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DDTea
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[*] posted on 30-6-2005 at 09:53
Microwave-made Nitric Acid


A few days ago, a friend and I bought a cheapo microwave whose sole purpose would be experimenting/destruction for July 4 (that's the US Independence Day, for you non-Americans ;) ) . So we resolved that we'd meet up in a few days with a list of things we want to throw in the microwave/experiments we want to do.

I originally wanted to make a huge plasmoid that would melt the whole thing, but in every website I encountered about plasmoid construction, it warned to do all experimenting in a well-ventilated area because they generate Ozone and Nitrogen Dioxide.

Take a look at this jar full of NOx after a plasmoid experiment (courtesy of JL Naudin and his great website on plasmoid construction):

http://jnaudin.free.fr/images/oaplasmoid5.jpg

But to him, the NOx was an annoyance...I see it as an opportunity for easy generation of Nitric Acid!

I did a small-scale experiment in my home microwave--a "proof of concept" test (1.4 kW--not too shabby eh?). I took two graphite leads from a mechanical pencil holder and a toothpick, stabbed them all into a disc of aluminum foil, put it in the microwave with an up-turned glass jar over them. The plasmoid generation was successful, and mine were fairly stable!

I ran it for 10 seconds and afterward, there were no yellow/red/brown fumes in the jar, but I did detect their characteristic odor. I won't be running longer tests at home, in my kitchen, but I might be able to generate more NO2 with our cheapo test-microwave.

Attached is a diagram of the HNO3 setup I have imagined.

In the first jar, NOx fumes are generated with the plasmoid. In the second jar, water is heated and boiled, allowing some vapor to escape to the outside...When it condenses, I'm hoping it will form a vacuum which will pull the NOx fumes into the water to be absorbed.

One big problem I can see with it, however, iis that the water might hog the microwaves for its own heating--however, I was still able to generate a plasmoid in my own microwave even with a glass of water inside it too.

It's probably not a very efficient route, but theoretically it would be piss easy. In some ways it can be compared to the Birkeland-Eyde Reactor in that they both use plasmafied air to generate NOx. Once I get to run a microwave for say, 5 minutes with a plasmoid generator, I will get a better feel of how much NOx can be generated. Furthermore, some tweaking of the generator itself may be necessary--maybe the plasma I'm creating is not hot enough.

MicrowaveHNO3.GIF - 15kB




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Saerynide
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[*] posted on 30-6-2005 at 11:08


Sounds wonderful if it works as intended :D



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[*] posted on 30-6-2005 at 11:53
Microwave chemistry


This is wonderful Samosa !

It would be nice if we could devote a whole new thread to Microwave chemistry. Not only the drying of hygroscopic salts (NH4NO3: have not tried this one myself), but the field in which it can be applied seems to be ever growing.

Books on Microwave chemistry:
http://www.milestonesrl.com/analytical/resources/media.html

J.L. Naudin website on plasmoid construction:
http://jnaudin.free.fr/

[Edited on 30-6-2005 by Lambda]
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[*] posted on 30-6-2005 at 15:11


Using the components from the microwave (ie supply and magnetron) a microwave plasma torch can be constructed. Essentially the microwave energy is fed into a shorted tapered waveguide, and a stable plasma arc forms in the narrow taper, at 1/4 wavelength from the short circuit on the end of the waveguide. 3000 C is supposed to be acheivable.

I used to have some nice links, but I've lost them :(
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[*] posted on 30-6-2005 at 15:23


I want to make a suggestion to your nitric acid generator system. Lead the tube out of the microwave to a water absorber located outside the microwave. This will prevent any issues with boiling water, etc. I would think you would want the water to be cold to increase gas absorbtion capacity. This means you would have to permanently alter the microwave but that's what it's for anyway, right? ;)



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[*] posted on 30-6-2005 at 16:35


For continuous generation, an air pump (outside the microwave) would be useful.

Be careful with microwaves; I hear they’re not good for you. If they leak out, they affect various body parts adversely (notably the eyes).

Twospoons: that idea sounds pretty dangerous.
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[*] posted on 30-6-2005 at 18:53


AFAIK, microwaves aren't inherently dangerous, but they do heat things nicely, and notably the eyes don't sense heat well so you can quite easily cook them right in your head!

