[tinwhiskers] Re: the leachability study in the EPA article...
- From: "Bob Landman" <rlandman@xxxxxxxxxxxxxxxxx>
- To: <tinwhiskers@xxxxxxxxxxxxx>
- Date: Tue, 2 Jun 2009 16:04:18 -0400
No no Jake my good friend! The vapor pressure of lead at it's melting point is
infinitesimal. Perhaps at the PPB level.
Note from this paper that even at 1118C the vapor pressure is just 5.7mm
(remember standard atm is 760mm).
http://prola.aps.org/abstract/PR/v26/i6/p851_1
The Vapor Pressures of Metals; a New Experimental Method
Rodebush, Worth H.; Dixon, Alfred L.
Physical Review, vol. 26, Issue 6, pp. 851-858
Quasi-static method of measuring vapor pressures.-The vessel A containing
the liquid and surrounded by a furnace for maintaining a uniform temperature,
is connected by one tube C to a manometer M and a reservoir containing a
neutral gas such as nitrogen at a suitable pressure, and by another tube B to
an intermittent pump. Outside the furnace the two tubes are connected to
opposite sides of a differential manometer D. Successive portions of the
nitrogen are pumped off through B until the manometer D begins to show a
permanent difference of pressure; then the reading of M is the vapor pressure
desired. The action depends on the fact that when the pressure in M is less
than the vapor pressure, nitrogen can get from C to B to equalize any
difference of pressure caused by the pump, only by diffusion against the
up-streaming vapor in C, and inter-diffusion in the case of a tube 3 to 4 mm in
diameter is slow. A test of the method gave values for the vapor pressure of
mercury 170° to 203°C only.04 mm greater on the average than those of Smith and
Menzies. Vapor pressure of lead, 1118° to 1235°C was found to vary from 5.70 mm
to 19.70 mm in good agreement with the equation 10p(mm)=-10372T-10T-11.35,
which also fits the best results of Egerton at lower temperatures. The heat of
vaporization of lead at its melting point is calculated to be 46,300 cal. The
chemical constant comes out -1.40 which is close to the value -1.59 computed
from the quantum theory of monatomic gases.
DOI: 10.1103/PhysRev.26.851
Alas, there is now no lower limit for lead toxicity (according to the EPA).
Like Denny, I find that ludicrous. Like others here, I'm no dummy and I've
been sniffing lead for many decades.
Proper recycling is what we need to be doing on a national scale. But that
makes too much sense.
Bob Landman
H&L Instruments
-----Original Message-----
From: tinwhiskers-bounce@xxxxxxxxxxxxx
[mailto:tinwhiskers-bounce@xxxxxxxxxxxxx] On Behalf Of ab3a@xxxxxxxxxxx
Sent: Wednesday, May 27, 2009 8:55 AM
To: tinwhiskers@xxxxxxxxxxxxx
Subject: [tinwhiskers] Re: the leachability study in the EPA article...
I think that lead vapor and dissolved lead in water are probably what most
medical studies are concerned about. So it seems reasonable that where lead
based solders are used, one ought to have some sort of protective ventilation
system. Still, once it is in place, I agree that the risk is relatively small
compared to other environmental hazards, both natural and man made.
A more important economic analysis needs to be done here. Never mind the lead,
think of all the other rare metals, ceramics, and plastics one finds in
conventional electronic hardware. We have got to find ways of recycling this
stuff safely.
Toward that end, what effects will the use of lead or the avoidance of lead in
solders have on the life-cycle and recycling of used electronics? Are we so
good at recycling this stuff that we can afford to have a significantly shorter
life-cycle for a piece of electronic equipment?
THAT's the question I think we should all be asking. Yes. It's hard. Honest,
careful stewardship of the environment involves many difficult decisions. If
it were obvious, it would have happened already.
As H. L. Mencken pointed out: "There is always an easy solution to every
problem - neat, plausible, and wrong. "
Jake Brodsky
Other related posts:
