Hot-isostatically-pressed, additive-free Si3N4 ceramics were implanted with aluminum at multi-energies and multidoses to achieve uniform implant concentrations at 1, 5, and 10 at. % to a depth of about 200 nm. The oxidation behavior of unimplanted and aluminum-implanted Si3N4 samples was investigated in 1 atm flowing oxygen entrained with 100 and 220 ppm NaNO3 vapor at 900-1100 degrees C. Unimplanted Si3N4 exhibits a rapid, linear oxidation rate with an apparent activation energy of about 70 kJ/mol, independent of the sodium content in the gas phase. Oxides formed on the unimplanted samples are rough and are populated with cracks and pores. In contrast, aluminum-implanted Si3N4 shows a significantly reduced, parabolic oxidation rate with apparent activation energies in the range of 90-140 kJ/mol, depending on the sodium content as well as the implant concentration. The oxides formed on the implanted samples are glassy and mostly free from surface flaws. The alteration of the oxidation kinetics and mechanism of Si3N4 in a sodium-containing environment by aluminum implantation is a consequence of the effective modification of the properties of the sodium silicates through aluminum incorporation.