Combustion synthesis of tin dioxide nanocomposites for gas sensing applications.

Abstract

The current work focuses on understanding the mechanisms controlling tin dioxide (SnO2) nanoparticle morphology in combustion synthesis systems and how nanoarchitecture affects performance of solid-state gas sensors. A range of analytical methods (including transmission and scanning electron microscopy, x-ray diffraction and XEDS) were used to characterize the materials properties as a function of the combustion synthesis conditions. A novel method of generating SnO2 materials was developed which provides a new degree of control over SnO2 morphology; including spherical, nanorod and encapsulated particle architectures. A simplified model for particle formation based on characteristic times was developed to identify the physical and chemical processes affecting the morphologies observed using transmission electron microscope imaging. The SnO2 nanoparticles evolve from primary particles sizes of 7 - 14 nm through the synthesis region, and the results indicate interparticle collision and sintering are the dominant mechanisms in determining particle size and morphology for the flame conditions studied. Metal acetates were used to create metal/SnO2 nanocomposite materials, and the processes controlling gold acetate decomposition in particular were explored. The results of the studies suggest a relationship between the precursor crystallite size and the product nanoparticles.

The well-characterized SnO2 particles were evaluated as the active materials for gas-sensing. Sensor sensitivity and time response to carbon monoxide in dry air was used to investigate microstructure-performance links. Excellent sensitivity (3 - 7, based on the ratio of the resistance of the sensor in air to the resistance in the target gas) and time response (4 - 20 seconds) were demonstrated for the thin film gas sensors. Fabrication studies demonstrated the sensor performance was a strong function of the film deposition method. A novel method for manufacturing sensors with outstanding consistency and performance was developed. This method was used to explore the effects of microstructure and composition on sensor performance. Gold and palladium doped SnO2 gas sensors indicated the introduction of dopants has potential to improve sensor performance; however, the effects are dependent on the additive distribution and location. The combustion synthesis and sensor fabrication methods studied studied will dramatically accelerate the design of new sensors and sensor optimization.