really high temperature measurement? (~2000C)

[keegreil]

High all, I'm new to this whole hobby, I have a rather oddball question.  

 

Background:  Fused silica happens to be the ideal substrate for making telescope mirrors.  It is basically just pure sand melted at about 2000 degrees C.  As a result they are really expensive.  While I don't anticipate being able to actually melt enough for a telescope mirror, I've been wanting to see if it is possible to melt a smaller (1cm x 1cm) amount in a solar powered "forge", using a big parabolic mirror.  Just for the fun of it, no good reason really.  Just to see if it is possible.  

 

I've got a mirror design to try, and I'm thinking the "forge" will be best made like a smaller version of the "backyard coffee can forge" I've seen floating around, probably using a couple of soup cans instead.  I'll have a nice small hole in one end to pour the sunlight in.  However there are a couple of things I haven't yet figured out, I was wondering if you would have any ideas. 

 

1.  At 2000C, I estimate 93% of the energy lost from the target sand is given off as IR radiation.  In order to maximize the amount of energy that stays in the sand, I would like to line the inside of my soup can with something that will reflect as much of that IR light back onto the sample as possible.  My first thought was a sheet of aluminum foil, but I'm afraid that might melt.  Do you know of anything else you guys line your forges with that reflects most of the IR and won't melt?  I suppose ideally the liner would never reach nearly the same temperature as the glass, but I don't know if that's possible.  

 

2.  I'd like to be able to track and measure the temperature inside the forge to check my progress and see how close I am to the goal of 2000, but I'm having trouble finding any thermocouple's/pyrometers that will go up to 2000C.  It seems most of the one's I'm finding top out around 1300-1500C, beyond which I assume they start melting.  Any ideas for higher temp versions?  (preferably cheap).  Should I look into going contactless instead, like a laser thermometer?

 

Thanks for any ideas, cheers!

 

-- Keegan

[swedefiddle]

Sounds to me that you are working way above the forging range. Find out who is making precision instruments, bend there ear. Sounds like you need to be the one writing the book!!

 

Neil

[ciladog]

Sounds like an ambitious project.

 

The only thermocouple that can measure 2000 degrees C is a type C (0-2320 degrees C) and can be purchased for between $100-200.  That is just for the thermocouple and you will still need a meter that can read a type C thermocouple.  The problem is that it can not be used in the presence of oxygen at temperatures above 260 C.  They use them in vacuum furnaces.

 

You could use an infared thermometer.  Extech makes one that will measure up to 2200 C at a price of about $400.

 

Good luck.

[Steve Sells]

Since you are talking glass making, you may need to talk to some on at a glass forum, there you may get real answers form people that have done it.  This being a blacksmithing site, and we dont forge too much glass around here,  except for Trying-it  he trys everything at last once :rolleyes:

[trying-it]

Who me?  :wacko:  :ph34r:  :D  :P

 

 

As for a can liner you might consider a castable silicon carbide refractory as used in high dollar crucibles and the same as steel mills use; I use it a lot inside my gassers as a topcoat over "wool" and love it as it is 100% flux-proof.

 

There is also a silicon carbide mortar mix I use in my microwave glass kilns. It allows microwaves in, but blocks their escape. Microwave kiln can also cook metal items such as precious metal clays and such without damaging the microwave.

 

I buy both from Hi-Temp Refractory Co. in Fenton, Mo.

 

You may want to talk directly to refractory suppliers and run your ideas past them. Hi-Temp is more than happy to assist and answer questions!

 

 

Stan