How does silver tarnish?

Don't know, but that black doesn't affect performance at all, and there is no reason to polish it at all...

snipped-for-privacy@netzero.com hath wroth:

Nope. The cooling fan sucks in all kinds of airborne chemicals that attack the silver. Fortunately, the insides of the cavities are not in the air stream. If you look carefully, your unspecified model spectrum analyzer probably has an air pressure equalization "air filter" somewhere on the cavity. The idea is to equalize the air pressure between the inside and outside of the cavity, without allowing large molecules into the cavity. It's the same with hard disk drives and some "waterproof" sealed devices (i.e. GPS, marine electronics, military electroncis, etc).

For the ultimate in tarnish and corrosion, I inherited a few pieces of test equipment that were formerly located on a mountain top radio site. Until about 3 years ago, the site was powered by a full time diesel generator. The diesel exhaust was sucked in by the cooling fans and over the years, neatly coated everything with a mixture of sulfuric acid, water, soot, mold, and oil. My first impression was that someone had painted the insides with black paint. This was the first time I had ever washed the insides of an HP 8640B generator, but it worked. However, the silver parts (cavity) remained tarnished. I used Brasso, which worked well enough. Unfortunately, many of the copper, brass and steel parts were corroded to varying degrees. I had to replace some of the stainless hardware. Strangely, the aluminum parts held up quite well.

Aluminum oxidizes quickly and the oxide is a tough, protective crust against further corrosion.

The only thing I ever heard concerning silver tarnish is that it is caused by exposure to sulfur compounds - - maybe gasses given off by rubber in the vicinity, with the effects accumulating over the years.

Back when I was doing chemistry, we were told that silver tarnish is a layer of silver sulphide (Ag2S) generated by the trace amounts of H2S normally present in the air.

As with with many of the things we were told, this may be an over- simplification - a little googling brought up this

The fourth project description describes silver tarnish as a mixture of silver oxides, sulphides, and sulphates, which is the sort of thing you can find out by X-ray fluorescence spectroscopy and other expensive techniques which have become more accessible since I was an undergraduate.

-- Bill Sloman, Nijmegen

I guess I have to find out how brass instruments (trumpets, etc) are silvered and stay silver. I'm guessing lacquer.

Didn't you know? Those silvery-colored instruments aren't silver-plated brass, they're solid silver! That's why they cost 5-7 times as much as the brass-colored ones.

Hope This Helps! Rich

Or nickel.

Heh. My mom has a "rusty" (which being at least partly nickel, is a pastel green sort of rust) flute, the case of which she has labelled "Frankenflute!". She puts it on display in her music office every october. ;-)

Tim

-- Deep Fryer: A very philos> >

They could be rhodium-plated.

Rhodium doesn't tarnish and is harder than silver, if not a conductive, which is why this isn't an option for microwave components, where the the surface conductivity is all-important due to the skin effect.

-- Bill Sloman, Nijmegen

Tarnish doesn't actually hurt the Q of silver-plated microwave cavities until it gets bad enough to cause surface roughening.

I have on my desk the first electronic thing I ever made for hire, which is a 14-GHz microwave absorption cavity. It's made of copper, and electroless copper plated, which makes the surface very smooth. The outside is pretty nasty looking now--I built it in 1981--but the inside is still perfect.

Cheers,

Phil Hobbs

"If not a conductive" ?? What is that supposed to mean? Rhodium IS conductive.

Two other metals that take hundreds of years to exhibit measurable amounts of tarnish (oxidation) are: Gold & Platinum.

He meant to type "as," you as.

It should have been "not as conductive". I do try to check for typo's but I miss some.

Gold looks yellow rather than silver, and platinum is more expensive than rhodium, not to mention softer. And you missed palladium

-- Bill Sloman, Nijmegen

snipped-for-privacy@ieee.org snipped-for-privacy@ieee.org posted to sci.electronics.design:

Rhodium plating, while possible, is not used for musical instruments. It results is a rather visible color difference.