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Best Laser for Melting Copper Powder?

jaden1010

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I'm working on a Science experiment in which I need to melt very very fine copper powder. I want to do this with a laser, which laser would be best for my application?

(More detail)
Because the copper powder is so fine it can easily vaporize in the oven, of course some will melt. But I want to retain as much metal as I can without burning it up because you loose some because it is so fine. So I want to use a laser to heat the powder causing it to melt. I think I will have better success with a laser than an oven.


Anyways I am told an infrared laser will work best, however what output would the laser community recommend I use? And at what wave length, and output power would be best? Again I don't want something to powerful that it smokes my powder, and not something to weak. Any links or suggestions to a laser product would be helpful.

Thanks,
 
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Meatball

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So are you sintering for a 3d printer?

I can only agree with the IR statement you made. I know its easier to make plasmas on a copper surface with a double YAG, rather than with an excimer. I have to say though, that I've seen a penny make nasty reflections from a CO2 beam.

Copper's specific heat is 0.386 J/g*K. So to make 1 gram of copper heat up by 1 Kelvin/ degree Celsius, you apply 386mJ. To melt copper, you need to heat it to 1,085°C. So from room temp ~25 degrees C, you need heat it by 1060 degrees C more. This means you need a laser pulse of 410 Joules to do the job on 1 gram of the stuff.

410J by the way, is super ridiculous to ask for from a single pulse. The problem is, if you don't deliver this energy quickly enough your Cu sample would keep cooling off. So lets say you somehow levitated this gram of copper in a vacuum. Nothing is touching the copper at all, so you could probably deliver this energy with several high powered pulses, but there would still be radiation losses.

So.. just some perspective I guess. If you had a 150W CO2 laser (and we assumed 100% absorption by the Cu) you could deliver the required energy to a gram of Cu in under 3 seconds. If we assume say... the Cu only absorbs 50% of the laser energy, it would happen in about 5.5 seconds.

In my opinion, heating a power so quickly would almost certainly come with "explosive" side effects. If you cause any plasmas to form, you could end up "pushing" the bits around. (I don't know if this applies to you or not, maybe you're not doing sintering for a printer)

So according to this fancy graph:



You might want to consider using several 808nm diode array bars. Better if fiber coupled. But I imagine if you were somehow able to focus those nasty beams from 3-4 100W arrays, into a square centimeter or so, you might see something melt.

Odd how copper just coincidentally peaks at the most common high power diode wavelength... neat huh?

(Goggles would be imperative for you and anyone else deciding to walk with a block your lab but hey, it build character)


EDIT: Hey, why not try induction heating? I know a guy who could build you a heater if you ask nicely. :D
 
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MarioMaster

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I see questions like this come up fairly often, and unfortunately for stuff like this a laser is probably not the best solution. The laser and power supply equipment would cost several hundred dollars at a minimum even for used stuff scrounged from ebay. Not to mention since lasers transfer energy via radiation, only the very surface of the copper powder would be absorbing the energy.

You would get much better results by purging your crucible with an inert gas and heating it with a conventional gas flame
 
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Cyparagon

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In reference to the graph... if copper absorbs red preferentially, wouldn't that make it appear cyan? Copper is a good reflector of IR, last I checked. I think they have absorption mixed up with reflectance.



Why do you need to melt the copper, and why does it come to you in a powder?
 
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Meatball

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Funny I searched for absorption spectra... :thinking:

I think all the graph shows is a peak near 80% at ~810nm. I hope I wasn't pushing for anything near 100%.
 




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