From: "Barry L. Ornitz" <ornitz+U@dpnet.net>
Subject: Re: PTFE Insulated wire, was: GE wire insulation problem
Date: 23 Apr 1999
Newsgroups: rec.antiques.radio+phono

Peter's information is somewhat deceptive here.  PTFE does not really have
a melting point in the sense that most people consider.  It softens
gradually and becomes clear, but it is not molten.  At higher temperatures,
it decomposes.

>Material               MPC           MPF
>Teflon(PTFE)           322            612
>Silver                 961           1762
>Tin                    232            450
>Copper                1083           1981
>
>Given that the melting point is very close to the extrusion point, it is easy
>to see why tin-plate is entirely unsuitable at the temperatures involved.

Teflon is not applied to the wire from a melt (at least not in W. L. Gore's
processes).  In fact, it is normally applied at room temperature or
slightly above.  It may be sintered at higher temperatures later during
processing.

>3. Silver is (as noted) an excellent conductor and "heat-sink". Therefore
>silver plated wire will carry more current at lower resistance (and
>therefore lower heat-loss as well) than similar gauge copper. Silver will
>also respond better than only copper in hostile environments.

Just how thick do you think the silver plating is?  Hint - it is measured
in microns.  The difference in electrical conductivity and thermal
conductivity of silver and copper is small (about 6% resistivity and 5% in
thermal conductivity).  Silver is not a good choice for many applications.

>Other points: Copper is sacrificial to Silver.... not that this means much in
>that they are very close, but it means that there is less chance of
>electrolytic action.

The galvanic potential between silver and copper is almost exactly the same
as between tin and copper (0.46 versus 0.48 volts) but the opposite
polarity.  This gives better corrosion resistance as the more
electropositive material should always be on the outside surface. [Copper
covered steel corrodes quite quickly if the copper coating is breached at
any point.]

        Dr. Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net

From: "Barry L. Ornitz" <ornitz@tricon.net>
Subject: RE: Teflon Coax
Date: 15 Nov 1998
Newsgroups: rec.radio.amateur.homebrew

birdsong wrote in message <364F0F73.7B31@phoenix.net>...
>While discussing teflon coax...Does anyone have any experience with the
>effects of cold-flow on the integrity of the coax?  For instance, if it
>turns any sharp corners, will the two conductors become eccentric over
>time?

Yes.  This is why it is very important that the minimum bending radius be
carefully observed.  It is especially true with the semi-solid dielectric
coax cable too.


Barry L. Ornitz   WA4VZQ   ornitz@dpnet.net

From: "Barry L. Ornitz" <ornitz+U@dpnet.net>
Subject: Re: PTFE Insulated wire, was: GE wire insulation problem
Date: 23 Apr 1999
Newsgroups: rec.antiques.radio+phono

PFJW wrote in message <19990423202733.24023.00000819@ng11.aol.com>...
>I respectfully disagree with this assessment, if only based on personal
>experiences coupled with mil-spec. information.


Remember that mil-spec information is simplified and not terribly accurate
from a scientific standpoint.

>1. The "melting point" is taken from Dupont's specifications supplied to the
>military.

The temperature you quoted should more accurately be 327 C.  This is the
temperature where all crystalline structure disappears in PTFE.  Above this
temperature, the material acts like an amporphous material much like a
rubber.  While this temperature is often quoted as a "melting" temperature
(even in some of Gore's advertising), the material is not really a liquid
above this temperature.  At lower temperatures, PTFE is quite crystalline
(about 90%).  Hence there is a distinct change in appearance and in many
mechanical properties, but scientifically PTFE does not melt in the strict
sense of a thermodynamic property terminology.  Some scientists refer to
the 327 C temperature as the gel point which is a good descriptive term.
To the lay person, PTFE might very well appear to melt, but a polymer
physical chemist has a much more restrictive definition.

>2. The material is extruded in a semi-molten condition, NOT "stretched" as a
>non-melting thermoplastic material would be (also part of the mil-spec.)

I am not sure what you mean by "stretched".  Different companies may have
different methods of manufacture.  W. L. Gore, DuPont's (and the entire
world's) largest customer for PTFE resin, uses a compression/extrusion
process at low temperatures to achieve high density.  Sintering preformed
later in the processing adds strength.  Unfortunately my nondisclosure
agreements with Gore prevent me from going into very much detail here.

>3. Three years as a machinist working with teflon seal faces did teach me
>that PTFE does "melt". It does decompose, true. And the differential
>between melting point and decomposition point is close (why "coated"
>fry-pans have definite heat limits), the two points are distinct. Few
>situations have the actual controls required to straddle the points.....
>however, my employer did. As I remember, the differential was less than
>5C.

The decomposition temperature range is normally considered to start well
above 327 C at 360 C.  Decomposition becomes appreciable above 400 C.
Depending on the application, the normal service temperature for PTFE is
200 to 260 C.  Contrary to popular opinion, PTFE can ignite in air when
heated to above 500 C.

Remember that when many people talk about Teflon, they are speaking about
generic fluoropolymers.  Technically, only PTFE is Teflon.  This is why I
always use the PTFE (polytetrafluoroethylene) name.  The other materials,
FEP, CTFE, and E-CTFE have very different structures and physical
properties.

For those interested, Lanza gives a excellent concise review of the
physical properties of PTFE at

http://www.gapigroup.com/proprigb.htm

A table of the general properties of the "Teflon Family" will be sent to
the alt.binaries.pictures.radio group.  Unfortunately this is a scanned
graphic and not machine readible text.  It is one I often used at Gore.

