Kunihiro Koide

Application of hydrogen sensor using proton conductive ceramics as a solid electrolyte to aluminum casting industries

Abstract A galvanic cell type of hydrogen sensor was developed using CaZrO3-based proton conductor as a solid electrolyte. It was clear that the hydrogen sensor could be used for the accurate determination of hydrogen concentration in molten aluminum alloys. The sensor probe exhibited stable EMF values and a fast response when the hydrogen concentration in the melt was changed. The application of this sensor to the real aluminum foundry was also investigated. This sensor could work very stably even when the flow rate of the liquid metal was very fast. In situ measurement was possible using this sensor anywhere in the casting shop, such as melting furnace, holding furnace, the degassing station, etc.

CaZrO3-type hydrogen and steam sensors: trial fabrication and their characteristics

Abstract Nernstian-type hydrogen and steam sensors have been constructed using a CaZr0.9In0.1O3-α proton conductor as a solid electrolyte. For these sensors, an AlPO4·xH2O-LaCoO3 mixture is used as a solid standard material to make the structure of the sensors simple and small in size. These sensors show stable and reproducible e.m.f. values corresponding to the partial pressure of hydrogen and steam. The response time of these sensors is quite short. The AlPO4·xH2O-LaCoO3 mixture exhibits good performance as a standard material for these hydrogen and steam sensors. This CaZrO3-type sensor works stably in CO2-containing atmosphere at high temperature.

Hydrogen sensor for molten metals usable up to 1500 K

Abstract A new hydrogen sensing system for molten metals usable up to 1500 K was developed by using two sort of galvanic cells employing proton conducting oxide CaZr0.9In0.1O3−δ and stabilized zirconia Zr0.91Mg0.09O2−δ respectively as the electrolytes. The system is founded on the principle that the accurate value of hydrogen potential at the measuring electrode of the galvanic cell based on CaZr0.9In0.1O3−δ can be obtained theoretically from its emf and the value of oxygen potential at the same electrode which is determined by an auxiliary galvanic cell based on Zr0.91Mg0.09O2−δ. The validity of the system was confirmed by experiments in a closed chamber using a controlled atmosphere. The performance of the system was checked in the practical melting processes of several industrial plants. These results showed that the system was very useful to monitor the hydrogen potentials in the plants.

A solid electrolyte steam sensor with an electrochemically supplied hydrogen standard using proton-conducting oxides

Abstract A high temperature solid electrolyte steam sensor with an electrochemically supplied hydrogen as a standard was designed and investigated. Two discs of proton-conducting oxide with porous platinum electrodes were stacked and a small hole was made in order to leak the gas at the interface. Constant voltage was applied to one cell in order to pump up hydrogen from water vapor in atmosphere. EMF of the other cell was measured using the pumped hydrogen as a standard gas. On applying a certain voltage, good EMF response against water vapor pressure was observed over a wide range of PH2O at 700°C.

Relation between proton conduction and concentration of oxide ion vacancy in SrCeO3 based sintered oxides

Abstract The relation between proton conduction and the content of oxide ion vacancy in SrCeO3 based oxides was investigated under various conditions by substituting trivalent Y and pentavalent Nb for Ce site in SrCeO3 lattice in an appropriate ratio, and protonic conductivity was measured under various conditions. It was found that protonic conductivity increased with increasing content of oxide ion vacancy but was almost independent of the dopant concentration. These phenomena indicate that it is not dopant cations but oxide ion vacancies themselves that directly affect the proton formation which might make the conduction protonic.