This paper considers the formation of spinel-type structures at the surface of Cr-doped CoO. This structure, which is formed at elevated temperatures, decomposes during slow cooling and impoverishment of the surface layer in Cr occurs. Analysis of the effect of cooling rate on the Cr concentration profile in the boundary layer indicates that the decomposition of the surface structure is controlling the process of Cr desegregation during cooling rather than Cr lattice diffusion.