[Milsurplus] [ARC5] roller inductors

[Bill Carns]

:-)  Ah….Now we are into it, and taking on the subtleties – are we?  Hmmmm….  Re the statement: The myth of silver sulfide being a conductor seems to be promulgated ad uendum by the chemically inert / unsophisticated.  Who is inert ??  Not me boy.

 

Yes, to be technically correct, Silver Sulfide is a “semiconductor” meaning it has typically lower conductivity than the usual conductors such as the commonly used copper or silver.. . . . . But that is a relative term and the use of the word “semiconductor” a perhaps not useful here generalization.

 

Silver Sulfide actually is not a “True” semiconductor in the physical sense of the word. A true semiconductor, particularly an intrinsic one, can be a very poor conductor.  This is true of the very low conductivity (Rhos) of intrinsic Germanium or Silicon – those elements that are usually thought of when you say the word “Semiconductor”  - in the physical sense. The extrinsic conductivity of any true semiconductor can be - of course -  put anywhere you want it by selecting the doping level desired.

 

To be more specific, the actual conductivity of Silver Sulfide is substantially more conductive than intrinsic, or even lightly normally doped Silicon or Germanium, and Silver Sulfide is certainly not an insulator - nor does it exhibit unidirectional conductivity characteristics as in a semiconductor junction device.  Silver Sulfide is a good conductor compared to what one would call a “normal” semiconductor. You should note, in fact, Silver Sulfide exhibits both electronic and Ionic conduction and both components are present under almost all normal environmental condition. This dual mode of conduction - in itself - distinguishes Silver Sulfide from the true physical definition of a “Semiconductor” material.

 

So, to try and negate my observation that Silver Sulfide is conductive, by saying that it is really a semiconductor is to jump into relativity land. I repeat my statement, that Silver Sulfide is conductive and therefore – NOT AN INSULTOR. It does, however, raise the contact resistance until molested (see below - and as you pointed out).

 

Some other notes:

 

I quote from a report by Tyco Electronics on the use of Silver in mechanically connected systems where tarnish can occur: “Silver tarnish films: Silver tarnish films can be many colors, anywhere from yellow to tan to blue to black. . . .A silver plated contact surface can appear discolored and still function very well if used correctly in the application. Tarnish films generated on silver finished surfaces exposed to most connector field applications are predominantly covalently bonded semiconducting α silver sulfide (Ag2S) and to a lesser extent, small amounts of insulating and harder to displace silver chloride (AgCl)

 

Notice that nowhere does it refer to Silver Oxide - which rarely forms (or forms extremely slowly) under most common environmental conditions.

 

After spending a career working in the semiconductor industry and using and designing with various metallic and semiconductor systems, I can assure you that Silver Sulfide is “relatively” conductive.  Is it as good a conductor as Silver or Copper ?  -  -  No. But, Silver Sulfide is a very soft film and typically running, or particularly wiping, contacts will overcome the increase in contact resistance that ensues when a Silver conductor or contact area is exposed to Sulphur and forms a Sulfide. Typically it will not, particularly in a running contact system, interfere with RF conduction.


Re your comments about the tarnish remover and how to handle, or “Not handle”, polishing the roller contact area, I could not agree more.

 

Just as an aside, there is a very sad story about an engineer at the National Bureau of standards that saw that some of their calibration standards were exhibiting contact resistance problems. They had Silver plated contacts. He got out his TarnX – seriously – and polished all the contacts. He then measured the standards again and found the problems gone. However, after a very short period of time, the contacts became completely unusable and when examined under a microscope, they were observed to be uniformly etched and completely unusable.  It was “New Standards” time.

