Degradation of Ceramic Surfaces and its Mitigation: From Electric Propulsion to Cultural Heritage

Citation

Chari, Celia S. (2023) Degradation of Ceramic Surfaces and its Mitigation: From Electric Propulsion to Cultural Heritage. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/22st-q436. https://resolver.caltech.edu/CaltechTHESIS:08312022-141029875

Abstract

Ceramics have played an evolving role throughout human history, with the earliest known fired clay figurines dating back to 29,000-25,000 BCE in what is today the Czech Republic. Such examples of porous, low-fired potteries transitioned into vitreous and heat-resistant porcelain with the advancements of kiln technologies, which steadily grew to reach temperatures up to 1270 °C by the time of the Song Dynasty (960-1279 CE). In the modern-age, furnaces technologies have become exceedingly more sophisticated, reaching ultra-high temperatures of up to 3000 °C with dedicated calibration systems. With the advancement of firing technologies came the advancement of materials processing methods, which have transformed the role of ceramics in everyday applications: from ceramic fibers used in tennis racquets, to ceramics used in space shuttle tiles and even in artificial joints. Indeed, ceramics are candidate solutions to the most stringent material problems faced today, including high-temperature applications like electric propulsion and turbine engine systems. However, in order to improve the long-term use and sustainability of ceramics, it is essential to evaluate both their performance and their eventual degradation from mechanical wear and chemical erosion.

This work explores the processing-microstructure-performance relationship of ceramics to better understand the performance and degradation mechanisms of ceramic surfaces. This relationship is investigated using a series of material case studies, including (i) advanced high-temperature ceramics composed of h-BN rich composites, and (ii) historic ceramics, ranging from low-fired pottery to porcelain. Details are provided for the design and manufacturing of novel high-performing ceramics, while simultaneously referring to ceramics of the past to understand how their surfaces have altered over their lifetime. Highlights of this work include the innovative use of carbothermic reactions to create h-BN surface layers for electric propulsion; self-healing strategies from AlN/BN composites; DFT-supported analysis of pottery corrosion in acidic soils; and nanoscale processing of historic porcelain glazes. These analyses provide us with an opportunity to learn from materials of the past to create more sustainable materials for the future, with an emphasis on ways of mitigating degradation by controlling processing conditions and environmental exposures.

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