Plasma chemical technology

Hi,

if you charge the oxide particles with enough electrons this should work.

Remove the glass top from a small bulb, heat it with less than nominal current, isolate it from the system and put it on negative high voltage.

This -or any other electron gun - will flood your system with electrons, charging the particles .

If the powder strem is only a few millimeter in cross section this may work to separate the particles.

If it is bigger there is some self shielding so then its working only on the outside.

Additionally it may be a good idea to put a strong axial magnet beneath the powder spray location and a magnetic return behind the collector wall. This will force the charged particles to diverging path lines.

How do you operate your collector ?

Have success

RHABE

Dear RHABE,

Your comments are simply precious, I must say but there seems to be a small misunderstanding here, either due to my inability to express the experiment clearly or due to your unconsciously elevating my experiment to loftier heights!

I have stainless steel belljar, which is double-jacketed and water-cooled, so that it can handle plasma heating inside, up to 600 degrees Celsius. The cathode is a mild steel plate and the vessel walls are the anode. A DC voltage of 1000 volts is impressed across these electrodes separated by 50mm. It can work at much lower voltages too. The glow discharge certainly starts at much lower voltages, however using hydrogen as the reducing gas, I prefer to work at about 500 degrees C. In my experiment thetop layer of the oxide powder seemed almost fully reduced but beneath that layer, there was no chemical reaction I presume. Hence the idea of using some kind of vibration of a fluidizing action.

Your suggestion to turn an ordinary incandescent bulb into an electron gun is a masterpiece worth its weight in gold -but will not the glow discharge have some effect on the filaments, since plasmas do conduct electricity and I am wary of introducing an AC into the naked filaments when the plasma all around them conduct happens. to be conducting...

Kindly review my description, in light of these facts and let me know -I am very fascinated by the idea of using an electron gun in my experiment. May be I could use the electron gun and the plasma alternately? One minute of electron bombardment and one minute of plasma heating? The bottomline here is, a hydrogen plasma is far more effective as a reducing agent than any other material under these circumstances.

Thanks a lot, please continue this thread, I am curious.

Warm rgds,

Plasmaspecialist

Daer Plasmaspecialist,

I forgot to mention that the power supply for the bulb has to be very well insulated on both terminals - a 3KV isolation transformer with AC heating the bulb will do it - else you will kill the power supply with the superimposed negative DC voltage that is needed to drive away the electrons that are emitted from the heated filament by the high temperature. You are right about the conductive coupling of the plasma to the filament but if you use the isolated transformer there is no problem with DC plasma.

It is not suitable to use the electron gun and the DC plasma alternatively as the lifetime of both electrons and excited atoms are only microseconds or below.

In your arrangement you do not need temperature as the energy in the plasma will be much higher than the temperature will provide but it will help to speed up the reduction by simple chemical reduction.

Your process stops at the top layer because there is a shielding of the interior by the top layer.

So I think you are right to try to suspend the particles.

What about: simple stirring, transport up with a conveyor belt and let ist fall down again, ultrasonic acceleration will require a thin layer of oxide only ontop of the ultrasonic oscillator in order to get enough initial velocity in the particles.

What about blowing the oxide in with your hydrogen?

How do you get the water out? The energy of your 1KV discharge is high enough to crack the water molecules and let the OH react once more with your metallic particles.

How do you get the metallic particles out?, fine iron particles do ignite in contact with the atmosphere.

How much do you want to produce? Did you consider sputtering the metal with Argon in a much higher pressure than ordinary sputtering is done? (1 to 10mbar instead of 1 to 30µbar)This will result in condensation of the metallic atoms before these can reach the walls of your vacuum pot.But the process is slow as most sputtering processes.

We do DC sputtering in argon and nitrogen in order to produce metallic and nitride coatings mostly aluminum and aluminum nitride but also titanium, different alloys, also carbon.

Regards

RHABE

Dear RHABE,

Electrically isolating the high voltage bias given to the filaments may be a neat solution -but will the plasma surrounding the filaments not cause any problems considering the fact that the filaments are at high voltage with AC, a supply different from the pulsed DC that forms the plasma? Can a wiremesh around the filamemnt help? Perhaps it will hopefully ground the plasma but allow the electron flux to rush out...

