Date: Sat, 7 Jul 2018 12:58:26 -0400
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
To: amps@contesting.com
Subject: Re: [Amps] Use Caution when using Silicon Dielectric Greases
<I didn't find any reference ti Silicon Carbide in Tom's write-up.
There is no carbon involved and unless it's carbon contacts, decomposing
Silicone dioxide does not form silicon carbide.? The formation of
Silicon Carbide "normally" requires a high temperature and always the
presence of carbon.? Typical formation is decomposing HSiCl3 on red hot
carbon (roughly around 1100C IIRC) The normal result with Silicone
greases being decomposed by an electric arc is Silicon Dioxide (SiO2)
which is as abrasive as Silicon Carbide. It just doesn't last quite as
long.?? Automotive greases (hydrocarbon based) will carbonize in arcs,
or at high temperatures.
I agree with almost everything Tom said except the way he uses the term,
Viscosity. Having worked in the Silicone and Silicon industry since
1961, I have seen Silicones with viscositys ranging from 5 to well over
6000 Cs.? 5 is used for dry fly treatment for all you fly fishermen.
6000 is like a very thick taffy
5 is essentially like alcohol except it forms a water repellent coating
causing the "dry fly" to float.? I don't know what something with a
viscosity of 6000 would be used for, although there are several types of
Silicone rubber with some used at fairly high temperatures. At any rate,
I'd not call a grease, low viscosity. It's maybe a little less resilient
than what is used in a standard grease gun.
His uses do not go back far enough, as I said earlier, DC4 Compound
(dielectric grease) was developed to use in the spark plug seals on B17s
in WWII by Dow Corning. Its use prevented arcing at very high altitudes.
Other compounds including Silastic RTVs were developed from that.? DC
did not patent the compound, but rather kept the constituents and
process proprietary.? This kept them ahead of the game for over 50 years
until a competitor reverse engineered the compound. Patent life was far
shorter back then.? Once the product was reverse engineered, silicones
became a commodity instead of a specialty product which made for a
drastic reduction in price.
Oh! Depending on what he means by high power, but Flooded UHF connectors
will work well beyond the legal limit.? OTOH I've been told it is not
normally a good idea to flood all the connectors in a coax run.
I do have one caveat when using Silicone dielectric grease. Even
fingerprints with a filim of Silicone grease on them will prevent
adhesives and epoxies from sticking to the.? Electrical tape will not
even stick to rubber like cable jackets where those fingerprints exist.
73, Roger (K8RI)
##### From his site I posted....... on the paragraph entitled.... Switches,
Movable Contacts, and Relays
Contact arcs have the ability to alter composition of greases. Silicone
greases can be converted by arcs to silicone carbide, which is highly abrasive.
For this reason, silicone grease should be avoided when contacts are "hot
switched" and have any chance of arcing.
## I downloaded the DC-4 pdf..and also the DC-5 pdf. Sez NOT to use
DC-4 anywhere near silicone rubber, or the DC-4 will destroy it asap. I
use a LOT of silicone rubber. Type N and also DINs have and use silicone
rubber O rings etc, so no way do you want to flood connectors with anything,
esp stuff like DC-4 that eats silicone rubber. DC-4 is white. DC-5
is grey.
## Im gonna try some of the conducto lube goop for an experiment, on the
roller coil....... since its ground up pure silver.. in mineral oil. Supposed
to be good up to 410 F. I will report results.
## I found better dielectric grease than either DC-4 or DC-5. I will use
the dielectric grease, a tiny bit, for stuff like the threads on 7-16 DIN
connectors..and also a tiny bit on the 7-16 Din center pin.
## Penetrox and noalox is just ground up zinc in grease. Good for yagis and
al tubing. Dont use it on roller coils. Copper kote is another one I would
not use. Its ground up copper powder in grease. We used it on bolting
mating buss bars together at the telco I worked at.
Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|