In the preceding paper, it was shown that aluminum ion implantation significantly improves the oxidation resistance of Si3N4 ceramics under the influence of sodium. Not only is the oxidation rate reduced by up to an order of magnitude, the phase and morphological characteristics of the oxides grown on aluminum-implanted samples are improved as well. The role of aluminum in negating the detrimental effect of sodium on the oxidation resistance of Si3N4 ceramics can be interpreted on the basis of network modification of the oxide layers by sodium and aluminum cations. The degree of improvement in the oxidation resistance does not, however, necessarily increase with the aluminum concentration. A simple quantitative analysis is presented which correlates the optimum aluminum implant concentration and the sodium content in the gas phase for the optimization of the oxidation resistance of Si3N4 ceramics.