J. Mod. Phys., 2010, 1, 236-243
doi:10.4236/jmp.2010.14035 Published Online October 2010 (http://www.SciRP.org/journal/jmp)
Making and Study of Moderate Pressure Glow Discharge
on the Basis of Electrolytic Foamy Cathode, Prep ared as
the Aqueous Solution of NaHCO 3
Dmitry V. Vyalykh, Alexander E. Dubinov, Igor L. L’vov, Sergey A. Sadovoy, Victor D. Selemir
The Russian Federal Nuclear Center All-Russian Scientific Research Institute of Experimental Physics,
Sarov, Nizhny Novgorod region, Russia
Received July 8, 2010; revised August 9, 2010; acce pted August 18, 2010
Abstract
A method to generate the dynamic moderate pressure dc glow discharge on the basis of electrolytic cathode
in the form of aqueous solution of sodium bicarbonate NaHCO3 is described. Photo and video images of the
discharge are presented as well as the synchronized therewith “oscillograms” of current and voltage. Differ-
ent phases of the discharge were discovered, one of which is a quasi-stationary glow discharge with the
foamy cathode, was recorded for the first time. It was shown, that in this phase the discharge is supported by
a so-called three-dimensional cathode spot, having the finite volume. The time-spatial diagram was plotted
for the discharge. The Rayleigh-Taylor instability in the two-layered electrolytic cathode was recorded.
Keywords: Glow Discharge, Electrolytic Cathode, Aqueous Solution, Sodium Bicarbonate, Foamy Cathode,
Rayleigh-Taylor Instability
1. Introduction
Dc gas discharges with liquid electrolytic electrodes are
the objects of special scientific interest and varying
chemical-technological applications. A huge amount of
studies was done with these discharges in air under at-
mospheric pressure (see, e.g., the reviews and the origi-
nal papers [1-11]). The authors believe that dc glow dis-
charge at the low gas pressure is worth generating and its
properties are worth studying.
The main obstacle, preventing generation of the above
discharge is air pressure lower than 10 Torr, which cor-
responds to the boiling threshold of electrolyte solution.
By way of example, air pressure, achievable by pumping
from the camber, containing an electrode in the form of
aqueous solution, reaches 25-30 Torr, whereas at the
pressure slightly exceeding 30-50 Torr the chamber is
filled with electrolyte vapor, although the boiling can be
avoided. At such pressures a stationary dc glow dis-
charge can be generated, which, according to classifica-
tion [12], is referred to the moderate pressure glow dis-
charges.
The first studies of moderate pressure glow discharges
over the boiling threshold of electrolytic electrode were
done in [13,14]. The experiments were to study the
cathodes in the form of CuSO4 and KMnO4 aqueous so-
lutions, which resulted in revealing different hydrody-
namic instabilities at plasma-liquid interface.
Being presented in this paper are the results of dy-
namical studies, electro-technical characteristics and
photo/video images of dc moderate pressure glow dis-
charge, generated with electrolytic cathodes in the form
of sodium bicarbonate NaHCO3 (baking soda) aqueous
solution, as well as with the two-layered liquid cathode.
2. Elements of Chemistry of Sodium
Bicarbonate Aqueous Solution
Presented below are the essentials of electrochemistry of
NaHCO3 aqueous solution, without knowing which it is
impossible to apprehend the results of the study. Liquid
H2O, as is well known, is a weak electrolyte, in which
ions of H+ and OH are dissolved as so as other bigger
molecules, molecular ions, complexes and clusters. With
NaHCO3 added to the solution the last dissociates in the
following reaction:
NaHCO3  Na+ + HCO3
. (1)

D. V. VYALYKH ET AL.
237
The resulting from the above reaction ion HCO3
 may
interact with ions H+ and OH by forming the weak car-
bon acid:
H+ + HCO3
 ↔ H
2O + CO2, (2)
or, alternatively as:
OH + HCO3
 ↔ H
2O + CO3
2. (3)
Thus, according to (1) and (2), as soda dissolves in
water, some carbon dioxide is released and chemical
equilibrium is obtained. The solution itself stays color-
less and transparent. With some H+ ions further added to
the solution, in the form of a droplet of an acid, for in-
stance, chemical equilibrium shifts to the side, deter-
mined by reaction (2) and the bubbles of carbon dioxide
gas occupy the solution. The same result may be ob-
tained by locally increasing the concentration of H+
somewhere in the solution, for example near the nega-
tively charged electrode.
