Ultrasonication in liquid nitrogen 3

[hick12]

Hello,

I am trying to design working parts of an ultrasonic desintegrator that would work on a liquid nitrogen suspension (minus 195 degrees Centigrade) containing biological materials. The desintegrator has a steel tip (which is dipped into the treated liquid) and I am planning to replace that tip with one made of austenite steel. This way the tip may not crumble at ultralow tempratures because austenite steel is supposed to retain toughness in these conditions (whereas regular steel becomes brittle). The vessel containing the liquid nitrogen suspension I am planning to mold of poly-tetra-fluoro-ethylene (also supposed to be tough at ultralow temperatures). The question is: will the austenite steel work for this experiment? Is there a better material for the tip that would not crumble from ultrasonication in liquid nitrogen?

Many thanks for any advice.

 

[cloa]

Which austenitic steel? What was the original steel grade?

http://steel.keytometals.com/Articles/Art61.htm

recommends 9% Nickel Steel.

http://www.zeusinc.com/technicalser...echnicalinformation/lowtemperaturerating.aspx

lists PTFE as tough as low as -267 C.

You'll need to be thinking about thermal stress- ie. trying to slowly cool to the working temperature.

What sort of stresses will the parts see?

 

[arunmrao]

Austenitic stainless steels can be considered for the application. They do not undergo a phase transformation and are stable at low temperatures.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[cloa]

Suggest you post a new thread in Cyogenic Engineering with a link back to this one

 

[EdStainless]

Just about any austenitic stainless steel will work fine at these temperatures. If you need strength and toughness though for the long term I suggest a Co based alloy such as Ultimet.

You do need to worry about how cold your transducer will get. They don't like being too cold.

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Plymouth Tube

 

[hick12]

Warmest thanks to everyone who replied! Now I will be thinking long and hard about your comments.

@cloa: the grade of the original steel was not specified by the manufacturer of the desintegrator. But I will try to contact them, in case the tip is already made of austenitic steel. The working parts, the vessel and the tip, will see the most stress (the tip normally heats up by 30 to 40 degrees Centigrade within 5 minutes of operation at full output, if it is dipped in room temperature water). I don't know yet, but I will have to sonicate the liquid nitrogen suspension for different lengths of time, anywhere from one to 15 minutes. As EdStainless suggested, it is possible that the transducer will freeze to death and crack if I try liquid nitrogen. I will post a link in the Cryogenic Engineering section.

Thanks again.

 

[Compositepro]

A more important potential problem of sonication in liquid nitrogen is that it will probably be far less effective than you imagine. LN2 is a liquid at its boiling point. Sonication works by creating bubbles that collapse and create large forces when liquid hits solid at high velocity. In a boiling liquid the bubbles will be filled with vapor and this will prevent high velocity collapse. It would be similar to sonicating in boiling water rather than cold water.