Electrically conductive stainless steel at 700º?
Electrically conductive stainless steel at 700º?
(OP)
I'm seeking some advice since this is completely out of my realm of experience. Here's a quick background and then I'll get right to the problem. Working on a test fixture for measuring materials from RT to 700ºC. The fixture inside a small furnace is made from 316L and alumina, the alumina to act as an electrical insulator and the 316L since it's fairly inexpensive, easy to machine, easy to weld, and resistant to high temperature. Any wiring inside of the furnace chamber is also 316L with alumina fish spine beads. The contacts we're using are an unknown type of stainless steel, just labeled as "stainless steel". Initially, everything was working well but after a dozen or so tests the contacts have developed some scale and ceased to function as a decent electrical conductor. The contacts are bars (~100mm x 10mm x 1mm) which pivot at one end and have a fine tip (almost like a stylus on a turntable) on the other. I'm looking for a material that can be used which wouldn't develop a similar problem under the test conditions, cycling from room temp to 700º several times a day. I'd rather avoid having to cap the tip of contact with platinum or something similar and I'm hopeful some type of stainless steel would be suitable for this application. I appreciate any advice or information you can provide. Thank you in advance.





RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?
What are the contacts making contact with? How much current do you want the contacts to pass?
Without evactuating the chamber, or purging with inert gas, there is no way to prevent the build up of scale on typical stainless steels at that temperature. Nichrome might oxidize more slowly.
What might work, is to use fine-grain graphite contacts, though they will slowly oxidize in air at that temperature (but the oxide is CO2, which is a gas, and won't stick around on the surface to impede electrical conduction). You would get longer life from them with a nitrogen or argon purged atmosphere.
Gold plating on steel or stainless will eventually peel off, as the oxygen in air will still get past the plating film to oxidize the metal underneath.
RE: Electrically conductive stainless steel at 700º?
The contacts will generally be in contact with Ag or Pt pads. The current will be quite low but it will vary depending on the material under test. It's characterizing various dielectric insulators by measuring resistance across a temperature range. Voltage would be anywhere from 0.1 to 100V, current generally down in the nA or µA range. Resistance measurements can be around 10^11 ohms down to 10^2 ohm (meter has low limit of 200 ohm) depending on the temperature.
Unfortunately, the furnace will need to be operated without nitrogen or argon. We have plenty of both but it would invalidate the data we're after.
Right now I'm trying a few different formulations with Au/glass and Pt/glass to see what sticks to the random stainless probes. I'll look into the fine-grain graphite contacts as I'm completely unfamiliar with it.
Thank you for the help, I really appreciate it.
RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?
TTFN (ta ta for now)
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RE: Electrically conductive stainless steel at 700º?
But coating the W with Au would be a good option.
The problem with your test stand is that you are at the mercy of the contact resistance, and unless the metals involved are soft, oxidation resistant, and good conductors you can easily have more resistance is just the contact than in the entire rest of the circuit.
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RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?
RE: Electrically conductive stainless steel at 700º?