Mixed Si/Ge Apatite-Type Phase Produced by Mechanical Alloying

The aim of the present work is to study the influence of the partial substitution of Si by Ge on the formation of the apatite-type La9.33Si2Ge4O26 phase by mechanical alloying and subsequent annealing. Powders of La2O3, GeO2 and SiO2 were dry milled in a planetary ball milling at increasing rotation speeds of 150, 250 and 350 rpm and milling times up to 50 h. The resulting mixtures were subsequently annealed at increasing temperatures up to 1100 °C. Single phase apatite-like La9.33Si2Ge4O26 was obtained during mechanical alloying at high rotation speed. The higher the rotation speed the lower was the time required for the lanthanum germanosilicate phase formation. For the samples in which complete reaction between initial phases did not occur during milling, La9.33Si2Ge4O26 was always obtained during the annealing process. The more severe was the mechanical alloying process the lower was the annealing temperature required for the apatite phase formation. The formation of apatite phase during mechanical alloying did not provoke significant changes in densification behavior of the milled samples. The addition of GeO2 as raw material promotes a faster formation of the apatite phase as compared to the results obtained using only La2O3 and SiO2.