Senior Design Expo 2023

Applied Physics & Applied Mathematics
Thin Film Coating to Decrease Low Temperature Degradation of Yttria Stabilized Zirconia
Dental Devices
Sam Lossef
Advisor: Professor Siu-Wai Chan
In this project, the sol-gel process was successfully used to deposit thin film coatings of alumina
onto yttria stabilized zirconia substrates for the purpose of delaying or preventing low
temperature degradation (LTD), and enhancing lifespan of zirconia dental devices.
Yttria stabilized zirconia is a ceramic material that is widely used in dental devices and implants
due to its high strength and hardness, favorable optical qualities, and relatively low cost.
However, interaction with aqueous saliva can result in low temperature degradation, a
phenomenon in which tetragonal to monoclinic (t-m) phase transformations occur at the surface
of zirconia ceramics, causing volume enlargement of grains, which in turn results in surface
roughening, decreased optical translucency, micro-cracking, loss of strength, and potential
catastrophic device failure. It was hypothesized that deposition of a thin film sol-gel layer of
alumina on the surface of zirconia dental devices would act as a water barrier to delay or prevent
the tetragonal to monoclinic phase transformations that are responsible for low temperature
degradation.
A viscous sol-gel was prepared by dissolving aluminum nitrate nonahydrate and carbamide in
water and heating under reflux for 10 hours. Yttria stabilized zirconia samples (5 mol % yttria)
were dip coated in either hot and cold sol-gel solutions, before being slowly withdrawn over a 30
second interval. Coated samples were then heated in a kiln at 600° C for 6 hours to fuse the
alumina coating to the zirconia substrate. Accelerated aging was then performed in a steam
autoclave to simulate the effects of low temperature degradation on control and coated samples.
EDS elemental analysis confirms that alumina was successfully deposited onto the zirconia
substrate. SEM images suggest that coated zirconia samples had slightly smoother surfaces than
uncoated samples. However, Raman spectroscopy indicates that coated samples unexpectedly
had higher concentrations of weaker monoclinic crystals than uncoated samples, possibly related
to the oven sintering at 600° C. Further research should be conducted to optimize kiln
temperatures to ensure good adhesion of thin films to zirconia, while at the same time preserving
the initial tetragonal crystal structure of the substrate.
Keywords: Yttria stabilized zirconia, dental devices, low temperature degradation, thin film
coatings, alumina coatings, sol-gel coatings.
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