The Detection of Hydrogen in Molten Aluminium

The presence of hydrogen in aluminium poses problems to the foundry and casting industries, because high residual hydrogen contents in molten aluminium cause significant porosity in the solid aluminium after casting. This usually renders the product useless as it may fail mechanically. Therefore, fast, accurate and reliable techniques are required for monitoring the dissolved hydrogen content in molten aluminium, but this particularly harsh environment places considerable restrictions on the equipment that can be used. Several methods are available for the determination of hydrogen in aluminium melts, but they either suffer problems of accuracy, reliability and longevity or are not applicable to industrial environments. It is considered that the most appropriate device for the hydrogen analysis in aluminium melts should be an electrochemical sensor, which employs a proton conducting solid electrolyte in conjunction with a measuring electrode and a suitable reference electrode. The electromotive force of such a cell allows direct calculation of the hydrogen concentration in the melt. However, all the electrochemical sensors reported in the literature thus far exhibit distinct drawbacks. This article discusses the various techniques for the determination of hydrogen in molten aluminium with particular emphasis on the benefits and shortcomings of the existing electrochemical sensors.