Cool...thanks.
A couple of questions.
1. Some hi-fi purist advertising promotes "oxygen free copper" as having
better properties for propagating audio. I alway assumed that was the
fanciest possible way to say "not corroded". What do you (or the list)
think?
2. Sometimes people talk about the the crystal structure of the copper in
cables. Seems like BS to me. Any possible effects?
3. Most weird of all. Some people check their cables for directionality.
It's AC, people!!! Any possible effects on that one?
(Could I start a company selling premium oxygen free, grain oriented, coax
cable with a directional arrow and get rich???...maybe call it Monster
Coax?? oops that's taken)
4. More ham radio related. How can I model the increase in resistivity of
a coil or stripline at high frequencies due to skin effect? I'd like to
make the smallest possible tank circuit that doesn't have too much loss.
That means large wire or stripline...but how large is enough???
jeff
----- Original Message -----
From: "Jim Smith" <jimsmith@bigvalley.net>
To: <amps@contesting.com>
Sent: Friday, September 08, 2000 11:24 PM
Subject: [AMPS] Properties of Different Metals
>
> I came across this manufacturer's white sheet today, and thought the
> reflector could use some new material. I thought it might be of interest
to
> those considering silver plating or those considering different contact
> metals. It does not appear to be copyrighted. I've edited the company
name,
> manufactured products, and impertinent materials.
> I hope this is useful to someone.
> Jim Smith, KQ6UV
>
> The word "corrosion" is defined as the destructive alteration of a
metal
> by reaction to its environment. An example would be the effect of removing
> rust from an iron bar that has developed over an extended period of time
> from the exposure to oxygen and water vapor. When the rust is removed, the
> surface of the iron is pitted and deformed to the point that the
structural
> integrity is compromised. The term corrosion is sometimes used
> interchangeably with the term tarnish. However, it should be remembered
that
> tarnish is not destructive to the silver plating and the use of the term
> tarnish means to discolor or to loose luster.
> It is true that tarnish can form on the silver plating of contacts.
But
> since it is not destructive, the action is inhibited once the tarnish
> completely covers the exposed silver, thereby acting as a protective
coating
> over the base silver. In addition, tarnish is not mechanically bonded
> through the tarnish process and can be removed with a minimal amount of
> mechanical pressure.
> Fortunately, there is more oxygen in the environment than there is
> sulfur. Tin reacts with oxygen while silver, under ordinary circumstances,
> does not oxidize. It is true that silver reacts with sulfur compounds, and
> due to environmental pollution, hydrogen sulfide (H2S02) readily exists,
> thereby causing silver to tarnish. But tin also reacts with sulfur dioxide
> under moist conditions.
> Electrically, silver has several unique properties over other
materials
> used commercially for plating.
> The resistivity factor of silver is superior to most metals used for
> plating. It can be easily seen from the following data, the electrical
> superiority of silver over other common metals.
>
> Silver 1.63 X 10-6 ohms/centimeter
> Copper (pure) 1.70 X 10-6 ohms/centimeter
> Gold 2.44 X 10-6 ohms/centimeter
> Tin 1.15 X 10-5 ohms/centimeter
> Lead 2.20 X 10-6 ohms/centimeter
>
> The low resistivity of silver has another advantage in relation to the
> skin effect at higher frequencies. High frequency signals transmitted
> through a conductor do not travel through the center of the conductor, but
> instead travel along the outside surface "skin" of the conductor.
> Another example of the superiority of silver over tin, is the work
> function potential difference that exists when either of the two metals
are
> connected with a copper conductor. The work function difference between
> silver and copper is 0.21 volts. The work function difference between tin
> and copper is 0.24 volts.
> If the tin plating on a contact happens to be tin/lead (which is very
> common), this value increases to 0.29 volts. To prevent destructive
> corrosion, the recommended work function potential between any two
> dissimilar metals should always be equal or less 0.40 volts. Both silver
and
> tin when joined with copper are under this value, but this is another
> indication of the superiority of silver over either tin or tin/lead
plating.
> Because silver has a lower resistivity than tin, silver can carry a higher
> level of current. For example, a wire made from 22 AWG silver has a fusing
> point of 21 amps, whereas a 22 AWG wire made of tin has a fusing point of
> only 6.61 amps.
> From the mechanical aspect, silver is the most optimum choice to use
for
> contact plating.
> The following table will show the mechanical difference between the
> three most common metals used in contact plating.
>
> METAL RELATIVE HARDNESS
> TENSILE STRENGTH kg/mm2
> Gold 2.5
> 11.5
> Silver 2.7
> 15.1
> Tin 1.8
> 1.4
>
> The relative hardness of a metal is its resistance to scratching by 1
of
> 15 materials (from talc to diamond) according to the Mohs scale
> The tensile strength of a material is a measure of how much stress can
> be applied before shearing occurs, Silver has the obvious advantage over
> tin. Tin has a low tensile strength which would indicate that it's
> durability would be much lower the design that utilizes silver plating.
> It has been our experience, that there has never been a case where
> silver tarnish has caused any kind of detriment in the product
performance,
> regardless of the system application.
>
> SUMMARY OF MOST SIGNIFICANT ADVANTAGES OF SILVER (X = SUPERIOR
> PERFORMANCE)
>
> METAL GOLD
> SILVER TIN
> RESISTIVITY
> X
> CURRENT CAPACITY
> X
> RELATIVE HARDNESS
> X
> TENSILE STRENGTH
> X
>
> Bibliography:
> The Encyclopedia of Chemistry, Van Nostrand Reunhold, 1973
> Buschaum's Complete Handbook of Practical Electronic Reference Data,
Walter
> Buscham So. D 1980
> Reference Data for Radio Engineers, ITT, 1975
>
>
>
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/amps
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
>
>
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|