| Topic: |
Science > Physics |
| User: |
"Dave Lister" |
| Date: |
14 Apr 2006 05:05:31 PM |
| Object: |
metal bonding |
Metals have been described as the nuclei floating in a sea of electrons. If
this is the case, why does not the joining of very clean cuts result in
immediate welding?
--
Elect a Crook - Vote Republican
.
|
|
| User: "" |
|
| Title: Re: metal bonding |
14 Apr 2006 06:35:02 PM |
|
|
Dave Lister <retsildivad33@hotmail.com> wrote:
Metals have been described as the nuclei floating in a sea of electrons. If
this is the case, why does not the joining of very clean cuts result in
immediate welding?
It does if the surfaces are clean enough, but that's hard to obtain
in the real world.
Google friction welding.
--
Jim Pennino
Remove .spam.sux to reply.
.
|
|
|
|
| User: "srp" |
|
| Title: Re: metal bonding |
14 Apr 2006 11:14:01 PM |
|
|
Dave Lister a écrit :
Metals have been described as the nuclei floating in a sea of electrons.
Hardly. In solids, nuclei are solidly captive at the center of each its
normal escort of electrons. They will move only if the atoms concerned
are mechanically torn away or forced out by heating.
If this is the case, why does not the joining of very clean cuts result
in immediate welding?
It does when done properly. In the most recent aircraft engines, the
fan blades are welded with such a process.
André Michaud
.
|
|
|
| User: "Dave Lister" |
|
| Title: Re: metal bonding |
15 Apr 2006 12:50:15 PM |
|
|
srp <srp2@globetrotter.net> wrote in
news:44406DDB.6090403@globetrotter.net:
Dave Lister a écrit :
Metals have been described as the nuclei floating in a sea of
electrons.
Hardly. In solids, nuclei are solidly captive at the center of each
its normal escort of electrons. They will move only if the atoms
concerned are mechanically torn away or forced out by heating.
http://en.wikipedia.org/wiki/Metal
"Metals are sometimes described as a lattice of positive ions (cations)
surrounded by a cloud of delocalized electrons."
"The properties of conductivity are mainly because each atom exerts only a
loose hold on its outermost electrons (valence electrons); thus, the
valence electrons form a sort of sea around the close-packed metal nuclei
cations."
--
Elect a Crook - Vote Republican
.
|
|
|
| User: "srp" |
|
| Title: Re: metal bonding |
15 Apr 2006 04:40:38 PM |
|
|
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44406DDB.6090403@globetrotter.net:
Dave Lister a écrit :
Metals have been described as the nuclei floating in a sea of
electrons.
Hardly. In solids, nuclei are solidly captive at the center of each
its normal escort of electrons. They will move only if the atoms
concerned are mechanically torn away or forced out by heating.
http://en.wikipedia.org/wiki/Metal
"Metals are sometimes described as a lattice of positive ions (cations)
surrounded by a cloud of delocalized electrons."
"The properties of conductivity are mainly because each atom exerts only a
loose hold on its outermost electrons (valence electrons); thus, the
valence electrons form a sort of sea around the close-packed metal nuclei
cations."
Not in contradiction. Very few of metal atoms electrons are free to
circulate like that and you just named them, the valence electrons,
which are located on the outermost layer of an atom's electronic
escort. The reason is that these are located at about equal distances
from the nuclei of all neighboring atoms, which causes them to be
equally attracted by neighboring nuclei and allows them to easily
leave their lose mooring, at the slightest pull or push due to
changes in electric equilibrium.
André Michaud
.
|
|
|
| User: "Dave Lister" |
|
| Title: Re: metal bonding |
15 Apr 2006 06:23:08 PM |
|
|
srp <srp2@globetrotter.net> wrote in
news:44415FC4.2090608@globetrotter.net:
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44406DDB.6090403@globetrotter.net:
Dave Lister a écrit :
Metals have been described as the nuclei floating in a sea of
electrons.