If CO2 is intensively released, the bubbles generate
violently and rise to the surface, thus making the surface
foamy. This is just the property of soda, which is used by
cooks for loosening pastry, when they add several drops
of acetic acid to the solution.
3. Experimental Setup
A gas-discharge chamber, containing the glass tube of
550 mm length and of 60 mm diameter, located verti-
cally was used for experimental work. Electrodes made
of stainless steel were located at the edges of the glass
tube, the lower one being the cathode, and the upper one
being the anode (see Figures 1(a), (b)).
The glass tube was filled with the liquid electrolyte up
to 280 mm height. Aqueous solution (5-10%) of sodium
bicarbonate played the role of electrolyte. Then a vac-
uum pump was used to increase the air pressure over
electrolyte up to 30-50 Torr.
It should be mentioned, that after the pump is disabled,
the pressure inside the chamber goes on growing due to
evaporation of electrolyte. By way of example, during
one discharge event, lasting for several tens of seconds,
pressure inside the chamber grows for almost 100 Torr.
Thus, the experiments [13,14] were to be setup in the
above mode of jumping pressure. In the present instance
the pump and the automatic valve, connected to pressure
gauge, sustained the constant pressure in the chamber
during the whole event (up to 1 minute) with  2 Torr
shift.
A high-voltage dc supply was used to create the dis-
charge. The 600 Ohm ballast resistor was connected in
the circuit to limit the discharge current. Then the
gas-discharge chamber was switched on. Digital current
meter MASTECH M-830B and voltmeter DIGITAL
(a)
(b)
Figure 1. Gas discharge chamber: (a) chamber scheme
(1-anode, 2-tube, 3-electrolyte, 4-cathode); (b) outer view of
the chamber with the burning discharge; the rising foamy
mushroom can be noticed below (current meter-on the
right, voltmeter-on the left).

D. V. VYALYKH ET AL.
238
MULTIMETER PT9208A equipped with LCD indica-
tors were used to read the discharge current and the tube
voltage. The above devices showed the current in am-
peres and the voltage in kilovolts in real time mode (Fig-
ure 1(b)) using the specially matched dividers.
The discharge was photographed and video recorded
using SONY DCR-SR85 camera featuring 25 Hz frame
repetition rate. The indicators of the current meter and
the voltmeter were always captured by the camera eye,
which provided for digital readout of current and voltage
of the discharge during one pulse (characteristic time of
process from 2 to 60 s, that is why standard pulsed oscil-
lography could have been hardly used).
4. Experimental Results
4.1. Time-Spatial Dynamics of Glow Discharge
Generated by Electrolytic Electrode
One of the examples of video record (150 shots) of the
dynamic picture of the discharge, obtained at 5% con-
centration of NaHCO3 in water and 30 Torr pressure is
shown in Figure 2.
Let us describe the dynamic picture of the discharge.
The sliding discharge is being ignited along the surface
of the glass tube (shots 7-28 in Figure 2). Sometimes the
surface discharge has the branchy structure (Figure 3 ). If
air is exhausted from the chamber inaccurately, the solu-
tion is spit. Some of the droplets stick to the walls of the
tube. If the surface discharge goes through this droplet,
the discharge glows yellow brighter than along the violet
channel (Figure 4).
