Reverse polarization experiments

Fig. 4.3 Reverse polarity experiment [5], Proc SPIE 2011, reprinted with permission...

In practice, for a ternary system, the decomposition voltage of the solid electrolyte may be readily measured with the help of a galvanic cell which makes use of the solid electrolyte under investigation and the adjacent equilibrium phase in the phase diagram as an electrode. A convenient technique is the formation of these phases electrochemically by decomposition of the electrolyte. The sample is polarized between a reversible electrode and an inert electrode such as Pt or Mo in the case of a lithium ion conductor, in the same direction as in polarization experiments. The... 

The pulse sequence used in the reverse DEPT experiment is shown in Fig. 2.16. Presaturation of the protons removes all H magnetization and pumps up the C population difference due to nOe. Broad-band decoupling of the C nuclei may be carried out. The final spectrum obtained is a one-dimensional H-NMR plot that contains only the H signals to which polarization has been transferred—for instance, from the enriched C nucleus. 

What are the principles governing reverse polarization transfer experiments Why are reverse experiments more sensitive than normal experiments ... 

Only for larger fields exceeding 10 V in reversed polarization direction will mobile surface charges contribute to the overall signal SAC in pfm (deposited upon switching). In contact experiments, however, such mobile charges are directly eliminated via the conductive tip. 

The symmetrical reversal of the above chemical polarization experiment is the sudden replacement of the oxygen partial pressure on x = L by the original one Then the concentration profiles decay by chemical depolarization (allowing again for a measurement of Lf). If, however, the gas flow at that gas chamber is just stopped, the gas pressure equilibration takes more time in that it not only affects the sample volume but also the volume of the gas chamber. This directly connects with the permeation technique described in the next section. 

The experiments have shown that devices with tip-contacts from this set of metals can be separated into two groups, depending on the metal work function The first group with metals above 4.8 eV (Au, Pt, and Mo) shows a switching characteristic with regular polarity. The second group (Zn, Al, In, Zr) with 4.7 eV and below, switches at reverse polarity, with unreproducible results for W (4.6 eV). 

A violet spot at the needle tip during an online sheathless CE/MS experiment indicates electrical (Corona) discharge, which is prone to occur in particular under sheathless unpressurized reverse polarity CE/MS. If such an event occurs, the ESI and the counterelectrode voltages are to be stepwise decreased. 

Figure 5 Example of the computed transient electrical birefringence An(t) obtained in a reversing pulse experiment (2 fis per data point). The central spike coincides in time with the polarity reversal (Fig. 4). (Reprinted with permission from Ref 40. Copyright 1995 American Chemical Society)...

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