 

Bill

 

 

From: Brian [mailto:brianclarke01 at optusnet.com.au] 
Sent: Monday, January 25, 2016 11:16 PM
To: Bill Carns <wcarns at austin.rr.com>; 'Dennis Monticelli' <dennis.monticelli at gmail.com>; 'Joe Munson' <prc74b at fuse.net>
Cc: 'ARC-5 List' <arc5 at mailman.qth.net>; 'Milsurplus' <Milsurplus at mailman.qth.net>
Subject: Re: [ARC5] [Milsurplus] roller inductors

 

Please look up the electro-chemistry of silver. In particular, check the conductivity of silver sulphide - it is a semi-conductor. The myth of silver sulphide being a conductor seems to be promulgated ad uendum by the chemically inert / unsophisticated.  The removal of tetra-ethyl lead from petrol / gasoline has exacerbated the effect of sulphur oxides in the air where there are motor vehicles. Pure gasoline has no sulphur – the refiners add various compounds to promote their vision of economic glory. Silver oxide is almost as good a conductor as silver, but is of a similar colour. Only an analytical metallurgist or chemist can tell you what your specific tarnish is. The point I make is that the amount and kind of tarnish you get will depend on what’s in the air where your equipment resides.

 

If your preferred ‘tarnish remover’ can convert silver sulphide back to pure silver and carry off the sulphur, what a lucky person you will be. So will your bank manager. Most ‘tarnish removers’ take away the silver sulphide and leave a larger surface area on the remaining silver – increased porosity – thus increasing susceptibility to air-borne tarnishers. If the silver is a 2 um to 20 um plating, then the tarnish remover may remove the silver completely and irreversibly. Silver sulphide is not the only tarnishing compound. However, proper design of silver-to-silver contacts can wipe away enough silver sulphide and other contaminants to redeem appropriate conductivity. Leaving an oil or grease layer on a roller inductor may protect the untouched underlying silver from air-borne attack. But as soon as you traverse the roller over the wound inductor, you reveal the underlying silver, allowing it to tarnish. This effect can be accelerated by traversing when high current is flowing, giving rise to sparking and formation of contamination. So, tune up at very low power!

 

If all you want is a pretty-pretty roller inductor, then by all means polish it till it reflects and then coat it in a transparent varnish – but don’t expect it to work. If, on the other hand, you want your roller inductor to work, then attach a milli-Ohm meter between the roller support axle and one end of the inductor, traverse through the whole range of the inductor – perhaps a few times – observing in detail the resistance vs traverse position. Deal only with places on the inductor or the roller where resistance is unacceptable.

 

There is a faint possibility you will be pleasantly surprised.

 

73 de Brian, VK2GCE.

 

On Tuesday, January 26, 2016 1:14 PM, Bill said:

 

It should be noted regarding these instructions to “Clean off the oxide” with Deoxit on the roller inductor, that silver tarnish is NOT an oxide, but a Sulfide.  Silver Sulfide is CONDUCTIVE and is not the reason that the contacts are bad somewhere.  Using any cleaner may also remove dirt and other contamination and Deoxit is as good as several others at doing this.  I would use the DL100 Deoxit that does not have a small percent lubricant as does the D5 Deoxit.  It is best to not leave any lubricant or anything at all on the contact. 

 

Many use just lab grade Isopropyl Alcohol for a cleaner.  I use both and they both seem to work equally well. 

 

The following post in the thread after the Deoxit advice that suggest that the problem could be, and probably is, related to the follower spring contact on the contact bar is worth pursuing.

 

While polishing the heck out of those roller contact areas may make you feel good, and it sure looks nice, it is a fool’s errand for the following reason.  There is Sulphur in the atmosphere..  Some environments have it more than others.  That is why your mother’s Silver tarnishes. When the Silver Sulfide forms, it uses up (eats up) a monolayer or two of Silver. The Silver Sulfide is more or less self-limiting.  Once a layer of the Sulfide forms, it way slows down the process.  When you shine it up, you remove all the Sulfide – which includes that Silver Plate monolayer – and the process starts all over again – at high speed…  and the Silver plating gets thinner and thinner.  This is not desirable.

 

So, clean all the contaminants off the roller coil with either Deoxit or Isopropyl and then look for the other causes that may be there as suggested.

 

By the way, do not even think about using Silver Polish..  That is a disaster – especially Tarnex or similar acidic processes.

 

Bill

 

 

 

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