Hardly. In solids, nuclei are solidly captive at the center of each
its normal escort of electrons. They will move only if the atoms
concerned are mechanically torn away or forced out by heating.
http://en.wikipedia.org/wiki/Metal
"Metals are sometimes described as a lattice of positive ions
(cations) surrounded by a cloud of delocalized electrons."
"The properties of conductivity are mainly because each atom exerts
only a loose hold on its outermost electrons (valence electrons);
thus, the valence electrons form a sort of sea around the
close-packed metal nuclei cations."
Not in contradiction.
Well, yes, it is. Better luck next time.
--
Elect a Crook - Vote Republican
.
|
|
|
| User: "srp" |
|
| Title: Re: metal bonding |
16 Apr 2006 09:19:19 AM |
|
|
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44415FC4.2090608@globetrotter.net:
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44406DDB.6090403@globetrotter.net:
Dave Lister a écrit :
Metals have been described as the nuclei floating in a sea of
electrons.
Hardly. In solids, nuclei are solidly captive at the center of each
its normal escort of electrons. They will move only if the atoms
concerned are mechanically torn away or forced out by heating.
http://en.wikipedia.org/wiki/Metal
"Metals are sometimes described as a lattice of positive ions
(cations) surrounded by a cloud of delocalized electrons."
"The properties of conductivity are mainly because each atom exerts
only a loose hold on its outermost electrons (valence electrons);
thus, the valence electrons form a sort of sea around the
close-packed metal nuclei cations."
Not in contradiction.
Well, yes, it is. Better luck next time.
Sure.
Ok, then, next time you capture another metal nucleus loosely
floating in a sea of electrons, no doubt with your bona fide wiki
rubber stamped nuclei blotter, well, let us know.
André Michaud
.
|
|
|
| User: "Dave Lister" |
|
| Title: Re: metal bonding |
16 Apr 2006 11:40:12 AM |
|
|
srp <srp2@globetrotter.net> wrote in news:4442457E.8060707
@globetrotter.net:
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44415FC4.2090608@globetrotter.net:
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44406DDB.6090403@globetrotter.net:
Dave Lister a écrit :
Metals have been described as the nuclei floating in a sea of
electrons.
Hardly. In solids, nuclei are solidly captive at the center of each
its normal escort of electrons. They will move only if the atoms
concerned are mechanically torn away or forced out by heating.
http://en.wikipedia.org/wiki/Metal
"Metals are sometimes described as a lattice of positive ions
(cations) surrounded by a cloud of delocalized electrons."
"The properties of conductivity are mainly because each atom exerts
only a loose hold on its outermost electrons (valence electrons);
thus, the valence electrons form a sort of sea around the
close-packed metal nuclei cations."
Not in contradiction.
Well, yes, it is. Better luck next time.
Sure.
Ok, then, next time you capture another metal nucleus loosely
floating in a sea of electrons, no doubt with your bona fide wiki
rubber stamped nuclei blotter, well, let us know.
Who said "loosely"? Besides, several other people disagreed with you.
--
Elect a Crook - Vote Republican
.
|
|
|
| User: "srp" |
|
| Title: Re: metal bonding |
16 Apr 2006 12:40:22 PM |
|
|
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in news:4442457E.8060707
@globetrotter.net:
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44415FC4.2090608@globetrotter.net:
Dave Lister a écrit :
srp <srp2@globetrotter.net> wrote in
news:44406DDB.6090403@globetrotter.net:
Dave Lister a écrit :
Metals have been described as the nuclei floating in a sea of
electrons.
Hardly. In solids, nuclei are solidly captive at the center of each
its normal escort of electrons. They will move only if the atoms
concerned are mechanically torn away or forced out by heating.
http://en.wikipedia.org/wiki/Metal
"Metals are sometimes described as a lattice of positive ions
(cations) surrounded by a cloud of delocalized electrons."
