I rarely come into this forum alone!
A management professor of mine once said "You don't have to have all the answeres-but you should know where to find them.With that in mind-after reading the question posed by David, I thought my brother in law could shed some light.I emailed him this page and his reply follows.I would like to preface his reply by saying he is a good teacher as well as a physisist, but like many teachers, he won't spoon feed you.Before dismissing his "I dunno!" go back and re-read what he has written.Pay no attention to his Washington statements!:D :D :D
his reply:
> From,
> hcjilson
> Bob this subject just came up and I was wondering if you could shed any light on this phenomena.Welding spatter sticks to
glass...but not plastic lenses.( I say sticks because it feels like whatever it is stuck to the lens)They say "burned" and
maybe they're right.Whatever happens, it doesn't happen with plastic.I thought you might have the answer locked away
somewhere.Tv from harry
>
> OptiBoard Discussion Forums takes no responsibility for messages sent through its bulletin board systems.
Hi Harry-
(Sent directly to you, not to the forum)
Phew: at first I thought the subject was "wedding spLatter".
There seems to be two questions, they appear to ask why spatter
bounces off plastic lenses, but burns glass, and you talk about
"sticks to glass." I guess you feel the answer is "burns because
it sticks."
OK, first answer is that science and physics (my speciality)
gives one some ideas for answering such questions and/or
calculating from first principles the results of real-world
events, but in the end, given some ideas about mechanisms of
causation, only experimentation can confirm them as being correct
or not.
Aristotle held that a heavy object dropped from a height will
fall faster than a light object, which seems intuitively
"obvious". But some 2000 years later Galileo, in his Tower of
Pisa experiment showed that this was completely false. Another
400 years passed before Einstein revealed the reason for
gravitation in a satisfying and consistent theory called the
General Theory of Relativity.
So with this is mind, on the "sticks to" side, surface contact,
wetting, etc. is a very complex and poorly-understood subject.
During my extremely long Ph.D. research (a.k.a., "the
crucifixion"), I needed to solder wires to leads of a envaporated
coating of a metal structure on a glass (Pyrex) plate. To do
this I had to first paint gold-resin electrodes onto the glass
plate and then bake it in an oven to create the gold electrodes.
I then used pure gallium solder and an absolutely brand-new,
clean miniature soldering iron to glob molten gallium onto the
gold electrode, while simultaneously bonding on a very thin wire
of copper. This then worked at liquid helium temperatures.
I "knew" this would succeed because it was part of the
laboriously gathered lore of low temperature physicists, who must
battle extreme materials problems due to thermal contraction and
the failure of substances at very low temperatures near absolute
zero.
Gallim sticking to glass was not intuitive nor could it be looked
up or calculated (as far as I know.)
I would think sticking would have to do with the details of the
chemical and physical nature of the surface, and for sure whether
it could be presumed clean or not. But it would seem only some
experiments would settle matters.
In sum, you see from the above that I am saying, "I dunno". :)
Check back in about 300 hundred years, "they" will probably know
by then. Maybe.
(Given the current know-nothings in Washington and the state of
science knowledge and funding, "maybe never".)
Bob
--
Robert Lynch Berkeley CA USA
As Chad is my witness...:)
Hello,
I'm back. Chad and I both went back into the lab, started up the old soldering torch and did a little experiment. With a monetary shot of blue flame on the surface of a CR-39 plastic lens the surface remained clear but slightly crinkle if you caught it in the right light. Then we held the torch on the surface for two seconds and got a cloudy but not burned spot on the surface. I ran my fingernail across this spot and found it to be waxy feeling (who would have figure ;) Then we held the torch on the surface in another spot for about three seconds and got a much more pronounce indentation and again the cloudy looking spot.
We then took the torch to the outer edge of the lens and held it there and we did see it liquify for split second and then turn chalky and remained slightly pliable while being heated. So Chad and I have done the experiment and deduced that we are correct :)
Take care,
Darris C.
Oxy-Acetylene makes a big bang!
Darris,
I was wondering if C2H2 was the same gas we once filled a 35 gallon Trash bag with, and sent up on a weather balloon with a 6 min fuse attached on a 4th of July during my misspent youth?....Could be!:D :D
Have a good weekend! hj