Nucleation in the system calciumsulphatesubhydrates / water

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The nucleation controls the hydrations process of calcium sulphate hemihydrates. Because this is the first step of formation of the plaster structure and it is important to understand this process in detail. The microstructure, strength development and hydration speed are determined through the nucleation, seed formation and seed growth. Thus, determine the properties of gypsum binders at the final stages. This works within the framework of the DFG-Project contributed to the deep understanding of the nucleation and seed formation process. The results were verified that the mechanism of seeds formation is consisting of both homogeneous and heterogeneous nucleation, due to the different speeds of the dissolution, reaching the saturation level and different amounts of heterogeneous seeds. These mechanisms in the real system run parallel, but based on varying conditions. Therefore, different experimental models were carried out to understand and examine the influence of these parameters on the individual processes. A pure hemihydrate should be prepared to have homogeneous nucleation and addition of a very well-defined crystals to study the influence of these heterogeneous seeds on the real system during the hydration process. In the second step other surfaces, which are normally exist in the real system, can be added to study its influences. Furthermore the influence of heterogeneous seeds this systematic approach will lead to better understanding. The results, which were obtained from the second and third work package were applied in the implementation of the fourth work package. This approach will ensure the optimal implementation of the working packages and maximize the gained knowledge. Within the framework of the project will the morphology (LM and ESEM), the phase composition (QXRD, STA), the growth rate of the formed reaction products (LM), the composition of the solution phase ([Ca2 +]-SE and LE), the kinetics (DCA, ultrasonic method (US)) determines and examines the structure of processes and the mechanical properties.Investigations of the effect of the heterogeneous nucleation during the hydration process of calcium sulphate hemihydrate gives more information about the history of hydration, microstructure formation, crystal morphology, mechanical properties and microstructure of gypsum-based binding with stone. On the basis of the expected results, it should be possible to investigate the influences of the above individual processes and starting with the heterogeneous nucleation at the nano level structure formation on micro - and macro-level better understanding of crystal growth on the micro level. This enables to a direct control of nucleation and crystal growth in terms of technical properties.The main aim of this investigations is positively influencing the nucleation of calcium sulfate system, its end-use properties and the strength of calcium sulfate-based binders.