Vibrating condenser method

In the dynamic condenser, or the vibrating plate or vibrating condenser method (Fig. 5), also called Kelvin, Zisman, or Kelvin-Zisman probe, the capacity of the condenser created by the investigated surface and the plate (vib. plate) is continuously modulated by periodical vibration (GEN.) of the plate. The ac output is then amplified and fed back to the condenser to obtain null-balance operation (E,V). " " ... 

The principle of the vibrating condenser method, originally proposed by Thomson, is depicted in Fig. 3.6. Space A between the metal phases ocy a ... 

Fig. 3.6 Thomson s vibrating condenser method. A, space filled with an inert gas at low pressure P, potentiometer G, null instrument...

The two metals act as the plates of a condenser, one of the plates being used for adsorption of the gas and the other being a reference electrode. Adsorption of gas causes a change in contact potential equal to the change in work function. Disappearance of the electrical field between the two plates may be detected either by the steady condenser method or the vibrating condenser method ... 

A cell suitable for measurements by the vibrating condenser method was devised by Mignolet and is shown in Fig. 15. The principle is that of an electrically driven hollow tuning fork with the tail rigidly fixed in an iron block. The funda-mental vibration frequency is about 450c. sec and it will stand an amplitude of... 

As the nature of the electrified interface dominates the kinetics of corrosive reactions, it is most desirable to measure, e.g., the drop in electrical potential across the interface, even where the interface is buried beneath a polymer layer and is therefore not accessible for conventional electrochemical techniques. The scanning Kelvin probe (SKP), which measures in principle the Volta potential difference (or contact potential difference) between the sample and a sensing probe (which may consist of a sharp wire composed of a conducting, stable phase such as graphite or gold) by the vibrating condenser method, is the only technique which allows the measurement of such data and therefore aU modern models which deal with electrochemical de-adhesion reactions are based on such techniques [1-8]. Recently, it has been apphed mainly for the measurement of electrode potentials at polymer/metal interfaces, especially polymer-coated metals such as iron, zinc, and aluminum alloys [9-15]. The principal features of a scanning Kelvin probe for corrosion studies are shown in Fig. 31.1. 

Disc-shaped green specimens were prepared by vibration-condensation method and then sintered at 930°C following the firing schedule recommended by the manufacturer. After filing, the specimens were machined and mirror-polished with diamond suspensions down to 1 pm. For each test condition at least 10 specimens (12.5 mm in diameter and 1 mm in thickness) were prepared. 

The (average) work function of the gas-exposed catalyst electrode surface can be measured in situ, i.e., during reaction at atmospheric pressure and temperatures up to 300°C, by means of a Kelvin probe (vibrating condenser method) using, e.g., a Besocke Delta-Phi Kelvin probe with a Au vibrating disc as described in detail elsewhere. 

As shown in Figs. 15 and 16a, Eqs. (42) and (43) have been verified experimentally by directly measuring the work function of catalyst electrodes using a Kelvin probe (vibrating condenser method) under reaction conditions. ... 

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