Surface composition of anhydrous tricalcium aluminate and calcium aluminoferrite

Electron spectroscopy and optoacoustic spectroscopy (OAS) have been used to study the surfaces of synthetic tricalcium aluminate, Ca₃Al₂O₆ and calcium aluminoferrite, Ca₂AIFeO₅. The surfaces of these compounds have compositions which differ markedly from those of the bulk. The surface of tricalcium aluminate is depleted in calcium and enriched in aluminium and also carries relatively stable hydroxyl groups, which can be detected by OAS. Calcium aluminoferrite has a surface enriched in aluminium and depleted in calcium and iron. Again, some hydroxyl groups are present on the surface. These differences in surface composition are discussed with particular reference to the early stages of reaction with water.