Jeff Liebermann wrote in message . ..
On Sun, 21 Mar 2004 08:47:34 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in mppp50ho4dr08ahkb3dlbqkcfkp0ih
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.

I didn't know that it wasn't linear. I just assumed that it takes the
same amount of energy to peel electrons off of a single atom (ionize)
regardless of gap seperation. A wider gap requires more voltage to
ionize more atoms to create a longer conduction path, but the energy
per atom is the same. I also couldn't find (Google) any useful
references that showed this non-linearity. Unless the heat generated
by the ionization contributes to assisting furthur ionization, my
seat-o-de-pants physics says it should be linear (for DC).

You need to read up on the physics involved. The critical point is
that a free electron in the gas has to have a long enough mean free
path to pick up enough energy by falling down the electric field to be
able to ionise a molecule when it does hit one, generating one more
electron in an inelastic collision.

If it hits a molecule before it acquires enough energy, in an elastic
collision, it will end up travelling in a different direction with the
same energy, but with a good chance of losing the energy that it had
accumulated. Think "drunkards walk".

The minimum in the Paschen curve corresponds to the point where the
mean free path is longer than the gap.

There's also the minor detail of RF excitation versus DC. As I
vaguely remember from my 35 years ago college welding classes, TIG
welding uses RF to strike the arc because it takes less
power/energy/whatever to start the arc. We're allegedly talking about
striking an arc across 0.001" with a 5 watt, 27MHz transmitter
terminated with a 50 ohm load. If it's non-linear in the opposite
direction, the calcs are gonna be no fun.

RF excitation works better than DC becasue it doesn't sweep the
electrons out of the gap as they are created (by cosmic rays or local
radioactivity) in the way that a DC field does. Like I said earlier,
the physics was worked out about a hundred years ago, and the
calculations shouldn't be too difficult now that we can use computers
for the tedious bits.

I have everything it takes to test this. Microscope slide, with two
sewing pins glued with hotmelt goo and seperated by 0.001". Apply RF
and watch through the microscope. I'll see if I can throw something
together and post photos (time permitting).

Everything except a sound undertanding of the theory. I've got a copy
of a reprint of volume 2 of "Conduction of Electricity Through Gases"
- Ionisation byCollision and the Gaseous Discharge - by J.J. Thompson
and G.P. Thompson.
My copy was published by Dover Press in 1969, and reprints the 1933
third edition. The first - singe volume - edition was published in
1903. I bought it when I was fiddling around building a starter for a
xenon arc lamp, back in 1972. It proved quite useful.

-------
Bill Sloman, Nijmegen

On Sun, 21 Mar 2004 23:00:47 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in c1tr509eqipks7lt08ttt5cvnpkumu
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
I didn't know that it wasn't linear.

Google for Paschen's Law. For high voltages it is linear enough for
calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)

Yep. That's it. Thanks. Haven't seen that since kollege. Also saw
your comments on the topic in other usenet news articles. So much for
my simplified view of ionization.

Online spark gap calculator:
http://www.cirris.com/testing/voltage/arc.html

Minimum breakdown voltage in air at STP is about 350VDC. For RF, that
would be:
350 * 0.707 = 192 Vrms
Into a 50 ohm antenna at the coax connector,
P = E^2 / R = 192 * 192 / 50 = 737 watts
for any size spark gap. I don't know of any kilowatt cell phones
around, but that's the power output needed to arc at the antenna
connector. It might be somewhat lower due to the effects of RF vs DC.
Also a suitably weird antenna could be fabricated to dramatically
increase the voltage at some point. However, those coils are usually
up in the air where they cannot get close to a ground suitable for
forming a spark gap.


--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
(831)421-6491 pgr (831)336-2558 home
http://www.LearnByDestroying.com AE6KS

Jeff Liebermann says...

John Woodgate wrote:

Google for Paschen's Law. For high voltages it is linear enough for
calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)

Yep. That's it. Thanks. Haven't seen that since kollege. Also saw
your comments on the topic in other usenet news articles. So much for
my simplified view of ionization.

I am removing Mr. Woodgate from my killfile. I was under the
impression that he only wanted to post about politics in the wrong
newsgroup, but obviously I was wrong. My apologies to Mr. Woodgate.


--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/

"Nico Coesel" wrote in message
...

I'm pretty sure that it won't work that simple. There are other
factors at play that make controlling things with a telephone a lot
harder to achieve than you think... For everyone's safety I'm not
going into the details.

