Measurement of Hydrogen Content in Molten Metal by electrochemical cell based on oxide proton conductor.

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At first, the electrochemical properties of the proton-conductive solid electrolyte to be used, CaZrO_3(+In_2O_3), were investigated by measuring the hydrogen solubility, the total conductivity, and the electronic conductivity. By these measurements, it was confirmed that the protonic-conductive domain of CaZrO_3(+In_2O_3) extends to the higher temperature region than that of SrCeO_3(Yb_2O_3). Then, the hydrogen sensor for molten aluminum based on the hydrogen concentration cell was constructed by using this material as the electrolyte and the performance of this sensor was investigated. The accurate measurement of the hydrogen potential in molten aluminum is possible when the cell was designed to measure the hydrogen potential of the gas phase equilibrated with the molten metals.The similar type of hydrogen sensor for molten copper was also studied. It was found that the insertion-type sensor operates well for molten copper. But, in these high temperature and high oxygen potential, the EMF values deviate from the theoretical one owing to the appearance of positive hole conductance. The simultaneous measurement of oxygen potential was found to be necessary to evaluate the correct hydrogen potential in molten copper.An apparatus to evaluate the hydrogen activity in metals were also developed. This apparatus is based on Sieverts' method, where the partial pressure of hydrogen is determined electrochemically using the same proton-coductive solid electrolyte. The performance of this apparatus were also studied.Consequently, all the items planned in the start of this research project were accomplished successfully.