Probe for determn. of active oxygen in molten metals - using solid electrolyte contg. alumina, minerals, flux, and silica forming vitreous phase

The amt. of O2 is measured via the electromotive force of a cell which uses a carrier (1) functioning as a reference electrode and also a conductor. Carrier (1) is coated with a layer (2) which includes gamma-Al2O3; and only after immersion in the molten metal is the gamma-Al2O3 converted into beta-Al2O3 which conducts oxygen ions so layer (2) forms the solid electrolyte. Layer (2) pref. also contains Na2O, FeO, and/or K2O; plus a flux, esp. an alkali(ne earth) fluoride, e.g. CaF2, NaF, and/or clay or felspar; and also SiO2. Carrier (1) is pref. a metal bar; and plasma flame spraying is pref. used to apply layer (2) to bar (1), followed by using compressed air at min. 5 atmos. to compact layer (2) on bar (1). Reliable determn. of active O2 even below 0.001% at temps. above 1250 degrees C, e.g. in molten cast iron.