Platinum Contacts

To set up a saturated calomel electrode, a saturated solution of potassium chloride is first prepared from pure potassium chloride and de-ionised water, and this is then shaken for some hours with analytical grade mercury(I) chloride so that the solution is also saturated with this substance. Pure mercury is placed in the electrode vessel to a depth of about 1 cm the platinum contact must be... 

Metal leads (e.g. platinum contacts) used solely as electrical connector and being identical at both cell terminals are not always explicitly mentioned. 

Fig. 3.10. Reaction cell. 1 - Atom gun 2 - Thermostate 3 - Metal evaporator 4 - Pt/Pt-Rh thermocouple 5/7 - Collimation holes (diameter 3 mm) 8 -Shutter 9 - ZnO semiconductor sensor 10 - Mobile quartz weight 11 - Platinum contacts terminals 12 - Vitrificated iron bars controlled by a magnet 13 -Quartz guides...

Glass tube Platinum contact Saturated KCI solution... 

The graphite paste electrode, introduced into voltammetry by Adams [1], has an analogue in an ISE where a mixture of graphite powder with an ion-exchanger solution functions as the electrode membrane, into which a platinum contact is immersed [16, 129, 149]. 

At the platinum contact with the solid Na2C03 the electrochemical reaction is ... 

If the terminal metals are made, as they usually will be, of a metal other than platinum, no difference is made to this argument if of copper, a platinum-copper contact potential is added to the right-hand end of this chain of phases, and a copper-zinc one is substituted for a platinum-zinc one at the left-hand end. The difference between the copper-zinc and the copper-platinum contact potentials is equal to the zinc-platinum contact potential, so that the e.m.f. of the cell is unaffected. It is always the platinum-metal contact potential that is included. 

The experimentally measured reversible electrode potential, E q, includes not only the above emf but also the potential difference at the metal-platinum contact. The electrons are the electromotively active particles at this junction, and it may be assumed that at equilibrium an electrical potential difference exists between the two metals which equalizes the electrochemical potential of the electrons in the two phases. As is well known, it is equivalent to the Volta potential difference and is given by the following ... 

Figure 26 A scheme for automation unit (1) countercurrent columns (2) regeneration column (3) screws (4) feed pumps (5) pumps for moving resin (6,7) top and bottom resin tanks (8) solution feeders (9) electric motors (10) valves-collectors (11) platinum contacts (12) screw tanks (13) jets (14) resin valves (15) solution distributions (16) a delivery cap (17) tanks for regenerated resin (18) bypass pipe (19) solution tanks.

The so-called open type of platinum microelectrode is made by a simple platinum contact with the whole investigated medium. The results obtained with this type of electrode are not always quite reproducible, as the surface active substances can inactivate the electrode. Such an electrode can serve as an oxygen monitor measuring the decrease or increase of oxygen content in biological medium only. 

M) directly to the analyte solution, so that during the preelectrolysis, the mercury codeposits with the species to be determined. The resulting mercury films are often less than 100 A thick. Since the MFE has a much smaller volume than the HMDE, the MFE shows a higher sensitivity. There is evidence that mercury electrodes with platinum contacts dissolve some platinum on prolonged contact, with possible deleterious effects hence platinum is usually avoided. Solid electrodes (e.g., Pt, Ag, C) are used (less frequently) without mercury for ions that cannot be determined at mercury (e.g., Ag, Au, Hg). 

The zirconia electrode served as a reference electrode not only for the platinum electrode measuring the oxygen fugacity of the melt, but also for the platinum contact of the ZS crucible during the reaction between ZS and melt and was also short-circuited with the ZS contact in order to change the course of the reaction. The study resulted in an electrochromic-type... 

Experimental arrangement for studying a heterogeneous reaction between zirconium silicate (ZS) refractory (1) and oxidic melt (2). The zirconia electrode (3) is used as a reference electrode for the platinum electrode (4) measuring the oxygen fugacity of the melt, for the ZS crucible (1), and for a short-circuit with ZS, via platinum contact (3). 

FIGURE 1.8 (a) Schematic diagram of CNTs linking prepatterned platinum contacts in a... 

Figure 3.8 (a) Ceramic cup for potential measurements in the alloy system Ag u, . (1) Ag plate with connecting Pt wire (8), (2) Ag electrode, (3) glass film melted on the Ag electrode (thickness ca. 0.1 mm), (4) Ag Ati alloy electrode with platinum contact wire (8) in a ceramic cup, (5) pressed on the electrolyte layer by the cover of the ceramic cup (6), and an alumina tube (7). (b) Apparatus used for potential measurements in the alloy system Ag u, with the ceramic cup (5) shown in detail in Figure 3.8a. (7) alumina tube, (8) platinum wire connections to the electrodes, (9) wire to hold the ceramic cup, and (10) thermocouple. ... 

Laser pulse photocurrent transients in solid-state Schottky barrier junctions between dry Ti02 and a platinum contact have been studied by Konenkamp and coworkers [57]. They observe a power law dependence of the collected photocurrent on time,... 

The partial pressures of oxygen, po, on both sides of the membrane are used instead of activities as in electrolyte solutions. When air is used as the reference gas on one side of the membrane, the potential of the sensor will be determined by the partial pressure of oxygen in the sample gas. In some of the latest modifications air as the reference gas has been replaced by solid nickelous oxide in contact with the zirconium dioxide providing a constant concentration of ions at the platinum contact electrode. 

A typical composition is 90 Zr02 by weight with 7 % yttrium oxide and 3 % erbium oxide. With platinum contact it can be operated at 1800 C and typical power dissipation is 1.2 Watt per square millimeter (6). Its relative emissivity is close to 0.8 and constant above 10 ym (fig. l). 

With industrial furnace one thousand of hours of operation at 2100 K were obtained in 1973 (7) with specially designed heating elements withstanding 150 C cm" thermal gradient and having platinum contact. 

F. 8.1 Cross section of zirctmia reference tube electrode. Only the bottom part of the zirconia tube contains the platinum contact and the thermocouple both buried in zirconia grit and in intimate ctmtact with the zirconia tube. The reference potential is thus strictly isothermal. Because it is easily broken, the use of the zirconia tube is restricted to laboratory measurements... 

Contacting was performed by mechanically pressing platinum contacts elastically on the film. By means of small screws, the pressure of the contacts could be adjusted. For the Montgomery method, this adjustment could be done for each of the contacts separately. Different sample holders were used for different sample sizes. For most of the conductivity experiments presented here, we used samples of 19 X 2 mm2 and 14 x 6 mm in size for the standard four-probe and Montgomery techniques, respectively. 

Contacting samples with carbon, gold or silver paints was possible. However, it turned out that the solvents in these paints lead to a change of the properties of the doped samples around the contacts, among others to a reduction of the local conductivities mainly at low temperatures, and different temperature dependences of the conductivities are found if parts of the sample are damaged by the use of conducting paints. For this reason, all results presented in this paper were obtained with mechanical platinum contacts. 

A number of workers (30, 31) have described cells with external mercury reservoirs in the form of leveling bulbs to permit the introduction or withdrawal of the cathode material without introduction of air or other contaminants. Electrical contact may be maintained directly through the mercury or, if it is desired to have a stopcock between the reservoir and the electrolysis vessel, through a platinum contact sealed into the wall of the cell. 

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