Electrode Pulling

With proper cushioning of the mass or solenoid assembly after fracture of the glass has occurred, it is possible to produce two electrodes simultaneously, one in the fixed clamp and the other attached to the mass or solenoid unit. 

The length of the heater and, to some extent, the pulling force control the geometry of the finished micropipettes with regard to shoulder taper and shank length. Detailed discussion and performance graphs are given by Frank and Becker (1964). 

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The importance of this can be assessed by running a cyclic voltammogram with the electrode pulled back from the window, and comparing it to one collected with the electrode pushed against the window. The influence of IR drop is discussed in a little more detail in section 2.2.7. 

Figure 2.112 Cyclic voltammograms of a P( electrode immersed in N2-saturated I M NaOH solution, and (a) in the absence and (b) in the presence of I M ethylene glycol. Scan rate 100mVs-1, the voltammograms were taken using the IR spectroelectrochemical cell with the electrode pulled back from the cell window. From Christensen and Hamnett (1989).

The lower two spectra were recorded in CO saturated solution which contained 0.1 M C H,.CN. The adsorbate layers were produced by cycling the potential with the electrode pulled away from the window as described above, except that a different final potential was chosen to end each cycle. Spectrum c was recorded at a final potential of 0.05 V. At this point no v(C0) band is observed. Spectrum d was recorded at a final potential of 0.55 V (c.f. Figure 1), and shows the band at v(C0) - 2078 cm" that we assigned to a partial coverage of adsorbed CO. We can show that this change in the spectrum is irreversible by returning the potential to 0.05 V. The v(C0) band is still observed with the same peak area, and the frequency is shifted by only the amount predicted by the known potential dependence. 

The copper electrode, which pulls electrons from the external circuit, is considered to be the positive pole of the celL... 

The inner layer (closest to the electrode), known as the inner Helmholtz plane (IHP), contains solvent molecules and specifically adsorbed ions (which are not hilly solvated). It is defined by the locus of points for the specifically adsorbed ions. The next layer, the outer Helmholtz plane (OHP), reflects the imaginary plane passing through the center of solvated ions at then closest approach to the surface. The solvated ions are nonspecifically adsorbed and are attracted to the surface by long-range coulombic forces. Both Helmholtz layers represent the compact layer. Such a compact layer of charges is strongly held by the electrode and can survive even when the electrode is pulled out of the solution. The Helmholtz model does not take into account the thermal motion of ions, which loosens them from the compact layer. 

In a crystal-pulling procedure using a tri-arc furnace (Fig. 2), a resistor box, a d.c. power supply (300 A, 80/40 V) and a set of water-cooled power cables are used to bring power and water to the electrodes. The upper part of the furnace is equipped with three equally spaced copper cathodes, to which are fixed W-Rh electrodes. The upper part (cathode) is separated from the lower part (anode) by a transparent quartz glass tube. In the bottom of the furnace there is a tapered opening for a water-cooled copper hearth containing the boride melt. All parts of the furnace are also water... 

Figure16.6 (a) Schematicdrawingofexperimental set-upforthe evaluation of the interfacial tension under potential control, (b) Relative change in contact angle as a function ofthe potential after the substrate was inserted into (open circles) and pulled from the nitrobenzene phase. Insets are schematic drawings of the side views of the contact lines. The potential was described with respect to the Au/AuO f reference electrode.

Pull the copper wire and the electrode inside the length of pipette. 

Electrons pass through the external circuit into the copper electrode, where they are consumed in reducing Cu2+ ions in the solution to copper atoms. This is represented by the reduction half reaction (c). The copper electrode which pulls electrons from the external circuit is labeled positive, and is the cathode of the cell. 

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