This makes me curious about aluminum, chromium, and stainless steel (which as far as I know is just steel with a lot of chromium in it). I know that technically aluminum corrodes instantly and then maintains a stable corroded state. Will it work as a conductor that way? I have no idea whether chromium is like aluminum, corroding and becoming stable, or if it resists corroding to begin with.
And yep, they're corrosion resistant because the chromium instantly forms an oxide layer that protects the underlying metal.
Stainless steels are expensive partly because they're difficult to work with, generally having poorer machinability than regular carbon steels, and tend to work harden more rapidly too.
resistivity $/kg
Cu 1.7e-8 10.3
Au 2.4e-8 63600
Ag 1.6e-8 827
Fe 1.0e-7 ? (cheap)
Al 2.8e-8 3.23
Gold itself looks about 50% worse than copper while being more than six thousand times as expensive, so for gold to be used, resistance to corrosion must be important.
Silver is the best metal listed in the table, and slightly better than copper, so I assume the cost difference explains why we have lots and lots of copper wiring and not so much silver wiring.
Aluminum is a bit (17%) worse than gold for resistivity, but aluminum is cheap. Why use gold? I can imagine a few reasons:
- This table gives values at 20 centigrade, but things change at a more relevant temperature.
- There's some kind of important threshold around 2.5e-8 ohm-meters, so that gold is on the right side of usability and aluminum just misses it.
- Aluminum's corrosion resistance is different in nature from gold's, and the difference matters.
Are any of those true?
from google, copy pasta: "Gold plating is the deposit of a thin layer of gold metal on a substrate, typically in the 0.25 – 5 micron range (0.00001”-0.0002”)."
Not a lot of gold is used in plating the business ends of an RCA cable or TRS connector.
Al, yes, more copy pasta: "Aluminum has a very high affinity to oxygen. When a new aluminum surface is exposed in the presence of air or any other oxidizing agent, it quickly develops a thin, hard film of aluminum oxide (or hydrated oxide in non-stagnant water). This aluminum oxidation is precisely what makes aluminum so corrosion-resistant."
But I doubt the thin, hard film of aluminum oxide conducts as well as gold. Nope.[1]
Gold plated PCBs are also completely standard (google ENIG). In this case the plating is even thinner and just serves to ensure solderability and avoid corrosion. It's so thin that it immediately dissolves in the solder during the solder reflow process; it's just there to allow that process to happen properly, and to avoid corrosion in non-soldered areas. Almost every modern high tech PCB
Gold containing solder, on the other hand, is nonsense.
Well, actually™, it turns out gold-tin alloys (which is what this probably is) get used a lot for solder, particularly in optoelectronic and microelectronic device packaging. You may already know this, but I didn't until tonight, when I thought, "Hey, is this really a thing?" and looked it up. :)
(I can't see anything that suggests it helps with "clearer sound," of course. I also searched for "audio-grade solder" out of curiosity and it seems there are some companies that market solder that way, but they seem to generally be (a) silver alloy, not gold, and (b) regarded rather skeptically.)
Yep. Occasionally I read comments to the effect of "sure, gold is technically going to resist corrosion much better, but that's never going to be an issue in practice," to which I can only think: you didn't grow up in Florida without central air conditioning. :)
I admit that it's a pet peeve of mine that "gold audio cables" have become an anti-audiophile meme. There are absolutely a lot of, ah, dubious cables out there, but to my knowledge none of them are using gold for the wire. There are only audio cables with gold-plated connectors, and it's not like they're $300+ specialty items; they're cheap and common.
They don't know either. Audiophiles are by and large the dumbest consumers on the planet, willing to pay for huge sums of money to grifters and lying companies for imaginary gains that are either not measurable or well below the threshold any human could conceivably hear a difference. And they are so deep in that trap that they get angry when they are called out on their bullshit (see MQA for example).
Someone should make a YouTube channel with this kind of content, adding laugh tracks to every way they try to close to sale