High Temperature Dielectric Coating

[DanatAMFL]

I'm looking for some sort of dielectric coating that can be used at high temperatures. I'm working on trying to create a voltage point charge in a high temperature steam environment using a coated accupuncture needle. The goal is to be able to coat the needle thinly and uniformly, leaving only the very tip of the needle exposed and electrically conductive with the rest completely insulated. Therefore I'm looking for something that can be applied in extremely thin coatings (~.05mm thickness) through a dipping process, meaning it has to have a low enough viscosity (~200 cP) to achieve this thickness. The coating should be resistant to cracking once cured and be able to adhere to stainless steel accupuncture needles. The steam environment that the coating and needle will be subjected to will have temperatures ranging up to 500 deg C.

Do you have any suggestions?

So far I have discovered a few coatings made by Aremco (SGC4000 and GC4000) that seem like they may work. Has anyone had any experience with these coatings?

Thanks!

 

[berkeman]

I'm looking for some sort of dielectric coating that can be used at high temperatures. I'm working on trying to create a voltage point charge in a high temperature steam environment using a coated accupuncture needle. The goal is to be able to coat the needle thinly and uniformly, leaving only the very tip of the needle exposed and electrically conductive with the rest completely insulated. Therefore I'm looking for something that can be applied in extremely thin coatings (~.05mm thickness) through a dipping process, meaning it has to have a low enough viscosity (~200 cP) to achieve this thickness. The coating should be resistant to cracking once cured and be able to adhere to stainless steel accupuncture needles. The steam environment that the coating and needle will be subjected to will have temperatures ranging up to 500 deg C.

Do you have any suggestions?

So far I have discovered a few coatings made by Aremco (SGC4000 and GC4000) that seem like they may work. Has anyone had any experience with these coatings?

Thanks!

Welcome to the PF.

Parylene looks like it's good up to 350C, but it sounds like that isn't enough for your application:

http://en.wikipedia.org/wiki/Parylene

You might give them a call to see if they have something that could work for you.

 

[Enthalpy]

What about anodic oxidation, instead of dipping? With a needle of tantalum you get a good insulator.

 

[DanatAMFL]

berkeman:
We have looked into the teflon coatings and it seems as though the coating is a little too thick and we cannot shape it in the desired way.

Enthalpy:
Would it be possible to anodize a needle that small? The accupuncture needles have a diameter ~120 microns. Also, how would we control the process so that the tip could be exposed?

 

[Enthalpy]

120µm diameter is no worry, and leave the tip outside the anodizing bath to keep it naked, or cover it with some insulating varnish that you strip afterwards.

BUT... In acupuncture, your choice of materials is very limited! It must be accepted by the human body. This should be checked first, as it restrict the choice more than other constraints. Tantalum maybe? Titanium yes. Niobium? Beware the detailed alloy composition matters both for medicine and for anodization.

Or: use a stainless steel alloy or similar, like cobalt-chromium. Anodize the shaft, cover the tip so it won't develop a thick oxide layer when you put the needle in 500°C vapour.

Do you have a wide choice of tip materials for acupuncture? A metal that stays clean and conductive in 500°C vapour is difficult: gold, platinum, maybe molybdenum...

 

[Enthalpy]

120µm diameter is no worry, and leave the tip outside the anodizing bath to keep it naked, or cover it with some insulating varnish that you strip afterwards.

BUT... In acupuncture, your choice of materials is very limited! It must be accepted by the human body. This should be checked first, as it restrict the choice more than other constraints. Tantalum maybe? Titanium yes. Niobium? Beware the detailed alloy composition matters both for medicine and for anodization.

Or: use a stainless steel alloy or similar, like cobalt-chromium. Anodize the shaft, cover the tip so it won't develop a thick oxide layer when you put the needle in 500°C vapour.

Do you have a wide choice of tip materials for acupuncture? A metal that stays clean and conductive in 500°C vapour is difficult: gold, platinum, maybe molybdenum...

 

[DanatAMFL]

I'm not sure that anodizing will be an option for us. We are not looking to use the needles for accupuncture. We are trying to develop a sensor that can detect the interfaces of bubbles in a high temperature flowing steam environment. We do this currently in a flowing air-gas mixture at room temp by using a urethane coated needle with the tip exposed (conductive) and applying a voltage to the water. In this way, we can see when (and, due to the size and known location of the exposed tip, where) a bubble interface passes the sensor due to the drop in voltage of the sensor while it is inside the bubble (in the non-conductive air). We are looking to do the same thing, or something similar in the high temperature environment.

 

[geneiusxie]

I'm looking for some sort of dielectric coating that can be used at high temperatures. I'm working on trying to create a voltage point charge in a high temperature steam environment using a coated accupuncture needle. The goal is to be able to coat the needle thinly and uniformly, leaving only the very tip of the needle exposed and electrically conductive with the rest completely insulated. Therefore I'm looking for something that can be applied in extremely thin coatings (~.05mm thickness) through a dipping process, meaning it has to have a low enough viscosity (~200 cP) to achieve this thickness. The coating should be resistant to cracking once cured and be able to adhere to stainless steel accupuncture needles. The steam environment that the coating and needle will be subjected to will have temperatures ranging up to 500 deg C.

Do you have any suggestions?

So far I have discovered a few coatings made by Aremco (SGC4000 and GC4000) that seem like they may work. Has anyone had any experience with these coatings?

Thanks!

You could plate titanium on the needle and then use medical titanium anodizing to make the insulating layer. You would prevent the tip from being coated by simply not submerging it in the solution along with the rest of the needle.

-Gene

 

[geneiusxie]

I'm not sure that anodizing will be an option for us.

Why no anodizing?
Well, you could try vacuum vapor deposition of all sorts of ceramic materials. Titanium Nitride, Silicon Carbide, etc. That's how they coat drill bits and cutting tools. Just remember to cover the tip somehow so it doesn't get coated.
At 500C, polymers are just out of the question. The only way is some sort of ceramic dielectric. And simplly dipping isn't going to work with ceramic coatings.