A continuous fl ow microwave system based on a transmission line short-circuited waveguide reactor concept is described. The continuous fl ow reactor is capable of operating in a genuine high-temperature/high-pressure process window (310 ° C/60 bar), applying a microwave transparent and chemical resistant cylindrical γ -Al 2 O 3 tube as reaction zone. The system can be operated in an extremely energy effi cient manner, utilizing 0.6 -6 kW microwave power (2.45 GHz). The application of the reactor for processing four chemical transformations in a high-temperature/high-pressure regime with a throughout of 3.5 -6.0 l/h is demonstrated.

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The past decade has seen greatly increased interest in ceramic materials with special combinations of properties. Their hardness, high resistance to abrasive and erosive wear, and their good corrosion resistance when used under extreme mechanical and thermal conditions have made ceramics increasingly attractive for applications in mechanical and apparatus engineering. Silicon nitride (Si3N4) in particular, is suitable for the development of a high‐performance, high‐temperature material for vehicle engine construction. Although the properties of Si3N4 materials have been consistently improved in the last few years, they are still not adequate to allow these materials to be used in series production parts, for example as valves in automotive engines. One of the main reasons for this is the wide scatter and low reproducibility of the property parameters, which means that component reliability does not yet meet market requirements. Hence, one aim of Si3N4 materials development is to reduce the structural flaws resulting from physical and chemical inhomogeneity. This objective can only be achieved through a fundamental understanding of all the processing steps, from powder production to the final processing of the components.