The use of a beta'-alumina electrolyte as sodium vapor sensor for the determination of sodium hydroxide in a glass tank

A β″-alumina electrolyte was used as a Na vapor sensor at 1500°C for application in the determination of NaOH in a glass tank. The difference in NaOH potential between both sides of the electrolyte gives the potential difference. Several experiments were carried out in a glass tank simulator at 1500°C while batch was added to the furnace. Also some experiments were done under controlled conditions (520–625 ppm NaOH and 1500°C) in a small tube furnace. Some stability experiments were done at 1400 and 1500°C and 250 and 1040 ppm of NaOH for both temperatures at several times. The sensor responded to sudden changes in sodium hydroxide (NaOH) every time that batch was added to the glass furnace. Decay in the mV signal was observed in those experiments. Experiments under controlled conditions also showed decay in the signal for NaOH concentrations in the range of 520–625 ppm of NaOH. XRD analysis, and SEM and CL micrographs from samples used in the stability experiments, as well as samples from the glass furnace and tube furnace, showed changes in the microstructure. The β ″ phase transformed to β and α-alumina during the exposure to the furnace at 1500°C for several hours. The change in phase changes the Na₂O activity in the electrolyte and therefore was one factor contributing to the decrease in the signal. Sensors can be used to show relative changes in NaOH. The use of an electrolyte containing a mixture of α + β is proposed and justified.