On Aug 1, 2007, at 12:58 PM, Michel Jullian wrote:
I do not share your worries about ground potential jumping to
hundreds of kV, but it's always a good idea to run an electrical
experiment in a Faraday cage so whatever your reasons they are fine
by me.
It was just an example. However, it happens here sometimes that the
northern lights descend to ground or close to it. I think the
ionosphere is typically .2 to .5 MeV different. Cumulus clouds
sometimes induce a pretty strong ground charge too.
Now what remains to be found is the dielectric material whose
product of dielectric constant by dielectric strength is the
highest of all dielectric materials, agreed?
Yes, that maximizes charge density per power supply volt, so assuming
conductivity or other things are not a problem.
Optical properties, conductivity, hydrogen permeability,
availability, and price might be important too.
Barium titanate comes in a wide range of composites, with a
dielectric constant up to 18,000, but 6000 or less is a more
realistic maximum for a hot CF cell, and a dielectric strength of
about 2 MV/m, less than air. I don't know about cost or
availability. BaTi3 has high optical reflectivity. See:
http://www.avxcorp.com/docs/techinfo/mlcmat.pdf
"Class 2 high dielectric-constant materials are
relatively homogeneous barium titanate formulations that
have grains grown to more than 3 μm. Their high K stems
from the addition of substituents with the same valences.
These shift the Curie point to the room temperature
region. Sr(2 +) or Zr(4 +) are often used, making peak
dielectric constants as high as 18,000 available. Such
materials can lose up to 50 percent of their dielectric
constant at 50°C, but find general applications in
computers and other commercial low-power electronic
equipment requiring a limited temperature range.
For “Z5U” requirements (capacitance loss of less than
56 percent at 80°C) calcium is most often added in the
form of calcium zirconate. The resultant dispersion
in the dielectric characteristics widens the K versus
temperature curve, and controls the maximum
capacitance loss at 85°C. Room temperature dielectric
constants of more than 8000 are then seen. These
materials also contain inhomogenuities in the form of
unreacted, relatively pure, grain cores."
It is interesting BaTiO3 looks a lot like co-deposited D/Pd cathode
material under a SEM. It might be a very good approach to forget the
laser and try to sinter a very good Pd, Ag, or Ti or some CF active
metal bond with BaTiO3, and then build the cathode material from
there by codeposition. Some forms of BaTiO3 are a silver composite.
I wonder just how permeable BaTiO3 is to hydrogen. There are so many
kinds, made from varied grain sizes, and different composites.
Horace Heffner
http://www.mtaonline.net/~hheffner/
