Mechanistic features for hydroxyl anion emission from the modified 12CaO.7Al2O3 surface

OH(-), O(-), and H(-) emissions from the Ca(24)Al(28)O(64)](4+).4(OH(-)) (defined as C12A7-OH(-)) surface were investigated by time-of-flight (TOF) spectrometry. The emission intensities were sensitive to surface temperature and extraction field. The apparent activation energies of anions decreased with the increase of applied extraction field. At an extraction field of 800 V/cm, the emission ratio of OH(-) to total anions is 0.98-0.65 in the temperature range of 870-1075 K. The OH(-) emission from C12A7-OH(-) was described by the following kinetic processes: the OH(-) anions in the cages migrated onto the sample surface by field enhanced thermal diffusion, and then desorbed to form the gas-phase anions of OH(-). The O(-) emission originated from the dissociation of O(2-) and OH(-). Similarly, H(-) emission was also attributed to the dissociation of OH(-) on the C12A7-OH(-) surface.