Corundum From Thermite Slag

Since I've not been able to complete my Verneuil furnace yet, I've been playing with thermite seeded with oxide feed material for making synthetic ruby and sapphire.

These pictures are under my microscope showing the formation of trigonal, hexagonal and tetragonal crystal structures, as well as some fascinating non-uniform crystals which might be rutile from the titanium dioxide in the sapphire feed material. I do have some blue colored corundum from these experiments, but I only have a couple rough shots which aren't that great looking.

I'll continue to sort through the slag and get some better shots of fused ruby and sapphire feedstock. For now, I just have "white sapphire" pics to upload since these were the prettiest crystal formations.



[Edited on 27-12-2018 by Doped-Al2O3-fusion]



[Edited on 27-12-2018 by Doped-Al2O3-fusion]

Quote: Originally posted by MrHomeScientist

Nice! What was the composition of your thermite? Did you do anything special to yield these crystals, or are they present in normal thermite?

I just used typical iron+aluminum thermite (3:1 ratio). The pictures are from the last batch I created weighing in at approximately 240g total starting material. I first dried the iron (III) oxide in the oven for a few hours to reduce moisture in the mix.

I added a layer of thermite mix on the bottom of the flower pot about 1/4 of the volume of mixture, then added a layer of ruby feedstock on one side (97%Al2O3+3%Cr2O3), then sapphire feestock (99.88% Al2O3+0.3% TiO2+0.9% FeO - by weight) on the other half. I then poured in the remainder of the thermite mix and packed it down as well as I could without going too crazy.

I ignited the pile with KMnO4 and glycerin. I kept a stainless steel campers mug over the double flower pots to assist with prolonging heat retention, though I doubt it helped too much in the formation of crystals to be honest. I also purposely didn't further dry out the oxide ruby & sapphire feedstock as it was already fairly dry, but I felt any moisture would form larger cavities allowing for a microscopic layer of crystals to form like a geode. Again, I doubt this added much to the result since the amount of released gasses would do that anyways.

Sorry for the large reply. I just figured if anyone wanted to repeat my experiment for similar results, then I could state as much detail as possible.

These crystals should actually be present in normal thermite as well, but it really depends on the batch size since the crystals will have a chance at forming in slag that takes longer to cool before going below the melting point of alumina. Here are some random pictures of the mix.

Quote: Originally posted by MineMan

Super interesting! Have you tried making diamonds from OB- explosives? There is a place in grant New Mexico that does that....