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Evan
07-09-2003, 01:08 PM
Greg,
I had a funny feeling about tantalum so looked up the MSDS. WARNING! Extremely flammable. May ignite spontaneously on exposure to air. Dust/air mixtures may ignite or explode.

DO NOT try machining this metal.

Negligible fire hazard in bulk form. Dust/air mixtures may ignite or explode. May ignite if exposed to shock, friction or heating. Avoid friction and static electricity.

Thermal decomposition may release toxic and/or hazardous gases.


[added]

Health Haz Acute And Chronic: MAY BE HARMFUL BY INHALATION, INGESTION/SKIN
ABSORPTION. CAUSES EYE & SKIN IRRITATION. MATERIAL IS IRRITATING TO MUCOUS
MEMBRANES & UPPER RESPIRATORY TRACT.



[This message has been edited by Evan (edited 07-09-2003).]

Greg Parent
07-09-2003, 02:48 PM
Hello Evan,
Thanks for the heads up. I know what I am going to do with the stuff now...bring it to the toxic waste dump across town.
Thanks again.
Greg

STAN
07-09-2003, 03:58 PM
Rather than the dump, call a scrap dealer. Ta
scrap is worth $ even if it only few lbs.

Greg Parent
07-09-2003, 10:15 PM
Thank you Stan, Another good idea. Waste not, want not.

Oso
07-11-2003, 09:05 AM
Just one question...........

Tantalum capacitors (solid tantalum, not wet type) are very common in electronic equipment.

They are known for turning into short circuits, BUT, in the process I have NEVER seen one burn, or offer to. I HAVE seen them get rather hot.

If the stuff is that explosively flammable, it seems that one might see the capacitors burn.

Are you sure the MSDS is not being over-conservative?

Did you look at the MSDS for aluminum?

Did you check one out for distilled or de-ionized water?

(BTW, the MSDS I saw for lab-grade distilled/deionized water has a number of dire cautions, including that the container should not be re-used for any purpose...........same as if it was poisonous material)

And one for sand is full of well-meaning cautions which argue strongly for having the beaches closed and sand volleyball banned.........

[This message has been edited by Oso (edited 07-11-2003).]

STAN
07-11-2003, 09:57 AM
I too was curious about the flammability danger of Ta. But I don't know enough to give advice concerning the safety of a kid working with it. I'm sure somebody on the board has expertise in refractory metals.

Evan
07-11-2003, 10:59 AM
I imagine the tantalum in a capacitor is fully oxidised, as in tantalum dioxide. No fire hazard there.

Incidentally, If aluminum is powdered finely enough and kept in a vacuum, it will explode upon being thrown in the air as a dust.

[This message has been edited by Evan (edited 07-11-2003).]

Oso
07-11-2003, 01:01 PM
If the tantalum were oxidised, it would not be conductive, and hence would not function.

The parts are polarized electrolytic parts, not made with some sort of tantalum-based ceramic.

Evan
07-11-2003, 01:06 PM
Quite a few metal oxides are conductive, silver oxides and tin oxide for example. Tin oxide is also transparent and is used for the conductive traces on an LCD panel. It is also used for the anti-static coating on a CRT.

As it happens, in a tantalum capacitor the tantalum oxide is the dielectric. Newer tantalum capacitors will use tantalum pentoxide which has a much higher K value.



[This message has been edited by Evan (edited 07-11-2003).]

CompositeEngr
07-11-2003, 01:11 PM
I have seen the tantalum caps burn during ICT test.
They aren't nearly as dramatic as an electrolytic cap inserted backwards though.
The tantalum caps that burned were a defective lot, and were installed correctly.

Evan
07-11-2003, 01:52 PM
A heads up for everyone,

In 2000 there was a case of industrial espionage. An employee of a large Japanese capacitor maker stole the electrolyte formula and took off to Taiwan where he sold it to half a dozen major capacitor manufacturers. This formula has been used up until last fall to make about 1/3 of the worlds aluminum electrolytic capacitors, especially the filter and decoupling capacitors in computer components like power supplies and motherboards. After the formula was stolen and put into production by the Taiwanese it was discovered by the Japanese manufacturer that the formula would not produce acceptable life test results. The Japanese manufacturer kept quiet about this as it was to their advantage to do so.

The result of this is that millions of computers have been produced by all brands including IBM, Compaq, HP, Dell and white boxes that have defective capacitors. The initial symptoms are general system instability progressively getting worse until the system has trouble booting. In power supplies sometime the capacitors will explode. It is easy to diagnose on a motherboard. Just look at all the bypass and filter caps. The top of the cap is scored to provide overpressure relief. A good capacitor will have a perfectly flat top. A bad one will be slightly or even greatly bulged and may even be leaking electrolyte. In my computer repair business I have seen quite a few of these lately and it has even happened to one of my machines.

Evan
07-11-2003, 02:56 PM
Composite, Oso,

When a tantalum cap burns it is called an "ignition failure". A tantalum cap is composed of powdered tantalum which is then fully surface oxidised during construction. Every microscopic pellet of Ta is covered by a glassy coating of tantalum pentoxide as the dielectric. If the voltage rating of a Ta cap is exceeded it may indeed burn.