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I am looking to be able to heat a sample of material, typically less than 500mg and sitting in a fused silica sample holder about 10mm diameter. Wondering about using (say) a 5W LED with narrow emission angle. The overall sample chamber of the machine is quite small, so ideally I need a small source, possibly with a light pipe. I certainly do not want the thermal mass of something like a halogen bulb. So, the questions...

Does this seem feasible?

What type of LED (in terms of wavelength) is the most efficient?

Does wavelength matter in terms of heating the sample? [Typically the archetypal "white powder"]

Now, I expect you to ask me what sort of temperature I want to get. The answer is "not sure", but probably 80 degC would be adequate. It is to drive off moisture.

The only cooling I have is a small ambient temperature airflow. Other possibilities (that I have not yet examined in detail) are low power uwaves and maybe changing the pan from silica to steel and using induction heating.

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  • \$\begingroup\$ White stuff is hard to heat with visible light as it reflects a lot - what's the color in the infrared spectrum? If it is black there you might want to use a high power IR LED. \$\endgroup\$
    – Arsenal
    Commented Oct 21, 2015 at 10:30
  • \$\begingroup\$ What problem does the thermal mass of a halogen bulb give you? \$\endgroup\$
    – user1844
    Commented Oct 21, 2015 at 10:40
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    \$\begingroup\$ The rapidity of cooling is important as it limits the rate at which measurements can be taken. The more "stuff" that gets heated the worse the problem. As for IR characteristics of the material, that is unknown since it can be almost any chemical or material. \$\endgroup\$ Commented Oct 21, 2015 at 10:45
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    \$\begingroup\$ In case you're dismissing the halogen route prematurely, do consider that the light/heat source could be quite some distance from the sample, and that its contribution of (radiant) heat would stop pretty much instantly when you turned it off. There is an interesting thread here, which you may have seen: candlepowerforums.com/vb/… \$\endgroup\$
    – user1844
    Commented Oct 21, 2015 at 11:18
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    \$\begingroup\$ Depending on the design you could use some nichrome wire instead of a bulb... depending on the thickness used it should be able to heat the sample holder well as it can be formed(wound around) to hug the holder... \$\endgroup\$
    – Spoon
    Commented Oct 21, 2015 at 11:19

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It really depends on what kind of sample you want to heat up, but the most common way would be to use IR LEDs, like these. I'd use a small lens to focus the beam on the sample (could be tuned precisely enough using visible light from red LED). Make sure you protect your eyes when you power up the IR LED though - its emission is invisible and doesn't make your iris contract or your eyes hurt, so it has potential to burn your retina when visible light would be mostly harmless.

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  • \$\begingroup\$ Maybe change the pan to black steel or Aluminium... However, for the reasons you mentioned I would rather use visible rather than IR \$\endgroup\$ Commented Oct 21, 2015 at 11:58

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