"The properties of conductivity are mainly because each atom exerts
only a loose hold on its outermost electrons (valence electrons);
thus, the valence electrons form a sort of sea around the
close-packed metal nuclei cations."
Not in contradiction.
Well, yes, it is. Better luck next time.
Sure.
Ok, then, next time you capture another metal nucleus loosely
floating in a sea of electrons, no doubt with your bona fide wiki
rubber stamped nuclei blotter, well, let us know.
Who said "loosely"? Besides, several other people disagreed with you.
Any number of people can disagree all they want, but nothing can change
the verified fact that in solids, nuclei are solidly captive at the
center of each its normal escort of electrons and will move only if
the atoms concerned are mechanically displaced or forced out by
heating.
André Michaud
.
|
|
|
|
|
|
|
|
|
|
| User: "Angelo" |
|
| Title: Re: metal bonding |
14 Apr 2006 06:45:54 PM |
|
|
Dave Lister ha scritto:
Metals have been described as the nuclei floating in a sea of electrons. If
this is the case, why does not the joining of very clean cuts result in
immediate welding?
Since such conclusion is false (in general), you'd think that
the premise is incorrect. Only a (tiny) fraction of electrons
are free in a metal, the outermost ones above the highest
valence shell electrons. Those free electrons stack up in
a *non completely filled conduction band* (a set of quasi
continuum energy levels) until they reach their Fermi level.
The electrons just below that band can (and usually) form
metal-metal bonds, and such bonds may be strong or weak.
They are responsible for mechanical metal hardness, high
melting points, etc. OTOH, those in that conduction band
explain the electrical and thermal conductivities, the look
and feel of a metal, its typical and distinctive appearance
(metallic lustre and shining).
Except for mercury (and gallium, perhaps a few others),
you have to heat to (or near to, if in a pressure aided fashion)
the melting point in order to weaken enough those M-M bonds,
allowing their easier redistribution, and so obtain the desired
weldind.
What you get by joining two pieces of the same metal at
room temp. is to extend electrical conduction, as in closing
a switch.
Hope this may help.
Best regards
Angelo
.
|
|
|
|
| User: "tadchem" |
|
| Title: Re: metal bonding |
14 Apr 2006 05:40:48 PM |
|
|
Dave Lister wrote:
Metals have been described as the nuclei floating in a sea of electrons. If
this is the case, why does not the joining of very clean cuts result in
immediate welding?
It often does. Google 'pressure welding'
http://www.twi.co.uk/j32k/protected/band_3/ksedn002.html
Commercial compounds are produced specifically to inhibit what is
called 'seizing' between bolts ans nuts.
Sometimes (for some metals, especially active ones such as aluminum or
iron) there is a thin oxide coat that inhibits welding that must be
removed. Welding and soldering fluxes are designed to remove this
coating before attaching two pieces of metal together.
Absent the oxide coating, the extent cold-welding depends also on how
efficiently contact is made between the two work pieces. Ideally a
mirror-smooth finish with no oxide coating present can be pressure
welded with barely any more pressure than it takes to squeeze the air
out from between the two surfaces.
Electropolished stainless steel is notorious for seizing readily, as
are brass and copper.
Tom Davidson
Richmond, VA
.
|
|
|
|
| User: "Gregory L. Hansen" |
|
| Title: Re: metal bonding |
15 Apr 2006 08:55:39 AM |
|
|
In article <Xns97A599870ABE8retsildivad33hotmail@70.169.32.36>,
Dave Lister <retsildivad33@hotmail.com> wrote:
Metals have been described as the nuclei floating in a sea of electrons. If
this is the case, why does not the joining of very clean cuts result in
immediate welding?
Because air sticks to the surfaces.
--
"The ability to quote is a serviceable substitute for wit". --William
Somerset Maugham
.
|
|
|
|
|
Related Articles |
|
|