Next the volumetric glow discharge is ignited (starting
from shot 29). The discharge is torn away from the walls
and is slightly contracted, which is typical for moderate
pressures. The color of the discharge is violet, but some-
times it glows bright yellow over the entire volume (for
instance, shots 57-61), or in some certain locations (shots
51 and 92). These bright glows are, apparently, due to
sodium penetration into plasma during evaporation of the
solution.
Apparent bifurcation of volumetric discharge column
near the electrolyte surface (for instance, on shots 64-66
and 84-86) most likely stand for the integral picture of
Figure 2. Video record of the dynamic picture of the discharge with 25 Hz shot repetition rate (pulse # 229).

D. V. VYALYKH ET AL.
239
Figure 3. Video record of the branched surface discharge
(pulse # 182).
Figure 4. Video record of the surface discharge going th r ou g h
the droplets of electrolyte solution (pulse # 182).
circular motion of the cathode spot of unbranched col-
umn over liquid surface, similar to the picture, observed
in [7]. Such the motion can be resolved in time only us-
ing high-speed camera (for instance, in [7] the camera
featuring 1 kHz frame frequency rate was used).
The behavior of electrolyte attracts attention as well. It
is easy to understand, that under the effect of the applied
voltage some equilibrium quantity of H+ ions drifts to the
cathode, whereas OH ions move to the plasma-liquid
interface. Such an electric separation of ions urges the
chemical equilibrium of the solution to shift, thus result-
ing in reaction (3) to take place near the plasma-liquid
interface and reaction (2) to take place near the cathode,
accompanied with intensive carbon dioxide release. This
becomes evident starting, approximately, with shot 37. It
can be seen, that during the entire discharge event the
bubbles of carbon dioxide are intensively generated near
the cathode and go up under the effect of Archimedian
force. Behind the front of the uplifting bubbles a specific
medium is formed. It is foam, represented by the hetero-
geneous mixture of electrolytic aqueous solution of Na-
HCO3 and CO2 bubbles.
Under the effect of hydrodynamic instability the rising
front of the bubbles is subject to the growing perturba-
tions (shot 50), one of which takes the form of a mush-
room (shots 51-90). In the course of time the bubbles
become so numerous, that they augment the summarized
volume of electrolytic cathode: it can be seen, that start-
ing from shot 100 the level of the plasma-liquid interface
rises. Having inspected the shots of rows 2 and 3 in fig-
ure 2 as a whole, one can see, that the front of bubbles,
and, consequently, the level of plasma-liquid interface,
rises almost uniformly at first, accelerating further on
significantly. The instantaneous CO2 release during
chemical reactions in electrolyte can be judged by the
level, the interface rises to (basically over channel (2)).
Gradually the level of the foam (in practice, the upper
surface of the mushroom) overtakes the plasma-liquid
interface (shot 115). From this moment on we have the
brand new form of glow discharge: stationary dc moder-
ate pressure discharge with foamy electrolytic cathode, in
which CO2 bubbles are densely packed. The glow dis-
charge with foamy electrolytic cathode of this type had
never been observed earlier.
It has to be mentioned occasionally, that another type
of discharge with foamy cathode—the arc discharge at
atmospheric pressure—was described recently in paper
[15]. There they used pouring beer with a foamy cap as a
cathode (remember, that the beer foam in its essence is
the carbonic acid). In this particular paper it is reported
that carbon multi-walled nanotubes, nanocapsules and
lamellar nanoparticles, reminding of cabbage head are
formed in the arc, which can be of interest for studies
related to nanoelectronics. Above all, intensive CO2
bubbles release was observed as well in the barrier dis-
charge, generated in soda solution [16,17].
Why the discharges involving foamy electrodes are
interesting? Specialists used to think, that dc discharges
are supported by the area of cathode surface, named
cathode spot. From this point of view the cathode spot is
a two-dimensional object. Dramatically different situa-
tion is with the discharge involving foamy cathode: the
cathode spot here is a three-dimensional object, having
the finite volume (Figure 5). It is important, that just this
type of the cathode spot—the three-dimensional one—is
often observed in natural discharges: lightening coming
from rainy clouds, dust clouds, releases from volcanoes,
releases of soil associated with explosive works, etc.
