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SimonB
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Measuring Very Thin Fluid Layers on a Surface

05/31/2018 7:40 AM

I am trying to find a successful method of measuring a very thin fluid (oil) layer on a metal surface such as a cylindrical drum. The thickness layer is 1 micron with a tolerance of 5 nanometers. I have read some literature suggesting ultrasound, and also ultra-thin film interferometry as possible solutions.

Would appreciate if anyone could advise.

Thank you
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IdeaSmith
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#1

Re: Measuring Very Thin Fluid Layers on a Surface

05/31/2018 10:02 AM

Maybe check out wet paint thickness gauges.

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Doorman
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#2

Re: Measuring Very Thin Fluid Layers on a Surface

05/31/2018 11:34 AM

The surface irregularity of the substrate will likely render any such measurement meaningless.

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Rixter
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#4
In reply to #2

Re: Measuring Very Thin Fluid Layers on a Surface

05/31/2018 2:21 PM

You're right on that one. The fused silica gyroscopes used in the Gravity Probe B experiment had a surface "roughness" in the neighborhood of 10nm, and when manufactured, were the most perfect spheres ever manufactured.

https://en.wikipedia.org/wiki/Gravity_Probe_B

λ/10 - λ/20 is considered excellent for a telescope mirror. 5nm is more like λ/100 and is like 10-20 atoms high!
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Doorman
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#7
In reply to #4

Re: Measuring Very Thin Fluid Layers on a Surface

05/31/2018 5:05 PM

Precisely - 1 micron film thickness measured... where?

Further, the coated surface is defined as a drum, so gravity will constantly affect this uncured film.

Once the desired WFT is measured, it is meaningless - in 30 seconds it will change.

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lyn
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#3

Re: Measuring Very Thin Fluid Layers on a Surface

05/31/2018 11:38 AM

Don't bother with wet film gauges.

The only way you are going to do this is with laser interferometry.

5 nanometers is an extremely small number.

Interferometry - Wikipedia

ZYGO Laser Interferometers | The Industry Standard | zygo.com‎
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Dr. Harry
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#5
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Re: Measuring Very Thin Fluid Layers on a Surface

05/31/2018 3:23 PM

I agree with Lyn on this one. I used this technique for just such measurements in the lab; I get the impression that you are looking for a field-use instrument. Good Luck as I'm not sure that such a system exists..
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redfred
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#6
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Re: Measuring Very Thin Fluid Layers on a Surface

05/31/2018 4:11 PM

When that gravity wave rolls by all measurements will be off.

GA

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JimmyGG
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#8

Re: Measuring Very Thin Fluid Layers on a Surface

06/01/2018 3:04 AM

I agree with Lyn, you could contact the people at Nirox for their advice.
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SimonB
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#9

Re: Measuring Very Thin Fluid Layers on a Surface

06/01/2018 3:10 AM

Thanks for all the responses guys! This is all useful food for thought!
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Codemaster
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#10
In reply to #9

Re: Measuring Very Thin Fluid Layers on a Surface

06/01/2018 4:00 AM

Can you find the volume of oil applied, and divide by the drum surface area? Obviously that will only give average film thickness.

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IdeaSmith
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#14
In reply to #10

Re: Measuring Very Thin Fluid Layers on a Surface

06/06/2018 6:04 AM

Another option is to wipe the surface and measure the amount of oil collected for a certain area and time.

The wiper has to be exceptionally good.

Or boil off the oil and measure the amount of gas coming of the area.

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jhammond
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#11

Re: Measuring Very Thin Fluid Layers on a Surface

06/01/2018 5:43 AM

Agree with other posts, whatever you use is almost certainly going to involve light. Ellipsometry is also a possibility and there are commercial systems available.

jhammond

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Jpfalt
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#12

Re: Measuring Very Thin Fluid Layers on a Surface

06/01/2018 11:18 AM

Any chance of using dielectric constant, such as set up a curved plate concentric with the surface at a fixed gap. Establish a capacitance for no oil and then watch the capacitance change as oil film replaces a portion of the air gap. Since oil has a dielectric constant different from air or vacuum, the capacitance will change as the oil thickness changes.
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#13

Re: Measuring Very Thin Fluid Layers on a Surface

06/04/2018 8:02 AM

<...to find a successful method of measuring a very thin fluid (oil) layer on a metal surface such as a cylindrical drum...> Why?

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Users who posted comments:

Codemaster (1); Doorman (2); Dr. Harry (1); IdeaSmith (2); jhammond (1); JimmyGG (1); Jpfalt (1); lyn (1); PWSlack (1); redfred (1); Rixter (1); SimonB (1)

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