Bunke, FalkFalkBunkeHeinrich, StefanStefanHeinrich2026-07-312026-07-312026-07-14Powder Technology 484: 122951 (2026)https://hdl.handle.net/11420/64127In this experimental study, two highly spherical 1.5 mm sized zirconia particles are brought into collision in free space at moderate impact velocities and at different collision angles. The collision is recorded by two synchronized high-speed cameras and the particle movements are analyzed in three dimensions. The focus of the investigation is on the tangential restitution coefficient, which depends on the collision angle. Several series of experiments are carried out with varying surface roughness of the particles adjusted by mechanical treatment. It is shown that even at relatively low surface roughness levels, the tangential restitution coefficient tends to exhibit strong inconsistency in the form of scattering, which increases with increasing surface roughness. Nevertheless, the fundamental dependence on the collision angle remains unaffected by the parameter variations carried out in this study.en0032-59102026Elsevierhttps://creativecommons.org/licenses/by/4.0/Contact mechanicsFree fall test setupParticle collision dynamicsSurface roughnessTangential restitution coefficientTechnology::620: Engineering::620.1: Engineering Mechanics and Materials ScienceJournal Article10.1016/j.powtec.2026.12295110.15480/882.17692