Type
Text
Type
Dissertation
Advisor
Venkatesh, T.A. | Gouma, Pelagia Irene | Halada, Gary | Liu, Mingzhao | Camino, Fernando | .
Date
2016-12-01
Keywords
Materials Science -- Engineering | Ceramics, Flame spray pyrolysis, Polymorphism
Department
Department of Materials Science and Engineering
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76144
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Polymorphism is an important phenomenon exhibited by many materials, including ceramic oxides. The availability of multiple structural configurations for the same chemical composition opens the pathway to a large number of phases with distinct properties. The formation of the crystal structures can be directly correlated to the processing temperature and/or pressure as well as the particle size for nanomaterials. This work focuses on the tailored synthesis of the desired polymorphs of binary and ternary metal oxides through nanoscale processes with emphasis on flame spray pyrolysis. Flame spray pyrolysis (FSP) is a scalable nano-manufacturing process used for the synthesis of oxide based ceramics. The advantage of this process lies in ease of operation and inexpensive processing as well as the uniformity in the particle size distribution of the products. It is a rapid solidification process involving the atomization of precursor using high temperature gradients and low residence times in the flame. Thus, metastable polymorphs have successfully been synthesized by FSP. Although a wide variety of studies have been conducted on the synthesis and applications of ceramics via FSP there has been scarce knowledge on the actual dynamics of crystal structure formation during the process. Various solution parameters were studied to understand the particle and crystal structure formation for the FSP powders. The process parameters were kept the same; 1.5 slm methane and 3.0 slm O2 was used as fuel for the flame, 5slm oxygen was used as dispersion gas and the precursor was fed at 5ml/min. MoO3 was synthesized using different concentrations of precursor and the particle sizes obtained were correlated to the materials parameters such as solution concentration and amount of organic precursor solvent. Another study was conducted on formation of WO3 polymorphs using organic precursor salts dissolved in organic solvent. The solution was prepared to obtain low particle sizes and to obtain the metastable ε-WO3, which only exists below -17ºC in bulk. The study was further extended to ternary system by synthesizing VOPO4. The effect of solvent on the polymorphic behavior was evaluated. The use of ammonium salts in aqueous solutions led to lower temperatures and resulted information of intermediate compounds and micron sized particles. VOPO4 was easily obtained from the intermediate compounds by calcination. Secondary phases were obtained upon calcination and were related to the processing parameters. The result of the study showed that the precursor solution had a direct correlation with the formation of different polymorphs through fsp. Aqueous precursors resulted in partial decomposition of solute and resulted in secondary salts with large particle sizes. The addition of organic solvent resulted in formation of a nano-sized particles, the amount of particles formed was directly proportional to the % organic precursor used. Use of a combustible organic solute favors formation of nanoparticles by increasing the flame temperature and lowering the residence time of the particles in the chamber. The smaller sizes and low residence time may result in formation of metastable phases. This study can further be extended to other oxide ceramics and will aid in precursor selection for their synthesis. | Polymorphism is an important phenomenon exhibited by many materials, including ceramic oxides. The availability of multiple structural configurations for the same chemical composition opens the pathway to a large number of phases with distinct properties. The formation of the crystal structures can be directly correlated to the processing temperature and/or pressure as well as the particle size for nanomaterials. This work focuses on the tailored synthesis of the desired polymorphs of binary and ternary metal oxides through nanoscale processes with emphasis on flame spray pyrolysis. Flame spray pyrolysis (FSP) is a scalable nano-manufacturing process used for the synthesis of oxide based ceramics. The advantage of this process lies in ease of operation and inexpensive processing as well as the uniformity in the particle size distribution of the products. It is a rapid solidification process involving the atomization of precursor using high temperature gradients and low residence times in the flame. Thus, metastable polymorphs have successfully been synthesized by FSP. Although a wide variety of studies have been conducted on the synthesis and applications of ceramics via FSP there has been scarce knowledge on the actual dynamics of crystal structure formation during the process. Various solution parameters were studied to understand the particle and crystal structure formation for the FSP powders. The process parameters were kept the same; 1.5 slm methane and 3.0 slm O2 was used as fuel for the flame, 5slm oxygen was used as dispersion gas and the precursor was fed at 5ml/min. MoO3 was synthesized using different concentrations of precursor and the particle sizes obtained were correlated to the materials parameters such as solution concentration and amount of organic precursor solvent. Another study was conducted on formation of WO3 polymorphs using organic precursor salts dissolved in organic solvent. The solution was prepared to obtain low particle sizes and to obtain the metastable ε-WO3, which only exists below -17ºC in bulk. The study was further extended to ternary system by synthesizing VOPO4. The effect of solvent on the polymorphic behavior was evaluated. The use of ammonium salts in aqueous solutions led to lower temperatures and resulted information of intermediate compounds and micron sized particles. VOPO4 was easily obtained from the intermediate compounds by calcination. Secondary phases were obtained upon calcination and were related to the processing parameters. The result of the study showed that the precursor solution had a direct correlation with the formation of different polymorphs through fsp. Aqueous precursors resulted in partial decomposition of solute and resulted in secondary salts with large particle sizes. The addition of organic solvent resulted in formation of a nano-sized particles, the amount of particles formed was directly proportional to the % organic precursor used. Use of a combustible organic solute favors formation of nanoparticles by increasing the flame temperature and lowering the residence time of the particles in the chamber. The smaller sizes and low residence time may result in formation of metastable phases. This study can further be extended to other oxide ceramics and will aid in precursor selection for their synthesis. | 129 pages
Recommended Citation
Jodhani, Gagan, "Novel processing of ceramics with polymorphic control" (2016). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2089.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2089