I'm under the impression silver tarnishes; that's to say, there's a layer of staining sitting on top of the surface of the silver, which is easily wiped away with lime juice.
I've been thinking copper corrodes; that's to say, there's a chemical reaction within the copper itself, which is destructive and similar to rust in iron.
Anybody have a more precise explanation? Just curious.

In article ,
John R Leddy wrote:

Java Jive;94051 Wrote:
On Sat, 13 Jun 2015 15:35:44 +0100, RJH wrote:
Unlike gold, silver corrodes quite easily. That's why your family
silver needs constant cleaning by the ball of your butler's thumb
wrapped in a suitable cloth.
I'm under the impression silver tarnishes; that's to say, there's a
layer of staining sitting on top of the surface of the silver, which is
easily wiped away with lime juice.
I've been thinking copper corrodes; that's to say, there's a chemical
reaction within the copper itself, which is destructive and similar to
rust in iron.
Anybody have a more precise explanation? Just curious.

As regards switch contacts, silver is certainly a better choice than
copper in terms of staying low resistance. But there may well be a better
'plating' than silver which is also cheaper than gold.

My old car has copper contacts on much of the switch gear. If it is
handling high current, seem to stay working. The same design switches
which are only controlling a relay so low current need frequent cleaning.
They are a design which is is easy to open up, and all the internal copper
parts are often green after a few years. ;-)

--
*The average person falls asleep in seven minutes *

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
wrote:
In article , John R Leddy
wrote:

Java Jive;94051 Wrote:
On Sat, 13 Jun 2015 15:35:44 +0100, RJH wrote:
Unlike gold, silver corrodes quite easily. That's why your family
silver needs constant cleaning by the ball of your butler's thumb
wrapped in a suitable cloth.
I'm under the impression silver tarnishes; that's to say, there's a
layer of staining sitting on top of the surface of the silver, which
is easily wiped away with lime juice. I've been thinking copper
corrodes; that's to say, there's a chemical reaction within the copper
itself, which is destructive and similar to rust in iron. Anybody have
a more precise explanation? Just curious.

As regards switch contacts, silver is certainly a better choice than
copper in terms of staying low resistance. But there may well be a
better 'plating' than silver which is also cheaper than gold.

IIRC There are a number of different treatings which can generate a 'hard'
(i.e. resistant to being scraped away) don't tarnish, etc. Even 'gold'
tends to be a series of layers of alloys, etc. By itelf, gold tends to wipe
off metal surfaces very easily. I think the coatings involve layers /
alloys using things like rhodium, tec.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Jim Lesurf wrote:

In article , Dave Plowman (News)
wrote:
In article , John R Leddy
wrote:

Java Jive;94051 Wrote:
On Sat, 13 Jun 2015 15:35:44 +0100, RJH wrote:
Unlike gold, silver corrodes quite easily. That's why your family
silver needs constant cleaning by the ball of your butler's thumb
wrapped in a suitable cloth.
I'm under the impression silver tarnishes; that's to say, there's a
layer of staining sitting on top of the surface of the silver, which
is easily wiped away with lime juice. I've been thinking copper
corrodes; that's to say, there's a chemical reaction within the copper
itself, which is destructive and similar to rust in iron. Anybody have
a more precise explanation? Just curious.

As regards switch contacts, silver is certainly a better choice than
copper in terms of staying low resistance. But there may well be a
better 'plating' than silver which is also cheaper than gold.

IIRC There are a number of different treatings which can generate a 'hard'
(i.e. resistant to being scraped away) don't tarnish, etc. Even 'gold'
tends to be a series of layers of alloys, etc. By itelf, gold tends to wipe
off metal surfaces very easily. I think the coatings involve layers /
alloys using things like rhodium, tec.

I recall on a particular project some years ago, a make of relay
that had been fine previously was suddenly giving great problems
- they appeared to be physically closing the contacts, but not
passing current.

After much head scratching the story emerged that the supplier's
moulds were wearing, but they didn't have time to replace them
and meet our large order schedule. Instead, to get the plastic
components down to size, they had been linished. After assembly
and test they were then individually bagged and shipped, and we
duly built them into our kit, tested as OK and delivered the
finished equipment.

The dust from linishing, trapped in the plastic bag, formed a
thin film over the contacts, and once they had opened under load
a few times (this was a 110 V dc system) the arcing was
sufficient to fuse a little of the material into an insulating
layer. Routine testing alone was sadly insufficient to trigger
this.

No butlers were required, but the simple solution was the service
engineer's thumb, which was sufficiently abrasive to clean the
contacts without damaging the material.

Chris
--
Chris J Dixon Nottingham UK


Plant amazing Acers.

In article , John R Leddy
wrote:

Java Jive;94051 Wrote:
On Sat, 13 Jun 2015 15:35:44 +0100, RJH wrote:
Unlike gold, silver corrodes quite easily. That's why your family
silver needs constant cleaning by the ball of your butler's thumb
wrapped in a suitable cloth.
I'm under the impression silver tarnishes; that's to say, there's a
layer of staining sitting on top of the surface of the silver, which is
easily wiped away with lime juice. I've been thinking copper corrodes;
that's to say, there's a chemical reaction within the copper itself,
which is destructive and similar to rust in iron. Anybody have a more
precise explanation? Just curious.

Both copper and sliver tarnish quickly when exposed to air, etc. However if
undisturbed the coating of tarnish does then to partly act as a barrier to
further tarnish. Only 'partly' though.

Most metals sold for general uses are impure or alloyed. So can suffer from
all kinds of degrading. Problem is that as the punter you often can't tell
what you're getting despite fancy labels.

So much for the way fancy cable makers can obsess about 'skin effect'.

All that said, I've never had problems with 'copper' *cables* deteriorating
in use, despite buying fairly basic types for which no fancy claims are
made or fancy prices charged. I've used much the same cables for over 30
years in some case.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html