# glass or ceramic as flashlight body material?



## marcspar (Jul 10, 2006)

Would some sort of strengthened glass like pyrex or the ceramic used for knife blades work for a flashlight body?

Wouldn't this allow for even better heat dissipation then metal?

I realize that you would need to add a metal "strip" to conduct electricity....

Marc


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## Kryosphinx (Jul 10, 2006)

A thick glass flashlight body would be AWESOME. I have no idea of the feasibility though.


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## scott.cr (Jul 10, 2006)

A ceramic body would actually do a great job at retaining heat, plus would be relatively fragile (if dropped). And making the threaded end caps!! I cringe at the thought of it. ;-)

Kind of a side story here, but I once drilled a hole through a ceramic flooring tile. It was by far the hardest material I've had to work with because of its hardness. Using a carbide "fuzz" hole saw, I had to submerse the tile in a five-gallon bucket of machining coolant to get the hole saw to last the duration of the surgery, otherwise it would heat to red hot! (And after drilling one 2-inch hole, the entire bucket of coolant raised to a temp of over 120 degrees F from the friction.)


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## Cliffnopus (Jul 10, 2006)

Might be OK but I wouldn't drop it.Cliff


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## mudman cj (Jul 11, 2006)

I happen to be a ceramic engineer (which is why my handle is mudman cj-since essentially I make stuff out of little more than "mud"), so I can answer your questions with as much detail as you like. Yes, you could make a ceramic flashlight. You could even mold them to have threads in large quantities (but it wouldn't be cheap!). 

Your suggestion of material (ceramic knife blades) is spot on for mechanical properties. Those are made from one of the very toughest ceramics known, partially yttrium oxide stabilized zirconium oxide. It would be virtually impossible to scratch it, except of course with a diamond, and it is quite impact resistant. Zirconium oxide has a lower thermal conductivity than most metals, and so heat would tend to build up at the bezel, as scott.cr added. Aluminum oxide is a good heat conductor (but not as good as metals), and is in fact used as a substrate for some circuits for that reason, but would not be as tough and would therefore be more susceptible to failure when dropped. SiC would be one of the best heat conductors, but is still only about 2/3 as good as Ti in this regard. It too could be made to be rather strong, but again, not as strong as the zirconium oxide material.

I am not sure why you said ceramic would have better heat dissipation than metal, but you may be thinking about emissivity of radiation at the surface. At high temperatures this would actually be true, but this effect is dependent on temperature to the 4th power (Stefan-Boltzman relation) and is negligable at flashlight operating temperatures compared to heat dissipation through convection.

If you really wanted to make a flashlight out of ceramic and didn't care too much about fracture resistance, it could be done using one of the machinable ceramic materials that are commercially available. Using the manufacturer's suggested machining conditions, it could be turned on a lathe, threaded, etc. almost like a metal. There is also a somewhat less machinable aluminum oxide material available, but I think it would work for most everything except maybe threading. If anyone decides to do this I can provide you with suggestions, sources, and I will even get it sintered for you.

C.J.


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## marcspar (Jul 11, 2006)

Thanks for the great info, C.J. and all.

I just assumed that ceramic and glass were good at heat dissipation based on how quickly a coffee or tea glass will get hot...

One knife maker, Boker, is selling a "ceran-titan" blade which they claim address a lot of the fracture resistance issues by combining titanium and ceramics.

All the best,

Marc


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## greenlight (Jul 11, 2006)

Cool post, CJ. Do you make household items for yourself out of fancy ceramics? Do you have one of those ceramic hammers?


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## evan9162 (Jul 11, 2006)

> I just assumed that ceramic and glass were good at heat dissipation based on how quickly a coffee or tea glass will get hot...



There are two things at play there - thermal mass and thermal conductivity. 

Glass and ceramic mugs have a relatively low thermal mass, so they can heat up more quickly. However, their thermal conductivity isn't that great, hence the handle on mugs - notice that you can pick up a mug full of boiling-hot water by the handle and not get burned at all.

Now make a mug out of aluminium or copper, and you will quickly see how much better those metals are at conducting heat. The handle on a copper mug would be all but useless, as it would get nearly as hot as the liquid in the mug.


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## mudman cj (Jul 11, 2006)

Funny stuff greenlight...but I haven't found the need to replace everyday objects with ceramics. I like to use the best material for the job. However, I do have this desire to replace components in anything that makes light...

I am going to have to look into this ceramic/titanium knife thing...


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## monkeyboy (Jul 14, 2006)

marcspar said:


> Would some sort of strengthened glass like pyrex or the ceramic used for knife blades work for a flashlight body?
> 
> Wouldn't this allow for even better heat dissipation then metal?
> 
> ...


 
Just for the novelty value, I like your idea of a glass body. A completely clear flashlight would be cool. no need for the metal strip, coat the glass in Indium tin oxide (transparent conductor). The electronics (for an LED) could be hidden behind a silvered parabolic reflector along with the LED. Not sure about a see-through switch though.
I guess there would be no practical reason for making one of these other than to get through metal detectors.


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## Handlobraesing (Jul 17, 2006)

marcspar said:


> Thanks for the great info, C.J. and all.
> 
> I just assumed that ceramic and glass were good at heat dissipation based on how quickly a coffee or tea glass will get hot...



The thickness of material that heat has to travel through is thin. Notice how the ceramic handle doesn't get hot, but a metal tea kettle has a resin handle rather than all metal? 

If it was all metal, it would get bloody hot very quick.



monkeyboy said:


> Just for the novelty value, I like your idea of a glass body. A completely clear flashlight would be cool. no need for the metal strip, coat the glass in Indium tin oxide (transparent conductor). The electronics (for an LED) could be hidden behind a silvered parabolic reflector along with the LED. Not sure about a see-through switch though.
> I guess there would be no practical reason for making one of these other than to get through metal detectors.



They have see through shake lights made of polycarbonate


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