Fabrication of Gas Ionization Sensor to Recognize Gases and Measure Pressure and Humidity

Abstract

Single Ionic gas sensor (IGS) was fabricated to measure pressure, humidity and recognizes the gases. Anodic method was used to create TiO2 nanotubes (TNTs) (with internal diameter from 45 to 90 nm) on the surfaces of pure Ti and Ti-6Al-7Nb alloy. Covered surface with TNTs was operated as negative electrode to build high localized electric field and minimize breakdown voltage (Vbd). The distance between the electrodes was fixed at 60 μm. Local electric field enhancement β factor was calculated by Fowler–Nordheim plot. Its value was 857 for anodized Ti (ATi). After annealing at 800 °C; TNTs on pure Ti surface transformed to parallel rods with diameters (from 95 to 550 nm). But on alloy surface, TNTs were transformed to protrusions. Sensitivity of measuring pressure for anodized samples decreased with increasing mean free path of testing gases. For all gases; there was increment in Vbd with pressure increasing. For each gas there was specific Vbd at definite pressure and humidity; this value represented a “fingerprint” for each gas recognized it from other gases. Sensitivity of humidity for both anodized and annealed IGSs increased with increasing of relative humidity (%RH). (Vbd, Humidity) curve was approximately linear for annealed Ti and its alloy.