Working with Electrically Heated Electrodes

Experiments with indirect electrode heating can be done without any special precautions and with all the common equipment available for electrochemical investigations. Additionally, there is necessary only some kind of heating power supply. Commercial units are suitable and even simple line transformers have been utilised. With indirect heating, it does not matter whether DC or low frequency AC is applied. 

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The vacuum-tube diode, invented by Fleming24 in 1904 [2,3], works because of the relative geometrical shapes of the two concentric electrodes, the cathode and the anode. It consists of a cylindrical glass enclosure that is partially evacuated, bonded, and sealed to a metal base. It contains an inner metallic thin-wire "cathode" (negative electrode, consisting of W, oxide-covered W, or a Th-W alloy), placed along the cylinder axis. This cathode is electrically heated to 900 K or above, using an auxiliary filament circuit, typically driven by a 6.3-V power supply, to foster thermoionic emission of electrons from the cathode. This cathode is cylindrically surrounded by a metallic outer electrode, the anode or "positive electrode" or "plate," which is a hollow metallic cylinder, whose axis coincides with that of the cathode. The... 

Fig. 5.4 Schematic diagram of the CE-ECL detection system equipped with an electrically heating CPE. WE working electrode RE reference electrode CE counter electrode a the grounding of high-voltage power b, d connect to the function generator c connect to the potentiostat e the Ag/AgCl electrode /platinum wire. Reprinted with permission from Ref. [20].

Working electrodes were prepared as follows Pt disks (dia =3.3 mm) were heat-sealed onto the surface of Kel-F cylinders by melting the Kel-F around the disk with a heat gun and then physically pressing the Pt into the heat-softened surface. Electrical contact was made to the back of the Pt disk with silver epoxy (Epo-Tek 410E, Epoxy Technology). The electrodes were then polished as described previously (21). 

As an example consider a reaction run in an electro-chemical cell There are two half cells with an electrode in each of the two half cells. If the electrodes are shorted (connected with a wire) then the reaction produces no work, only dissipation (heat). If a potential is applied externally across the electrodes, equal and opposite to that generated by the electro-chemical cell, then the reaction is at equilibrium. A differential change in the applied potential produces an infinitesimal electron current and an infinitesimal, reversible amount of electrical work. For a finite amount of electrical work produced reversibly we have... 

Shielded metal arc welding is the most widely used method of arc welding. With SMAVtJ often called stick welding, an electric arc is formed between a consumable metal electrode and the work. The intense heat of the arc, which has been measured at temperatures as high as 13,000°F, melts the... 

A microwave-heated platinum disc detector has been used in a capUlary-electrophoresis arrangement [59]. A gold disc electrode with indirect electric heating worked as a detector in micro-capillary electrophoresis [60]. Dopamine and catechol were determined successfully. In a similar arrangement, the catalytic activity of copper for detection of shikimic acid and carbohydrates was utilised with an indirectly heated copper disc electrode [40]. 

Fig. 6.15 Schematic diagram of an ECL detection system equipped with an electrically heated, temperature controlled cylindrical microelectrode. WE working electrode, RE reference electrode, CE counter electrode, PMT photomultipliCT. From [63], with permission...

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