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Results from Brownian dynamics simulations of hard sphere diffusion in polymer networks of wormlike chains are presented. The influence of the size of the diffusing particles, the polymer concentration, the polymer radius, and the persistence length of the chains were investigated. The diffusion coefficients obtained in systems of stiff chains were compared to a theory [Macromolecules 24, 6024 (1991)]. The agreement between the simulation data and the theory was satisfactory, except for dense systems where the theory predicted somewhat too high diffusion coefficients. To account for the diffusion in systems of more flexible polymers, we derived a semiphenomenological theory based on ideas from the concept of fractals. By this approach we could show how the available volume fraction for particles in polymer networks scales with the particle radii. The scaling is not a power law, but instead is a stretched exponential, and is related to the local structure of the polymer chains. Finally, the inherent assumptions in the theoretical descriptions, e.g., the negligence of the hydrodynamic interactions, and the applicability of the theory to real polymer systems, are thoroughly discussed.

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In order to increase the corrosion resistance and simultaneously maintain the creep resistance of 9-12% Cr steels at 650°C, a new alloy design concept was proposed, using thermodynamically stable Z-phase (CrTaN) precipitates to strengthen the steel. A new trial Zphase strengthened 12% Cr steel was produced and creep tested. The steel exhibited good long-term creep resistance. Dense nano-sized Z-phase precipitates were formed at the early stage, and coarsened slowly. They remained small after more than 10,000 hours.Martensitic 9-12% Cr steels offer an optimal combination of the critical properties, i.e. creep strength, corrosion resistance, thermal conductivity and thermal expansion, at a relatively low cost. Therefore, they are by far the most used material for steam pipes and turbine components in steam power plants [1]. The thermal efficiency of these plants is limited by the maximum allowed steam temperature and pressure, which in turn are determined by the longterm creep and corrosion resistance of economically viable materials. Although austenitic steels have better creep and corrosion resistance, the superior thermal properties of 9-12% Cr steels (high thermal conductivity and low thermal expansion) make them better suited for future power plants. For these plants thermo-flexibility is an essential requirement to accommodate the fluctuating nature of many of the major renewable sources of energy, such as wind and solar power. The cost of 9-12% Cr steels is also substantially lower than austenitic steels, which is of great importance for the economy of introducing improved