Silica and magnesia dopant distributions in alumina by high-resolution scanning secondary ion mass spectrometry

Trace SiO2 and MgO additive distributions in sintered alumina have been studied using high-resolution scanning secondary ion mass spectrometry (SIMS). When doped with each additive individually, evidence is seen for both strong silicon segregation to grain boundaries (C-gd/C-grain approximate to 300) in SiO2-doped alumina and strong magnesium segregation to grain boundaries (C-gb/C-grain approximate to 400) in MgO-doped alumina. When codoped with both SiO2 and MgO, segregation of both ions to grain boundaries is reduced by a factor of 5 or more over single doping. The additive concentrations increase proportionally in the grains, and both dopants become more uniformly distributed throughout the bulk. It is concluded that codoping with these additives increases their mutual bulk solid solubility and decreases their interfacial segregation over single doping. The beneficial effect of MgO additions in controlling microstructure development in alumina and improving corrosion resistance to aqueous HF stems from its ability to redistribute silicon ions from grain boundaries into the bulk.