Improvements in the determination of the gas content of liquid metals

摘要

The hydrogen dissolved in a molten metal, such as aluminium, is measured by causing a free surface of the metal to form at a location within the body of the metal and circulating a volume of inert gas, e.g. nitrogen or argon, in contact with the metal below said free surface, a plurality of times through this location and a path extending externally of the body of the metal and determining the hydrogen content of the circulated gas when it is substantially in equilibrium with the hydrogen content of the molten metal. The thermal conductivity or the pressure of the gas may be used as a measure of the quantity of gas. The free surface may be formed by immersing in the metal a hollow body having at least a part of its wall composed of a material pervious to hydrogen and to the inert gas but impervious to the molten metal and removing hydrogen from the metal by circulating the volume of inert gas once every second for a period of the order of 1 1/2 minutes. As is shown in Fig. 2, and is described in a similar earlier Specification 684,865, measurement may be made by means of a palladium thimble and measurement of the pressure developed by a manometer. Alternatively, as is shown in Fig. 1, the thermal conductivity of the gas may be measured in an apparatus which comprises an immersion head 1 by means of which the inert gas is to be brought into direct contact with the molten metal 2 below the surface thereof; a pump indicated generally at 3 by means of which the gas is to be circulated to and from the immersion head 1: and means indicated generally at 4 for measuring the concentration of hydrogen in the gas as it circulates externally of the molten metal. Ceramic materials such as alumina may be used for the immersion head but the preferred head is made of stainless steel (18-8 Cr-Ni type) coated with a vitreous enamel and preferably protected with a refractory wash which adheres firmly to the enamel. Nitrogen is admitted to the gas circulation circuit from 31 under the control of a cock 30. An electrical measuring device comprises two platinum spirals 20 and 21 which are connected electrically into a normal Wheatstone bridge arrangement with two fixed resistances 37 and 38.