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Sensor Array Devices Utilizing Nano-Structured Metal-Oxides for Hazardous Gas Detection

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Sensor Array Devices Utilizing Nano-Structured Metal-Oxides for Hazardous Gas Detection Sensor Array Devices Utilizing Nano-structured Metal-oxides for Hazardous Gas Detection DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Mark A. Andio, M.S. Graduate Program in Materials Science and Engineering The Ohio State University 2012 Dissertation Committee: Professor Patricia Morris Adviser Professor Sheikh Akbar Professor John Morral Copyright by Mark A. Andio 2012 Abstract Methane and carbon monoxide are two hazardous gases which require continuous monitoring by gas sensors in underground coal mines for explosion prevention and toxicity, respectively. This work explored implementing miniaturized gas sensors in this area to simultaneously detect both gases for benefits of increased portability and reduced power consumption of the chemiresistive gas sensor device. The focus of this research was to understand how the particle size, morphology, and microstructure of the metal- oxide film affected the gas sensor performance to the two gases of interest on miniaturized gas sensor devices in the form of microhotplate platforms. This was done through three main research studies. The first was conducted by growing SnO2 nanowires from SnO2 particles using an Au-catalyst. Growth conditions including temperature, time, and oxygen partial pressure were explored to determine the formation aspects of the SnO2 nanowires. Gas sensor studies were completed that provided evidence that the SnO2 nanowires increased detection to a fixed concentration of carbon monoxide compared to SnO2 particles without nano-structure formation. A second research study was performed to compare the gas sensor performance of SnO2 nanoparticles, hierarchical particles, and micron-size particles. The nanoparticles were developed into an ink and deposited via ink-jet printing on the microhotplate substrates to control the microstructure of the metal-oxide film. By preventing ii agglomeration of the nanoparticle film, the SnO2 nanoparticles displayed similar gas sensor performance to methane and carbon monoxide as the hierarchical particles. Both nano-structures had much higher gas sensor response than the micron-size particles which confirms the surface area of the metal-oxide film is critical for reaction of the analyte gas at the surface. The last research study presented in the dissertation describes an oxide nanoparticle array developed for detecting methane and carbon monoxide in the presence of one another. A design of experiments was constructed and principal component analysis was used for determining the optimum temperatures of the metal-oxide elements. A four element array was developed with the SnO2 and TiO2 sensor elements able to detect methane concentrations of interest and the ZnO and NiO sensor elements able to detect the carbon monoxide concentrations. A linear based prediction model was developed and tested for accuracy and reproducibility of the model to a series of random gas concentrations. iii Dedication This document is dedicated to Beth and my family. iv Acknowledgments I would like to thank my thesis adviser, Dr. Patricia Morris, for giving me the opportunity to work on a challenging and exciting project during my graduate studies. She gave me the freedom to think independently and grow personally, and she also challenged me to explore difficult subjects and manage students which will be invaluable throughout my career. I would also like to thank, Dr. Sheikh Akbar, for helpful discussions on gas sensor technology. The Orton Ceramic Foundation provided funding for the duration of the research project and without their financial support; this dissertation would not be possible. I would like to thank Dr. John Morral for his role on the Orton board and for serving on my dissertation committee. I would also like to thank the numerous undergraduates who worked on various projects with me which include those working on the senior design project, especially Justin Bennet, as well as the undergraduate students on the FeMET project. I would specifically like to thank Paul Browning for his work helping me construct the gas sensor testing facility and for developing the LabVIEW program to perform the gas sensor tests. I received significant assistance from several graduate students, but especially Dr. Elvin Beach, Dr. Krenar Shqau, and Dr. Ben Dinan for helpful support. v I would also like to thank my parents for giving me the drive and passion to pursue my academic and career goals. Without their encouragement, I would not be where I am today. To my fiancé, Beth, your understanding and support during my graduate studies have been tremendous. Seeing your ambition for your career has shown me how much strength and courage you have, and to always pursue our dreams and goals. vi Vita 2003................................................................Lakeview High School 2007................................................................B.S. Materials Science & Engineering, The Ohio State University 2009................................................................M.S. Materials Science & Engineering, The Ohio State University 2007-2012 ......................................................Graduate Research Associate The Ohio State University Publications Journal Articles 1. Andio MA, Bennett JR, Ramsdell MM, Akbar SA, Morris PA, Nanowires grown on SnO2 particles using an Au catalyst: formation and applications in gas sensing, Materials Chemistry and Physics, (submitted) 2012. 2. Andio MA, Browning PN, Morris PA, Akbar SA, Comparison of gas sensor performance of SnO2 nano-structures on microhotplate platforms, Sensors and Actuators B: Chemical, 165 (2012) 13-18. 3. Andio MA, Beach ER, Morris PA, Akbar SA, Synthesis of Nano-Structured Metal-Oxides and Deposition via Ink-Jet Printing on Microhotplate Substrates, Science of Advanced Materials, 3 (2011) 845-852. vii Fields of Study Major Field: Materials Science and Engineering viii Table of Contents Abstract ............................................................................................................................... ii Dedication .......................................................................................................................... iv Acknowledgments............................................................................................................... v Vita .................................................................................................................................... vii List of Tables ................................................................................................................... xiii List of Figures .................................................................................................................. xiv Chapter 1: Introduction ....................................................................................................... 1 1.1 Detecting Hazardous Gases for Coal Mining Applications ............................ 4 1.1.1 Methane................................................................................................. 6 1.1.2 Carbon Monoxide ................................................................................. 7 1.2 Implementing Miniaturized Sensors ............................................................... 9 Chapter 2: Chemiresistive Gas Sensor Technology.......................................................... 16 2.1 Working Principles of Gas Sensors ............................................................... 17 2.1.1 Adsorption at Surface and Band Bending ........................................... 17 2.1.2 Reaction of Oxidizing/Reducing Gases .............................................. 21 2.1.3 Electron Motion between Particles ..................................................... 23 ix 2.1.4 Sensor Properties ................................................................................ 24 2.2 Particle Size and Film Microstructure Importance for Gas Sensing ............. 31 2.2.1 Particle Size Importance ..................................................................... 32 2.2.2 Film Microstructure Importance on Gas Sensing ............................... 35 2.3 Metal-Oxide Nano-structures for Gas Sensing ............................................. 39 2.3.1 Hierarchical Structure ......................................................................... 39 2.3.2 Hollow Spheres ................................................................................... 45 2.4 Conclusions from Literature Review and Research Group Findings ............ 49 Chapter 3: Growth of Nanowires from SnO2 Particles using Au Catalyst ....................... 53 3.1 Introduction ................................................................................................... 54 3.2 SnO2 Nanowire Growth from Dense Pellets and Particles ............................ 57 3.2.1 Au-Deposition on SnO2:CoO pellets .................................................. 57 3.2.2 Au-Deposition on SnO2 Particles........................................................ 59 3.2.3 SnO2 Growth on Pellets and Particles ................................................. 63 3.3 Gas Sensor Testing ........................................................................................ 73 3.3.1 Sensor Preparation and Thick-film Gas Sensor Testing Facility ........ 74 3.3.2 Gas Sensor Performance ..................................................................... 76 3.4 Conclusions ..................................................................................................
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