| dc.description.abstract | As alumina plays ever more important roles in advanced technologies, such as
substrates for in vivo biological sensors, catalysts for water purification and components
of novel fuel devices, it is exposed to various environments. These environments lead to
wear and degradation due to chemical and mechanical forces. Macroscale tribological
tests including the scratch test and indentation are unable to analyze nanoscale properties
due to their limited sensitivity. Today, nanotribologists incorporate three main tools to
analyze nanoscale tribological properties: atomic force microscopy (AFM), the
nanoindentor and surface force apparatus. Of these, AFM is the instrument of choice
due to the sensitivity to and diversity of surface properties analyzed in a single setting.
Through adhesion measurements and scratch testing under known loads the AFM was
used to analyze the effect of OH- on the degradation of the alumina surface. Fourier
transform infrared spectroscopy (FTIR) and AFM were also used to analyze the stability
of self-assembled monolayers (SAMs) on the alumina surface.
Through scanning a region of the surface with a defined force in an aqueous
environment, the tribochemical surface properties were found. The pressure required to induce degradation of the first O-Al layer (~2 �) ranged from 3.10 GPa at a pH 3 to 1.58
GPa at pH 10. Further analysis of adhesion across the surface and within a defect region
exposed significant changes in the forces of adhesion as the alumina surface experienced
wear. At pH 3, 5, 7, and 10 the adhesion was approximately double that of the defect
free surface.
Two well known molecules were examined for their ability to protect the surface
from bond rupture due to the catalytic effect of OH-. SAMs of octadyclephosphonic acid
(OPA) and Octadycletrichlorosilane (OTS) were assembled on the alumina surface.
FTIR spectra indicated well ordered monolayers formed from each molecule. The
exposure of OPA to aqueous environments of pH >7 lead to the degradation of the SAM.
OTS, on the other hand, demonstrated significantly more resilience to degradation as
indicated through FTIR and AFM analysis. | en |
