Three types of contacts

Folks

I've got three types of contacts here on a batch of telecoms equipment that's landed with me today.

I may be wrong and I'm happy to take some advice but I think that the dark contacts (corroded) on the right are silver, as they polish up. I think the grey contacts on the left may be palladium. The ones in the middle are pretty self explanantory 8)

Do you guys concur, or have any alternate suggestions?

I processed a lot of contacts from relays and motorized contacts that were part of the 1950's to 1960's phone system that served a 5 story commercial office building. Most of the equipment was Western Electric. The majority of the contacts were palladium and some were silver.

Don't assume nothing till you have tested all of them.

I won't assume chaps. I'm still getting to grips with recognising Palladium visually as opposed to silver.

I know silver tarnishes, does Palladium?

My guess is that a silver palladium alloy could tarnish. If a pure palladium contact point would tarnish I don't know but I don't think it would.

A simple test would be to put a contact point in a drop of nitric and watch the color of the solution.

Blue - Copper (and silver)
Green - Copper and palladium (and silver)
Red - Palladium (and silver)

Silver is easily detected with some salt.

Göran

Thanks Goran- - one drop right?

I'll try that.

Ok tried it on a couple of samples- what happens if it fizzes green then settles to blue?

spaceships said:

Ok tried it on a couple of samples- what happens if it fizzes green then settles to blue?

Click to expand...

That it digested the palladium plating under the drop, and then the underlying copper knocked it back out of solution?

/noobguess

Sounds like a silver copper solution. My guess is that the NOx is coloring the drop with some red until the gas dissipated.
... unless you have exposed copper that cements the palladium and silver. I hope you removed the contact point from the base metals first.
If there is any exposed copper or cemented metals should be obvious from looking at the result.

I suggest that you do a few acquaintance experiments with known alloys, pure copper for example to see if it is fizzing green too.

Göran

I like this game. Goran gets to teach me and I'm a willing study when I'm out of my "zone." 8) 8)

ROFLMAO :lol:

Palladium should be possible to test for by dissolving a contact point, dropping the silver with salt or HCl and then testing the remaining solution with stannous.

Göran

Cheers. Thanks I'll have a go at this in the next couple of days.

Jon

Or just test for palladium with DMG.

Dave

Guess I have to find my few gramms of contact points due to this inspiration

Jon

The points on the left are most likely silver - or at best an alloy of silver & PGMs which (if alloyed) could be ether Pd &/or Pt "maybe" even Ir

The ones in the center are again as above only gold plated

The ones on the left you & I already talked about privately back in mid September - these are the ones where you will find that at least "some" of them are pure Pd & some of them are Ag --- its even possible they could be all Pd --- or there is a chance (but I doubt it) that they are Ir --- these will not be an alloy

As I mentioned in our PM discussion --- a couple years ago I picked up a literal ton of these points (point on the right) from a scrap yard - that was a ton with the relays still mounted on there mounting rails

There is no way to identify them (the Ag from the Pd) just by looking them & you don't need to anyway (in order to separate the Ag ones from the Pd ones for processing)

Why ? --- because first off they are ether silver - or they are Pd - & the acid (nitric) will separate them for you --- now I know everyone is going to say - "wait a minute Kurt if you put Ag points in nitric along with Pd points isn't it just going to dissolve both the Ag & the Pd"

The answer to that is both yes & no --- but "by far" more no then yes - if you do it right - you can dissolve all of the copper/brass & Ag away leaving behind (un-dissolved) just the Pd points - only a very small "trace" amount of Pd will going into solution

How can that be ? --- it has to do with the reactive series & the "potential" of the acid (nitric) to work on the metals its trying to dissolve --- it is true that nitric will dissolve Pd - but its "potential" to do so is VERY low (slight) compared to nitric's "potential" to dissolve copper/brass &/or Ag

