Chem process chamber with microwave heating.

[hotrhodium]

I have a proof of concept i am working on and i was hoping someone could give me some pointers on the three main problems i am having

1:I need a window that the microwaves can pass through and still hold a vacuum. will glass work? Plastic? how much loss/heat to get rid of off the glass plate. If nominal it will be fine.

2:I need to be able to change the output very precisely because i need to be able to count the BTU's in and out of the chamber. Can i use pulse width modulation? Does the magnetron turn on off that fast? If i lower the input voltage it will just shut off rite?

3:I am hoping to drop the energy directly into the crucible if there is a metal plate in it it will absorb the microwaves and i will not need to "tune" the chamber rite?

Well thanks if anyone can help note that i will have a metal shield around the output of the magnetron and have no holes in chamber (other than window for said microwaves to go in) and have no intention of microwaving myself.

 

[VEBill]

Many high powered radar systems use pressurized waveguides. Therefore it is obviously possible to find a material that will pass microwaves and sustain a pressure difference.

Why not use induction heating? About a hundred times less complicated.

 

[hotrhodium]

I like that idea, would i be able to calculate the BTU input with induction heating? I will be heating an insulating liquid in the final form but that is not important now. I already have the magnetron but it brings so many problems with it like the interference it will cause with the thermocouples. I know i can take the magnetron power and subtract the inefficiency and divide by the duty cycle to get close and then just correct on data from the chamber but i don't know what will be lost to the chamber walls. My prof of concept will use potassium thiocyanate as the melting point is so low but the final idea is sapphire from melt @nearly 2000C. Now if i can't get there i can always work my up the ladder with other crystals CaF and then to silicone and then sapphire but i am a realist and know i will be looking for investors before that happens. Because my idea is about controlling the growth of a crystal in final form i will need to know with high procession BTU input or at least have it very constant. I will now do some research on induction heating and thanks for the ideas.

 

[biff44]

glass can mean many things. You really want to use fused quartz if you are talking about a high power window. Borosilicate glass (pyrex)....is too lossy and will heat up and melt!

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[biff44]

BTW, you can plate the very edge of the glass sheet, and braze it into a kovar ring. Solder or weld that ring into whatever your chamber is and it will hold a vacuum.

If you look at microwave glass window patents, you will find some that can withstand hundreds of psi (I think they use them in submarines).

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting