The Orientation of Spinel Formed by MgO-Al<sub>2</sub>O<sub>3</sub> Solid State Reaction between 1400° and 1600°C

Abstract

Closely joined couples of single-crystalline MgO with single-crystalline Al2O3, single-crystalline MgO with poly-crystalline Al2O3, poly-crystalline MgO with single-crystalline Al2O3 and poly-crystalline MgO with poly-crystalline Al2O3 were heated at certain temperatures below 1600°C for certain periods shown in Table 1, so as to form spinel layers. The joined surfaces of single crystals were {100} for MgO and {0001} for Al2O3.The orientation of crystals at certain parts of the formed spinel layers were found comparing the intensity of diffractions from many faces.The following conclusions were obtained.(1) The textures of spinel formed on either side of the initial interface is different each other. (2) The mode of orientation of the spinel crystals formed at the position of single-crystalline Al2O3 is that the direction of the hexagonal closed packing of oxygen in the Al2O3 coincides with the direction of the cubic closed packing of oxygen in the spinel. (3) The mode of orientation of the spinel crystals formed at the position of single-crystalline MgO is that a-face of the MgO coincides with the a-face of the spinel. (4) The mode of orientation of the spinel crystals formed at the position of poly-crystalline MgO and Al2O3 are random.