High pressure, glass electrode

Mercury arcs are employed in these lamps because of the spectral distribution they emit, and because mercury vapor is relatively inert. It does not attack either the glass or the electrode materials (Kirk 1982). This contributes to the long lifetimes of mercury lamps. Low pressure mercury lamps are commonly called fluorescent lamps. High pressure mercury lamps are used in industrial environments and for street lighting and floodlighting. Other applications for mercury vapor lamps include motion-picture projection, photography, and heat therapy. 

The electrochemical reduction of CO in fhe COj-methanol solution was carried out under high COj pressure. The high pressure apparatus was assembled from a SUS-316 sfainless steel tube. A glass inner tube was used to avoid contact of the electrolyte with the metal apparatus. Various metal electrodes were used in this study. The details have been described previously [9]. A Ft counter electrode and a silver quasi-reference electrode were used. Reagent grade methanol was used as the solvent. Tetrabutyl or tetraethyl ammonium salts were used as supporting electrolytes. 

The use of pressurized, sterilizable combined glass electrodes mounted through the reactor vessel wall is widely established. A high degree of accuracy and stabihty is needed to provide a good basis for the control loop. However, a recahbration is necessary both after sterilization and at regular intervals. This is easily done by external measurement after sampling the reactor, because the pH of the sample drifts very slowly. 

Fig. 6.7 A high-pressure electrochemical cell with an Ag/Ag reference electrode and an Au disc working electrode a platinum wire auxiliary electrode is shown on the left (a) bomb electrical terminals, (b) brass connectors, (c) mounting plate, (d) Kel-F backing screw, (e) Kel-F electrode housing, (f) Teflon sleeve, (g) upper cell body, (h) reference-electrode compartment, (I) internal piston with a Vycor glass frit, (j) O-rings, (k) Teflon piston, and (I) screw plug. ...

Fig. 6.3. Cross section of a high-pressure luminescent lamp. / glass bulb 2 luminescent powder J quartz envelope for gas discharge 4 lamp cap 5 electrodes...

Commercial glass electrodes, mostly for pH measurements, differ in construction because they have to serve different purposes. The electrode tips may have different shapes, including tubular flow-through electrodes (Figure 3). Special electrodes are used under conditions of high pressures or high temperatures or... 

The potentiometric determination of pH by means of glass electrodes as described in Chapter 7 and the corresponding calibration procedures can be used for in situ determinations in surface water (to a depth of about 30 m) without any modification other than using a submersible electronic unit. There is no pressure dependency of the electrical electrode signal according to the Nemst equation (see Chapter ) but the mechanical construction of the electrode has to consider the ambient pressure. High pressure affects the asymmetry... 

Yasuda et al. performed dielectric relaxation measurements on metastable solid MBBA, using a parallel-plate capacitor. Glass plates with strips of transparent tin-oxide-conducting coating served as electrodes. The cell was mounted in a copper beryllium pressure vessel, pressurized with liquid isopentane. A similar setup was used for the study of ferroelectric liquid crystals. Ferroelectric liquid crystals have also been studied by Chandrasekhar and co-workers who used a sapphire cell setup in a high-pressure apparatus. The sample was sandwiched... 

Moura-Ramos and Williams have studied LC siloxane polymer P/Si/8/CN in the pressure range 0.1-152 MPa, the temperature range 50-75°C, and the frequency range 10-10 Hz. The substance exhibits a smectic phase between 363 K (the clearing temperature) and 274 K (the glass transition temperature, T ). Dielectric studies were performed with disk samples placed between metal electrodes of a three-terminal high-pressure cell. The results are presented as loss curves in terms of G/w = e"C , where G is the measured equivalent parallel conductivity of the sample, e" is the dielectric loss factor, and Q the inter-electrode geometric capacitance. 

Despite its early date of pubhcation, one of Schwabe s most important publications till today concerns pH measurements under extreme conditions. It discusses extremely acidic and extremely alkaline solutions. It goes into measurements at high and low temperatures and tmder increased pressure. Finally nonaqueous solutions and the use of metal electrodes are discussed. For certain technical applications, particularly with extremely alkaline solutions, glass electrodes are not suitable as the glass surface is too severely affected this led to Schwabe s successful investigations into the use of bismuth electrodes for pH measurement. 

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