As large as a 1/4" hole should be okay in the chamber, if you really want to do it well you should put some aluminum screen inside the tubing, um, use aluminum tubing, too. Aluminum is resistant to nitrous gasses, no?

Ah, I'm getting a premonition of the apparatus... Quartz or pyrex reaction vessel (with graphite rods installed for arc-starting), spherical more or less. One tube enters nearly tangentially from the bottom, so that air passed through it moves into the plasmoid. Another tube, mounted similarly, is attached to a PE or PP hose which leads to an aluminum tube which passes out of the chamber, into the collection vessel. This just bubbles into water, or perhaps a basic solution to improve collection (distilling off the HNO3 with sulfuric acid). The collection vessel has a vacuum pump on it, or else the reaction vessel has an air pump connected to it. The latter would require a second connection through the microwave oven.

This thing's probably going to run for a looong time, so it would be wise to improve cooling on the magnetron and power transformer.

Tim




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[*] posted on 30-6-2005 at 19:30
Possible Success?


I did a series of 10 second tests at home throughout the day and I'll summarize my results here.

-It's very fun to watch!

-Pointy, thin pieces of conductive metal vaporize quite nicely and give a nice plasma cloud and flash of light. I'm reminded of the electric field theory concerning pointed edges...but my understanding of physics is poor, so if someone will explain this for me better it would be appreciated :)

-A single graphite lead will generate a plasmoid quite effectively; the toothpick is not necessary. In fact, it may lead to a purer mixture of gases without the toothpick.

-Be careful with the glass jars--the heating, particularly when the aluminum foil vaporizes, may crack them.

-After a series of 5 tests (total of 50 seconds), with some breaks in between to allow the magnetron to cool, upon removing the jar a colorless gas can be seen coming out of it. It did not smell like ozone (yes, I did get a whiff of it), there was no water present in the setup so it wasn't water-vapor, so would it be a fair conclusion to say it was Nitrogen Monoxide--which would indicate a partial success with this method (It can be oxidized to NO2, especially if it's a mix of NO and O3 ) ??

-A glass of water significantly decreases the performance of the plasmoid generator. I can't quantify that statement for you, unfortunately, but results were much worse when I had it in the microwave with the setup. Therefore, it will be necessary to be gentle with your magnetron; even so, a few breaks between runs isn't a real draw-back.

-Throughout these tests, I used 3 different "plasmoid generators:"
1. Aluminum foil disk with a pencil lead in it.
2. Aluminum foil disk with a toothpick and pencil leads.
3. Aluminum foil by itself.




"In the end the proud scientist or philosopher who cannot be bothered to make his thought accessible has no choice but to retire to the heights in which dwell the Great Misunderstood and the Great Ignored, there to rail in Olympic superiority at the folly of mankind." - Reginald Kapp.
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[*] posted on 30-6-2005 at 20:45


Quote:
Originally posted by neutrino
Twospoons: that idea sounds pretty dangerous.

Well of course its dangerous! But when has that ever stopped anyone here?

I went googling for the lost links, but all the best papers are "pay to download".

The microwave plasma torch is commonly used for air pollution analysis by spectroscopy.

Samosa: did you actually check the temperature of your magnetron? Its possible the plasmoid was absorbing enough energy to keep the magnetron safe.
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[*] posted on 30-6-2005 at 20:57
Two connector plasmoid reaction vessel


Mabe the plasmoid reaction vessel may just have 2 connections to it. Namely: 1) The mixgas input. 2) The NOx and unreacted mixgas output.

The gasses are lead into a basic solution as 12AX7 sugested (the absorbtion vessel). The the unreacted gasses are then lead back via a T-connection to the input of the plasmoid reaction vessel. The T-connection is connected to the replenishing gas supplies. Gasses are led into this T-connecton to compensate the los of NOx which has been captured by the absorption vessle. One pump is required, and used after the absorbtion vessel. Maybe a long heated tube above the absorbtion vessel can be used, which makes use of rising heated gasses. One valve will be required then or carefull temperature controle of the heated gas rising pipe. The trick however, is to determen how long these reacting gasses must/may stay in the plasmoid vessel.

If two stainless steal gauzes are used, just before the input and output pipes leave the magnetron, then this should block all hazardouse microwave radiation to the outside world. These gauzes may then have the same hole-dimentions as that on the microwave oven door.

