plastics
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UV light sources for photochemistry
I am very interested in performing photochemical reactions such as synthesis of benzal chloride
(https://www.sciencemadness.org/whisper/viewthread.php?tid=10...).
In order to do this I need a UV light source which I want to build myself. Unfortunately with no experience in this field I am rather confused by the
terminology and components required (ballast/ignitor/control gear etc).
There are a couple of other places on SM where UV set-ups are mentioned but again I find the terminology and the components required somewhat of a
mystery
https://www.sciencemadness.org/whisper/viewthread.php?tid=86...
https://www.sciencemadness.org/whisper/viewthread.php?tid=16...
After some internet searching I have found what looks to be a suitable UV bulb:
http://www.gbbulbs.co.uk/acatalog/Philips_Cleo_HPA.html
Does this sound reasonable? If so what other bits and pieces would I need to get it to work.
I am aware of the dangers of UV light and the need for skin and eye protection as well as the large amount of heat these bulbs can produce
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Yamato71
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You will also need a suitable ballast to be able to run this lamp from the AC mains. Direct connection to the AC mains without using a ballast will
result in an instantaneous and spectacular explosion of the lamp. Yes, that is experience talking.
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kristofvagyok
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We've got 2 "photoreactors" for making reactions under UV light.
They are quite simple. A big 2-3 neck flask and one neck is fitted with a double walled quartz tube. In the inner tube a simple Hg vapor bulb is
placed (without it's borosilicate protective glass) and between we circulate some water as cooling.
So get a quartz tube and good luck(:
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smaerd
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About what temperature of water is run typically kristofvagyok? Would ice-water risk cracking the lamp?
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kristofvagyok
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We use normal tap water, but if preferred ice water could be also used, because of the quartz tubes.
A quartz tube could be identified by a simple method: heat it up red hot and simply put it into water. If it cracks it is not from quartz.
I have a blog where I post my pictures from my work: http://labphoto.tumblr.com/
-Pictures from chemistry, check it out(:
"You can’t become a chemist and expect to live forever." |
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Magpie
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This may be useful:
http://www.sciencemadness.org/talk/viewthread.php?tid=8695#p...
The single most important condition for a successful synthesis is good mixing - Nicodem
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Lambda-Eyde
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I've been thinking of commisioning something like this from the glassblower, do you have any pictures? It didn't occur to me to use a water jacket
between the lamp and the mixture.
Quote: Originally posted by kristofvagyok  | | A quartz tube could be identified by a simple method: heat it up red hot and simply put it into water. If it cracks it is not from quartz.
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A less (potentially) destructive method could be to induce stresses in the glassware with a torch, and use a polariscope to see if there are any
stress lines in the glass. With quartz, this doesn't happen.
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IrC
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A solid state lamp regulator such as is used in say a Savin 770 copy machine would work well. Around 80 volts at a max of 4.5 amperes is about right
for this type of Quartz-Halogen lamp. This is based upon the roughly 10 inch length of the exposure lamp in the liquid toner model copy machine I
mentioned. Possibly the shorter bulb you list operates at a lower voltage, you really need to find the data for the bulb. Do not touch the bulb with
your hands ever. Clean the lamp with a good solvent wearing Vinyl gloves before use just in case anyone has touched it, during packaging for example.
Otherwise it will blacken the quartz envelope (of the bulb itself) early on in operation. Wear the gloves whenever you handle the bulb.
I think the outer water jacket is not such a good idea because heat buildup inside the first tube will be a problem. A strong air flow through the
single tube will work well, a ducted fan at one end of the tube where said Quartz tube passes through the reaction vessel which allows hot air to exit
the other end. A fusor fan from an 840 Savin copier is perfect for the tube. I mention these models as I once had a source for my hacker junk box from
these models. No doubt other similar items would work as well.
Quartz tubes used to house mercury vapor lamps in water purifiers are cheap surplus and perfect for the job. Using a dremel tool with a diamond disc
cuts the tubing to the desired length. Goes through it like cutting butter.
No water, no plumbing, good cooling of the bulb. If keeping heat from the lamp out of the reaction area is important then an outer jacket for water
makes sense. Even with it the air inside the first (lamp housing) tube and the surface of the lamp gets extremely hot if mere radiation into the water
jacket is all you have. Meaning to best protect the lamp the inner airflow is a good idea.
[Edited on 12-6-2012 by IrC]
"Science is the belief in the ignorance of the experts" Richard Feynman
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watson.fawkes
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| Quote: Originally posted by IrC | | I think the outer water jacket is not such a good idea because heat buildup inside the first tube will be a problem. A strong air flow through the
single tube will work well, a ducted fan at one end of the tube where said Quartz tube passes through the reaction vessel which allows hot air to exit
the other end. |
Cooling the bulb protects two different things: the bulb itself and the enclosure. The fans
in, say, digital projectors are there to protect the enclosure much more than the bulb. Sometimes you need to protect the bulb, but quartz is worked
with hydrogen or acetylene torches, so you have be pretty hot to need to do that. The big 1000 W industrial bulbs (metal halide, for example) are in
enclosures made of metal, ceramic, and glass with plenty of distance between the bulb and enclosure (so there's plenty of surface area) and they are
passively air cooled. In the confined space of appliances with plastic bodies, it's not the bulb that's at risk.
In the present situation, it's not the bulb that needs protection, it's the solution being irradiated. You're not trying to protect it from the UV
(which is the point) but rather all the excess heat thrown off the bulb. There's going to be heating of the solution, so the purpose of the water
jacket is to cool the solution. Now that also has the effect of cooling the bulb as well, which is good. The problem with air cooling is that it
doesn't have enough heat flow capacity to remove adequate heat from the solution.
