Sweep variation

Why, in general, are recordings not made by a sweeping variation of voltage ... 

Fig. 21 Small amplitude (linear) burning rate response to sine sweep variation in pressure with 1% amplitude. Mean input parameters are nominally those of non-dimensional case E 1)...

Figures 16.7 and 16.8 illustrate the effect of sweep variation on module performance. An average sweep fraction of 0.1 was used for the calculations.

Figures 16.9 and 16.10 compare the effects of inner diameter and sweep variation on module performance. Like sweep variability, inner diameter variability is detrimental to performance - dry gas recovery and flow rate deaease as the variability increases. However, the effect of inner diameter variability is significantly larger. The dry gas flow rate decreases by a factor of two with 20% inner diameter variation for the lower dry gas dew points. Changes in dry gas recovery are smaller and do not exceed 5% at the lowest dew points considered.

Figure 16.7 Effect of sweep variation on dry gas flow rate as a function of dew point solid - sweep variation = 0, short dash - sweep variation = 0.1, long dash - sweep variation = 0.2...

The sweeping test, following X, Y and Z axes, on the aluminum plate containing four standard defects and the processing software comparing between the impedance variation of the sane reference and the sample to be controlled allow the reconstitution of an image of the piece. 

A fourth mechanism is called sweep flocculation. It is used primarily in very low soflds systems such as raw water clarification. Addition of an inorganic salt produces a metal hydroxide precipitate which entrains fine particles of other suspended soflds as it settles. A variation of this mechanism is sometimes employed for suspensions that do not respond to polymeric flocculants. A soHd material such as clay is deUberately added to the suspension and then flocculated with a high molecular weight polymer. The original suspended matter is entrained in the clay floes formed by the bridging mechanism and is removed with the clay. 

One more variation to the many methods proposed for sulfur extraction is the fire-flood method. It is a modem version of the Sickian method, by which a portion of the sulfur is burned to melt the remainder. It would be done in situ and is said to offer cost advantages, to work in almost any type of zone formation, and to produce better sweep efficiency than other systems. The recovery stream would be about 20 wt % sulfur as SO2 and 80 wt % elemental sulfur. The method was laboratory-tested in the late 1960s and patents were issued. However, it was not commercially exploited because sulfur prices dropped. 

The potentiostatic technique has a number of variations and the potential may be increased or decreased incrementally, changed continuously at a predetermined rate (potential sweep) or applied as pulses of very short duration. The applications of the potentiostatic technique are considered in detail in Sections 1.4, 1.5 and 19.2, and will not be considered here. 

Taking into account the variation in the oxidized area as a function of the overpotential, and the counter-ion flows, the charge consumed during the potential sweep in those regions where the structure was previously opened under conformational relaxation control, is given by... 

Linear Potential Sweep Infra-Red Spectroscopy (LPSIRS) is a variation of EMIRS techniques where the absorbance at a particular wavenumber is monitored during a potential sweep. 

Figure 3.13 Curve A Cyclic voltammogram for a Pt electrode in 0.5 M H2S04. Electrodes are 1.13cm2. scan rate 0.1 cycles per second. Curve B corresponding variation in the charge passed (in pC) vs. potential. Each point on the A and plots is the average of points obtained from four successive sweeps From Greef (1969),...

The experimental mechanistic study of the anodic cyclization reactions requires values for the variation of the peak potential (Ep) in LSV with the sweep rate (v), the concentration of substrate (C) and the concentration of added base (B). The plots of dEp/dlogv, dEp/dlogC, and dEp/dlogB provide an effective tool for qualitative mechanistic analysis. The diagnostic criteria developed for discrimination between the various possible mechanisms [5] and adopted for oxidative cyclizations are presented in Table 1. 

In order to illustrate the application of LSV in mechanistic analysis we can look at the redox behavior of the formazan-tetrazolium salt system which we studied some years ago [17], 1,3,5-Triphenyl formazane was oxidized at controlled potential in CH3CN-Et4NC104 solution to 2,3,5-triphenyl tetrazolium perchlorate which was then isolated in quantitative yield. Coulometry showed that the overall electrode reaction was a two-electron oxidation. It has been shown that the rate of variation of Ep with log v was 30 mV per decade of sweep rate and that there was no variation of the peak potential with the concentration of 1,3,5-triphenylformazan. According to Saveant s diagnostic criteria (Table 1), four mechanistic schemes were possible e-C-e-p-p, e-C-d-p-p, e-c-P-e-p and e-c-P-d-p. If cyclization is the rate-determining step, then the resulting e-C-e-p-p and e-C-d-p-p mechanisms would not imply variation of Ep with the concentration of base. However, we have observed the 35 mV shift of Ep cathodically in the presence of 4-cyanopyridine as a b e. These observations ruled out the first two mechanisms. The remaining possibilities were then e-c-P-e and e-c-P-d, as shown in Scheme 3. 

The rate of dE/dt is always kept constant during a potential scan, although obtaining a series of polarograms as a function of v can be extremely informative. (The variation of the sweep rate can be regarded as being equivalent to a variation of varying the time-scale of observation of an electrochemical experiment, as will become clear later in Section 6.4.3.)... 

---