any good conductor metals not prone to oxidation? - Page 1
Forum section: electronics / general

author: engineheat
author_rank: Frequent Contributor
timestamp: September 05, 2019, 02:29:14 pm
content: For electrical contact, repeated arcing can form a layer of oxides on the surface with affects performance. This may happen to a mechanical switch for example.Are there any way to eliminate this issue? Will using silver contacts eliminate this issue?Thanks

author: windsmurf
author_rank: Frequent Contributor
timestamp: September 05, 2019, 03:57:01 pm
content: Gold.

author: Benta
author_rank: Super Contributor
timestamp: September 05, 2019, 04:43:02 pm
content: Quote from: windsmurf on September 05, 2019, 03:57:01 pmNope. Gold plating will burn away quickly. Relay switches are often made with tungsten/wolfram alloys.For small-signal applications, mercury wetting was also used, but environmentally problematic.

author: Gyro
author_rank: Super Contributor
timestamp: September 05, 2019, 05:34:00 pm
content: Quote from: engineheat on September 05, 2019, 02:29:14 pmYou're getting a bit tangled up here. Yes, non-Noble contact materials do build up oxides, but they are typically used in applications where there is sufficient voltage across the closing contacts to break this down. Various Silver alloys such as Silver Cadmium and yes, Tungsten are used for heavily stressed contacts but they haveminumumcontact ratings as well as maximum, ie. they are not suitable for dry switching.Gold, Platinum, Paladium, Ruthenium plating and also Mercury wetted contacts are suitable for low current switching but will not tolerate arcing.Note that even Mercury wetted relays (which have very high contact life) will be very easily damaged by arcing and need appropriate snubbers to hit their maximum ratings... to get true arc resistant switching you need liquid Mercury displacement relays, they will happily tolerate arcing almost indefinitely, within their duty cycle ratings.The important thing for all relay contacts is to minimize or eliminate arcing by a combination of correct contact material, conservative rating and use of appropriate snubber networks.To get arelevantanswer to your question, you need to specify your switching requirements in detail [EDIT: Including Voltage, Current, AC/DC and nature of the load (inductive / resistive / lighting - incl. type / Motor etc).]

author: bob91343
author_rank: Super Contributor
timestamp: September 05, 2019, 07:11:51 pm
content: Gold will erode, so use solid gold as long as it lasts, then replace it. It will, in general, not oxidize. Gold plating, as mentioned above, will eventually be melted away, leaving base metal.Silver oxidizes readily. The other metals have varying degrees of susceptibility to oxidation. Read the readily available literature on the subject. Switches have been in production for well over a century and their design has nearly the status of a commodity.Switch ratings are based on current, voltage, circuit configuration, and number of operations. Select a switch that meets your requirements; the information you need is in the data sheet.There are other parameters as well, such as contact resistance, bounce, capacitance, etc.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 05, 2019, 10:33:43 pm
content: Quote from: Benta on September 05, 2019, 04:43:02 pmHe didn't say gold-plated. He said gold.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 05, 2019, 10:45:42 pm
content: But more seriously, I'd say a platinum-iridium alloy.It's expensive shit though.

author: coppice
author_rank: Super Contributor
timestamp: September 05, 2019, 10:49:09 pm
content: The traditional approach to avoiding corroded and eroded metal contacts is to use a liquid metal - mercury.

author: notsob
author_rank: Frequent Contributor
timestamp: September 06, 2019, 12:45:13 am
content: Another consideration is arc control. Have a look at mike's video on a circuit breaker he tested.link:

author: MyHeadHz
author_rank: Regular Contributor
timestamp: September 06, 2019, 03:33:01 am
content: Quote from: engineheat on September 05, 2019, 02:29:14 pmYou can reduce it with methods mentioned by others above. Soft-starting is another option, though it has drawbacks. If you want to eliminate it completely, you need to avoid arcing and contact completely. You can do this with various ways, such as magnetic coupling. There are limitations and drawbacks to contact-less solutions, and they are generally only used when there is no other option... or as a marketing gimmick.As others have pointed out, more details need to be known to find out what is best for your situation. The best overall solutions are usually basic common ones like replaceable silver contacts.

author: ggchab
author_rank: Frequent Contributor
timestamp: September 06, 2019, 09:26:50 am
content: I am wondering if the circuit breaker is not supposed to be mounted vertically ? The hot air goes up and drives faster the arc into the copper plates block.

author: richard.cs
author_rank: Super Contributor
timestamp: September 06, 2019, 09:39:12 am
content: Quote from: ggchab on September 06, 2019, 09:26:50 amUsually the arc is deflected into the combs magnetically, the field coming from either a permanent magnet or more often from the fault current itself.