Electrode straightness

Hold the electrode straight up and place a drop of KC1 solution on the probe. Carefully place the membrane over the probe so that an air bubble is not trapped in the KC1 solution. To hold the membrane in place, push an O ring over the end of the probe. 

The next step is to put some silicone around the rim of the 1" cap that seats the negative mesh electrode. Take a 1" rubber o-ring, slip it over the mesh and slide it down to the 1" cap, seating it on the cap. The rubber o-ring will steady and keep the mesh electrode straight. It is important for the mesh electrode to stand straight up and not be seated at an angle. 

Replaced ambiguous 8.3 Electrode straightness text with language and illustration from ANSI/AWS A5.12/A5.12M-98. It was Electrodes shall not deviate straight by more than 0.5 mm over any 100 mm of length or less. ... 

In most quantitative analyses we are interested in determining the concentration, not the activity, of the analyte. As noted earlier, however, the electrode s response is a function of the analyte s activity. In the absence of interferents, a calibration curve of potential versus activity is a straight line. A plot of potential versus concentration, however, may be curved at higher concentrations of analyte due to changes in the analyte s activity coefficient. A curved calibration curve may still be used to determine the analyte s concentration if the standard s matrix matches that of the sample. When the exact composition of the sample matrix is unknown, which often is the case, matrix matching becomes impossible. 

As the electrons move from cathode to anode, they undergo elastic and inelastic collisions with gas atoms. The paths of the electrons are not along straight lines between the electrodes because of the collisions. In effect, the movement of each electron consists of short steps between... 

In a vacuum (a) and under the effect of a potential difference of V volts between two electrodes (A,B), an ion (mass m and charge ze) will travel in a straight line and reach a velocity v governed by the equation, mv = 2zeV. At atmospheric pressure (b), the motion of the ion is chaotic as it suffers many collisions. There is still a driving force of V volts, but the ions cannot attain the full velocity gained in a vacuum. Instead, the movement (drift) of the ion between the electrodes is described by a new term, the mobility. At low pressures, the ion has a long mean free path between collisions, and these may be sufficient to deflect the ion from its initial trajectory so that it does not reach the electrode B. 

The system for shielded-metal arc welding, shown in Figure 2a, is the simplest system. It consists of the power source, electrode and holder, the base metal, and the electrical cables or leads. When the arc is stmck, a complete electrical circuit is provided. With d-c welding, the electrode maybe either negative (straight polarity) or positive (reverse polarity). Shielded metal arc welding is only used manually. 

Magnetic flow meters are sometimes utilized in corrosive Hquid streams or slurries where a low unrecoverable pressure drop and high rangeabiHty is required. The fluid is required to be electrically conductive. Magnetic flow meters, which use Faraday s law to measure the velocity of the electrically conductive Hquid, are relatively expensive. Their use is therefore reserved for special situations where less expensive meters are not appropriate. Installation recommendations usually specify an upstream straight mn of five pipe diameters, keeping the electrodes in continuous contact with the Hquid. 

Production of carbon electrodes is a capital-intensive business. Two suppHers dominate the prebaked market. Carbon paste producers are more numerous and tend to serve local markets. There is no international standard for the threaded joints on carbon electrodes. Manufacturers of straight pin carbon electrodes have followed the physical specifications adopted for graphite electrodes (37). Unified standards do not exist for pinless joints resulting in limited interchangeability among brands. Electrode diameters are offered in both English and metric sizes with no restrictions on new or unique diameters. 

A typical Evans diagrams for the corrosion of a single metal is illustrated in Fig. 1.26a (compare with Fig. 1.23 for two separable electrodes), and it can be seen that the E -I and E -I curves are drawn as straight lines that intersect at a point that defines and (it is assumed that the resistance for the solution is negligible). E can of course be determined by means of a reference electrode, but since the anodic and cathodic sites are inseparable direct determination of /co by means of an ammeter is not... 

Plot the observed e.m.f. values against the concentrations of the standard solutions, using a semi-log graph paper which covers four cycles (i.e. spans four decades on the log scale) use the log axis for the concentrations, which should be in terms of fluoride ion concentration. A straight line plot (calibration curve) will be obtained. With increasing dilution of the solutions there tends to be a departure from the straight line with the electrode combination and measuring system referred to above, this becomes apparent when the fluoride ion concentration is reduced to ca 0.2 mg L-1. 

Pores generally are not of a hose-like configuration of constant diameter, in a straight-line direction from one electrode to the other. In practice, separators pores are formed as void between fibers (Fig. 1),... 

The path taken by an ion from one electrode to the other will not be a straight one, as it has to evade the solid structures by making detours. The ratio of the mean... 

The cyclic voltammograms of ferrlcyanlde (1.0 mM In 1.0 M KCl) In Fig. 2 are Illustrative of the results obtained for scan rates below 100 mV/s. The peak separation is 60 mV and the peak potentials are Independent of scan rate. A plot of peak current versus the square-root of the scan rate yields a straight line with a slope consistent with a seml-lnflnlte linear diffusion controlled electrode reaction. The heterogeneous rate constant for the reduction of ferrlcyanlde was calculated from CV data (scan rate of 20 Vs using the method described by Nicholson (19) with the following parameter values D 7.63 X 10 cm s , D, = 6.32 X 10 cm s, a 0.5, and n =1. The rate constants were found to be... 

The polarization relations found in the region of high polarization are usually plotted semilogarithmically as AE vs. log i (Eig. 6.1). These plots are straight lines, called Tafel lines (curve 1 in Eig. 6.1), when relation (6.3) holds. More complicated polarization functions are found at many real electrodes in the region of high polarization. Sometimes several Tafel sections can be distinguished in an actual polarization curve (curve 2 of Eig. 6.1) each of these sections has its own characteristic values of parameters a and b). 

Figure 6.20 Extrapolated current density at t = 0 obtained from chronoamperometric experiments for Pt(l 11), Pt(lOO), and Pt(l 10) electrodes in 0.2 M HCOOH + 0.5 M H2SO4 on electrode. The straight lines show the regions where the Tafel behavior is observed. (Data taken from Herrero et al. [1994].)...

Figure 7.3 Plot of the platinum (hydrogen plus anion) charge density versus the charge density associated with the adatom redox process (Bi or Te, as indicated) on a Pt(l 11) electrode in 0.5 M H2SO4 solution. Straight lines represent the expected behavior for the stoichiometry indicated in the figure.

By plotting E against log(icd - i)/i one can assess the reversibility of the electrode process, because a straight line with slope 2.303RTjnFshould then be obtained from the slope one can also find n many workers determine the slope by simply calculating Ei - Ei, which yields... 

So, corresponding to id for a reversible electrode reaction, Jp is a linear function of concentration the greater sensitivity of the latter permits determinations down to 10 1M(instead of 10 6 Mfor id). Apart from this advantage, the second derivative curve, by means of the difference between its maximum and minimum as a function of concentration, offers an even better check on reaction reversibility32 than the straight-line plot of E (according to eqn. 3.49) against log(tcd - i)/i (see also p. 120), especially because Ip, as a property at the halfwave potential, is more sensitive to the occurrence of irreversibility (cf., pp. 124-127). 

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