However, the volumetric cathode spots had never been
studied; Moreover, they had never been referred to any-
where. It may also be added, that the discharges in such a

D. V. VYALYKH ET AL.
240
Figure 5. Video record of volumetric discharge with a volu-
metric cathode spot (pulse # 187).
micro-structured media as foam are close as to their pa-
rameters to the parameters of the discharges met in porous
bodies and powders. The discharges of this type are be-
ing intensively studied today [18-22].
Let us continue describing the dynamic discharge ac-
cording to Figure 2. It can be seen, that the height of the
foamy cathode grows, however the 5-th row in Figure 2
points, that rising of the foam at the stage of burning
proceeds with noticeable deceleration. The discharge at
this point goes through the stage of hindered burning,
after which it attenuates (shot 148). Thus, the new form
of glow discharge, although living temporarily (~ 1.5 s),
can be considered as stationary at such a long duration.
Evolution of the discharge is finished with gas-dy-
namic expansion of electrolytic foam till the moment it
fills the discharge chamber as a whole. At the same time
the level of the foam moves with acceleration, on the
contrary, after attenuation of the discharge.
The above dynamic picture turns to be typical for glow
discharge with electrolytic cathode in the form of aque-
ous solution of sodium bicarbonate. The present dynam-
ics was repeated approximately in 250 discharge events
at 30-50 Torr pressure and 5% and 10% soda concentra-
tion in the solution.
After processing the video record from Figure 2 the
time-spatial picture of the discharge was drawn in the
form of characteristic region boundaries, as well as in the
form of synchronized curves of the discharge voltage and
current (Figure 6).
(a)
(b)
Figure 6. Synchronized dynamic and electro-technical
characteristics of the discharge (according to the data of
video processing from Figure 2): (a) time-spatial dynamics
of glow discharge (1-surface discharge region, 2-volumetric
discharge region, 3-liquid electrolyte solution, 4-foam, 5-
foamy mushroom); (b) oscillograms of the discharge voltage
and current (1-voltage, 2-current).
Let us scrutinize these curves in more detail. Upper-
most it has to be explained, that the stepped form of the
curves is due to the frequency mode of indication (~ 2
Hz) and inertia of current meter and voltmeter. As a re-
sult the most reliable are the records, corresponding to
the shots at the beginning of each step. As for the voltage
curve, several sections, related to different discharge
phases can be distinguished: high-voltage phase, lasting
for 1.5 s and corresponding to surface discharge; follow-
up voltage drop, corresponding to transition of the dis-
charge into volumetric form; renovated growth of volt-
age, starting approximately at the 3 second and testifying
to the growing resistance at the discharge tube. Appar-
ently, the last growth is stipulated by foaming of electro-
lyte and geometrical drop of its conductivity. After the

D. V. VYALYKH ET AL.
241
foam reaches the surface of the liquid the discharge
voltage drops again. As a whole, the current curve shows
the noticeable growth of the discharge current at the
phases of voltage drop.
Another peculiarity of the above discharge was re-
vealed by video recording featuring lower exposure time
in each shot (in practice it means the lower light flux,
going through the camera lens). Bright spots of two types
were discovered in the discharge plasma: the immovable
ones and the ones, flying towards the anode. The im-
movable bright spots could be located both inside and
outside the discharge region at the video record (Figure
7). They were identified as plasma in the vicinity of
evaporating droplets of electrolyte inside the inner sur-
face of the discharge tube. The movable spots were iden-
tified also as the evaporating liquid droplets, flying to-
wards the anode. Using two adjacent shots (Figure 8)
one can estimate their speed, which was recorded in the
range of 0.1-2 m/s depending on the discharge event,
which points to cumulative character of their nucleation.
