[PLUG] LCD thingies (lead glass)

[Keith Lofstrom]

On Sun, 3 Dec 2006 16:27:00 -0800
Keith Lofstrom <keithl at kl-ic.com> dijo:

> plastic and glass, and those are very low toxicity (non-leaded glass
> is just modified sand, mostly).  
 
On Sun, Dec 03, 2006 at 05:26:22PM -0800, John Jason Jordan wrote:
> At the risk of going off-topic, this discussion has me wondering a bit
> about lead and glass. Meine elders were Deutsche and I have inherited
> the odd "lead crystal" object. Now, it occurs to me that, in the
> unlikely event such items made their way into a landfill, the lead
> would be pretty much trapped inside the glass. Not that I am going to
> drink high acid wine from them, but do we really need to worry about
> lead inside of glass? Yes, I suppose given enough time the lead would
> leach out. But I'm guessing we're talking about tens of thousands of
> years here. Surely Ma Nature can handle that, right? For that matter, I
> can go to any of a number of stores right here in PDX and buy more lead
> crystal. Were it really that evil, wouldn't it be banned by now?
> 
> So why are we so worried about lead in the glass in CRTs? Or is this
> just one of those pop culture things where people hear the word "lead"
> and freak out without thinking things through?

It is a matter of quantity and disposal rates, I think.  There are 
many pounds of lead glass in a CRT to cut down X-rays, at the maximum
possible lead concentration; sometimes 5 pounds of lead in a large CRT.  
The CRT works for about 5 years, then off to the landfill it goes.
OTOH, your inherited lead crystal objects have much less lead by
weight in them, and are kept for a long time, as your example shows
(I have some similar 80yo objects).  So the rate that the material
enters the landfill is far lower.

As far as how fast it leaches out, that partly depends on how thick
it is (diffusion time is proportional to the square of the thickness)
and how small the fragments are.  But it does come out, quite a bit
faster than thousands of years, and it can be somewhat nasty if some
ends up as airborne particles and somebody is nearby to breath it in.

I agree that the fretting probably does more damage than the lead
does, but it is wasteful to make a mess when you don't need to. 
So I look forward to the day when we make CRTs go away, and also the
day when people find something better to do than worry uselessly.

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs