| Mr.Yokoo |
: |
The same phenomenon occurs when the solder
hardens from the liquid state. Even if it
looks hardened, it may not have completely
hardened yet. If the target metal is moved
in such a condition, a soldering failure occurs.
"Eutectic" means a composition with
the lowest melting point and with no difference
between the melting temperature and the hardening
temperature. Therefore, as with pure substance,
eutectic solder will instantaneously melt
and harden at a constant temperature. Do you
understand this? |
| Hikaru |
: |
I understand it completely. |
| Mr.Yokoo |
: |
OK, you learn quickly. In passing,
I'll briefly explain about lead-free solder
now.
Well, Hisasi. |
| Hikaru |
: |
I'm Hikaru. |
| Mr.Yokoo |
: |
Don't worry about the details. Do you know
why lead-free soldering is required? |
| Hikaru |
: |
That's because lead is harmful to the body. |
| Mr.Yokoo |
: |
That's right. Lead has toxicity
that affects the central nervous system in
the human body. But, lead was contained in
face powder and pigment in the past. Now,
lead is not used for that because its toxicity
was proven. Lead caused Kabuki actors to suffer
from a kind of occupational disease at that
time. By the way, do you know that lead was
also used in tap water piping in the past? |
| Hikaru |
: |
What?! That is terribly dangerous, isn't
it? |
| Mr.Yokoo |
: |
No, it is not always dangerous. When lead
is combined with carbonic acid and oxygen
dissolved in water, a film of lead compound
(2PbCO3EPb(OH)2) is deposited on the inner
surface of the lead pipe. Because this compound
is not soluble in water, it prevents lead
from dissolving into the water. Tap water
was clean in the past. |
| Hikaru |
: |
Is lead used in tap water piping even now? |
| Mr.Yokoo |
: |
It is not used now. Because the water quality
has deteriorated, a large quantity of disinfectant
is contained in tap water and the lead compound
film is difficult to deposit on the inner
surface of the lead pipe. |
| Hikaru |
: |
I see. |
