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Cloner
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[*] posted on 6-12-2005 at 07:36
microwave modifications


In order to practise chemistry in a microwave, one can either buy a cheapo microwave, drill a hole in it and build the experimental setup in it. Or buy a scientific MW instrument which has a price that has two digits more than reasonable.

I would try the first approach, that is buy a microwave, make a hole in the top and put a refluxer in it, and a stirrer below. The thing I find disturbing is the 'electrosmog'. Probably the machines are all shielded to compliance of certain strict norms, but not anymore when you tamper with it. Did anyone who uses microwaves measure electrosmog or whatever you can call it, that appears out of customized microwaves?
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[*] posted on 6-12-2005 at 10:16


Without mentioning adding some kind of shielding to block the microwaves from coming out and making your head explode and your eyeballs popping? Nor any mention of a microwave leakage testor to insure safety? Stupid, irresponsible ideas are not what people need!
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[*] posted on 6-12-2005 at 13:38


This is the sort of scenario where one needs to build the electrical equivalent of a fume hood : which is a Faraday cage.



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[*] posted on 6-12-2005 at 14:03


Stray microwaves are indeed very dangerous. They can destroy your eyes, leaving you blind. Assuming you're a male, you will go sterile. There's other stuff I can't recall right now, but the bottom line is that you really need some kind of shielding.
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[*] posted on 6-12-2005 at 15:08


Quote:
Originally posted by neutrino
Assuming you're a male, you will go sterile.


Not to dissipate the seriousness of the suggestions made, but surely it's not a dead cert that you'll go sterile? If it were THAT awful then they'd never licence them for use in home kitchens!




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[*] posted on 6-12-2005 at 15:19


They'll make you go sterile if you let it MICROWAVE YOUR TESTICLES. Likely, you would notice the intense burning sensation before you suffer permanent damage.

There's nothing boogeymonsterish about microwaves, damn they're just slow infrared, they tend to make things heat up and that's about it!

The eyeballs are a concern because they may heat up (from the rays) before you realize they're cooked. Good way to get cataracts/glaucoma (I forget which), or worse.

Tim




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[*] posted on 6-12-2005 at 15:39


"If it were THAT awful then they'd never licence them for use in home kitchens!"

They DON'T license the models with open unshielded holes in the top!
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[*] posted on 6-12-2005 at 16:08


I don't quite understand the problem.

All you need to do is to shield the apparatus with and the whole with a mesh that is also used in the door. That mesh's hole width is around the diameter of the microwave wavelength, hence it's absorbed. That's why glass, and that mess is sufficient for shielding.

Shouldnt be too hard to set this up properly.

I see more of a problem to make a hole through the middle, because that's where the magnetron is located, right - which'll obviously be in the way.


Other than that... of course a remote switch is always good, i.e. you can turn it on and off from a distance.
While in operation, the greater the distance, the better, of course.
You could always protect yourself behind such a mesh yourself (i.e. like a portable shield), while the magnetron is on.


I honestly don't see as much the problem, as long as you keep a good distance during operation, and a good shield made of metal mesh.




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[*] posted on 6-12-2005 at 16:32


I too have told that microwaves are very dangerous so do it outside and use remote switch. You probably can drill hole somewhere. Tube with 14/23 joints in both ends that goes through hole should let you connect liebig condenser with small flask that is located inside microvawe. You can use bent tube so that some shielding can be put over the hole.

[Edited on 7-12-2005 by chromium]
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[*] posted on 6-12-2005 at 17:22


Don't forget to ground the shielding continuously around all edges.

Holes can be, at most, maybe a half wavelength. (I forget what a good number is, and it depends on attenuation and distance. With electronics, signals aren't *blocked*, they get attenuated a number of decibels (a log scale), and in engineering a system, you have to decide how much attenuation counts as "blocked")

2.45GHz is almost 1cm long.

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chloric1
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[*] posted on 6-12-2005 at 17:52
modifications


I am going from memory here but if you where to drill a 1cm hole I think a 6 inch long copper tube leading out of the hole would provide adequate sheilding. I believe this from Chemical Abstracts or the like.



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[*] posted on 6-12-2005 at 17:57


Wavelength is 12cm at 2.45 GHz. And for significant attentuation the holes need to be less than 1/20 of the wavelength, or under 5mm in this case. Slots count as holes as large as the length of the slot.

[Edited on 7-12-2005 by Twospoons]




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[*] posted on 6-12-2005 at 23:59


I've noticed microwaves travel through metal objects inserted into holes even if microwaves don't normally do so. I drilled a hole into a microwave, no microwaves came through, I stuck a screwdriver in the hole and suddenly my hand got pretty warm.

The dangers of magnetrons are real but greatly exagerrated. I've run magnetrons in the open, lit up fluorescent tubes in the open, warmed my hands etc. The radiation spreads out so rapidly that holding your hand just a few inches in front of a 1000 watt magnetron only makes it feel like it is in a hot tub.
It is a very interesting feeling because your entire hand is warmed, not just the surface.

However, going blind is a possibility so you do have to be careful. Also, since it probably jams every wireless signal in a good distance, be considerate to your neighbours etc.
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[*] posted on 7-12-2005 at 05:52


.....The dangers of magnetrons are real but greatly exagerrated. ........

Do not try this at home!

An interesting story from the early days of microwave ovens which were developed by Amana from radar technology.

To allay the safety fears of the company bosses who were trying to decide if this new product (microwave oven) would be released a japanese engineer put his head into the micro oven for a few moments. Apparently he lived a long life thereafter with no untoward after effects.
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[*] posted on 7-12-2005 at 08:44


Quote:
Originally posted by Chris The Great
I've noticed microwaves travel through metal objects inserted into holes even if microwaves don't normally do so. I drilled a hole into a microwave, no microwaves came through, I stuck a screwdriver in the hole and suddenly my hand got pretty warm.


