It was asked this way.
> << Anyone know if it is ok to swish with cs if you are wearing braces, the
> metal ones? Does it discolor the braces or the wires or bands?
> >>
> It depends on the metal. Your braces and wires are probably stainless steel
> (ask the orthodontist) which I think won't be affected. However, I would be
> more concerned over oxidation than discoloration. I have 11 implants which
> are titanium and braces that are stainless steel.
Greetings Exuberant Practitioners of the CS art.
Let us delve into the way metals react to each other. We are mostly
concerned with silver and how it reacts to other metals under various
conditions. This is a technical post, but most CSer`s should find it of
interest and easy to grasp.
We will examine several series; Activity, Galvanic, Electromotive, and
Electrochemical.
We start with an interesting version of the Galvanic series. Galvanic
means that the two metals are electrically connected with an electrolyte
of some kind (a conductive fluid) and a current flows between them. This
is usually bad, because it means that one metal is being reduced to
nothingness. On boats, airplanes, and cars it means that something will
fall off or stop working because the metal was eaten away. Lets see the
Galvanic action in a salt solution.
Metal Voltage Potential
Magnesium -1.6
Zinc -1.1
Aluminium -0.75
Steel -0.7
Iron -0.7
Tin -0.45
Brass/Bronze -0.27
Copper -0.25
Monel -0.2
Stainless steel -0.2
Nickel -0.15
Silver 0.00
Gold +0.15
Right away we notice that this list is unusual. Silver is the
reference metal (not hydrogen). This series was made for marine work.
If two metals with a voltage difference of more than 0.2 volts is seen,
one of them will be destroyed. As we see, the difference between silver
and stainless is not more than 0.2 volt, however the difference between
gold and stainless shows that the stainless will be destroyed in due
time. Now remember that this is a salt solution, not what you would find
in your mouth on a regular basis.
The above list is arranged so that gold (noble cathodic metal) is at
the bottom and Magnesium (active anodic metal) is at the top. Most lists
are shown with the most noble at the top.
Even in an alloy, one of the metals can attack the other in the alloy.
Oxygen is a primary factor in the rate of corrosion. With out oxygen the
corrosion can not take place. Higher temperatures will cause faster
corrosion.
The noble metal is protected and the active metal is sacrificed or
lost. As we see, the silver and gold will not affect each other, but
copper will sacrifice to silver and gold. Gold is often used to plate
electrical contacts because of its ablity not to corrode, where as
silver will oxidize in ozone created by electric arcs of opening and
closing contacts.
The Electromotive and Electrochemical series are interchangable and are
referenced to hydrogen as used in a half cell. Different tables will
give different values depending on the electrolyte used. For practical
purposes the order of ranking stays the same. Here is a typical
Electrochemical series. Again the noble metal (protected) will be at the
bottom.
Element Potential diff. (ref to H)
Li -2.96
K -2.92
Mg -2.4
Al -1.7
Zn -0.76
Fe -0.44
Ni -0.23
Sn -0.14
H 0.0
Cu +0.34
Ag +0.8
Au +1.5
If the two metals are being used to make a cell, the voltage of the
cell is easy to determine by looking at the difference between them.
Remember that different electrolytes will change the readings. Example
would be a copper-zinc cell. Its voltage would be 1.1 volt. This table
was made by bubbling hydrogen gas over a spongy platinum conductor,
known as a hydrogen electrode.
The Handbook for Electrical engineers gives the following list. This
time we will put the noble metal at the top. Only ranking will be shown.
Platinum
Gold
Silver
Hastelloy
18-8 Stainless steel
Chromium stainless steel
Inconel
Silver solder
Monel
Bronze
Copper
Nickel
Tin
Lead
Lead solders
Cast iron
Steel
2024 Aluminum
Cadmium
1100 Aluminum (pure)
Zinc
Magnesium
The greater the separation the greater the likelihood of corrosion.
The electrolyte is a solution of ions and a film of condensed moisture
will serve.
Now lets look at a practical Activity series, it will show the
reaction of the metals.
There will be five column headings;
1. R-displaces hydrogen at room temp.
E-displaces hydrogen at high temps.
2. X-displaces hydrogen from acids
3. X-combines directly with oxygen
4. X-oxides decompose by heating
H-reduced by hydrogen
5. X-metals occur free in nature
Metal 1 2 3 4 5
Potassium R X X
Magnesium E X X
Aluminum E X X
Zinc E X X
Iron E X X H
Nickel X X H
Tin X X H
*Hydrogen X H
Copper X H X
Mercury X HX X
Silver HX X
Platinum HX X
Gold HX X
This table is arranged in decreasing order of activity. The activity
being the release of hydrogen from water or acids. The relationship of
oxygen to the metal activity is also shown.
Bless you Bob Lee
--
oozing on the muggy shore of the gulf coast
[email protected]
--
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