If there a chance of stopping the conductive coupling of the plasma simply by using an isolation transformer, wow, nothing like it. We are alredy employing an isolation transformer for the six thermocouples which tend to pick up electronic noise due to the plasma acting on their tips, and since my system is PLC-driven with automation, we certainly don't want all that funny business in temperature measurement. In fact we have gone one notch higher, and employed an opto-islator to simply rule out all possibilities of electrical noise playing havoc with our whole measurement system.

Yes of course, the idea of using them alternatively, the electron gun and the DC pulsed plasma seemed dubious to me also, and indeed I overlooked the microsecond nature of the pulses. I thought the electron flow would be continual since the filaments will keep glowing steadily as long as there is the high voltage supply to them, even though the plasma is pulsed.

Again, focusing on the plasma electronic energy is certainly a better bet than using the temperature as the experiment involves the use of low pressure precisely for encouraging the electro-kinetic mechanisms. The same applies to deploying an electron source too.

Blowing in the oxide powder seems like a very fascinaing new idea, and please let me sleep over it for a day or two -there indeed are vibratory and fluidizing solutions but somehow blowing in the oxide powder with the gas seems easier to. In vacuum vessels one prefers the less complicated solution, one with lower number of moving parts.

Addding a sputtering phase to turn the metal particles truly metallic is a brilliant suggestion, I don't know if all metal particles are pyrophoric in nano-form. Iron is definitely out, since my experiment involved the use of selenium oxide, tellurium oxide and some other exotic elements. Sputtering at higher pressures would surely be a very desirable addition and I will incorporate that gladly. The process being slow does not really matter as right now we are in the 'feasiblility' stage and the commercial viability comes next. Quite a bit of tying up the loose ends needs to be fixed before reaching the next stage in our experiment.

Did you have any experience with nitriding of carbon nano-tube under similar circumstances, please? Would doping of an alumina substrate with nitrogen atoms be practical in the same set up ?

You've been extremely helpful, sir/madam. I am surprised at the short time span within which so many creative ideas have flooded this thread, all of them precious and hugely practical. Thanks a lot... this means lot to me.

Warm regds,

Plasmaspecialist

This is a very interesting discusion, some of the equipment needed for these experiments probably dont exist 'YET".

There will be a large quantity ofsurplus of Cathode ray tubes available soon. It may be possible to let one down by breaking at the vacuution point and remove the front screen.

This will give you an isolated electron gun or three. a high efficiency ceramic coated heater. and if you do find a decent road side TV set the . EHT and heater circuit may be intact, Turning it into a servicable Bell Jar might be a challenge. The scan coils might prove usefull for focusing the electron beam, and there will be plenty of room under your improvised jar for additional equipment.

GF

There used to be several manufacturers that made fluid bed dryers and vibrating conveyors. At least two (one was a division of Carrier) made a vibrating fluid bed device. The active bed was a shaking container with a motor and counterweight. Connections were through a flexable boot or hose. It seams they made a small model for materials testing.

They offered lab testing if you provide a sample.

Good luck

Dear Paddler,

It would indeed be fascinating to know more about these vibrating devices. I just hope they can work under near-vacuum conditions in a plasma environ. I employ a low pressure, something like 1x10-3mbar. Of course I would not expect you to comment on these concerns, and I would rather hunt for the possible suppliers of the vibrating or fluidizing beds.

I am glad you mentioned Carrier's division, that may prove to be a clue somehow. Thanks a lot, and do keep coming back to this thread, I am thrilled to see two comments in one day.

Warm regds

Plasmaspecialist

I don't see any problem operating in a vacuum, I do all the time.. get it?

But seriously, If you have flexible connections or a long tube run (or coil) to isolate the vibrating container from the stationary platform it should work. When I installed one many years ago I had several discussions about the spring constants and the variable weight of the equipment I was installing. The design was not what I expected.

How big, heavy and what is the difference in weight between empty and full is the vacuum container you need to fluidize?

A alternate supplier may be the Sweco screen company. They make several lines of vibratory screens. They make several lines of vibrating equipment. I bet they know how to fluidize a bed.

Hi Paddler,

Those are lovely suggestions, let me look around and report my progress.

Thanks a lot.

Regds

Plasmaspecialist