Thanks neutrino, I have corrected "grinds" typo"n"-> "grids" into "gauzes".

[Edited on 1-7-2005 by Lambda]
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[*] posted on 1-7-2005 at 03:43


What exactly do you mean by ‘grinds’?
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[*] posted on 1-7-2005 at 04:03


Hm, I think the "N" was a typo ("grids";).

This morning's thoughts: you need something to withstand the heat. Quartz glass would be nice, but expensive. You could make a cordierite, mullite or magnesite pot for the reaction vessel. Hmm, the problem with magnesite is it's basic and could reduce yield, plus it's commonly bonded with carbon, a semiconducting no-no in a microwave. Otherwise, you're stuck with refractory metal oxides such as zirconia and thoria, (if even µwave transparent), at great expense of course, making fused quartz look good!

Tim




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[*] posted on 1-7-2005 at 04:10


But such setup won't be stable like say extended periods of time, no? Usually, people generating the plasma don't switch on the microwave for like more than a few seconds. You yourself, only tested 10 secs for each trial. It is inherently unstable, unless the microwave could be specially modified for this purpose. In most cases, a spherical glass bowl is used to contain the plasma, but i think with extended periods of time, plasma might "burn" through the top of the glass. Perhaps it might be better to confine the plasma in the middle with perhaps say electrostatic or magnets.



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[*] posted on 1-7-2005 at 11:21


A lot of these ideas are getting far too complex for this process... Indeed, they would be great improvements, but what I was going for here was a dirt-cheap route to NOx.

Darkflame is right when he says that these plasmoid setups are only run for a few seconds at a time. So what sounds to me like a suitable alternative to quartz glass and magnetic fields (although this is definitely something I'd like to try when I get suitable magnets) is to simply turn the oven off, wait a minute, then turn it back on--this will even be easier on your magnetron. If the reaction vessel is sealed from the outside, the NOx isn't going anywhere--really :).

This cycling on and off could be repeated until the graphite lead or plasmoid generator has been completely vaporized--and it will take a while! I was surprised by what little amounts of aluminum foil caused such big plasmoids.

At this point, it would be worth reviewing the traditional synthesis of Nitric Acid from Nitric Oxide, courtesy of

http://www.schoolscience.co.uk/content/5/chemistry/catalysis...

We can ignore the first step involving ammonia, and for our purposes replace it with the reaction between Oxygen and Nitrogen, so I'm going to predict the whole process goes as follows (check my work please)

a. N2 + O2 --> 2 NO , dH = -179 kj/mol

b. 2 NO + O2 <--> 2 NO2 , dH = -900 kj/mol
2 NO2 <--> N2O4 , dH = -58 kj/mol

c. 3 N2O4 + 2 H2O <--> 4 HNO3 + 2 NO, dH = -103 kj/mol

and the net reaction...

3 N2 + 6 O2 + 2 H2O <--> 4 HNO3 + 2 NO, dH = -3514 kj/mol

Looking at it this way, the task looks trickier... Having a container of water in the microwave will hinder the ability of plasmoids to form, so now I'm lead to believe that it would be better to have the plasmoid vessel in the microwave by itself. And more than that, cycling it on and off might lead to higher yields of NO2 and N2O4--allowing the vessel to cool would shift the equilibrium in favor of the products, no?




"In the end the proud scientist or philosopher who cannot be bothered to make his thought accessible has no choice but to retire to the heights in which dwell the Great Misunderstood and the Great Ignored, there to rail in Olympic superiority at the folly of mankind." - Reginald Kapp.
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[*] posted on 1-7-2005 at 11:34


Why not lead the water in as steam? There shouldn’t be too much heating sucking energy from the NOx generation. The steam could even react with gaseous NOx to form the acid more efficiently than liquid water due to the intimate contact.
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[*] posted on 1-7-2005 at 12:27


Just throwing my 2cp about safety with microwaves oven. One day I noticed that I had a huge black spot covering most of my visual field in my right eye. I went to a doctor and after taking some pictures of my cornea ,he told me 'it would probably stay like this for life'. Perhaps after a month or 2 it disappeared and now I am ok. I am 99% sure this caused it : I recall having the habit to watch my pizza cooking in the microwaves 1 inch from the grid/glass thinking that it should prevent leakage. Just imagine making holes on the grid or anywhere in the oven to get pipes in/out. If you do, stay far away form it when its on.

