Detection of hydrogen in inert gases using a piezoelectric crystal coated with palladium

A hydrogen gas sensor using s piezoelectric quartz crystal coated with thin palladium film has been developed for detection of small amounts of H2 in inert gases. The principle of detection by a piezoelectric crystal is that the frequency of vibration of an oscillating crystal decreases with an increase in mass of a coating material on its surface. The gas is selectively adsorbed by a coating on the crystal surface, thereby increasing the mass on the crystal and decreasing the frequency. Sorption and desorption cycles of hy drogen were measured (Fig.2) and they exhibited, exponential curves (Fig.3). Frequency shift (δF), response and recovery time were calculated from the curves. This sensor showed relatively slow response at room temperature, however the frequency shift had a linear relation with the partial pressure of hydrogen (250-5000 ppm H2 in N2) at room temperature (Fig.4). Several parameters (flow rate, temperature and interferences of other gases) were investigated; no interferences were observed by the presence of CH4, CO2 and SO2 contained as impurities in the inert gas and the. effect of flow rate was hardly observe (Figs.7 and 8).δF, response and recovery time were dependent on temperatur(25-100°C). they decreaseadt higher tempera-tures (Figs.5 and 6). Therefore, the effect of temperature was the trade-off between sensitivity and response or recovery time. At room temperature and a low concentration of hydrogen (250-5000ppm), the rates of sorption and desorptionp rocesseso f hydrogen in and from palladium film are expressed by first-order kinetics involving surface migration as proposed by Bucur et al. for high temperature(80°C) and higher H2 concentration(2.O-70.9Torr) processes.