@SrRochardBunson @ClaraListensprechen@universeodon.com @Ralph058 @sergio_101 Yes. Mica (the mineral, but carefully selected sheets of it) has been used for like 100 years to make capacitors. No capacitor dielectric can equal its performance, yet.
These fabulous characteristics of mica used to be very important in the design and manufacture of "analog" radios. Their importance is far less today for two main reasons. Modern radio designs don't depend on capacitor performance to maintain frequency stability. 1) We use digital methods to produce extremely precise frequencies locked to a quartz crystal reference. 2) Transmitters are solid state and run on low voltages so the high voltage capability of mica is unimportant. You can use any old material for coupling caps.
Mica still shines in certain niche applications like high powered radio transmitters like 250 kW and 500 kW shortwave transmitters. Those still use vacuum tubes that are supplied with 10,000 to 15,000 volts at 10, 20, 30 amps. Here you'll find mica caps. Some are the size of a basketball and weigh 25 pounds.
@arjun @SrRochardBunson @ClaraListensprechen@universeodon.com @Ralph058 @sergio_101 Yes, purity and the ability to split into large sheets makes it very valuable. Mica was used for so many things in the 19th and 20th centuries I'd imagine the really good stuff is gone.
It's an amazing mineral.
@arjun @shuttersparks @SrRochardBunson @ClaraListensprechen @sergio_101
This is from 1915, but it has some interesting stuff about the geology and mining of mica. https://pubs.usgs.gov/bul/0580f/report.pdf
I remember having a chunk about the size of my foot someplace. I don't think it was mine. I think it was somebody's doorstop.
@arjun @shuttersparks @SrRochardBunson @ClaraListensprechen @sergio_101
Now I remember where I saw it. An art gallery I frequented was about 20 miles from here.
@Ralph058 @arjun @SrRochardBunson @ClaraListensprechen@universeodon.com @sergio_101 Wow, great. I saved that PDF. It's a wealth of info.
Yeah, we were just talking about mica capacitors, but it also appeared in most vacuum tubes to support the element rods at top and bottom. The toaster I grew up with was made in 1951 and the nichrome heating elements were supported by slabs of mica.
@SrRochardBunson @ClaraListensprechen@universeodon.com @Ralph058 @sergio_101 In discussing mica I simply said "RF". What do I mean by that? What I mean is something called dielectric loss. Dielectrics are not perfect. Some are terrible but you can still use them in certain applications.
Mica has no dielectric soaking effect and extremely low dielectric loss. This matters a lot in a high powered transmitter like I mentioned. Try pushing 500,000 watts of RF power through anything but a mica capacitor of similar size and volume and it will simply vaporize or explode. But a mica cap will just cruise along for years doing this 24/7. And when the transmitter is decommissioned you can pick the capacitor up, install it in a new transmitter and do it again.
@shuttersparks @SrRochardBunson @ClaraListensprechen @Ralph058 @sergio_101 I live in Chennai, India. In my childhood days (a long time ago), I remember visiting a town in neighbouring Andhra Pradesh, called Nellore, which was noted for its mica mines. The owners of these mines were, as always, incredibly wealthy people. I was fascinated by how mica was organised as delicate sheets that you could tease apart. I wonder what has happened to these mines.