The High-Temperature Solubility Limit of Carbon in Alumina

events hall

MSc Candidate Ms. Li-or Cohen

04.07.2021

Room 302, Meidan, and via ZOOM

14:30

Alumina (Al2O3) is one of the most studied ceramic systems, mostly due to its use in corrosive environments, resistance to abrasion, reasonable fracture strength, etc. Alumina is commonly sintered in air, but some sintering techniques utilize graphite dies (e.g., spark plasma sintering) and/or graphite furnace elements. During sintering in graphite-based furnaces, carbon is thought to dissolve into alumina, but its solubility limit and the mechanism by which it influences the properties of alumina are not yet known.
In this study, a method to determine the carbon content in alumina grains was developed, and the high temperature (1600°C) solubility limit of carbon in alumina was measured by fully standardized wavelength dispersive spectroscopy (WDS). For the measurements, polycrystalline alumina was sintered under flowing He in a graphite furnace (which correlates to a relatively low oxygen partial pressure), at a carbon concentration resulting in precipitation of secondary phases (characterized as graphite), and saturation of the alumina grains. At equilibrium, the carbon-saturated alumina grains represent the solubility limit of carbon in alumina. Undoped polycrystalline alumina and sapphire were used to quantify the amount of carbon deposited on the surface of samples because of hydrocarbon contamination in the electron microscope, and this quantified background level was removed from the signal measured from carbon-doped samples by WDS.
The solubility limit of carbon in alumina at 1600°C was found to be 375 ± 11 ppm, which was determined at a measured detection limit of 5 ppm. At the low partial pressures of oxygen used in this study it is believed that carbon substitutes oxygen as an anion, and this is charge-compensated by the formation of oxygen vacancies.

Advisor: Prof. Wayne D. Kaplan

The lecture will take place in room 302, Meidan, for green pass holders, or via ZOOM.

Meeting ID: 995 9239 6977

Passcode: mt302m