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IrC
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Interesting but I guess you did not read further where I said :
"If keeping heat from the lamp out of the reaction area is important then an outer jacket for water makes sense. Even with it the air inside the first
(lamp housing) tube and the surface of the lamp gets extremely hot if mere radiation into the water jacket is all you have. Meaning to best protect
the lamp the inner airflow is a good idea."
I have been using quartz halogen lamps over 40 years and allowing the bulb to overheat from lack of airflow wrecks the halogen cleaning cycle.
Resulting in premature blackening of the bulb envelope.
"Science is the belief in the ignorance of the experts" Richard Feynman
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Lambda-Eyde
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An idea: Fill the cavity containing the bulb with a nonconducting, high-boiling, thermally stable, UV-transparent fluid. The liquid will act as a heat
conductor and will be cooled down by the jacket.
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IrC
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Sounds like a good idea on the surface, never used one surrounded by anything other than air and the quartz gets extremely hot. At excessive
temperatures Tungsten hits the wall atom by atom so hard the Iodine cannot react with it and pull it back out. That or the Tungsten Iodide vapor
cannot react with the filament redepositing the Tungsten freeing the Iodine back up. Or both are routes of failure. These are my theories anyway I
have never read anywhere a comprehensive in depth analysis as to the mechanisms. The result is a mirror on the ID of the Quartz and thin spots from
Tungsten loss in small portions of the filament. Which causes the temperature to skyrocket at the thin portion and burn open the filament. By the way
dead copy machine exposure lamps are great sources of cheap Quartz tubes for mad science. The Savin 770 copier from the 80's used one around a foot
long and 7/16" in diameter. Diamond wheel cutting the ends off yields a nice tube. Not sure the best way to remove the Tungsten flash from the ID
nothing I tried ever worked very well.
http://donklipstein.com/bulb1.html
http://en.wikipedia.org/wiki/Halogen_lamp
http://www.teklight.com/faq_s.html
[Edited on 12-6-2012 by IrC]
"Science is the belief in the ignorance of the experts" Richard Feynman
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watson.fawkes
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| Quote: Originally posted by IrC | | I have been using quartz halogen lamps over 40 years and allowing the bulb to overheat from lack of airflow wrecks the halogen cleaning cycle.
Resulting in premature blackening of the bulb envelope. |
Fair enough. I was focused on protecting the
solution, assuming that that would also draw enough heat away from the bulb to protect it as well. I agree that forced air might be required in some
cases, though I suspect that just not sealing the air volume and allowing passive convective cooling may be adequate.
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IrC
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I think you are right assuming the lamp is not run too high, yet at the other extreme some kind of soft start needs to be used if the lamp is reduced
in output too far. These lamps are pressurized enough to violently explode under the right circumstances. Oddly enough a low voltage start (but not
too low) can cause this to occur. I always assumed the solid state regulator provided too high of a current pulse when this happens. Reading some of
the links I posted gave more insight on the exploding bulb mechanisms. Just don't be holding a cup of coffee at the time. Looked like I didn't make it
to the restroom which brought a lot of laughs as I had no way to leave work and nothing else to wear. The good thing was the machine it was in kept me
from being targeted by shrapnel.
"Science is the belief in the ignorance of the experts" Richard Feynman
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smaerd
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I recall in my organic chemistry lab we did a photochemical experiment using a little sodium lamp. The reaction failed because it was more moisture
sensitive then we thought it would be, but never-the-less, the bulb was actually outside of the flask.
I know borosilicate glass(~<300nm) does adsorb more light then quartz(~<150nm) does but I don't think many photo reactions would be severely
hindered by this. I suppose even water absorbs in the U.V. range as well? So just as a petty reminder it might not be necessary in all cases to have
an in-flask light source for every given reaction although it may be ideal.
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plastics
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| Quote: Originally posted by Yamato71 | | You will also need a suitable ballast to be able to run this lamp from the AC mains. Direct connection to the AC mains without using a ballast will
result in an instantaneous and spectacular explosion of the lamp. Yes, that is experience talking. |
Thanks guys - only taken 5.5 months to get a debate going!
Whilst I've got some attention would a 400W ballast similar to that listed here be OK?
http://www.grotec.co.uk/products.php?DepartmentID=54#Ballast...
Am I likely to require any other equipment or can I simply attach the bulb to the ballast and ballast to mains and switch on?
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IrC
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Since you did not get an answer, yes it will work. Just be sure to match the wattage between lamp and ballast. I prefer solid state versions to steel
and wire. No enamel to eventually melt between turns.
"Science is the belief in the ignorance of the experts" Richard Feynman
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morganism
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why wouldn't you use UV LEDs for this ?
look up UV glue curing, and do it cheap and cool.
will need more bulbs, but can run it off PS with just some resistors instead of ballasts and cooling jackets.
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watson.fawkes
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Because low pressure mercury lamps emit in the UVC band and the LED
curing lamps tout the benefit of eliminating UVC output. The emission lines in a low-pressure Hg lamp have λ = 185 nm and λ = 254 nm. There are only a few
commercially available LED's that emit in the UVC band. For example, TaoYuan has an LED at 265 nm, but it's the 185 nm line that will make ozone.
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killer_lapin
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Ballast
You should check on ebay, last year I bought a UV germicidal lamp kit to reveal my TLCs. Not to advertise but i bought mine from Rexim, LLC; he sells
full kits.
Neon tube can be tricky if you don't use the proper ballast. They are kind of expensive for a lamp so you don't want to blow them up.
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Texium
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Thread Moved
20-11-2023 at 12:48 |
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