[NewCandle] Anodizable metals and essential conditions for glow discharge?

[Nick Reiter]

Things that make me go hm.

Over lunch today, I took a soda pop can (still filled,
so it could be chilled) and I polished the heck out of
the bottom bowl with some Al2O3 felt then some Mothers
polish and buffing.  Got it close to a mirror /
specular image brightness.  I then set it up with
oxalic and carbon rod configuration, and nudged it to
a decent visibly bright blue-white light.  Left it
there for about 10 minutes, then shut it down, guzzled
the soda, and then snipped a piece out of the bottom.

I think both the chilling and polishing made for a
brighter, more distinctively blue-white-greenish light
- the traditional AGD.  Without polishing or chilling,
it edges toward the yellow "flashlight" hot mode.

Now the thing is, when I looked at this with the SEM,
the oxide coating indeed looks more uniform, but even
as high as I could go in mag and still see anything at
all, let alone get pictures, I could see no pores. 
Either it is pore-less, or the pores are far beyond
anything visible, meaning they are less than a couple
hundred angstroms across.

So as Horace has suggested, maybe the blue-white-green
glow is from tunneling, whereas the yellows and
reddish hues are from an operating mode where
breakdown nano-arcs exceed the tunneling mode
carriers.  Seeing such a featureless oxide coating
that had indeed made a nice blue-white milky glow
makes me ponder.

Now I did also see a little partial side view of a
coating flake where I had punched a scribe line, and
this gives a hint that the oxide coating in this case
is about 1000 angstroms thick, no more than 2000.

I hope your tinfoil helmets are not shielding the
thought I am sending now herewith...

...

Could one take say a sputtered conformal coating of
Al2O3, or SiO2, or ZnO, make it 1000A thick on an
aluminum or other metal substrate, and get an AGD from
it?  Does the oxide coating have to be constantly
re-generating, or native, or just there as dielectric
layer for tunneling?

It may be a couple of weeks until I can try this out,
but I do have the ability to sputter some SiO2 as a
dielectric barrier.

But more to come in the meantime...

n

> > Hey Nick + Horace,
> >
> > You got me to wondering about other metals. A
> quick survey of
> > capacitor manufacturers yielded this list of
> candidates.
> >
> > aluminum, niobium, tantalum, titanium, tungsten,
> zirconium.
> >
> > I know we've tried the first and last, but how
> about the others?
> > Anyone? Is glow unique to aluminum? Of course,
> disruptive discharge
> > due to dielectric failure would be seen on all of
> them, as
> > Nick described with zirconium. If it is unique to
> aluminum,
> > perhaps the reason is that you need the porous
> > structure to see glow. That would be a good
> question to answer
> > with the scope. If you can get glow from Zr, is
> the oxide structure
> > porous?
> >
> > K.
> >
> 
> 
> Some random thoughts.
> 
> I've written in my experiment notes that I haven't
> seen the glow  
> occur at all until passivation occurs, i.e. until a
> clearly  
> rectifying (i.e capacitive when on both anode and
> cathode) component  
> shows up in the i vs V trace, an "eye".  I haven't
> seen the blue- 
> green glow occur at all for metals where a
> significant capacitive  
> layer does not form, like Cu, Pb, or Pt.  If memory
> serves, Ti works  
> well to produce a glow.  I've also noted on various
> occasions that  
> upon examination of (thin) electrodes from the side
> it *appears* the  
> glow is in, or extends into, the electrolyte, and is
> not just on the  
> surface, but even at the time I said that clearly
> could be an  
> illusion.  If I had to make a bet, though I would
> still say the glow  
> from some metals running at high voltage is in the
> electrolyte, and  
> due to ionization of the electrolyte due to the high
> field strength  
> present at a passified (conditioned, or rectifying) 
> surface.  I also  
> think the glow is triggered by electrons tunneling
> through the  
> conditioned surface, but once a tunneling occurs at
> the surface it  
> can trigger a cascade back into the highly polarized
> electrolyte near  
> the surface.  The higher the barrier strength, the
> further from the  
> surface the glow extends. 


The Holy Grail 'neath ancient Roslin waits.
The blade and chalice guarding o'er Her gates. 
Adorned in the masters' loving art, She lies;
She rests at last beneath the starry skies.