AbstractIn the first sinter stage, the two basic mechanisms neck growth and centre approach influence the microstructural evolution in a sinter body. To quantify them, in this work an improved two particle model based on simple geometry and fundamentals of thermodynamics is introduced. The geometrical model allows particles of different size and is totally described by seven degrees of freedom. The occurring volume fluxes are driven by the gradients of chemical potential. To determine the local chemical potential, a novel and unifying formulation for surface and grain boundary regions is introduced, which uses only material properties and the current geometry of the model. The model's plausibility is substantiated by the results of the determination of surface and grain boundary diffusion coefficients.