Pd is "much less reactive" to the nitric then the copper/brass & Ag --- it takes a "great deal" more time - along with heat - to dissolve pure Pd with nitric compared to that of copper/brass &/or Ag

So you can use "that fact" to make the separation of the "pure" Pd points from the Ag points with the nitric - here is what you do (I will be providing pics along with this which will take several postings)

First you want to harvest the points to be processed - then you want to factor "about" how much nitric you are going to need to dissolve the Cu/brass & Ag (at this point - when you weigh what you harvested - just consider it all cu/brass & Ag) --- lets say you figure you need 1 liter 68% nitric & 1 liter D-water (this is just an example) - then --------

(1) put all the points in your reaction vessel

(2) put ALL the D-water in - but only 400 - 500 ml of the nitric --- DO NOT use any heat at any point in this process - just let the nitric do its work on its own

Note; - you are using a 2 parts H2O to 1 part nitric solution here as opposed to the normal 50/50 - this is to help keep the reactive potential down thereby helping to prevent dissolving of the Pd

Then you can do one of 2 things --- this first treatment of nitric is going to dissolve both Cu/brass & Ag - so you can ether --------

(A) when the nitric slows to a crawl in its reacting with the metals add more nitric - 100 - 150 ml & continue to do so each time the reaction slows to a crawl until all the nitric has been added &/or all cu/brass & Ag are dissolved --- or

(B) because this first treatment is only going to dissolve about half of the Cu/brass (along with "some" Ag) you can let it run to completion (No heat) any Ag that went into solution will then cement out on the remaining Cu/brass - let it do so & when it test negative for Ag - decant to you Cu waste

Then (if you go with B above) go back to following step 2 only this time (because you have only used about half your acid so far) start with 400 ml H2O & 200 ml nitric (68%) & now dilute your remaining nitric (about 300 ml) 50/50 & proceed with additions of 150 - 200 ml (because its already diluted) as in A above - because this time around you will not have enough Cu/brass to cement all the Ag back out - so you need to dissolve all Cu/brass & Ag - then cement you Ag with additional Cu

The point is that IF you control the potential of the nitric to react with the Pd (because it is "pure" Pd) you can dissolve all the Cu/brass & Ag away leaving behind nothing but the Pd points - having only a very, very small "trace" amount of the Pd dissolve into solution

When I processed the ton I got from the scrap yard I ended up with something like (+/- a bit) 2 ozt of "un-dissolved" Pd points using the above procedure

Pics coming up in the next few posts

Kurt

I took these pics back in September when Jon & I discussed this by PM - I actually went back to the scrap yard & dug around to come up with the material to make this demonstration for him

These are the relays still on there mounting rails & after removing them from the mounting rail

My thanks Kurt

Really appreciate all that. :idea:

Jon

Once the relays are removed from the mounting rail you need to harvest the points - the best way to do this is to use a tile saw but you need to set the tile saw up in a shielded surrounding & it needs to be padded because some of them are going to want to fly a bit & without the padding they can bounce out of the shielded surround - with the padding they have less bounce & stay in the surrounding shield --- I used the top sheet metal cover from a "large" microwave to make my shield (screwed down to a piece of plywood)

You will notice there is an iron shield in front of the brass contact point reeds (bus bars) & then there is the iron frame at the back (between the relay reeds & the coil)

The diamond tile saw blade will cut both the iron & the brass - so you set the relay on the table & feed it into the blade (ware gloves & eye shield) because of the curve of the blade the bottom of the relay (on the table) will hit the iron frame (between reeds & coil) first - when it does you will see sparks - that means the bottom point have been cut of - now pivot (rotate) the relay up to feed the top into the blade until it hits the iron frame as well & all the points should now be cut off

Doing it this way is a "huge" time saver (as opposed to hand nip each one) & reduces the amount of Cu/brass you need to dissolve (as opposed to disassembling the whole reeds from the coil body & then nipping them &/or having to dissolve the whole reeds)

use a magnet to remove the iron cut of from the front shield