Measuring Oxygen Partial Pressure with an MFC: Flow vs. Pressure?

[DivGradCurl]

How is oxygen partial pressure measured? Can a mass flow controller (MFC) be used to control it? If so, what is the relationship between flow [sccm] and pressure [Pa]?

Thanks!

 

[pixel01]

How is oxygen partial pressure measured? Can a mass flow controller (MFC) be used to control it? If so, what is the relationship between flow [sccm] and pressure [Pa]?

Thanks!

In principle, the percentage of O2 in air can be calculated by measuring air's density. To measure the density of air, a MFC can be used.

 

[DivGradCurl]

I've read that MFC's are not the best option because of hysteresis. If you set it to a particular flow (sccm), the partial pressure is not going to be constant. In other words, a vacuum chamber with reactive gases like oxygen needs a partial pressure sensor (also known as a "residual gas analyzer" or RGA) in combination with a partial pressure monitor for that RGA (to adjust the flow in real-time and match the desired partial pressure). My idea may be an overkill, though.

 

[manyoolo]

Hellow Thiago
Did you manage to get the relationship you asked? Can you share with me!
Thanks

How is oxygen partial pressure measured? Can a mass flow controller (MFC) be used to control it? If so, what is the relationship between flow [sccm] and pressure [Pa]?

Thanks!

 

[manyoolo]

How is oxygen partial pressure measured? Can a mass flow controller (MFC) be used to control it? If so, what is the relationship between flow [sccm] and pressure [Pa]?

Thanks!

I met one doc saying 1sccm =1.69Pa;
Tell me what the case with you?

 

[Borek]

Note: this thread is almost two years old.

 

[DivGradCurl]

Hi manyoolo,

The short answer is: I would advise you to do literature research and run tests in your system to get the an accurate answer. Here is what I think:

The experiments I've done back in 2009 led me to use MFC's and no active form of partial pressure control to minimize cost. I believe you can use an RGA (along with auxiliary required tool control systems) to obtain live partial-pressure data and actively control the oxygen partial pressure, and that is something that has significance if you are working with thin films; the micro structure is dependent on the surrounding gases.

I wanted to improve a thin film sputtering process with RGA active controls and do cross-sectional TEM analysis, but instead I simply ran experiments with a cheap MFC and evaluated the thin film sheet resistance, which was the main criterion for my application. Depending on what you are doing, you may be able to get away with coarse controls.

I hope this helps.

Final note: partial pressure cannot be directly controlled by MFC; the pressure will vary in your chamber.