Experiment 57: Microwave Furnace Melting Metal

A while ago, I saw a YouTube video showing someone smelting gold from ore using a common household microwave.  Intrigued, I researched microwave furnaces further.  Amazingly, the microwave found in nearly any kitchen can melt metals like gold, copper, and aluminum!  Microwave furnaces work by surrounding the crucible or the metal to be melted with something that absorbs microwaves (a susceptor) and turns them into heat.  Some common microwave susceptors are charcoal and silicon carbide, as well as water--food gets hot in a microwave because of its water content.

To make my microwave furnace, I grabbed the alumina-silica light-density firebrick that was my arc furnace body and cleaned the metal residue from its inside.  The furnace body is simply one brick with a 2" diameter hole 1.5" deep in it and another brick as the lid.  Each brick is about 4" by 4" by 2.5", so this leaves a 1" thick bottom on the furnace body.

I added a 1/8" layer of crushed lump charcoal to the bottom of the furnace's inside and put my soup can crucible on top of that.  Then, I added some aluminum TIG welding filler rod scraps and set the furnace in an experiments-only microwave.  With everything in place, I nuked my furnace for six minutes on high heat.  Amazingly, the aluminum was completely molten and glowed bright orange!  I was quite impressed, so I tried zinc in the microwave furnace.  After four minutes, it was a mere puddle.

I read on a forum somewhere that charcoal can heat things to at least 1000°C as a microwave susceptor, so I suppose I shouldn't be surprised that the furnace works so well.  With a simple soup can as its crucible, though, it has limitations.  I tried melting copper, and while the copper melted (around 20 minutes on high), it also ate through the steel and leaked out everywhere.  A graphite crucible might be a better choice.  However, I am still impressed that a common microwave can melt a metal like aluminum in less than ten minutes!