28 CHAPTER 2: Gas Phase Nanofication: A Strategy to Impart Fast Response in Sensors containing 100 ppm CO balance CO 2 was used as the CO source. A similar strategy was adopted in the case of oxygen partial pressure modulation in WO 3 in the light of the theoretical data illustrated in Figure 2.1c. In the case of titania thick films electrodeposited on cp Ti plates and wires, the clacined samples were subjected to reduction experiment in 5% H 2 /Ar mixture (flow rate of 100 sccm) at 700°C for 6 h. In one case, reduc- tion was carried out for 8 h. 2.4.4 Gas sensing experiments The sensor was placed on a flat platform in an all-quartz experimental set- up which was located in the uniform temperature zone of a compact hori- zontal Lindberg furnace (MiniMite) and the lead wires were taken out of the furnace through a twin-bore alumina tube. A type-K thermocouple was also placed just above the sensor to monitor the temperature and its varia- tion (if any) during the test. The ends of the gold wires were connected to a high impedance Agilent 34220A digital multimeter, which in turn was con- nected to a desktop PC via HPIB interface card. Sensor resistance data was acquired and displayed in real time with the help of IntuiLink software. A gas stream consisting of 10% O 2 ­90% N 2 (v/v) mixture was obtained by blending dry compressed air with high purity nitrogen to obtain the back- ground (reference) gas. The sensor was first heated to a selected temperature in the background ambient and allowed to equilibrate at that temperature till a steady baseline resistance ( R b ) was established. Given amount of CO from a CO/N 2 tank was then bled in and allowed to blend. Sensitivity of a given film was measured by recording change in film resistance with respect to R b upon introduction of a given amount of CO in the stream. The sensor behaviour was monitored both with increasing and decreasing levels of CO in the ambi- ent to confirm the reversibility attribute of the sensor. The response time ( t 90 ) was calculated by discerning from the recorded data, the time it took for the signal to attain 90% of the difference between the two steady states, viz., in the background ( R b ) and that after CO was introduced ( R g ). 2.5 RESULTS AND DISCUSSION 2.5.1 Mo- and MoO 3 -based studies 2.5.1.1 Microstructural evolution in MoO 3 derived from Mo foil oxidation In order to first verify that modulation of oxygen potential in the vicinity of a metal or its oxide affects the morphological artefacts, small (25 mm 12.5 mm) coupons cut from an Mo foil were subjected to several redox schemes and were characterized at the end of each treatment by XRD and SEM.