PDA

View Full Version : Chemistry Riddle



traceur
2012-Feb-07, 05:37 PM
If i needed to melt the very same materials that the tools i am melting the material with are made of, without melting those tools in the process, how would i do it?

profloater
2012-Feb-07, 06:05 PM
Is this a trick question or a real question? If with means in, then cool the tools and have a surface coating to avoid sticking such as an oxide layer. Or can you refine the question?

kzb
2012-Feb-07, 06:25 PM
If you mean the crucible is made of the same material as what you want to melt: put your material in your crucible and aim a powerful laser at the materials centre. It will melt from the inside out. When the melt zone approaches the crucible walls, turn down the power so that you always have an unmelted layer between the melt and the walls.

It would also be possible to do this with spaced electrodes dipped in the material instead of the laser beam.

Do I win a prize?

Swift
2012-Feb-07, 06:26 PM
Look up information about the Skull Melting process, used for crystal growth. The link (http://www.theimage.com/newgems/synthetic/syntheticanimate3.html) gives particulars for using it for zirconium oxide, but it has been used for lots of materials.

The "container" for Skull Melting is basically just a water cooled metal jacket (which would melt at the temperature). You fill the container with the powder of interest, and use RF heating to melt it. The water cooled jacket keeps a thin layer of material solid on the inside surface of the metal jacket, and that thin layer (as well as the water cooling) keeps the jacket from melting.

The process has been used since at least the mid 20th century.

Swift
2012-Feb-07, 06:35 PM
There is also the Verneuil process for crystal growth, though some people don't consider it a "melt" technique.

Wikipedia article (http://en.wikipedia.org/wiki/Verneuil_process)

The powder of the material of interest (the original work was done with alumina - aluminum oxide) is introduced into a high temperature jet (usually hydrogen-oxygen). The powder melts in the flow from the jet, and the droplets are impacted against a seed crystal or rod (sometime it is water cooled) and crystallize on the rod, slowly building up a crystal.

traceur
2012-Feb-07, 07:09 PM
If you mean the crucible is made of the same material as what you want to melt: put your material in your crucible and aim a powerful laser at the materials centre. It will melt from the inside out. When the melt zone approaches the crucible walls, turn down the power so that you always have an unmelted layer between the melt and the walls.

It would also be possible to do this with spaced electrodes dipped in the material instead of the laser beam.

Do I win a prize?

maybe, but i can't use a laser. what kind of electrodes? and how do i prevent the electrodes themselves from melting under the tempreture they generate?

Swift
2012-Feb-07, 07:34 PM
what kind of electrodes? and how do i prevent the electrodes themselves from melting under the tempreture they generate?
What kzb is describing is an electric arc furnace (http://en.wikipedia.org/wiki/Electric_arc_furnace). It is an alternative way of heating the system, but it doesn't particularly help you with the issue of melting your container. As the arc melts the material, the molten material will carry the heat to the walls (unless they are cooled); the heat doesn't stay confined to the volume between the electrodes. It can be used as a heating method for the Skull Melting I talked about (as opposed to RF).

In the set-ups I know of it, the electrodes are usually carbon.

Are you actually thinking of doing this stuff? What exactly do you want to melt and what is the melting point of it? A lot of this technology is potentially expensive and dangerous. The amount of power required, even for small volumes, is usually very high, the temperatures are dangerous and in certain systems, if the temperature is high enough, a leak of the cooling water such that it sees those temperatures, will result in the thermal decomposition of water and the potential for a hydrogen explosion. I have 30 years experience in crystal growth and high temperature materials processing, I have used some of this technology, and I would not do any of it in my basement.

kzb
2012-Feb-08, 06:30 PM
^ I wasn't sure if this was some kind of conundrum or trick question at first, but if you could tell us exactly what you want to melt and why, we might be able to help. But like Swift says, there are some serious safety issues to consider. It's not something an inexperienced chemist should be doing at home.