Inserts Made from Different Materials

As addressed in the previous section, there is a wide range of material variants available for barrels with replaceable inserts. Processing-related functions such as heating and cooling can be integrated into the outer barrel, which is generally made of heat-treated steel. The outer barrel can also incorporate elements for devolatilization, side intake, etc., so the actual insert has become a simple component that can therefore be made from a variety of different material, such as ... 

Where applicable an undercut insert in the mold can remain as an insert in the finished part. Such inserts can be held in place by the undercut. If possible, they should be made from the same material used in forming the part so there will be no difference in thermal expansion and contraction. 

From the materials point of view, it is now clear that there are no "simple" catalysts which can be used for the partial oxidation of a paraffin. All of the best systems are either constituted by several different components which cooperate in achieving the final product, or made of multicomponent structures which perform the different functions for selective conversion. These different functions seem, therefore, to be a necessary feature for the activation of the C-H bond in the saturated substrate, and for the multi-electron oxidation and oxygen insertion onto the latter. It is more or less elear that the cooperation of aeidic and suitable oxidizing properties is a necessary condition. However, this is not sufficient, and best catalytic performances are obtained only when these properties are structured in such a way to allow the final product to be quickly reached, and rapidly desorbed before further oxidative transformations may lower seleetivity. 

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