j_sum1 - 14-10-2014 at 22:37
I have a large clunky 20 inch computer monitor dating from the days when these things took up the whole desk. It still goes fine but I have no need
for it and I guess no one else does either. I rescued it from the dumpster on the basis that I might salvage from it a high voltage power supply
suitable for gas discharge tubes. I may still do that but I have found a different solution so there is no need.
What I am wondering is what else I might salvage from it. Capacitors may be useful I suppose. My real interest is in building an element collection.
What elements or interesting compounds might be gleaned from its carcass?
I know there is likely to be europium and umm... a couple of other things at the front of the screen. Well beyond my ability to refine at this stage,
but could be worth collecting. There is obviously copper wire. I might find some gold connectors. Aluminium heat sinks -- but what purity? What
have I missed?
hyfalcon - 15-10-2014 at 02:08
If it's been plugged in within the last 6 months, be very careful. Those crt screens have a capacitor in them that can pack quit a wallop. 20 inch
will take you to your knees if it bites you.
NexusDNA - 15-10-2014 at 03:51
I've been in that dilemma some time ago! I don't think it's worth the effort and danger of scavenging compounds from the screen. Very carcinogenic
stuff and the wield is very low. The most profitable part I believe it's the deflection coils of the electron gun, you can get tons of copper from
that. Mine didn't have heat sinks. Maybe there's something unusual in the electron gun, I don't know. In short, the thing is the treasure chest of
copper.
That said, be very careful. See some videos on how to disarm the CRT (which is the capacitor itself). The flyback transformer is versatile to make
some projects, I would save it. Have fun!
diddi - 15-10-2014 at 04:07
PC monitors have a crappy flyback that wont run plasma discharge, so don't bother. you can buy a small HF/HV supply for about $30. you need an old
flyback like a b/w TV style to get high current. there is yttrium, praseodymium, europium. you wont get any of the out tho. new crt will have
tantalum capacitors and if there are surface mount electrolytic capacitors you will get some silver and ruthenium. but they are hard work for small
returns. there may be aluminium radiation deflection shields and the usual heatsinks. the best use for most crts is bin fodder. the gold content is
virtually zero. there is a bit of copper, needless to say. in old crts there are a family of diodes with the prefix 0Axx that have germanium
filiments
confused - 15-10-2014 at 08:16
the phosphors from the CRT screen maybe?
Artemus Gordon - 15-10-2014 at 10:45
from <a href="http://en.wikipedia.org/wiki/Phosphor#Cathode_ray_tubes">Wikipedia</a>:
Red: Yttrium oxide-sulfide activated with europium is used as the red phosphor in color CRTs. The development of color TVs took a long time due to the
long search for a red phosphor. The first red emitting rare earth phosphor, YVO4,Eu3, was introduced by Levine and Palilla as a primary color in
television in 1964.[16] In single crystal form, it was used as an excellent polarizer and laser material.[17]
Yellow: When mixed with cadmium sulfide, the resulting zinc cadmium sulfide (Zn,Cd)S:Ag, provides strong yellow light.
Green: Combination of zinc sulfide with copper, the P31 phosphor or ZnS:Cu, provides green light peaking at 531 nm, with long glow.
Blue: Combination of zinc sulfide with few ppm of silver, the ZnS:Ag, when excited by electrons, provides strong blue glow with maximum at 450 nm,
with short afterglow with 200 nanosecond duration. It is known as the P22B phosphor. This material, zinc sulfide silver, is still one of the most
efficient phosphors in cathode ray tubes. It is used as a blue phosphor in color CRTs.
I don't know if you have a RYGB tube or just a RGB tube, but in either case, the phosphors are all together in a very thin and very fine-grained
pattern of dots or rectangles. Scraping it off the glass would mix all the phosphors together, and in any case you would probably only get a few
micrograms of material.
phlogiston - 15-10-2014 at 11:28
The glass from the CRT tube usually contains barium and lead for radiation shielding. Good luck isolating it from the glass though.
There may also be a very thin metallic layer of barium in the tube. It is used as a 'getter'.
Mesa - 15-10-2014 at 16:52
DONT skimp out on discharging the caps!
I used to repair CRT's quite a bit back in my teens, where some of the calibrations required the monitor to be powered on. I remember a friend
throwing a loose screw at me when I was doing this, subsequently shorting the caps when it hit a bit of PCB. Still one of the scariest moments of my
life.
j_sum1 - 15-10-2014 at 17:24
Yep. I will discharge the capacitors. Although it has been a year since it was last turned on. I am not about to be stupid with this.
hyfalcon - 15-10-2014 at 23:57
There will be a high voltage line going into the side of the crt in the back and to the side of the display tube. Normal insulated tools aren't
insulated enough to shield you from the high voltage. Heavy rubber gloves are in order when you do this. There's enough voltage to overcome most
insulators. That line has to come out before it's safe to work on. I've been bit more than once. It isn't fun.
zenosx - 19-10-2014 at 17:37
We used to work on these in school.. Take a flathead screwdriver and using a jumper ground it to the board.. Stick it up under the suction cup at the
top of the CRT. You should hear a "POP" if you don't.. try a different grounding point. Keep going until you hear the "POP" or your sure it's been
discharged. Then keep the ground under that cup until you dismantle what you want. Some of those larger CRT's can have heart stopping power in the
capacitance they have... BE Careful!
They also have the nasty habit of spontaneously recharging over time. People can say I am full of shit, but I've personally been hit by one that was
discharged days before and BAM...
[Edited on 20-10-2014 by zenosx]