Polyynes: Synthesis with the Submerged Electric Arc - Polyynes: Synthesis, Properties, and Applications - page 153

FIGURE 8.1 Submerged electric arc between graphite electrodes at 10A.

The d.c. power supply we used in our study was the model Cosmo 3000
from KERT srl, Via P. Vigano` 21, 31031 Caerano di S. Marco (TV), Italy.

E-mail: [e-mail] . Web site: www.kert.it

In our standard conditions we have arced the graphite electrodes by
setting the current at 10A and moving slightly up and down by hand one of
the two electrodes in contact with the other, leaving the tension to change
freely in the range of 15-30 V (WARNING! Always wear suitable insulating
gloves! Avoid touching the electrodes directly!). The electrodes were inserted
into insulating rubber supports. It is also possible to deliver into the solution
more than 10A, for instance 20 A, by connecting in parallel two or more
d.c. power supply, but the volume of the solvent must be increased
adequately otherwise the enormous amount of energy delivered into the
solvent causes its vaporization and decomposition [33]. By working with
10A, it is sufficient to externally cool the flask with a bath of cold water
and ice, avoiding extensive vaporization. The arc is ignited immediately
after the power is switched on and is sustained by the small movement of
one electrode over the other. A bright white light is emitted in the contact
area (see Figure 8.1) between the two graphite electrodes. The anode is
consumed and this can be observed by extensive cratering of its surface
in the contact area. Also, the cathode undergoes changes with the deposition
of macroscopic carbon bulges. Periodically, arcing can be interrupted
for sampling the solution. Polyynes accumulate in the solution and can
be easily detected by electronic absorption spectroscopy [32-34,40].
A UV spectrometer (Shimadzu model 160A) was used in our laboratory.