DIY Arc Furnace

Here is a simple DIY arc furnace for melting refractory metals such as nickel, molybdenum or tungsten under an inert gas atmosphere. The furnace requires a current source - a 200A stick welder works just fine for our purposes. The furnace can reach temperatures in excess of 3500°C (6332°F). The design is based on the Arc lamp or the furnace of Henri Moissan. The positive electrode and the crucible (which itself is the negative electrode) are made of graphite.

The crucible

The graphite crucible is mounted to an aluminium base. The cavity should have a conical shape suited to the melt. The large cross-section of the crucible (here 3") prevents its overheating (which would increase the carbon contamination unnecessarily). For the inside edge of the cavity, sharp edges are to be avoided, since they will concentrate the arc and melt, introducing further carbon into the melt.

I use an old stainless steel vacuum evaporation chamber. These pop up occasionally on eBay. This chamber has two windows, originally made of borosilicate glass. On the first try, only a few seconds of operation were sufficient to break one of the windows from thermal shock. For prolonged use, it would be best to use 99.995% SiO₂ windows, with some method of cooling.

First try

First try; the chamber is filled with argon gas and a small nickel charge is introduced. The positive electrode is placed manually (with some difficulty). The graphite of the positive electrode glows red, but the crucible remains relatively cool.

The nickel charge melts within a few seconds. If left running for too long, the nickel may combine with the carbon and form hazardous concentrations of nickel carbonyl vapor. On second try, the vapors ignited causing a small explosion.

So with some effort, we've managed to turn some commercially pure nickel into a piece of carbon-contaminated nickel, generating explosive vapors of extreme toxicity in the process! Have fun!