Conductivity as material oxidizes

[grasfulls]

As those materials most commonly used in wiring oxidize, how is their conductive property impacted?

I recently had someone ask me if the "patina" effect of copper reduces its conductive properties. I have no idea. I was told long ago, when working in corrosive environments, such as sewage treatment, to use things with silver coated contacts as silver oxidizes it becomes a better conductor. I must say, I just took the direction at face value and never researched it.

I have been looking around the net and in the forums, but have not found anything definitive. I apologize if this is already in here someplace.

 

[billsnuff]

some info

some info

http://www.sjsu.edu/faculty/selvaduray/page/papers/mate234/yingzheng.pdf

http://answers.google.com/answers/threadview/id/397640.html

http://www.copper.org/applications/electrical/building/wire_systems.html

 

[kwired]

I have always understood copper oxide is not much different from copper. Aluminum oxide is a horrible conductor and the reason anti oxidation compounds were used on old alloys. Newer alloys don't require compounds so I would assume in normal environment oxidation is not much of a problem.

 

[gar]

101016-1018 EDT

If you search with the appropriate words you can find some useful information.

Generally copper oxide is considered a good conductor. In contrast aluminum oxide is a very poor conductor. Anodized aluminum is a thick layer of aluminum oxide and a very good insulator.

Copper oxide with appropriate impurities is a rectifier. Good conduction in one direction and poor in the other. But reverse breakdown voltage is very poor. Do a search for -- copper oxide rectifier -- one result is http://www.jmargolin.com/history/trans.htm
An interesting discussion for a number of historical reasons.

.

 

[grasfulls]

http://www.sjsu.edu/faculty/selvaduray/page/papers/mate234/yingzheng.pdf

http://answers.google.com/answers/threadview/id/397640.html

http://www.copper.org/applications/electrical/building/wire_systems.html

Thanks for the links. I will take some time to read each. I do note within the second link/article this statement
"Certainly, copper and aluminum are much better conductors than their corresponding
oxides at any temperature linemen will encounter."

From that statement alone I imagine minimizing oxidation is important. I do wonder if, like in a j-box, the surface areas in contact with one another inhibit or even prevent oxidation, making it a good idea to pretwist, the more twists and tightness the better (barring cracking or stressing the wire itself).

 

[grasfulls]

101016-1018 EDT

If you search with the appropriate words you can find some useful information.

Generally copper oxide is considered a good conductor. In contrast aluminum oxide is a very poor conductor. Anodized aluminum is a thick layer of aluminum oxide and a very good insulator.

Copper oxide with appropriate impurities is a rectifier. Good conduction in one direction and poor in the other. But reverse breakdown voltage is very poor. Do a search for -- copper oxide rectifier -- one result is http://www.jmargolin.com/history/trans.htm
An interesting discussion for a number of historical reasons.

.

Thanks, I will try other keywords. I never would have imagined using "rectifier".

 

[grasfulls]

I have always understood copper oxide is not much different from copper. Aluminum oxide is a horrible conductor and the reason anti oxidation compounds were used on old alloys. Newer alloys don't require compounds so I would assume in normal environment oxidation is not much of a problem.

I am leaning this way as well... I asked because a landscape lighting person asked me and I had no idea.

 

[broadgage]

Copper oxide is a much worse conductor than copper, however with proper materials and workmanship this should not be a problem.
When conductors are jointed by screw terminals, wire nuts or the like, the wires are forced into such tight contact that no oxide film can form on the mating surfaces.
Prior to installation, the wire is protected from oxidation by the insulation, and with normal good workmanship reliable contact is assured.
If however old wire is to be re-terminated, and it no longer has a bright copper surface, then extra care is required to prevent the oxide forming a high resistance joint.

Bare wire for overhead lines is bright and clean if fairly new, but can be heavily oxidised if exposed to the weather for decades, special crimp terminals that are claimed to "bite" through the oxide film are used in such cases.
Despite this, joints in old overhead conductors are more prone to failure than similar joints in new.

 

[zog]

As those materials most commonly used in wiring oxidize, how is their conductive property impacted?

I recently had someone ask me if the "patina" effect of copper reduces its conductive properties. I have no idea. I was told long ago, when working in corrosive environments, such as sewage treatment, to use things with silver coated contacts as silver oxidizes it becomes a better conductor. I must say, I just took the direction at face value and never researched it.

I have been looking around the net and in the forums, but have not found anything definitive. I apologize if this is already in here someplace.

Copper oxide is a horrible conductor, silver oxide is an excellent conductor, which is why many oints in power systems, like breaker contacts are silver plated. It is very important to be sure this plating is intact.

However, is a surphur rich atmosphere, as found in sewage treatment plants, silver can create some unique problems.

 

[ELA]

When conductors are jointed by screw terminals, wire nuts or the like, the wires are forced into such tight contact that no oxide film can form on the mating surfaces.

You often hear that a "gas tight connection" is preferred to prevent oxidation.

I have recently been looking into "UltraSonic Wire Welding" as a method for making electrical connections. This would be for a device that is sensitive to the elevated temperatures of soldering. This method does not add much heat during the process.

I find it quite interesting. I do not have any direct experience with this method.

Anyone else had good/bad experiences with such connections?

Here is a brief video of a machine operating to bind two conductors.

http://www.youtube.com/watch?v=XXclBqO_a1M