We report on the influence of heat treatment on the surface chemistry of an α-alumina crystal. We compare its electrical double layer behaviour with that of 150 nm diameter α-Al₂O₃ particles. Surface spectroscopy and zeta potential studies are used to understand the changes in surface chemistry. The pH_pzc of an α-Al₂O₃ (0001) single crystal (∼4) is more acidic than that of α-Al₂O₃ particles (8.5), a difference explained by the dominance of Al₂OH surface groups on the single crystals and their charging behaviour. Heat treatment of the alumina surface causes a substantial decrease in the number of surface OH groups. Heating at 500 °C decreases the surface density of hydroxyl groups. Heating at 1050 °C also affects surface morphology and surface chemistry. The increased magnitude of the zeta potential and the pH_pzc shift to lower pH suggest a surface reconstruction and the appearance of more acidic aluminium sites.