to 30 minutes does not influence the surface potential of the PP films. 

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