4.2. Peculiarities of the Dynamics of
Two-Layered Liquid Cathode
The afore described method, developed and tested to
generate the average pressure glow discharge using the
cathode in the form of electrolyte solution was further
used to study hydrodynamic processes in a two-layered
cathode.
Presented below are the results of the experiment,
where the cathode was prepared as a 5% solution of so-
dium bicarbonate, on the surface of which a layer of di-
electric oil BM-6 of 10 mm thickness was poured. As is
well known, the oil itself is a good insulator, and the
layer serves as a peculiar liquid barrier.
The goal of the experiment was to demonstrate, how
the electric discharge mode can be used to manipulate
hydrodynamics of the oil layer, in particular, to cripple
its surface. Crippling could have been caused both by
uplifting CO2 bubbles and by breakdown in the discharge
channel. The process can be useful as applied in optional
environmental technologies (remember the ecologic
damage incident in Mexican gulf).
However, in case of sodium bicarbonate solution, the
unexpected effect was revealed: oil jets were released
and dispersed inside the solution for about 100 mm depth.
In Figure 9 the fragments of video record of the above
effect are shown, taken in the mode, when the discharge
was activated for some short time (a few seconds) only
to initiate the intensive generation of CO2 bubbles. In
this mode the bubble front went to the surface, forming
the extensive foam at the absence of the discharge.
Obviously, the foamy layer possesses the significantly
lower mass density, than the continuous electrolyte and
can be considerably lighter than oil. As a result, the
heavier liquid goes up and the conditions for the
Rayleigh-Taylor instability development are formed,
Figure 7. Two adjacent shots from pulse # 247; arrows
show immovable spot.
Figure 8. Two adjacent shots from pulse # 249; arrows
show movable spot.

D. V. VYALYKH ET AL.
242
Figure 9. Detached shots from video record of pulse # 289 with oil layer at 40 Torr: A–initial picture; B–discharge stage;
C–lifting of bubbles; D–phase of the Rayleigh-Taylor instability (25 Hz); E–oil jet is spitted into droplets.
which urges the oil jet to go down and be split into drop-
lets.
After the long (over 10 min) relaxation gas release
process is stopped, the oil goes up and uniformity of the
layer is recovered.
It is interesting, that the similar process can be ob-
served in the nature, for instance when the intensive gas
release may occur near the ocean bed due to volcanic
activity or another reasons. A vessel or a swimmer, find-
ing itself in such a foam, may lose buoyancy and sink.
The analogous reason for mysterious disappearance of
ships is described in [23-25].
The popular on-line encyclopedia “Wikipedia” pre-
sents this process as follows*: “It has been hypothesized
that periodic methane eruptions (sometimes called “mud
volcanoes”) may produce regions of frothy water that are
no longer capable of providing adequate buoyancy for
ships. If this were the case, such an area forming around
a ship could cause it to sink very rapidly and without
warning.” Now, what we may add to these words is that
if another buoyant liquid enters the foamy region, it does
not sink, moreover, it is split into jets and droplets as a
result of the Rayleigh-Taylor instability.
5. Conclusions
The paper presents the results of experimental studies of
the dc glow discharge of moderate pressure based on
electrolytic cathode, prepared in the form of aqueous
solution of sodium bicarbonate NaHCO3. The example
of video record of the discharge is also presented. Dif-
ferent phases of the discharge were discovered, one of
which is the discharge generated by the foamy cathode,
was recorded for the first time. Time-spatial diagram of
the discharge was developed and its electro-technical
characteristics were measured. Small glowing spots in
the discharge plasma were discovered, which may be
explained by ionization around the evaporating droplets
of electrolyte.
Study of the two-layered electrolytic cathodes was
performed and development of the Rayleigh-Taylor in-
stability in the volume of electrolytic cathode was re-
corded, when the lighter liquid—foamed electrolyte
—finds itself under the heavier layer made up of oil.
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