You could, only there are no details.

Using a ringer's voltage levels is indeed easy, there is really nothing to
hide because every EE student can figure out the details for himself. Let's
use an example. Since I'm not a terrorist, I assume that the circuit is used
to light a lamp as an aid for a hearing-impaired person who could than turn
on his hearing aid in case it was off, and do not encourage anyone to put
anything else in place of that lamp. To make it even less usable for certain
people, the following example relies on the ringer NOT being removed from
the circuit so it would ring (this way an additional time delay cannot be
used). The amplifying of the ringer signal can be done with only one
transistor, the voltage offsets be provided with a normal and a shottky
diode. Let's also assume that the ringer is a dynamic and not a
piezoelectric one, since with a piezo the circuit would differ slightly. A
reed relay could do the switching. Using an NPN, the circuit would look like
this: Negative ground, connected with ringer's "-", to battery "-" and
through a forward-biased shottky to the emitter. The transistor's base
connected through a 2K2 resistor to battery "+". Base also connected to
diode "+", while diode "-" is connected to ringer "+". Collector through
relay coil to battery "+", a capacitor across the relay coil. That's it. The
relay contacts can be used to switch on a lamp, connected to the same
battery and placed so that the hearing-impaired person can easily see it.
Note to hearing-impaired preople: this circuit may not always work, it
depends on the type of ringer and on the volume setting. I did not test it
with any ringers either, but I think many old-style ones should do.

(Don Klipstein) wrote in message ...
In , Bill Sloman wrote
in part:

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

If this produces anything near 10x the energy per weight of TNT or PETN,
then a version with controlled reaction rate would make one heck of a
rocket propellant.

I thought the ultimate energy per mass was magnesium and oxygen (or was
it beryllium and oxygen?), just a few times as much energy per mass as TNT
and not good like usual rocket propellants for producing gas to use as
rocket exhaust.

It depends on the electrochemical gradient, I think.
Hydrogen burning in fluorine probably produces more combustion
energy than anything else, per unit mass.


I am surely skeptical of changing one isomer of a molecule to another
producing even comparable energy to, let alone more energy than
decomposition of a similar or somewhat greater mass molecule of high
explosive.

I share this skepticism. Burning TNT probably would produce 10x more
free energy than detonating it.



John

John Michael Williams

Jeff Liebermann wrote in message . ..
On Sun, 21 Mar 2004 23:00:47 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in c1tr509eqipks7lt08ttt5cvnpkumu
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
I didn't know that it wasn't linear.

Google for Paschen's Law. For high voltages it is linear enough for
calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)

Yep. That's it. Thanks. Haven't seen that since kollege. Also saw
your comments on the topic in other usenet news articles. So much for
my simplified view of ionization.

Online spark gap calculator:
http://www.cirris.com/testing/voltage/arc.html

Minimum breakdown voltage in air at STP is about 350VDC. For RF, that
would be:
350 * 0.707 = 192 Vrms
Into a 50 ohm antenna at the coax connector,
P = E^2 / R = 192 * 192 / 50 = 737 watts
for any size spark gap. I don't know of any kilowatt cell phones

Then again, some users seem to be able to put in kilohours of talk.
Does that count? (just kidding).

Seriously, into air at the antenna,

P = E^2/377 ~= 97 W.

A very sharp tip would create an additional gradient,
which suggests trying to spark with a sharpened antenna against
something metallic at AC ground.


around, but that's the power output needed to arc at the antenna
connector. It might be somewhat lower due to the effects of RF vs DC.
Also a suitably weird antenna could be fabricated to dramatically
increase the voltage at some point. However, those coils are usually
up in the air where they cannot get close to a ground suitable for
forming a spark gap.

John

John Michael Williams

(John Michael Williams) wrote in message . com...
(Don Klipstein) wrote in message ...
In , Bill Sloman wrote
in part:

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

If this produces anything near 10x the energy per weight of TNT or PETN,
then a version with controlled reaction rate would make one heck of a
rocket propellant.

Not really. The crucial feature of chemical explosives is that they
produce their energy fast, which is to say by intra-molecular
rearrangement. Burning a hydrocarbon in oxygen produces a lot more
energy per unit mass of fuel and oxidiser than does letting off TNT or
PETN where the oxygen comes from the nitro groups attached to the
hydrocarbon core, whence the popularity of fuel-air bombs, but you
don't get the same brissance.

