Abstract: Two samples of oil well cement ( one was added with silica fume and the other was not ) were soaked in aqueous solutions containing different ions, and
the resultant element concentrations within the sam-ples were determined with energy spectrometry. It was found that Cl - and SO42 - had seeped into
the cement while Mg2 + had not, and silica fume can hinder diffusion of the ions. It is pointed out in this paper that the diffusion of SO42 - ions within
the cement is not only a physical but also a chemical process. The key to prevent corrosion by SO42 - is to change the composition of the resulting hydrated product.

Key words: Oil well cement, Corrosion, Energy spec-trometry, Composition, Diffusion