[Edited on 1-7-2005 by Archimede]
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[*] posted on 1-7-2005 at 13:13
The cancer/mutation properties of microwaves


You are so right Archimede, the dangers of microwaves are greatly underestimated. It enoys me when those commercial people talk about the temperature rise, and nothing ells. You were most probably victum to this phenomenon. But, even more tricky are the mutations that are caused by microwaves. These are longlasting and unnoticible. I may honestly say, that of the maybe 50 people that I know who have been a radar opperator or had anything to do with high energy microwaves all have cancer. Many of them allso suffer from retinaeral damage, and have had there eye
net membrane transplanted. Burning away your net membrane goes fast when exposed directly, and is unnoticible when the radiation dose is relatively low, what ever low may mean.
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[*] posted on 1-7-2005 at 14:32
Microwave chemisty


Allthough this has nothing to do with nitric acid, I could not resist it but to make this information available to you. Here are a few good articals on microwave chemistry that may be of interest to you.

Microwave organic chemistry review (1.63 mb) 58 pages.
Microwave Irradiation in Drug Synthesis-Curr Med Chem, 2002, 9, 1251-1283 (997 kb) 33 pages.
Microwave in the rationalization of Organic Synthesis-chemistry (698 kb) 25 pages.

Microwave chemistry (2.85 mb)
http://rapidshare.de/files/2737800/Microwave_chemistry.rar.h...

[Edited on 1-7-2005 by Lambda]
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[*] posted on 1-7-2005 at 15:58


You do realize that 2.45GHz electromagnetic radiation has a wavelength of about 1dm = 4", and that the 1/16" holes in the door screen are essentially solid metal?

Matter of fact, you might even find some microwave-speed diodes and build a field meter to check for yourself. :)

Reacting water with it will create ammonia too, might be a good way to get ammonium nitrate I suppose, if at who knows what mixture. Might as well keep it simple as N + O.

Tim




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[*] posted on 2-7-2005 at 01:53


It seems that using microwaves to make nitric oxide may be the easiest and best way to go.

At first I wondered if there would be a problem with impedance matching, but based on information I've found, it looks like it may work quite well.

The following paper describes a plasma generator comprised of a 2.45 Ghz magnetron and a shorted waveguide with a triple stub tuner, that resulted in a reflected power of less than 1%; but even without the tuner, the reflected power was "typically less than 10%". That's good news.

More good news is that with an airflow rate of 28 lpm, plasma flame temperatures of over 6000 degrees kelvin were achieved...that should make lots of nitric oxide.

http://psfcwww2.psfc.mit.edu/library/01JA/01JA005/01JA005_ab...

Finally, patent #6696662 describes a similar arrangement for creating a microwave plasma, only simpler in that it has neither a tuner nor the tapered waveguide section.
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[*] posted on 2-7-2005 at 17:38


protect yourself by all means but

the over heating - is this just a function of thermal rise meaning a call for greater flow of air around the magnetron tube or is something else happening within?

a modification of cooling could be done of course.


in conjuction with that question - how directional is radiation of the tube both with and without the typical wave guide of a MO?

shielding - grounded shielding i am assuming will stop radiation. if the containment vessel around the magnetron is complete that is like a can with only the "antenna" sticking would not the leakage be controllable?

jim wiggins

edit- what I mean is a solid hole free grounded metal container. I mean i have constructed many air/water tight containers and if these were made of a nonferrous metal - like copper then the leakage should be contained. i value my sight but this techonology is almost irressitable - at least to me.

the power produced with mw is both the blessing and the curse, eh?

[Edited on 3-7-2005 by jimwig]
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12AX7
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[*] posted on 2-7-2005 at 18:40


Quote:
Originally posted by jimwig
the over heating - is this just a function of thermal rise meaning a call for greater flow of air around the magnetron tube or is something else happening within?


Overheating is generally a result of a bad load. Too much (or too little) load on the magnetron and it starts heating up more than whatever it's feeding. This is due to reflected energy, and further explanation has to do with transmission line theory and other RF hocus-pocus that even I am not too clear on!

