|Oxidation is not a serious problem with zirconium in sodium peroxide fusions. With sodium or potassium carbonate fusions, the reducing flame of a Bunsen burner (except for finishing the fusion) is far preferable to a muffle furnace.
NEVER use a muffle furnace with Zirconium unless a blanket of inert gas such as argon or helium is also used. Zirconium metal reacts, when heated in air, to form a dark mixed surface layer of oxide plus nitride. It is not necessary to remove this layer between successive fusions. If occasional scouring becomes necessary, fine zircon sand has proven most effective.
For best results in peroxide or peroxide-plus-carbonate fusions, use a finely ground sample and about ten times the sample weight of flux material. Mix well. Fusion should be completed 2 to 3 minutes after melting begins at 600-700 C
Gentle swirling of the molten mixure at temperature and while cooling, accelerates decomposition of sample and increases life of crucible. DO NOT EXCEED 900 C or zirconium crucibles will enlarge and oxidize (turn pinkish white).