Glass sensitive

The hydrogen electrode is not practical, and commercial pH meters are constructed with a glass electrode that has a sensing element made of a thin membrane of a special glass sensitive only to H ions (Figure 9.4a). The potential of the electrode is found to be proportional to the pH of the surrounding solution, and the response of this electrode is similar to that of a hydrogen electrode. 

In parallel with glass sensitivity studies, tests on inactive full-scale prototypes were conducted to determine the sensitivity of the melter to variations in process parameters, such as different melting temperatures, variations in time periods between glass pours, and variations in glass-to-frit ratios or frit-to-calcine ratios. 

Armistead WH, Stookey SD (1964) Photochromie silicate glasses sensitized by silver halides. Science 144 150-154... 

Table 10.1 summarizes the characteristics of common ISEs and a number of new sensors in this field. We have not included in this table the liquid or polymer membrane-based electrodes which are selective, but rather fragile (for more details on such membranes see References 58,59). ISEs of the first kind are not very numerous, e.g., F -ISE (monocrystalhne membrane based on LaFj), Ag" -ISE (silver salts), or Na" -ISE (Na alumino-silicate glass or polyciystalline NASICON [Na super ionic conductor] membranes). Most of the ISEs are of the second kind and are based on insoluble silver salts for example, halide ISEs (CE, Br, I"), Cd ", Pb ", Cu ", etc. Such ISEs use mixtures of insoluble salts based on silver sulfide or silver selenide. Recently, Vlasov etal. and Neshkova have proposed several glasses sensitive to transition metals. Typical ISE devices are shown in Figure 10.5. Thin-layer chemical sensors based on chalcogenide glasses have also been developed. ... 

Silicon and germanium readily react with even very dilute solutions of caustic alkali. Silicon is so sensitive to attack that it will dissolve when boiled with water which has been in contact with glass ... 

Silanes are very sensitive to attack by alkalis and will even react with water made alkaline by contact with glass this reaction is in marked contrast to the reactions shown by alkanes. Unlike alkanes, silanes are found to have marked reducing properties and will reduce, for example, potassium manganate(VII) to manganeseflV) oxide, and iron(III) to iron(II). 

Photomultipliers are used to measure the intensity of the scattered light. The output is compared to that of a second photocell located in the light trap which measures the intensity of the incident beam. In this way the ratio [J q is measured directly with built-in compensation for any variations in the source. When filters are used for measuring depolarization, their effect on the sensitivity of the photomultiplier and its output must also be considered. Instrument calibration can be accomplished using well-characterized polymer solutions, dispersions of colloidal silica, or opalescent glass as standards. 

Light-sensitive glasses Light-sensitive materials Light sources... 

The immersion of glass electrodes in strongly dehydrating media should be avoided. If the electrode is used in solvents of low water activity, frequent conditioning in water is advisable, as dehydration of the gel layer of the surface causes a progressive alteration in the electrode potential with a consequent drift of the measured pH. Slow dissolution of the pH-sensitive membrane is unavoidable, and it eventually leads to mechanical failure. Standardization of the electrode with two buffer solutions is the best means of early detection of incipient electrode failure. 

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