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Rare Earth Oxide Coating with Controlled Chemistry Using Thermal Spray

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Date Issued:
2012
Abstract/Description:
Cerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent consolidation, specially using thermal spray.This dissertation aims to develop a scientific understanding towards the development of pure and doped ceria- based coating for a variety of technological applications, from SOFC applications to corrosion resistant coating. Atmospheric plasma spray (APS) and solution precursor plasma spray (SPPS) techniques for the fabrication of nano ceria coating were investigated. For feedstock powder preparation, a spray drying technique was used for the agglomeration of cerium oxide nano particles to achieve high density coating. Deposition efficiencies and coating porosity as a function of processing parameters were analyzed and optimized using a statistical design of experiment model. The coating deposition efficiency was dependent on the plasma temperature and vaporization pressure of the ceria nanoparticles. However, low standoff distance and high carrier gas flow rate were responsible for the improved density upto 86 (&)#177;3%.An alternative novel SPPS technique was studied for a thin film of cerium oxide deposition from various cerium salt precursors in doped and undoped conditions. The SPPS process allows controlling the chemistry of coating at a molecular level. The deposition mechanism by single scan experiments and the effect of various factors on coating microstructure evolution were studied in terms of splats formation. It was found that the precursor salt (nitrate of cerium) with lower thermal decomposition temperatures was suitable for a high density coating. The high concentration and low spray distance significantly improve the splat morphology and reduced porosity (upto 20%). The feasibility of the trivalent cations (Sm 3+ and Gd 3+) doping into cerium oxide lattice in high temperature plasma was discussed and experimentally studied. XRD analysis revealed the nano crystalline characteristic of the coating and lattice expansion due to doping. The extensive transmission electron microscopy, Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric were conducted to evaluate the precursors, and coating microstructure.Due to facial switching between Ce4+ and Ce3+ oxidation state, the cerium oxide surface becomes catalytically active. Thus, the APS ceria coatings were investigated for their applicability under extreme environmental conditions (high pressure and temperature). The air plasma sprayed coated 17-4PH steel was subjected to high pressure (10 Kpsi) and temperature (300 oF) corrosive environment. The coated steel showed continuous improvement in the corrosion resistance at 3.5 wt% NaCl at ambient temperature for three months study whereas, high pressure did not reveal a significant role in the corrosion process, and however, one needs to do further research. The ceria coated steel also revealed the improvement in corrosion protection (by 4 times) compared to the bare steel at low pH, 300 oF and 4000 Psi environment. This study projects the importance of cerium oxide coatings, their fabrication, optimization and applications.
Title: Rare Earth Oxide Coating with Controlled Chemistry Using Thermal Spray.
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Name(s): Singh, Virendra, Author
Seal, Sudipta, Committee Chair
Coffey, Kevin, Committee Member
Raghavan, Seetha, Committee Member
Heinrich, Helge, Committee Member
Zhai, Lei, Committee Member
University of Central Florida, Degree Grantor
Type of Resource: text
Date Issued: 2012
Publisher: University of Central Florida
Language(s): English
Abstract/Description: Cerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent consolidation, specially using thermal spray.This dissertation aims to develop a scientific understanding towards the development of pure and doped ceria- based coating for a variety of technological applications, from SOFC applications to corrosion resistant coating. Atmospheric plasma spray (APS) and solution precursor plasma spray (SPPS) techniques for the fabrication of nano ceria coating were investigated. For feedstock powder preparation, a spray drying technique was used for the agglomeration of cerium oxide nano particles to achieve high density coating. Deposition efficiencies and coating porosity as a function of processing parameters were analyzed and optimized using a statistical design of experiment model. The coating deposition efficiency was dependent on the plasma temperature and vaporization pressure of the ceria nanoparticles. However, low standoff distance and high carrier gas flow rate were responsible for the improved density upto 86 (&)#177;3%.An alternative novel SPPS technique was studied for a thin film of cerium oxide deposition from various cerium salt precursors in doped and undoped conditions. The SPPS process allows controlling the chemistry of coating at a molecular level. The deposition mechanism by single scan experiments and the effect of various factors on coating microstructure evolution were studied in terms of splats formation. It was found that the precursor salt (nitrate of cerium) with lower thermal decomposition temperatures was suitable for a high density coating. The high concentration and low spray distance significantly improve the splat morphology and reduced porosity (upto 20%). The feasibility of the trivalent cations (Sm 3+ and Gd 3+) doping into cerium oxide lattice in high temperature plasma was discussed and experimentally studied. XRD analysis revealed the nano crystalline characteristic of the coating and lattice expansion due to doping. The extensive transmission electron microscopy, Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric were conducted to evaluate the precursors, and coating microstructure.Due to facial switching between Ce4+ and Ce3+ oxidation state, the cerium oxide surface becomes catalytically active. Thus, the APS ceria coatings were investigated for their applicability under extreme environmental conditions (high pressure and temperature). The air plasma sprayed coated 17-4PH steel was subjected to high pressure (10 Kpsi) and temperature (300 oF) corrosive environment. The coated steel showed continuous improvement in the corrosion resistance at 3.5 wt% NaCl at ambient temperature for three months study whereas, high pressure did not reveal a significant role in the corrosion process, and however, one needs to do further research. The ceria coated steel also revealed the improvement in corrosion protection (by 4 times) compared to the bare steel at low pH, 300 oF and 4000 Psi environment. This study projects the importance of cerium oxide coatings, their fabrication, optimization and applications.
Identifier: CFE0004230 (IID), ucf:49023 (fedora)
Note(s): 2012-05-01
Ph.D.
Engineering and Computer Science, Mechanical, Materials and Aerospace Engineering
Doctoral
This record was generated from author submitted information.
Subject(s): Cerium Oxide -- Thermal Spray -- Plasma Spray -- Solution precursor plasma spray -- Coatings -- Corrosion
Persistent Link to This Record: http://purl.flvc.org/ucf/fd/CFE0004230
Restrictions on Access: campus 2013-05-15
Host Institution: UCF

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