As for my experience with PTFE, I directed Gore's online instrumentation
and metrology program in their Cherry Hill facility in Elkton, MD.  This
facility serves as their central R&D location and also the central raw
material processing site.  This facility supplied the Eastern Cluster of
Gore plants (MD/DE) making Gore-Tex fabric, industrial products, and
speciality wire and cable manufacturing.

        Dr. Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net

From: "Barry L. Ornitz" <ornitz+U@dpnet.net>
Subject: PTFE Insulated wire, was:  GE wire insulation problem
Date: 22 Apr 1999
Newsgroups: rec.antiques.radio+phono

Brad Thompson wrote in message <371F1779.597D@pop.valley.net>...
>Harry Rogin wrote:
>>
>> While we're on the subject of teflon insulated wire, here's
>> another obscure problem with it:
>>
>> Most teflon insulated wire is made to Military Specification.  As
>> such the copper strands must be plated, and the plating metal
>> is usually silver.  Now, when teflon and silver come into contact
>> with transmission fluid, something called the "Red Plague"
>> occurs.  What this is exactly, I'm not sure, but I've been led
>> to believe that toxic fumes may be emitted by the chemical
>> reaction that takes place. (Battle tanks use tin plated, teflon
>> insulated wire, which is 3x the price because it is not available
>> off-the-shelf).


It is readily available off-the-shelf.

>> So...... if you happen to re-wire your radio with this type of
>> wire, and you mount it in your automotive engine compartment, and
>> your transmission springs a leak, make sure that your windows are
>> open......
>
>Hello--
>That's interesting! IIRC, wire manufacturers use silver plating
>over copper because the heat at which Teflon gets extruded onto the
>conductors would promote oxidation of the copper.


No, this is not the reason.  This wire, because of its exceptionally low
dielectric loss at radio frequencies is used in high-speed applications.
With the higher frequencies involved, the skin-effect becomes prominent.
Silver plating increases the surface conductivity improving the performance
of the wire.

PTFE _can_ be extruded over bare copper.  Tinned wire is used only to
improve soldering, just like with any other wire insulation.  For high
temperature applications, nickel-plated wire is used.  Most PTFE insulated
wire has silver-plated conductors because of the intended application.  The
savings of tinned wire versus silver-plated is pretty small, and for
non-critical applications other wire insulation materials are quite
adequate and _far_ less expensive.

>Questions:
>--Does anyone know what the chemical nature of "red plague" is?
>  Teflon is *supposed* to be inert, but perhaps the transmission
>  fluid is reacting with or displacing the silver, allowing red
>  copper oxide to form?


The PTFE is not reacting.  Transmission fluid varies considerably by
manufacturer.  The main ingredient is generally a blended mineral oil.
Additives are included to improve the properties like polymers for improved
viscosity and high temperature stability.  Zinc compounds are used by some
companies, while boron compounds are used by others.  Sulfonated compounds
are also common.  I suspect these additive compounds (especially the sulfur
containing ones) are reacting with the silver.  Also remember most
transmission fluids contain red dyes.

>--Does the Teflon get applid over tinned copper in normal
>atmosphere, or does the process get carried out in a reducing or
>inert atmosphere?


I cannot say for all manufacturers, but when I worked at W. L. Gore's
central facility, no special precautions seemed to be taken.  The wire
coating method is totally unlike that used by companies making wires with
thermoplastic insulations.  Some applications called for a special
sintering step at high temperatures after the wire was coated.

I once bought some nickel-plated wire with PTFE insulation.  You learn to
tin the ends immediately after stripping the insulation.  If you wait a
while, the nickel oxidizes and it is virtually impossible to solder to it.
Nickel oxide is the reason that stainless steel can resist oxidation and
corrosion.

        73,  Dr. Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net

From: "Barry L. Ornitz" <ornitz@tricon.net>
Subject: Re: Will Teflon hold up to UV and weather?
Date: 13 Nov 1998
Newsgroups: rec.radio.amateur.homebrew

Jim, WA0AXB, asked about the ability of plenum-rated cable to withstand the
weather and ultraviolet radiation.  Some good replies were given by Jim,
N8EE, my old friend Tom Bruhns, and Roy, W7EL.
Before commenting on PTFE (polytetrafluoroethylene, the generic name for
DuPont's Teflon(r)), let me mention that not all plenum-rated cable is PTFE
insulated.  Kynar (r) (polyvinylidene  difluoride), Tefzel, Kel-F, some
FEP's and some other plastics may also be used.  Most of these,
fortunately, have similar characteristics to PTFE for your application.

PTFE will hold up to weather just fine.  It will shrug off acid rain,
ozone, and virtually all air pollutants.  UV resistance is variable.  PTFE
does not hold up to ionizing radiation well at all.  Thus short-wave
ultraviolet (UVA) can eventually do some damage.  Long-wave ultraviolet
(UVB) should not damage it at all.  So if WA0AXB lives in a high altitude
desert  (as opposed to the nearly underwater Tom), his cable might suffer
some UV damage by 50 years or so.  If the jacket is pigmented in black or
another dark color, it might last even longer.  Likewise if titanium
dioxide filler is used to make it bright white, it should last a looong
while.  So avoid using X-rays on it too often and keep it away from neutron
sources.

The abrasion resistance mentioned is somewhat confusing.  PTFE is slippery
and is a good lubricant.  However its true abrasion resistance is not that
good.  Rough materials sliding over a PTFE surface will soon wear away the
PTFE.

If you have more questions about PTFE, please ask.  I was recently employed
by W. L. Gore & Associates, the world's largest consumer of PTFE resins, in
their central research and manufacturing facility.  PTFE is amazing
material, and I learned things about it that still are difficult to
believe.  Some of the Gore chemists talked of PTFE as being almost a living
material.


Barry L. Ornitz   WA4VZQ   ornitz@tricon.net