In the 70's I bought some computer dump stuff, these were boards with digital circuits with germanium transistors in a metal housing, of size 2n2905.
I opened them and a white powder came out. I hope it is not some berillium compound, but the best reason to have something in there would be cooling, so that could make sense. Normally I would think it would be a paste that dried out, but the can is hermetically sealed.
What could that powder be? (It can take decades to die from berillium poisoining so my time is up.)
Groetjes Albert
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How much of it, and what does it look like? Almost all white heatsink grease is made from zinc oxide, as used on babies' bottoms the world over.
The big beryllium scare was in the very early'50s, so I wouldn't expect beryllium oxide in heatsink grease from the transistor era. (I've heard anecdotal reports, but it's all FOAF stuff.)
Cheers
Phil Hobbs
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Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
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About say 10% of the TO5 can. What do you mean, what does white powder look like?
If it is zink oxide that is easy to check. ZnO turns yellow when heated. I'll try and report back here, some time.
Remember that these were not commodity items, possibly military.
There seems to be substantial BeO in micro waves, so industrial use of Be has not totally ceased.
Groetjes Albert
--
This is the first day of the end of your life.
It may not kill you, but it does make your weaker.
If you can't beat them, too bad.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst
Penaten. Zinc Oxide. 110 years of service. Good for bedsores from hospital stays. Almost useless for anything else.
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Heatsink grease often dries out. I notice this from salvaging CPUs from older computers. IBM used to have huge heat dissipation problems on their mainframes, but an extensive search doesn't reveal what they used for their thermal grease.
I have switched to using mineral oil. It fills all the gaps and is less likey to evaporate. So far it is working fine.
That would probably be a 2N107 or 2N404 in a TO-5 package. The cans were made from brass, copper, tin, or aluminum depending on the creativity of the manufacturer. Some were zinc plated.
How much white powder? The reason I ask is that I doubt that there was enough plating on the transistor to produce very much white powder. If you found a substantial amount of white powder, a better guess would be zinc or lead oxides.
Beryllium produces a self protective oxide layer which will prevent decomposition into a powder. The only way beryllium can produce a powder is to grind it into a powder, which is VERY hazardous to one's health. I used to deal with beryllium oxide heat spreaders in the base of RF power transistors used in marine atmospheres and never saw the beryllium decompose to a powder.
At the time (1970's), a problem we had with beryllium was the lack of a cheap and easy indicator for the presence of beryllium oxide. So, every white ceramic had to be considered a hazardous substance.
The addition to BeO to ceramics improves the head conduction about
15%. Unless you were dealing with ancient germanium power transistors, there would be no need to use BeO in comparatively much lower dissipation T0-5 packages. If you're looking for beryllium, look for power devices.
There's no clue where your mystery boards have been. It is possible to chemically attack beryllium with strong halide, sulfate, or nitrate solutions. If that were the case, you would certainly have found corrosive damage to some of the other components on the PCB's.
That probably means that the PCB's were not attacked by outside chemical agents. That leaves something inside the allegedly hermetic seal. My guess(tm) would be a bad job of PCB cleaning after wave soldering. The fluxes uses are corrosive and will eventually attack the lead and zinc in the solder.
Zinc and/or lead oxide.
Remember, you have but one life to give to your profession.
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It probably takes a very high temperature until gases develop.
But then, I found a box of 20 BFQ135 transistors this week when sorting my parts inventory.
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A pinhead of the ceramic in the lung is pretty sure to give you lung cancer. Well, it takes some time, maybe too long for me, but the word "expiration date" gets a completely new meaning in the context of lung cancer.
The transistors are nicely packed in a styro foam tablet, individually.
Solid chunks of BeO are pretty safe as long as you don't put a grinder on them--it's a hard refractory ceramic. It's just the powder that's dangerous.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Beryllia melts at 2500C and boils at 3900C. You'd really have to put it to the torch to have anything to worry about.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
You're obviously not a dad. ;) Zinc oxide ointment (Desitin by preference) fixes diaper rash right up.
TCMs don't use grease. When I left IBM about a dozen years ago, they were using some Shin Etsu paste with about 3 W/m/K conductivity.
Polydimethylsiloxane (Dimethicone) is the liquid of choice. Non-toxic, very low vapour pressure.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
TCMs initially used helium gas, then switched to oil. They never used paste or grease.
Dunno exactly, but it varies by viscosity. The carbon or silicon dominates the molecular weight, whereas the hydrogen dominates the van der Waals forces, so for the same chain length I'd expect the vapour pressure to be much lower.
BITD I ordered it from Clearco--about $70 per gallon, if you need that much. ;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Air : 0.024 Dimethicone : 0.15 Mineral Oil : 0.136
Problems with thermal paste: poor repeatability, non repeatable distribution, poor spreading, air gaps, dries out, insulating if too thick.
Videos:
Do You Even NEED Thermal Paste? Arctic MX-4 Vs Toothpaste Vs Mayonnaise Vs Vegemite - compares bare metal against various organic substances, recommends mineral oil.
How Thermal Compound Spreads
- uses glass plate to show distribution of thermal paste
How To Apply CPU Thermal Paste Methods - Compare and Benchmark
- uses Thermal Compound Arctic MX-4 and glass plate to measure different spreading methods. Temperature ranges from 87C to 82C.
Saying Goodbye to Thermal Paste? Carbonaut Tested
- thermal paste dries out
Homemade solutions to replace CPU thermal paste
I have removed the CPU's from three computers that used mineral oil for over a year. There was complete uniformity in the distribution (it covered the entire surface of the CPU), and no evidence of evaporation.
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