The other reason is, microwaves are inherently designed to run for only ten or twenty minutes maximum. When's the last time you used one for more than even three minutes? See, not much point in equipping it for continuous use. So they wind the MOT to an absolute minimum (running 1.5kVA through a core size otherwise suitable for only 500VA!). The magnetron is also undercooled for the same reasons. Note that all ovens (at least all I've taken apart) have a thermal switch or fuse on the magnetron in case it overheats, so at least it's somewhat protected.

Quote:
a modification of cooling could be done of course.


If you want to mod an oven for HNO3, it would be wise to swap out the main blower for a higher volume one, or perhaps even add water cooling (not too far out, the magnetron cathode is operated negatively so the anode casing is safely grounded).

Quote:

in conjuction with that question - how directional is radiation of the tube both with and without the typical wave guide of a MO?


The way I heard it, the magnetron tip emits radially. Inside a waveguide it goes wherever it is directed (of course).
If you look inside an oven, you'll notice the magnetron is mounted at a right angle to the waveguide axis.
An open waveguide will basically spray AFAIK. A horn can be mounted to direct it a bit better.

Quote:

shielding - grounded shielding i am assuming will stop radiation.


Not even a continuous Faraday cage is necessary- solid sheet metal or screen spanning a few wavelengths will shield a small area behind it (farther off, it diffracts around and once again closes in). If you box it in within say 1", it should still do a reasonable job.

Let me put it this way - you're dealing with light more than electricity. The photons just happen to be about the size of your fist.

Quote:
if the containment vessel around the magnetron is complete that is like a can with only the "antenna" sticking would not the leakage be controllable?

jim wiggins

edit- what I mean is a solid hole free grounded metal container. I mean i have constructed many air/water tight containers and if these were made of a nonferrous metal - like copper then the leakage should be contained.


Heck, any metal of adequate thickness will do it; your oven uses stainless and/or painted mild steels. Now that's horribly lossy (you can feel the loss in the walls after nuking something for a few minutes)!

Lining the surfaces with copper sheet, mesh or perforated stock would be very nice, although I doubt it really makes many decibels difference in a cubic foot sized device.

New revelation: can you put some water in the bottom of a flask, with a pencil lead pointing up out of it? So the NOx generated is absorbed by the (soon boiling) water? It would form HNO2/HNO3 directly from the steam too.

I'm gonna have to try that right now ;)

Tim




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[*] posted on 2-7-2005 at 18:52
Extremely dangerouse radiation and a waist of power


These microwaves bounce through your house like a superball. They are absorbed more or less by certain materials, but the risk of any radiation getting out must be prevented at all cost. These microwave elements may be PWM (puls width modulated) to regulate the output power. If the microwaves produced by the microwave element (magnetron element) is aimed directly at the target (reaction vessel), then I do not see the need of using exorbitant high power. This is a waist of power, with an added disadvantage of having to take all power soaking (absorbing) measures. Microwaves have very strait lined directional properties, wich are beneficial with respect to focusing the beam on a target..
Quote:
I advise you to use goggles with a (stainless) steal mesh to protect your eyes with. It should be snugfitting against your head.

As 12AX7 rightly remarked, the MOT (transformer) used in a microwave oven is underdimensioned for continues use. They tend to overheat fairly soon. With a bigger core and more copperwire this would not have been a problem (more expensive). But the problem remains, and one way to solve it would be to immerce the MOT in cooling oil. This will not only guide off excessive heat, but allso instantly quench any arcing that may ever ocure. A cheap motor oil may be used for this purpose, without to much added high-tech anti-motorwear garbage. This stuff may bring down the electric isolation properties of the oil.

[Edited on 3-7-2005 by Lambda]
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[*] posted on 2-7-2005 at 19:45


Microwaves in house = electronics die. Microwaves will induce electrical currents which semi-conductors don't like.

Microwaves are stopped by grounded metal, as are all electromagnetic waves. As long as the hole is smaller than 1/4 wavelength, then it won't go through unless there is some metal there. I drilled a whole into a microwave to attach another magnetron (yeah, I'm crazy) and no microwaves came through when I turned it on with the hole just sitting there. Stuck my screwdriver in and it guided them out the hole, which I felt by my hand heating up to a very warm temperature very quickly. So, DON'T shield the outgoing tube with metal, or the microwaves will go through it etc and make alot of trouble for you.

