Aerosol Deposition of Functional Oxide Ceramics: Exploratory Research for Modifying Microstructures
Final Report Abstract
The focus of the project was the aerosol deposition (AD) method. Two custom-built AD apparatuses as well as student time and work at UBT made the work possible. A large number of AD experiments were conducted utilizing not only commercially available Al2O3 powders with wide ranging size and surface area, but also specially prepared Al2O3 and Bi4(Cu.1V.9)2O11 powders with platelet morphology, and also ceramic mixtures. The goal was to create new microstructural variants of thick films, and learn more about the mechanisms of the aerosol deposition process. With respect to the specific objectives of the research, we can offer the following suggestions/hypotheses from observations: 1) Which particle characteristics are most important for successful AD of thick films?: This depends on the ceramic and the substrate. For hard Al2O3 on a hard alumina substrate, high surface area with minimal agglomeration appears to be necessary in order to form a high quality anchor layer. For glass substrates, where anchor layer formation is relatively easy, the compressibility index appears to be a good figure of merit for predicting high deposition rates during stage 2 buildup of the film. 2) Is it possible to generate controlled texture in an AD film?: Yes, but likely not by using anisometric (platelet or acicular) particles as the starting powder. Hard (Al2O3) platelets undergo severe comminution into much smaller equiaxed particles. Softer ceramics like bismuth vanadates appear to retain some platelet habit in the deposited film, but there is no motivation for orientation. Texture can be achieved through annealing deposited films with high degree of residual stress, promoting exaggerated grain growth. 3) Is it possible to deposit mixtures of ceramic particles?: Yes, in fact, mixtures of ceramic powders with differing hardness and density can enhance deposition rates and thickness. The harder particle can be expected to end up as the dispersed phase in the more ductile particle matrix, which continues to get fractured, deformed and densified by impact events. 4) Is there a chemical reaction during impact?: Possibly. XRD analysis provided evidence of a small amount of BiVO4 formation from the simple oxides during impact consolidation. This type of mechano-chemical activation is more likely to occur with compounds of lower lattice energy. 5) Is it possible to obtain controlled porosity in an AD film?: Yes. An unexpected method to produce uniform porosity was discovered when AD composite mixtures were annealed. This work is expected to have significant impact on the material science and engineering community. Four articles published in peer reviewed journals (including a very extensive review article), and three conference presentations were a direct result of this project. One further paper is almost ready to be submitted. Future technology impacts may include improved gas sensors and other functional material devices.
Publications
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“Aerosol deposition of (Cu,Ti) substituted bismuth vanadate films,” Thin Solid Films, 573 (2014) 185-190
J. Exner, P. Fuierer, R. Moos
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“Aerosol Co-deposition of Ceramics: Mixtures of Bi2O3-TiO2 and Bi2O3-V2O5”, Journal of the American Ceramic Society 98 (2015) 717-723
J. Exner, P. Fuierer, R. Moos
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“An Overview of the Aerosol Deposition Method: Process Fundamentals and New Trends in Materials Applications”, Feature Article in Journal of Ceramic Science and Technology 6 (2015) 147-182
Hanft, J. Exner, M. Schubert, T. Stöcker, P. Fuierer, R. Moos
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“Powder Requirements for Aerosol Deposition of Alumina Films”, Advanced Powder Technology 26 (2015) 1143-1151
J. Exner, M. Hahn, M. Schubert, D. Hanft, P. Fuierer, R. Moos