I thought the ultimate energy per mass was magnesium and oxygen (or was
it beryllium and oxygen?), just a few times as much energy per mass as TNT
and not good like usual rocket propellants for producing gas to use as
rocket exhaust.

It depends on the electrochemical gradient, I think.
Hydrogen burning in fluorine probably produces more combustion
energy than anything else, per unit mass.

Atomic hydrogen recombining into molecular hydrogen would be better
(as a rocket fuel) but has never been reduced to practice. What I
remember from what I read on the subject - many years ago - was that
hydrogen-fluorine was the best possible fuel-oxidiser combination.
Nasty exhaust fumes ...

I am surely skeptical of changing one isomer of a molecule to another
producing even comparable energy to, let alone more energy than
decomposition of a similar or somewhat greater mass molecule of high
explosive.

Check out the published literature - that is all that I was doing at
the time.
Chemical explosives are relatively wimpy as far as energy per unit
mass goes - the rate of energy release is the crucial feature.

I share this skepticism. Burning TNT probably would produce 10x more
free energy than detonating it.

Trinitrotoluene is C7H5N3O6 and would burn to 7 CO2 molecules, 2.5 H2O
molecules and 1.5 N2 molecules - for which you'd need 10.5 extra
oxygen atoms, over and above the six oxygen atoms available in the
original TNT molecule.

Being simple-minded about it, 16.5/6 is 2.75, not ten, and that
exaggerates the advantage, because burning carbon to carbon monoxide
release quite a lot more energy than burning carbon monoxide to carbon
dioxide, which is where you use up seven of your extra 10.5 oxygen
atoms.

The exact amounts of energy involved are all available in the open
literature - that is where I found them, some thirty years ago, and
I'm sure that they are still available now.

-------
Bill Sloman, Nijmegen

In article , John
Michael Williams wrote:
(Don Klipstein) wrote in message ...
In , Bill Sloman wrote
in part:

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

If this produces anything near 10x the energy per weight of TNT or PETN,
then a version with controlled reaction rate would make one heck of a
rocket propellant.

I thought the ultimate energy per mass was magnesium and oxygen (or was
it beryllium and oxygen?), just a few times as much energy per mass as TNT
and not good like usual rocket propellants for producing gas to use as
rocket exhaust.

It depends on the electrochemical gradient, I think.
Hydrogen burning in fluorine probably produces more combustion
energy than anything else, per unit mass.

That one is up there, but let's check heat of formation...

HF gas: 63.991 KCal/mole, 3.19955 KCal/gram

MgO: 145.76 KCal/mole, 3.644 KCal/gram, but with no gaseous output.

I am surely skeptical of changing one isomer of a molecule to another
producing even comparable energy to, let alone more energy than
decomposition of a similar or somewhat greater mass molecule of high
explosive.

I share this skepticism. Burning TNT probably would produce 10x more
free energy than detonating it.

The usual high explosives contain nitrate or nitro-group molecule
portions, or other oxidizers.

TNT does not have enough oxygen in its nitro groups for complete
combustion, so you get some more energy burning it than detonating it.
On the other hand, nitroglycerin and RDX have enough oxygen in their
nitrate groups for complete combustion.

- Don Klipstein )

John Michael Williams wrote:
I share this skepticism. Burning TNT probably would produce 10x more
free energy than detonating it.

When you detonate it, what happens to the 90% lost energy?
Fails to actually detonate?
--
73, Cecil http://www.qsl.net/w5dxp



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In article ,
DarkMatter TheBartenderBuyMeADrink wrote:

First, tell me how one "burns TNT". It is a high explosive. I
think its "burn rate" would be pretty fast, and not manageable.

High explosives certainly can burn - burning and detonation are
physically different processes.

I remember reading stories of demolition-team soldiers in Vietnam,
heating their rations by taking a small pellet of C-4 plastic
explosive (RDX) and igniting it. It makes a hot flame, quite
sufficient to toast up the C-rations, and does not explode. [Not a
terribly good substitute for a real camp stove, though, as C-4
produces toxic fumes when burned.]

Burning is, in fact, the standard way for the military to dispose of
C-4 from unwanted munitions.

It appears that burning is also a viable method of destroying TNT.
http://www.humanitarian-demining.org...tral/remic.asp
describes a method for destroying land mines "in situ" via burning.
It's a neat trick - a small shaped charge of explosive creates a
high-velocity gas jet which breaks open the (TNT-loaded) land mine,
and also delivers a charge of a pyrogenic chemical which ignites and
burns the TNT without detonating it.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!