Direct Observation of Mg and Ca Segregation in Sintered Al2O3

Distributions of Mg and Ca in 250 ppm MgO-doped Al₂O₃ are examined using a scanning ion microprobe in combination with secondary ion mass spectrometry (SIMS). The high spatial resolution and analytical capabilities of this technique permit compositional mapping of these elements with unprecedented detail. Segregation of Mg to the Al₂O₃ grain boundaries is observed, providing strong evidence that the primary role of MgO is to reduce grain boundary mobility through a solute-drag mechanism. Surfaces of internal pores are also found to be enriched with Mg. Ca, a background impurity in the AI2O3 is seen to co-segregate to grain boundaries and pore surfaces. Implications of these Mg and Ca distributions to sintering are discussed.