High emissivity IR paint

jarra

I'm having problems measuring the temperature of a steel surface with varying emissivity with a pyrometer. So I thought one way to overcome the varying emissivity is to paint the surface with a paint that has a high uniform emissivity in the IR region.

The paint should:

• Have high emissivity in the 7-15µm range and be transparent in the visible range.
• Not change it's emissivity in the temperature range 50-200^oC.
• It is also preferable that the paint is non-toxic.

Does anyone know of a paint that matches these criteria?

nucleus

There is paint that changes color at a certain temperature, but have you looked into temperature crayons:

http://www.omega.com/pptst/OMEGAMARKER.html

mgb_phys

Why do you need it to be transparent in the visible?
Otherwise the best easiest high emissivity surface is carbon, soot from a smoky candle or charcoal from a barbecue is about as good as it's possible to get.

jarra

The surface I'm supposed to measure is a drying cylinder in a paper machine. I'm supposed to measure the temperature while the machine is running. So in order not to colour the paper the paint needs to be transparent in the visible.
It is my master project I'm working on so if anybody have an alternative method on how to measure the temperature I would be all ears.

Thank you for your help!

mgb_phys

Non contact ir thermometer is a classic method.

Still not clear why it needs to be transparent.
The drying is going to be by contact so as long as it isn't super insulating the paint isn't going to have any effect on the drying.

If the metal is only at 100-200C the peak emission is going to be well out into the IR band so just the metal may be black enough, you could also calibrate the emissitvity by measuring the IR signal and the temperature of the part while it is not moving.
See http://www.raytek.com/Raytek/en-r0/IREducation/ for more info on IR thermometers

jarra

While drying the paper is in direct contact with the cylinder so if the paint had a colour the paper would probably be coloured as well.

I don't think calibrating the emissivity would work well either. Because the surface is not uniform. When trying to calibrate the emissivity I obtained emissivities in the range 0.2-0.6 for different areas.

I've been searhing the net for pyrometers that are "independent" of the emissivity and I've found two-/multi-band pyrometers, and pyroreflectometers. But they use photodetector sensor that doesn't work in the temperature range 90-200 C.

Thank you again for your replies.