Dissertation Investigations of Nitrogen Oxide Plasmas
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DISSERTATION INVESTIGATIONS OF NITROGEN OXIDE PLASMAS: FUNDAMENTAL CHEMISTRY AND SURFACE REACTIVITY AND MONITORING STUDENT PERCEPTIONS IN A GENERAL CHEMISTRY RECITATION Submitted by Joshua M. Blechle Department of Chemistry In partial fulfillment of the requirements For the Degree of Doctor of Philosophy Colorado State University Fort Collins, Colorado Fall 2016 Doctoral Committee: Advisor: Ellen R. Fisher Nancy E. Levinger Charles S. Henry Christopher R. Weinberger Copyright by Joshua M. Blechle 2016 All Rights Reserved ABSTRACT INVESTIGATIONS OF NITROGEN OXIDE PLASMAS: FUNDAMENTAL CHEMISTRY AND SURFACE REACTIVITY AND MONITORING STUDENT PERCEPTIONS IN A GENERAL CHEMISTRY RECITATION Part I of this dissertation focuses on investigations of nitrogen oxide plasma systems. With increasing concerns over the environmental presence of NxOy species, there is growing interest in utilizing plasma-assisted conversion techniques. Advances, however, have been limited because of the lack of knowledge regarding the fundamental chemistry of these plasma systems. Understanding the kinetics and thermodynamics of processes in these systems is vital to realizing their potential in a range of applications. Unraveling the complex chemical nature of these systems, however, presents numerous challenges. As such, this work serves as a foundational step in the diagnostics and assessment of these NxOy plasmas. The partitioning of energy within the plasma system is essential to unraveling these complications as it provides insight into both gas and surface reactivity. To obtain this information, techniques such as optical emission spectroscopy (OES), broadband absorption spectroscopy (BAS), and laser induced fluorescence (LIF) were utilized to determine species energetics (vibrational, rotational, translational temperatures). These temperature data provide mechanistic insight and establish the relationships between system parameters and energetic outcomes. Additionally, these data are also correlated to surface reactivity data collected with the Imaging of Radicals Interacting with Surfaces (IRIS) technique. IRIS data demonstrate the ii relationship between internal temperatures of radicals and their observed surface scatter coefficients (S), the latter of which is directly related to surface reactivity (R) [R = 1-S]. Furthermore, time-resolved (TR) spectroscopic techniques, specifically TR-OES, revealed kinetic trends in NO and N2 formation from a range of precursors (NO, N2O, N2/O2). By examining the rate constants associated with the generation and destruction of various plasma species we can investigate possible mechanistic implications. All told, such data provides unparalleled insight into the chemistry of these plasma systems. Part II of this work is focused on understanding the efficacy of a general chemistry recitation program. Such programs can be an valuable tool for improving students’ problem- solving skills and understanding using methods that are difficult to implement in large lecture settings. Here, general chemistry students at Colorado State University participated in a variety of recitation activities throughout the first semester of a 2-semester general chemistry sequence, including peer-led exercises, games, and scaffolded worksheets. Through weekly surveys, students were asked to evaluate and assess recitation activities for both interest and effectiveness as part of their course homework. Also included in these survey assignments were content questions relevant to the weekly themes, providing a measure of student learning of recitation topics. Student opinions were correlated with content retention, and these data were compared against student responses to a pre-survey administered before the first recitation session. This analysis allows for monitoring students’ expectations of recitation courses and how well those expectations are met through the various types of activities employed. Ultimately, this work has found that students have positive feeling with respect to individual assignments, but that perspectives on chemistry and the course in general decrease dramatically from the beginning to the end of the semester. Thus, this work can serve as a significant starting points for future 3 efforts to monitor and record student perceptions in the general chemistry recitation classroom, leading to further investigation into the source of changing attitudes and the role that week-to- week activities have on global course attitudes. 4 ACKNOWLEDGMENTS I lack the ability to succinctly thank all of those responsible for this academic journey, as the list is long and brevity is not my strength. Still, there are some that I would be remiss to not mention here. First, Joyce Brown, the woman who introduced me to chemistry and started me on this path: your classroom was a haven, a place of mystery and excitement unlike anything I had ever experienced. Those at Truman State University, especially Dr. Russell Baughman and Dr. Eric Patterson: you fostered a love of research and were constant mentors both in the classroom and outside of it. My advisor, Prof. Ellen R. Fisher: your patience and support has known no bounds throughout these years, even in times when it felt underserved. Your impact on me as a scientist and as a person is without measure, though there is no doubt that you have shown me how to be both confident and humble, and to fight for the things that matter while letting go of the things that don’t. Other members of the Fisher Group: in you I have found kindred spirits and life-long friends. My parents, Ronald and Alice: you always believed in every crazy dream that I had and encouraged them whole-heartedly. There is no doubt that it is you are the ones that taught me the value of education and showed me that school was not a chore, but instead a great beast to be conquered simply for the love of learning. My brother, Alexander: you continually push me to reach higher and farther. More than a brother, you have been a friend, confidant, and inspiration each and every day. And finally, my wife, Lindsey: you are my best friend and my ultimate role-model. Your strength and passion drive me to achieve far beyond what I think I am capable of, and you were there to listen, coach, motivate, scold, comfort, and otherwise be everything I needed every step of the way. Thank you all. 5 DEDICATION To my grandparents, for their guidance and love: Frank and Theresa Schaefer, Robert and Margaret Blechle, George and Ruth Hafley 6 TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii ACKNOWLEDGMENTS .............................................................................................................. v DEDICATION ............................................................................................................................... vi TABLE OF CONTENTS .............................................................................................................. vii CHAPTER 1. Introduction to Plasma Chemistry ........................................................................... 1 1.1 Plasma Chemistry ................................................................................................... 1 1.2 Motivation for Nitrogen Oxide Studies ................................................................... 6 1.3 Research Overview ................................................................................................. 9 1.4 References ............................................................................................................. 12 CHAPTER 2. Experimental Details for the Investigation of Various Nitrogen Oxide Plasma Systems ......................................................................................................................................... 15 2.1 Plasma Systems .................................................................................................... 15 2.2 Optical Spectroscopies ......................................................................................... 15 2.3 Mass Spectrometry ............................................................................................... 18 2.4 IRIS Technique .................................................................................................... 20 References ................................................................................................................... 25 CHAPTER 3. The Design and Implementation of a Broadband Absorption Spectroscopy System for Ground State Temperature Measurements .............................................................................. 26 3.1 Introduction .......................................................................................................... 26 3.2 System Development ........................................................................................... 27 3.3 Results and Discussion ......................................................................................... 42 3.4 Summary .............................................................................................................. 54 References ................................................................................................................... 56 CHAPTER 4. Determination of Internal Temperatures within Nitric Oxide Inductively-Coupled Plasma Systems ............................................................................................................................