I've been using what I believe is a "pure graphite crucible" for about 5 aluminum melts and it's already looking quite badly oxidized. I also tried a smaller pure graphite one for copper and half of it burned up. When I say "pure graphite" I believe this means those cylindrical ones that are used in tabletop furnaces like this one https://images-na.ssl-images-amazon.com/images/I/61RbK3XpdAL._AC_SL1179_.jpg. I think a large part of the oxidization is that I'm using it in a homemade electric furnace with quite a large volume (about 6 liters), which would allow more oxidation.
My question is whether "clay graphite crucibles" which are the ones that can be used with charcoal foundry's would work any better with an electric furnace? I'm interested in one of those cheap unbranded chinese ones to start off with. probably this one; https://www.ebay.com.au/itm/Casting-Clay-Graphite-Crucible-Refining-Melting-Aluminium-Copper-Brass-Tool-3KG/392383749577?hash=item5b5be4ddc9:g:gTAAAOSw7fVdVTpv . Is their any estimation of how many melts of aluminium and copper I can get from such a crucible with an electric furnace? feel free to comment any other info on your experiences with these particular crucibles.
much appreciated!