Development of chemical sensor to measure Al concentration in molten Zn bath using composite mixed salt electrolyte.

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Chemical sensors using composite mixed salt electrolyte have been developed to measure aluminum content in molten Zn alloys. The present sensors are composed of composite type electrolyte of molten mixed halides of NaCl and AlCl_3 saturated with solid NaCl. A variable solid to liquid volume ratio enables one to obtain a wide range of mechanical properties as a sensor component from almost pure liquid characteristics to solid ones as those of solid electrolytes.Two types of sensors, with and without beta-alumina membrane electrolyte to separate electrolytes contacting with pure Al reference and molten Zn electrodes, were tested for its performance in both laboratory scale (less than 10kg) and practical Zn bather (greater than 4,000kg). The former sensor can be expressed as ;Zn-Al*NaC1<@D2sat.@>D2+AlC1<@D23@>D2(+ZnC1<@D22@>D2):<@D7(Na<@D1+@>D1)(/)beta-alumina@>D7:Nac1<@D2sat.@>D2+AlCl<@D23@>D2*AlThe results obtained through this project are as follows :(1) Two types of sensors with and w … More ithout beta-alumina membrane electrolyte in order to prevent from counter diffusion of ZnCl_2 through the electrolyte showed excellent reversibility, reproducibility above 100 mass ppm Al.(2) Both sensors showed good agreement with each other, but the former showed better performance in start-up duration and its life time.(3) Thermochemical properties of dilute Zn-Al and Zn-Fe-Al alloys were determined in order to evaluate activity coefficient of Al in molten Zn by EMF method using the composite electrolyte.(4) The applicability of the present sensor with beta-alumina in CGL line test was proved, and relative error of 30 ppm around 1500 ppm Al and life time of 10 days as an average was performed.(5) The life time was governed by adhesion of ZnO particles to electrolyte and the evaporation of AlCl_3.(6) The sensor life time or the validity can be estimated by on-line monitoring of an ac impedance of the sensor.(7) Through theoretical and experimental examinations, the present composite mixed salt electrolyte is proved to be valid for chemical sensors to measure concentration or chemical potential of a wide variety of component in molten metals and alloys, for example, Zn in molten Cd, Na in Al alloys, and so on. Less