HF resistant material for vacuum chamber

[BigBunny]

Hello Engineers,

I have a difficult application where I am struggling with materials. I have designed a gas diffuser that will be used in a vacuum chamber. It has lots of small holes to choke & spread the gas flow out as it enters the process chamber. I have made one from PTFE, but we are having lots of trouble with metals contamination and moisture retention. The tricky part is that it needs to have a working temperature >= 120 C, and also be resistant to HF vapor. Any suggestions on a specific grade of PTFE that would be best suited to this environment? Or, any alternate materials that might work better?

As a point of interest, I have tried several cleaning techniques to free the proto PTFE unit from metals and moisture. Initially I used a clean ultrasonic bath and a low-temp bake out (~45 C). That didn't work very well. We went a big step farther and washed it with aqua regia, then aqueous HF, then the ultrasonic bath and bake out. This last time, dimples have risen up in many places on the surface (it is about 10 mm thick). They are very hard, not thin like a surface blister, so it appears something has expanded inside the base material. Any idea what mechanism would cause this? This material is supposed to be virgin PTFE, but I don't have certs on purity.

Thanks in advance!

 

[tomwalz]

Glass or fused quartz

Glass ain't just glass any more. Seriously, I have a huge amount of respect and admiration for the folks at Corning.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[IRstuff]

HF vapor? ackkk... HF in solution is scary enough.


I don't know much about HF vapor; we never used HF in vapor form. Have you thought about some sort of plasma etch? My recollection is that sapphire/alumina was absurd resistant to plasma oxide etching, which seems to translate to HF:

http://www.idonus.com/txt/products/...materials for release by vapor hf etching.pdf

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[BigBunny]

Thanks for the suggestions.

HF is used to etch amorphouse SiO2 (quartz/glass), so we had written that one off a long time ago. We are actually using sapphire for chamber view ports, since the crystalline Al2O3 is very good vs. HF. However, our part is a bit too large for sapphire to be practical due to cost & availability.

 

[Compositepro]

The traditional material for gas diffusers in chem labs is sintered glass frit. Teflon is the newer version as it is better at preventing liquids from flowing backwards through the pores due to surface tension effects.

 

[IRstuff]

Unless you need the transparency, you could use alumina, then.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529