I have done things to magnetrons and microwaves that many people would consider "cruel and unusual" (for lack of a better descripiton) and I have found that older microwaves kick ass, while newer ones suck. An old microwave will often have a MOT rated for 1.5kVA and is able to take that without cooling, deshunt it and it will do that forever assuming the output is limited, if not it rapidly throws breakers. The magnetrons have very nice fans that keep the temperature constant no matter the runtime or what is being destroyed in the microwave.

I think the best was a 60W light bulb, the filament explodes into a plasmoid that it INSANELY bright, and it lasts for about 15 to 20 seconds before the glass melts and the bulb explodes with a huge BANG. Cleaning up a million little shards of glass isn't fun, but I highly recommend it as it's cool and pretty safe (as far as putting things in a microwave goes).

Anyway, if you really want to run for a long time, get an older (1980's) microwave that has a rated power of 1500W, as these will outperform a modern microwave and have no trouble for multi-hour runs. I ran one of those transformers so hot that the glue began to liquify and run down the sides and it was going along fine. For testing this idea a smaller microwave will be fine but if you want to really produce this stuff, try to look for an old, brown, big, really heavy one.

Deshunting one of those big MOTs is simple and recommended. The shunts prevent too much power from flowing by looping the magnetic field back into the primary coil. The problem is that this causes:
-loss of efficiency
-the core gets really hot (even further loss of efficiency and creates cooling problems)
The shunts are pieces of metal stuck in between the two coils on the microwave, and connect the two side parts of the core to the middle. Disconnect the transformer, remembering what connected to what, and take it out. Knock out the two pieces of metal with a hammer and metal rod (bolts work very well), and then put it back. Don't try this with small transformers, if the thing isn't 15 to 20 pounds it's small and the shunts will not come out easy and you'll probably break the transformer. Sometimes they are fairly large on smaller transformers, so who knows. Unless they are about 1cm in hieght, don't try. This isn't necessary but will help with the cooling for longer runs, I've run one deshunted with a suped up magnetron circuit (2000 watts) without it heating up at all while making plasmoids and destroying old computer parts.
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DDTea
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[*] posted on 6-7-2005 at 19:51


My friend stopped by today and we got to run a few more tests on the microwave. The big conclusion of the day is that reasonable yields will only be obtained from large reaction vessels--the higher the volume, the better.

Another interesting find was that the plasmoid generator works just as well if it is suspended from the lid of the container instead of sitting at the bottom. This might be useful if the bottom of the container is filled with water, then we could have the evolved gases immediately dissolve in the water. Also, it would allow ice to be placed on top of the generator, since colder temperatures would shift the equilibrium in favor of the products.

The generator we used today was more successful than all the others in creating those nice sky-blue plasmoids (this is one of the ways I'm measuring success, btw--when Oxygen is excited, doesn't it emit that sky blue color? )--it was a graphite pencil lead wrapped in aluminum foil.

We also found a way to measure microwave hot spots and cold spots. We took household Iodine (as from the pharmacy), poured a bit into a bowl of water, and then put some printer paper into the solution. This paper was then put in the microwave.

The logic behind this was that since Potassium Iodide is colorless when dry and otherwise shows as a dark purple when wet on the printer paper and water absorbs microwaves so well, hot spots would show up as white on the printer paper and cold spots would show up as a dark purple. This isn't entirely necessary to do, but it's useful if you're doing small-scale test runs and want to know where to place your plasmoid setup.

Overall though, we didn't get much of the desired Nitric Oxide. More than anything, we were getting Ozone...

Just like women: there is already a shortage of them and the few there are want to bond with themselves (i.e., be lesbians). Here, Oxygen is the limiting reagent since it only composes about 20-25% of the air whereas Nitrogen is a whopping 70%, and instead of bonding with Nitrogen it bonds with itself to form Ozone!

Do you think the plasmoid still isn't hot enough?

Well hey, if we don't get a working Nitric Acid setup, at least we've found a new way to cook chicken :P




"In the end the proud scientist or philosopher who cannot be bothered to make his thought accessible has no choice but to retire to the heights in which dwell the Great Misunderstood and the Great Ignored, there to rail in Olympic superiority at the folly of mankind." - Reginald Kapp.
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