Interesting experiment :o

Does illustrate coupling pretty nicely though. You have to bypass, ground and bond everything as good as possible! A rod floating in a hole like that will act as an antenna inside and out, coupling things quite nicely. In fact, if it's exactly a half wavelength long (I think), it will act as a dipole, live on both ends and, for all intents and purposes, null in the center, right where it passes the chassis -- hard to ground a voltage that isn't there! Remember to avoid situations like these.

Edit: yes thanks I missed a factor of ten... 3 x 10^8 m/s / 2.45GHz is indeed 12cm = 4 3/4 inches.

Tim

[Edited on 12-7-2005 by 12AX7]




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[*] posted on 7-12-2005 at 09:11


Leaky microwave ovens can cause cateracts without a doubt and as chris found out imprfect shields, badly grounded bits of metal or sticky outy bits can resonate, or retransmit radiation. Its a messy subject and I'd question why anyone would want to go into it for chemistry. ITs *just* a heat source, make a heating mantle and things are much safer.
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[*] posted on 17-1-2006 at 00:54


I've seen microwave ovens - running 1kW magnetrons do some nasty damage to objects several meters away. I remember a few years ago a Comm- Tower had one of its horns point at a housing complex for 4 days after a large storm knock down the horn. I have no clue as to how much energy is in one of those tower horns but all I can tell you is that the entire subdivision suffered.

1. Sleep disruptions**
2. Locallised heating of certian areas of homes- very spiratic
3. Constant malfunctions with sensitive electronic equipment
4. Data storage divices suddenly erased- VHS/audio tapes were the problem media here.
5. Incandecent light bulbs/ tube light fixtures would glow after switch cut power to circuits
6. fine metal objects would emit sound- buzzing. Some claimed to hear the radio coming from filiments in their toasters!

So far no lasting effects have been reported.




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[*] posted on 17-1-2006 at 12:17


As chloric1 says, you need to solder a length of metal tubing to the hole. This will act as a waveguide, reflecting the microwaves back in to the oven. The tube must be soldered all the way around - any gap will act as a slot, radiating microwaves.

In this case, the tube diameter is much smaller than the microwave wavelength, so the attenuation in dB is proportional to length/diameter of tube. With diameter of 20 mm and length of 80 mm, gives you around 120 dB of attenuation.
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[*] posted on 18-1-2006 at 05:55


You might be able to use the signal strength indicator on a WiFi equiped laptop as a measure of leakage.

I know you can see the leakage from a 10 year old microwave in the following way. My satellite receiver is in an upstairs room. In order to get a cable to the kitchen I would have needed to drill through a couple of brick walls. Instead I purchased a video transmitter/receiver pair from Radio Shack. These operate at the same frequency as microwave magnetrons. When the microwave is operating in the kitchen you can see the interference on the TV in the kitchen. It is possible to make qualitative judgements about the level of the interference from the picture distortion. So just measure the amount of interference before you drill a hole in the microwave and then when you have finished your modifications, play with the shielding until you get the interference level back down to something like what it was at the beginning.
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[*] posted on 18-1-2006 at 10:42


bullstrode, that wouldnt be a waveguide and may just start oscillating lengthwise ala magnetron coupling.

fizzy, err, not reliable and you can actually buy microwave leek testers, so I dont see the point.
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[*] posted on 18-1-2006 at 15:53


Of course it is a waveguide.
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[*] posted on 18-1-2006 at 20:31


If one could find a microwave with a long base, it could be set up on its side so it is enlogated vertically. Your apparatus would also need to have the right length to fit.



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[*] posted on 19-1-2006 at 12:31


I had an idea and I would like to know from some of you guys, who surely know a lot more than I do regarding microwaves, if it is feasable.

What I had in mind is to simply place the apparatus inside the microwave chamber (i.e. the place where one usually places the food, just to make sure we're on the same wavelength here :P) and drill small holes of a diameter of 1mm each in a small area on the posterior wall of the microwave oven chamber. The apparatus 'piping' would be led to the region where these holes are and the pipe, for example glass, which has a diameter greater than the area covered by the collection of the holes made is bonded to the wall by some strong inert binder (although I know that 'inert' does depend on the solvents being used in the rxn etc...). Opposite to this region of holes is bonded another glass tube, in the same manner, so that this other tube is connected to the inner tube by means of the holes, but separated from it by the wall with small holes which serves as a shielding (but at the same time allows movement of chemicals in and out). Attached is a rough sketch of what is explained above (freehand, so please be kind).

Obviously, if this could work, I guess that a number of these 'connections' could be made so as to allow as number of inflow and outflow tubes in and out of the microwave oven, without running the risk of 'microwave-leakage' which I would very much like to avoid at all costs. Any comments, suggestions, critiques, et cetera are more than welcome.

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[*] posted on 19-1-2006 at 13:50


yes it should work. Its really just an extension of the ventillation fan system thats already in your standard microwave oven. If you are really paranoid, a matching perforated graphite plate could be used on the outside of the 1mm holes, as an additional absorber.



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[*] posted on 19-1-2006 at 16:17


I think it was organikum who posted details for modifying a microwave to accept a distillation column; I don't remember where - maybe it was on the Hive. You can Google stuff for this. There is lots of info around on using attenuating waveguide ports for Faraday cages as well as microwaves.

The graphite plate might need to be quite thick due to the skin depth - it isn't necessary for mm sized holes anyway. Even a cm sized hole wouldn't leak that much.
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