High selectivity, enhanced sensitivity, short response time and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. Since the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of higher aspect ratio, large surface area and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence, is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/ submolecular level under conditions of "oxygen deprivation", with exotic morphological features has been achieved in a number of metal oxides that are potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of two model systems, viz., tungsten oxide (WO3) and titanium oxide (TiO2).
Ceramic sensor based on TiO2-Al2O3 systems were thermally cycled in the temperature range of 21 degree(s)C to 685 degree(s)C for different number of cycles. Thermal wave imaging technique (TWI), a non-destructive and non-contact evaluation method was used to characterize the bonding of sensor films with the substrate. Based on the thermal wave signal amplitudes, an assessment of bond strength was made. The results indicate that samples with 700 degree(s)C heat treatment show the best bonding characteristics. Furthermore, with increasing number of thermal cycles, bonding quality turns out to decrease as damage occurs. Thermal wave imaging is a powerful NDE tool. Results from a number of material evaluation efforts indicate that the technique has great promise.
Conference Committee Involvement (1)
Sensors for Harsh Environments III
3 October 2006 | Boston, Massachusetts, United States
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