Verneuil corundum: an integrated PBC and white beam synchrotron radiation X-ray topography analysis

Abstract

In order to give a deeper insight into the cracking of the Verneuil corundum boules, several samples of different colors and from different industrial sources have been analyzed by means of white beam synchrotron radiation X-ray diffraction topography (WB-SR-XRDT) and PBC analysis (Hartman and Perdock theory). The cracking occurs along an irregular surface containing the elongation axis of boules, and the WB-SR-XRDT analysis shows that this surface is nearly parallel to the { 1 2 ̄ 0 } crystallographic planes. Following Hartman and Perdock theory, these planes form F-planes with a high density of PBC directions: 3 PBC directions—[2 1 1], [2 1 0] and [ 4 ̄ 2 ̄ 1 ]—have been recognized as parallel to the 1 2 ̄ 0 plane. The 1 ̄ 02 planes that are normal to the cracking surface of boules are F-planes too, but they show a lower bond density per unit area with respect to the 1 2 ̄ 0 planes. Ab initio calculations show that these planes have lower surface energies with respect to other hk0 planes, such as {1 0 0} and {0 1 0}.