GB934758A - Improvements relating to the determination of the activity of oxygen or the activities of other ionic species in molten materials - Google Patents

Abstract

934,758. Determining relative quantities of fluid mixture constituents. UNITED STEEL CO. Ltd. Dec. 7, 1961 [Sept. 7, 1960], No. 30846/60. Class 37. The activity coefficient of an ionic species (oxygen) in a molten metallic mass is determined by measuring the potential difference between an electrode and the molten mass, the electrode being isolated from the molten mass by a sheath that is dipped into the molten mass and which is permeable only to the ionic species (zirconia in the case of oxygen), and being maintamed at a fixed reference potential by maintaining within the sheath a constant known activity of the species the activity coefficient of which is being determined. The electrode is of a metal (molten silver, platinum, or rubidium, in the solid state) in which the species is soluble and the standard potential is maintained by circulating within the sheath a gas which dissociates into the ionic species. The molten mass is contacted also by a geometrically similar sheath of substantially the same thermal capacity which comprises a cermet of molybdenum and aluminium, the voltage between this contact sheath and the electrode in the other sheath being measured by a valve voltometer to indicate the electrolytic potential developed across the wall of the zirconia sheath by any difference between the activity of the species on each side of the wall. The contact electrode is purged with an inert gas such as argon to remove the ionic species being determined. A molten silver electrode 5, Fig. 2, has oxygen bubbled through at a known pressure by a silicon tube 13 dipping into it. A platinum meter lead 14 is provided and a mild steel pipe 9 supporting the housing is protected by graphite sleeves 8. In a modification described with reference to Fig. 3 (not shown), the sheaths are lined with solid platinum and contact is made by spirals of platinum wire. Some water cooling is applied to the housing. In a further modification, the molten silver is in direct contact with the molten electrolyte. Sheaths of silicon nitride and cerium sulphide for determining the nitrogen and sulphur activity in copper are also described.