ELECTRODE GLOW DURING ELECTROLYSISGALVANOLUMINESCENCE
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Submitted by: Santi R. Palit, Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-32, INDIA Checked by: D. Michael Barnes, David J. Dorson, Richard W. Jones, and William C. Daubert, Hiram College, Hiram, Ohio 44234 PREPARATION
Have available 0.2 N KC1 or BaCI,, a source of 200-V direct current with a minimum of Lamp current. (This can be obtained from the 115 ac mains by using a Variac voltage regulator, a step-up transformer, and a rectifier. A high capacitor is also recommended), a U-tube (20 mm i.d. with 25-cm limbs), two platinum wire electrodes 3-cm long and about 0.1-mm diameter (the cathode should be smaller in diameter than the anode wire), and an ice bath to keep the U-tube cool. DEMONSTRATION
Nearly fill the U-tube with the 0.2 N 1 ~ solution ~ 1 and insert the electrodes with the finer wire as cathode. on closing the electrical circuit gas bubbles will be briskly liberated a t both the electrodes and the solution will become progressively heated. The current will he observed to rise with time from about one-third
of an amuere to about three-fourths of an amnere. At this a stage will come when the current'will suddenly drop to a low value of about 200-300 mA. This is the glow point where the cathode will start emitting a bright glow. The glow point is recognized by the following characteristics: The steep fall in current strength as mentioned above; the bubbles will now be liberated in spurts of big bubbles instead of the usual streams of small ones; the disturbances so long visible near the electrodes may calm down; and often a hissing or a monotonic sound will be audible. I t sometimes happens that though the glow point bas apparently been reached in these resuects as mentioned above, the luminescence itself does not appear. I n such a the glow can be made appear if the cathode is taken out of the solution and is slowly placed back near the original ~osition. This is the trick to produce the glow (Continued below)
GALVANOLUMINESCENCE (Continued) REMARKS
Electrode glow during electrolysis has been observed and reported off and on for over a century but it appears to be little known among physical chemists. Hickling and Ingram (1) have quoted some early references and have termed the phenomenon contact glow discharge electrolysis to distinguish it from glow discharge electrolysis ( 2 ) vhere the electrode is in the vapor phase. Following the proposal of Ivey (9) we shall call this phenomenon by the more apt term "galvanoluminescence." In the well known "anode effect" (4) for molten salts, as also in glow discharge electrolysis and contact glow discharge electrolysis, the glow prefers to appear on the anode. Though there is a strong preference for the galvanoluminescence to appear a t the cathode, under somewhat changed conditions (for example, using a thinner and smaller anode and an alkali solution as the electrolyte) the glow may be easily made to appear at the anode. Galvanoluminescence as produced above is of great theoretical interest as it has the following features (5) u~hichare not yet well understood; (1) the cathode gas is a mixture of hydrogen and oxygen; the proportion of oxygen may be as high as 50% by volume; (2) the gas evolved is a few- times more than that given by Faraday's law of electrolysis; (3) the glow as well as the current is strongly depressed by a strong applied
magnetic field. Evidently, the current conduction is by a non-Faradaic mechanism, and there is still much to be learned about it. I t is generally supposed (6) that there is a thin mantle of gas surrounding the glowing electrode and so galvanoluminescence is a discharge through a gas mantle between the electrode and the solution. The present author has, however, observed (yet unpublished results) that galvanoluminescence can he produced with current as low as a few milliamperes; also the glow can be produced with some systems at room temperature. These and other observations are difficult to reconcile with the gas discharge theory and a more extensive study is indicated. As a source of direct current a bank of lead accumulators containing 100 to 125 cells (i.e., 200-250 V) can also be effectively used. I n such case there is less turbulence and the results are more reproducible. LITERATURE CITED (1) HIcn&mo. A,. *No Ixon~na,M. D., Tlons. Forodoy Soo.. 60, 783 (1964). (2) HICXLING. A., AND INGRAM, M . D., J . flleclronal Chcm., 8, 65 (1964). (3) IYEY, H. P.,"Eieetrolumine~~ence and Related EReets." Academic Press. N.Y..1963. (4) MANTELL, C. L.. "Eleetroehemioal Engineering." McGrsw Hill, 1960, p. 359.369. ( 5 ) PALIT,S. R., Indian J. Phys., 41, 860 (1987):42, 414(1968). (6) K E L L O ~H. G , H.,J . Elecl~achem.Soc., 97, 133 (1950). Jovrnol of Chemical Education
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Nouember 1971
Volume 48, Number 11, November 1971
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