L. Satyanarayana

LIQUID-PETROLEUM-GAS SENSOR BASED ON A SPINEL SEMICONDUCTOR, ZNGA2O4

Abstract A liquid-petroleum gas sensor has been developed with high selectivity and sensitivity based on an oxygen deficient spinel semiconductor, ZnGa2O4. The operating temperature of the sensor element has been optimised under different operating conditions. Palladium doped zinc gallate sensor, on exposure to LPG at about 320°C showed a change of 4–5 orders in the resistance. The response time also decreases from about 20 min in virgin ZnGa2O4 to less than 1 min in the palladium doped element. The electronic interaction between additive and semiconductor is proposed to account for the sensitisation effects in the sensor element.

Device optimization of CO2 gas sensor using planar technology.

A planar type Li+ ion based potentiometric CO2 micro gas sensor of size 2 x 3 mm has been fabricated on alumina substrate by combining thin and thick film technology. The heater, electrodes and electrolyte were deposited by thin film deposition technique and the sensing and reference electrodes were printed by silk screen printing technology. The optimal thickness and sintering temperature of electrolyte are 1.2 microm and 775 degrees C. The sensor with Li2CO3 and 20 mol% BaCO3 not only exhibits a good Nernstian behavior but also consistent results over a long time at 450 degrees C in dry as well as 70% RH humidity condition between 160-5000 ppm CO2 concentrations. The spreading effect of the sensing and reference materials was controlled by the addition of Al2O3:B2O3 (1:2 mol%) glass.

A Potentiometric

A low-temperature lithium ion based potentiometric CO₂ sensor has been developed by adding 10 mol% of SiO₂, B₂O₃, Li₂O, and Bi₂O₃ composite metal oxide mixture to (Li₂-Ba)CO₃ sensing bicarbonate. The sensors added with different mol% of oxides were tested at different operating temperatures. The sensor with 1:2:1:1 mol% of the SiO₂:B₂O₃:Li₂O:Bi₂O₃ composite metal oxide showed a fair Nernstian correlation and obtained n value equal to 2 at 300degC, where n is the number of reaction electrons. A glassy sensing phase resulted that improved response and recovery. The sensor is also found stable against humidity (70% RH) at 300 degC. However, it is further observed that the performance of the sensor deteriorated with increasing Li₂O or decreasing B₂O₃ content. The sensor performance could further be improved at lower temperatures with the introduction of dioctyl phthalate (DOP) plasticizer into the sensing electrode.