On Jan 17, 2006, at 9:01 PM, Michael Foster wrote:
I haven't messed with this for a while, so I just stuck
a couple of aluminum strips cut from a pie plate into
a drinking glass full of saturated borax solution.
What was the source of the borax?
The
aluminum strips were hooked in series with a 65 watt
light bulb plugged into 120 volts AC.
The light bulb turned on at full brightness, but dimmed
to no light at all within two minutes. The aluminum strips
gave off their characteristic blue glow, which at this
voltage requires almost total darkness to see. Tiny sparks
are seen at random on the surface of the aluminum strips,
especially where they enter the borax solution and at
their edges.
This is the electrospark regime. It actually suppresses the anode
glow regime by draining current. It also eats up anodes very fast,
at least foil ones. You want to avoid the sparks by reducing voltage
until the anode is conditioned to take that voltage without
penetration of the anode film.
If you move your eyes back and forth rapidly, you can see
that typical 60Hz flicker, meaning that that the glow
doesn't continue between cycles.
The glow is turned off when an electrode is acting as a cathode. It
turns on when the voltage passes a critical positive threshold. I
think at that threshold electrons can tunnel through or at least into
the anode film, and the gradient is sufficient to ionize water. The
electrons are stripped from the OH-, thus creating an ion free zone,
the interphase. The cations are repelled from the interphase. Once
that happens ionization of neutral molecules is required to conduct
major current. Here are the prospects.
Molecule Energy (eV)
-------- ---------
H 13.6
H2 15.4
OH 13.0
H2O 12.6
HO2 11.4
H2O2 10.5
Table 1 - Molecular Ionization Potentials in Gas
I think a field gradient of about 12.6 - 13 volts per 1-2 angstroms
will do the job. A couple hundred volts across the anode interphase
is plenty to get a 10 to 20 molecule thick interphase where protons
freed at the anode surface can zip through the interphase creating an
ion-liquid mix.
It would be interesting
to find out just how fast the glow turns on.
Yes, good to quantify it, though I think if you measure it you will
find out the rise time is a function of cell electrodynamics, not the
start-up time for the glow. The cell has a lot of capacitance, so
things are slowed down by that. The glow turns on very fast once
the critical voltage is passed in the AC cycle. The critical voltage
depends on the conditioning of the electrode and what is in the
electrolyte. As documented earlier, I think the critical voltage is
that voltage at which water or OH at the face of the anode, probably
at the tip of a dendrite, can be ionized. This is spelled out in:
http://www.mtaonline.net/~hheffner/GlowExper.pdf
I had formed the idea, after seeing the hollow columnar
structure Bill provided a link to,
What's this all about? Bill Beaty? What columnar structure?
that a plasma must be
forming within the aluminum oxide cells. This doesn't seem
to be the case.
It depends on just what you call a plasma. I think there is a lot of
ionized stuff in the 10-20 nm or thicker interphase next to the
anode. It doesn't last long though once the proton passes!
I looked at one of the strips with a
diffraction grating and was surprised to see a continuous
spectrum, not line spectra indicating ionization.
This could be indicitive of partial orbitals similar to those formed
in metal hydrides under high fugacity. It is a possible indication
of atomic expansion at work. Then again we all see what we would
like to see, and I have too active an imagination. 8^) More
realistically, it is probably because you are in electrospark mode
and thus may be seeing mostly spectra of the sparks, or arcs which
would be characteristic of dark body radiation for their
temperatures, and/or aluminum oxidation. Probably a lot of the
latter if you are getting white.
Further,
the glow really isn't blue, it's white.
Wow, you *are* running hot. You must be seeing aluminum oxidation.
The reason it has been called "blue glow" is that I called it that in
1997 when I observed what I considered to be a turquoise version of
it. I got tired of typing blue-green so unfortunately just dropped
the green part. On the bright side, "Project Blue Glow" sounds a lot
respectable and original than "Project Green Glow", don't you think?
It's just that it's
so dim that we tend to see it as blue or blue-green.
Photos show it as blue-green, green or green-yellow too. I think it
takes on an orange tint if the electrode has lots of very tiny arcs
on its surface due to poor conditioning. I turned a nice green anode
into an orange on just by pushing the current up briefly, and thus
destroying the conditioning. See:
http://www.mtaonline.net/~hheffner/OrangeGlow.pdf
A full
continuous spectrum from red to violet is visible, although
it doesn't seem to be as bright on the red end.
That must be a high temperature to peak up on the blue end. Do you
know your surface area and current?
I was particularly surprised not to see some evidence of the
sodium double D lines, which usually overwhelm the spectra
of other elements, since borax is sodium tetraborate.
Sodium is a cation. It should be pushed right on out of the interphase.
The
sodium line was only occasionally visible in some, but not
all of the random sparks.
Sparks are different from the interphase. Their plasma can be
expected to penetrate the interphase as well as the anode film.
I also occasionally saw what I
took to be a hydrogen red line in the sparks.
I'm fresh out of fluorescent dyes, so I just opened up a
yellow fluorescent Hi-liter pen and soaked it in the borax
solution. This worked well in showing that there is apparently
some UV being emitted. I have a UV spectromenter good to
190nm, but it's made for very high power and no reading could
be had at all.
Water may be absorbing most of the UV lines.
Since the voltage gradient across the aluminum oxide semi-
conductor layer must be tremendous, I'm wondering if this
isn't just high temperature incandescence.
You probably have incandescence in the sparks or arks at the anode
surface. It would be good to take a look at the spectrum for a well
conditioned glow though. Another thing to consider is electron-hole
annihilation. If the oxide or hydroxide film is a hole conductor,
then electrons stipped from the electrolyte will produce photons upon
annihilation. I don't think that is happening, but it is something
to consider.
The total heat
would be low, but the local temperature might be very high.
I plan to do these same tests at higher voltage and with DC.
Any thoughts on this, Horace?
Yes. Condition the electrode. You need a variac or light dimmer to
do that. It is done by increasing voltage slowly. I can post the
basic method if you need it.
Horace Heffner
