Hydrogen pressures, sensor response

Test Results. The pH response of the zirconia tubes was tested at elevated temperatures and pressures using the apparatus previously described. Standard HC1 and NaOH solutions were pumped through the test chamber while the EMF of the sensor was monitored. The pH values at temperature and pressure were calculated from the room temperature pH measurement based on hydrogen ion mass balance using the data of (11). 

Test objectives were established to provide a comparison based on reproducibility and response time in liquid hydrogen at various ullage pressures. The test method chosen to meet these objectives consisted of moving the sensors in and out of a quiescent liquid. 

The potentiometric response of a polymer sensor is shown in Fig. 3.12b, and, as is typical for poten-tiometric sensors, can be detected over many orders of magnitude in concentration. The EMF dependence on the logarithm of the hydrogen partial pressure is very close to linear but is non-Nems-tian. A nonlinear least-squares fit (NLLSF) of the data yielded a slope of 166 mV, well above the value predicted by the Nemst equation. If the data for 0.01% hydrogen is discarded, the value of the resultant... 

---