improving cavity Q by metal plating

[biff44]

I have a pretty large cavity (microwave heating experiment) that I am doing experiments in. It has to hold a high pressure (200 psi), so initially it was design out of steel. But now I find that the energy is not being absorbed so much in the load as I expected, but it is also being simultaneously absorbed by the cavity walls. I either need to plate the cavity walls with some higher conductivity metal, or make the entire cavity out of something like aluminum (not as strong).

My problem is that the process gives off nasty vapors, like sulfuric acid, etc. If I just plate the cavity inside with copper or silver, I am afraid that the acidic environment will cause it to blister/degrage in short time.

So, does anyone know some plating scheme that would give me a higher cavity Q, but uses metals that are relatively immune to acidic fumes?

I once remember silver plated waveguides, with a thin rhodium flash on the exposed surface, as being relatively tough. Any ideas like that?

Alternatively, has anyone experience of adding a reflecting surface plate inside of a large cavity? Maybe a thick (sacrificial) copper plate that would reflect microwave energy that could be hung inside of the larger steel cavity in strategic positions?

Thanks
Rich

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[VEBill]

Gold is both noble and highly conductive.

 

[biff44]

I guess you are right, gold is worth considering! For some reason (probably the size of the cavity) it did not even enter my mind.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[Higgler]

I'd use silver, it's cheaper and it's 23% lower loss than gold.
Copper is better than gold too.
Aluminum is only a little worse than gold and much better than steel too.

kch

 

[biff44]

For future reference, you CAN plate up the inside of a large vessel. You have to be able to ship it to a plating house that can handle it. Cost is between $1000 and $2000 for a 2' diameter, 6' long cylinder with some other requirements, like splashplating the flange rim too. They were talking 150 uinch minimum copper plate for that price. Apparently they stand it on end, fill the thing with solution, throw an electrode inside, and come back the next day. So you would need to have it fluid-tight when standing on-end. For slightly smaller diameter pipes, they could go much longer (30'), because they could just drop it into a tank.

Brush plating is apparently not designed for such a large surface area project, and the cost would be more like $10,000 with a less-controlled plating thickness afterward.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[biff44]

BTW, I asked about a Rhodium flash over the copper, and they just laughed. I guess Rhodium is unbelievably expensive nowadays, AND hard to get.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[RecoveringEngr]

How hot do you expect it to get?

What's the operating frequency?

As an alternative to gold if that's not possible, I might consider using a silver or copper plate and coating it with a low loss tangent material like teflon for acidic protection. You would have to avoid coating the connecting surfaces. I believe there are commercially available microwave heaters that are constructed similarly.

I'm curious about the reflecting plate inside a cavity. Can you tell me more about what you are trying to do?

 

[biff44]

That project is dead, so it is a moot point now. I was trying to retort oil out of shale rocks with microwaves. It was interesting to find out that you can electroplate something that is huge!

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[biff44]

If you are interested, you can see a picture of the microwave shale rock retort project here:

http://www.maguffinmicrowave.com/pastrfdesigns.html

Scroll to the end of the list of pictures to find it.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting