Preferred orientation of precipitates in alumina-rich manganese aluminate spinels

Abstract

Single crystals of manganese aluminates having compositions round about MnAl 2O 4 have been grown by means of a floating zone technique. Precipitation of γ-(Mn, Al) 2O 3 and α-Al 2O 3 has been studied using optical microscopy and micro-Laue back-reflection technique. The γ phase precipitates as lamellae on {001} planes of the Mn-Al spinels, and α-Al 2O 3 precipitates as platelets on {111} planes with orientation relations {0001} α/{111} spine1 and 〈1̄0〉 α/〈1̄〉 spine1 in majority and occasionally {0001} α/ {001} spine1. Nucleation of corundum in the vicinity of the intermediate γ phase is discussed, the formation of the latter being shown to produce the contraction of the oxygen framework necessary for the precipitation of corundum.