In this work we solve the problem of the simultaneous growth and competition of intermediate phases. The crystal lattice as the frame of reference for diffusion is defined, based on the volume continuity equation. It permits the computation of the material velocity in a system in which reactions at several moving interfaces occur. All reactions lead to the lattice shift due to the difference of diffusivities and molar volumes. We simulate the CVD process followed by annealing in a non-oxidizing atmosphere. The computed kinetics and concentration profiles are compared with experimental results.