This article presents a new electrochemical hydrogen analyser for use in molten aluminium and its alloys. The sensor relies on a proton conducting solid electrolyte that compares the hydrogen partial pressure at the measuring side with a known hydrogen partial pressure at the reference side. The sensor is protected from the melt by means of a specially designed sheath. Equilibration between the measuring electrode and the melt occurs through a gas pervious plug. The hydrogen partial pressure at the reference side is generated by an encapsulated solid metal/hydrogen mixture. The sensor is operated in the current reversal mode, in which a symmetric square-wave potential is applied across the electrolyte and the resulting currents for both directions of polarisation are recorded. The current ratio determined in this way is a direct and quantitative measure of the hydrogen content in the melt. Particular advantages of the new analyser are ease of fabrication and simple application, as well as on-line use and fast response. Results obtained with prototypes both in the laboratory and in field trials are presented and discussed.
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