Alicia Mayville Thesis Defense

Copies of Alicia’s thesis will be on display in BINNS, room 160 and McMahon in the CACT Office. The manuscript investigates the potential of ceramic particles with tailored surface chemistry as a passive pH control device to adjust the pH of aqueous environments in specific applications. The initial motivation was to utilize colloidal behavior to adjust the pH of coral reef ecosystems locally. Ocean acidification is a contributing factor to destroying these diverse and essential ecosystems.

ABSTRACT

This manuscript investigates the potential of ceramic particles with tailored surface chemistry as a passive pH control device to adjust the pH of aqueous environments in specific applications. The initial motivation was to utilize colloidal behavior to adjust the pH of coral reef ecosystems locally. Ocean acidification is a contributing factor to destroying these diverse and essential ecosystems.

The research initially focused on α-Al2O3 due to its substantial research on isoelectric point, point of zero charge values, and behavior in aqueous environments. However, further investigation was needed after instability in the pH of α-Al2O3 particles while aging in water systems was observed. The results suggest that washing procedures promote the formation of a hydroxide layer on the particle surface. While the formation of a hydration layer is a known phenomenon for many oxides, this study proposes that, in specific cases, this layer might lead to the gradual degradation of α-Al2O3 particles in water.

The behavior of α-Al2O3 particles in water expanded to investigating the feasibility of ceramic particles as a passive pH control device and how factors like water composition and particle surface area concentration influence alumina's pH and effectiveness as a pH buffer. The findings reveal that the surface area concentration of α-Al2O3 particles significantly impacts the stabilized pH (pHstb) of the suspensions. These results suggest that tailoring the surface chemistry of ceramics could enable them to achieve the desired pH in aquatic environments. Therefore, doped oxide systems were chosen to be investigated, primarily dope zirconia due to the dopant cations integrating throughout the lattice, unlike doped alumina systems where the dopant is only near the particles' surface.

With current variabilities between synthesis methodologies for partially stabilized zirconia (PSZ) and the limited number of dopant levels from manufacturers, investigating synthesis methods to form a variety of dopant levels and reduce the discrepancies between the samples was undergone. This investigation developed a more simplified path for doping zirconia powder.

Finally, several point of zero charge (PZC) determination methods were investigated for synthesized ceria (CeSZ) and magnesia (MSZ) doped zirconia systems. The salt addition method demonstrated variability in pH stability and potential repeatability issues, whereas the potentiometric titration method highlighted the need for a comprehensive understanding of chemistry and data analysis. These findings underscore the complexity of PZC determination in doped zirconia systems and the importance of rigorous methodological approaches.