Material Science exam question

[Chris Danger]

hi all,

an intersting question in our exam today. we were asked to identify a material given these requiremets "that could have been extracted from product design specifications"

"thermally non-conducting, strong at temperatures in excess of 600K, and optically transparent."

any ideas?

 

[Gokul43201]

I bet the Pope would've gotten that one right.

 

[Astronuc]

Optically transparent requirement kind of rules out metals.

What materials are optically transparent?

Then which ones are strong at 600 K (327°C), while being thermally non-conducting?

 

[PerennialII]

... makes you want to "look out" to the window ... if not mistaking with values of conductivity ... and don't kind of know how to comprehend "strong" here ... nice product specs .

 

[Chris Danger]

yeah, the way i saw it, glass is quite thermally conductive. also it is certainly not strong, and it softens readily with the application of heat (although i wasn't sure if 300 C is anywhere close to the TG)

also diamond is way too expwnsive for any application that does not require extreme strength (like a cutting tool) even if it couldbe made to fit the geometry of the problem.

what else is transparent?

 

[PerennialII]

Yeah, the strength part kind of leaves it open for glasses ... even if thinking 'relatively' ... conductivity of some borosilicate glasses for one is under & around 1 W/mK ... probably easiest to figure out optically transparent materials first ... polymers are out ... can we find anything from electronic materials, displays & their coatings or so ?? ... lucky don't have to take your exams .

 

[Astronuc]

What would constitute strong (YS = 10 ksi / 70 MPa, or > 30 ksi / 210 MPa).

One candidate for the material might be Pyroceram, but that depends on quantifying strength.

 

[Chris Danger]

yeah, i was lying in bed thinking about this one last night. glass is pretty (thermally) non-conductive come to think of it. Also it is quite strong when not supplied in thin sheets (or after tempering), and 300 C is not that hot, really.

perhaps it is glass!

 

[Gokul43201]

I was initially thinking of bulletproof glass, but I'm not sure the polycarbonate film can handle much heat.

But then, if glass is good enough for rocket nose cones, perhaps that's enough for it to qualify as "strong".

 

[Astronuc]

The other material that comes to mind is "sapphire", a form of Al₂O₃.

See - http://www.crystalsystems.com/sapphys.html

Thermal and mechanical properties -http://www.crystalsystems.com/proptable.html